With mounting concerns over climate change, the utilisation or conversion of carbon dioxide into sustainable, synthetic hydrocarbons fuels, most notably for transportation purposes, continues to attract worldwide interest. This is particularly true in the search for sustainable or renewable aviation fuels. These offer considerable potential since, instead of consuming fossil crude oil, the fuels are produced from carbon dioxide using sustainable renewable hydrogen and energy. We report here a synthetic protocol to the fixation of carbon dioxide by converting it directly into aviation jet fuel using novel, inexpensive iron-based catalysts. We prepare the Fe-Mn-K catalyst by the so-called Organic Combustion Method, and the catalyst shows a carbon dioxide conversion through hydrogenation to hydrocarbons in the aviation jet fuel range of 38.2%, with a yield of 17.2%, and a selectivity of 47.8%, and with an attendant low carbon monoxide (5.6%) and methane selectivity (10.4%). The conversion reaction also produces light olefins ethylene, propylene, and butenes, totalling a yield of 8.7%, which are important raw materials for the petrochemical industry and are presently also only obtained from fossil crude oil. As this carbon dioxide is extracted from air, and re-emitted from jet fuels when combusted in flight, the overall effect is a carbon-neutral fuel. This contrasts with jet fuels produced from hydrocarbon fossil sources where the combustion process unlocks the fossil carbon and places it into the atmosphere, in longevity, as aerial carbon - carbon dioxide. 2 to aviation jet fuel.Design and discovery of catalysts to make clean energy and mitigate the harmful effect of greenhouse gases remains a massive challenge. Here the authors report a combustion-synthesised iron-based catalyst of high activity and selectivity for directly converting CO Nevertheless, the use of fossil fuels continues to grow with an expected annual increase of 1.3% to 20302, continually exacerbating this problem in the form of climate change Air transport, playing a significant role in the modern world in worldwide social contact, business and marketing, is a recognized source of high CO2 emissions3.For more than a century our industrial society and humankind’s prosperity, wealth and well-being, have been based on the combustion of hydrocarbon fossil fuels. However, it is abundantly clear this has disturbed the natural environment by the emission of greenhouse gases, most notably carbon dioxide 41, There have been limited studies on producing liquid hydrocarbons of molecularity C5+44.Nevertheless, the activation of CO2 to liquid hydrocarbons; an indirect route, which converts CO2 to CO or methanol and subsequently into liquid hydrocarbons, or the direct CO2 hydrogenation route, which is usually described as a combination of the reduction of CO2 to CO via the reverse water gas shift (RWGS) reaction and the subsequent hydrogenation of CO to long-chain hydrocarbons via Fischer-Tropsch synthesis (FTS)45. Jet fuel can then be obtained from the products after industrially recognized treatments such as distillation or hydro-isomerization. The second, direct route is generally recognized as being more economical and environmentally acceptable as it involves fewer chemical process steps, and the overall energy consumption for the entire process is lower46.There are two ways to convert COThe relevant chemical reactions for hydrocarbon fuel production are:2:Hydrogenation of COThe RWGS reaction:The FTS reaction:2 into fuels through these various reactions has attracted great attention in recent years, and a compilation of some of these investigations is highlighted in Table 2 to jet fuel range hydrocarbons47. The key to advancing this process is to search for a highly efficient inexpensive catalyst, that can preferentially synthesise the target hydrocarbon range of interest48. Iron-based catalysts, widely used in both the RWGS and FTS reactions, are typically prepared by chemical co-precipitation routes, which unfortunately consumes significant amounts of water52.The direct conversion of CO2 to jet fuel range hydrocarbons. In brief, the Fe–Mn–K catalyst shows a CO2 conversion of 38.2% and selectivity to C8–C16 hydrocarbons of 47.8% with a correspondingly low selectivity for CH4 and CO. In addition, the process also shows a high molar production ratio of olefin-to-paraffin for C2–C4 hydrocarbons.In this investigation, we report the preparation of iron-based catalysts using the Organic Combustion Method (OCM) and determined their catalytic performance for the direct and efficient conversion of CO2 into sustainable, synthetic hydrocarbons fuels, particularly in the synthesis of renewable aviation fuels. At the heart of any progress in this area, the all-important conversion process is closely related to the development of advanced catalysts of high performance for the CO2 hydrogenation reaction. Therefore, the utilization of novel methods of catalyst preparation represents an important strategy to produce advanced catalytic formulations having high-performance levels. Among the catalyst synthesis methods, the so-called OCM is recognized as an energy-efficient and economically viable approach for the one-pot synthesis of a variety of nanostructured solid catalysts. In this method, the utilization of an organic fuel, having also a cation-complexation character, to yield a homogenous redox solution of the different metal precursors is highly advantageous. In addition, a relatively moderate self-sustaining exothermic reaction of the redox gel may be beneficial to produce the necessary nanostructured catalysts with an efficient promoter effect due to the well-controlled aqueous chemistry of the preparation route and ensuing combustion conditions.The rising concerns over climate change and the stringent environmental regulations to deplete the utilization of fossil-derived fuels have generated great opportunities—and major scientific challenges—on the transformation of CO2 and H2 to hydrocarbons and CO, the product selectivities, the Anderson–Schulz–Flory (ASF) product distribution, together with the molar ratio of olefin-to-paraffin ratio for C2–C4 from the hydrogenation of CO2 using a Fe–Mn–K catalysts, is shown in Fig. 2 hydrogenation are shown for a reaction time of 20 h over a variety of Fe-based catalysts. The GC-MS spectrum of the collected liquid products from the hydrogenation of CO2 on the catalyst Fe–Mn–K is also shown in Fig. 2 hydrogenation for a reaction time of 20 h, using an example Fe–Mn–K catalyst, is presented in Supplementary Fig. In terms of the conversion of CO2 hydrogenation. The CO2 and H2 conversion increased rapidly with onset of reaction time in the first 5 h, reaching a stable value of around 40%. The methane selectivity decreased from 30 to 10% from the beginning of the reaction until 20 h, and decreased by a small amount after a further 20 h. In contrast, the light olefin selectivity (C2–C4 olefins) increased to an apparent limiting value of 25% at a reaction time of 10 h and above. The liquid product (C5+) selectivity was stable at around 60% and showed a small increase with reaction time. Similarly with FTS, the hydrocarbon products from CO2 hydrogenation on Fe–Mn–K generally follow the ASF distribution. Figure 53, whose chain growth probabilities (αi) is 0.79 for α1 within the C1–C12 carbon range and α2 is 0.57 for C12+. A high chain growth probability (α1) means a low methane selectivity whilst the chain growth decreases when the carbon number is above 12, indicating lower selectivity for higher (heavier) hydrocarbons.The data in Fig. 5+) yield, with the catalyst presenting both high CO2 conversion and high C5+ selectivity.Compared with the literature results in Table 2 methanation over the catalyst active sites (χ-Fe5C2). They produced a high pressure of water and unconverted CO2 which, importantly, can then oxidize χ-Fe5C2 to Fe3O4. The CO produced via the RWGS reaction on Fe3O4 active site reacts with H2 (Fisher-Tropsch synthesis (FTS)), and the CO2 conversion increased rapidly  prior to catalytic performance evaluation, with a GHSV (gas hourly space velocity) conditions of 1000 mL g−1 h−1 at atmospheric pressure, a temperature of 320 °C and for 24 h duration. The powder X-ray diffraction (XRD) spectra of the catalyst precursor, together with the activated and used Fe–Mn–K catalysts are shown in Fig. The catalyst precursor was firstly activated in situ with syngas . The reflections in the powder diffractogram from the used catalyst phase were considerably more complex, consisting of mixtures of Fe3O4, Fe2O3, and χ-Fe5C2. Importantly, χ-Fe5C2 is widely acknowledged to be the active catalytic species in the in situ hydrogenation of CO and/or CO2 and this iron carbide phase plays a crucial role in the subsequent C–C chain growth reactions57.It can be seen from Fig. 5C2 during the in situ activation process, whilst Fe3O4 is partially regenerated during the first hours of the catalytic reaction, hence explaining the increases in H2 and CO2 conversion during this period. This finding is perfectly consistent with the recognized “Tandem mechanism” in which these two catalytically active phases (χ-Fe5C2 and Fe3O4) are responsible for the conversion of CO2 and H2 to syngas and for the subsequent C–C chain growth step to produce jet fuel60.We have observed that the catalyst precursor is almost fully converted to χ-Fe2O3 in the used catalyst probably arises from the oxidation of Fe3O4 by CO2 and/or water during the reaction, while the Fe2O3 was reduced to Fe3O4 in the presence of H2 . In Fig. 2O3. In addition, in Fig. Surface elemental compositions and the oxidation states of the metals were analyzed using XPS in the region 0–800 eV. The survey spectrum Fig.  clearly The XPS spectra of the C 1s present Fig.  showed t63 reported that the surrounding carbonaceous matter could indeed facilitate the formation of iron carbides during activation, hence improving the higher liquid products selectivity.Temperature-programmed oxidation (TPO) results of Fe–Mn–K catalyst precursor prepared with citric acid combustion method shown in Supplementary Fig. Scanning electron microscopy (SEM) images of both the catalyst precursor and the used catalysts are shown in Fig. 3O4, respectively. In addition to the Fe3O4 phase  than catalysts of Fe–Cu–K (40.8%) and Fe–Zn–K (45.1%).In contrast, the promoter-added catalysts, Fe–Zn–K, Fe–Cu–K, and Fe–Mn–K showed high CO70. K is known to promote the formation of longer-chain hydrocarbons, the carburization of surface Fe, and the suppression of CH4 formation, all of which are advantageous for liquid hydrocarbon synthesis. In addition to K, various base metal compounds of Na have also been used as promoters for FTS catalysts72. Therefore, these base metals have also been tested as promoters for the catalytic hydrogenation of CO2 and their various catalytic performance are summarised in Fig. The impact of potassium (K) compounds on the performance of Fe-based catalysts for FTS has been studied extensively2 hydrogenation and high selectivity for hydrocarbons in the jet fuel range. However, the Li promoted catalyst showed high selectivity for methane formation but not for long-chain hydrocarbons  than Fe–Mn–Na (44.4%) or Fe–Mn–Cs (44.0%).It is clear from the data in Fig. ons Fig. . There aCrystallite sizes calculated using the Scherrer equation for the different base metal promoted catalysts precursor are listed in Table 73. In order to investigate the fundamental, underlying efforts of organic fuel compounds, the catalyst prepared without fuel also been synthesised. It is clear that the catalyst prepared without fuel showed lower catalytic activity (CO2 conversion of 28.6%) compared with the catalyst prepared with citric acid (CO2 conversion of 38.2%). In addition to using citric acid as a fuel in the OCM catalyst preparation, we have also investigated other organic chemicals as potential fuel sources. A series of catalysts of the Fe–Mn–K type were therefore prepared with different organic compounds in the catalyst preparation by the combustion route and their catalytic performances for the hydrogenation of CO2 are listed in Table Recently, the Organic-Combustion Method (OCM), also known as the Solution Combustion Method, has been developed to prepare highly active metal catalysts for a variety of processes2 conversion and higher jet fuel range hydrocarbon selectivity. The catalysts prepared with EDTA, citric acid, oxalic acid, NTA, DTPA, Tartaric acid, HEDTA, and salicylic acid also exhibited good catalytic performance for both CO2 conversion and jet fuel selectivity. In general, all these organic fuels could also act as chelating agents and hence facilitating the formation of nanostructured catalysts.It is clear, therefore, that compared to the catalyst prepared without an organic fuel, all the Fe–Mn-K catalysts prepared with organic compounds generally showed both higher CO2O3. However, most of the catalysts prepared with organic fuel compounds showed Fe3O4 as the dominant crystalline phase which clearly indicates that part of Fe3+ present in Fe2O3 was partially reduced to Fe2+ in Fe3O4 during the catalyst preparation stage. The catalyst prepared with oxalic acid showed XRD reflections corresponding to Fe2O3 instead of Fe3O4. This implies that under the conditions applied in this investigation, oxalic acid did not reduce the Fe2O3 to Fe3O4 consistent with its low reducing power compared to the other organic fuels.The XRD spectra of various catalysts are shown in Supplementary Fig. The crystallite sizes of catalysts calculated from the Scherrer equation are listed in Table 52, we show that the OCM is a particularly facile production process where, in addition to high yields and selectivity for jet fuels, additional advantages are savings in both energy and time74.Compared to the co-precipitation method, widely applied in the preparation of Fe-based catalystsAn optimal organic compound in our catalyst preparation should act both as a reducing agent and should react with nitrates non-violently, produce nontoxic gases and also act as an effective chelating agent for metal cations.The catalysts prepared using organic fuels showed high activity as stable organic chelate compounds formed with metal cations are particularly suited to the formation of uniform, highly dispersed metal oxide catalysts via the combustion method.2, CO2, and H2O. Using citric acid as an example, the stoichiometric reactions can be described as follows, according to the principle of propellant chemistry:The gaseous products from the organic compound and nitrate combustion reactions are N75.These combustion reactions are highly exothermic and lead to a rapid evolution of a large volume of gaseous products during the catalysts preparation process. This release of gas depletes the fuel combustion heat and hence limits the rapid temperature rise, thereby advantageously reducing any premature local partial sintering of the primary metals oxides particles. The gas evolution also results in limiting any extended crystal growth or inter particle contact, thereby contributing to smaller particle size catalysts76. which is known to enhance the interaction between Fe3O4 and the promoter, further improving catalytic performance. It is interesting that most of redox gel when combusted at a calcining temperature of 350 °C, produces Fe3O4 without any apparent O2 participation from the atmosphere However, the main products are Fe2O3 when the calcination temperature increased to 500 °C, one presumes clearly as a consequence of the participation of atmospheric oxygen and/or the associated oxygens from the complexing ligands.Although combustion was nominally carried out at 350 °C, the in situ flame temperature during combustion can be very high due to the combustion of gases produced during the decomposition of metal nitrates and the organic compounds. This high-temperature persists for a few minutes and disappears, producing a rapid quenching effectIn general, the Fe–Mn-K catalysts synthesised with carboxylic acids and polycarboxylic acids as fuels showed superior catalytic performances than those prepared using urea and sugar (glucose) and the catalyst prepared without fuel. Our assertion is that this trend probably derives from two crucial roles  that these organic molecules play in the organic-combustion approach. The first role can enhance the homogeneity of the solution through the intimacy between the constituent metal  precursors, hence hindering their precipitation or aggregation during the gel formation, whilst the second (fuel) function can closely control the severity of the combustion reaction and hence the aggregation of the nanostructured catalysts. Obviously, this leads to changes in the crystallite sizes that show the Fe–Mn–K catalysts with particle sizes between 7 and 28 nm and usually prepared by carboxylic acid-type fuels are significantly more active and selective than the catalysts with larger crystallite sizes .2 hydrogenation activity and jet fuel range hydrocarbon selectivity. The catalytic performance for CO2 hydrogenation of catalysts prepared with different fuels are shown in Supplementary Figs. Finally, we have also examined commercial sugar and flour powders as possible fuels in the catalyst preparation process. Catalysts prepared with these fuels also showed high CO5C2) is widely accepted to be the active catalytic species in the FTS and this iron carbide phase plays a crucial role in the C–C chain growth reactions57. The χ-Fe5C2 usually prepared by activation of hematite under syngas atmosphere at temperature of 200–450 °C, the whole activation process contains a three-step reduction process of Fe2O3 to iron (Fe2O3 → Fe3O4 → FeO → Fe) and then followed by carburisation of Fe to χ-Fe5C277. In our experiments, the χ-Fe5C2 was reduced and carburized from Fe3O4, in the process of magnetite (Fe3O4) → wüstite (FeO) → iron metal (Fe) → Hägg carbide (χ-Fe5C2). Wei et al.44 have proposed a comprehensive reaction scheme where χFe5C2 is involved in the hydrogenation of CO2 to gasoline fuel range hydrocarbons, using a Na-Fe3O4/Zeolite multifunctional catalyst. We believe that a related, but slightly different, reaction scheme is operating here for the hydrogenation of CO2 to aviation jet fuel and this is illustrated schematically in Fig. Hägg carbide χ-FeC2 is wid44 who described catalysts prepared by a one-pot synthesised Na-Fe3O4 catalyst with zeolite, we have prepared catalysts using the direct OCM route which showed higher liquid products yield on CO2 hydrogenation. Thus the Fe3O4 catalyst precursor is fully carburized to χ-Fe5C2 during our catalyst activation (reduction) process, whilst Fe3O4 is partially regenerated from the oxidation of χ-Fe5C2 by CO2 /water in the first hours of the catalytic reaction. Jet fuel synthesis via CO2 hydrogenation initially takes place by the RWGS reaction (CO2 + H2 → CO + H2) on the catalytically active sites of Fe3O4, and subsequently by the FTS reactions (CO + H2 → CnHm + H2O) on catalytically active sites on χ-Fe5C257.In contrast to the report by Wei et al.3O4 to FexCy carbides and vice versa can occur under appropriate reaction conditions. This relatively facile and reversible phase transformation makes possible the incorporation of carbon atoms from the carbide surface into the reaction products via Mars-van Krevelen mechanism as was determined by Gracia et al.78 through a computational study of the CO hydrogenation on an iron carbide surface. Remarkably, this Mars-van Krevelen-like mechanism on supported Fe catalysts rationalised the enhanced reactivity of highly dispersed iron carbide particles in the initiation of chain growth in F-T synthesis79.Using iron-based catalysts for FT synthesis a fast and reversible exchange of Fe2 hydrogenation reaction on Fe catalysts. Obviously, this reaction is more challenging than conventional FT synthesis since the catalyst must have an excellent balance of active sites (phases) to catalyse—in tandem mode—the reverse-water gas shift reaction  and also the CO hydrogenation via the FT reaction to produce Jet Fuel. Our tandem mechanism through the participation of Fe3O4 and χ-Fe5C2 can easily rationalise the jet fuel formation and give a wider picture of the evolution of the gas, liquid and solid phases during the catalytic reaction. Further work is needed to gain further insight into the possible occurrence of Mars-van Krevelen-like mechanism in the FT stage through carbon isotopic labelling studies. In a flowing gas system these will clearly be experimentally—and financially (!)—challenging.As far as we know, there is not a single report in the scientific literature of the Mars-van Krevelen mechanism operating in the CO5C2 which plays a principal role in the formation of hydrocarbons via FT reaction57. According to the literature and our own results, the carburization process of Fe nanoparticles during the catalytic reaction forms the Fe carbide phase, which through a FT pathway favours the C–C condensation reactions to produce large hydrocarbons within the range of aviation fuel. In our experiments, the χ-Fe5C2 was formed during the catalyst activation/reduction process, in the beginning of the reaction what it is happening is mainly CO2 methanation reaction on χ-Fe5C2, the relatively high pressure of water can then oxidize on χ-Fe5C2 to Fe3O4, and the Fe3O4 was simultaneously carburized by CO80. In model experiments, Fe2O3 was produced from the oxidation of Fe3O4 by CO2/H2O, and Fe2O3 was steadily reduced to Fe3O4 by H2 in the reaction system  and converts CO2 into value-added products84. This CO2 Circular Economy is a valid and highly powerful alternative route to simply burying huge volumes of captured CO2 underground and one in which future generations will surely expect us to have formed a major aspect of sustainable CO2 management.The Circular Economy (CE) is an attractive, holistic concept gradually and steadily positioning itself as an alternative and reliable alternative to the present, “Business-as-Usual”, unsustainable Linear Economy (LE) based on the “Take, make and dispose” paradigm2 conversion as an integral part of carbon recycling. The advances reported here offer a route out of the current, worldwide LE for jet fuels, based on the (present) Production-Consumption- Disposal/Emission structure, where the valuable natural resource, crude oil, is extracted, shipped across oceans, transformed into jet fuel and then combusted, with the combustion product either emitted into the atmosphere, or trapped and buried underground (through Carbon Capture and Storage). On the other hand, the CE approach is based on fundamentally—different Production—Consumption—Recycling/Recovery structure or Carbon Capture and Utilization, where, in this case, CO2 is indeed recognized as a powerful “Resource” to be recirculated using renewable energy to yield carbon-neutral jet aviation fuel.Renewable jet fuels offer considerable potential in the worldwide drive for a future Sustainable Circular Economy Future for the aviation industry. The vision centres on CO2 into aviation jet fuel as an additional driving force for the inevitable and urgently required transition toward a circular fuel economy centred on renewable CO2 utilization.Obviously, our advance can contribute significantly to more sustainable fuel production process if we input renewable energy into the chain for transforming CO2 Circular Economy, the “Goods” (here the Jet Fuel) are continually reprocessed in a closed environment, which saves the natural fossil resources and preserves the environment, whilst also, of course, creating significant numbers of new jobs, new economies and new markets.Within a Jet Fuel CO2 is derived from renewable energy, and CO2 is directly converted to Aviation Jet Fuel using our novel catalysts with CO2 captured from the atmosphere (“Air Capture”). Note the fundamental difference between the Jet Fuel Linear Economy, as compared to the CO2 to Jet Fuel Circular Economy, where the entire latter process is a closed loop and hence a CO2 neutral process. This CO2 Circular Economy for aviation can surely empower worldwide momentum toward not only major economic development for countries but also achieving the UN’s sustainable development goals.In Fig. 3O4 which catalyses the conversion of carbon dioxide to CO via the RWGS reaction whilst the second active Fe phase (χ-Fe5C2) catalyses the hydrogenation of CO through the Fischer-Tropsch process.A series of Fe-based catalysts were prepared by the OCM for the conversion of carbon dioxide into jet fuel range hydrocarbons. This synthetic process can be used to produce homogeneous, ultrafine and high-purity crystalline metal oxide powder catalysts. The as-prepared catalysts, following activation, showed high carbon dioxide hydrogenation activity and high jet fuel range selectivity as a consequence of the small (ca. 15 nm) nanoparticle size and the presence of two catalytically active Fe phases that operate in tandem. The first phase corresponds to FeThis catalytic process provides an attractive route not only to mitigate carbon dioxide emissions but also to produce renewable and sustainable jet fuel. The recycling of carbon dioxide as a carbon source for both fuels and high-value chemicals offers considerable potential for both the aviation and petrochemical industries. It also represents a significant social advance; thus, instead of consuming fossil crude oil, jet aviation fuels and petrochemical starting compounds are produced from a valuable and renewable raw material, namely, carbon dioxide. These advances highlight carbon dioxide recycling and resource conservation as an important, pivotal aspect of greenhouse gas management and sustainable development. This, then, is the vision for the route to achieving net-zero carbon emissions from aviation; a fulcrum of a future global zero-carbon aviation sector.Catalysts were prepared by the OCM method; citric acid was used as the organic compound. Typically, a Fe–Mn–K catalyst was prepared from citric acid monohydrate , Iron (III) Nitrate nonahydrate , Manganese(II) nitrate tetrahydrate  and potassium nitrate , in a molar ratio of citric acid: (Fe(or Co) + Mn + K) = 2, and a weight ratio of (Fe- and Mn- and K-precursors + citric acid)/water = 2:1. This initial mixture was stirred to form a homogeneous aqueous solution and heated at 50 °C for 1–2 h to obtain a citric acid-based slurry. This paste was then ignited at 350 °C in the air for 4 h to produce a carbon-free powder.Catalyst samples with different first-row transition metal  promoters were also prepared using the same method; Fe–Cu–K and Fe–Zn–K catalysts were prepared using copper (II) nitrate trihydrate , and zinc nitrate hexahydrate  as transition metal precursors respectively. Similarly, catalysts with different Fe–Mn–Li, Fe–Mn–Na, and Fe–Mn–Cs base metal promoters were prepared using lithium carbonate , sodium carbonate  and cesium carbonate , respectively. Typically, the molar ratio of Fe: transit metal: base metal used was 10:1:1.Fe–Mn-K catalysts were also prepared using other organic compounds other than citric acid, specifically; urea , tannic acid , Ethylenediamine Tetraacetic Acid , oxalic acid , Nitrilotriacetic acid , Diethylenetriaminepentaacetic acid , tartaric acid , N-(2-Hydroxyethyl) ethylenediamine-N,N’,N’-triacetic acid , salicylic acid . In all discussions catalysts were prepared with citric acid as the organic compound unless otherwise stated.2 hydrogenation experiments were carried out in a stainless steel fixed bed reactor with an inner diameter of 1.0 cm  with a typical 2.0 g catalyst load. Prior to the reaction, the catalyst was in situ reduced with syngas (H2:CO = 2:1) at atmospheric pressure, with a GHSV (gas hourly space velocity) of 1000 mL g−1 h−1, at 320 °C for 24 h. Following reactor cooling to below 50 °C, a mixture of gas with an H2/CO2 ratio of 3 and N2  was introduced at a gas flow of 40 mL min−1 (GSVH = 2400 mL g−1 h−1). The reactor was then heated at a rate of 2 °C/min to 300 °C. The reaction pressure was fixed at 10 bar (1 MPa) using a back pressure regulator. The effluent gaseous products were analysed using an online Gas Chromatograph (Perkin Elmer Clarus 580 GC) with flame ionization (FID) and thermal conductivity detectors (TCD), and the collected liquid products were analysed by Gas Chromatograph Mass Spectrometry (SHIMADZU GCMS-QP2010 SE).CO2 and H2 conversion and product selectivity’s were calculated from the following relationships:The COThe selectivity of oxygenates  was not further considered in this study as it was below 1.0%.Powder XRD analyses of catalysts used a Cu Kα (0.15418 nm) X-ray source  in a Bruker D8 Advance diffractometer. Diffraction patterns were recorded over a 10–80° 2θ angular range using a step size of 0.02°.2. Data were recorded at pass energies of 150 eV for survey scans and 40 eV for high-resolution scans with 1 and 0.1 eV step sizes respectively. Charge neutralisation was achieved using a combination of low energy electrons and argon ions. The resulting spectra were analyzed using Casa XPS peak fitting software and sample charging corrected using the C 1s signal at 284.8 eV as a reference.X-ray photoelectron spectroscopy (XPS) of samples was performed using a Thermo Fisher Scientific Nexsa spectrometer. Samples were analysed using a micro-focused monochromatic Al X-ray source (72 W) over an area of ~400 × 200 µmThermogravimetric analysis (TGA) was used to characterise the resulting carbon depositions in our catalyst samples. A TPO was carried out to determine the thermal stability of the produced carbons. The sample was heated from room temperature to 1000 °C at a heating rate of 10 °C/min under an air atmosphere with a flow rate of 100 ml/min.The catalyst morphology was characterised using scanning electron microscopy (SEM JEOL 840F) at an accelerating voltage of 6.0 kV.High-resolution scanning transmission electron microscopy (STEM) annular dark field (ADF) and bright field (BF) images were obtained using a probe corrected JEOL ARM200F at the David Cockayne Centre for Electron Microscopy operated at 200 kV with ADF inner and outer detector angles of 28–104.36 mrad, respectively, a 13.20 mrad BF outer angle, and a 14 mrad convergence semi-angle.Further information on research design is available in the Supplementary InformationPeer Review FileReporting summary


Authors would like to correct error in affiliation in the original publication of the article. Correct affiliation of Thorbjörn Sievert is updated here.Correct affiliation of Thorbjörn Sievert to (3) not (2).


When immobilized on ITO, Co@CB[5] exhibited a turnover frequency (TOF) of 9.9 s−1 at overpotential η=550 mV in a pH 9.2 borate buffer. Meanwhile, when Co@CB[5] complex was immobilized onto the surface of BiVO4 semiconductor, the assembled Co@CB[5]/BiVO4 photoanode exhibited a low onset potential of 0.15 V (vs. RHE) and a high photocurrent of 4.8 mA cm−2 at 1.23 V (vs. RHE) under 100 mW cm−2 (AM 1.5) light illumination. Kinetic studies confirmed that Co@CB[5] acts as a supramolecular water oxidation catalyst, and can effectively accelerate interfacial charge transfer between BiVO4 and electrolyte. Surface charge recombination of BiVO4 can be also significantly suppressed by Co@CB[5].A host–guest complex self‐assembled through Co 2+ and cucurbit[5]uril (Co@CB[5]) is used as a supramolecular catalyst on the surface of metal oxides including porous indium tin oxide (ITO) and porous BiVO4 for efficient electrochemical and photoelectrochemical water oxidation.A host–guest complex self‐assembled through Co Photoelectrochemical (PEC) water splitting is a promising strategy for converting solar energy into renewable fuels, such as hydrogen,2 and IrO2 under alkaline conditions.4) showed great prospect as a photoanode material to be coupled with catalysts for OER, due to its appropriate band structure.4 has been coupled with various OER material catalysts, such as Co3O4,Recent studies have reported considerable improvements in the OER catalyzed by non‐precious metal‐based catalysts such as cobalt, iron and nickel in the form of oxide, hydroxide and alloy with activity and stability benchmarks surpassing those of RuOn]) is a kind of macrocyclic host compounds, which can readily coordinate with metal cations as carbonyl groups directed towards the cavity of its cyclic structure. Strong complexes can be formed with cations by ion‐dipole interactions.[n] can be anchored or physiosorbed onto the surface of metal oxides (MOx),[n] and a metal cation could be immobilized onto the surface of a metal oxide‐based semiconductor through the remaining carbonyl groups. In the CB[n] family, CB[5] and CB[7] are moderately soluble in water (with concentration of 20–30 mM),2+ cation for the supramolecular assembly, and immobilized Co@CB[5] on the surface of metal oxides to study its activity for electrochemical and PEC water splitting. For the first time, we could demonstrate a host–guest complex Co@CB[5], which is applied to a porous ITO or BiVO4 surface, achieving the electrochemical and PEC water oxidation performance comparable with that of state‐of‐the‐art heterogeneous water oxidation catalysts, but with a much simpler preparation procedure. These new findings show the huge potential of host–guest supramolecular complexes as catalysts for efficient OER.Cucurbituril . The BiVO4 thin film was prepared by modifying a method reported by Choi and co‐workers.4 film has the advantages of improving electron‐hole separation and suppressing bulk carrier recombination,4 film was composed of worm‐like particles as indicated by SEM images . A cross‐sectional view of the film showed that the BiVO4 layer had an average thickness of approximate 1 μm . Energy dispersive spectroscopy (EDS) mapping analysis was performed on a selected cross‐sectional area to determine the elemental distribution , which demonstrated a homogeneous distribution of Bi, V, and O elements in the film of the porous BiVO4.The Co@CB[5] supramolecular complex was assembled on the porous indium tin oxide (ITO) and porous BiVO4 electrodes was briefly illustrated in Scheme 3)2 in a molar ratio of 1:1. Mass‐to‐charge ratio (m/e) of 454.0879 corresponding to Co@CB[5]+H3O (m/e 454.0979) could be found by electrospray mass spectrometry . Then, the porous ITO and BiVO4 substrates were immersed in the solution of Co@CB[5] for 30 min, after washing with deionized water, resulting in the generation of Co@CB[5]/ITO and Co@CB[5]/BiVO4 electrodes, respectively. The attenuated total reflection infrared (ATR‐IR) spectra of Co@CB[5]/ITO, CB[5]/ITO electrode and bare CB[5] powder were acquired using an infrared spectrometer with a resolution of 0.09 cm−1 . Red‐shifts of ca. 9 and ca. 3 cm−1 were observed for the carbonyl portal of the CB[5] component on Co@CB[5]/ITO and CB[5]/ITO electrode compared to that of CB[5] powder (1738 cm−1), respectively. A similar red‐shift on the carbonyl portal of the CB[5] component on Co@CB[5]/BiVO4 and CB[5]/BiVO4 could also be observed . These ATR‐IR spectra suggested strong interaction between CB[5], Co cations and porous MOx substrates,4.The preparation of Co@CB[5]/ITO and Co@CB[5]/BiVO3+ as the primary ion source was further employed to detect the presence of Co@CB[5] on the surface of ITO and BiVO4. As shown in the SIMS images of Co@CB[5]/ITO and Co@CB[5]/BiVO4 , some related secondary ions assigned to cobalt combined with the fragments of CB[5] could be observed uniformly distributing on the surface of electrodes, indicating that Co@CB[5] was successfully immobilized on the surface of ITO and BiVO4.A time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) with BiThe morphological features of Co@CB[5] functionalized electrodes were then investigated by SEM. As shown in Figures S8 and S9, no obvious morphological changes were observed after the immobilization of CB[5] and Co@CB[5] on the porous substrates, because the assembly process is a molecular level surface modification.x substrates. The XPS survey spectra of Co@CB[5]/ITO, Co@CB[5]/BiVO4 and reference electrodes are shown in Figures S10 and S11. In XPS high‐resolution spectra of CB[5]/ITO and Co@CB[5]/BiVO4 . Please note that the binding energies of Co 2p for Co@CB[5] complex were different from those of Co‐based oxides or hydroxides,[x surfaces.X‐ray photoelectron spectroscopy (XPS) measurements were performed to analyze the molecular level surface composition and electronic states of the Co@CB[5] complex functionalized MO Figures , when CBdroxides,21, 22x, the surface and morphology properties of the Co@CB[5]/ITO and Co@CB[5]/BiVO4 samples were studied at atomic level by spherical aberration corrected transmission electron microscope (ACTEM). As revealed by high‐angle annular dark‐field (HAADF) images in Figure S12, the Co@CB[5]/ITO nano‐particle exhibited octahedron shape with regular and clear edge. As shown in Figure To further demonstrate that the Co@CB[5] is a molecular catalyst on MO4 was characterized by high‐resolution transmission electron microscope (HRTEM), as shown in Figure 4 nanoparticle. Unfortunately, when high energy electron beam was focused on BiVO4, the surface of BiVO4 was damaged, detailed structure information for the surface of Co@CB[5]/BiVO4 could not be obtained by atomic resolution AC‐STEM. HAADF‐STEM and corresponding EDS mapping images of Co@CB[5]/BiVO4 showed that elements of Co, N and C contents in the Co@CB[5] complex were uniformly distributed on the surface of the BiVO4 nanoparticles . The Co/ITO electrode exhibited a much lower anodic current density than that of the Co@CB[5]/ITO electrode. Linear fitting of the Co@CB[5]/ITO electrode gives a Tafel slope of 59.5 mV dec−1 . When a total charge of 3.6 C passed through the electrode, 8.62 μmol of O2 was detected by GC, leading to a Faraday efficiency of 92.6 % .The OER performance of Co@CB[5]/ITO was first evaluated by linear sweep voltammetry (LSV). LSV measurements were performed at 25 °C in a standard three‐electrode cell with 1.0 M borate buffer solution (pH 9.2) as the electrolyte. As shown in Figure 1 Figure . The ste1 Figure . The Co@2+ on the surface of ITO was estimated as 4.54×10−9 mol cm−2 according to the linear relationship between the peak current of Co2+/3+ and the scan rate , and the order of magnitude for such catalyst loading is consistent with that of molecules immobilized on the surface of porous metal oxide substrates.2+ was further confirmed by inductively coupled plasma optical emission spectrometer (ICP‐OES). The total Co2+ loading amount is 4.98×10−9 mol cm−2, which was slightly larger than the redox active Co2+. The turn over frequencies (TOFs) of Co@CB[5]/ITO based on the Co2+ loading (redox active) current densities vs. various overpotentials were calculated based on LSV data (operated in a low scan rate of 10 mV s−1) and Eq. S3.−1 was achieved at η=460 mV, which reached 9.9 s−1 at η=550 mV. Table S1 lists the performance of Co@CB[5]/ITO in the current work and previously reported anodes for electrocatalytic water oxidation, including molecular and inorganic material catalysts immobilized on conducting glass. This comparison shows that the Co@CB[5]/ITO electrode is one of the best OER anodes in terms of overpotential, current density, and TOF.The effective coverage of Co4 photoanode was measured by linear sweep voltammetry (LSV) with a scan rate of 10 mV s−1. The absorption spectrum of BiVO4 did not change after Co@CB[5] was immobilized on the surface of BiVO4 , hence, the band gap of BiVO4 and Co@CB[5]/BiVO4 were the same.The PEC water oxidation performance of Co@CB[5]/BiVO4 at 1.23 V vs. RHE was approximate 1.8 mA cm−2. In the presence of sulfite as hole scavenger, the photocurrent density of BiVO4 increased to 5.4 mA cm−2. These results are comparable with previously reported values,4 film in our work is reliable. When Co@CB[5] was immobilized on the surface of BiVO4, the photocurrent density of the Co@CB[5]/BiVO4 electrode was measured to be 4.8 mA cm−2 at 1.23 V vs. RHE without the hole scavenger sulfite, which is much greater than that of unmodified BiVO4, CB[5]/BiVO4 and Co/BiVO4 electrodes. The CB[5]/BiVO4 electrode exhibited an similar anodic photocurrent density curve than that of the pristine BiVO4 electrode , indicating CB[5] itself can not affect the water oxidation of BiVO4. After immersing BiVO4 in Co2+ solution for 30 minutes, the photocurrent density of Co/BiVO4 electrode at 1.23 V vs. RHE increased to 2.3 mA cm−2, which is much lower than that of the Co@CB[5]/BiVO4 electrode (4.8 mA cm−2). The applied bias photon to current efficiency (ABPE) was calculated from the corresponding LSV curve in Figure 4 was 0.32 % at 0.88 V vs. RHE. However, the maximum ABPE of Co@CB[5]/BiVO4 was 1.79 % at 0.60 V vs. RHE  of BiVO4 and Co@CB[5]/BiVO4 were measured and calculated according to Eq. S5. As shown in Figure 4 and Co@CB[5]/BiVO4 were approximate 35 % and 88 % at 420 nm (1.23 V vs. RHE), respectively. The values of the ABPE and IPCE demonstrated the high photon‐to‐O2 conversion efficiency of the host–guest complex assembled Co@CB[5]/BiVO4 photoanode. On the basis of these measurements, the photocurrent densities were 4.85 mA cm−2 at 1.23 V vs. RHE and 2.9 mA cm−2 at 0.6 V vs. RHE for Co@CB[5]/BiVO4, as estimated by integrating the IPCE curves over the AM 1.5G solar spectrum . These calculated values are in agreement with the measured data in Figure −2 at 1.23 V and 2.8 mA cm−2 at 0.6 V).As shown in Figure E Figure , which i4 only generated a low photocurrent density less than 0.25 mA cm−2 at a constant applied potential of 0.6 V vs. RHE; however, the Co@CB[5]/BiVO4 photoanode generated a photocurrent density of ca. 2.4 mA cm−2, underlining the indispensable role of Co@CB[5] in water splitting . The photogenerated O2 in the headspace was quantified by GC. Assuming a 4 e− process for O2 evolution, the number of electrons passing through the electrode agreed well with the amount of O2 detected, representing a Faradaic efficiency of 90.3 % for Co@CB[5]/BiVO4 photoanode .Under chopped‐light illumination, the bare BiVOg Figure . During 4 are compared to those previously reported systems and the results are shown in Table S2. The performance of Co@CB[5]/BiVO4 exceeded those of many catalyst‐modified undoped‐BiVO4 photoanodes in both parameters. The host–guest complex assembled Co@CB[5]/BiVO4 photoanode can avoid complicated organic synthesis, and the high activity of Co@CB[5]/BiVO4 holds potential for supramolecular catalysts capable of replacing state‐of‐the‐art metal oxides and molecular catalysts.The photocurrent density at 1.23 V vs. RHE and the maximum ABPE obtained from Co@CB[5]/BiVO4 after OER test maintained a porous surface without significant changes. The composition and electronic states of the Co@CB[5]/ITO and Co@CB[5]/BiVO4 samples after OER test were analyzed by XPS technique . The binding energies of both N 1s and Co 2p for Co@CB[5]/ITO and Co@CB[5]/BiVO4 were consistent with that of before OER test, indicating that Co@CB[5] was stable for OER. The EDS elemental mapping images with different magnitudes in Figures S30a, S31 and S32 confirmed the uniform distribution of Co, N and C in Co@CB[5]/ITO following the OER tests. Figure S30b showed the atomic‐resolution TEM images of tested Co@CB[5]/ITO particle. By further observing the edge of sample under greater magnification, a clear and well‐ordered surface could be observed of tested Co@CB[5]/ITO, indicating that there was no other amorphous layer or heterojunction film formed to covered ITO nano‐particle surface during the OER process . In addition, according to the results of EDS analysis in selected area, the metal composition ratio of Co: In: Sn for tested Co@CB[5]/ITO particle was calculated to be 1: 91: 8, which was almost the same as the ratio of pristine Co@CB[5]/ITO. The EDS elemental mapping images with different magnitudes in Figure S33 and S34 confirmed the uniform distribution of Co, N and C in Co@CB[5]/BiVO4 after the OER tests. Figure S35 showed the HRTEM images of the tested Co@CB[5]/BiVO4 particles, there are no nanoparticles generated on the surface of Co@CB[5]/BiVO4 during the OER process, indicating that Co@CB[5] was stable on the surface of BiVO4 during the OER. By integrating the information obtained from the above characterizations, it can be convincingly concluded that Co@CB[5] maintains its supramolecular nature and is stable during the OER.Post‐characterization of the electrode after the OER test is necessary for further proof of reaction mechanism and the stability of the as‐fabricated hybrid electrodes. As shown in ATR‐IR spectra , Co@CB[5] maintained on the surface of electrodes after the OER test. As shown in Figures S24 and S25, the SEM images revealed that the Co@CB[5]/ITO and Co@CB[5]/BiVO2SO3) as a hole scavenger, extremely fast oxidation kinetics and negligible surface recombination were expected, as shown in Figure S36, the charge transfer efficiency (transη) at the electrode‐electrolyte interface was calculated according to Eq. S6 and the data from Figure transη of Co@CB[5]/BiVO4 was achieved (88 %), compared with that of bare BiVO4 (33 %) at 1.23 V vs. RHE. This result suggests that the Co@CB[5]/BiVO4 electrode has more rapid water oxidation kinetics than the bare BiVO4.To investigate the transfer of carriers in the PEC system constructed by this novel Co@CB[5] supramolecular catalyst, kinetic studies were carried out. With sodium sulfite  obtained from the diameter of the semicircles. A smaller semicircle indicates better charge transfer of the corresponding photoanode at the interface. Notably, the Co@CB[5]/BiVO4 electrode had a markedly smaller Rct (96 Ω) value than that of bare BiVO4 (303 Ω) under illumination at 0.6 V vs. RHE, illustrating a better ability to transfer holes at the electrode‐electrolyte interface of Co@CB[5]/BiVO4, which was consistent with its high charge transfer efficiency (transη).Electrochemical impedance spectroscopy (EIS) was performed to examine the charge transport phenomena in the bulk and at the surface of the electrodes. As shown in Figure 4 and the rate of surface charge recombination. The deuterium kinetic isotope effects (KIEs) can reflect the proton transfer kinetic information on water oxidation reactions and help us to interpret the rate determine step (RDS) of the catalytic process.The charge transfer efficiency depends on the rate of water oxidization catalytic processes on the surface of BiVO4, the value of KIEs for Co@CB[5]/BiVO4 photoanode was around 1.0 with the applied bias increasing, indicating the O−H bond cleavage is not involved in the RDS for light driven water oxidation by Co@CB[5]/BiVO4 photoanode  and shift the RDS of BiVO4 photoanode to a non proton transfer involved process. Thence, Co@CB[5] indeed played an important role in the light‐driven catalytic water oxidation processes in this Co@CB[5]/BiVO4 supramolecular assembly photoanode.As shown in Figure e Figure . In cont5 Figure , suggestx modified hematite and BiFeO3 passivated BiVO4 photoanodes. on the semiconductor inhibited surface charge recombination by acting as a surface passivation layer. The charge transfer and surface recombination kinetics were quantified by intensity modulated photocurrent spectroscopy (IMPS) to understand the real role of Co@CB[5] on the BiVO4. Figure 4 and Co@CB[5]/BiVO4 photoanodes in the complex plane. The IMPS spectrum consists of two semicircles in the 4th and 1st quadrants, which correspond to the resistance‐capacitance attenuation and the competition between charge transfer and recombination, respectively.ktrans) and charge recombination (krec) rate constants (ktrans+krec=2πfmax). The low frequency intercept in the normalized form, at which the imaginary part is equal to 0, corresponds to a charge transfer efficiency of ktrans/(ktrans+krec).krec and ktrans are therefore readily accessible.Our results confirmed that Co@CB[5] can effectively promote BiVO4 photoanode did not change notably as the applied potential was increased, the value of krec remained nearly constant with increasing potential for bare BiVO4 , the value of krec was 3.5 s−1 for bare BiVO4, which is 6.5 times as large as that of Co@CB[5]/BiVO4 (0.54 s−1). At higher potentials, this factor increased to 30 at 0.8 V vs. RHE. These results suggest that the charge recombination was markedly suppressed by the Co@CB[5]. Figure ktrans of Co@CB[5]/BiVO4 surpassed that of BiVO4 at all potentials. Particularly, at a potential of 0.6 V vs. RHE (the max point of ABPEs), the ktrans of Co@CB[5]/BiVO4 was more than 4 times as great as that of BiVO4. The charge transfer efficiency, defined as ktrans/(ktrans+krec), showed the same trend as the value determined by Jwater/Jsulfite, indicating the reliability of our measurements . The ratio of krec/ktrans was positively proportional to the semicircle in 1st quadrant and a small value indicated faster charge transfer than charge recombination.4, but also reduces the surface charge recombination.Moreover, the upper semicircle of the BiVO4 Figure , indicat4 was summarized and shown in Scheme 4, the photo generated holes can be directly consumed for water oxidation (pathway 1), or recombined with electrons that trapped by surface state (pathway 2). Due to the low intrinsic OER catalytic activity of BiVO4, the injection of holes to electrolyte was limited by the proton transfer involved water oxidation reaction, leading to a primary KIEs for bare BiVO4. When Co@CB[5] was immobilized on the surface of BiVO4, owing to the high OER catalytic activity of Co@CB[5], the photo‐generated holes could be effectively transferred and consumed for water oxidation (pathway 3); meanwhile, due to the faster consumption of holes, the photo‐generated electrons will have less chance to recombine with photo‐generated holes at the surface of BiVO4, leading to the higher charge transfer efficiency of Co@CB[5]/BiVO4 in comparison to that of the bare BiVO4.Based on the OER kinetics analyzed above, the function of Co@CB[5] on BiVO4 substrates. This supramolecular catalyst Co@CB[5] showed a high activity for electrochemical water oxidation when immobilized on a porous ITO substrate, the fabricated Co@CB[5]/ITO electrode exhibited a TOF of 9.9 s−1 at an overpotential of 550 mV in a pH 9.2 borate buffer with good stability. When Co@CB[5] was immobilized on the surface of the porous BiVO4 n‐type semiconductor, the integrated photoanode Co@CB[5]/BiVO4 showed an excellent PEC performance with a high photocurrent density of 4.8 mA cm−2 at 1.23 V (vs. RHE) under 100 mW cm−2 (AM 1.5) light illumination. KIEs and IMPS results confirmed that Co@CB[5] serves as a supramolecular water oxidation catalyst which can effectively accelerate surface charge transfer. Furthermore, the surface charge recombination of BiVO4 can also be suppressed by this host–guest supramolecular complex. The host–guest complex Co@CB[5] shows a remarkable performance for electrochemical and PEC water oxidation, which can open new opportunities for the development of supramolecular complexes as catalysts for not only efficient water oxidation, but may also for other catalytic reactions.A host–guest supramolecular complex Co@CB[5] as a molecular water oxidation catalyst was successfully immobilized on porous ITO and BiVOThe authors declare no conflict of interest.As 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.SupplementaryClick here for additional data file.


DNA double‐strand breaks, of which only a few result in crossovers. A small number of genes, which drive the resolution of DNA crossover intermediate structures towards non‐crossovers, have been identified in Arabidopisis thaliana. In order to explore the potential of modification of these genes in interspecific hybrids between crops and their wild relatives towards increased production of crossovers, we have used CRISPR/Cas9‐mutagenesis in an interspecific tomato hybrid to knockout RecQ4. A biallelic recq4 mutant was obtained in the F1 hybrid of Solanum lycopersicum and S. pimpinellifolium. Compared with the wild‐type F1 hybrid, the F1 recq4 mutant was shown to have a significant increase in crossovers: a 1.53‐fold increase when directly observing ring bivalents in male meiocytes microscopically and a 1.8‐fold extension of the genetic map when measured by analysing SNP markers in the progeny (F2) plants. This is one of the first demonstrations of increasing crossover frequency in interspecific hybrids by manipulating genes in crossover intermediate resolution pathways and the first to do so by directed mutagenesis.Crossover formation during meiosis in plants is required for proper chromosome segregation and is essential for crop breeding as it allows an  combination of traits by mixing parental alleles on each chromosome. Crossover formation commences with the production of a large number of CRISPR/Cas9‐mutagenesis results in increased recombination between the two genomes.Increasing crossover frequency during meiosis can speed up or simplify crop breeding that relies on meiotic crossovers to introduce favourable alleles controlling important traits from wild relatives into crops. Here we show for the first time that knocking out an inhibitor of crossovers in an interspecific hybrid between tomato and its relative wild species using  In the first place, the formation of crossovers is essential for proper chromosome segregation during gamete formation. Secondly, the reciprocal exchange between homologous chromosomes enables the reshuffling of parental genetic information and transfer of the recombined material to the next generation. This makes meiotic crossover formation an important target in crop breeding. Meiosis starts with the formation of a large number of DNA double‐strand breaks (DSB), most of which are repaired in non‐crossover events and do not result in recombinant chromosomes. In most organisms, and especially in plants, only a few (one to three) DSBs per chromosome are processed into actual crossovers , and the DNA helicases RECQ4 (RecQ helicase 4) and FANCM (Fanconi Anaemia of Complementation group M). They may dissolve D‐loops or double DNA Holliday Junctions into non‐crossovers  together with MLH1 (MutL Homolog 1) and HEI10 (Homolog of ENHANCER OF CELL INVASION NO.10) control the formation of class I crossovers. The non‐interfering class II crossovers are generated via an alternative pathway involving the MUS81 (MMS AND UV SENSITIVE 81) nuclease , and orthologs with similar functions can be readily identified in yeast  and plants  1 and 2 . Plants with a figl1‐1 mutation show 1.7‐fold increased crossovers, while in a figl1‐1 fancm‐1 double mutant even a sixfold increase has been observed , which can interbreed with a number of wild relative species such as (but not limited to) S. pimpinellifolium, S. chilense, S. cheesmanii, S. chmielewskii, S. pennellii and S. habrochaites, introgression of pathogen or arthropod resistance genes, as well as of abiotic stress tolerance and fruit quality traits is an important aspect of crop breeding  x S. pimpinellifolium. The tomato genome contains only one ortholog of RECQ4. We applied the CRISPR/Cas9 technique to generate mutations in RECQ4 alleles of both parents directly in the F1 hybrid. Diakinesis analysis of meiocytes in the mutant plant showed a significant increase of chiasmata, which is suggestive of an increase in crossovers during male meiosis. Moreover, the hybrid background allowed the tracing of genome‐wide crossover events by genotyping F2 progeny and thus directly establishing the positive effect of RECQ4 knockout on homeologous crossovers in a crop breeding intermediate.Here we studied the effect of Arabidopsis, RECQ4 consists of two paralogs, RECQ4A (At1g10930) and RECQ4B (At1g60930). Sequences of the closest homologs from Arabidopsis and tomato were collected from BlastP searches in Genbank proteins. Grape (Vitis vinifera) as a distant relative of tomato and Arabidopsis was added to support the analysis. These were used to make a phylogenetic tree from Arabidopsis RECQ1‐5, SIM and RECQ‐Like proteins and their putative orthologs in the other two species , confirming the analysis of plant RECQ4 proteins published elsewhere : a DEAD/DEATH box helicase domain (PF00270), a Helicase conserved C‐terminal domain (PF00271), a RecQ zinc‐binding domain (PF16124), the RECQ family‐specific RQC domain (PF09382) and a HRDC  domain. The tomato RECQ4 has the same domains, and in the same order, in common with the Saccharomyces cerevisiae Sgs1 protein and human BLM protein  revealed the presence of a single RECQ4 ortholog in this Solanum species with 99.8% nucleotide identity, encoding a protein of identical size with only two amino acids substitutions  relative to the tomato RECQ4.In s Figure . A fork RECQ4A Atg10930 ann Figure , only thRECQ4 alleles in the F1 hybrid S. lycopersicum (cv. Moneymaker) X S. pimpinellifolium (G1.1554). We generated these mutations using CRISPR/Cas9 and designed four single‐guide RNA's for inclusion in a binary Cas9/guideRNA‐expression vector  and mutant F1 plant flowers and analysed by gel electrophoresis. Whereas in wt F1 flowers a single band of the expected size was observed, mutant flowers contained a new band representing the product of the deletion allele of cv. Moneymaker  four cuttings were taken and grown into flowering plants for microscopic analysis of meiotic aberrations and gametophytic crossover frequency. Crossover frequency was estimated by analysing chiasmata in diakinesis cells and counting ring bivalents, the hallmark of two crossovers occurring at opposing ends of a chromosome pair. Quantification of the ring bivalents revealed significantly more bivalents  per nucleus in the recq4 mutant  against 9% in wild type  compared with anaphase I . This suggests that RECQ4 is also critical during the sister‐chromatid repair pathway or that DSB repair via the homolog repair pathway is less frequently used compared to the sister‐chromatid repair pathway. The latter would be in contrast to yeast, where DSB repair by the homologous chromosome is preferred rather than the sister chromatid  hybrid (n = 103) and of the recq4 hybrid (n = 104). Genotype scoring tables for all F2 progeny and all good markers are shown in Table recq4 mutant is shifted upwards for all chromosomes  for the crossover rates . In almost all cases, higher frequencies of crossovers were found in the recq4 mutant . These intervals were mostly located on chromosome ends. For all 12 chromosomes, the numbers of detected crossovers had increased substantially and significantly in the recq4 mutant as compared to the progeny of wt F1 plants by a factor of 1.53  of 997 cM for the wt F1 hybrid and one of 1766 cM estimated for the t Figure . These ret al.  and pea (Pisum sativum). In that study, a tomato intraspecific cross (cv. Microtom and cv. M82) was used, and crossovers were measured for two chromosomes (4 and 7). Their observed 2.7‐fold increase in recombination is higher than the 1.5‐fold increase observed by us for these two chromosomes. This may be due to the differences between intraspecific and interspecific hybrids, which suggests that the interspecific genetic background may have weakened the effect of the recq4 mutation. The sequence divergence between the parents used here, tomato cv. Moneymaker and S. pimpinellifolium G1.1554 was previously estimated to amount to approximately 0.6%  crossovers, possibly correlated with an increased role for parallel crossover‐limiting pathways. On the other hand, a fancm mutation in an Arabidopsis hybrid  for 5 min. Under a binocular microscope, flower buds were dissected to obtain the anthers (or meiotic cells) and prepared essentially according to , at 37 °C in a moister chamber for 3 h in the dark. After sufficient digestion, the enzyme mix was removed and replaced by citrate buffer. Anthers were then macerated in the citrate buffer using a clean needle to obtain a cell suspension (bigger debris were removed). This was then transferred into an Eppendorf tube and conserved at 4 °C/on ice.Entire flower buds of the biallelic mutant and wt F1 plants were fixed in ethanol/acetic acid 3:1 and conserved for several weeks at 4 °C the fixative solution. Flower buds were rinsed three times for 5 min) in distilled water and then rinsed twice in citrate buffer  in PBS for 10 min and washed in PBS for two times 5 min. Slides were mounted with 10 μL of Vectashield and a 24 × 32 mm coverslip. Observations were made using a Zeiss Axioskop 2 microscope or with a Nikon instrument A1 confocal laser microscope. Photographs were taken using a Zeiss AxioCam 503 colour camera.et al., For marker analysis in F2 plants, progenies of a mutant and wt F1 plants, the F1 itself, and the two parental lines were used. In total, 115 polymorphic SNPs selected from a previous publication  and tomato.Figure S2 (a) RECQ4 cDNA from the recq4 F1 hybrid (left lanes) and wild‐type hybrid (right lanes) showing the single band for the wild‐type alleles’ cDNA (top right), the 1nt‐insertion allele of Solanum pimpinellifolium (top left), and the additional band for the 254 bp deletion of the cv. Moneymaker allele. (b) Sanger sequencing traces of the S. pimpinellifolium wild type and 1 nt‐insertion allelesFigure S3 Cumulative genetic map length in cM for the twelve chromosomes of wild‐type F1  and recq4F1  of the Solanum lycopersicum x S. pimpinellifolium cross.Table S1 List of KASP markers used for obtaining the genetic maps and their physical position in the tomato genome version SL2.40Table S2 Statistical analysis of differences in crossover frequencies per chromosome performed through a Chi‐square test with the application of Bonferroni correction for the wild‐type (wt) F1/recq4 F1 comparison.Table S3 Genetic distances in cM for each calculated marker interval compared for wild‐type F1 and recq4 F1, respectively.Table S4 Guide RNA sequences, cloning vectors and PCR or sequencing primers.Click here for additional data file.Data S1 Marker scoring tables for the wild‐type and recq4 mutant F2 progenies.Click here for additional data file.


Profiting from an octa‐aldehyde precursor complex, the ideal dimensions of the interlinking structures are determined by reversible Schiff‐base formation, before irreversible Wittig olefination provided the rigidified complex. Reversed‐phase HPLC enables the isolation of the all‐trans isomer of the Fe(II) terpyridine complex 1, which is fully characterized. While temperature independent low‐spin states were recorded with superconducting quantum interference device (SQUID) measurements for both, the open precursor 8 and the interlinked complex 1, evidence of the increased rigidity of the ligand sphere in 1 was provided by proton T2 relaxation NMR experiments. The ligand sphere fixation in the macrocyclized complex 1 even reaches a level resisting substantial deformation upon deposition on an Au(111) surface, as demonstrated by its pristine form in a low temperature ultra‐high vacuum scanning tunneling microscope experiment.The coordination sphere of the Fe(II) terpyridine complex  Caging an Fe(II) ion: Like a cube the fourfold interlinked bisterpyridine ligand surrounds the Fe(II) ion. The post‐coordinative macrocyclization rigidifies the ligand sphere and guaranties the preservation of the properties of the complex. Switches are essential components in electronic devices and driven by the ongoing miniaturization, molecular switches move into the focus of interest.2) complexes are particularly appealing as potential switching motives due to their coordination geometry sensitive spin crossover (SCO) properties. And indeed, single molecule junctions with tailor‐made Fe(II)tpy2 complexes investigated at low temperature displayed bistability features pointing at SCO events triggered by the distortion of the ligand sphere. Examples are the mechanical spin‐state manipulation of a homoleptic Fe(II)tpy2 complex in a mechanically controlled break junction (MCBJ),E‐field) sensing junctions with heteroleptic Fe(II)tpy2 complexes with push–pull systems integrated in one tpy‐ligand.E‐field triggered switching was recently improved by separating the active Fe(II) complex from the electrodes.Iron bis‐terpyridine (Fe(II)tpy2 complexes as switchable subunits were encouraging, scanning tunneling microscopy (STM) may provide insights into the arrangement of the molecule at the electrode surface and its electron transport. In a first attempt, the arrangement of both tpy‐ligands around the central Fe2+ ion was stabilized by macrocyclization, providing chiral Fe(II)tpy2 complexes.While these MCBJ based single molecule experiments showing the potential of Fe(II)tpy2 complexes with rigidified coordination sphere. Fourfold interlinking of both tpy‐ligands freezes their spatial arrangement further improving the stability of the central Fe(II)tpy2 complex in 1 tpy1 was considerably reinforced as displayed by Carr‐Purcell‐Meiboom‐Gill‐NMR experiments. The improved structural integrity of 1 even enabled its investigation by UHV STM experiments.Indeed, the coordination sphere of the isolated target complex 8 diboron (Bpin)2 as borane source, bis(triphenyl‐phosphine)palladium(II) dichloride (Pd(PPh3)2Cl2) as catalyst, and potassium acetate (KOAc) as base. The required 4,4′′‐dichloro‐2,2′:6′,2′′‐terpyridine building block was assembled following our already published protocol.5. Using potassium carbonate (K2CO3) as base and bis(di‐tert‐butyl(4‐dimethylaminopehnyl)phosphine) dichloropalladium (II) (Pd(amphos)Cl2) as catalyst with a toluene/water solvent mixture in a sealed tube at 116 °C, provided the desired tpy‐ligand 6 in 75 % isolated yield after column chromatography (CC). To liberate the aldehydes prior to Fe2+ coordination, two reported protocols were combined.7 was obtained in 85 % yield by treating 6 with pyridinium p‐toluenesulfonate as proton source in a mixture of acetone and water at 100 °C in a microwave reactor. The homoleptic Fe(II) complex 8 was assembled by the addition of iron (II) chloride (FeCl2) to a solution of the ligand 7 in a dichloromethane (DCM) and methanol (MeOH) solvent mixture. An immediate color change to deep purple indicated the complex formation. After solvent removal and precipitation from a NH4PF6 water solution, the octa‐aldehyde complex 8 was isolated in 94 % yield.Indeed, as displayed in Scheme 1H‐ and 13C‐NMR spectroscopy, and high‐resolution mass spectrometry. Single crystals suitable for x‐ray diffraction of the complex 8 were obtained by diffusing diethyl ether vapor into an acetonitrile solution of 8. The solid‐state structure  the formation of an eightfold condensation product with 8 was observed among a variety of possible condensation products by direct injection electrospray mass spectrometry . While reaction conditions favoring the formation of the fourfold interlinked complex 2 could be found  for 10 days, Figure SI19 in the Supporting Information), all attempts to isolate the fourfold interlinked structure 2 failed, pointing at the lability of the imine bonds. Numerous efforts to reduce the imine linkers to more robust amine bonds employing a variety of reducing agents were also not successful.Initial attempts using ethylene diamine as linker  failed, the focus moved towards aromatic diamines, hoping that the increased delocalization of the imine π‐systems additionally favors the interlinking. And indeed, with 2, the experiments were indicative to identify the dimension of the ideal interlinking structure.Thus, in spite the fact that the mass signal in the DI‐ESI‐MS remains the only indication of the existence of the fourfold interlinked complex 2 by the olefins in 1. Like that the interlinking structure would be of comparable dimension and by using Wittig chemistry, 1 should be accessible from the same octa‐aldehyde precursor Fe(II)tpy2 complex 8. Indeed, treating 8 with 10 equivalents of )bis(triphenylphosphonium) dibromide in −20 °C cold dimethylformamide using 1,8‐diazabicyclo[5.4.0]undec‐7‐ene as a base resulted in a crude reaction mixture with the mass of the expected fourfold interlinked complex 1 (1330 m/z) as main signal recorded in a matrix‐assisted laser desorption ionization mass spectrometer (MALDI‐MS). However, even though the interlinking reaction proceeded smoothly, the purification remained challenging due to the lack of conformational selectivity in the double bonds formed by the Wittig reaction. With the Dh2 symmetry of 1, 64 different isomers are possible in theory due to cis/trans configurations of the eight double bonds. Even though not all of them are likely to be formed, the uninterpretable NMR spectrum of the crude reaction mixture points at several isomers being present. Thus, the crude material was subjected to reversed‐phase HPLC and after two runs, the all‐trans isomer could be separated in 4 % yield . The similar MALDI‐MS signals of all isolated peaks confirmed the hypothesis of various olefin isomers being formed during the interlinking Wittig reaction. The 1H‐NMR spectrum of the all‐trans isomer of 1 is displayed in Figure trans‐connection of the double bonds. The all‐trans isomer of 1 was further characterized by 1H‐, 13C‐, COSY‐, ROESY‐, HSQC‐, and HMBC‐NMR spectroscopy, UV/Vis spectroscopy, and high‐resolution electrospray ionization mass spectrometry .In order to improve the stability of the fourfold interlinked complex the strategy was to replace the reversible and hydrolysis sensitive imine‐bonds of trans isomer of 1, which was analyzed by the comparison of the spin–spin relaxation times T2 for the protons of 1  and the octa‐aldehyde precursor complex 8. In these complexes of comparable molecular weight, the spin–spin relaxation correlates with the intramolecular mobility of the spin and is thus a sensitive probe for the flexibility of the spin bearing protons. Using a Carr‐Purcell‐Meiboom‐Gill (CPMG) spin echo pulse sequence, T2 was measured for all aryl protons . The recorded values display for every proton a decreased T2 by a factor of 1.20 to 1.75 for the all‐trans isomer of 1 compared to 8 , pointing at a substantial rigidification of the ligand sphere upon fourfold interlinking. The experiment even allows to localize the mobility of individual subunits in both complexes. While the protons of the central pyridine ring A are the most static part, the ortho‐positioned B rings are more mobile in both compounds. Interestingly, the protons of the C and D rings as subunits of the linker structure of 1  displayed flexibilities in between the values recorded for A and B, suggesting a tight fixation of the interlinking bridges. In contrast, the C ring of 8 displayed an up to three‐fold T2 increase, as expected for the higher degree of freedom of a rotating subunit. Another observation pointing at the rigidity of 1 is the increased uniformity of the values recorded for T2 (max/min: 1.52) compared with the ones observed for 8 (max/min: 3.04). While the molecular weight increase from 8 to 1 is with 20.9 % too small to rationalize the recorded differences in T2, an aggregation of 1 to oligomers might be an alternative explanation for the observation. To disqualify this hypothesis, the hydrodynamic radii of both complexes were determined by diffusion ordered NMR spectroscopy . The observed difference of 5.2 % in diffusion coefficients corresponds to a mass increase of 16.4 % of 1 compared to 8, corroborating that both complexes were analyzed as dissolved monomeric complexes.Of particular interest was the rigidity gained by the fourfold interlinking in the all‐1 and to gauge the ring strain energy of the large ring system surrounding the [Fe(tpy)2]2+ core of the complex. DFT calculations were completed for compound 1 using a B3LYP functional and a 6‐31G  basis set using the Gaussian 09 suite 2]2+ is located on the Fe d orbitals and is the origin of the well‐studied MLCT transition of the complex. In contrast, the calculated HOMO of compound 1 is exclusively located on the large π system of the ring and the first metal contributions do not reveal itself until reaching the 1.5 eV more stable HOMO‐8 and the degenerate pair HOMO‐9 and HOMO‐10. The reaction enthalpy of an isodesmic reaction separating the peripheral ring and the metal complex moiety was estimated by DFT calculations and revealed that the overall ring strain energy for 1 is around 16 kcal mol−1. The strain is distributed over 4 ring systems formed by more than 70 atoms making it negligible. Details of these calculations are documented in the Supporting Information .Density functional theory (DFT) calculations were performed to obtain a better understanding of the electronic structure of e Figure . An unre1  was also observed in its magnetic behavior recorded in a superconducting quantum interference device (SQUID) magnetometer. In a temperature range between 5 K and 365 K, complex 1 remained in its low spin state. While the observation supports the claim of a fixed coordination sphere in the all‐trans isomer of 1, it does not qualify to account for an increased rigidity by fourfold interlinking, as also the open octa‐aldehyde 8 remains in its low‐spin state in this temperature range.The rigidity of 1 was even preserved upon deposition on a gold surface in a STM experiment. Employing an electrospray setup with in line mass selection1 on an Au(111) surface  enabled its deposition and subsequent investigation of the sample with a STM at 4.4 K under UHV conditions. The electrospray deposition ensured the absence of counter ions on the surface. A STM constant‐current topograph of a typical molecule is displayed in Figure 1, although a degree of distortion may be present. The geometry of 1 on Au(111) is most likely the one represented in the side view .1, further documenting the structural integrity gained by fourfold interlinking of the tpy ligands. The charge of 1 cannot be unambiguously clarified from the present data.To our delight, the structural integrity of w Figure  b, expos on an Au1 surface1, but also is expected to preserve the functionality of the Fe(II)tpy2 complex caged in the center of the macrocycle upon adsorption, which was not the case for less tightly fixed Fe(II)tpy2 model complexes . And indeed, two‐level fluctuations of the tunneling current are observed at slightly elevated sample voltages tpyThe approach holds perspectives not only for spin‐switch functionality, but also to couple the spin of the complexes to more reactive ferromagnetic substrates,The authors declare no conflict of interest.As 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.SupplementaryClick here for additional data file.


This suggests that membrane‐associated Nar1, comprising NarG1, NarH1, and NarI1 subunits, might not act as a classical menaquinol oxidase but could either receive electrons from the 3bcc‐aa supercomplex, or require the supercomplex to stabilize the reductase in the membrane to allow it to function. To address the biochemical basis for this dependence on the 3bcc‐aa supercomplex, we purified two different Strep‐tagged variants of Nar1 and enriched the native enzyme complex from spore extracts using different chromatographic and electrophoretic procedures. Polypeptides associated with the isolated Nar1 complexes were identified using mass spectrometry and included components of the 3bcc‐aa supercomplex, along with an alternative, spore‐specific cytochrome b component, QcrB3. Surprisingly, we also co‐enriched the Nar3 enzyme with Nar1 from the wild‐type strain of S. coelicolor. Two differentially migrating active Nar1 complexes could be identified after clear native polyacrylamide gel electrophoresis; these had masses of approximately 450 and 250 kDa. The distribution of active Nar1 in these complexes was influenced by the presence of cytochrome bd oxidase and by QcrB3; the presence of the latter shifted Nar1 into the larger complex. Together, these data suggest that several respiratory complexes can associate in the spore membrane, including Nar1, Nar3, and the 3bcc‐aa supercomplex. Moreover, these findings provide initial support for the hypothesis that Nar1 and the 3bcc‐aa supercomplex physically associate.In order to reduce nitrate  3bcc‐aa oxidase supercomplex. One possibility is that the supercomplex redirects electrons to Nar1 from menaquinol (MK), as indicated by the red dotted arrow. This study reveals Nar1 copurifies with subunits of the 3bcc‐aa supercomplex, supporting this hypothesis.Spore‐specific respiratory nitrate reductase (Nar1) uses nitrate as an electron acceptor when oxygen is limiting. Nar1 activity is totally reliant on the cytochrome  Such a dependence on the 3bcc‐aa supercomplex could have a potentially beneficial consequence for the bioenergetics of spores if Nar1 can accept electrons from the bcc complex while still allowing the Q‐cycle to function, essentially replacing the 3aa oxidase. The redox potentials of the redox cofactors within the 3bcc‐aa supercomplex from C. glutamicum have been determined [E. coli are also known [S. coelicolor, these potentials nevertheless suffice to serve as a model to indicate that coupling of Nar1 with the Q‐cycle is in principle feasible. Assuming involvement of the dual cytochromes c of QcrC, electron transfer directly to the heme bD and heme bP pair within NarI1 would be on a similar redox potential level as transfer to the CuA center in CtaC of the terminal oxidase. With a redox potential difference (ΔE) between menaquinol (Eo’ = −75 mV) and the NO3−/NO2− couple (Eo’ = +430 mV) of approximately 505 mV under standard conditions, coupled with the fact that NO3− reduction occurs in the cytoplasm, this should be sufficient to allow the Q‐cycle to move 4 H+ ions against a proton motive force of ~ 150 mV [+ ions would be translocated rather than the usual 6 H+ ions translocated when O2 acts as acceptor, that is, 4 H+ ions via the Q‐cycle plus a further 2 H+ ions via the proton‐pumping cytochrome c oxidase [+ ions when nitrate is used as acceptor would be 2 H+ ions more that would be translocated compared to when Nar acts directly as a quinol oxidase [3− reduction would be highly beneficial to the persistence of spores in environments where O2 becomes limiting or during anaerobiosis [If Nar1 indeed interacts with a form of the ggestion  that eletermined  .Fig. S2. The presence of QcrB2 (SCO7120) does not influence the migrations mobility of the Nar1 complexes.Fig. S3. Schematic representation of the plasmid constructs used to test restoration of Nar1 activity to strain COE192 (Δqcr‐cta).Click here for additional data file.Table S1. Detailed list of MS data.Click here for additional data file.Table S2. Detailed list of MS data.Click here for additional data file.Table S3. Detailed list of MS data.Click here for additional data file.