Allosteric inhibitors that bind to the middle domain (MD) or C-terminal domain (CTD) of Hsp90 have become promising drug leads for the development of effective and nontoxic chemicals in anticancer drug discovery. The structure of MDCC-labeled Hsp90α MD and CTD reported here provides the first direct visual insight into allosteric binding inhibitors of Hsp90 MD or CTD and provides a basis for the design of novel drugs for the treatment of cancer and neurodegenerative diseases. N-carbamoyl]coumarin}, which is located in a hydrophobic pocket that is formed at the Hsp90αMC hexamer interface, is reported. MDCC binding leads to the hexamerization of Hsp90, and the stabilization and conformational changes of three loops that are critical for its function. A fluorescence competition assay demonstrated that other characterized coumarin and isoflavone-containing Hsp90 inhibitors compete with MDCC binding, suggesting that they could bind at a common site or that they might allosterically alter the structure of the MDCC binding site. This study provides insights into the mechanism by which the coumarin class of allosteric inhibitors potentially disrupt the function of Hsp90 by regulating its oligomerization and the burial of interaction sites involved in the ATP-dependent folding of Hsp90 clients. The hydrophobic binding pocket characterized here will provide new structural information for future drug design.The 90 kDa heat-shock protein (Hsp90) is an abundant molecular chaperone that is essential to activate, stabilize and regulate the function of a plethora of client proteins. As drug targets for the treatment of cancer and neurodegenerative diseases, Hsp90 inhibitors that bind to the N-terminal ATP-binding site of Hsp90 have shown disappointing efficacy in clinical trials. Thus, allosteric regulation of the function of Hsp90 by compounds that interact with its middle and C-terminal (MC) domains is now being pursued as a mechanism to inhibit the ATPase activity and client protein-binding activity of Hsp90 without concomitant induction of the heat-shock response. Here, the crystal structure of the Hsp90αMC protein covalently linked to a coumarin derivative, MDCC {7-diethylamino-3-[ The structure identified a hydrophobic binding pocket for the coumarin scaffold, which could represent an allosteric binding site for Hsp90 inhibitors containing the common coumarin core. This structure provides the first direct visual insight into the mechanism of Hsp90 MD or CTD allosteric inhibitors, and provides a basis for the design of new drugs.Various computational approaches have been utilized to identify potential allosteric binding sites in Hsp90 . The protein was eluted in elution buffer (loading buffer plus 250 mM imidazole) and was subsequently subjected to TEV protease cleavage at a 1:100 mass ratio while dialyzing against loading buffer at 4°C overnight. The protein was then collected as the flowthrough from a second subtracting Ni–NTA column. The protein was further purified to homogeneity by size-exclusion chromatography using a buffer consisting of 20 mM HEPES Na pH 7.2, 150 mM NaCl. The protein was concentrated to 12 mg ml−1 for crystallization. Hsp90α_293–554 (Hsp90αM), Hsp90α_433–696 (Hsp90αC+) and Hsp90α_23–699_E47A (FL Hsp90α) were cloned, expressed and purified using the same procedure as for Hsp90αMC. This version of full-length (FL) Hsp90α was constructed to favor the open conformation of Hsp90, which is the conformation observed for the Hsp90αMC construct. The E47A mutation inhibits ATP hydrolysis but not its binding  was cloned into a modified pET vector with an N-terminal 6×His tag, including a Tobacco etch virus (TEV) protease cleavage site between the tag and the protein sequence. The recombinant protein was expressed in 2.2.M sodium acetate pH 6.0, 12%(v/v) PEG 3350 using the sitting-drop vapor-diffusion method at 20°C. To obtain MDCC {7-diethylamino-3-[N-carbamoyl]coumarin}-labeled protein, 0.2 mM Hsp90αMC was mixed with 0.5 mM MDCC (Sigma) and incubated on ice for 30 min. The sample was then centrifuged at 14 000 rev min−1 at 4°C to remove the precipitate that formed and the supernatant was used for crystallization. MDCC–Hsp90αMC crystals were obtained in a condition consisting of 0.1 M succinic acid pH 6.5, 12%(v/v) PEG 3350, 20 mM calcium chloride. 20% glycerol was added to the mother liquor as a cryoprotectant before flash-cooling in liquid nitrogen.Hsp90αMC was crystallized in the condition 0.1 HKL-3000 . The structure was deposited in the Protein Data Bank with accession code 7ry1.All data were collected on beamline 19-ID at the Advanced Photon Source (APS), Argonne National Laboratory. Diffraction data were processed using s Table 1. All mol2.3.−1 Hsp90αMC in 20 mM HEPES pH 7.2, 150 mM NaCl and 3 mg ml−1 Hsp90αMC incubated with 0.5 mM inhibitors  on ice for 30 min in 20 mM HEPES pH 7.2, 150 mM NaCl, 5%(v/v) DMSO, were loaded into the cuvette for DLS measurements at 25°C. The estimated molecular mass from DLS was used to analyze the oligomeric state of each protein with or without incubation with inhibitors. For the Hsp90αM protein, 2.1 mg ml−1 Hsp90αM was incubated with the inhibitors using the same procedure. Hsp90αC+ at 1.0 mg ml−1 and FL Hsp90α at 2.1 mg ml−1 were also used in DLS measurements with the same procedure as described above. All of the samples were centrifuged at high speed (14 000 rev min−1 for 15 min at 4°C) to remove precipitate before loading into the cuvette.The particle and molecular sizes of protein with or without inhibitors were analyzed using a Malvern Zetasizer DLS instrument. 5 µl of each of the proteins, 3 mg ml2.4.M) in fluorescence assay buffer  to a final concentration of 50 µM and incubated at room temperature for 3 h. MDCC was subsequently added to give final concentrations of 1 µM Hsp90αMC and 1 µM MDCC in a total volume of 200 µl. Fluorescence recording was started immediately and continued every 5 min for 1.5 h. The same method and procedure were used for the competition assay of Hsp90αM. Due to the aggregation effect of MDCC on Hsp90αC+ and FL Hsp90α, neither of these proteins were used in fluorescence competition studies.Fluorescence measurements were performed in black 96-well microtiter plates (Corning #3650) using a Biotek Synergy H1 plate reader. MDCC fluorescence was excited at 419 nm and emission was recorded at 474 nm. For the competition binding studies, the Hsp90 allosteric inhibitors dissolved in DMSO were added to Hsp90αMC protein  and subjected to co-crystallization screening using numerous conditions together with different putative allosteric inhibitors, including derrubone, chlorobiocin, coumermycin A1, celastrol and garcinol. Unfortunately, no inhibitors were observed in our co-crystal structures.In our initial studies to identify the binding site for Hsp90α MD and CTD inhibitors, Hsp90αMC (residues 293–699) was expressed and purified carbamoyl]coumarin (MDCC), which contains the coumarin ring that is shared among many previously characterized Hsp90MC inhibitors. MDCC contains an N-ethylmaleimide moiety that could form a covalent link to exposed reduced cysteines . The MDCC–Hsp90αMC structure contains three molecules in the asymmetric unit, which further form a hexamer through crystallographic symmetry . This hexameric association of the MDCC–Hsp90αMC complex structure is similar to that observed in the apo Hsp90αMC structure  of 0.86 Å over 393 aligned Cα atoms. The current structure differs from the previous structure in three loop regions that become ordered upon MDCC binding. These include two loops in the MD, loop 394-LPLNISREMLQQ-405 . The main chains and some of the side chains in these three regions could be clearly traced in the current structure, while they were all disordered in previous human Hsp90αMC structures  and the coumarin core are clearly visible, while the diethylamino tail is disordered . The NEM head is found to only be covalently linked to Cys374 and not to any of other six cysteines in the complex structure .In the current structure, each protomer binds an MDCC molecule in the MD and a total of six MDCC molecules are located in the Hsp90αMC hexamer interface Fig. 1. The eleed Fig. 2a. The Na). The hydrophobic loop 368-VFIM-371 and the hydrophobic residue Leu396 located in the catalytic loop of molecule C, as well as the aromatic residues Phe349 in the Src loop of molecule A and Phe352 in the Src loop of molecule B, form the hydrophobic binding pocket for the coumarin core of MDCC . The NEM head of MDCC is also surrounded by hydrophobic residues, including Ile370, Met371, Cys374, Leu394, Leu396 and Leu409, in each protomer . Besides these hydrophobic interactions, the carbonyl group of MDCC forms a hydrogen bond to Gln405 at the end of the catalytic loop in the MD .Each of the MDCC molecules is located inside a composite hydrophobic pocket at the hexamer interface, contacting Hsp90αMC mainly through hydrophobic interactions. The hydrophobic MDCC-binding pocket is constructed mainly by four loops from three neighboring Hsp90αMC molecules. Each pocket includes parts of the Src-loop regions (349-FDLF-352 from one protomer and 352-FEN-354 from the other in the Hsp90αMC homodimer), as well as the loop region 368-VFIMDNCEEL-377 and the catalytic loop 394-LPLNISREMLQQ-405 from a third molecule Fig. 2a. The hCC Fig. 2b. The Ner Fig. 2b. Besid3.3.et al., 20112cge; Ali et al., 20066xlb; Liu et al., 20205fwk), Hsp90α–FKBP51–p23 (PDB entry 7l7i) and Hsp90α–p23 . In contrast, the corresponding Phe residues in Hsp82 turn totally inwards. Strikingly, when in complex with Aha1 (6xlb), both Phe side chains in Hsc82 are rotated outwards in similar orientations as in the current structure, contacting Phe264 and Tyr335 of Aha1 through hydrophobic interactions . In the closed-state, full-length Hsp90α–p23 complex (PDB entry 7l7j), Phe349 adopts the same outwards direction as in the current structure, while Phe352 adopts an opposite orientation , displaying the same conformations as in the structures of the Hsp90β–Cdc37–Cdk4 and Hsp90α–FKBP51–p23 complexes (not shown). Our structural comparison suggests that MDCC binding could block the binding of the Src loop by cochaperone and client proteins.The Src-loop region is disordered in apo human Hsp90αMC hexamer structures  displays an open ‘active’ state that forms a hydrogen bond to the γ-phosphate of the bound ATP in the NTD  and the closed-state dimer structure  of human Hsp90α (PDB entry 7l7j). Structural superimposition showed that the MDCC in our current structure overlaps with the position of Arg336 in the catalytic loop of E. coli HTPG in the open-state dimer, which positions Arg400 in an opposite orientation with respect to the ATP-bound closed-state dimer structure of human Hsp90α . Our structure suggests that MDCC binding locks Arg400 in a conformation which cannot stabilize the γ-phosphate of ATP during hydrolysis.The conformation of the catalytic loop is flexible in Hsp90α MD. It has been shown in the ATP-bound closed-state human Hsp90 dimer structure that the catalytic residue Arg400 . Three regions are involved in hexamerization. The first region at the hexamer interface involves the catalytic loops and Src loops. The binding of MDCC stabilizes these loops, making them clearly visible. The catalytic loop of each protomer in the Hsp90αMC homodimer intrudes into the MC domain of a third molecule from another Hsp90αMC dimer, in turn forming an interdigitated homohexamer . However, the purified dimeric Hsp90αMC protein displayed a strong tendency to oligomerize into a hexameric state over time as observed from DLS. Interestingly, we found that in the presence of known allosteric inhibitors, including derrubone, chlorobiocin and coumermycin A1, the oligomerization of dimeric Hsp90αMC into its hexameric state was greatly accelerated and stabilized  and FL Hsp90α was a hexamer  in solution. However neither protein was stable in the presence of MDCC and inhibitors, which led to the formation of large aggregates (Supplementary Table S1).The current complex structure suggests that the binding of an MD/CTD inhibitor could stabilize the Hsp90αMC hexamer interface. We therefore analyzed the oligomeric states of Hsp90αMC and Hsp90αM in solution by gel filtration (SEC) and dynamic light scattering (DLS) with and without allosteric inhibitors. Hsp90αMC purified mainly as a dimer in solution by SEC, while Hsp90αM purified mainly as a monomer in solution by SEC . In contrast, we did not observe similar competition effects of the inhibitors with MDCC for Hsp90αM . These data are consistent with our structural observation that the MDCC binding pocket is a composite binding site at the hexamer interface and is stabilized by both the MD and CTD, and that the coumarin/isoflavone core contained in the inhibitors could compete with MDCC for binding to a common site on Hsp90.To evaluate whether the hydrophobic pocket of MDCC represents a common allosteric binding site for other Hsp90 coumarin core-containing inhibitors, we performed a competitive binding assay by monitoring the fluorescence signal of MDCC. The quantum yield of the coumarin ring in MDCC is dependent on the local environment in which it is bound .We next attempted to build models of the coumarin-related Hsp90 inhibitors binding to the MDCC binding site. Our modeling shows that both derrubone and chlorobiocin could fit into the MDCC binding pocket at the hexamer interface , which adopt unique conformations and contribute to Hsp90 hexamer association . The structure suggests that MDCC binding locks Hsp90 into an inactive hexamer, with one key residue Arg400 oriented away from the ATP-binding pocket so that the stabilization of the NTD and MD that is required for optimal ATP hydrolysis is not possible  suggests that the C-terminal domain of Aha1 could capture dimeric Hsp90 by binding to Phe352 in the Src loop  that are required for Hsp90-dependent protein folding are sequestered at the hexamer interface, including the catalytic loop, the Src loop and the CTD loop: the catalytic loop is essential for ATP hydrolysis, while the Src-loop and CTD-loop regions are involved in client binding. The catalytic loop of each protomer within the current structure is enveloped by a third molecule, which stabilizes the homodimer block of Hsp90 in the open state with the catalytic loop in an inactive orientation that differs from that of the closed conformational state of Hsp90 during ATP hydrolysis and client binding . Upon this reorientation of the domains, the conformation of the catalytic loop also reorients to coordinate the γ-phosphate of ATP and the client is captured in the hydrophobic pocket formed at the interface between the Src loop and CTD loop (Verba et al., 2016et al., 2020et al., 2020et al., 2014et al., 2012Based on the recent cryo-EM structures of yeast Hsc82 in complex with Aha1 (PDB entries In summary, our data suggest that the hydrophobic binding pocket for the coumarin core of MDCC in the MD could be an allosteric inhibitor-binding site of Hsp90. This class of inhibitor could block the functions of Hsp90 by locking it into an inactive oligomeric state lacking either ATPase activity or productive client binding. Therefore, the MDCC binding pocket could serve as a new drug target for combating cancer and neurodegenerative and infectious diseases.Hsp90α MC domain covalently linked to MDCC, 7ry1PDB reference: 10.1107/S2059798322002261/qh5073sup1.pdfSupplementary Table and Figures. DOI:


Unfortunately, the low energy conversion efficiency is still an open challenge. Here, multiple‐pulse, flow‐type triboelectric plasma with dual functions of harvesting mechanical energy and driving chemical reactions is introduced to efficiently reduce CO2. CO selectivity of 92.4% is achieved under normal temperature and pressure, and the CO and O2 evolution rates reach 12.4 and 6.7 µmol h−1, respectively. The maximum energy conversion efficiencies of 2.3% from mechanical to chemical energy and 31.9% from electrical to chemical energy are reached. The low average electron energy in triboelectric plasma and vibrational excitation dissociation of CO2 with low barrier is revealed by optical emission spectra and plasma simulations, which enable the high energy conversion efficiency. The approach of triboelectric plasma reduction reported here provides a promising strategy for efficient utilization of renewable and dispersed mechanical energy.Mechanical energy‐induced CO 2 reduction to CO, efficiently increasing the overall energy efficiency from mechanical to chemical energy. Moreover, this system shows well‐suited to the irregularity and volatility of mechanical energy and the flow of CO2 gas. This strategy exhibits potential in mechanical energy storage and mechanical energy‐driven CO2 reduction.Triboelectric plasma creates simultaneously harvesting mechanical energy and driving CO An ideal method to store mechanical energy is to use it to produce chemical fuels as they are considered green mechanical energy carriers. In this context, the most appealing method is the use of mechanical energy to reduce CO2 emissions because it can solve the problem of mechanical energy storage and reduce global carbon emissions, alleviating the environmental damage caused by greenhouse gases. However, the mechanical energy‐induced reduction of chemically inert CO2 molecules is difficult at room temperature and pressure. Moreover, reports on the direct use of mechanical energy to convert CO2 are insufficient.Low‐frequency mechanical energy is abundant, clean, and renewable and can be harvested from sources such as wind energy, water energy, and ocean wave energy.1 Unfo The electrochemical CO2 reduction systems have also been proposed by combining TENGs and electrochemical reactions, which directly collect mechanical energy and drive electrochemical reactions. However, due to the mismatch of the low required voltage of electrochemical reaction (≈V) and the high output voltage of TENG (≈kV), the power management and storage units are introduced in these systems, resulting in a lot of energy losses and low energy conversion efficiency from mechanical to chemical energy . It has been reported that the high output voltage of TENGs enables the generation of triboelectric plasma from a gas discharge at normal temperature and pressure. Previously, Li et al. constructed a static, mono‐pulse corona type triboelectric plasma for CO2 reduction, and achieved a conversion efficiency of 5.2% from electrical to chemical energy. However, the energy conversion efficiency is still low, which is attributed to the high average energy of electrons in the triboelectric plasma and CO2 decomposition via a high‐energy‐barrier pathway. Therefore, to achieve a higher energy conversion efficiency, it is urgent to conduct triboelectric plasma CO2 reduction through a low‐energy‐barrier pathway. Moreover, as a type of nonthermal micro‐plasma, triboelectric plasma could simultaneously harvest mechanical energy and drive CO2 reduction reactions, which could be utilized to develop mechanical energy‐induced CO2 reduction system. This system has the advantages of high efficiency and low cost, since the triboelectric plasma is produced by renewable and dispersed mechanical energy, and no power management and energy storage units are needed in the system.The conversion of low‐frequency mechanical energy into electrical energy using a triboelectric nanogenerator (TENG) has gained popularity in recent years.6 The 2 reduction system was proposed based on a dual‐function, multiple‐pulse, flow‐type triboelectric plasma, which simultaneously harvested mechanical energy and drove CO2 reduction reactions. The system was well‐suited to the instabilities of mechanical energy and the fluctuating CO2 gas flow. As the discharge distance was 0.8 mm, CO and O2 evolution rates of 12.4 and 6.7 µmol h−1, respectively, were achieved. The CO selectivity was 92.4%. The conversion efficiency from electrical to chemical energy (ηele − chem) was 31.9%; this value is higher than those previously reported for nonthermal plasma‐triggered CO2 reduction systems. The maximum energy conversion efficiency from mechanical to chemical energy (ηmech − chem) was 2.3%, the highest value reported to date. We investigated the pathway of CO2 dissociation using plasma simulation and optical emission spectroscopy. Finally, field experiments were conducted at a wind speed of 4.0 m s−1, achieving the maximum CO yield of 16.8 µmol h−1. Our work demonstrates a potential candidate for efficiently converting mechanical energy into chemical energy.Herein, a mechanical energy‐induced CO22.12 reduction system based on dual‐function, multiple‐pulse, flow‐type triboelectric plasma is shown in Figure 2 reduction reactor. The TENG was used to collect mechanical energy from nature and convert it into electrical energy to generate the triboelectric plasma. The plasma CO2 reduction reactor comprised a flow‐type needle‐plate gas‐discharge device for CO2 reduction. When polytetrafluoroetheylene (PTFE) and Cu films came in contact, negative and positive triboelectric charges were generated on the PTFE and Cu surfaces, respectively, due to the difference in triboelectric sequence. There was a periodic potential difference between the two groups of Cu electrodes of the TENG when the PTFE was rotated and the open‐circuit voltage reached 4.8 kV  was 0.8 mm and the TENG rotational speed was 180 rpm. In half a cycle, four discharge voltage peaks (V) of ≈2.1 kV each and four discharge current peaks (I) of ≈79.1 µA each were generated  of the triboelectric plasma increased from 2.1 to 4.0 mW and the CO evolution rate (rCO) increased from 8.2 to 16.2 µmol h−1 as the rotational speed increased from 90 to 210 rpm  to reaction gas of 0.1 eV molec−1, outperforming other nonthermal plasmas  via dynamic torque measurement and the CO yield. ηmech − chem was ≈2.1–2.3%  of the electrochemical reaction device and the high output voltage (≈kV) of TENG. In our system, the triboelectric plasma could effectively decrease the impedance of TENG, enhancing the TENG output and improving the efficiency of the entire mechanical energy‐driven CO2 reduction system.Next, we measured the power of mechanical energy provided for the TENG Pmech via 2.42 decomposition pathway to understand the reason for the high energy conversion efficiency and selectivity of CO2 reduction via triboelectric plasma. According to the literature, the conversion of CO2 into CO can proceed via four mechanisms, that is, electronic excitation dissociation (CO2(D)), electron impact ionization (CO2(I)), electron attachment dissociation (CO2(E)), and vibrational excitation dissociation (CO2(V)), whose intermediates and energy barriers differ significantly  and CO2(I) pathways exhibit high energy barriers of 10.5 and 13.8 eV, respectively, whereas the CO2(E) and CO2(V) pathways exhibit low energy barriers of 4.7 and 5.5 eV, respectively.We carefully analyzed the CO(CO2(V)),14 who2 dissociation. The emission spectra measured using a QEpro‐High Performance Spectrometer at d values of 0.2 and 0.8 mm are shown in Figure d of 0.2 mm, a medium‐intensity spectral line attributable to the transition of C atoms from the 1P state to the 1S state was produced at 247 nm, indicating the occurrence of a high‐energy consumption process of CO2 decomposition into C. This line almost vanished at a d of 0.8 mm, suggesting that CO2 decomposition into C ceased. A set of broad emission bands was observed at 206–258 nm at a d of 0.2 mm, which can be attributed to the excited‐state transition of CO from the a3П state to the X1Σ state (Table 2(D) pathway since this is the only mechanism that proceeds via excited‐state CO, whereas the other three pathways involve ground‐state CO. These bands almost vanished at a d of 0.8 mm, indicating the disappearance of the energy‐intensive CO2(D) pathway. The formation of triboelectric plasma requires the generation of CO2+ ions, whose dissociation involves no potential barrier. Therefore, the CO2(I) pathway cannot be avoided. At d of 0.2 and 0.8 mm, three bands were observed at 351.1, 367.4, and 434.2 nm, which correspond to the transition from the A2П state to the X2П state of the intermediate CO2+ ions in the CO2(I) process. Two strong O atoms transitioned from the 3p state to the 3s state, producing bands at 777.5 and 844.7 nm, respectively. This spectrum represents the excited O atoms produced by the CO2(I) and CO2(V) processes. The intermediate CO2− ions in the CO2(E) pathway have a very short lifetime and decompose before producing luminescence, which renders them undetectable by conventional OES. Using 5,5‐dimethyl‐1‐pyrroline‐N‐oxide (DMPO) as a capture reagent, the intermediate CO2− species was detected by electron paramagnetic resonance (EPR) spectroscopy  pathway. The CO2(E) pathway is determined by two factors: the generation of CO2− ions and the energy provided by the triboelectric plasma. The above results suggest that compared with the d of 0.2 mm, the two high‐energy dissociation pathways (CO2(D) and the direct decomposition of CO2 into C) almost disappear at the d of 0.8 mm. Hence, CO2 dissociation could proceed via the CO2(I), CO2(E), and CO2(V) pathways.The optical emission spectra (OES) of the intermediates or products in the four dissociation processes can help elucidate the mechanism of COociation.15 The2 decomposition pathway, we calculated the electron density (en) and average electron energy (eE) at various spatial positions during the evolution of a simulated triboelectric plasma with time at different d values. The results are shown in Figure d increased from 0.2 to 1.0 mm. The plasma channel had the greatest volume at the d of 0.8 mm . With increasing d, the en in the plasma channel decreased, the channel volume increased, and the total number of electrons remained virtually unaltered   pathway, are mainly produced during the plasma formation process  pathway), as shown in Figure 2(E) pathway occurs primarily within 0.1 mm of the needle tip. The CO2(V) pathway gradually excites the ground‐state CO2 molecules until it overcomes the energy barrier of CO2 decomposition  process, the energy required for each excitation step is less than 0.3 eV. Consequently, in the CO2(V) pathway, CO2 molecules could use all the low energy electrons in the plasma channel to dissociate into CO and O in the most energy‐efficient manner. According to the above analysis, the CO2(I) process occurs only during the plasma channel formation, whereas the CO2(E) and CO2(V) processes can still occur within the following 1 ms. In terms of spatial distribution, the CO2(E) process mainly occurs in the area near the tip, whereas the CO2(V) process can occur in the entire plasma channel.When eE (less than 3.0 eV) than traditional nonthermal plasma , which is suitable for the CO2(V) pathway with low energy and disfavors the high energy‐consuming CO2(D) pathway. Consequently, the ηele − chem for CO2 reduction is extremely high. Simultaneously, the low eE hinders the high energy‐consuming direct dissociation of CO2 into C and improves the selectivity of the reaction.The triboelectric plasma driven by mechanical energy has a lower 2.52 reduction system can convert CO2 to CO with high efficiency and selectivity and efficiently collect mechanical energy from nature and convert it into chemical energy. We measured the amount of CO product through our system in the environment at a wind speed of 4.0 ± 0.2 m s−1, finding that after four consecutive cycles, COr was 12.8–16.8 µmol h−1 , they highly depend on fossil fuels. Meanwhile, the photocatalytic CO2 reduction utilizes renewable, green solar energy, albeit with an energy conversion efficiency below 1.0%. Conversely, the present system uses abundant mechanical energy from nature, is easy to operate, does not require catalysts or additional reagents, and can be turned on and off on demand, rendering it suitable for decentralized carbon fixation.Our COil fuels.20 Mea32 reduction system using dual‐function, multiple‐pulse, flow‐type triboelectric plasma that operates under mild conditions to realize the collection and conversion of mechanical energy to chemical energy. This system was well‐suited to the fluctuation of mechanical energy and the flow of CO2 gas. The CO and O2 evolution rates were 12.4 and 6.7 µmol h–1, respectively, at an optimal discharge distance of 0.8 mm. The CO selectivity was 92.4%. ηele − chem was 31.9%; this value is higher than those reported for CO2 reduction methods using nonconvertible energy and other nonthermal plasma systems. The maximum ηmech − chem was 2.3%, the highest value reported to date. Plasma simulations and OES tests revealed that the average energy of electrons in the triboelectric plasma was low and CO2 reduction was primarily accomplished via vibrational excitation dissociation with a low energy barrier. Finally, our system was tested in the environment using wind as a mechanical energy source, obtaining a maximum COr of 16.8 µmol h−1.This work demonstrated a mechanical energy‐induced CO4The free‐rotating TENG comprised two parts: an electrode stator and a rotator Figure . A coppe2 gas into one end of the glass reactor and the other end was used for the gas inlet extending to a gas chromatograph. High‐speed photographs of the triboelectric plasma were obtained using high‐speed cameras .The multiple‐pulse, flowing triboelectric plasma reactor is shown in Figure 2) were detected by an online gas chromatograph (Agilent 7890B) equipped with a Shincarbon column , a thermal conductivity detector, and a flame ionization detector with a mechanized oven. Exceptionally pure He served as the transport gas. The concentration of gaseous products was calibrated using standard curves from standard gases. The conversion rate of CO2 was estimated as follows.nCO is the mole of CO product per time, and nCO2 is the initial mole of CO2 substrate per time.The gaseous products (CO and OThe discharge voltage and current were measured using two programmable electrometers (Keithley 6514) at different ranges. Before connecting it to the circuit, the electrometer measuring the discharge voltage was connected in series with the appropriate sampling resistor (≈GΩ). The measured signals were fed into a high‐speed data acquisition system controlled by LabView software.Pave was calculated using the following equation.V is the discharge voltage (V), I is the discharge current (A), and t is the discharge time (s).ηele − chem was estimated as follows.HR is the reaction enthalpy of CO2 splitting to CO (279.8 kJ mol−1).Pmech provided for the TENG, a dynamic torque measurement system was constructed. The fabrication of the TENG used to measure ηmech − chem was different from that of the TENG used to determine the activity of CO2 dissociation at different rotational speeds and needle‐plate distances. The former TENG was constructed using triboelectric layers of rabbit hair and PTFE because the two triboelectric layers were easy to connect to the dynamic torque measurement system. In fact, no significant differences were observed in the energy conversion efficiencies of the CO2 reduction systems using the two TENGs. The Pmech provided for the TENG was accurately measured using the torque sensor  and n is the rotational speed of the TENG (r min−1).The ηmech − chem.HR value is the same as that described in Equation  and the CO sensor was used for online detection. The maximum range of the CO sensor was 1000 ppm; therefore, the experiment was terminated when the CO concentration in the reactor reached 1000 ppm. The experiment was repeated four times.To confirm whether the triboelectric plasma‐triggered CO13C‐ and 18O‐isotope labeling experiments were performed using 13CO2 or C18O2 as substrates under the same conditions used in previous triboelectric plasma‐triggered CO2 reduction reactions. The isotopic products produced by the triboelectric plasma were introduced into a sealed bag for analysis. The composition and concentration of the gaseous products were analyzed at Wuhan New Radar Gas Co., Ltd, Hubei province, China.2 reduction system. The DMPO solution was degassed at least twice by performing freeze–pump–thaw cycles using CO2 gas. Once the triboelectric plasma process ended, a certain amount of solution was collected through the capillary tube and placed into a quartz nuclear magnetic resonance tube together with the DMPO solution. Then, the tube was put into the EPR equipment for detection and analysis.EPR experiments were implemented at room temperature (16–18 °C) using a Bruker EPR A200 X‐band spectrometer . DMPO purchased from Sigma, Shanghai, China, was used to capture the reactive species generated in the CO The code used in this work has been well validated by high resolution experimental measurements of electric field, optical emission, discharge morphology, as well as voltage‐current profiles. Details could be found in the literature for point‐to‐plane discharges, in the literature for surface discharges, and in the literature for point‐to‐point discharges. The non‐Maxwellian EEDF, electron swarm parameters, and electron impact reaction rates were obtained with the help of the BOLSIG+ package under the two terms approximation of the Boltzmann equation of electrons.The spatial‐temporal distributions of electron density and electron energy density of the triboelectric plasma were calculated using the 2D PASSKEy  code under the cylindrical axis. The code solved a set of drift‐diffusion‐reaction equations coupled with Poisson's equation, and detailed mathematical formulas and proofs could be found in the literature.22 TheV, I, Pave, COr, O2 generation rate, CO selectivity, ηele − chem, ηmech − chem, and CO2 conversion rate were obtained by averaging the data. All the data were performed using Origin Software , obtaining the average value and error bar (the standard deviation). EPR spectrum was simulated and analyzed using the biomolecular EPR spectrum software. Triboelectric plasma simulation and analysis were performed using the method previously reported in the literature.All the experiments in this paper were operated at least twice, independently. There were few differences between the two experimental data. The The authors declare no conflict of interest.Supporting InformationClick here for additional data file.


Activation of the robust C–H bond of methane is hardly induced by the direct interaction with photogenerated holes trapped at the surface of photocatalyst; instead, the C–H activation is significantly promoted by the photoactivated interfacial water species. The interfacial water hydrates and properly stabilizes hydrocarbon radical intermediates, thereby suppressing their overstabilization. Owing to these water-assisted effects, the photocatalytic conversion rates of methane under wet conditions are dramatically improved by typically more than 30 times at ambient temperatures (~300 K) and pressures (~1 atm) in comparison to those under dry conditions. This study sheds new light on the role of interfacial water and provides a firm basis for design strategies for non-thermal heterogeneous catalysis of methane under ambient conditions.On-site and on-demand photocatalytic methane conversion under ambient conditions is one of the urgent global challenges for the sustainable use of ubiquitous methane resources. However, the lack of microscopic knowledge on its reaction mechanism prevents the development of engineering strategies for methane photocatalysis. Combining real-time mass spectrometry and  operando infrared absorption spectroscopy with ab initio molecular dynamics simulations, the authors explore the role of interfacial water in C–H activation during the photocatalytic conversion of methane.Photocatalytic methane conversion under ambient conditions holds immense promise for sustainable use of methane resources, but incomplete knowledge of reaction mechanisms hampers the development of engineering strategies for methane photocatalysis. Here, combining real-time mass spectrometry and  Therefore, conversion of the most unreactive hydrocarbon of methane under mild reaction condition is challenging, remaining one of the globally important agendas for the development of a green society1. Industrially, methane is utilized in the catalytic steam reforming reaction (CH4 + H2O → CO + 3H2) at high temperatures and pressures (700–1100 °C and 20–40 atm) to produce synthesis gas, a feedstock for the production of various chemical products3. To overcome this energy-intensive process5 and realize on-site and on-demand methane conversion technologies for sustainable methane utilization3, it is indispensable to develop an effective methane activation method at ambient temperatures and pressures.Methane, the main component of natural gas and a ubiquitous natural carbon resource, has the most robust C–H bonds (bond dissociation energy: 439 kJ/mol) and the highest activation barrier among the hydrocarbon species8, CO2 reduction9, and organic synthesis with water10 can be photocatalyzed at ambient conditions beyond thermodynamic limitations11. Recently, the application of photocatalytic technology to the conversion of methane with robust C–H bonds has been reported13. In principle, the oxidation and reduction reactions are induced on the surface of photocatalysts by photogenerated holes and electrons, respectively. However, despite intensive research in the past, the microscopic mechanism of non-thermal methane activation is not yet clear13.Photocatalysis is a promising technology in which redox reactions are promoted by light; endergonic reactions such as water splitting18 and fluorescence spectroscopy21, have shown that photogenerated holes can be present on the surfaces of photocatalysts in various forms, such as holes trapped at surface lattice oxygen (Olat) sites and holes trapped as surface hydroxyl radicals or ad-atom oxygen radicals derived from adsorbed water species28. However, definitive identification of the hole-derived reactive species in the non-thermal methane conversion has been difficult with these traditional ex-situ measurement techniques owing to the huge gap between the measurement and actual working conditions for methane photocatalysis. Measurements are generally conducted at liquid-nitrogen temperature18 or in the presence of additive molecules, such as spin trap scavengers15 or radical marker molecules21. Because these differences in environmental conditions inevitably disturb the inherent reaction system of methane, in-situ/operando identification of reactive species and intermediates with non-invasive detection techniques are of crucial importance to elucidate the mechanism of non-thermal C–H activation of methane and to develop engineering strategies for effective interfacial chemical systems at the molecular level.The lack of an accurate and comprehensive understanding of the microscopic mechanism obscures the design strategies of optimal reaction system for the photocatalytic conversion of methane. Because methane is a fully reduced molecule, its activation is driven solely by the oxidation reaction induced by the photogenerated holes. Various observation methods, such as electron spin resonanceoperando infrared (IR) absorption spectroscopy and ab initio molecular dynamics (AIMD) simulations to provide microscopic insights into non-thermal photocatalytic conversion of methane. We employed three metal oxides as representative d10 (Pt/Ga2O3) and d0 (Pt/NaTaO3 and Pt/TiO2) photocatalysts8. Systematic experiments on these photocatalysts under controlled pressures of methane gas and water vapor clearly showed that interfacial water species play a key role in the photocatalytic methane conversion under ambient conditions. The interfacial water is preferentially oxidized by photogenerated holes trapped at photocatalyst surfaces, and the preactivated water species effectively catalyze the C–H bond breaking of methane. Moreover, the interfacial hydrogen-bond network prevents the overstabilization of the intermediates and contributes to increasing the photocatalytic reactivity of methane at ambient temperatures and pressures.Here, we combined real-time mass spectrometry with 2O3, NaTaO3, and TiO2 as representative d10 (Ga2O3) and d0 (NaTaO3 and TiO2) photocatalysts whose conduction bands are composed predominantly of sp and d orbitals, respectively8. These photocatalyst samples are known to have stable activities and significant robustness without catalyst deactivation, e.g., photo-corrosion30. In addition, TiO2 is a well-known model material in photocatalysis because the TiO2 photocatalyst has been studied for over half a century31 since the discovery of Honda-Fujishima effect6.We employed Ga22.The reaction activity was evaluated under dry 34. In this case, the conversion rate was extremely low (~0.2 μmol/h). By contrast, in the presence of adsorbed water layer under the wet condition, the methane conversion rates drastically increased  but also the production of carbon monoxide (CH4 + H2O → CO + 3H2) and ethane (2CH4 → C2H6 + H2) was confirmed as methane derived species  was 11.6 ± 0.3 μmol/h, which is over 30 times higher than the value obtained in the absence of water. The hydrogen formation rate also increased under the wet condition . Note that the methane conversion rate was independent of water isotopes. As shown in Fig. 18O species to 16O species indicates that the contribution of interfacial water (18O species) to CO2 formation is substantially dominant to that of Olat (16O species) regardless of the photocatalyst sample used. This indicates that the photocatalytic oxidative methane conversion is not mainly induced by photogenerated holes trapped at surface Olat sites; instead, it is dominated by interfacial water species preactivated with photogenerated holes. This observed sample-independent feature is in stark contrast to previous studies on the pure water splitting reaction, for which the involvement of Olat in photocatalysis depends on whether photocatalyst material is d10 (Pt/Ga2O335) or d0 (Pt/NaTaO336 and Pt/TiO237).To verify the contribution of interfacial adsorbed water on methane conversion, reaction experiments were conducted for all photocatalysts using isotopically labeled water (H4 → C2H6 + H2). Thus, ethane formation under wet conditions must be mechanistically different from the non-oxidative coupling of methane previously reported in the absence of water34. This implies that the interfacial water species contribute by catalyzing the first oxidative C–H cleavage process (CH4 → •CH3) and promote the subsequent homocoupling (2•CH3 → C2H6)17.Notably, ethane production was also dramatically enhanced for all photocatalysts owing to the presence of interfacial water Fig. , althougoperando IR spectroscopy with isotope-labeled water (D2O) under the reaction conditions. Almost no isotope effect was observed on the conversion rate and selectivity  derived from the hydrogen-bonded adsorbed HDO molecules emerged under UV irradiation  at the photocatalyst surface, as follows:To shed new light on the role of interfacial water in the C–H cleavage process, we conducted ity Fig. , indicatsee Fig.  and S2-3see Fig. . No appr•OD(ad) is preferentially formed via the oxidation of adsorbed D2O molecule by the surface-trapped holes at Olat site24 as follows:The 3 radical (•CH3) in Eq.  + •OH(gas) → •CH3(gas) + H2O(gas))38.If the CH) in Eq.  is the fres Fig.  to confi4 → •CH3). Under dry conditions, C–H cleavage is induced via hydrogen abstraction only by direct hole transfer from surface Olat. The presence of interfacial water offers another C–H cleavage process via hydrogen abstraction by photoactivated interfacial water species (Eq. (4(gas) + •OH(ad) → •CH3(ad) + H2O(ad)). Owing to the water-assisted process, the production of reactive •CH3 radicals would become more efficient, and the homocoupling reaction (2•CH3 → C2H6) is accelerated under wet conditions.The pronounced increase in the ethane production rate under the wet conditions Fig.  can be ries  states that are presumably involved in the pristine reaction. The details of calculation procedure are presented in the “Methods” section.To provide detailed molecular-level insights into the photocatalytic C–H activation kinetics, AIMD simulations were carried out with density functional theory (DFT) calculations with hybrid fuctional on a lat site on the bare Ga2O3 surface  would occur simultaneously via proton-coupled electron transfer (PCET). Then, we examined the potential energy curve (PEC) for the •CH3 formation and found that the •CH3 formation is exothermic  and results in further hydrogen abstraction from •CH3 to form other hydrocarbon species and coke34.First, we confirmed in our calculations that a hole exists in the Oace Fig. . Therefo2O3 surface is covered with several layers of adsorbed water, which is preferentially activated by interacting with the hole center on the Olat (H2O + •OH + H–Olat) via PCET , which indicates that surface holes exist as •OH. Therefore, under the wet condition, the water-assisted activation pathway of methane emerges: CH4 + •OH → •CH3 + H2O. Figure 4 and •OH. The C–H activation of methane via hydrogen abstraction by •OH has an energy barrier of 38.4 kJ/mol, which can be adequately overcome at ambient temperature43. In this case, the produced •CH3 is moderately stabilized by the hydration with water (ΔE = −50.2 kJ/mol). The proper stabilization of the reaction intermediates in the order of 50 kJ/mol is crucial for the methane conversion to proceed under ambient reaction conditions , which is discussed in detail in the following section.This overstabilization is strongly altered by hydration with interfacial water. Under wet conditions, the GaCET Fig. . Our calE ~ −50 kJ/mol under the wet condition, Fig. E ~ −15 kJ/mol, Fig. 41. By contrast, the barrier for water activation is ~20 kJ/mol . As shown in Figs. 45), the formation rates would increase linearly with 2O3, Pt/NaTaO3, and Pt/TiO2 photocatalysts, indicating that the reaction mechanism is common in the three samples and that methane partial pressure is a key parameter for the occurrence of non-thermal methane conversion.The methane conversion rates were divided into the formation of each product (Hmentclass2pt{minim4(gas) + •OH(ad) → •CH3(ad) + H2O(ad)) with a relatively low activation barrier  + H2O(ad) → CH4(gas) + •OH(ad)) or undergoes multistep surface reactions to form C2H6, CO, and CO2 through multiple intermediates  of each molecule under steady-state reaction condition is simply described by the following equation: R ∝ •CH3(ad) intermediate and n is the reaction order: n = 1 for the CO and CO2 formations and n = 2 for the C2H6 formation.As discussed in the previous section, photoactivation of interfacial water is not rate-determining and the methane from the gas phase is cleaved by these photo-activated water species  and reverse (desorption of methane) reactions of Eq. (K ≡ kad/kde ∝ exp(U/kBTs). kB and Ts are the Boltzmann constant and surface temperature, respectively, and U is the stabilization energy of the •CH3(ad) intermediate (X1) relative to that of methane in the presence of interfacial water  to 101 kPa (10−1 atm) as U increases from 15 kJ/mol to 40 kJ/mol. The considerable difference between the dependences of As discussed in detail in Supplementary Note mentclass2pt{minimter Fig. . The \doale Fig. . As shown can be clearly distinguished, and the stabilization energy U can be evaluated by curve fitting. For ethane formation, the reaction intermediate is assumed to be •CH3(ad), while the reaction order n is 2 for the homocoupling. As shown in Fig. 2, with the U values ~40 kJ/mol  as Rj ∝ j = CO or CO2) with the U values listed in Table 2 are formed through multiple reactions with various intermediates  at the later part of the multiple surface reactions , our main conclusion regarding the water-assisted effects is essentially unaffected. As discussed in detail in Supplementary Note 2 formation rates vs. Rj ∝ j = CO or CO2), where the constant K is proportional to exp(U/kBTs) and U is the stabilization energy of the corresponding rate-determining intermediate . Furthermore, most of the metal oxide surfaces interact with methane molecules quite weakly in comparison to water molecules: thus, methane molecules cannot substantially adsorb on surfaces without UV irradiation. Therefore, the interfacial water molecules have much opportunity to accept photogenerated holes from the surfaces in comparison with gaseous methane molecules, and are kinetically advantageous for the hole-driven oxidation. The water-assisted effects would be universal among the metal oxide photocatalysts with these features.0 and d10 oxide photocatalysts  with the different band-gap energy that the photocatalytic activation of the robust C–H bond of methane is efficiently accelerated by interfacial water species at ambient temperatures and pressures. Combining real-time mass spectrometry, operando IR spectroscopy, and AIMD simulations, we have shown that the methane conversion is hardly induced by the direct interaction with the trapped hole at the surface Olat site; instead, activation is significantly promoted by low barrier hydrogen abstraction from methane by the photoactivated interfacial water species. In the water-mediated processes, the photocatalytic C–H activation is not the rate-determining step, which is in stark contrast to the case of traditional thermocatalytic methane reforming. Moreover, owing to the moderate stabilization of •CH3 in the hydrogen-bond network of water, the overall photocatalytic conversion rates are dramatically improved by typically more than 30 times at ambient temperatures (~300 K) and pressures (~1 atm). As essentially opposed to thermal catalysis, methane photocatalysis no longer requires high-pressure methane gas (>20 atm) in the presence of adsorbed water layer. The water-assisted effects are noticeable also in ethane formation, although water is not explicitly involved in the homocoupling reaction equation (2CH4 → C2H6 + H2). These results indicate that the interfacial water kinetically plays crucial roles beyond the traditional thermodynamic concept of redox potential, in which oxidation of water by surface trapped holes is less thermodynamically favored than methane oxidation: 40 and 41 versus SHE at pH7. Our work not only expands the molecular-level understanding of the non-thermal C–H activation and conversion but also provides a fundamental basis for the rational interface design of photocatalytic systems toward the effective and sustainable utilization of methane under ambient conditions.In summary, we have demonstrated for the three representative d2 window in a chamber filled with water vapor  and methane (CH4). Methane (>99.99% purity) and water vapor  were pre-degassed in an ultrahigh vacuum gas line via freeze-pump–thaw cycles and introduced in the chamber with a base pressure lower than 1 × 10–3 Pa. The partial pressure of the water vapor was fixed at 0 kPa or 2 kPa, whereas the partial pressure of methane was varied in the range of 5 kPa (0.05 atm) to 120 kPa (1.2 atm). The light source was a Xe lamp with a high intensity in the deep UV region , and light was led to the catalysts using an optical fiber. The intensity of the light irradiated on the catalysts was approximately 90 mW cm–2 at a wavelength of 250 nm. The temperature of the samples was measured using a chromel–alumel thermocouple (type-K). The product gases were measured using a quadrupole mass spectrometer . For all photocatalysts, the yield of the reaction products increased almost linearly with the UV irradiation time ; therefore, the associated decrease in the inlet CH4 pressure can be neglected. Under 2 kPa of water vapor, less than 4% of the adsorbed water was consumed during the reaction experiments . The catalysts were irradiated with UV light through a CaFme Figs.  and S2-32O3 powder , 0.2 wt% Pt-loaded La-doped (1 mol%) NaTaO3 (Pt/NaTaO3), and 1 wt% Pt-loaded commercial anatase TiO2 powder . The SEM and TEM images of these photocatalyst samples are shown in Fig. 3 sample was prepared by a flux method43. Pt was loaded onto the Ga2O3 and NaTaO3 samples using an impregnation method30. Each sample was soaked in an aqueous H2PtCl6 solution (corresponding to 1 wt% or 0.2 wt% Pt). The solution was heated to 368 K until dry. The dried samples were calcined at 673 K for 2 h. Pt was loaded on the TiO2 by a photodeposition method46 using a Xe lamp . TiO2 was dispersed in an aqueous ethanol solution (3 vol%) containing H2PtCl6 (corresponding to 1 wt%) and exposed to light for 1.5 h with continuous stirring. The solution was heated to 393 K until dry. Typical X-ray diffraction patterns of Pt were confirmed. Methane conversion rates for bare photocatalyst sample without Pt cocatalyst were typically less than a tenth of the methane conversion rates for Pt-loaded samples.The samples used in this study were 1 wt% Pt-loaded commercial Gaoperando DRIFT spectroscopy of the catalyst surfaces was conducted using a homemade diffuse scattering measurement setup47 coupled with a Fourier transform infrared spectroscopy system  with a HgCdTe detector at a resolution of 4 cm–1. The background for the DRIFT measurements was obtained with each photocatalyst sample at a stable temperature (~318 K) under the reaction conditions  the β-Ga2O3 unit cell in the lateral directions. Water molecules were distributed in the upper and lower parts of the Ga2O3 surface. To obtain a single H2O solvation layer on the Ga2O3, the following procedure was followed: first, 40 H2O molecules were included in the system. Preliminary MD calculations were performed, and the H2O molecules that were not included in the first solvation layer were removed, leaving 34 H2O molecules on the surface. The unit cell of the H2O–Ga2O3 surface contained 222 atoms; see Fig. 48, and the PBE0 was used for the hybrid DFT calculations50. Hybridized DFT should be considered more accurate because the exact exchange is admixtured. Because the GGA is known to yield a delocalized electronic state, its accuracy (including that of the electron hole), is questionable26. Therefore, the PBE functional was used for the preliminary calculation of the ground state, whereas the PBE0 was used for the productive calculations. The MOLOPT basis set and Goedecker–Teter–Hutter pseudopotential were used to represent the valence and core electrons, respectively51. The DZVP basis set was used for the valence electrons of all elements. The convergence threshold of the electronic energy was 1.0 × 10−5 eV. The cut-off energy of the plane wave was 400 eV. After geometry optimization, an equilibration MD run was performed for 10 ps at the GGA level. Then, the additional equilibration run at hybridized DFT was conducted for 3 ps, followed by a production run for 7 ps after these equilibration steps. MD simulations were performed with the NVT ensemble, where the Nose–Hoover thermostat was used to control the temperature to 300 K ± 30 K. In the PEC calculation, the difference of the following two distances, namely, (i) between Ga and the O atom of H2O 2) was applied with the K parameter of 1.0 × 10−3 (a.u). The distance between the O atom of •OH and the H atom of CH4 was considered as the reaction coordinate in the •CH3 formation reaction in the presence of water. The distance between the H atom of CH4 and Olat was considered as the reaction coordinate in the CH3 formation reaction in the absence of water. The average value of the potential energy over the production run (7 ps) was used for the PEC.The GaPeer Review FileSupplementary Inforamtion


The activation of aziridines typically involves the use of strong Lewis acids or transition metals, and methods relying on weak interactions are rare. Herein, we report that cooperative chalcogen bonding interactions in confined sites can activate sulfonyl-protected aziridines. Among the several possible distinct bonding modes, our experiments and computational studies suggest that an activation mode involving the cooperative Se···O and Se···N interactions is in operation. The catalytic reactions between weakly bonded supramolecular species and nonactivated alkenes are considered as unfavorable approaches. However, here we show that the activation of aziridines by cooperative Se···O and Se···N interactions enables the cycloaddition of weakly bonded aziridine-selenide complex with nonactivated alkenes in a catalytic manner. Thus, weak interactions can indeed enable these transformations and are an alternative to methods relying on strong Lewis acids. The activation of aziridines is typically achieved via reaction with strong Lewis acids or transition metals. Here, the authors report that cooperative Se ∙ ∙∙O and Se ∙ ∙∙N noncovalent interactions can activate sulfonyl-protected aziridines, which enables their use in cycloaddition reactions with nonactivated alkenes. Amongst these interactions, catalysis with hydrogen bond plays a dominant role while halogen4, as well as chalcogen bonding catalysis9, has lately attracted ever-increasing research interest. Since the weak interactions restrict both the reactivity and the concentration of equilibrating supramolecular complex, this catalysis discipline has its constraint boundary considering the limitations of the activation targets and reaction patterns10. Even though weak interactions can activate a range of molecules such as carbonyl compounds, imines, nitro olefins, etc., it is a challenging task for these interactions to activate target molecules like aziridines which were conventionally handled by strong Lewis acids or transition metals. , indicating that the interaction between selenium and aziridine induces the change of the 77Se signal. The interaction of Ch4 with 1a also resulted in an observable variation of the 77Se signal (0.11 ppm). In sharp contrast, an as much as 1.23 ppm down-filed shift of the 77Se signal was observed in the presence of Ch6. Since 1a was not stable enough in the presence of Ch5, the variation of 77Se signal, in this case, is invalid. Further investigation using aziridine 1b shows a similar trend of perturbation and the interaction of Ch6 and 1b gave the most dramatic change in the 77Se signal. These observations pose a confusing phenomenon that the variation of the 77Se signals of Ch5 and Ch6 is much more dramatic than chalcogen bonding donors Ch3 and Ch4.Upon forming intermolecular interaction with ent Fig. . AnalysiCh3, Ch5, and Ch6 associated with a Ch4 associated with 31 and it would provide insightful information to elucidate its structure herein. The intramolecular chalcogen bonding interactions were observed in the crystal structures Ch3-5  data of Ch3-6 are in agreement with the simulated results from corresponding single crystal diffraction data  almost remains unchanged while the chemical shift of the more remote Cβ (two bonds from S) varies dramatically when comparing the bonding performance of monodentate catalyst Ch2 (Ch2:m1 2:1) and their counterparts, bidentate catalysts Ch5 and Ch6 (Ch:m1 1:1)  to a mode of double interaction with oxygen  would lead to almost no perturbation of the chemical shift of Cα while resulting in a marked variation of Cβ. Instead, the dramatic change of Cβ attached to nitrogen indicates that a double interaction mode involving the direct interaction with nitrogen  is a reasonable binding mode to explain the experimental results. For a much sharper contrast, the formation of the complexes between Ch5/6 and m1 led to a negligible variation of Cα (0.07 and 0.06 ppm) while resulting in a much more pronounced change of Cβ (0.65 and 0.55 ppm), which also suggests the direct interaction with nitrogen  to be the active complex. To give a more direct comparison, twofold Ch7 (Ch7:m1 2:1) was used, i.e., monodentate version of Ch5 and Ch6, and similar results were obtained. Further using m2 as a model Lewis base gave similar observations.To investigate the active bonding modes Fig. , a range:1) Fig. . For a bSC6 as the active binding species. As shown in Fig. 1a′, its ring-opening counterpart m3 almost gave no change in the chemical shift of Cβ regardless of in the presence of a monodentate or a bidentate catalyst. These observations indicate the structure of the nitrogen part is critically important to the chalcogen bonding interactions. The distinct perturbation of the chemical shift of Cβ between aziridine 1a′ and its ring-opening counterpart m3 suggests a direct interaction with nitrogen  is in operation rather than interaction with the relatively more remote oxygen (SC4 or SC5).The subsequent molecular control experiments further support SC4 and SC5). For Cβ in the piperidine ring, the variation of the chemical shift decreased from m4 to m5. However, a reverse variation of Cβ′ relative to Cβ was observed, that is, a decreased variation of the chemical shift of Cβ leads to an increased variation of the chemical shift of Cβ′. These molecular balance experiments indicate the equilibrating interaction with one of the two nitrogen parts is more favorable, thus suggesting binding modes SC6 is operative rather than SC4 or SC5. Further investigation reveals that the substitution group in the aziridine ring has a pronounced effect on the variation of the chemical shift of the ring carbons attached to nitrogen  resulted in a marked variation of the chemical shift while the ring carbon Cβ in m7 with an aromatic substitution  almost remains unchanged (Ch4) or even shifted to a reverse direction . These experiments indicate the substitution group in the aziridine ring can largely affect the interactions, thus pointing out a mode involving the direct interaction with the nitrogen atom . Therefore, the molecular control experiments depicted in Fig. SC6 is the active binding mode of bidentate chalcogen bonding donors Ch4-6.The results of the molecular balance experiments in Fig. gen Fig. . It was SC6 between Ch5 and 1-(phenylsulfonyl)aziridine were further corroborated by DFT calculations , suggesting that the formation of SC6 is more favorable and feasible. These calculated energies are in a reasonable range considering the literature precedents39. Natural bond orbital (NBO) analyses of SC3 and SC6  to give reactivity in the presence of a transition-metal catalyst43. To achieve this reaction by a weak interaction, there are two challenging problems , the reaction did not work. Furthermore, only a trace amount of product 3a (<5%) was obtained using a stoichiometric amount of a hydrogen-bonding catalyst H1 (1.0 equiv), indicating inertness of this reaction under activation by weak interactions. Considering the poor reactivity of this cycloaddition reaction, we envisioned that cooperative chalcogen–bonding interactions with aziridine would enhance the activation ability and provide more stabilization of the supramolecular species, thus improving the reactivity. However, to match the confined Lewis basic binding sites in phenylsulfonyl protected aziridines, the judicious use of bidentate chalcogen bonding donors that are capable of precisely recognizing the proper Lewis basic sites of aziridine is critically important to give catalytic activity aziridine  and 10 mol% selenide Ch5 in DCE by TLC revealed that 1b was fully decomposed after only 80 s at room temperature, which was further supported by 1H NMR analysis of this mixture. In sharp contrast, for a reaction mixture of N-(p-nitrobenzenesulfonyl)aziridine 1a and 10 mol% selenide Ch5 in DCE, 76% 1a remained unchanged after 80 s. To corroborate these observations, further analysis of a 1:1 competitive mixture of 1a and 1b in the presence of 10 mol% selenide Ch5 in CD2Cl2 indicated that 1b was fully decomposed while 81% of 1a remained unchanged in this reaction mixture after 80 s. Therefore, in order to suppress side reaction pathways, nitrobenzenesulfonyl protecting group is an optimal choice.Further investigation of the catalytic performance of the bidentate catalysts Ch4 (<5% 3a). In line with the analysis as depicted in Fig. SC6 was generated and it is susceptible to completive bonding.Since the weak nature of chalcogen bonding interactions restricts both the reactivity and the concentration of equilibrating aziridine-selenide complex, the control experiment Fig.  demonstrCh6 could act as an effective bidentate chalcogen bonding donor to form complex SC6, however, Ch6 is less efficient to activate electron-deficient Ns-protected aziridines in contrast to its counterpart Ch4 or Ch5. On the other hand, comparable results on the interactions of more electron-rich aziridines m1-2 with Ch5 and Ch6 were observed .While the experiments in Fig. ved Fig. , indicatout Fig. . The con3a was improved from 77 to 85% upon conducting the reaction at 50 °C. Tracing the reaction system by 31P NMR reveals that catalyst Ch4 is stable in this reaction process and only the 31P signal of catalyst Ch4 was observed . Furthermore, alkynes were also effective substrates44, and products 5a-5i were obtained in 60–79% yields  at 0 °C under argon was added TMSOTf . The reaction mixture was allowed to warm up to room temperature and stirred for 40 min to give a dark orange solution. Then 1.0 mmol phosphine ]bis(diphenylphosphine) for Ch3; bis(diphenylphosphine) for Ch4; bis(diphenylphosphino)methane for Ch5; 1,2-bis(diphenylphosphino)ethane for Ch6; 1,5-bis(diphenylphosphino)pentane for Ch8) dissolved in dry CH2Cl2 (4.0 mL) was added over 5 min at 0 °C. The reaction mixture was allowed to warm up to room temperature and stand for 1 h. The white solid suspension was filtered and washed by anhydrous diethyl ether. Then sodium tetrakisborate  was added to a solution of the above white solid (1.0 mmol) in dry CH2Cl2 (10.0 mL) under argon and the reaction mixture was stirred at room temperature for 24 h. Then the reaction mixture was filtered and the filtrate was concentrated to give a saturated solution under reduced pressure and then 10.0 mL n-hexane was slowly added. The two-phase solution was placed at room temperature under argon and the desired product precipitated out as a white solid. Then the precipitated white solid was collected by filtration and recrystallized twice from CH2Cl2 (or ether) and n-hexane to afford the pure catalyst.To a red solution of PhSeCl  in dry EtCh2 and Ch7) or 3,5-F2C6H3SeCl  in dry Et2O (6.0 mL) at 0 °C under argon was added TMSOTf . The reaction mixture was allowed to warm up to room temperature and stirred for 40 min to give a dark orange solution. Then 1.0 mmol phosphine  dissolved in dry CH2Cl2 (4.0 mL) was added over 5 min at 0 °C. The reaction mixture was allowed to warm up to room temperature and stand for 1 h. Then sodium tetrakisborate  was added to the above reaction system and stirred at room temperature for 24 h. Then the reaction mixture was filtered and the filtrate was concentrated to give a saturated solution under reduced pressure and then 10.0 mL n-hexane was slowly added. The two-phase solution was placed at room temperature under argon and the desirable product precipitated out as a white solid. Then the precipitated white solid was collected by filtration and recrystallized twice from CH2Cl2 and n-hexane to afford the pure catalyst.To a red solution of PhSeCl  and catalyst Ch4  in a 10-mL-Schlenk tube was added DCE (1.0 mL) under argon atmosphere. Then the corresponding reactant alkene 2 or alkyne 4 or ketone 6  was added to the above reaction mixture. The reaction was stirred at indicated temperature  until the completion of the reaction as judged by TLC analysis. Then the solvent was removed under reduced pressure and the residue was purified by flash chromatography on silica gel using petroleum ether/ethyl acetate (v/v = 30:1 to 10:1) as eluent to give the desired products.To a reaction mixture of aziridine Supplementary Information


The nanocomposite was fabricated by simple in situ synthesis of PANI at the surface of rGO sheet which was followed by stirring with AEC biosynthesized AgNPs to form a nanocomposite. The AgNPs, GO, rGO, PANI, rGO–PANI, and AgNPs–rGO–PANI nanocomposite and their interaction were studied by UV-vis, FTIR, XRD, SEM, EDX and XPS analysis. AgNPs–rGO–PANI nanocomposite was loaded (0.5 mg cm−2) on a glassy carbon electrode (GCE) where the active surface area was maintained at 0.2 cm2 for investigation of the electrochemical properties. It was found that AgNPs–rGO–PANI–GCE had high sensitivity towards the reduction of H2O2 than AgNPs–rGO which occurred at −0.4 V vs. SCE due to the presence of PANI (AgNPs have direct electronic interaction with N atom of the PANI backbone) which enhanced the rate of transfer of electron during the electrochemical reduction of H2O2. The calibration plots of H2O2 electrochemical detection was established in the range of 0.01 μM to 1000 μM (R2 = 0.99) with a detection limit of 50 nM, the response time of about 5 s at a signal-to-noise ratio (S/N = 3). The sensitivity was calculated as 14.7 μA mM−1 cm−2 which indicated a significant potential as a non-enzymatic H2O2 sensor.The current study aims at the development of an electrochemical sensor based on a silver nanoparticle–reduced graphene oxide–polyaniline (AgNPs–rGO–PANI) nanocomposite for the sensitive and selective detection of hydrogen peroxide (H 2O2).The current study aims at the development of an electrochemical sensor based on a silver nanoparticle–reduced graphene oxide–polyaniline (AgNPs–rGO–PANI) nanocomposite for the sensitive and selective detection of hydrogen peroxide (H In addition to this, H2O2 is also produced as a by-product of several enzyme-catalysed reactions such as cholesterol oxidase, glucose oxidase, glutamate oxidase, lactate oxidase etc.3 Therefore, the development of simple and cost effective analytical techniques for the selective and quantitative detection of H2O2 has become an immense challenge after the researcher engaged in the detection of H2O2.4 So, far several analytical techniques such as such as spectrophotometry.5 Fluorimetry,6 electrochemical7 and chemiluminescence8 have been employed for the determination of H2O2. Among these, the electrochemical method offers a rapid and simple approach for the sensitive detection of H2O2. The electrochemical method is performed through enzyme and non-enzyme based biosensor. Although, the enzyme-based sensors so far developed, are simple with high sensitivity and selectivity but the instability, high initial cost, complex immobilisation procedure and shorter lifetime has limited the practical applicability in biosensing applications.9 For avoiding these problems, several studies have been made out to develop non-enzyme based biosensors having a high and broad range of response.Hydrogen peroxide . But the major drawback of the rGO is agglomeration and reverting to graphite. To overcome these problems, at present the researchers are focused on the preparation of the nanocomposite of rGO with conducting polymers which provide stability to it by combining with the oxygenated functional groups. Therefore, new polymer nanocomposite with superior conducting properties can be obtained by surface coating of the rGO with conducting polymer due to a synergistic effect. This effect facilitates the shorter ion diffusion path with π–π interaction which enhances the transport of electron. Among several conducting polymers, polyaniline (PANI) is considered as a perfect conducting polymer which has attracted the interest of the researchers because of its low cost, light weight, environmentally good, high energy density, controllable electrical conductivity, and faster loading/deloading rate during charge/discharge process.17,18 But, the lower processing ability and weaker mechanical strength of PANI and its sensor could be enhanced by fabricating with metal nanoparticles (MNPs). The MNPs–rGO–PANI can modify the transfer of an electron to a greater extent which owed to the strong electronic interaction among MNPs, rGO, and PANI. Several nanocomposites containing MNPs, rGO, and PANI have been prepared which corroborated the enhanced electrocatalytic activity as compared to pure graphene, PANI, and MNPs. For example, Zheng et al., 2016 has prepared the CuNPs/graphene/PANI nanocomposite for highly sensitive electrochemical sensing of glucose.19 Ghanbari & Moloudi, have detected uric acid and dopamine using ZnO/rGO/PANI nanocomposite.20The development of nanoscience and nanotechnology has offered new avenues for the application of carbon-based nonmaterial such as graphene,2O2 by an electrochemical technique where the rGO was first modified with PANI to avail the hydrophilic functional –NH2 groups which facilitated the decoration of AgNPs on rGO–PANI and formed AgNPs–rGO–PANI nanocomposite.In the current work, AgNPs–rGO–PANI nanocomposite was prepared to detect H2.2.13PO4), sulfuric acid (H2SO4) and potassium permanganate (KMnO4) were procured from Sigma-Aldrich. Hydrazine (NH2NH2) and ammonium hydroxide solution (28–30% NH3 basis) were purchased from SD Fine Chemicals. Aniline, AgNO3, ammonium persulphate (APS), hydrogen peroxide  were procured from Sigma-Aldrich. Sodium phosphate (NaH2PO4 and Na2HPO4), potassium chloride (KCl) and acetone were procured from Merck, India whereas Nafion solution was procured from Alfa Aesar. The deionized double distilled water (DW) was used for making solutions in all the experiments.The graphite powder (mesh size 150 mm), phosphoric acid  then, 15 g KMnO4 was poured slowly into the reaction mixture. Thus, obtained final reaction mixture was continuously stirred at 50 °C for 12 h which was followed by the cooling at room temperature and poured into 1 L of DW by keeping it on the ice bath. Then 3 mL of H2O2 (30%) was added with continuously stirring for additional 2 h. After that, the reaction product was collected by centrifugation at 10 000 rpm for 15 min. Further, the obtained material was collected and followed by several times washing with 5% HCl and then many times with DW. Then final washed solid material i.e. GO was placed in the vacuum oven at 70 °C for 24 h. Thus obtained powdered GO was suspended in DW (1 mg mL−1) and well dispersed using ultrasonication for 1 h and then centrifuged  at 10 000 rpm for 10 min to avoid the unexfoliated GO. The brown colored GO suspension was reduced hydrothermally using ammonia solution (NH3) and hydrazine (NH2NH2) as a reducing agent. Briefly, the pH of the suspension was maintained to 10 using ammonia solution which was followed by the addition of N2H4 and stirred for 10 min. Further, the suspension was transferred to an autoclave (Teflon-lined) and kept at 200 °C for 5 h. The final black colored suspension thus obtained was collected by centrifuging several times with DW  was added slowly into the above mentioned solution. After this, the solution was followed by continued stirring for 5 h wherein it turned to dark green which indicated the synthesis of the rGO–PANI nanocomposite. After stirring, the rGO/PANI nanocomposite thus obtained was centrifuged at 10 000 rpm for 15 min and washed with distilled water. The above process was repeated four times for the removal of uncoordinated impurities and thereafter dried at 60 °C.The schematic diagram of AgNPs–rGO–PANI nanocomposite preparation is shown in 23 Further, the reaction was stirred for next 10 h. After this, the final AgNPs–rGO–PANI nanocomposite was centrifuged at 10 000 rpm for 15 min and washed several times with distilled water and dried at 60 °C.The nanocomposite of three component system (AgNPs–rGO–PANI) was prepared by a self-assembly method. For this, 0.01 g rGO–PANI nanocomposite was added into the 25 mL colloidal AgNPs obtained through our previously reported work.2.42O2 was performed by AgNPs–rGO–PANI modified glassy carbon electrode (AgNPs–rGO–PANI–GCE) which was prepared by deposition of ethanol–water (2 : 1) suspension of AgNPs–rGO–PANI on GCE. After drying at room temperature, the AgNPs–rGO–PANI on GCE, 15 μL of 1% Nafion solution was drop cast over it to enhance its adherence. The loading of electrochemical sensor mass was maintained 0.5 mg cm−2 on GCE. The GCE was found to be possessed 0.2 cm2 active surface.24 The effect of PANI on the enhanced electrocatalytic performance on H2O2 reduction was compared with an electrode without PANI (AgNPs–rGO–GCE) prepared by the same procedure. All the experiments and measurements were conducted at room temperature  was performed by applying the frequency in the range of 0.01–105 Hz at open cell potential.CV and amperometric response of AgNPs–rGO, AgNPs–rGO–PANI–GCE was performed in 0.1 M PBS solution containing 0.5 M KCl at pH 7. The amperometric response of AgNPs–rGO–PANI–GCE in PBS in the presence of H2O2 with an AgNPs–rGO system has been studied extensively due to its similar behavior with artificial peroxidase.25,26 However, the detection of a precise cathodic current by examining the contribution of the PANI in the AgNPs–rGO nanocomposite plays an essential role that allows the selective detection of preferred analytes in several practical applications. In the current work, the AgNPs–rGO–PANI composite modified GCE was employed as a simple electrochemical sensor for the rapid determination of H2O2 cathodically, through the involvement of PANI in AgNPs–rGO–PANI nanocomposite.The electrocatalytic reduction of H2.6−1. The X-ray Diffractometer (Rigaku Miniflex II) having Cu Kα radiation source and Ni filter was applied to investigate the crystallinity of the synthesized AgNPs in the range of 20° to 80° and at a scanning rate of 6° min−1 with 0.02° of step size. Primarily, the size and shape of the AgNPs was investigated using Field Emission Scanning Electron Microscopy with Energy-Dispersive X-ray . The elemental speciation and the purity were confirmed by EDX analysis. The Transmission Electron Microscopy  at accelerating voltage 200 kV was used to confirm the shape and size of the biosynthesized AgNPs. The Selected Area Electron Diffraction (SAED) demonstrated the concentric diffraction rings which also confirmed the crystallinity of the synthesized AgNPs. The X-ray Photoelectron Spectroscopy  with Mg Ka (1253.6 eV) radiation as an X-ray source was conducted for the speciation of the nanocomposite.The UV-visible spectrophotometer  was used for preliminary study of AgNPs in the range of 300 to 800 nm. The involvement of various functional groups was investigated using Fourier transform infrared spectrophotometer  in the range of 4000–400 cm2) was used as a counter electrode, saturated calomel electrode (SCE) as a reference electrode and GCE as a working electrode.The electrocatalytic activity of AgNPs–rGO–GCE and AgNPs–rGO–PANI–GCE was investigated by an electrochemical technique. Cyclic voltammetry (CV), amperometric determination and electrochemical impedance spectroscopy (EIS) were performed on a three electrode system assembly in the single chamber Pyrex glass cell. Potentiostat/galvanostat (Biologic M150) was used to take electrochemical measurements. A platinum foil  scale" fill="currentColor" stroke="none"><path d="M0 440 l0 -40 320 0 320 0 0 40 0 40 -320 0 -320 0 0 -40z M0 280 l0 -40 320 0 320 0 0 40 0 40 -320 0 -320 0 0 -40z"/></g></svg>C and n–π* transition of CO respectively.28 The absorption spectra of rGO shown in C bond with a red shift to 270 nm which clearly indicated the reduction of GO into rGO as well as restoration of CC bond in the rGO sheet.29 The UV-visible spectra of PANI shown in 30,31 The peak at 270 nm, 355 nm, 440 nm and 782 nm confirmed the grafting of PANI at the sheets of rGO  of OH, CC–H, and CC respectively. Whereas the band at 1628 cm−1, 1385 cm−1, and 1061 cm−1 were due to the presence of νs of CC, CC and O–C respectively which were same as that of peaks present in tannic acid and aqueous extract of Croton bonplandianum (AEC) as shown in Fig. S1.−1 (νs of OH), 2927 cm−1 (νs of sp2 hybridized C–H), 2852 cm−1 (νs of sp3 hybridized C–H), 1735 cm−1 (νs of CO carbonyl), 1665 cm−1 (νs of CC), 1374 cm−1 (νd of C–OH), and 1050 cm−1 (νs of epoxide). Whereas the FTIR spectrum of rGO revealed the development of a new peak at 1565 cm−1 (sp2 hybridized CC) and disappearance of peak at 1050 cm−1. The disappearance of 1050 cm−1 (νs of epoxide), as well as appearance of a peak at 1565 cm−1 (sp2 hybridized CC), confirmed the successful reduction of GO to rGO. The FTIR spectrum of PANI represented the absorption bands at 3421 cm−1, 2923 cm−1, 2853 cm−1, 1570 cm−1, and 1156 cm−1. The band present at 3421 cm−1 and 2923 cm−1 and 2853 cm−1 were due to N–H νs of PANI and aromatic sp2νs of C–H. The band present at 1570 cm−1 and 1156 cm−1 attributed to CC stretching deformation of the quinoid ring and aromatic C–H inplane bending.32 These characteristics bands confirmed the existence of emeraldine salt phase of PANI.33 The FTIR spectrum of rGO–PANI showed the characteristics bands of rGO and PANI at 3432 cm−1 (νs of NH), 2923 cm−1 (νs of C–H) 1618 cm−1 (νs of CC), 1381 cm−1 (νs of C–N), and 1013 cm−1 (νs of CC). The presence of these bands revealed the successful coating of PANI at the sheets of rGO. The observed bands of AgNPs at 862 cm−1 attributed NC stretching of an aromatic amine and metal interaction which advocated the adherence of AgNPs with PANI deposited at the sheets of rGO. Such an interaction of PANI, a sheet of rGO and AgNPs confirmed the formation of AgNPs–rGO–PANI nanocomposite.The FTIR spectra were recorded to investigate the presence of different functional groups in AgNPs, rGO and PANI as well as their interaction in rGO–PANI, and AgNPs–rGO–PANI nanocomposite which is shown in θ ≤ 80° at 6° min−1 of scanning rate and 0.02° of step size. The XRD spectrum of AgNPs depicted the diffraction peaks at 2θ = 38.09°, 44.04°, 64.26°, and 77.26°. These peaks were matched with the JCPDS file no. 040783 for the standard diffraction data of AgNPs which attributed to the (111), (200), (220) and (311) Bragg's reflections. These Bragg's reflections advocated the crystalline planes of metallic silver with face-centered cubic (fcc).34 The XRD spectrum of GO revealed the most apparent diffraction peak centred at 2θ = 10.9° which corresponded to the 002 Bragg's reflections with significantly expanded d-spacing of 0.83 nm comparatively 0.34 nm for pristine graphite.21 The comparatively larger d-spacing of rGO than pristine graphite advocated the intercalation of different oxygen bearing functional groups and water molecules between the graphitic layers. After reduction, the diffraction peak observed at 2θ = 10.9° disappeared and a broad peak centered at 2θ = 23.9°, and 43.0° was observed which attributed to (002) and (011) Bragg's reflections respectively with d-spacing of 0.418 nm. The decreased d-spacing of rGO strengthened the fact of the removal of oxygen-bearing functional groups. In addition to this, the broad peaks suggested the amorphous nature along the stacking direction of rGO sheet and the presence of layers of rGO which were different from of crystalline graphite and GO. The X-ray diffraction pattern of PANI showed the diffraction peaks at 2θ = 14.7°, 20.9° and 25.0°. These peaks corresponded to the (011), (020) and (200) Bragg's reflections respectively which advocated the crystalline planes of emeraldine salt form of PANI.35 The XRD spectra of rGO–PANI nanocomposite corroborated the presence of only two characteristics peaks of rGO at 24.6° and 43.3°. The peaks of PANI were found to be completely disappeared due to its low content and noncrystalline nature. The XRD spectra of AgNPs–rGO–PANI revealed the presence of a characteristic peak of rGO and AgNPs confirming the AgNPs–rGO–PANI nanocomposite formation.To further investigate the crystalline nature of the synthesized AgNPs, rGO, PANI and formation of rGO–PANI and AgNPs–rGO–PANI nanocomposite, XRD analysis was carried out which is shown in 27 , indicated the formation of metallic AgNPs (Ag0).23 The O 1s core level spectrum fitted into an individual component is represented in O whereas the peaks at 532.3 eV and 533.1 eV represented to the C–OH/C–O–C and OC–O respectively. The high-resolution curve fitted XPS spectrum of N 1s is shown in 3 salt used for AgNPs synthesis respectively. The XPS analysis of the AgNPs–rGO–PANI was performed to examine the elemental composition and their different possible bonding interaction. The wide scan spectrum of AgNPs/rGO/PANI is shown in ectively . Fig. 6C3.23.2.1−1 scan rate and −0.6 to 0.6 V potential range in 0.1 M PBS (pH 7.0). The bare GCE did not show any significant redox whereas the AgNPs–rGO–GCE and AgNPs–rGO–PANI–GCE showed a distinct pair of redox peaks at the potential of 0.06 V and −0.4 V which corroborated the oxidation and reduction of AgNPs.36–38 As shown in 2O2. However, the composite AgNPs–rGO–PANI–GCE showed a drastic increase in reduction current which indicated better electrocatalytic activity towards H2O2 than AgNPs–rGO–GCE  so that it may enhance the electron-transfer kinetics during its electrocatalytic reduction. Such findings provided the valuable information on the use of AgNPs–rGO–PANI–GCE as an electrode modifier; the presence of PANI along with AgNPs–rGO–GCE character increased the analytical performance. Based on previously reported mechanism,25,39,40 the electrocatalytic reduction of H2O2 on electrocatalyst occurred according to the following mechanism:–rGO–GCE . It was ncreased . The pre2O2 on the AgNPs gained an electron from it and produced adsorbed OH (OH)ads and OH−. After that, the (OH)ads received another electron from AgNPs and produced H2O. Herein; the reduction rate depends mainly on two factors: (1) the adsorption of H2O2 at the surface of electrocatalyst and (2) transfer of an electron from electrocatalyst to (OH)ads. Therefore, the property of enhancement of adsorption and electron transfer of electrocatalyst is necessary for the electrocatalytic reduction of H2O2  of 0.99 and 0.96 respectively , which intern reveals towards the electron-transfer kinetics occurring at the electrode interface. It is observed that the value of Rct in case of AgNPs–rGO–PANI–GCE was lower (9 Ω) as compared to AgNPs–rGO and blank GCE (27.5 and 37 Ω), revealing that AgNPs–rGO–PANI–GCE given the more electroactive surface area and facilitated the electron transport between the medium and electrode.43The EIS technique has been used for measuring the resistance of the modified electrode as a function of frequency because of variation in the interfacial properties. 3.2.42O2 was performed by recording the amperometric response on AgNPs–rGO–PANI–GCE by the addition of varying concentrations (0.01 μM to 1000 μM) of H2O2 in 0.1 M phosphate buffer (pH 7.0) at a working potential of −0.4 V vs. SCE. On the basis of the voltammetric results explained above, the amperometric measurement was performed to analyse the performance of AgNPs–rGO–PANI–GCE towards the electrochemical detection of H2O2, 2O2 detection on AgNPs–rGO–PANI–GCE by successive addition of H2O2 concentration. It was observed that the when the H2O2 was added into the stirring phosphate buffer, the response current was found to be increased rapidly and reached a steady state within 5 s which indicated a fast amperometric response towards the reduction of H2O2. The plot of current vs. concentration of H2O2 showed a linear relationship in the range of 0.01 to 1000 μM with a high correlation coefficient (R2 = 0.99) while the detection limitation was estimated to be 50 nM based on a signal-to-noise ratio  was added it showed a strong amperometric response which confirmed the selectivity of the AgNPs–rGO–PANI–GCE towards H2O2.The influence from common interference species such as ascorbic acid (AA), dopamine (DA) and glucose was also investigated. 4.2O2. Several instrumental techniques like UV-vis, FTIR, XRD, SEM, EDX, and XPS were used for the characterization purpose which advocated successful synthesis of AgNPs, GO, rGO, PANI, rGO–PANI and AgNPs–rGO–PANI nanocomposite. Thus obtained AgNPs–rGO–PANI nanocomposite was loaded (0.5 mg cm−2) on glassy carbon electrode (GCE) with 0.2 cm2 active surface area for the investigation of electrochemical properties. The AgNPs–rGO–PANI–GCE showed an excellent electrocatalytic performance on the reduction of H2O2. The amperometric current (μA) vs. time (s) curve displayed a linear range of 0.01–1000 μM (R2 = 0.99) with the low detection limit of 50 nM toward the electrochemical sensing of H2O2 which was due to the direct electronic interaction of AgNPs with N atom of the PANI backbone on the rGO sheet. This interaction enhanced the electron transfer kinetics during the electrochemical reduction of H2O2. High sensitivity, selectivity, wide linear range and low detection limit made the AgNPs–rGO–PANI–GCE as an excellent amperometric sensor for the detection of H2O2.In the present study, we have constructed the AgNPs–rGO–PANI nanocomposite as a simple electrochemical sensor towards the sensitive and selective detection of HThere are no conflicts to declare.RA-008-C7RA11466D-s001


Dynamic covalent polymers of different topology have been synthesized from an aromatic dialdehyde and α,ω‐dinitroalkanes via the nitroaldol reaction. All dinitroalkanes yielded dynamers with the dialdehyde, where the length of the dinitroalkane chain played a vital role in determining the structure of the final products. For longer dinitroalkanes, linear dynamers were produced, where the degree of polymerization reached a plateau at higher feed concentrations. In the reactions involving 1,4‐dinitrobutane and 1,5‐dinitropentane, specific macrocycles were formed through depolymerization of the linear chains, further driven by precipitation. At lower temperature, the same systemic self‐sorting effect was also observed for the 1,6‐dinitrohexane‐based dynamers. Moreover, the dynamers showed a clear adaptive behavior, displaying depolymerization and rearrangement of the dynamer chains in response to alternative building blocks as external stimuli. Dynamic covalent nitroaldol polymers of different topology is presented. Linear dynamers were generally produced, from which specific macrocycles were formed through depolymerization, driven by precipitation. The dynamers showed a clear adaptive behavior, displaying depolymerization and rearrangement of the dynamer chains in response to alternative building blocks as external stimuli. Complex entities constructed by reversible covalent bonds have demonstrated fascinating dynamic behaviors and rich functionalities.16, 17A variety of dynamic covalent reactions have been applied to dynamer formation, such as imine formation ,31, 32Due to its efficiency in generating new C−C bonds, the nitroaldol (Henry) reaction has been widely applied in organic synthesis since it was first discovered in 1895.50, 51In our previous study,An important challenge with dynamers is the generation and control of different oligomeric and polymeric topologies, as well as their relative stimuli‐responsive properties. Since dynamer systems rely on multiple, sequential or parallel dynamic covalent reactions, the systems may undergo complex topology changes over time, potentially leading to self‐sorting of specific structures. Furthermore, such processes may lead to emergent property changes, and a detailed understanding of these processes is, therefore, of significant value for future applications.Herein, we report the generation and evaluation of complex nitroaldol systems involving a dialdehyde and a series of α,ω‐ dinitroalkanes. In all cases, dynamers were formed, and the interplay between different topologies were studied. The dynamerization process was evaluated with respect to dinitroalkane structure, catalyst loading, and feed concentration, and kinetic studies were performed. Intriguingly, specific macrocyclization was observed in several systems, occurring in competition with the formation of linear dynamers. This gave rise to polymerization/depolymerization processes, in several cases undergoing further self‐sorting through phase changes Figure . Moreove1) was chosen as the dialdehyde building block because of its high reactivity in the nitroaldol reaction. In complement to this, eight α,ω‐dinitroalkanes (2), including 1,3‐dinitropropane (2a), 1,4‐ dinitrobutane (2b), 1,5‐dinitropentane (2c), 1,6‐dinitrohexane (2d), 1,7‐dinitroheptane (2e), 1,8‐dinitrooctane (2f), 1,9‐dinitrononane (2g), and 1,10‐dinitrodecane (2h), were selected as dinitroalkane building blocks  was used as base throughout, and all reactions were carried out in acetonitrile due to the high solubility of the starting materials in this solvent. Under these conditions, dual entrypoint equilibration analysis indicated that the proposed nitroaldol polymerization operated under thermodynamic control  and the α‐protons of the nitroalkane (4.57–4.38 ppm) nearly disappeared.Polymers were generated from all systems within 48 h, as demonstrated by the broad signals in the a Figure . Interes−10 cm2/s in all eight dynamer systems, indicating the formation of oligomers or polymers  and gel permeation chromatography (GPC). The DOSY experiments revealed the formation of species with diffusion coefficients in the range of 0.26–1.10)×10.10×10−103a to dynamer 3d and reached a plateau at around 34 from dynamer 3d to dynamer 3h. The lower degree of polymerization for the shorter dinitroalkanes is likely an effect of steric hindrance (dynamer 3a), possibly coupled with the precipitation of insoluble products (dynamers 3b–3c). On the other hand, the comparable structure and reactivity of the longer dinitroalkanes (2d–2h), resulted in the generation of dynamers with very similar degrees of polymerization. Given the high solubility of the products, this is a reflection of the concentration‐dependent polymer growth and the dynamics of the polymerization reaction. At a concentration threshold of around 45 mM of the starting materials, the rates of polymerization and depolymerization were thus balanced. Moreover, dynamers 3a–3c showed relatively low polydispersity indices (Đ), indicating the formation of shorter, more homogeneous oligomers; whereas dynamers 3d–3h all had a wider molecular weight distribution (Đ=1.7).Further information of the molecular weights and the weight distributions of the dynamers were provided by GPC Table  from whi1 and dinitroalkane 2b, as well as dialdehyde 1 with dinitroalkane 2c, were composed of small molecules instead of polymers  indicated that the precipitates in the systems involving dialdehyde exchange.57, 581 and dinitroalkane 2b were dissolved in acetonitrile at a feed concentration of 0.5 M. After adding 10 mol % of Et3N, aliquots of the solution were withdrawn periodically and analyzed by GPC. The resulting GPC‐profile revealed that the reaction products were mainly short oligomers  in the early stage of the reaction. However, at longer reaction times, the oligomer concentration decreased while the amount of lowellane 7, composed of two of each building block (DP corresponding to 2), increased .At room temperature, the precipitation‐driven process was only observed with dinitroalkanes s Figure a. This f1 and dinitroalkane 2d at room temperature in CD3CN. The 1H NMR spectra show that the reaction proceeded rapidly during the first hour after Et3N was added  of 1.27×10−3/s  and the conversion of dialdehyde 1 from the GPC and 1H NMR data approximately fits a step‐growth polymerization model  on the reaction kinetics was also investigated by 1H NMR. The reaction was found to be approximately first order in Et3N, and the reaction rate constant increased with the amount of Et3N within the first hour . On the other hand, the GPC results reveal clearer differences between the polymers (Table S4). The Mn of the polymer prepared using 5 mol % of Et3N was slightly lower than those made with higher ratios of base, although the difference was not significant in the range of 10–25 mol % , and DOSY analysis revealed a clear inverse dependency between the diffusion coefficients and the feed concentration . However, the GPC analysis resulted in a clearer influence of the feed concentration  or bifunctional compound 2b as stimuli. The results indicate that the dynamer underwent substantial changes in response to the added reagents. Thus, after exposure to the stimuli, the product solutions produced significantly higher diffusion coefficients than the original dynamer sample .The responsive behavior of the polymers was investigated by adding monofunctional compounds . These results all demonstrate the depolymerization of the dynamer induced by different stimuli.However, as shown by GPC analysis . 2,6‐Pyridinedicarboxaldehyde , α,ω‐dinitroalkane (0.75 mmol), and triethylamine  were dissolved in CD3CN (0.5 mL). The solution was kept at r.t. for 48 h without stirring and the resulting solution analyzed by NMR. The volatiles were then removed in vacuo and the residue was dissolved in THF for analysis by GPC.Synthesis of dynamer 1) and the corresponding α,ω‐dinitroalkane  as a precipitate, washed several times by ethyl ether and dried under vacuum.Synthesis of lowellanes. The lowellanes were collected from the reaction between 2,6‐pyridinedicarboxaldehyde (3N.4) and 1‐nitropropane (5) were mixed in anhydrous CD3CN and stirred at rt under N2. Et3N (10 mol %) was added and the reaction was followed by NMR over time, indicating that equilibrium was reached within 24 h. From product: 2‐nitro‐1‐(pyridin‐2‐yl)butan‐1‐ol (6) was dissolved in anhydrous CD3CN and stirred at r.t. under N2. Et3N (10 mol %) was added and the reaction progress followed. The same equilibrium as from the starting components was reached within 24 h.Dual entrypoint equilibration analysis. Performed using model system in deuterated acetonitrile in the presence of EtThe authors declare no conflict of interest.1As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re‐organized for online delivery, but are not copy‐edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors.Supporting InformationClick here for additional data file.