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A membrane with a low methanol permeability and high proton conductivity (σ p) is essential for the effective operation of a direct methanol-based fuel cell. Herein, a bio-metal organic framework was prepared with natural α-amino acids as ligands and then combined with hydrolyzed polyacrylonitrile (PAN) nanofibers (AA-MOF@PAN). The resulting nanocomposite membranes were subsequently integrated into a Nafion matrix (AA-MOF@PAN/Nafion). The –NH 2 groups on AA-MOF@PAN interact with –SO 3 H groups on Nafion, forming long-range acid-base pairs along the interface between the matrix and nanofibers. This interaction creates abundant proton-conducting sites for proton exchange membrane. Notably, the AA-MOF@PAN-4h/Nafion membrane demonstrated an exceptional proton conductivity (σ p) of 0.25 S cm−1 and a higher power density of 117.61 mW cm−2 compared to the recast Nafion membrane. This study offers valuable insights into the three-dimensional ordered design of a natural α-amino acids as a proton transfer sites and highlighting their potential applications in proton exchange membranes. • In situ growth of uniformly distributed AA-MOF onto hydrolyzed PAN nanofiber. • AA-MOF@PAN were introduced as proton-conducting channels. • AA-MOF@PAN-4h/Nafion exhibited the highest proton conductivity of 0.25 S cm−1 at 80 °C. • Introduction of AA-MOF@PAN resulted in a reduced fuel crossover. [ABSTRACT FROM AUTHOR]

Photosynthetic hydrogen generation by cobalt(II) tris(2‐pyridylmethyl)amine (TPMA) complexes is mainly limited by protonation kinetics and decomposition routes involving demetallation. In the present work we have explored the effects of both proton shuttles and improved rigidity on the catalytic ability of cobalt(II) TPMA complexes. Remarkably, we demonstrate that, while a small enhancement in the catalytic performance is attained in a rigid cage structure, the introduction of ammonium groups as proton transfer relays in close proximity to the cobalt center allows to reach a 4‐fold increase in the quantum efficiency of H2 formation, and a surprising 22‐fold gain in the maximum turnover number, at low catalyst concentration. The beneficial role of the ammonium relays in promoting faster intramolecular proton transfer to the reduced cobalt center is documented by transient absorption spectroscopy, showcasing the great relevance of tuning the catalyst periphery to achieve efficient catalysis of solar fuel formation. [ABSTRACT FROM AUTHOR]

SIRT5, one of the mammalian sirtuins, specifically recognizes succinyl‐lysine residues on proteins and catalyzes the desuccinylation reaction. In this study, we characterized SIRT5 mutants with hydrophobic amino acid substitutions at Q140 and N141, in addition to the catalytic residue H158, known as an active site residue, by the Michaelis–Menten analysis and X‐ray crystallography. Kinetic analysis showed that the catalytic efficiency (kcat/Km) of the Q140L and N141V mutants decreased to 0.02 times and 0.0038 times that of the wild‐type SIRT5, respectively, with the activity of the N141V mutant becoming comparable to that of the H158M mutant. Our findings indicate that N141 contributes significantly to the desuccinylation reaction. [ABSTRACT FROM AUTHOR]

The interaction of H, H2, and MgH2 with graphene is investigated using the density functional theory to explore the possibility of exploiting graphene or functionalized graphene as a hydrogen storage medium. The H atom is positioned at various distances from the graphene surface and the energetics are computed in detail. The extent of interaction of the s electron of H with graphene's pz electrons is well brought out. Similar investigations are carried out for H2, MgH2. In the case of H atom, a HC covalent bond is formed. This process turns out to be a prerequisite for proton transfer through graphene. Interactions of H2 and MgH2 with graphene are different from that of H. It leads to the conclusion that functionalized graphene will better substrate/candidate for applications like hydrogen storage. [ABSTRACT FROM AUTHOR]

The electrocatalytic recycling of waste nitrate (NO3RR) is a promising decentralized route for green ammonia synthesis. Nonetheless, it suffers from the competing hydrogen evolution reaction and the insufficient proton supply in high pH conditions. Herein, iron oxide nanoparticles anchored on ZnO is introduced as a strategy to enhance the water dissociation ability and proton transfer rate, advancing NH4+ production from alkaline NO3RR. Supported by a set of ex situ and in situ characterization, the findings reveal the reduction of iron oxides, along with improvements in charge transfer properties and proton generation from H2O. Theoretical calculations show that iron oxides reduce the kinetic barrier of the rate‐limiting step (*NO2‐to‐*NO2H) and result in a thermodynamically favorable process to hydrogenation steps, which in turn reduce the overall energy barrier of alkaline NO3RR. Optimal catalytic activity is realized with a Fe loading of 0.5 wt.%, delivering a Faradaic efficiency of ≈83% for ammonium with a NH4+ yield rate of 31 nmol s−1 cm−2 at −0.7 V versus RHE. The results pave the way for the utilization of bi‐metal interaction to tune the reaction pathway for achieving sustainable ammonium synthesis in alkaline, contributing to ongoing efforts to achieve a sustainable nitrogen cycle via N‐based electrochemistry. [ABSTRACT FROM AUTHOR]

In this study, the density functional M06‐2X/6‐311++G(3df,3pd) method was employed to investigate the mutual isomerization reaction mechanism of 5‐chlorouracil from diketone to diol under the catalysis of water, methanol, formic acid, and an electric field. Parameters such as reaction enthalpy, activation energy, activation Gibbs free energy, and proton transfer reaction rate were obtained. The computational results show that under the same conditions, formic acid demonstrates the best catalytic effect, while the influence of electric field catalysis on the reaction barrier is minimal. [ABSTRACT FROM AUTHOR]

The potential energy surfaces for the reactions of 1,3‐butadiene with 2‐hydroxythioacrolein and 2‐aminoacrolein exhibit ambimodal transition states leading to both dipolar (4 + 3) and Diels–Alder (4 + 2) cycloaddition products, thereby demonstrating a post transition state bifurcation feature. We have investigated the bifurcation dynamics of these reactions using three molecular dynamics (MD) methods: quasi‐classical trajectory, classical MD, and ring‐polymer MD simulations. The trajectory calculations were performed with the semiempirical GFN2‐xTB method with the element‐specific parameters optimized to reproduce the density‐functional theory calculations. The effect of water solvation was examined using an implicit solvation model, revealing significant differences in bifurcation dynamic between gas‐phase and solution‐phase reactions. Nuclear quantum effects were found to play a crucial role in the proton‐transfer process from the (4 + 3) intermediate to the (4 + 3) product in the case of the 2‐aminoacrolein reaction. [ABSTRACT FROM AUTHOR]

The effect of the external electric field on the ground-state tautomerism in 8-(benzo[d]thiazol-2-yl)quinolin-7-ol has been studied by using density functional theory. The compound exists as an enol tautomer (off state) and under the influence of the external electric field a long-range intramolecular proton transfer can occur, placing the tautomeric proton at the quinolyl nitrogen atom (on state). This is a result of the much higher dipole moment of the end keto tautomer and indicates that the external electric field can be used to mimic the implicit solvent effect in tautomeric systems. In the excited state, the further stabilization of the most polar on state leads to a situation when the excited-state intramolecular proton transfer becomes impossible, limiting the intramolecular rotation to the conical intersection region. [ABSTRACT FROM AUTHOR]

Abstract In this study, a newly developed composite of biochar-poly(m-phenylenediamine) (BC-PmPD) exhibiting a distinct skeletal structure was synthesized for the purpose of extracting Cr(VI) from aqueous solutions. BC was employed as a supportive carrier onto which PmPD nanoparticles were uniformly affixed through in-situ polymerization and oxidation synthesis, both within and outside the layered configuration of BC. The structural stability and morphologies of BC-PmPD were assessed utilizing Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, thermogravimetric analysis, analysis of specific surface area and pore size, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction. In comparison to other modified BCs reported, BC-PmPD exhibited the highest Cr(VI) removal rate. Specifically, at 303 K, BC-PmPD achieved a maximum Cr(VI) removal capacity of 775 mg g−1, surpassing the capabilities of unmodified BC and PmPD by 10.4 and 2.13 times, respectively. Analyses involving XPS, FTIR, and density functional theory calculation confirmed that proton transfer happened between protonated amine (−NH2) functional group within the structure of BC-PmPD and HCrO4 − before the formation of hydrogen bond. Subsequently, environmentally persistent free radicals facilitated the reduction of the adsorbed Cr(VI). Quantification of the functional groups indicated that the amino group was responsible for 93.0% of the Cr(VI) adsorption in BC-PmPD. BC-PmPD displayed potent adsorption and reduction capabilities, alongside notable stability, repeatability, and promising potential for application in the remediation for high concentrations of Cr(VI) in electroplating wastewater scenarios. Graphical Abstract

This paper is dedicated to the research of phenomena noticed during tests of biodegradable carrageenan-based force and pressure sensors. Peculiar voltage characteristics were noticed during the impact tests. Therefore, the sensors' responses to impact were researched more thoroughly, defining time-dependent sensor output signals from calibrated energy impact. The research was performed using experimental methods when a free-falling steel ball impacted the sensor material to create relatively definable impact energy. The sensor's output signal, which is analogue voltage, was registered using an oscilloscope and transmitted to the PC for further analysis. The obtained results showed a very interesting outcome, where the sensor, which was intended to be piezoresistive, demonstrated a combination of behaviour typical for galvanic cells and piezoelectric material. It provides a stable DC output that is sensitive to the applied statical pressure, and in case of a sudden impact, like a hit, it demonstrates piezoelectric behaviour with some particular effects, which are described in the paper as proton transfer in the sensor-sensitive material. Such phenomena and sensor design are a matter of further development and research. [ABSTRACT FROM AUTHOR]

[Display omitted] Understanding the mechanisms of proton transfer on quartz surfaces in water is critical for a range of processes in geochemical, environmental, and materials sciences. The wide range of surface acidities (>9 p K a units) found on the ubiquitous mineral quartz is caused by the structural variations of surface silanol groups. Molecular scale simulations provide essential tools for elucidating the origin of site-specific surface acidities. We used density-functional tight-binding-based molecular dynamics combined with rare-event metadynamics simulations to probe the mechanisms of deprotonation reactions from ten representative surface silanol groups found on both pristine and defect-rich quartz (1 0 1) surfaces with Si vacancies. The results show that deprotonation is a highly dynamic process where both the surface hydroxyls and bridging oxygen atoms serve as the proton acceptors, in addition to water. Deprotonation of embedded silanols through intrasurface proton transfer exhibited lower p K a values with less H-bond participation and higher energy barriers, suggesting a new mechanism to explain the bimodal acidity observed on quartz surface. Defect sites, recently shown to comprise a significant portion of the quartz (1 0 1) surface, diversify the coordination and local H-bonding environments of the surface silanols, changing both the deprotonation pathways and energetics, leading to a wider range of p K a values (2.4 to 11.5) than that observed on pristine quartz surface (10.4 and 12.1). [ABSTRACT FROM AUTHOR]

The impact of the polymeric matrix on the photophysical characteristics of monomeric dyes responsive to excited‐state intramolecular proton transfer (ESIPT) was investigated through UV–Vis absorption as well as steady‐state and time‐resolved emission spectroscopies. For this purpose, two benzoxazole monomers (M1 and M2) with acryloyl groups at different positions in their molecular structures were employed to facilitate covalent bonding within a styrene chain. Our findings reveal significant variations in their excited‐state properties due to the proximity of the acryloyl groups, which affects the energy barrier of the ESIPT reaction, the emission wavelength, and the balance between the normal and tautomeric forms. The experimental results were corroborated through theoretical investigations at the DFT/TDDFT level, specifically using the B3LYP‐D3/def2‐TZVP methodology. Three notable observations emerged: donor/acceptor groups at the meta/para positions induced electron distribution changes, causing red‐shifted emission for M2; in the polymer film, particularly in PM1, intramolecular hydrogen bond deactivation favored N* emission over T* emission; and the zwitterionic character of the T* species. This study underscores the advantages of functionalization in polymers, which can lead to colorless films and prevalent N* or T* emission, and contributes valuable insights into molecular design strategies for tailoring the photophysical properties of polymeric materials. [ABSTRACT FROM AUTHOR]

The development of carbon capture and storage technologies has resulted in a rising interest in the use of carbonic anhydrases (CAs) for CO2 fixation at elevated temperatures. In this study, we chose to rationally engineer the α-CA (NtCA) from the thermophilic bacterium Nitratiruptor tergarcus, which has been previously suggested to be thermostable by in silico studies. Using a combination of analyses with the DEEPDDG software and available structural knowledge, we selected residues in three regions, namely, the catalytic pocket, the dimeric interface and the surface, in order to increase thermostability and CO2 hydration activity. A total of 13 specific mutations, affecting seven amino acids, were assessed. Single, double and quadruple mutants were produced in Escherichia coli and analyzed. The best-performing mutations that led to improvements in both activity and stability were D168K, a surface mutation, and R210L, a mutation in the dimeric interface. Apart from these, most mutants showed improved thermostability, with mutants R210K and N88K_R210L showing substantial improvements in activity, up to 11-fold. Molecular dynamics simulations, focusing particularly on residue fluctuations, conformational changes and hydrogen bond analysis, elucidated the structural changes imposed by the mutations. Successful engineering of NtCA provided valuable lessons for further engineering of α-CAs. [ABSTRACT FROM AUTHOR]

The model of thylakoid membrane system (T-M model) (Belyaeva et al. Photosynth Res 2019, 140:1–19) has been improved in order to analyze the induction data for dark-adapted samples of algal (Scenedesmus obliques) and cyanobacterial (Synechocystis sp. PCC 6803) cells. The fluorescence induction (FI) curves of Scenedesmus were measured at light exposures of 5 min, while FI and P700 redox transformations of Synechocystis were recorded in parallel for 100 s intervals. Kinetic data comprising the OJIP-SMT fluorescence induction and OABCDEF P700+ absorbance changes were used to study the processes underlying state transitions qT2→1 and qT1→2 associated with the increase/decrease in Chl fluorescence emission. A formula with the Hill kinetics (Ebenhöh et al. Philos Trans R Soc B 2014, 369:20130223) was introduced into the T-M model, with a new variable to imitate the flexible size of antenna AntM(t) associated with PSII. Simulations revealed that the light-harvesting capacity of PSII increases with a corresponding decrease for that of PSI upon the qT2→1 transition induced by plastoquinone (PQ) pool oxidation. The complete T-M model fittings were attained on Scenedesmus or Synechocystis fast waves OJIPS of FI, while SMT wave of FI was reproduced at intervals shorter than 5 min. Also the fast P700 redox transitions (OABC) for Synechocystis were fitted exactly. Reasonable sets of algal and cyanobacterial electron/proton transfer (ET/PT) parameters were found. In the case of Scenedesmus, ET/PT traits remained the same irrespective of modeling with or without qT2→1 transitions. Simulations indicated a high extent (20%) of the PQ pool reduction under dark conditions in Synechocystis compared to 2% in Scenedesmus. [ABSTRACT FROM AUTHOR]

In this study, a newly developed composite of biochar-poly(m-phenylenediamine) (BC-PmPD) exhibiting a distinct skeletal structure was synthesized for the purpose of extracting Cr(VI) from aqueous solutions. BC was employed as a supportive carrier onto which PmPD nanoparticles were uniformly affixed through in-situ polymerization and oxidation synthesis, both within and outside the layered configuration of BC. The structural stability and morphologies of BC-PmPD were assessed utilizing Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, thermogravimetric analysis, analysis of specific surface area and pore size, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction. In comparison to other modified BCs reported, BC-PmPD exhibited the highest Cr(VI) removal rate. Specifically, at 303 K, BC-PmPD achieved a maximum Cr(VI) removal capacity of 775 mg g−1, surpassing the capabilities of unmodified BC and PmPD by 10.4 and 2.13 times, respectively. Analyses involving XPS, FTIR, and density functional theory calculation confirmed that proton transfer happened between protonated amine (−NH2) functional group within the structure of BC-PmPD and HCrO4− before the formation of hydrogen bond. Subsequently, environmentally persistent free radicals facilitated the reduction of the adsorbed Cr(VI). Quantification of the functional groups indicated that the amino group was responsible for 93.0% of the Cr(VI) adsorption in BC-PmPD. BC-PmPD displayed potent adsorption and reduction capabilities, alongside notable stability, repeatability, and promising potential for application in the remediation for high concentrations of Cr(VI) in electroplating wastewater scenarios. Highlights: Novel 3D material was prepared and the removal rate of Cr(VI) on BC-PmPD was the highest as compared to reported BCs. The maximum adsorption amount of Cr(VI) on BC-PmPD was high up to 1034 mg g−1 at 323 K and −NH2 adsorbed 93.0% HCrO4–. DFT calculation confirmed proton transfer happened between protonated −NH2 and HCrO4− before the formation of H bond. [ABSTRACT FROM AUTHOR]

Based on our previous study in chemical subtleties of the proton tunneling distance for metal hydride formation (PTD‐MH) to regulate the selectivity of CO2 reduction reaction (CO2RR), we have developed a family of Mn terpyridine derivatives, in which urea groups functions as multipoint hydrogen‐bonding hangman to accelerate the reaction rate. We found that such changes to the second coordination sphere significantly increased the turnover frequency (TOF) for CO2 reduction to ca. 360 s-1 ${{s}^{-1}}$ with this family of molecular catalysts while maintaining high selectivity (ca. 100 %±3) for CO even in the presence of a large amount of phenol as proton source. Notably, the compounds studied in this manuscript all exhibit large value for icat/ip ${{{\bf i}}_{{\bf c a t}}/{{\bf i}}_{{\bf p}}}$ as that achieved by Fe porphyrins derivates, while saving up to 0.55 V in overpotential with respect to the latter. [ABSTRACT FROM AUTHOR]

Tautomerization paths of β‐alanine with explicit inclusion of water molecules, (H2O)n, were investigated by DFT calculations, wB97X‐D/6‐311+G(d,p) SCRF=PCM. Structures of zwitterions of the alanine of trans (t−) and gauche (g−) conformations with seven water molecules (n=7) were examined. On the basis of those geometries, elementary processes of the tautomerization were investigated. For the t‐conformer of β‐alanine, reaction models of n=8, 10, 14, 18 and 24 were scrutinized. While reaction processes are slightly modified with different number of water molecules, n=18 and 24 models afforded three elementary reactions, t‐alanine with cis‐COOH→t‐ion pair→t‐alanine with trans‐COOH→t‐zwitterion. The (H2O)4 hydrogen‐bonded chain participates in the reactions. For the g‐conformer, models of n=7, 10, 14 and 18 were investigated, and the tautomerization was found to take place concertedly via (H2O)2. [ABSTRACT FROM AUTHOR]

The Cu−O−Cu core has been proposed as a potential site for methane oxidation in particulate methane monooxygenase. In this work, we used density functional theory (DFT) to design a mixed‐valent CuIII−O−CuII species from an experimentally known peroxo‐dicopper complex supported by N‐donor ligands containing phenolic groups. We found that the transfer of two‐protons and two‐electrons from phenolic groups to peroxo‐dicopper core takes place, which results to the formation of a bis‐μ‐hydroxo‐dicopper core. The bis‐μ‐hydroxo‐dicopper core converts to a mixed‐valent CuIII−O−CuII core with the removal of a water molecule. The orbital and spin density analyses unravel the mixed‐valent nature of CuIII−O−CuII. We further investigated the reactivity of this mixed‐valent core for aliphatic C−H hydroxylation. Our study unveiled that mixed‐valent CuIII−O−CuII core follows a hydrogen atom transfer mechanism for C−H activation. An in‐situ generated water molecule plays an important role in C−H hydroxylation by acting as a proton transfer bridge between carbon and oxygen. Furthermore, to assess the relevance of a mixed‐valent CuIII−O−CuII core, we investigated aliphatic C−H activation by a symmetrical CuII−O−CuII core. DFT results show that the mixed‐valent CuIII−O−CuII core is more reactive toward the C−H bond than the symmetrical CuII−O−CuII core. [ABSTRACT FROM AUTHOR]

Free acids commonly exist in anhydride and esters because they are unstable and tend to break down into free acids, which affect the quality of subsequent products in industrial production. Phthalic anhydride and ethyl acetate undergo hydrolysis reactions to form phthalic acid and acetic acid. A differential pulse voltammetry method for the determination of phthalic acid and acetic acid was developed with a bare glassy carbon electrode. Phthalic acid and acetic acid caused a new cathodic peak at more positive potential during the reduction of 1,4‐benzoquinone in acetonitrile or aqueous solution. The new peaks are attributed to the drastic increase in pH at the electrode surface caused by the consumption of protons in the benzoquinone reduction reaction. The peak current of the new cathodic peak was dependent on the concentration of phthalic acid and acetic acid but independent of BQ, phthalic anhydride, and ethyl acetate. This method does not cause hydrolysis of anhydride and ester because no external base is introduced. Furthermore, the method is sensitive, rapid, and does not require pretreatment. [ABSTRACT FROM AUTHOR]

The tautomerism in the title compound as a potential long-range proton transfer (PT) switch has been studied by using the DFT and TD-DFT approaches. The data show that in aprotic solvents, the enol tautomer dominates, while the increase in the content of the keto tautomer (short-range PT) rises as a function of polarity of the solvent. In ethanol, due to specific solute–solvent stabilization through intermolecular hydrogen bonding, a substantial amount of the keto forms exists in solution. The irradiation leads to two competitive processes in the excited state, namely ESIPT and trans/cis isomerization around the azomethine bond as in other structurally similar Schiff bases. The studied compound is not suitable for bistable tautomeric switching, where long-range PT occurs, due to the difficult enolization of the coumarin carbonyl group. [ABSTRACT FROM AUTHOR]

We report a detailed investigation of the vibrational modes, structure, and dynamics of glutathione (GSH) solutions using ultrasonic relaxation spectroscopy, FT-IR vibrational spectroscopy, and electronic absorption measurements. The experimental data were analyzed using density functional theory (DFT) and molecular docking calculations. Three distinct Debye-type relaxation processes can be observed in the acoustic spectra, which are assigned to conformational changes between GSH conformers, the self-association of GSH, and protonation processes. The standard volume changes for each process were estimated both experimentally and theoretically, revealing a close resemblance among them. The higher the effect of the relaxation process in the structure, the greater the induced volume changes. From the temperature dependence of specific acoustic parameters, the thermodynamic characteristics of each process were determined. The experimental FT-IR spectra were compared with the corresponding theoretically predicted vibrational spectra, revealing that the GSH dimers and extended conformers dominate the structure of GSH solutions in the high-concentration region. The absorption spectra in the ultraviolet region confirmed the gradual aggregation mechanism that takes place in the aqueous GSH solutions. The results of the present study were discussed and analyzed in the framework of the current phenomenological status of the field. [ABSTRACT FROM AUTHOR]

The mini review focuses on the work carried out in our laboratory over the last two and a half decades to unravel various facets of photoinduced processes, viz. photoinduced electron transfer (PET), excited state proton transfer, energy transfer etc., using fluorescence spectroscopy and imaging. We have demonstrated that PET is manifested by formation of exciplex and that its parent spin state is authenticated by observing steady-state fluorescence in presence of magnetic field, which is quite a non-conventional set-up. It is observed that dielectric constant of the medium governs the magnetic field effect. We have synthesized and explored fluorophores which act as sensors for hydrogen bonds and protic media. Our group has studied the protonation equilibrium of Acridine, which is a good fluorophore in various confined media and observed the perturbation of this equilibrium in presence of DNA bases using steady-state and time-resolved fluorescence techniques. Excimer formation of 9-Aminoacridine Hydrochloride Hydrate (9AA), another strong fluorophore, has been investigated in several solvent matrices and photoinduced interactions of 9AA with amines and viologens are studied. Further, we have utilized fluorescence upconversion technique to segregate direct and diffusion-controlled electron transfer within picosecond-femtosecond time domain. Then attempts have been made to study DNA-ligand and protein-ligand interactions comprehensively, utilizing different techniques of fluorescence spectroscopy. Furthermore, we have synthesized fluorescent carbon dots and have made an endeavor to find their fruitful biological significance. We have also synthesized riboflavin (Rf)-gold nano-assemblies (RfS@AuNPs) by covalently attaching thiolated Rf to gold nanoparticles (AuNPs) and have observed that these RfS@AuNPs accumulate in the nucleus of cancer cells, leading to plasma membrane blebbing and binucleated apoptotic bodies, consistent with activation of apoptosis. Finally, some very recent examples as well as the future prospect of fluorescence spectroscopy have been discussed.

A theoretical investigation of the microsolvation effect on proton exchange (PE) between carbonic acid and methylamine (CA-MTA) has been explored by quantum dynamics simulations. The structural, energy, and dynamic properties of the CA-MTA complex with and without an explicit water molecule are elucidated at the molecular level. The reactions from this study have been clarified into different types: single-step PE (SSPE) and stepwise PE (SWPE). Without the water molecule, the SSPE mechanism is hardly found but observable with a low probability of 0.2. In particular, the water molecule interacting through intermolecular hydrogen-bonded network between CA and MTA in CA-MTA-Win could affect PE by showing both SSPE and SWPE mechanisms. In addition, the existing water molecule plays the significant role in shortening intermolecular hydrogen bonding interactions within the complex resulting in increasing the probability of PE up to 0.92 especially in CA-MTA-Wout. Hence, one water molecule could be used to provide reliable results to represent the significant activity that occurs for the proton exchangeability of the CA and MTA complex.

After drawing comparisons between the reaction pathways of cytochrome c oxidase (CcO, Complex 4) and the preceding complex cytochrome bci (Complex 3), both being proton pumping complexes along the electron transport chain, we provide an analysis of the reaction pathways in bacterial ba3 class CcO, comparing spectroscopic results and kinetics observations with results from DFT calculations. For an important arc of the catalytic cycle in CcO, we can trace the energy pathways for the chemical protons and show how these pathways drive proton pumping of the vectorial protons. We then explore the proton loading network above the Fe heme a3-CuB catalytic center, showing how protons are loaded in and then released by combining DFT-based reaction energies with molecular dynamics simulations over states of that cycle. We also propose some additional reaction pathways for the chemical and vector protons based on our recent work with spectroscopic support. [ABSTRACT FROM AUTHOR]

High catalytic activity, low-cost and stable cathode in a temperature range 550–700 °C is essential for the development of protonic ceramic fuel cells (PCFCs). Doping nickel into perovskite La 0.5 Sr 0.5 MnO 3-δ (LSM) is designed as a cobalt-free cathode based on theoretical calculations and experiments. La 0.5 Sr 0.5 Mn 0.9 Ni 0.1 O 3-δ (LSMNi) as cathode shows higher proton conductivity and ORR activity than the undoped LSM. The PCFCs with LSMNi exhibit low polarization resistance and high peak power density 1.1 W cm−2 at 700 °C. The density functional theory simulations indicate that doping with nickel decreases the oxygen vacancy formation energy and promotes the formation of hydroxide defects. The decrease in proton transfer energy barriers and hydration energy improves the proton conductivity. The improved performance is attributed to fast proton transfer and rapid kinetics of oxygen reduction on the surface of LSMNi. This work provides a novel approach to design cobalt-free cathode for a protonic ceramic fuel cell. [ABSTRACT FROM AUTHOR]

The identification and quantification of hydrogen (H)‐bonded complexes form the cornerstone of reaction‐mechanism analysis in ultrafast proton‐transfer reactions. Traditionally, the Benesi–Hildebrand method has been employed to obtain the formation constants of H‐bonded complexes, given that H‐bonding additives induce an alteration in spectral features exclusively through H‐bond formation. However, if the additive introduction impacts the bulk polarity of the solution, inducing a spectral shift, the spectroscopic method's accuracy in analyzing the H‐bond formation becomes compromised. In this study, we scrutinize H‐bond formation under the influence of an H‐bond accepting solute in an aprotic solvent. This is achieved by quantifying the fractions of two concurrent pathways involved in the excited‐state proton transfer (ESPT) of a super‐photoacid: the ultrafast ESPT of an H‐bonded complex versus the diffusion‐controlled ESPT of the free acid. Our method offers improved accuracy compared to conventional steady‐state spectroscopic techniques, by directly quantifying the H‐bonded complexes using the time‐resolved spectroscopic method, thereby circumventing the aforementioned limitation. [ABSTRACT FROM AUTHOR]

Proton transfer reaction mass spectrometry has a so far little exploited potential for the analysis of high-purity process and inert gases. In order to protonate impurities like saturated hydrocarbons, precursor ions with very low proton affinity must be used, which in turn leads to a large energy release upon protonation of molecules with high proton affinity, potentially causing fragmentation of the product ions. To explore the potential of low-proton affinity precursor ions like ArH+ and N2H+ for analytical purposes, we studied their gas-phase reactions and kinetics with acetone by Fourier transform ion cyclotron resonance (FT–ICR) mass spectrometry. The dominant product ion in both cases is protonated acetone, but fragment ions formed include C2H3O+, C3H5+ and CH3O+, which are formed in higher abundance with ArH+ compared to N2H+. The reaction efficiencies are determined to be close to 100%. Quantum chemical calculations reveal energetically favorable reaction pathways and explain the loss of water leading to the formation of C3H5+, as well as loss of methane to yield C2H3O+via dissociative proton attachment, which corresponds to the main product in the EI mass spectrum of acetone. Formation of protonated formaldehyde CH3O+ involves rearrangement of the C–C bonds to eliminate ethylene. [ABSTRACT FROM AUTHOR]

A precise, reproducible, rapid, and highly sensitive spectrophotometric procedure was created for the micro determination of Tetracycline hydrochloride (TCH) in bulk form and pharmaceutical formulation. The suggested method depends on the proton transfer reaction by coupling the substance to be determined with the reagent 2,6-diaminopyridine in the basic medium to form a colored complex that shows the maximum absorption value at the wavelength of 385 nm. To reach the optimum conditions, different factors were studied. It was observed that Beer's law is followed in the range of (3-32 µg/mL) with a molar absorptivity of 18.755 L/mol.cm. The methods indicated a high degree of sensitivity in terms of limit of detection which was described to be as low as 0.137 µg/mL while the quantification limit was 0.458 µg/mL. The average recovery value was 97.45%, and the relative standard deviation value (RSD) was less than 4.3%. The correlation ratio with the detector was 2:1 (drug: reagent). Therefore, the proton transfer reaction was then applied successfully for the quantitative assay of tetracycline in its pharmaceutical preparations with satisfactory results. [ABSTRACT FROM AUTHOR]

This work presents the pH sensing ability of a fluorescent indolin‐3‐imine derivative. Protonation of the weakly basic imine (pKa=8.3 of its conjugate acid) results in a significant red‐shift of the absorption band. The fluorophore acts as a photobase, with a basicity increase of approximately 6 units upon photoexcitation. This behavior promotes excited state proton transfer from weak acids such as protic solvents. The characteristics of the fluorophore enable sensing of water fractions in organic solvents and differentiation between methanol, ethanol, and longer chain alcohols. Initial cell studies indicated the future potential of indolin‐3‐imines as fluorophores for bioimaging applications. [ABSTRACT FROM AUTHOR]

The double proton transfer (PT) reaction has been investigated in the [2,2′‐bipyridyl]‐3‐3′‐diol, a complex molecule where the proton movements is coupled to significant rearrangement of the electronic structure. Moreover, the reaction could be concerted, that is the two protons are exchanged simultaneously, or stepwise, where the two protons are transferred sequentially. To this end, a static exploration of the potential energy surface (PES) was carried together with the analysis of the free‐energy surface (FES), both surfaces being evaluated at density functional theory level and different exchange‐correlation functionals. While the concerted mechanism has been clearly discharged, the characteristics of the stepwise PT significantly depends on the chosen functionals, some suggesting a clear stepwise mechanism characterized by a stable reaction intermediates and two transitions states, whereas other approaches propend for a asynchronous PT, with a single TS. These features appear on both PES and FES, albeit some differences appears due to their different nature. [ABSTRACT FROM AUTHOR]

In this study, quantum mechanical calculations and a semi-classical approach were used to determine fusion the probability (Pfus), fusion barrier distribution (Dfus), and fusion cross section (σfus) for the systems 28Si + 90Zr, 28Si + 92Zr, 28Si + 94Zr, 41K + 28Si, and 45K + 28Si. The semiclassical approach involved the use of the WKB approximation to describe the relative motion between the projectile and target nuclei, and the Continuum Discretized Coupled Channel (CDCC) method of Alder-Winther (AW) to describe the intrinsic motion of the nuclei. The importance of the neutron and the proton transfer and exchange on the calculations of Pfus, Dfus, and σfus for the studied systems. The results showed that the consideration of the coupling-channel calculations for quantum mechanics and a semi-classical approach, are very important to be considered specifically around and below the Coulomb barrier. The results were compared with the measured data and found in reasonable agreement.

The effect of the external electric field on the ground-state tautomerism in 8-(benzo[d]thiazol-2-yl)quinolin-7-ol has been studied by using density functional theory. The compound exists as an enol tautomer (off state) and under the influence of the external electric field a long-range intramolecular proton transfer can occur, placing the tautomeric proton at the quinolyl nitrogen atom (on state). This is a result of the much higher dipole moment of the end keto tautomer and indicates that the external electric field can be used to mimic the implicit solvent effect in tautomeric systems. In the excited state, the further stabilization of the most polar on state leads to a situation when the excited-state intramolecular proton transfer becomes impossible, limiting the intramolecular rotation to the conical intersection region.

This paper is dedicated to the research of phenomena noticed during tests of biodegradable carrageenan-based force and pressure sensors. Peculiar voltage characteristics were noticed during the impact tests. Therefore, the sensors’ responses to impact were researched more thoroughly, defining time-dependent sensor output signals from calibrated energy impact. The research was performed using experimental methods when a free-falling steel ball impacted the sensor material to create relatively definable impact energy. The sensor’s output signal, which is analogue voltage, was registered using an oscilloscope and transmitted to the PC for further analysis. The obtained results showed a very interesting outcome, where the sensor, which was intended to be piezoresistive, demonstrated a combination of behaviour typical for galvanic cells and piezoelectric material. It provides a stable DC output that is sensitive to the applied statical pressure, and in case of a sudden impact, like a hit, it demonstrates piezoelectric behaviour with some particular effects, which are described in the paper as proton transfer in the sensor-sensitive material. Such phenomena and sensor design are a matter of further development and research.

After drawing comparisons between the reaction pathways of cytochrome c oxidase (CcO, Complex 4) and the preceding complex cytochrome bc1 (Complex 3), both being proton pumping complexes along the electron transport chain, we provide an analysis of the reaction pathways in bacterial ba3 class CcO, comparing spectroscopic results and kinetics observations with results from DFT calculations. For an important arc of the catalytic cycle in CcO, we can trace the energy pathways for the chemical protons and show how these pathways drive proton pumping of the vectorial protons. We then explore the proton loading network above the Fe heme a3–CuB catalytic center, showing how protons are loaded in and then released by combining DFT-based reaction energies with molecular dynamics simulations over states of that cycle. We also propose some additional reaction pathways for the chemical and vector protons based on our recent work with spectroscopic support.

Photo induced proton-coupled electron transfer (PCET) reactions comprehend the concerted transfer of an electron from donor to acceptor and a proton along the hydrogen bonded axis in same time scale. Photo-oxidations of hydrogen-bonded phenols by excited-state polyarene are utilized to extract concerted proton−electron transfer reactions rate and hydrogen bonding equilibrium constant. Experiments have examined fluorescence quenching of 7-Methyl benzo[a]pyrene (7-MeB[a]P) in all possible ways in solution phase by phenol-bases pairs (hydrogen bonded adducts) for two phenols, 4-Methoxy phenol (4-MeO PhOH) and 2,6- Dimethoxy phenol (2,6-DiMeo PhOH), and different pyridine derivatives, such as simple Pyridine (Py), 2,4-Dimethylpyridine (DMPy), 2,4,6-Trimethylpyridine (TMPy), 4-(N,N-Dimethylaminopyridine) (DMAPy), along with 1-Methylimidazole (IM). Detection of 7-MeB[a]P anion in femtosecond transient absorption studies and positive kinetic isotope effect confirm the fluorescence quenching of 7-MeB[a]P is due to PCET reaction where photo-oxidations of phenols proceed by intermolecular proton movement of phenolic proton to the base along the hydrogen bond axis concerted with electron transfer to the photo excited 7-MeB[a]P. The systematic fluorescence quenching experiments of 7-MeB[a]P by hydrogen bonded adducts are performed in two different ways: Case-1, variation of base concentration for fixed and dilute solution of 7-MeB[a]P and phenol mixture and Case-2, changing phenol concentration for fixed and dilute solution of 7-MeB[a]P and base. These two data sets are thus well described by non-linear Stern-Volmer type relation, providing a strong validation for the use of these approaches for determining hydrogen bonding equilibrium constants (KHB) along with rate constant (kQB) for PCET reaction. The estimated KHB values are fairly consistence to that observed in typical spectrophotometric method following Mataga-Tsuno relation. Thus, this is a very clear demonstration that the PCET reactions can be used to determine KHB in favourable cases where ground state hydrogen bonding is the essential and necessary condition for PCET reaction to occur.

The discovery of a simple and efficient detection method for biothiols would be scientifically significant due to the crucial role of them in various physiological processes. Recently, a simple fluorescent probe, DEMCA-NBSC, based on coumarin fragments, was developed by Ding et al., and provided an efficient way for real-time sensing of biothiols both in vivo and vitro. Theoretical insights to the fluorescence sensing mechanism of the probe were provided in this work. Details of the electron transfer process in the probe under optical excitation and the fluorescent character of the probe were analyzed using a quantum mechanical method. All these theoretical results could inspire the development of a highly convenient and efficient fluorescent probe to sense biothiols both in vivo and vitro.

Molecular models for tin dioxide nanoparticles containing 1-7 metal atoms and coordinated or constitutive water have been constructed. Dependent on the composition of the models, the coordination number of the tin atom varied from 4 to 6, and that of oxygen was 2 or 3. The considered models contained both terminal (Sn–OH) and bridging (Sn–OH–Sn) hydroxyl groups, and also bridging (Sn–O–Sn) groups. Their equilibrium spatial and electronic structures were calculated using the second-order Møller-Plesset perturbation theory method with the SBKJC valence-only basis set. To assess the gas-phase acidity of the dioxide surface, the deprotonation energy of the studied models was determined. The adsorption energy of water molecules and hydroxide ions on aprotic (incompletely coordinated) tin atoms, which act as Lewis acid centers, was calculated. In order to estimate the pKa value of the surface of tin dioxide, the Gibbs free energy was calculated for the process of formation of ion pairs due to the proton transfer from hydroxyl groups to adsorbed water molecules. Based on the analysis of the energy effects of the coordination of water molecules and of hydroxide ion, the removal of a proton and its transfer on the hydrated surface of tin dioxide, quantitative estimates have been made of the acid-base characteristics of the active sites of the SnO2 surface. The dependence of the acidity of hydroxyl groups and coordinated water molecules on the coordination number of the oxygen atom and the neighboring tin atom, as well as on the dimensions of the cluster model, was revealed. It is shown that the acidity of protonic and aprotic sites naturally decreases with an increase in the coordination number of the tin atom. The method of calculating the value of pKa used in the work for the smallest model of the SnO2.2H2O composition allows one to reproduce the experimental data for stannic acids. [ABSTRACT FROM AUTHOR]

Oxidative ring cleavage reactions have attracted great interest and various studies on the catechol ring-cleaving enzyme homoprotocatechuate dioxygenase (HPCD) have been reported in the literature. The available data on how the proton transfer takes place led us to design a potential HPCD model structure. A secondary sphere effect of utmost importance, the assistance of His200, which is critical for the catechol proton to migrate to dioxygen, was cautiously included on the first coordination shell. This was done mainly by modifying the axial ligands in the first coordination shell of HPCD such that the dual basic/acidic role in the proton transfer pathway of His200 was reproduced. Model systems with mono-, bi-, and tridentate ligands are reported. Energetically feasible reaction channels on synthetically promising ligand structures are identified. Key structural and electronic principles for obtaining viable proton transfer paths are outlined. [ABSTRACT FROM AUTHOR]

Here, we present a parametrization of the metadynamics simulations for reactions involving breaking the chemical bonds along a single collective variable coordinate. The parameterization is based on the similarity between the bias potential in metadynamics and the quantum potential in the de Broglie–Bohm formalism. We derive the method and test it on two prototypical reaction types: proton transfer and breaking of the cyclohexene cycle (reversed Diels–Alder reaction). [ABSTRACT FROM AUTHOR]

Laccases are industrially relevant enzymes. However, their range of applications is limited by their functioning and stability. Most of the currently known laccases function in acidic conditions at temperatures below 60 °C, but two-domain laccases (2D) oxidize some substrates in alkaline conditions and above 70 °C. In this study, we aim to establish the structural factors affecting the alkaline activity of the 2D laccase from Streptomyces griseoflavus (SgfSL). The range of methods used allowed us to show that the alkaline activity of SgfSL is influenced by the polar residues located close to the trinuclear center (TNC). Structural and functional studies of the SgfSL mutants Met199Ala/Asp268Asn and Met199Gly/Asp268Asn revealed that the substitution Asp268Asn (11 Å from the TNC) affects the orientation of the Asn261 (the second coordination sphere of the TNC), resulting in hydrogen-bond-network reorganization, which leads to a change in the SgfSL-activity pH profile. The combination of the Met199Gly/Arg240His and Asp268Asn substitutions increased the efficiency (kcat/KM) of the 2,6-DMP oxidation by 34-fold compared with the SgfSL. Our results extend the knowledge about the structure and functioning of 2D laccases' TNC active sites and open up new possibilities for the directed engineering of laccases. [ABSTRACT FROM AUTHOR]

Context: Proton transfer in acid–base systems is not well understood. Some acid–base reactions do not proceed to the extent that is expected from the difference in the pKa values between the base and acid in aqueous solutions, yet some do. In that regard, we have computationally studied the process of proton transfer from the acids of varying strength (benzenesulfonic acid (BSu), methansulfonic acid (MsO), and sulfuric acid (SA)) to the amines with different numbers of propyl substituents on the nitrogen atom (propylamine (PrA), dipropylamine (DPrA), and tripropylamine (TPrA)) upon complexation. Density functional theory calculations were used to thoroughly examine the energetic and structural aspects of the molecular complexes and/or ionic pairs resulting from the acid–base interaction. The potential energy curves along the proton transfer coordinate in these acid–amine systems were analyzed. The change in free energies accompanying the molecular complexes and ionic pair formations was calculated, and the relationship between the energy values and the ΔРА parameter (difference in proton affinity of the acid anion and amine) was established. The larger ΔРА values were found to be unfavorable for the formation of ionic pairs. Using structural, energy, QTAIM, and NBO analyses, we determined that the hydrogen bonds in the molecular complexes PrA-MsO and PrA-BSu are stronger than those in their corresponding ionic pairs. The ionic pairs with the TPrA cation possess the strongest hydrogen bonds of all the ionic pairs being studied, regardless of the anion. The results showed that hydrogen bonding interactions in the molecular complexes contribute significantly to the energies of the acid–base interaction, while in the ionic pairs, the most important energy contribution comes from Coulomb interactions, followed by hydrogen bonding and dispersion forces. The ionic pairs with propylammonium, dipropylammonium, and tripropylammonium cations have stronger ion–ion interactions than tetrapropylammonium (TetPrA)-containing ionic pairs with the same anions. This effect rises with the order of the cation: TetPrA → TPrA → DPrA → PrA, and the sequence of anions is SA → BSu → MsO. The results obtained here expand the concept of acid–base interaction and provide an alternative to experimental searches for suitable acids and bases to obtain new types of protic ionic liquids. Methods: All quantum-chemical calculations were carried out by using the DFT/B3LYP-GD3/6-31++G(d,p) level as implemented in the Gaussian 09 software package. For the resulting structures, the electron density distribution was analyzed by the "atoms in molecules" (QTAIM) and the natural bond orbital (NBO) methods on the wave functions obtained at the same level of theory by AIMAll Version 10.05.04 and Gaussian NBO Version 3.1 programs, respectively. [ABSTRACT FROM AUTHOR]

Phosphate is an indispensable metabolite in a wide variety of cells and is involved in nucleotide and lipid synthesis, signaling, and chemical energy storage. Proton-coupled phosphate transporters within the major facilitator family are crucial for phosphate uptake in plants and fungi. Similar proton-coupled phosphate transporters have been found in different protozoan parasites that cause human diseases, in breast cancer cells with elevated phosphate demand, in osteoclast-like cells during bone reabsorption, and in human intestinal Caco2BBE cells for phosphate homeostasis. However, the mechanism of proton-driven phosphate transport remains unclear. Here, we demonstrate in a eukaryotic, high-affinity phosphate transporter from Piriformospora indica (PiPT) that deprotonation of aspartate 324 (D324) triggers phosphate release. Quantum mechanics/molecular mechanics molecular dynamics simulations combined with free energy sampling have been employed here to identify the proton transport pathways from D324 upon the transition from the occluded structure to the inward open structure and phosphate release. The computational insights so gained are then corroborated by studies of D45N and D45E amino acid substitutions via mutagenesis experiments. Our findings confirm the function of the structurally predicted cytosolic proton exit tunnel and suggest insights into the role of the titratable phosphate substrate.

We report a detailed investigation of the vibrational modes, structure, and dynamics of glutathione (GSH) solutions using ultrasonic relaxation spectroscopy, FT-IR vibrational spectroscopy, and electronic absorption measurements. The experimental data were analyzed using density functional theory (DFT) and molecular docking calculations. Three distinct Debye-type relaxation processes can be observed in the acoustic spectra, which are assigned to conformational changes between GSH conformers, the self-association of GSH, and protonation processes. The standard volume changes for each process were estimated both experimentally and theoretically, revealing a close resemblance among them. The higher the effect of the relaxation process in the structure, the greater the induced volume changes. From the temperature dependence of specific acoustic parameters, the thermodynamic characteristics of each process were determined. The experimental FT-IR spectra were compared with the corresponding theoretically predicted vibrational spectra, revealing that the GSH dimers and extended conformers dominate the structure of GSH solutions in the high-concentration region. The absorption spectra in the ultraviolet region confirmed the gradual aggregation mechanism that takes place in the aqueous GSH solutions. The results of the present study were discussed and analyzed in the framework of the current phenomenological status of the field.

BaSnO 3 is a relatively new family of proton-conducting materials, which are attractive for high-temperature applications, including protonic ceramic fuel cells and protonic ceramic electrolysis cells. In this work, we synthesized the BaSn 1–x Y x O 3–δ (0 ≤ x ≤ 0.4) phases and provided their in-depth characterization utilizing high-temperature X-ray diffraction and dilatometry techniques to reveal the fundamental regularities in the variations of chemical and thermal strains depending on composition. It is found that chemical expansion/contraction effects become to be more important with increasing the Y-content. In particular, the weakly doped stannates exhibit predominantly thermal expansion, while the heavily doped stannates (especially, x = 0.4) display a notable chemical contribution. The mentioned effects are discussed in terms of the BaSn 1–x Y x O 3–δ defect structure and its ability towards hydration and dehydration. This work therefore provides valuable data for the real application of the studied materials (in both powder and ceramic forms) as well as other pronounced proton-conducting electrolytes. [Display omitted] [ABSTRACT FROM AUTHOR]

Field and laboratory observations strongly support the view that the development of electric fields in thunderstorms is caused by charge separation during rebounding collisions between ice crystals and graupels, followed by their gravitational separation. Although several plausible microphysical mechanisms have been proposed to explain the physics of charge separation, none have been found to be fully consistent with the experimental evidence, and a fresh approach is necessary. We propose a new mechanism for charge separation in ice‐ice collisions based on the fundamental molecular mechanism of charge transport in ice, involving the diffusion of H+ ions (excess protons or positive ionic defects) via a proton hopping relay along the hydrogen‐bond network of ice and the trapping and release of H+ ions from L‐orientational defects. The collision of two ice particles leads to the formation of a transient crystalline ice bridge at the contact point, which is spontaneously driven by the tendency for ice sintering, permitting rapid H+ diffusion between the two particles. Charge separation is achieved by the asymmetry in the concentrations of H+ ions or L‐orientational defects between the two ice surfaces. The proposed H+ transport mechanism successfully explains the direction and magnitude of charge transfer as well as its dependence on the relative growth rates of the two ice surfaces observed in laboratory studies. In addition, it offers a molecular‐level interpretation of the empirical rule that, during a collision, the faster‐growing ice surface is positively charged at the expense of negative charging of the slower‐growing or sublimating ice surface. Plain Language Summary: It is now generally accepted that the separation of charge in thunderclouds occurs during rebounding collisions between ice crystals and soft rime (graupel), followed by their gravitational separation. Although several plausible microphysical mechanisms have been proposed to explain the physics of charge separation, none have been found to be fully consistent with the experimental evidence, and a fresh approach is necessary. We propose a new molecular‐scale model for charge separation during ice particle collisions based on the rapid diffusion of H+ ions in ice, and their interaction with defects in ice. The charge is transferred across a transient crystalline ice bridge at the contact point. We show how the model successfully explains the direction and magnitude of charge transfer as well as its dependence on the relative growth rates of the two ice surfaces observed in laboratory studies. In addition, it offers a molecular‐level interpretation of the empirical rule that, during a collision, the faster‐growing ice surface is positively charged at the expense of negative charging of the slower‐growing or sublimating ice surface. Key Points: A new molecular‐scale model for charge separation during ice particle collisions is proposed, based on properties of pure ice aloneA crystalline ice bridge formed during the collision is the conduit for charge transfer via proton diffusion and trapping in L‐defectsThe model offers a quantitative explanation for the charge separation between colliding ice surfaces in the Mason‐Dash experiment [ABSTRACT FROM AUTHOR]

Electrochemical CO2 reduction reaction (CO2RR) is crucial to addressing environmental crises and producing chemicals. Proton activation and transfer are essential in CO2RR. To date, few research reviews have focused on this process and its effect on catalytic performance. Recent studies have demonstrated ways to improve CO2RR by regulating proton transfer dynamics. This Concept highlights the use of regulating proton transfer dynamics to enhance CO2RR for the target product and discusses modulation strategies for proton transfer dynamics and operative mechanisms in typical systems, including single‐atom catalysts, molecular catalysts, metal heterointerfaces, and organic‐ligand modified metal catalysts. Characterization methods for proton transfer dynamics during CO2RR are also discussed, providing powerful tools for the hydrogen‐involving electrochemical study. This Concept offers new insights into the CO2RR mechanism and guides the design of efficient CO2RR systems. [ABSTRACT FROM AUTHOR]

Hydrogen is a promising alternative to fossil fuels that can reduce greenhouse gas emissions. Decoupled water electrolysis system using a reversible proton storage redox mediator, where the oxygen evolution reaction and hydrogen evolution reaction are separated in time and space, is an effective approach to producing hydrogen gas with high purity, high flexibility, and low cost. To realize fast hydrogen production in such a system, a redox mediator capable of releasing protons rapidly is required. Herein, α‐MoO3, with an ultrafast proton transfer property that can be explained by a dense hydrogen bond network in the lattice oxygen arrays of HxMoO3, is examined as a high‐rate redox mediator for fast hydrogen production in acidic electrolytes. The α‐MoO3 redox mediator shows both a large capacity of 204 mAh g−1 and fast hydrogen production at a current rate of 10 A cm−2(≈153 A g−1), outperforming most of the previously reported solid‐state redox mediators. [ABSTRACT FROM AUTHOR]

From an academic and practical point of view, it is desirable to be able to assess the possibility of the proton exchange of a given molecular system just by knowing the positions of the proton acceptor and the proton donor. This study addresses the difference between intramolecular hydrogen bonds in 2,2′-bipyridinium and 1,10-phenanthrolinium. Solid-state 15N NMR and model calculations show that these hydrogen bonds are weak; their energies are 25 kJ/mol and 15 kJ/mol, respectively. Neither these hydrogen bonds nor N-H stretches can be responsible for the fast reversible proton transfer observed for 2,2′-bipyridinium in a polar solvent down to 115 K. This process must have been caused by an external force, which was a fluctuating electric field present in the solution. However, these hydrogen bonds are the grain that tips the scales precisely because they are an integral part of a large system of interactions, including both intramolecular interactions and environmental influence. [ABSTRACT FROM AUTHOR]

It has been shown for acetylacetone as an example that the intramolecular hydrogen bond significantly affects the radiolytic transformations of organic compounds by suppressing the proton transfer from the primary radical cation to the molecule and also by promoting cleavage of the C–OH bond in the enol form. Due to these effects, the major heavy product of radiolysis at 295 K is 4-oxopent-2-en-2-yl acetate. Under boiling conditions (413 K), hydrogen bonds are cleaved, resulting in the predominant formation of 4-hydroxy-2-pentanone, which is not detected at 295 K. [ABSTRACT FROM AUTHOR]