The particles of the WE43 powder were coated by the nanocrystalline oxide layer by means of a wet chemical deposition process. After that the powder is compressed into solid samples and deformed using high-pressure torsion at room temperature. A second phase is present, both, in pure WE43 alloy and in the one with deposited oxides. We observed that the modification of the alloy by the oxide layer deposition and deformation by high-pressure torsion changes the phase composition and properties of the samples. The samples modified by TiO The properties of nanocrystalline metallic materials, such as mechanical characteristics, corrosion rate, and others, came to the fore in the last few decades. Nanocrystalline materials showed unusual functional properties because they contain an extremely high proportion of atoms located at the grain boundaries and other defects in the crystal structure. The WE43 alloy containing rare earth metals (REM) is one of the most popular medical magnesium alloys . AlloyinAmong all the methods of obtaining nanocrystalline alloys, high-pressure torsion (HPT), which belongs to the family of methods of severe plastic deformation occupies a special place because it demonstrates a number of advantages in comparison with its competitors, for example, it makes it possible to produce nanocrystalline materials in relatively large volumes from both pure metals and alloys.The goal of this work is to investigate the possibility of altering the strength and corrosion properties of the WE43 alloy  by introducing oxide particles of various metals into the alloy and processing it by SPD. For this, the phase composition and properties of severely plastically deformed metal-ceramic composites based on the magnesium alloy WE43 modified with aluminum, titanium, magnesium and zinc oxides were studied.Usually, the Mg-based composites can be fabricated by the casting or ball-milling process. The casting methods can be used to fabricate large parts at a low cost but the main problem is the occurrence of coarse microstructural features and comparatively large grain sizes in the final samples, resulting in low strength. Moreover, the reactions between the Mg matrix and the reinforcements cause the degradation of the composites. Another difficulty arising in the production of Mg composites by casting methods is that it is complicated to introduce fine reinforcement particles into the melt, especially when the volume fraction of the reinforcement is large. Usually, large ceramic particles with a size of a few micrometers are added. The process is more complicated when the particle size is much smaller than a tenth of a micrometer or when it is of nanometer size. Therefore, ball-billing is often chosen as the preparation method for Mg-alloys and second component composites.2O5 [2 under a hydrogen atmosphere which directly led to the composite MgH2, and Mg2NiH4 [Numerous Mg-oxide composites were produced by the ball-milling technique. Zhenglong et al. produced a nanocrystalline composite of Mg–3Ni–2NiO (wt.%) by mechanical milling with nickel nano-powders under the hydrogen pressure . Song et2O5 . Li et a Mg2NiH4 .2O3 and ZnO [2O3 and ZnO and, additionally, with TiO2 and MgO.In this paper, the method of pyrolysis of organometallic compounds is used to deposit the oxide layer on the magnesium alloy powder. The idea is to crush the Mg alloy, cover the powder particles by a nanometer thick oxide layer, after that produce an Mg-ceramic composite by SPD. During the SPD process, the nanometer-thick oxide layer should break and mix with the Mg matrix, producing fine and well-distributed oxide particles. Earlier, we already successfully produced WE43 composites with Al and ZnO , now we 2O3, ZnO, MgO, and TiO2 were deposited onto WE43 particles using pyrolysis of organometallic compounds. This method has been developed under the supervision of Prof. A.A. Myatiev  for the deposition of nanocrystalline single- and multi-component oxide films. By pyrolytic decomposition of organic precursors containing salts of metals and carbon acids, we produce nanocrystalline oxide films [First, the WE43 alloy was mechanically crushed into particles of 0.5–1 mm size. Second, thin films of nanocrystalline Alde films ,13,14,15Extraction methods are used to prepare such solutions. As the extractant, a mixture of higher isomeric carboxylic acids (HICA) was used, the general formula of which:The hydrocarbon radical R can contain from one  up to 12 carbon atoms.Using this approach, the films can be deposited on various substrates. The deposited films are dense, non-porous, nanostructured, uniform, and non-textured. The chemical components in multicomponent films are distributed uniformly ,17.In order to deposit the oxides, the obtained powder was mixed with the organometallic solutions of aluminum or zinc and the resulting mixture was annealed in air at 400 °C. Thermal decomposition of the organic component of the solution and precipitation of films consisting of a metal oxide, the cation of which was introduced into the solution, occurs on the surface of the WE43 powder particles.In the previous study , all of After proper mixing of the coated and uncoated powders, the mixture was subjected to SPD by HPT. The powder was poured into the cavity in the lower anvil and compressed to obtain a solid pellet. Samples were deformed at a pressure of 6 GPa for 5 revolutions with 1 rpm rotation speed. The cavity in the lower anvil was of 0.2 mm depth.The microhardness was measured using a 402 MVD Instron Wolpert Wilson Instruments tester . The morphology of obtained samples and the composition of the matrix and second phase were studied by electron probe micro-analyzer (EPMA) using a Tescan Vega TS5130 MM scanning electron microscope  equipped with an Oxford Instruments energy dispersion spectrometer .The transmission electron microscopy (TEM) was performed on the FEI Titan 80-300 Transmission Electron Microscope  with a high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and EDAX S-UTW energy dispersive X-ray analysis (EDX) detectors.2 * day)) for the method of hydrogen evolution was calculated by the Equation (1):2; T—time, days.The study of the corrosion properties was carried out using the method of measuring the volume of hydrogen released during corrosion . As a teThe sample made only from the WE43 alloy, in the previous study , consistAs can be seen, the composition of a part of the second phase particles in the WE43 alloy after the HPT changes with the addition of oxides. The second phase particles in the pure WE43 alloy after HPT contain only the rare earth elements from the alloy. After modifying the WE43 alloy by oxides prior to HPT, a part of the second phase particles in the samples contains Al, Ti, or Zn from the oxide; It is observed as in SEM with a lower resolution, as in HAADF-STEM with a higher resolution. The uncertainty for the Al content in the TEM investigation is 0.05 at.%. The second phase of the samples with the addition of magnesium oxide, sometimes, shows a higher oxygen, Zr, or Nd content. Besides that, the samples with the addition of zinc oxide contain thin layers of the second phase on the borders of the initial particles or grain agglomerates, thus providing a higher strength.Under the action of SPD, the mobility of atoms and the mass transfer rate are increased to the extent typical for diffusion during annealing at elevated temperatures. This leads to the mixture of the magnesium alloy WE43 with oxides added prior to the SPD.The microhardness of the samples after the HPT was measured as an array of 15 × 15 points over the whole area of the samples. The measured microhardness on the middle of the sample radius after HPT is, as follows: for WE43 with aluminum oxide—969 ± 34 MPa, for WE43 with titanium oxide—1,017 ± 36 MPa, for WE43 with magnesium oxide—997 ± 36 MPa, and for WE43 with zinc oxide—986 ± 32 MPa.The microhardness measured in the previous study  for pure2O3 and TiO2 perform best in that task.The corrosion tests result in Samples /(oxide) composites were successfully produced. They are dense and it is possible to study their structure and properties.The oxide metals enter the second phase particles and promote more dispersive second phase segregation. That changes the phase composition after the SPD process and, accordingly, alters the properties of the composite.The strength of the samples increases compared to the results of the previous study; this is a result of a lower amount of modificating oxide. This reduction was planned and the results show that our study succeeded.2. The same is true for the microhardness.The corrosion resistance is higher for all modifying oxides compared to the pure WE43 after HPT but the best results were achieved for the TiO


Despite the outstanding chemical, thermal and transport properties of amorphous and glassy perfluorinated polymers, only few works exist on the preparation and transport properties of perfluoropolymer/molecular sieves mixed-matrix membranes (MMMs), probably because of their poor compatibility. In this review, the compatibilization of ceramic molecular sieves with perfluorinated matrices is considered first, examining the effect of the surface treatment on the gas transport properties of the filler. Then the preparation of the defect-free hybrid membranes and their gas separation capabilities are described. Finally, recent modelling of the gas transport properties of the perfluoropolymer MMMs is reviewed. The systematic use of molecular sieves of different size and shape, either permeable or impermeable, and the calculation of the bulk transport properties of the molecular sieves—i.e., the unrestricted diffusion and permeability—allow to understand the nature of the physical phenomena at work in the MMMs, that is the larger the perfluoropolymer fractional free volume at the interface, and restricted diffusion at the molecular sieves. This knowledge led to the formulation of a new four-phase approach for the modelling of gas transport. The four-phase approach was implemented in the frame of the Maxwell model and also for the finite element simulation. The four-phase approach is a convenient representation of the transport in MMMs when more than one single interfacial effect is present. Fluoropolymers display better chemical and solvent resistance with respect to similar hydrocarbon polymers, therefore they are widely used to prepare membranes for battery separators, microfiltration and ultrafiltration, membrane contactors and chemical reactors ,2,3,4,5.®) are semi-crystalline and hydrophilic PFPs. They are used as proton exchange membranes in fuel cells and for electrolysis, such as in the chlor-alkali process. Perfluoropolyacid-based mixed-matrix membranes (MMMs), i.e., mixtures of a filler in a polymeric matrix .,45.39,45Other MMMs were prepared by embedding 20–35% SAPO-34 crystals of different size (0.2–2 μm) and shape (AR 2–9), both permeable and impermeable, in Hyflon AD60X  43]. In. In43]. 4 units [Silicalite-1 is a hydrophobic medium pore zeolite (5.4–5.6 Å) with channels delimited by 10-member rings of SiO4 units . It is t4 units , and als4 units . HydrophAs a first important result, PFPs MMMs prepared with the fluorophilic silicalite-1 were all defect-free ,45: no g2/CH4 ideal selectivity, in excess of the 2008 upper bound [2/CH4 selectivity was also improved in a similar way, getting closer to the 2008 upper bound for this gas pair [2, N2 and CH4  (PTMSP) [4H10/CH4 selectivity indicated the active participation of silicalite-1, in which the strongly adsorbed butane excludes methane [Teflon AF2400 MMMs were tested for the n-butane/CHparation . Permeabparation . The incparation . Larger  (PTMSP)  and poly (PTMSP) , charact (PTMSP) ,52. The  methane .4 selectivity in the mixture experiments than the AF24_1500_40 membrane, with the same permeability [When the AF24_1500_40 membrane was fed with equimolar butane-methane mixtures, a reversal of the selectivity from methane to butane on increasing the butane partial pressure (from 50 to 106 kPa at 25 °C) was observed. It is also interesting to note the advantages of a larger aspect ratio of the silicalite-1 crystals on the transport properties of the MMMs. The AF24_dC5_40 membrane, containing same loading (40 w%) of platy silicalite-1 crystals  than the polymer, and less selective. This behaviour might be the effect of a larger permeability of silicalite-1, of the increase of the FFV around the crystals, similarly to the Teflon AF2400/fumed silica MMMs, or else of the voids in the crystal aggregates contained in the MMMs.Teflon AF1600 MMMs containing tiny silicalite-1 crystal (80 nm) were more permeable , MP is the gas permeability of the continuous phase (the polymer), and φ is the volume fraction of the dispersed phase. Since the experimental permeability of the polymer and of the MMMs were available, the gas permeability of silicalite-1 could be easily worked out. The different behaviour of the MMMs with silicalite-1 crystals of different size indicated that probably the filler does influence the physical state of the polymer. Therefore, it was decided to derive a theoretical permeability of the MMM from the gas permeability of filler and polymer, and to compare this value to the experimental results. The polymer permeability was readily measured, whereas the silicalite-1 permeability cannot be measured directly.In Equation (5), Care should be taken in the choice of the right gas permeability of a zeolitic molecular sieve from literature values. It has to be noted that in the literature a large scatter of the permeability values of different supported zeolitic membranes made of the same zeolite is found . This haIn practice, a more reliable method is to obtain the intrinsic gas permeability of a molecular sieve by combining solubility coefficients with the unrestricted intra-crystalline diffusion coefficients in Equation (2). Reproducible solubility of several gases in a variety of zeolites is available from experimental measurements; instead, the intra-crystalline gas diffusion coefficients are not, in general, available. The gas diffusion coefficients in molecular sieves, as obtained experimentally with different techniques, sometimes differ by three orders of magnitude or more. It is found that this scatter is the effect of surface and intra-crystalline barriers. The macroscopic techniques  based on gas uptake usually measure a slower gas mobility than microscopic methods (such as pulsed field gradient nuclear magnetic resonance (PFG-NMR) and neutron scattering techniques), which are able to probe unrestricted diffusion inside the crystals . Unfortu2 and CH4 in silicalite-1 obtained with a transient pulse-response technique [The diffusion coefficients of COechnique  were comechnique  in Equatechnique .2 and CH4 than Teflon AF 1600. As a consequence, the Maxwell Equation (5) predicted a larger permeability of the silicalite-1 containing MMMs with respect to the polymer. It was therefore surprising to discover that the experimental permeability of the MMM containing 30 w% of 350 nm silicalite crystals was smaller than the one of Teflon AF 1600 for both CO2 and CH4. The authors concluded that the silicalite permeability was strongly reduced by some barrier to the transport of gas at the surface or in the interior of the crystals [l is the thickness of the membrane and θ (the time-lag) is the intercept of the pressure vs. time asymptotic line at long times with the time axis , a natural zeolite. In SAPO-34, large cavities are connected by narrow ports (3.8 Å) delimited by eight member rings of TO4 units . Due to paration ,87,88, aectivity .On the basis of the experience with the PFP/silicalite-1 hybrids, new experiments were planned to make clear the importance for MMMs of interfacial polymer free volume and restricted diffusion in molecular sieves. Several Hyflon AD60X MMMs were prepared with different loadings (20–35 v%) of both permeable and impermeable SAPO-34 of different size and aspect ratios, with the aim to study in detail the effect of these variables on the final transport properties, and to isolate the behaviour of the polymer in the MMMs from the properties of the filler.2, N2, CH4, CO2) excluded the presence of defects. Transport features were dependent on the loading, the size and the shape of the crystals, as seen in the diagram of the Robeson’s plot for the CO2/CH4 gas pair . Inspection of In all cases the presence of SAPO-34 enhanced the selectivity of Hyflon AD60X for the COAs in the case of the PFP membranes containing silicalite-1, the approach for the understanding of the underlying physical phenomena was the derivation of the unrestricted, intra-crystalline gas permeability of SAPO-34 , and its use in the macroscopic modelling of the transport phenomena in the MMMs .2, N2, CH4 and CO2 in SAPO-34 was assumed to be equal to the one of an all-silica zeolite with the same CHA topology. Bulk permeability was calculated as the product of solubility and diffusion (Equation (2)) [2 molecular-sieve with the CHA structure, in the fugacity interval 100–600 kPa.The bulk permeability of He, Hion (2))  on the bion (2))  of the pAR is the aspect ratio of the filler,The macroscopic model calculation of the gas transport in the MMMs varied according to the aspect ratio of the SAPO-34 crystals . The resch cases ,93.The effective medium theory approach of Maxwell  was usedThe gas permeability of the MMMs containing flat crystals demonstrated the presence of barriers to the transport of mass at SAPO-34 . The gas2·cm−3, respectively, therefore the volume of interfacial polymer in the MMMs containing small and large fillers, being roughly proportional to the outer surface area, was several times larger for the former. This circumstance was used to explain why the gas permeability of MMMs containing large impermeable SAPO-34 ) and the Cussler (Equation (7)) models were used to calculate the expected ideal COt ratios . If masst ratios ,93. AnotThe modelling of gas transport in Hyflon AD60X/SAPO-34 MMMs with the effective medium approach (Cussler and Maxwell models) made it clear that, besides the unperturbed (bulk) polymer and filler, a region of interfacial polymer and some barrier at SAPO-34 must be considered. Starting from this evidence, Di Maio et al.  introduc2, N2 and CO2 permeation in Hyflon AD60X/SAPO-34 MMMs in two ways: by means of the effective medium analytical formula (4M Maxwell model), and through the finite element solution (FEM) of the transport differential equations [The new four-phase approach was implemented for He, Hquations .4 units—found a thickness of surface barriers of the same order of magnitude, i.e., 3, 7 and 14 nm for H2, CO2 and CH4, respectively [The 4M Maxwell model was inspired by a previous three-phase Maxwell model introduced by Koros and co-workers ,95, and ectively . For simNumerical simulation of the gas permeation through composite membranes was carried out by solving the finite-element approximation of the partial differential equations governing the relevant solution/diffusion processes , using ti,C the concentration of species i. The following equations:ijD of species i in material j is assumed uniform and isotropic, were solved. A concentration jump at the matrix/filler interface formed due to the different gas solubility. At the interface boundaries both uniform mass flux and the following equilibrium condition were applied:iS is the solubility of species i and the superscripts denote the two solid phases, I and II, in contact.Pure gas diffused continuously through the distinct matrix and filler domains. Diffusion was expressed in terms of Computational grids  were bui−5 to 1.1 × 10−4 (Maxwell 4M), or from 3.8 × 10−5 to 4.3 × 10−4 (FEM) [The inputs of the FEM simulations were: (i) SAPO-34 bulk diffusivity and solubility data from simulations see .; (ii) t−4 (FEM) .By the above assumptions, the results of both FEM simulations and macroscopic 4M Maxwell model compared well with the experimental data .Not surprisingly, the best fit was found with the MMMs containing the large fillers  in which the relative importance of the interfacial effects was minimal . In the The overall agreement of the experiments with both the macroscopic 4M Maxwell modelling and the FEM simulations is excellent if we consider the simplifying assumptions adopted, and namely: (i) the constant, average values of solubility and diffusion coefficients for polymer and filler bulk; (ii) the uniform constant features of the surface barrier for all of the three different samples of SAPO-34.The major advantages of the FEM simulation consist in the quantification of the contributions of the different phases to the overall gas transport and in the possibility to visualize the concentration profiles in a unit cell  as well The lesson learned from the study of the PFP/molecular sieve systems is that the macroscopic modelling of the transport properties of MMMs requires the understanding of the underlying physical phenomena. If we had only prepared MMMs with the high aspect ratio SAPO-34  , 129Xe N29Xe NMR , and the29Xe NMR  applied It has to be noted that the new four-phase approach is not restricted to the modelling of PFP MMMs, since it can be applied whenever two non-ideal phenomena are present, including those cases in which a rigidified polymer layer is observed. Besides the consistent interpretation of the physical phenomena, an adequate modelling of the transport properties of real systems allows predictive capabilities to guide the preparation of better MMMs.Crystalline porous materials, in real life, contain defects and are far from ideal. The modelling of mass transport in MMMs needs theoretical and experimental studies of diffusion in the fillers, both ideal and defective. The nature and the effects of the barriers to mass transport need to be studied in depth. In MMMs containing extremely thin, exfoliated layers, either zeolitic molecular sieves, porous graphenes, MOFs or others, the transport properties of the bulk materials may be altered to a large extent, and interfacial effects become of primary importance.Grafting perfluorinated tails on the outer surface of zeolitic molecular sieves improved the surface permeability and allowed the preparation of defect-free MMMs with hydrophobic and amorphous PFPs.2/CH4 and N2/CH4 ideal selectivity with respect to the polymer. The improvements were not expected, because the pores of silicalite-1 are not able to discriminate the above gases on the basis of size. Methane is more permeable than n-butane in Teflon AF2400 membranes, but the presence of silicalite-1 in Teflon AF2400 MMMs was able to revert the selectivity in favour of n-butane, probably because of the combined effects of a larger interfacial FFV and of the butane-selective molecular sieve. Other things being equal, large aspect ratio silicalite-1 increased the n-butane/CH4 selectivity even further.Silicalite-1/Hyflon AD60X MMMs displayed some improvement of the CO2, CO2, O2, N2 and CH4) to the polymer with less selectivity, whereas larger crystals induced a reduction of permeability and an increase of the gas/CH4 selectivity. In order to clarify this puzzling situation, a change of paradigm was introduced: instead of calculating the permeability of the filler from the performance of the MMMs through the Maxwell model (Equation (5)), the permeability of the filler was obtained from the gas solubility and diffusion, using this value to predict the performance of an ideal MMM through Equation (5). The comparison of the predicted vs. the experimental permeability (CO2 and CH4) and the evaluation of the experimental diffusion coefficients (time lag method) indicated the presence of two different non-ideal effects in the Teflon AF1600/silicalite-1 MMMs: a polymer allowing larger gas mobility, i.e., a larger polymer FFV, and a much less permeable filler, i.e., the presence of barriers to the transport of mass at silicalite-1.The gas transport properties of Teflon AF1600 MMMs containing silicalite-1 crystals were strongly dependent on the size of the filler. Small crystals added permeability . The predicted MMMs permeability was higher than the experimental results, evidencing the presence of barriers to the transport of mass at SAPO-34. On the basis of the experimental evidences, the transport properties of the MMMs were modelled through a new four phase approach, which explicitly considered the pristine two phases, i.e., the unperturbed, bulk polymer and SAPO-34, and two interfacial phases, namely the perturbed, high FFV polymer, and a superficial skin of the crystals, concentrating all of the additional resistance to the transport of mass (the barrier). The four-phase macroscopic modelling, implemented both via an extension of the Maxwell analytical method (4M Maxwell model) and by means of a FEM numerical simulation, nicely reproduced the experimental results. The new four-phase approach lends itself to interpret the transport data of those MMMs evidencing two simultaneous non-ideal behaviours.A new set of Hyflon AD60X MMMs were prepared with three different SAPO-34 crystals, of different size and aspect ratio, both permeable and impermeable. All of the MMMs where characterized by improvements in the ideal COThe above pioneering works clearly show: the feasibility of PFP/molecular sieve MMMs and their interesting properties for gas separation of technological relevance; the complexity and the competitive character of the processes at work in MMMs; the adequacy of four-phase models for the description of permeation in MMMs.


To figure out the reason for the observed phenomena, the kinetic parameters in primary pyrolysis and the secondary charring reaction were estimated by a differential evolution (DE) optimization algorithm. The prediction indicated that KCl shifted the initial degradation temperature of each component of MDF towards a lower temperature. Char and gas yields increased with the concentration of KCl, whereas the tar yield reduced. The changes in activation energies revealed that KCl played a catalyst role in the reaction of resin, hemicellulose and cellulose in primary pyrolysis. For lignin, KCl had little effect. In the secondary charring reaction, KCl apparently promoted the reaction of tar. The catalytic effect of KCl on MDF pyrolysis was the combination of primary pyrolysis and the secondary charring reaction. Finally, the optimal catalytic concentration for KCl on MDF pyrolysis was analyzed.The effects of potassium chloride (KCl) on the pyrolysis of medium density fiberboard (MDF) were investigated by using thermogravimetry/Fourier-transfer infrared spectroscopy (TG-FTIR). Five MDF samples treated with different KCl concentrations  were heated with a heating rate of 20 °C/min. The thermogravimetry (TG) results showed that KCl caused the primary pyrolysis stage towards lower temperatures. The FTIR results indicated that with the concentrations of KCl, the formation of CH A variation individual is determined byF indicates the scaling factor, and r1, Xr2, Xr3X represent three different random numbers that are different to iX.4: Crossover. The individual is updated viaCr denotes the crossover probability.5: Selection. The individual in the next iteration is selected byf(x) denotes the fitness function of the individuals. In this study, the fitness function φ is the error between model outputs and experimental results, which can be calculated ascal denotes the calculated results, exp refers to the corresponding experimental data, jn indicates the number of data points and k represents the number of heating rates. In order to make the weight of mass and mass loss rate equal, the weight coefficient c is set to 0.5. In respect to the algorithm parameters, population size, crossover probability, scaling factor and maximum iteration number are set as 60, 0.2, 0.5 and 1000 in this work, respectively. The update process is repeated until a satisfactory solution is obtained.iT indicates the initial temperature of the primary pyrolysis stage, maxT represents the temperature corresponding to the maximum mass loss rate, fT denotes the terminal temperature of the primary pyrolysis stage and maxt refers to the time corresponding to the maximum mass loss rate.Some characteristic parameters observed in mass fraction (TG)-mass loss rate (DTG) curves are shown in The mass fraction (TG) and mass loss rate (DTG) profiles of raw MDF and water washed MDF are compared in maxT decreased with the increasing concentration of KCl, from 383.5 °C of 0 wt% KCl to 345.7 °C of 3 wt% KCl. This revealed that the presence of KCl makes the pyrolysis reach the maximum mass loss rate in advance, and thus potassium had a catalytic effect on the MDF pyrolysis [yrolysis ,27,28,29yrolysis ,30. It iyrolysis ,32.maxT, the strongest characteristic absorbance can be obtained. Some possible compounds from FTIR characteristics absorbance bands, as summarized in maxT. The main gases released during raw MDF pyrolysis were obtained based on maxT. It was observed that the presence of KCl had effects on the amounts of pyrolysis gaseous products instead of the composition, which is consistent with the result reported by Feng et al. [FTIR was involved to characterize the gases the escaped in the pyrolysis process of MDF samples. With the temperature fixed at g et al. .−1 corresponded to the release of methane (CH4). The absorbance peak at 2358 cm−1 was attributed to the release of carbon dioxide (CO2). The absorbance peak at 2182 cm−1 indicated the release of carbon monoxide (CO). The absorbance peak at 1748 cm−1 represented the release of aldehydes, ketones and acids (C=O). The absorbance at the corresponding wavenumber were normalized to evaluate the effect of KCl concentration on pyrolysis gas products CH4, CO2, CO and C=O.According to the Lambert−Beer law, the gas concentration is linearly dependent on the absorbance at a specific wavenumber ,40. Ther4, CO2, CO and C=O. For each gas product, the evolution profile shifted to an earlier time with the KCl concentration, which was consistent with the trends of fT shown in 4 and C=O compounds, the peak absorbance dropped with the increase in KCl concentrations. On the contrary, as shown in 2 increased when the concentration of KCl increased. The trend of CO peak absorbance was similar to that of CO2. In addition, relatively high amounts of CO2 were released for each sample. Meanwhile, the release of CH4 was the minimum. As shown in 2 and CO showed another peak at higher temperatures. It implies that there was more CO2 and CO evolved in the secondary pyrolysis stage [is stage ,26.φ in Equation (19), the experimental data from heating rates of 20 and 30 °C/min were utilized. Making an adjustment of the search ranges for parameters listed in [In previous research , the proisted in , the optComparisons between the experimental TG/DTG data and calculated values of MDF samples with varying KCl loading concentrations at the heating rate of 20 °C/min are presented in Tf in Tf, there would be a reduction in tar yield curve. This was most likely when T > Tf, the secondary charring reaction occurred, and the generation rate of tar in primary pyrolysis was low, as compared with the consumption rate of tar in the secondary reaction.In order to find out the underlying reason of the observed changes in MDF components and pyrolysis products due to potassium, the changes in activation energies of primary reactions and secondary charring reaction were analyzed.E represents the activation energy, and r, h, c denote the reactions of resin, hemicellulose and cellulose in primary pyrolysis, respectively. tar denotes the secondary charring reaction and x indicates the mass fraction of potassium (%). As demonstrated in According to the fitting curve shown in In this work, the impact of 3 wt% KCl was an extraordinary one. When the addition of KCl increased to 3 wt%, the trends of characteristic parameters, including the initial decomposition temperature of each component, the yields of products and the activation energies of pyrolysis reactions, were found to be distinct from other cases. A limit on the concentration of KCl may exist to achieve the best catalytic effects on MDF pyrolysis. Based on the fitting curves shown in (1)The presence of KCl shifted the primary pyrolysis stage towards lower temperatures. As the addition of KCl increased, the characteristic initial temperature showed little change while the final temperature decreased. The temperature range of the primary pyrolysis process was narrowed by nearly 24−36 °C. The mass loss rate of the whole pyrolysis process reached its peak in advance with the concentration of KCl.(2)4 and C=O functional groups while promoting the formation of CO2 and CO. KCl affected the release of pyrolysis gaseous products in terms of amounts instead of composition. KCl inhibited the formation of CH(3)KCl changed the initial degradation temperature for each component of MDF. With the increasing concentration of KCl, the initial degradation temperature of resin, hemicellulose and cellulose dropped. For lignin, the effect of KCl on the initial degradation temperature was relatively weak.(4)Char and gas yields increased with the increasing concentration of KCl, whereas the tar yield was reduced.(5)KCl had an effect on the activation energies of reactions during the pyrolysis process. In the primary pyrolysis stage, the activation energies of resin, hemicellulose and cellulose decreased with the concentration of KCl. Aside from this, KCl had little effect on the activation energy of lignin. In the secondary charring reaction, KCl reduced the activation energy of tar. The catalytic effect of KCl on MDF pyrolysis manifested in the combination of the primary pyrolysis and secondary charring reaction.(6)It is reasonable to take 2 wt% and 2.5 wt% as the optimal concentrations of KCl for the catalytic effects on MDF pyrolysis in primary pyrolysis and the secondary charring reaction, respectively. In the present study, five MDF samples treated with varying potassium chloride (KCl) concentrations were heated by thermogravimetry/Fourier-transfer infrared spectroscopy (TG-FTIR) to investigate the effects of potassium chloride on the pyrolysis of medium density fiberboard (MDF). The kinetic parameters were estimated through a procedure based on experimental data and a differential evolution optimization algorithm. The major results and conclusions are summarized as follows:


Cardiovascular diseases are one of the most common complications of type 2 diabetes. They are considered the leading cause of death among diabetics. One of the mechanisms underlying diabetic cardiovascular complications is oxidative stress. Many phenolic acids are regarded as antioxidants. The aim of the study was to investigate the effect of rosmarinic acid (RA) and sinapic acid (SA) on oxidative stress parameters in the cardiac tissue and serum of type 2 diabetic female rats. Additionally, the effect of these compounds on glucose homeostasis and lipid profile in the serum was evaluated. Type 2 diabetes was induced with high-fat diet and streptozotocin. RA at the doses of 10 and 50 mg/kg and SA at the doses of 5 and 25 mg/kg were administrated orally for 28 days. Untreated diabetic rats exhibited unfavorable changes in glucose metabolism and lipid profile. Changes in the enzymatic and non-enzymatic markers indicated the onset of oxidative stress in these animals. The results showed that the higher doses of the tested phenolic acids—50 mg/kg of RA and 25 mg/kg of SA—revealed beneficial effects on oxidative stress in the cardiac tissue of diabetic rats. Diabetes mellitus (DM) poses a serious public health issue . As of 2It is believed that diabetic complications, such as diabetic-related cardiac dysfunctions, are directly connected with redox imbalance and oxidative stress ,12,13,14Both rosmarinic acid and sinapic acid are compounds commonly occurring in plants. These phenolic acids can be delivered to the organism on a daily basis in numerous herbs, vegetables, and fruits. Rosmarinic acid can be found mainly in Lamiaceae plants, such as rosemary, peppermint, lemon balm, or sage ,29, wherScientific literature shows that both rosmarinic and sinapic acids have a beneficial effect on parameters connected with the glucose metabolism in diabetic rats ,36,37,38Based on scientific reports, we hypothesize that disturbance in redox balance in the serum and cardiac tissue may develop in long-term hyperglycemia in type 2 diabetic rats. Moreover, we suppose that rosmarinic acid and sinapic acid could mitigate hyperglycemia and hyperlipidemia and they may act as antioxidants in cardiac tissue. Thus, this experiment was conducted in order to evaluate the effect of rosmarinic acid and sinapic acid on the parameters connected with glucose and lipid metabolism in the serum and on the markers of oxidative stress in the serum and cardiac tissue of female rats with type 2 diabetes induced with high-fat diet and streptozotocin.The experiment was carried out on sexually mature (3-month-old) female Wistar rats. The study was approved by the Local Ethics Commission in Katowice, Poland . The rats were provided by Center of Experimental Medicine, Medical University of Silesia . The animals were kept in standard laboratory conditions (EU Directive 2010/63).The following drugs and substances were used in the experiment: streptozotocin ; ketamine ; xylazine ; rosmarinic acid ; and sinapic acid .n = 10):Control, non-diabetic rats (C group)High-fat diet and streptozotocin (HFD + STZ)-induced type 2 diabetic control rats (DM2 group)HFD + STZ diabetic rats administered orally with rosmarinic acid at a dose of 10 mg/kg (RA10 group)HFD + STZ diabetic rats administered orally with rosmarinic acid at a dose of 50 mg/kg (RA50 group)HFD + STZ diabetic rats administered orally with sinapic acid at a dose of 5 mg/kg (SA5 group)HFD + STZ diabetic rats administered orally with sinapic acid at a dose of 25 mg/kg (SA25 group)During a one-week acclimation period the animals were randomly assigned to six experimental groups  was measured once a week by MicroDot glucometer equipped with test strips . During the whole experiment the animals had unlimited water supply and appropriate chow: rats in the C group were fed with a standard laboratory chow  and the rats in the DM2, RA10, RA50, SA5, and SA25 groups were fed for 2 weeks before STZ injection with high-fat diet (HFD) enriched with 32% of fat from lard . The HFD in these groups was continued till the end of the experiment. The overall duration of HFD in the groups with experimentally induced type 2 diabetes was 49 days. Before a single injection with streptozotocin  the rats were fasted for 8 h. Streptozotocin was dissolved in 0.1 M citric buffer and 1 mL/kg of this solution was injected. The rats from the C group were injected with an appropriate volume of 0.1 M citric buffer only. Seven days after the STZ injection random blood glucose level was measured. If the result of this test was higher than 200 mg/dL, the animal was considered diabetic. Administration of rosmarinic acid and sinapic acid started 7 days after STZ injection and lasted for 28 days. The phenolic acids suspended in water  were administered by gavage once a day. Control rats from the C and DM2 groups received water with Tween 20 by gavage at the same volume as the rats from the rosmarinic acid and sinapic acid-treated groups received the suspension of phenolic acids (2 mL/kg). The timeline of the in vivo part of the experiment is presented in the g, 15 min, +4 °C). The obtained supernatant was used for further examinations. All assays were measured in Tecan Infinite M200 PRO plate reader with Magellan 7.2 software .24 h after the administration of the last dose of phenolic acids and overnight fasting, rats were euthanized by injection of ketamine and xylazine mixture and cardiac exsanguination. In order to separate the serum required for biochemical assays, the blood obtained from the heart was centrifuged. Vital organs such as the heart, liver, right kidney and the uterus were excised from the animals and weighted. Then, each heart was homogenized separately in phosphate buffered saline (PBS), pH 7.4 (10% w/v), and centrifuged  were assessed with ELISA kits . Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities as well as uric acid and urea levels were measured spectrophotometrically with Biosystems kits ; the creatinine was assayed with Pointe Scientific Inc. kit .Glucose and fructosamine levels in the serum were evaluated with Pointe Scientific Inc. kits. Insulin levels in the serum were measured with the BioVendor ELISA kit . The homeostasis model assessment of insulin resistance (HOMA-IR) was calculated according to the following Equation:Advanced glycation end products (AGEs) in both the serum and cardiac tissue were assayed with ELISA method .Total cholesterol, triglycerides, low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) levels were assayed spectrophotometrically with Pointe Scientific Inc kits .Activity of superoxide dismutase (SOD) and catalase (CAT) was measured in both the serum and cardiac tissue. Additionally, glutathione peroxidase (GPx) activity was evaluated in cardiac tissue. All the enzymes were assayed with the use of Cayman kits  and their activity was expressed per 1 mg of protein. The protein level was assessed with the Pointe Scientific Inc kit .Non-protein sulfhydryl groups (NPSH) levels in the serum and cardiac tissue were examined according to the protocol proposed by Sedlak and Lindsay . In this5/M cm.Thiobarbituric acid reactive substances (TBARS) levels in the serum and cardiac tissue were evaluated with the Buege and Aust  method, The level of advanced oxidation protein products (AOPP) was obtained according to the Witko–Sarsat method , and chlp < 0.05. Additionally, data obtained from the cardiac tissue and serum were subjected to principal component analysis (PCA) using PAST 3.26 software [The results are presented as arithmetical means ± SEM. To evaluate statistical significance, one-way ANOVA followed by Fisher’s Least Significant Difference (LSD) post-hoc test was used . The results were considered significant if software . The PCAn = 10). However, in the DM2 control and phenolic acids-treated groups the number of rats varied based on the diabetes onset—only the rats classified as type 2 diabetic were included in analyses. After the classification, the final numbers were as follows: DM2, n = 7; RA10, n = 8; RA50, n = 6; SA5, n = 7; and SA25, n = 7, whereas C remained at n = 10. The number of rat subjects in each experimental group was equal at the beginning of the experiment  as well as after 8 and 15 days of rosmarinic and sinapic acid treatment there were no differences in the mean body mass of all the rats. On day 22 of phenolic acids treatment it was noted that the mean body mass of the DM2 rats was not significantly different from the mean body mass of the C rats, but the mean body mass of the rats from the RA10, RA50, and SA5 groups was significantly lower than in the rats in the C group. On day 28 (the last day of the treatment with rosmarinic acid and sinapic acid) a significant decrease in the mean body mass of the rats from the DM2, RA10, RA50, and SA5 groups in comparison with the C group rats was observed. The mean body mass of the SA25 rats was not significantly different from the mean body mass of the rats from the C and DM2 groups .In the DM2 rats the mean mass of the heart and liver was significantly higher than in the rats from the C group. The mass of the remaining organs did not differ between these groups. Administration of both rosmarinic acid and sinapic acid for 28 days did not alter the mass of any vital organ tested, as compared to the DM2 group of rats .In the serum of the rats with HFD + STZ-induced type 2 diabetes, a decrease in the level of interleukin 18 (IL-18) and urea, as well as an increase in the ALT activity was observed when compared to the rats from the C group. No significant differences were noted in the level of estradiol, uric acid, and creatinine or the activity of the AST after diabetes induction in comparison with the non-diabetic control rats. Administration of phenolic acids at both doses did not affect any of the tested parameters when compared to the rats from the DM2 group. The IL-18 level and the ALT activity in the serum remained significantly lower in all the phenolic acid-treated groups than in the serum of the C rats. Only in the RA50 and SA5 groups of rats there were no significant differences in the urea levels in the serum as compared to the C rats .At the day of STZ injection (14 days after HFD introduction) the mean random blood glucose level in all groups of rats was comparable. From the first day of phenolic acids administration  until the end of the experiment, the random blood glucose level in all the groups of rats which were fed with HFD and injected with STZ  was significantly higher than in the non-diabetic control rats. On the day 15 of treatment with both the doses of rosmarinic acid and sinapic acid a significant decrease of the random blood glucose level was observed when compared to the DM2 rats, and on day 22, only the higher dose of rosmarinic acid (50 mg/kg) significantly reduced the random blood glucose level in comparison with the DM2 rats. At the end of the experiment, before an overnight fasting, the random glucose level in all the phenolic acid-treated groups was not different from the random blood glucose level in the DM2 rats .The fasting glucose and fructosamine levels in the serum as well as the HOMA-IR were significantly higher and the QUICKI was lower in the DM2 rats than in the C rats. The levels of insulin and AGEs in the serum of the DM2 rats as well as AGEs level in the cardiac tissue from the animals of the same experimental group were not statistically different from their levels observed in the C rats. Administration of rosmarinic acid at the dose of 50 mg/kg and sinapic acid at the dose of 25 mg/kg for 28 days resulted in a significant decrease of the fasting glucose level in comparison with the DM2 rats, however this parameter remained significantly higher than in the rats form the C group. Treatment with the lower doses of phenolic acids did not affect fasting glucose level. The remainder of the parameters connected with glucose homeostasis in the serum or the cardiac tissue remained unchanged after phenolic acids administration to the diabetic rats .There were significantly higher total cholesterol, triglycerides and LDL-cholesterol levels in the serum of the control type 2 diabetic rats than in the control healthy rats. The HDL-cholesterol level was not changed in the DM2 rats as compared with the C rats. Administration of the lower doses of tested phenolic acids, i.e., 10 mg/kg of rosmarinic acid and 5 mg/kg of sinapic acid, resulted in an increase in the HDL-C level, while administration of higher doses (50 mg/kg of rosmarinic acid and 25 mg/kg of sinapic acid) effected in a decrease of the total cholesterol and LDL-C levels, when compared to the DM2 rats. There was no significant change in the triglycerides level between all the phenolic acid-treated groups of rats and DM2 rats. In the RA10 group of rats the levels of total cholesterol, triglycerides, and LDL-C were significantly higher than in the C rats, and as far as other doses of phenolic acids and other lipid profile parameters are concerned, there were no differences in comparison with the C rats .Induction of diabetes by HFD and STZ resulted in a disturbance in oxidative stress parameters in the serum of the rats as compared to the rats from the non-diabetic group C. In the DM2 rats there was a significant increase in the SOD and CAT activities as well as in the TBARS level. The diabetes induction did not affect the NPSH or AOPP levels in the serum, when compared to the C rats. Administration of phenolic acids at both the doses to the diabetic rats did not change any of the examined oxidative stress-related parameters in the serum. Moreover, in the RA10 rats there were no differences in the SOD and CAT activities in comparison with the C rats, and in the SA25 rats no differences in the TBARS level in relation to the C rats were noted .p < 0.001, LSD), whereas minor clustering between other groups was not, with regard to both the PC1 and PC2 axes. The main variables contributing to the separation across PC1 were fasting glucose and fructosamine concentrations followed by HOMA-IR, correlating with the DM2 group on the right-hand side, whereas the IL-18 level and the QUICKI correlated with the C group, on the left-hand side of the plot . The variation observed across PC1 was predominantly determined by the GPx, SOD, and CAT variables, correlating with the right portion of the plot, notably the DM2 group, as well as TBARS, which in turn correlated with the left portion of the plot and the C group. The separation across the PC2 was negligible as it did not produce any statistically significant differences between the groups  preceded by a 14-day treatment with a high-fat diet (32% of fat from lard). After streptozotocin injection, the high-fat diet was continued in the diabetic rats till the end of the experiment, i.e., for additional 35 days. This treatment induced disturbance in the glucose and lipid metabolism. Similarly to other reports, we observed increased random blood glucose level as well as the levels of fasting serum glucose, serum fructosamine, total cholesterol, and triglycerides. Moreover, induction of the type 2 diabetes resulted in the HOMA-IR increase and QUICKI decrease ,57,58,66In this study the level of interleukin 18 (IL-18) was measured, since this interleukin is engaged in metabolic homeostasis and it is sex hormone-dependent ,71. The In the presented study, rosmarinic acid and sinapic acid were administered to the type 2 diabetic rats at the doses of 10 and 50 mg/kg and 5 and 25 mg/kg, respectively. The lower doses of the tested phenolic acids correspond with the dietary achievable doses. The 5-fold higher doses were chosen in order to evaluate if they may have a better therapeutic effect than the dietary doses. The same doses for both the phenolic acids were used previously in ovariectomized rats. Both rosmarinic acid and sinapic acid lowered HOMA-IR in ovariectomized rats and rosmarinic acid additionally lowered fructosamine level in these rats ,40. In tRosmarinic acid and sinapic acid administered to the type 2 diabetic rats at the higher doses (50 and 25 mg/kg respectively) lowered total cholesterol in the serum of the rats, similarly to rats in the early stage of estrogen deficiency ,40. MoreBased on the PCA it was determined that the variables predominantly responsible for the variance observed between the C group and all of the diabetic groups of rats were fasting glucose, fructosamine, HOMA-IR, QUICKI, and IL-18. There were no differences in these variables after the phenolic acids administration, thus no separation between these groups  or DM2 was observed in the PCA. Even though there were minor differences in individual lipid profile markers, they were too weak to demonstrate the visible effect on the PCA, as much stronger effects were related to glucose metabolism. It is worth noting that random blood glucose measured in the capillary vessels was not affected after the phenolic acid administration for 28 days. This is in agreement with the PCA results. The results for oxidative stress parameters obtained from the cardiac tissue of the HFD + STZ-induced type 2 diabetic rats are surprising. The TBARS level in this tissue was significantly lower than in the control rats. The majority of the authors reports that the lipid peroxidation markers level increases in the heart during diabetes induced with streptozotocin alone ,51 or wiIn the cardiac tissue, similarly to the serum, the activity of antioxidative enzymes was elevated. These results are in line with some other reports ,61, but In our experiment we have observed a diverse effect of individual phenolic acids on oxidative stress parameters in the cardiac tissue. Furthermore, for each compound there were discrepancies in the effects of individual doses on specific markers of oxidative stress. However, the multivariate analysis performed on the cardiac tissue-derived variables has confirmed a negligible or no effect of phenolic acids when administered in dietary doses of 10 mg/kg and 5 mg/kg for rosmarinic and sinapic acid, respectively. However, it should be noted that higher doses of the aforementioned compounds did beneficially affect the oxidative stress markers, as evidenced by the PCA. These differences were masked in individual ANOVAs. This might be due to the fact that classic analysis of variance takes into consideration only quantitative characteristics of measured variables, whereas the specifics of the PCA introduce a qualitative component to the study, as the effect (weight) of individual variables on the total observed variation between experimental groups along PC1 and PC2 axes is not equal .In the current research we focused on biochemical parameters in the serum and oxidative stress markers in the serum and cardiac tissue in the female diabetic rats. Due to this fact, this study has several limitations. Firstly, we did not conduct histological analyses or examine the molecular mechanisms underlying the action of tested phenolic acids in the cardiac tissue. We did not evaluate the effect of diabetes and phenolic acids administration on the markers connected to inflammation , apoptosis (for instance caspase 3 or p53), or cellular function  in the cardiac tissue. Secondly, further studies regarding rosmarinic acid or sinapic acid should include the cardiac mechanical function. Finally, in order to find out whether sex hormone environment is an important factor in the response to phenolic acids treatment, the next experiment should be conducted on both male and female rats. Based on the presented study, it can be concluded that rosmarinic and sinapic acids did not affect glucose homeostasis or oxidative stress parameters in the serum. As a whole, the effects visible in the serum upon phenolic acid administration to the type 2 diabetic female rats can be considered minor. Only few specific parameters related to the lipid profile were slightly improved after administration of these plant-derived compounds. The effect of rosmarinic and sinapic acids on oxidative stress parameters in the cardiac tissue was demonstrated only when higher doses were administered, whereas the effect of dietary-achievable doses of these compounds on tested parameters was negligible in the type 2 diabetic female rats. Therefore, we suggest conducting further studies considering rosmarinic and sinapic acids focused on doses higher than achievable during the regular nutrition regimen, which might have a therapeutic effect in the cardiac tissue of diabetic subjects.Our study shows that multivariate analyses such as PCA can be considered useful for capturing relationships between all measured variables and the effects of pharmacologically active substances in model organisms and in various experimental set-ups.


Respiratory diseases are accompanied by intensification of free radical processes at different levels of the biological body organization. Simultaneous stress and suppression of various parts of antioxidant protection lead to the development of oxidative stress (OS) and nitrosative stress (NS). The basic mechanisms of initiation and development of the OS and NS in pulmonary pathology are considered. The antioxidant defense system of the respiratory tract is characterized. The results of the NS and OS marker study in various respiratory diseases are presented. It is shown that NS and OS are multilevel complex-regulated processes, existing and developing in inseparable connection with a number of physiological and pathophysiological processes. The study of NS and OS mechanisms contributes to the improvement of the quality of diagnosis and the development of therapeutic agents that act on different pathogenetic stages of the disease. Most diseases of the respiratory tract (RT) are accompanied by the intensification of free radical processes at different levels of the biological organization of the body with simultaneous stress and subsequent oppression of various links of antioxidant protection, which leads to the development of oxidative stress (OS)—imbalance in the reactive oxygen species (ROS) and antioxidant protection of the body –3.Over the past decade, much attention has been paid to studying the molecular mechanisms of the development of both oxidative stress and nitrosative stress (NS) in lung diseases, as well as the identification of prognostic and diagnostic markers in various biological media and the elucidation of the possibilities of therapeutic influence on OS and NS. These processes are inherently associated with the development and course of inflammatory and other physiological and pathophysiological mechanisms that are pathogenetic links in the development of the disease. The initiation of OS and NS can occur by an exogenous and/or endogenous pathway , 4–7.For the respiratory tract, the exogenous pathway of the OS and NS initiation is the most relevant. So, about 8000 liters of air containing various gases (oxygen and volatile oxides), infectious agents , pollutants, and allergens, which have prooxidant effects, passes through the lungs every day. The main air pollutants of the urban atmosphere are particulate matters (PM), which are a variable composition of organic and inorganic compounds with a carbon core. OS-induced air pollutants and damage to the respiratory tract occur with the participation of metals of variable valency, trace amounts of which are part of PM. In addition to the initiation of the OS and NS by prooxidants, free radicals can be also in significant amounts in the inhaled air. The gas phase of tobacco smoke contains about 1015 free radicals in one puff, including superoxide anion and hydroxyl radicals. Among the exogenous factors of the OS initiation, short-wave electromagnetic radiation  should also be considered .The endogenous pathway of the OS and NS initiation is represented by a wide variety of mechanisms. The redox reactions accompany a huge number of biochemical processes in vivo. One of the main intracellular sources of free radicals is mitochondrial respiration: 1-2% of electrons can “leak” from the respiratory chain . Radical2·−), hydroxyl radical (ОН·), peroxyl radical (НО2·), and alkoxy radical (RO). During the reaction, ROS derivatives are formed, such as hydrogen peroxide (H2O2) and lipoperoxides (ROOH). RNSs include nitric oxide (NO), other higher nitrogen oxides, nitrites, and peroxynitrite (ONOO−). Oxidases are involved in the generation of superoxide anion radical: NADPH oxidase, xanthine oxidase, cytochrome P-450 oxidase, etc. [The division into ROS and RNS is rather conditional since, in biochemical processes, the radical and nonradical forms of these compounds react with each other. Primary radicals, interacting with various compounds from their microenvironment, form secondary radical, tertiary radical, and so on; highly active nonradical forms; and stable products . ROS incse, etc. . The forse, etc. .The physiological role of NO in the respiratory tract  is also α and IL-1β, produced by alveolar macrophages (inducible NO synthase pathway). This stimulating effect is blocked by L-NMMA and restored with the addition of L-arginine, confirming the regulatory role of inducible NO-synthase in its implementation [NO synthase inhibitors slow down the frequency of ciliary beats of respiratory epithelial cells of cows stimulated with isoproterenol, bradykinin, and substance P. This effect is completely reversible when adding the precursor of NO L-arginine, which indicates the NO-dependent mechanism of ciliary motor stimulation by the above-named compounds. Ciliary motility is also activated by TNFentation .In addition to the activity of ciliary motility, the effectiveness of mucociliary clearance is determined by the properties of the airway surface liquid (ASL), the composition and volume of which, in turn, depends on the transport of electrolytes. The functional activity of ion channels is also highly susceptible to the modulating effect of NO. The NO molecule activates both the apical anion channels and the basolateral potassium channels along the cGMP-dependent pathway, acting as a physiological regulator of transepithelial ion exchange , 13.The ability of endogenous NO to modulate bronchial hyperreactivity (BHR) induced by various mediators has been experimentally confirmed. Nijkamp et al. revealed histamine-induced bronchoconstriction in guinea pigs by the inhibition of NO synthase in vivo, as well as a dose-dependent reduction under the action of histamine of the smooth muscles of the tracheal tube of the guinea pig in vitro . RicciarIntraluminal perfusion of the intact tracheal tube of guinea pigs with bradykinin, endothelin-1, substance P, adenosine, and calcitonin with a gene-bound protein led to dose-dependent relaxation , 15. At Further research demonstrated a rapid (within 2 seconds) release of NO in the respiratory epithelium of guinea pigs induced by bradykinin. This phenomenon was absent in the subepithelial layer, free from calcium ions , 15. TheAn additional mechanism NO bronchoprotective effect in the airways is the cGMP-dependent property of smooth bronchial myocytes. Thus, bradykinin-induced increase in cGMP production in the guinea pig airways was demonstrated. This effect was blocked by the addition of NO synthase inhibitors, which indicates the role of cGMP as a final mediator of NO-dependent epithelial bronchoprotection , 15.In vitro and in vivo studies have shown that BHR, caused by allergen exposure, does not increase with the preliminary addition of NO synthase inhibitors. The BHR-induced virus is completely blocked during exposure to L-arginine, which demonstrates the interrelation of this syndrome with the lack of endogenous NO. It has also been established that a deficiency in constitutive NO synthase production in guinea pigs leads to the BHR progression as part of an early allergic reaction , and the restoration of the NO level with inducible NO synthase contributes to the reverse BHR development during later timing (24-48 hours). These conclusions were made based on ineffective inhalation of a specific inhibitor of inducible NO synthase aminoguanidine on histamine-induced BHR after an early allergic reaction and significant BHR decrease after inhalation during the late allergic response , 15.κB-dependent expression of the inducible NO synthase [Moreover, Toward and Broadley found that lipopolysaccharide inhalation by guinea pigs suppressed respiratory NO production, which followed by an increase in histamine-induced hyperreactivity (one hour after exposure). 48 hours after inhalation, BHR to histamine decreased simultaneously with an increase of NO metabolites in bronchoalveolar lavage, suggesting a resumption of NO synthesis when activating the NF-synthase .The above NO-dependent mechanisms of bronchodilation, activation of mucociliary clearance, and bronchoprotective properties of NO become crucial during exercise with increase minute ventilation.In addition to direct registration in exhaled air, the production of NO in RT can be determined from the concentration of its more stable metabolites, such as nitrate and nitrite anions, 3-nitrotyrosine, and nitrosothiols in the exhaled breath condensate (EBC). Nitrate and nitrite anions are the most stable of these metabolites. The metabolism of nitric oxide and oxygen radicals has common points of contact; therefore, it is necessary to emphasize the importance of simultaneously evaluating several indicators of molecular metabolism in EBC for a more objective interpretation and interpretation of results.In recent decades, considerable evidence about the contribution of NO and its metabolites to the pathogenesis of many diseases of the respiratory tract has been accumulated. So, the total concentration of nitrates and nitrites (TNN) in EBC is significantly increased in patients with uncontrolled and controlled bronchial asthma compared with healthy children , 18. In The EBC concentration of 3-nitrotyrosine (3-NT) is higher in patients with controlled mild asthma not receiving corticosteroids, but it is lower compared with the moderate and severe asthmatics, using inhaled corticosteroids. The level of 3-NT correlates with the level of fractional exhaled NO (FeNO) only in controlled mild asthma , 19. The2−/NO3− were determined.The results of the studies of the exhaled NO level in chronic obstructive pulmonary disease (COPD) are contradictory. Kubysheva et al. demonstrated that the severity of the progression of COPD was linked with an increase in the concentrations of metabolites of nitric oxide in blood and in exhaled breath condensate , 22. ForHowever, it was found that smoking and disease severity are the most important factors affecting NO production . Active Other disorders associated with the activation of NS include bronchiectasis, active pulmonary sarcoidosis, active pulmonary fibrosis, and the transplant rejection reaction of the lungs .In cystic fibrosis (CF) remission, there is an increase in EBC nitrite anion , in contThe role of human microbiota in the nitric oxide cycle, the role of significant components of nitrite and nitrate-reductase systems in the nitric oxide cycle, and the mechanisms of their activation and deactivation  are determined under various conditions, which allows detailed control mechanisms of the NO cycle for targeted exposure to therapeutic agents .Recently published data demonstrate the potentially positive role of NOS inhibitors in the treatment of asthma and COPD –32. InflThere is evidence of the potential role of the NO donor in the treatment or modulation of asthma and COPD in viral exacerbations –38. RhinThe study of RNS and ROS concentrations in in vivo and in clinical practice, in particular, is very problematic, due to the specificity of the detected compounds. The lifetime of most ROS and RNS is hundredths of a second or less. Accordingly, a number of requirements of practical properties, characterized by ease of use and reproducibility of the results, are imposed on both the methods and the biological media in which the dynamic concentration of oxidants is monitored. In this regard, noninvasive techniques and biological media have the advantage of studying ROS and RNS in the respiratory tract: exhaled breath condensate (EBC) and exhaled air itself. EBC is a liquid formed as a result of cooling and subsequent condensation of exhaled air; therefore, its composition is determined by the composition of exhaled air. To determine the respiratory, ROS use indicators in the blood, which is, as a rule, a reflection of systemic changes in the redox status in the body. EBC and exhaled air markers help to identify the tension of oxidative and nitrosative status directly in the respiratory tract and the airway surface liquid, which is essentially the first line of lungs and whole-body protection from exogenous oxidants. Noninvasive methods of ROS and RNS studying can optimize diagnosis and treatment, as well as help clarify the molecular mechanisms of the pathogenesis of lung diseases , 14, 43.Among the identified OS markers, conditionally stable RNS and ROS and their metabolism products, other oxidation products of RNS and ROS, and ions of variable valency are the most popular in clinical practice , 14, 43.Despite the difficulties in determining the concentration of certain compounds in the EBC, researchers are now increasingly interested in identifying molecules involved in the reactions of the OS and NS, which are key elements in the development of most pulmonary pathologies, allows assessing noninvasively the state of the respiratory tract. Practically, all these molecules are united by the fact that their concentrations in EBC vary from micromolar to nanomolar, and this, in turn, requires the use of highly sensitive determination methods. Despite the high variability of studied parameters, by increasing the samples, statistically significant differences between groups are achieved in diseases such as asthma, COPD, and CF. Among the most intensively studied molecules, a special place is occupied by the markers of OS and NS: ROS and RNS. However, taking into account the specifics of EBC collection, namely, the duration of the procedure from 10 to 20 minutes and the possible change in the concentration of the molecules being determined during this time, the most promising role is assigned to stable metabolites of oxygen and nitrogen , 43.2O2). Hydrogen peroxide in vivo is the product of the superoxide anion radical (О2−) dismutation. The sources of such radicals are reactions involving xanthine oxidase and mitochondrial and microsomal electron transfer chains. The concentration of H2O2 in the inflammatory regions is especially high, due to which a change in the H2O2 level in biological fluids is one of the inflammatory markers [2O2 in tissue depends on many parameters. Thus, the concentration of any substance in the body at a given time, including hydrogen peroxide, is the sum of the synthesis rate and the rate of decomposition of this compound. When H2O2 is formed in the dismutation reaction of superoxide with the participation of SOD, the reaction rate constant is lower than during the interaction of superoxide and nitric oxide, which indicates the competition between NO and SOD [2O2 content even at high rates of its formation. This is due to the high rate of decomposition of H2O2 in the Fenton reaction with the formation of an extremely reactive hydroxyl radical [The most studied form of the ROS is hydrogen peroxide  status changes, namely, medium levels of catalase, peroxidase, peroxiredoxins, and other enzymes that have a high affinity for hydrogen peroxide. Such a high dependence on the concentration of other molecules present in the medium makes it necessary to measure along with hydrogen peroxide a number of parameters: the concentration of metal ions of variable valency , the level of nitric oxide (NO), and AO status of the organism [Changes in the Horganism .2O2 in EBC has been studied in many pathologies of the respiratory tract. In asthma, an increase in the concentration of H2O2 in EBC was shown to correlate with an increase in the level of sputum eosinophils and serum content of eosinophilic cationic protein, as well as with a decrease in FEV1 [2O2 content in EBC, observed in patients with moderate and severe asthma, can serve as an informative marker of the inflammation severity, unlike the FeNO level, which is highly dependent on the therapy  [2O2 level in the EBC is shown. In other inflammatory diseases of the respiratory tract, such as COPD [2O2 level in EBC is also observed. Increased H2O2 concentrations have also been observed in patients with pneumonia. A positive significant correlation was noted between the level of H2O2 and the content of thiobarbituric acid (TBA) in EBC on days 1 and 3 of the disease, as well as between the level of H2O2 in EBC and the concentration of C-reactive protein and the level of blood leukocytes on day 1. During the therapy, a decrease in OS parameters in EBC was revealed [Currently, the dynamics of changes in H in FEV1 , 47. It  as COPD –50 and b as COPD , an incrrevealed .2O2 level dynamics in EBC with these diseases may indicate an increase in the superoxide generation by cells involved in the inflammation process [Those H process , 54 and/ process .F2-isoprostanes (F2-IsoPs) are recognized as reliable markers of oxidative stress in lung diseases , 57. IsoDevelopment of sensitive and special radioimmunoassay (RIA) allowed measuring the content of 8-isoprostane, which is an isomer of prostaglandin-F2A, in the exhaled air condensate . An incrIsoPs are not only markers of oxidative stress but also play an important role in lung pathophysiology. In the respiratory tract, isoprostanes are able to regulate cellular processes that affect the tone of pulmonary vessels and smooth muscles of the airways  and to sThe main airway biomarkers of the oxidative and nitrosative stress in asthma and COPD are summarized in Due to the huge number of reactions occurring in cells and the formation of RNS, ROS, and other highly active compounds, antioxidant (AO) systems exist to regulate the redox balance. The components of these systems are variously distributed both in the cell and at the organ-tissue level. The respiratory tract, which is the first line of body defense against the effects of atmospheric pollutants , contain2·− to H2O2. The active center of SOD contains a transition metal ion. For the cytoplasm of eukaryotes, these are copper and zinc ions (Cu/Zn-SOD) [2·− is very high (the rate constant is about 109 M−1 s−1); it is necessary for the rapid control of the O2·− formation. However, the O2·− dismutation reaction can proceed more slowly and spontaneously without the participation of the enzyme. Excessive O2·−, at the same time, can react with a variety of cellular targets and impair their functions. For example, the enzyme of the tricarboxylic acid cycle aconitase is inactivated by O2·−, which can cause significant changes in cell metabolism [2O2 as a result of the O2·− dismutation reaction, like other ROS, can be toxic to cells and its concentration in cells is also controlled by AO systems.Superoxide dismutases (SODs) are one of the main AO enzymes that are expressed in almost all cells of the human body . The pro/Zn-SOD) , 89. Mit/Zn-SOD) . The rattabolism . So, gen2O2 to H2O and molecular oxygen. Glutathione peroxidase (GPx) is another group of proteins involved in the removal of H2O2. The reduction of H2O2 to H2O, carried out by this group of enzymes, is associated with the oxidation of glutathione. In addition to H2O2, GPx can interact with other peroxides in cells [Catalases are heme-containing enzymes that catalyze the decomposition of Hin cells .2O2 and lipid hydroperoxides formed in high concentrations at OS. The functions of the thioredoxin system overlap with the glutaredoxin-dependent system, which is also of great importance for AO protection. The component of this system is glutaredoxin (Grx), which is involved in thiol/disulfide exchange reactions. The oxidized Grx is reduced nonenzymatically by the reduced glutathione (GSH) pool. Oxidized glutathione (GSSG) restores a special enzyme glutathione reductase (GR). GR has some similarities with TrxR and is a FAD-containing enzyme that uses reducing equivalents of NADPH to restore GSSG [The thioredoxin system includes thioredoxin (Trx) itself and thioredoxin reductase (TrxR). Thioredoxins form a family of small-sized proteins with oxidoreductase activity. Trx restores oxidized disulfide peptides under OS. The reduction of oxidized Trx, in turn, is carried out by NADPH-dependent thioredoxin reductases (TrxRs) . In addiore GSSG .2O2 degradation. They were first found in yeast and then in other organisms [2O2 and organic peroxides to water and alcohol, respectively. In addition, some isoforms of peroxiredoxins can destroy peroxynitrite. Peroxynitrite reductase activity was first detected in bacterial peroxiredoxins and then confirmed for eukaryotic peroxiredoxins [Peroxiredoxins, a family of AO proteins with peroxidase activity, are also involved in Hrganisms , 86. In rganisms . The conredoxins . Neutralredoxins , 86. Bioredoxins , 86.The important role of Prx6 in the protective mechanisms of the bronchial epithelium which primarily include the activation of the Prx6 expression under various pathological conditions led to the assumption that the use of exogenous Prx6 can significantly accelerate the recovery of the affected respiratory epithelium. This hypothesis was tested on models of the acute inflammatory process in the trachea of the rat, caused by bacterial endotoxins, and thermal burns of the upper respiratory tract , 86.The study of AO enzymes in human lung pathology is hampered by a number of objective factors, namely, the inability to assess in vivo protein expression by immunohistochemical methods, the absence of large molecules in noninvasive biological media, the invasiveness of procedures for obtaining biopsy tissue of the lung, the lack of standardization for the evaluation of AO enzymes in the BAL, and induced sputum. The study of the role of enzyme AO systems is currently being evaluated in the blood, in model systems, and in animals. Due to the fact that the work of the AO systems often occurs site-specific (directly at the site of the development of the OS or NS), the evaluation of the AO systems in blood gives conflicting results.α-tocopherol, and some others [Various low molecular weight substances play the role of antioxidants. These include, in addition to glutathione, ascorbic acid, e others –98.α-tocopherol molecule (vitamin E) consists of a benzene core with a hydroxyl group  and a side wick chain that performs the hydrophobic interaction of the antioxidant with membrane structures. Vitamin E is able to quench ROS, interact with the hydroxyl radical, and restore the lipid radicals of the structure R· and ROO·. The most active in the lipid bilayer α-tocopherol restores peroxyl radicals. The resulting α-tocopherol radical is relatively little active due to the delocalization of the unpaired electron along the aromatic ring. It is believed that in the presence of water-soluble antioxidants, such as the reduced form of ascorbic acid, vitamin E is able to restore its AO potential through direct recycling. Retinol (vitamin A) in combination with α-tocopherol is also involved in the protection of biological membranes from damage by their prooxidants [The oxidants –98.2−·, НО2·, RO2·, 1O2, HO·, NO·, ONOO−, and nitrosamines. It also restores the oxidized form of α-tocopherol. In the presence of metal cations of variable valency, AA becomes a powerful prooxidant, which is a reliable regulation of the transition metal ion concentration [Ascorbic acid (AA) is an important representative of water-soluble antioxidants. The presence of two-phenolic groups in the AA molecule structure allows it to participate in redox transformations, acting as a donor and acceptor of electrons and protons. AA has an extremely wide range of AO properties related to hypohalides, Оntration –98.N-Acetylcysteine (NAC), an acetylated amino acid L-cysteine, inactivates free radicals and reactive oxygen species by directly reacting with them (direct antioxidant effect) and also supplying cysteine and promotes the synthesis of glutathione (indirect antioxidant effect). In turn, glutathione is an important component of the detoxification system of xenobiotics, peroxide compounds, and free radicals, which has a protective effect at the cellular level , 100.Of the three amino acids involved in the structure of glutathione , cysteine has the lowest intracellular concentration. At the same time, the main mechanism of glutathione replenishment is de novo synthesis. Consequently, cysteine efficiency may limit the rate of glutathione synthesis under conditions of oxidative stress.NAC has been used in clinical practice for over 50 years. The positive effect of NAC has been demonstrated on conditions characterized by decreased production of glutathione (GSH) or activation of lipid peroxidation (POL): tobacco smoking, cardiovascular diseases , acetami2O2, ONOO−, and O2-·) helps to reduce the intensity of reactions of OS and NS, which leads to the suppression of inflammation in chronic obstructive pulmonary disease (COPD), influenza, and idiopathic pulmonary fibrosis [The prevention of glutathione reserves depletion under the NAC action, and the direct neutralizing effect of the drug in relation to ROS and RNS  during exercise reflects dynamic hyperinflation and is a significant marker of physical training in patients with COPD. The NAC demonstrated the ability to modify small-diameter airways and the associated processes of pulmonary hyperinflation. In a randomized, double-blind, and placebo-controlled trial by Stav and Raz in 24 patients with moderate and severe stable COPD, there was an increase in IV and forced vital capacity (FVC) after a 6-week course of NAC therapy at a daily dose of 1200 mg. An increase in the ratio of residual lung volume (RV) to the total lung capacity (TLC) was also noted. The distance covered in the exercise test was also significantly greater in the NAC group compared with the placebo group –109.The effect of NAC on the severity of COPD symptoms was evaluated in a systematic review of randomized clinical trials. A statistically significant decrease of the disease symptom intensity in the NAC groups was found in all reviewed studies, in comparison with patients taking the placebo. As a result of a meta-analysis, it was concluded that in 26 out of 100 patients with COPD, NAC therapy reduces the severity of clinical manifestations (number needed to treat(NNT) = 3.8) .Decramer et al. demonstrated that N-acetylcysteine at a dose of 600 mg had no effect on the rate of decline in lung function and the frequency of exacerbations in COPD. However, the analysis in subgroups revealed that the frequency of exacerbations when using NAC was reduced in patients who did not receive inhaled corticosteroids .NS and OS are multilevel processes, existing and developing in inseparable connection with a number of physiological and pathophysiological processes. They accompany almost all diseases of the respiratory tract, and the study of their subtle mechanisms contributes to improving the quality of diagnosis and the development of therapeutic approaches.


Moreover, the performed analysis can assist in choosing crystal structure for docking studies, helping in selection of conditions providing the best discrimination between active and inactive compounds in machine learning-based experiments.Three-dimensional descriptors are often used to search for new biologically active compounds, in both ligand- and structure-based approaches, capturing the spatial orientation of molecules. They frequently constitute an input for machine learning-based predictions of compound activity or quantitative structure–activity relationship modeling; however, the distribution of their values and the accuracy of depicting compound orientations might have an impact on the power of the obtained predictive models. In this study, we analyzed the distribution of three-dimensional descriptors calculated for docking poses of active and inactive compounds for all aminergic G protein-coupled receptors with available crystal structures, focusing on the variation in conformations for different receptors and crystals. We demonstrated that the consistency in compound orientation in the binding site is rather not correlated with the affinity itself, but is more influenced by other factors, such as the number of rotatable bonds and crystal structure used for docking studies. The visualizations of the descriptors distributions were prepared and made available online at The online version of this article (10.1007/s11030-018-9894-4) contains supplementary material, which is available to authorized users. One of the most popular in silico strategies is virtual screening (VS), in which large libraries of compounds  undergo nonexperimental evaluation –3. Usualproaches , when onproaches , 6 and/obased VS ).P), pKa, number of hydrogen bond donors, number of hydrogen bond acceptors, number of atoms of a particular type, number of bonds of a particular type, atomic charges, polarity, molecular volume, etc. On the other hand, fingerprints are a result of the translation of compounds into the form of a bit string. Their two main groups can be distinguished: key-based and of a hashed type. Key-based fingerprinting annotates the presence (1) or absence (0) of particular chemical moieties in the molecule, whereas in the hashed fingerprints, bit strings are formed from the molecular graph, on the basis of which paths up to a fixed length are generated , and a hashing function is applied to encapsulate the structural information in the string. Fingerprints are used not only for chemical structure characterization, but they are also applied for description of ligand–receptor complexes obtained in docking. They provide information about the interaction of a ligand with particular amino acids of a protein, as in the case of interaction fingerprints (IFts) [One of the fundamental issues connected with the application of various computational methods in the search for new drug candidates is the provision of proper conversion of the chemical structure to a form that can be handled by computer methods. The most popular way to capture chemical information is the application of numerical descriptors or fingerprints –11. The s (IFts)  and strus (IFts) . The moss (IFts) , 15.ligand-based approaches usually make also use of various molecular descriptors. They are generated from the two-dimensional (2d) structure of the compound (2d descriptors), or they use their spatial orientation obtained either in minimization of a ligand solely or using the docking poses—three-dimensional (3d) descriptors [The criptors , 17.Predictive models (constructed most often with the use of machine learning methods of various complexities) based on such representations can be of great help in the search for new active compounds. Such approaches are widely known for the ability to deal with a large amount of information in a fast and efficient way, so the application of machine learning is rapidly growing also in the field of computer-aided drug design, mainly due to a significant increase in amount of data also in the field of cheminformatics and pharmacy. However, despite the great power possessed by various algorithms in the identification of new potentially active compounds, their performance strongly depends on experimental conditions, such as training set compositions, compounds representation, and parameters of particular learning algorithms themselves. Therefore, a multifactor optimization needs to be performed in order to obtain the optimal predictive power of such methods , 19.http://chem.gmum.net/vischem_stability), together with the possibility to manually analyze chemical structures referring to a particular data point. The differences in the distribution of 3d descriptor values indicate that not all crystal structures are effective in this type of experiments , and the prepared tool can be of great help during the design of such studies, especially by assisting in the selection of crystal structures for docking that would provide optimal performance of machine learning methods .In this study, we focused on one of the above-mentioned parameters influencing the performance of machine learning methods performance, that is, the compounds representation, 3d descriptors in particular. The variations of their values, depending on the input used for their generation (docking pose), were analyzed. It was examined whether the consistency of 3d descriptor values obtained for different orientations in the binding site of the same compound is correlated with the compound activity. All existing crystal structures of aminergic G protein-coupled receptors (GPCRs) were used for docking of known ligands and compounds with confirmed inactivity toward the respective proteins. The 3d descriptor values calculated for poses obtained from docking for active and inactive compounds were compared with those descriptors that were generated from compounds with minimized energies (prepared in LigPrep for docking) and compared with the analysis of variations in atom positions in the docking poses of a particular compound. The results of such study were also made available online  [Ki  values above 1000 nM. The considered targets were all aminergic GPCRs for which crystal structures are available, including serotonin receptors 5-HT1B, 5-HT2B, 5-HT2C; muscarinic receptors M1, M2, M3, M4; adrenergic receptors beta1, beta2; dopamine receptors D2, D3, D4; and histamine receptor H1. All respective crystal structures were fetched from the PDB database [The compounds with experimentally determined activity/inactivity were fetched from the ChEMBL database  accordin IC50/2) , and thedatabase , and theThe compounds were prepared for docking in LigPrep  . In addition, studies considering the first k conformations (for compound sets sorted by docking score) were performed with k adopting values 3, 5, and 10. Moreover, the stds of coordinates of each atom of a compound were calculated  and compared to determine how differences in descriptor values are related to differences in atom positions for various docking poses  between values of all descriptors obtained for all docking poses of a particular compound was calculated and visualized using LargeVis by embedding into a 2d space. The results of such analysis were prepared in an interactive way and made available online, so chemical structures referring to a particular data point can be manually analyzed  in comparison with inactive molecules, although intuitively and theoretically that should be the case.1B crystal structures, the std of both 3d descriptor values and atom coordinates was higher for active than inactive compounds for all cases. On the other hand, 5-HT2B ligands were, in general, more consistent in terms of the analyzed properties than compounds that were inactive for this receptor.The number of docking poses taken into account in the performed analyses has only a slight impact on the observed dependencies that were rather consistent for a particular crystal structure, in terms of both similarity between 3d descriptor values and consistency of compound orientations described as the std of their atom coordinates. For the 5-HT2C and ACM1 ligands were more consistent compared with inactive compounds in terms of atom coordinates but less consistent when 3d descriptors were considered. However, for the rest of the muscarinic receptors, the tendencies were again shifted toward higher inconsistency for active compounds.Interestingly, 5-HT1.Adrenergic receptors were, in general, characterized by higher consistency for active compounds in terms of both parameters considered; however, there are examples of crystal structures for which there were variations in the consistency of 3d descriptor values and atom coordinates—such as 2R4R, 2R4S, 3KJ6, 3P0G, and 5D5A. The above-mentioned differences occurred also for the crystal structure of histamine receptor H1B are presented in Fig. Example differences in docking poses for various crystal structures for two pairs of structurally similar active and inactive compounds  toward 5-HT1B, was docked very similarly to its 4IAQ and 5V54 crystal structures with conformation variations occurring for 4IAR.The docking results presented in Fig. 3.Example visualization of the 3d descriptors space is presented in Fig. http://chem.gmum.net/vischem_stability, together with the provision of compound structures referring to a particular data point  was stronger when a higher number of docked poses was taken into account. Example visualizations of such dependencies are presented in Fig. To explain the causes of such dependencies of the compound pose variations, the analysis of the relationship between the number of rotatable bonds and the std in 3d descriptor values, expressed as the Pearson correlation coefficient, was carried out (Table −18), whereas the highest std values were on average obtained for descriptors from the group of geometrical indexes, such as the geometric Petitjean index and the geometrical shape index (std of 0.5–0.7 on average). Relatively high fluctuations in descriptor values  were also observed for 3D-MoRSE descriptors calculated for a distance equal to 10.Moreover, an analysis of std of each descriptor values separately was performed . It was found out that the lowest variation occurred for 3D-MoRSE descriptors determined for a distance equal to 1 . Additionally, the ability to manually analyze all the information, including the analysis of chemical structures referring to particular data points, enables a better design of machine learning experiments conducted on such type of data, allowing for the maximization of the power of predictive models, for example by proper selection of crystal structures for studies (those that provide the best discrimination between active and inactive compounds in machine learning-based experiments) or the proper evaluation of the model applicability via the analysis of chemical structures with overlapping fragments of descriptors space.Supplementary File S1Analysis of the std of descriptor values calculated for each descriptor separately (XLSX 80 kb)Supplementary File S2Visualization of the correlation between the number of rotatable bonds and the variations in atom positions in the docked poses (ZIP 1316 kb)Below is the link to the electronic supplementary material.