Proton Donor Research Articles

ЭЛЕКТРОХИМИЧЕСКОЕ ЛЕГИРОВАНИЕ ЦИНКОВЫХ ПОКРЫТИЙ ХРОМОМ И НИКЕЛЕМ ИЗ ГЛИЦИНАТНЫХ РАСТВОРОВ

The purpose of this work is the electrochemical alloying of zinc coatings with chromium and nickel from electrolytes containing heteronuclear complexes. Zinc coatings are widely used to protect steel products from corrosion in the atmosphere of various climatic zones. To increase corrosion resistance, zinc coatings are chromated or phosphated. An effective way to increase the corrosion resistance of the coatings under study is their alloying with other metals. Obtaining such coatings makes it possible to reduce their thickness and increase their service life, solve environmental problems when replacing cadmium. The kinetics of the process on zinc and steel electrodes has been studied by removing cathode polarization curves. It is suggested that the absence of characteristic current peaks on the polarization curves is due to the convergence of the electrode potentials of individual metal ions recovering from heteronuclear compounds, as well as the concomitant discharge reaction of proton donors. X-ray fluorescence analysis has shown that in the studied range of current densities 1-5 A/dm2, the content of alloying metals in the coating reaches 1.4% for chromium and 9.8% for nickel. The obtained data on the elemental composition of zinc coatings indicate an abnormal co-deposition of zinc with nickel. Chromium in coatings is observed at higher current densities of 4-5 A/dm2.The data obtained in this work can be used in electroplating in the development of processes for alloying zinc coatings with chromium and nickel in order to replace cadmium coatings.

Deciphering the role of aromatic cations in electrochemical CO2 reduction: interfacial ion assembly governs reaction pathways

Imidazolium cations facilitate electrochemical CO2 reduction by (1) stabilizing CO2˙− with delocalized positive charge (π+) and (2) tuning the transport of proton donors to the electrochemical interface.

Dynamics of CH/n hydrogen bond networks probed by time-resolved CARS spectroscopy.

Hydrogen bond (HB) networks are essential for stabilizing molecular structures in solution and govern the solubility and functionality of molecules in an aqueous environment. HBs are important in biological processes such as enzyme-substrate interactions, protein folding, and DNA replication. However, the exact role of weakly polarized C-H bonds as HB proton donors in solution, such as CH/n HBs, remains mostly unknown. Here, we employ a novel approach focusing on vibrational dephasing to investigate the coherence relaxation of induced dipoles in C-H bonds within CH/n HB networks, utilizing time-resolved coherent anti-Stokes Raman scattering (T-CARS) spectroscopy. Using a representative binary system of dimethyl sulfoxide (DMSO)-water, known for its C-H backboned HB system (i.e., C-H⋯S), we observed an increase in the dephasing time of the C-H bending mode with increasing water content until a percolation threshold at a 6 : 1 water : DMSO molar ratio, where the trend is reversed. These results provide compelling evidence for the existence of C-H⋯S structures and underscore the presence of a percolation effect, suggesting a critical threshold where long-range connectivity is disputed.

Amino acid modified melamine foam as solid-state proton donor for CsPbBr3-based S-scheme heterojunction driven photocatalytic CO2 reduction

H2O as a proton source affects the stability of lead halide perovskites, restricting the photocatalytic CO2 reduction reaction (CO2RR). In this paper, l-lysine modified melamine foam (L-MF) is designed as an efficient solid-state proton donor to participate in CO2RR of CsPbBr3-based S-scheme heterojunction. On the one hand, abundant –COOH and –NH2 groups of l-lysine would break easily compared with H2O, which provides adequate protons for CO2RR. Moreover, the functionalized –COOH and –NH2 groups of l-lysine as Lewis base could coordinate with unsaturated Pb2+ of CsPbBr3, which could decrease the defect density of perovskite and improve the charge migration of catalyst. On the other hand, three-dimensional and porous melamine foam as a supporter could achieve gas-solid bi-phase CO2RR system, which contributes to mass transfer efficiency between CO2 gas and catalyst, accelerating CO2 conversion into high value-added fuels. Under sunlight irradiation, product yield of CO2RR reaches 73.47 μmol/g/h for L-MF/CsPbBr3/Bi2WO6, which is 2.8- and 72.7-fold of MF/CsPbBr3/Bi2WO6 (25.93 μmol/g/h) and CsPbBr3/Bi2WO6 powder (1.01 μmol/g/h) with H2O as proton source, suggesting the efficient proton supply for CO2RR from solid-state proton donor. This work could open a new avenue to utilize lead halide perovskites-based catalysts for energy conversion.

Enhanced Desalination Performance Using Phosphate Buffer-Mediated Redox Reactions of Manganese Oxide Electrodes in a Multichannel System.

Water desalination mediated by electrochemical reactions to directly capture and release salt at electrode materials offers a low-voltage method for producing freshwater. Developing new system designs has allowed electrode materials to maximize their capacity for salt separation, especially when a multichannel system is used to introduce a separate electrode rinse solution. Here, we show that the use of an additive can provide a new strategy for improving electrode capacity and, hence desalination performance, which so far has been limited to increasing the electrolyte concentration. A custom-built, 2/2-channel flow cell divided by two cation exchange membranes and an anion exchange membrane was fed with 50 mM NaCl as the feed (two inner channels) and 0.5 M NaCl containing up to 0.1 M phosphate as the electrode rinse (two outer channels). Using manganese oxide electrodes with phosphate buffer-mediated redox reactions exhibited an improved desalination capacity of 68.0 ± 5.2 mg g-1 (0.55 mA cm-2) and a rate of 5.6 ± 1.3 mg g-1 min-1 (0.96 mA cm-2). The improvement was attributed to the buffer that served as a proton donor for promoting the H+ insertion reaction of amorphous or poorly crystalline MnO2. Additionally, the buffering capacity against acidification and the creation of insoluble manganese phosphate on the electrode surface prevented the dissolution of Mn2+, which could otherwise occur at the anode due to a decrease in the local pH upon H+ deinsertion. Thus, the use of manganese oxide electrodes coupled with phosphate provides a new strategy of increasing electrode capacity for water desalination.

Influence of Acidity, Water and Temperature on the Double Layer Properties of Protic Ionic Liquids for Future Fuel Cell Applications

Polymer electrolyte membrane fuel cells (PEMFC) are a viable alternative to combustion engines and rechargeable batteries for automotive applications. However, the operating temperature of PEMFCs using sulfonated fluoropolymers, e.g. NAFION®, is limited below 80 °C (ambient pressure), because the proton conduction relies on the presence of water. A PEMFC operating above 100 °C would allow a much more simplified system setup for water and heat management. This requires novel non-aqueous protic electrolytes. Proton conducting ionic liquids (PIL) are promising candidates. [1,2]. However, the fuel cell relevant electrode reactions—oxygen reduction and hydrogen oxidation reaction (ORR/HOR)—are not as well understood as in aqueous electrolytes.In this study, we employed electrochemical impedance spectroscopy (EIS), cyclovoltammetry (CV), chronoamperomery (CA) and steady state current measurements to elucidate the double layer properties of the platinum electrode/PIL interface, the kinetics and possible mechanism of the ORR. Three PILs with different cation acidities with an Brønsted-acidic cation [HA+][X−] are compared, [Dema][TfO], [1-EIm][TfO] and [2-Sema][TfO].Comparing the PILs with different cation acidity strongly suggest that the first reduction step including the proton transfer to the (catalytic) active sites on the electrode is mainly determining the ORR rate. The presence of residual water, unavoidable also at fuel cell operation >100 °C, is another important parameter. H2O modifies the ordered structure of the electrochemical double layer. Its protolysis equilibrium with an acidic PIL cation results in the formation of H3O+ that serves as a proton donor in the rate determining step and thus influences the ORR kinetics. Highly acidic PIL cations serve as a proton donor as well, particularly at low H2O concentrations, whereas the role of H3O+ as proton donor in the ORR becomes more prominent at higher water concentrations [3]. In low acidic PILs, H3O+ is the predominant proton donor and the ORR rate is significantly smaller resulting in considerably higher overpotentials. Thus, the onset potential of the ORR in a PIL based fuel cell will depend on both the concentration of residual water and the PIL cation acidity.Plots of the potential-dependent data from EIS measurements in the complex capacitance plane (CCP) show that at least two differential double layer capacitances are present, depending on the cell potential U (vs. RHE), water concentration c(H2O) and temperature T. The double layer properties of the highly acidic [2-Sema][TfO] are significantly different compared to the less acidic PILs [1-EIm][TfO] and [Dema][TfO]. The potential dependent capacitance curves were discussed by taking a mean field model, the presence of water and short range correlations of ions into account. [4, 5] The combined electrochemical kinetics and double layer measurements provide a deeper insight into the double layer structure at the Pt electrode/PIL interface to reveal the rate limiting parameters of the ORR and its mechanism.[1] K. Wippermann, J. Giffin, S. Kuhri, W. Lehnert and C. Korte, Phys. Chem. Chem. Phys. 19, 24706 (2017)[2] K. Wippermann, Y. Suo and C. Korte, J. Phys. Chem. C 125(8), 8 (2021)[3] H. Hou, H. M. Schütz, J. Giffin, K. Wippermann, X. Gao, A. Mariani, S. Passerini and C. Korte, ACS Appl. Mater. Interfaces 13, 8370 (2021)[4] Z. A. H. Goodwin, G. Feng and A. A. Kornyshev, Electrochim. Acta 225, 190 (2017)[5] J. Friedl, I. I. E. Markovits, M. Herpich, G. Feng, A. A. Kornyshev and U. Stimming, ChemElectroChem 4, 216 (2017)Figure: ORR rate constant of PILs [HA+][X−] with different cation acidity vs. content of residual water (50 mol% H2O corresponds to 5–6 wt% H2O) Figure 1

Nitrogen Electrochemical Reduction into Ammonia: The Li-Mediated Pathway with Lights and Shadows

The lithium-mediated (Li-m) nitrogen reduction reaction (NRR) represents the most promising electrochemical process for renewable-driven and delocalized NH3 production. To move a step forward to the net-zero carbon emission policy and contrast the climate crisis, it is essential to find a complementary pathway to the Haber-Bosh (HB) process, independent from “grey” or “blue” H2 and combinable with renewables. Indeed, HB causes a global average of 2.86 tons of CO2 emitted per ton of NH3 [1].The outstanding reducing power of Li has been applied in different strategies; it is possible to distinguish between continuous processes and step-by-step systems. In the first case, N2 is reduced simultaneously to the protonation into NH3, while, in the second option, the Li nitridation is conducted in the absence of H+ to avoid the competitive hydrogen evolution reaction (HER).The continuous processes have nowadays reached a Faradaic efficiency approaching 100% [2], as well as a commercially relevant ammonia production rate of 153.28 μg/h*cm2 geo at a current density of 1 A/cm2 geo [3] in a batch cell at 20 bars of N2. These systems present some intrinsic drawbacks, such as the proton donor (e.g. ethanol) consumption and the system degradation, that still limit the scalability of the process. To overcome these limits, the E-NRR is recently studied in combination with H2 oxidation reaction and with proton carriers [4], [5].The step-by-step technology could ensure greater stability to the process exploiting the spontaneous chemical reaction between Li3N and H2O. Therefore, this pathway avoids organic molecule degradation, as well as H2 feedstock need and consumption [6]. Moreover, the Li–N2 reaction in a completely aprotic environment could maximize Li exploitation, enhancing scalability. Indeed, the Li reduction step is essential for the mediator recirculation, but it is the most energy-requiring step [6].Li nitridation has been studied both in a direct thermochemical reaction [6] and with promising Li–N2 galvanic cells [7]. In similarity with metallic Li–gaseous batteries (e.g. Li-O2 devices), Li-N2 devices have been recently tested both for NH3 production and for energy storage. Even if this technology is still in its infancy, a proof-of-concept of Li3N formation has been verified [7] and our laboratory is currently addressing this challenge within the SuN2rise project.

Promoting C-F bond activation via proton donor for CF4 decomposition.

Tetrafluoromethane (CF4), the simplest perfluorocarbons, is a permanently potent greenhouse gas due to its powerful infrared radiation adsorption capacity. The highly symmetric and robust C-F bond structure makes its activation a great challenge. Herein, we presented an innovated approach that efficiently activates C-F bond utilizing protonated sulfate (-HSO4) modified Al2O3@ZrO2 (S-Al2O3@ZrO2) catalyst, resulting in highly efficient CF4 decomposition. By combining in situ infrared spectroscopy tests and density function theory simulations, we demonstrate that the introduced -HSO4 proton donor has a stronger interaction on the C-F bond than the hydroxyl (-OH) proton donor, which can effectively stretch the C-F bond for its activation. Consequently, the obtained S-Al2O3@ZrO2 catalyst achieved a stable 100% CF4 decomposition at a record low temperature of 580 °C with a turnover frequency value of ~8.3 times higher than the Al2O3@ZrO2 catalyst without -HSO4 modification, outperforming the previously reported results. This work paves a new way for achieving efficient C-F bond activation to decompose CF4 at a low temperature.

Determining the Composition and Structure of a High-Performing SEI Layer for Lithium-Mediated Nitrogen Reduction to Ammonia

The industrial synthesis of ammonia (NH3) via the Haber-Bosch process has enabled mass production of fertilizer and the human population growth to 8 billion.1 NH3 also shows promise as a long-term, energy-dense fuel amenable to widespread distribution.2 However, the Haber-Bosch process operates at high temperatures and pressures in centralized facilities and accounts for 1.3% of global carbon emissions.1,2 To ensure a food-secure future and realize NH3 as a truly carbon-free fuel, we must develop an NH3 synthesis alternative that operates at ambient conditions and can be driven by renewables.One of the most promising NH3 synthesis method under mild conditions is the electrochemical, Li-mediated process (Li-NRR). In this process, Li is electrodeposited from solution and reacted with N2 to form Li3N. A proton shuttle, e.g., ethanol, protonates Li3N to form NH3.3 The electrodeposited Li forms a solid-electrolyte interphase (SEI) layer that controls N2, Li+, and H+ transport and is key to system performance. The use of fluorinated Li salts, e.g., LiBF4, have recently advanced Li-NRR system performance. Improved selectivity has been attributed to changes in the SEI layer, but evaluating SEI structure and composition remains a significant challenge.3 Neutron-based characterization methods, complementary to X-ray methods, offer unique benefits to study SEI layers containing light elements such as Li- and H; for example, an element’s neutron scattering cross section does not depend on its atomic number.4 In this work, we studied the formation of the SEI layer in-situ before and after applying -0.3 mA/cm2 in galvanostatic experiments (chronopotentiometry, CP) on a copper (Cu) working electrode. We utilized a combination of deuterated and non-deuterated solvents and proton donors to distinguish their contributions to the SEI. We found that the SEI forms two layers: a compact, lithium rich layer, and a diffuse layer with carbonaceous species (Figure 1).4 We also identified the presence of boron in the layers, indicated by neutron absorption. Finally, we observed more proton-rich species in experiments containing the non-deuterated H+ donor, corroborating previous studies that indicate that Li-ethoxide may be a major component of the diffuse SEI (Figure 1b-c).5 Compared to LiClO4-based electrolytes, the structure of these LiBF4-derived layers is consistent even after repeated current cycling, indicating a more stable SEI structure and suggesting a relationship between SEI stability and increased Li-NRR performance.References Nørskov, J. et al. DOE Roundtable Report (2016).Chang, F. et al. Advanced Materials 33, 2005721 (2021).Li, S. et al. Joule 6, 2083–2101 (2022).Blair, S.J., Doucet, M. et al. ACS Energy Lett., 7, 6, 1939-1946 (2022).Steinburg, K. et al. Nature Energy, 8, 138-148 (2023). Figure 1: (a) reflectivity curve before and after 4 mins constant applied current at -0.3 mA/cm2 (chronopoteniometry, CP) to plate Li using 1 M LiBF4 with 1 vol% ethanol, (b) resulting scattering length density (SLD) profile, and (c) schematic of layers indicated in SLD profile Figure 1

Features of proton transport mechanism in ESR, a retinal protein from <i>Exiguobacterium sibiricum</i>

Retinal-containing photosensitive proteins, rhodopsins, have been detected in many microorganisms. The interest in them is largely explained by their role in storing light energy and photoregulation in microorganisms and the prospects for use in optogenetics in order to control the activity of neurons, including for the treatment of various diseases. One of the representatives of microbial rhodopsins is ESR, a retinal protein from Exiguobacterium sibiricum. The presence of a lysine residue (Lys96) as a proton donor for the Schiff base distinguishes ESR from homologous proteins. This feature, along with the hydrogen bonding of the proton acceptor Asp85 with the His57 residue, determines its functional characteristics as a proton pump. The review examines the results of ESR studies conducted using various methods, including the method of direct electrometry. Comparison of the obtained data with the results of spatial structure determination and with other retinal proteins allows drawing conclusions about the mechanisms of transport of hydrogen ions in the ESR molecule and similar retinal proteins.

Mechanistic implications of the ternary complex structural models for the photoenzyme protochlorophyllide oxidoreductase.

The photoenzyme protochlorophyllide oxidoreductase (POR) is an important enzyme for understanding biological H-transfer mechanisms. It uses light to catalyse the reduction of protochlorophyllide to chlorophyllide, a key step in chlorophyll biosynthesis. Although a wealth of spectroscopic data have provided crucial mechanistic insight, a structural rationale for POR photocatalysis has proved challenging and remains hotly debated. Recent structural models of the ternary enzyme-substrate complex, derived from crystal and electron microscopy data, show differences in the orientation of the protochlorophyllide substrate and the architecture of the POR active site, with significant implications for the catalytic mechanism. Here, we use a combination of computational and experimental approaches to investigate the compatibility of each structural model with the hypothesised reaction mechanisms and propose an alternative structural model for the cyanobacterial POR ternary complex. We show that a strictly conserved tyrosine, previously proposed to act as the proton donor in POR photocatalysis, is unlikely to be involved in this step of the reaction but is crucial for Pchlide binding. Instead, an active site cysteine is important for both hydride and proton transfer reactions in POR and is proposed to act as the proton donor, either directly or through a water-mediated network. Moreover, a conserved glutamine is important for Pchlide binding and ensuring efficient photochemistry by tuning its electronic properties, likely by interacting with the central Mg atom of the substrate. This optimal 'binding pose' for the POR ternary enzyme-substrate complex illustrates how light energy can be harnessed to facilitate enzyme catalysis by this unique enzyme.

Sequence-Specific Relay Recognition of Multiple Anions: An Interplay between Proton Donors and Acceptors.

Ratiometric detection of analyte is highly deserving since the technique is free from background correction. This work reports the design and synthesis of a pyridine-end oligo p-phenylenevinylene (OPV) derivative, 1 and its application in ratiometric dual-mode (both colorimetric and fluorogenic) recognition of dual anions, bisulfate (LOD=12.5 ppb) followed by fluoride (LOD=18.2 ppb) by sequence-specific relay (SPR) technique. The colorless probe turns brown with addition of bisulfate and again becomes colorless with the sequential addition of fluoride ion. In addition to such naked-eye color change, interestingly the ratiometric spectroscopic signals are reversible and evidently, the probe is reusable for several cycles. Besides, in presence of bisulfate, the protonated probe molecules, owing to their larger amphiphilic characteristics, formed self-assembled nanostructures. In addition to colorimetric and fluorescent changes, 1 H NMR titration and systematic DFT study evidently establish the underneath proton transfer mechanisms. Such reusable OPV-based chemosensor particularly with the capability of naked-eye recognition of dual anions using the SPR technique is seminal and possibly the first report in the literature.

Boosting the hydrogen peroxide production over In2S3 crystals under visible light illumination by gallium ions doping and sulfur vacancies modulation

Hydrogen peroxide (H2O2) is a green oxidant that is widely used in daily life and industry. Artificial photocatalytic synthesis of H2O2 is a green and sustainable scheme, but the high complexation rate of electron-hole pairs during photocatalysis and the low activation capacity of the catalyst for O2 greatly inhibit the oxygen reduction reaction. Herein, the first synergistic modification of In2S3 using ion doping and vacancy modulation is used in this paper. An In2S3-based photocatalyst containing S vacancies and Ga3+ ions is designed and synthesized. After continuous irradiation under visible light (λ ≥ 420 nm) for 1 h, the H2O2 concentration of the system reaches 352.58 μmol L–1, which is 7.5 times than that of pure In2S3, and the apparent quantum yield at 450 nm is 4.64%. Appropriate concentrations of S vacancies promoted O2 adsorption, and theoretical calculations demonstrates that Ga3+ ions and S vacancies synergistically promote O2 activation and more favorable for 2e– oxygen reduction reaction. All these phenomena facilitate H2O2 generation. Furthermore, ESR analysis and radical trapping experiments show that the interaction between superoxide anion radicals (•O2–), singlet oxygen (1O2), h+, and proton donor (isopropanol) in the solution phase plays a key role in the photocatalytic synthesis of H2O2, which has been largely neglected in previous studies. We suggest that the S vacancy-regulated Ga3+ ion-doped In2S3 catalyst could provide a reference for the design of high-performance materials for the photocatalytic production of hydrogen peroxide.

Modeling the Weak pH Dependence of Proton-Coupled Electron Transfer for Tryptophan Derivatives.

The oxidation of tryptophan (Trp) is an important step in many biological processes and often occurs by sequential or concerted proton-coupled electron transfer (PCET). The apparent rate constants for the photochemical oxidation of two Trp derivatives in water have been shown to be pH-independent at low pH and to exhibit weak pH dependence at higher pH. Herein, these systems are investigated with a general, multi-channel model that includes sequential and concerted mechanisms as well as various proton donors and acceptors. This model can reproduce the kinetic data for both Trp derivatives with physically meaningful parameters and suggests that the weak pH dependence may arise from the competition between OH- and H2O as proton acceptors in concerted PCET. Deprotonation of an ammonium group for one of the systems leads to a more complex pH dependence at higher pH. This work demonstrates the importance of considering multiple competing channels for the analysis of the pH dependence of apparent PCET rate constants.

Oxygen reduction catalysis by [Cu(cyclen)Cl]Cl·H2O: The relationship of selectivity to proton in nonaqueous solution and aqueous solution

The reaction of 1,4,7,10‐tetraazacyclododecane (cyclen) with CuCl2·2H2O results in a novel five‐coordinated mononuclear copper complex, [Cu(cyclen)Cl]Cl·H2O, which has been characterized using physicochemical and spectroscopic methods. This copper complex can serve as a catalyst for oxygen reduction reactions (ORRs). The selectivity for 4e−/4H+ reduction to H2O νersus 2e−/2H+ reduction to H2O2 is determined by the relationship of the pKa value of the proton donor in nonaqueous solutions. The dissociation of Cl− from [Cu(cyclen)Cl]Cl·H2O creates an empty position on the copper centre, enabling to binding of dioxygen (O2) to form Cu(II)‐superoxo intermediate, which further reacts with a strong acid as a proton donor to form H2O and with a weak acid as a proton donor to form H2O2. Moreover, the faradaic efficiency for H2O2 production increases in an aqueous environment with the increase of pH.

Photocatalytic Three-Component Reaction for the Synthesis of Multifunctional Diaryl Sulfides.

A photocatalytic three-component reaction of a nitroarene, a thiophenol, and a ketone for the synthesis of multifunctional diaryl sulfides was reported using a nitro group as the nitrogen source and thiophenol as the sulfur source. Thiophenol also serves as a proton donor to reduce nitroarene to arylamine as a key intermediate for the formation of C-N and C-S bonds. Good functional group tolerance and mild reaction conditions make this method have practical synthetic value for diversified multifunctional diaryl sulfides.

Lithium-Mediated Ammonia Electrosynthesis with Ether-Based Electrolytes.

Ammonia is of great importance in fertilizer production and chemical synthesis. It can also potentially serve as a carbon-free energy carrier for a future hydrogen economy. Motivated by a worldwide effort to lower carbon emissions, ammonia synthesis by lithium-mediated electrochemical nitrogen reduction (LiNR) has been considered as a promising alternative to the Haber-Bosch process. A significant performance improvement in LiNR has been achieved in recent years by exploration of favorable lithium salt and proton donor for the electrolyte recipe, but the solvent study is still in its infancy. In this work, a systematic investigation on ether-based solvents toward LiNR is conducted. The assessments of solvent candidates are built on their conductivity, parasitic reactions, product distribution, and faradaic efficiency. Notably, dimethoxyethane gives the lowest potential loss among the investigated systems, while tetrahydrofuran achieves an outstanding faradaic efficiency of 58.5 ± 6.1% at an ambient pressure. We found that solvent molecules impact the above characteristics by dictating the solvation configurations of conductive ions and inducing the formation of solid electrolyte interphase with different compositions. This study highlights the importance of solvents in the LiNR process and advances the electrolyte optimization for better performance.

Development of cat-GRRM/MC/MD method for the simulation of cross-linked network structure formation with molecular autocatalysis

Epoxy resins, which are common matrices in carbon fibre-reinforced plastics, are derived from the curing of epoxy amines. Molecular dynamics (MD) simulations are commonly used to model the physical properties of such network polymers, but they do not account for chemical reactions. Quantum chemical (QC) calculations can elucidate reaction mechanisms and energies but are not suitable for models with thousands of atoms. To address these limitations, in this study, we developed a new method, cat-GRRM/MC/MD, that combines QC calculations in the Global Reaction Route Mapping (GRRM) program with reaction simulations involved in MD simulation methods. This approach allows the simulation of reaction pathways in which proton donor molecules such as alcohols and amines act as molecular catalysts (autocatalysis), and the reaction kinetics are realised in a Monte Carlo (MC) manner. Our results show that autocatalysis significantly reduces the activation energy of the epoxy resin reaction, bringing the calculated data closer to the experimental results. When these quantum chemical calculations were incorporated into MD simulations, it was found that the activation energy influenced the crosslinking results. Models including catalysis led to network polymers with larger carbon skeletons, and physical properties such as the Young's modulus and glass transition temperature become closer to experimental results. This study not only deepens our understanding of the mechanism of the self-catalytic reaction of epoxy resins but also provides a new tool for accurately simulating the performance of epoxy resins, thus enabling more precise control of their properties.

New Spectroelectrochemical Insights into Manganese and Rhenium Bipyridine Complexes as Catalysts for the Electrochemical Reduction of Carbon Dioxide.

This study aimed to demonstrate the behavior of different complexes using IR spectroelectrochemistry (SEC), a technique that combines IR spectroscopy with electrochemistry. Four different Mn and Re catalysts for electrochemical CO2 reduction were studied in dry acetonitrile. In the case of Mn(apbpy)(CO)3Br (apbpy = 4(4-aminophenyl)-2,2'-bipyridine), SEC suggested that a very slow catalytic reduction of CO2 also occurs in acetonitrile in the absence of proton donors, but at rather negative potentials. In contrast, the corresponding Re(apbpy)(CO)3Br clearly demonstrated slow catalytic conversion at the first reduction potential. Switching to saturated CO2 solutions in a mixture of acetonitrile and 5% water as a proton donor, the SEC of Mn(apbpy)(CO)3Br displayed a faster catalytic behavior.

Excited state proton transfer mechanism of a thiazolo [5,4-d] thiazole derivative in different solvents

In this paper, the excited state proton transfer mechanism of a thiazolo [5,4-d] thiazole derivative, 4-tert-butyl-2-(5-(5-tert-butyl-2-methoxyphenyl) thiazolo [5,4-d] thiazol-2-yl) phenol (MTTH), has been investigated in different polar solvents by using DFT and TDDFT methods. The hydrogen bond lengths, bond angles, and corresponding infrared vibrational frequencies of MTTH in three different polar solvents were compared, and the analytical results showed that the intramolecular hydrogen bonding of MTTH was enhanced in all S1 states. In addition, the simulated absorption and emission spectra values of MTTH are in good agreement with the experimental data, which further proves the rationality of the calculation method. Meanwhile, the electron density rearrangement between the proton acceptor and donor was found by analyzing the frontline molecular orbitals of the MTTH, which is favorable for the excited state proton transfer process. Finally, the potential energy curves of MTTH in three different solvents were calculated, and the results indicated that the weakly polar solvents were more favorable for the excited state intramolecular proton transfer of MTTH.