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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 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]

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]

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]

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.

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]

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]

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]

The interaction between (PNP)PdH (1); PNP = bis(2-diisopropylphosphino-4-methylphenyl)amide and different acids (CF3SO3H, HBF4∙Et2O, fluorinated alcohols and formic acid) was studied in benzene or toluene as well as in neat alcohols by IR and NMR spectroscopies. The structures of hydrogen-bonded complexes were also optimized at the DFT/ωB97-XD/def2-TZVP level. The nitrogen atom of the amidophosphine pincer ligand readily accepts proton not only from strong Brønsted acids but from relatively weak fluorinated alcohols. That suggests that binding to palladium(II) increases the diarylamine basicity, making it a strong base. Nevertheless, H+ can be taken from [(PN(H)P)PdH]+ (2) by pyridine or hexamethylphosphoramide (HMPA). These observations confirm the need for a shuttle base to form [(PN(H)P)PdH]+ (2) as the result of the heterolytic splitting of H2 by [(PNP)Pd]+. At that, a stoichiometric amount of formic acid protonates a hydride ligand yielding an unstable η2-H2 complex that rapidly converts into formate (PNP)Pd(OCHO), which loses CO2 to restore (PNP)PdH, whereas the relatively high acid excess hampers this reaction through competitive protonation at nitrogen atom. [ABSTRACT FROM AUTHOR]

The Nep1 protein is essential for the formation of eukaryotic and archaeal small ribosomal subunits, and it catalyzes the site-directed SAM-dependent methylation of pseudouridine (Ψ) during pre-rRNA processing. It possesses a non–trivial topology, namely, a 31 knot in the active site. Here, we address the issue of seemingly unfeasible deprotonation of Ψ in Nep1 active site by a distant aspartate residue (D101 in S. cerevisiae), using a combination of bioinformatics, computational, and experimental methods. We identified a conserved hydroxyl-containing amino acid (S233 in S. cerevisiae, T198 in A. fulgidus) that may act as a proton-transfer mediator. Molecular dynamics simulations, based on the crystal structure of S. cerevisiae, and on a complex generated by molecular docking in A. fulgidus, confirmed that this amino acid can shuttle protons, however, a water molecule in the active site may also serve this role. Quantum-chemical calculations based on density functional theory and the cluster approach showed that the water-mediated pathway is the most favorable for catalysis. Experimental kinetic and mutational studies reinforce the requirement for the aspartate D101, but not S233. These findings provide insight into the catalytic mechanisms underlying proton transfer over extended distances and comprehensively elucidate the mode of action of Nep1.

Modern Chemistry education shows acid-base reactions by proton transfer with regard to Bronsted’s theory. Understanding how protons can be transferred by particles in solutions is quite challenging. The study aims to presents how university-first-year students are figuring out involved particles which take and give protons. Further, the enrolled participants in this study should explain how the process of proton transfer is running by selected particles but not by substances. Fifty-four students participated in this study that started from revealing participant’s experiences on their previous education at senior high school. Subsequently, researchers conducted a pretest, learning planning, and learning implementation, finally a posttest. Qualitative analysis is preferred to analyze students’ conceptions on particle level. The result shows us that there are two categories of participant’s difficulties. First is determining the involved particles either all particles or reacting particles. The difficulties dominate on mixing terminology of atoms, ions, and molecules, also on preferences of memorizing and calculating oxidation state for chemical equations. The subsequent difficulty is the proton transfer process that caused by participant’s failure on how they selected reacting particles. The systematic sequence on introducing and interpreting chemical equations has also presented as breakthrough.

CoFe2O4 is a promising catalytic material for many chemical reactions. We used ab initio molecular dynamic simulations to study the structure and reactivity of the A- and B-terminations of the low-index CoFe2O4(001) surfaces to water adsorption at room temperature. Upon adsorption, water partly dissociates on both termination with a higher dissociation degree on the A-termination (30% versus 19%). The 2-fold coordinated Fe3+(tet) in the tetrahedral voids and the 5-fold coordinated Fe3+(oct) in the octahedral voids are the main active sites for water dissociation on the A- and B-termination, respectively. Molecular water, hydroxydes, and surface OH resulting from proton transfer to surface oxygens are present on the surfaces. Both water-free surface terminations undergo reconstruction. The outermost Fe3+(tet) on the A-termination and B-termination move towards the nearby unoccupied octahedral voids. In the presence of a thin film of 32 water molecules, the reconstructions are partially and completely lifted on the A- and B-termination, respectively.

Acid-base characteristics (acidity, pKa, and hydricity, ΔG°H− or kH−) of metal hydride complexes could be a helpful value for forecasting their activity in various catalytic reactions. Polarity of the M–H bond may change radically at the stage of formation of a non-covalent adduct with an acidic/basic partner. This stage is responsible for subsequent hydrogen ion (hydride or proton) transfer. Here, the reaction of tricarbonyl manganese hydrides mer,trans–[L2Mn(CO)3H] (1; L = P(OPh)3, 2; L = PPh3) and fac–[(L–L′)Mn(CO)3H] (3, L–L′ = Ph2PCH2PPh2 (dppm); 4, L–L′ = Ph2PCH2–NHC) with organic bases and Lewis acid (B(C6F5)3) was explored by spectroscopic (IR, NMR) methods to find the conditions for the Mn–H bond repolarization. Complex 1, bearing phosphite ligands, features acidic properties (pKa 21.3) but can serve also as a hydride donor (ΔG≠298K = 19.8 kcal/mol). Complex 3 with pronounced hydride character can be deprotonated with KHMDS at the CH2–bridge position in THF and at the Mn–H position in MeCN. The kinetic hydricity of manganese complexes 1–4 increases in the order mer,trans–[(P(OPh)3)2Mn(CO)3H] (1) < mer,trans–[(PPh3)2Mn(CO)3H] (2) ≈ fac–[(dppm)Mn(CO)3H] (3) < fac–[(Ph2PCH2NHC)Mn(CO)3H] (4), corresponding to the gain of the phosphorus ligand electron-donor properties. [ABSTRACT FROM AUTHOR]

The adoption of cocrystals into oral pharmaceutical formulations is expected to propel this, as yet, moribund field into clinical and monetary prominence. The increase in resources and research that will inevitably follow is expected to address long standing problems in crystal engineering. Ab initio predictions of heterosynthon structure, identification of molecular descriptors to enable bioavailability enhancing coformer selection and a priori prediction of the cocrystal lattice have thus far been insoluble. Solutions to the prediction of supersaturation levels and polymorphic transition of the cocrystal formulated API in GI fluids, and solvation barrier and solubilization free energies, remain empirical. Properties such as on-demand/environment, formulation enabled, proton transfer between API and coformer and the development of neural networks or AI, trained on empirical data to predict ideal API-coformer pairs without the need to explicitly understand mechanisms, remain obscure, and hence un-researched. It is ironic that failure mechanisms that result in the delayed appearance of a less-soluble polymorph in pharmaceutical formulations (disappearing polymorphs) could (and should) be gainfully utilized to facilitate the delayed appearance in vivo of less-soluble polymorph(s) in cocrystal formulations. The bioavailability increase afforded by cocrystal formulations has the potential to enable greater patient compliance due to favorable posology, introduce more efficacious drugs into the therapeutic armamentarium, enable line-extensions and expand intellectual property portfolios, reduce the cost-of-goods; and hence of medicines, and add one more valuable tool in the repertoire of the pharmaceutical formulation scientist. [ABSTRACT FROM AUTHOR]

Sulfamethazine [N1‐(4,6‐dimethylpyrimidin‐2‐yl)sulfanilamide] is an antimicrobial drug that possesses functional groups capable of acting as hydrogen‐bond donors and acceptors, which make it a suitable supramolecular building block for the formation of cocrystals and salts. We report here the crystal structure and solid‐state characterization of the 1:1 salt piperidinium sulfamethazinate (PPD+·SUL−, C5H12N+·C12H13N4O2S−) (I). The salt was obtained by the solvent‐assisted grinding method and was characterized by IR spectroscopy, powder X‐ray diffraction, solid‐state 13C NMR spectroscopy and thermal analysis [differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)]. Salt I crystallized in the monoclinic space group P21/n and showed a 1:1 stoichiometry revealing proton transfer from SUL to PPD to form salt I. The PPD+ and SUL− ions are connected by N—H+...O and N—H+...N interactions. The self‐assembly of SUL− anions displays the amine–sulfa C(8) motif. The supramolecular architecture of salt I revealed the formation of interconnected supramolecular sheets. [ABSTRACT FROM AUTHOR]

Criegee intermediates (CIs) are important zwitterionic oxidants in the atmosphere, which affect the budget of OH radicals, amines, alcohols, organic/inorganic acids, etc. In this study, quantum chemical calculation and Born–Oppenheimer molecular dynamic (BOMD) simulation were performed to show the reaction mechanisms of C2 CIs with glycolic acid sulfate (GAS) at the gas-phase and gas–liquid interface, respectively. The results indicate that CIs can react with COOH and OSO3H groups of GAS and generate hydroperoxide products. Intramolecular proton transfer reactions occurred in the simulations. Moreover, GAS acts as a proton donor and participates in the hydration of CIs, during which the intramolecular proton transfer also occurs. As GAS widely exists in atmospheric particulate matter, the reaction with GAS is one of the sink pathways of CIs in areas polluted by particulate matter. [ABSTRACT FROM AUTHOR]

The manuscript “Ionic Liquid Induced p-Nitrophenol Prototropism” deals with the acid-base properties of p-Nitrophenol molecule in the presence of two different Ionic Liquids (ILs). Prototropic equilibria of p-Nitrophenol (PNP) have been studied in water, ethanol, carbon tetrachloride, chloroform, cyclohexane and IL added aqueous solution with the help of Uv-vis absorbance spectroscopy. It was found that PNP mainly exists in neutral form when dissolved in ethanol, carbon tetrachloride, chloroform and cyclohexane. Interestingly, ground state ionization of PNP takes place in water and results into the formation of p-Nitrophenolate anion as a result of proton transfer to water and hence two absorbing species have been detected in the absorbance spectra. Inter-conversion of neutral to anionic and vice versa can be achieved with the addition of small amount of NaOH/HCl. Furthermore, in water/ethanol binary mixture both neutral and anionic forms exist. Interactions of surfactants sodium dodecyl sulfate (SDS) and cetrimonium bromide (CTAB) with neutral and ionic forms of PNP is also explored. To assess the potential role of ILs as a solubilizing media that facilitates proton-transfer reactions, p-Nitrophenol prototropism is investigated in water in the presence of small amount of added ILs. Interestingly, addition of small amount of hydrophilic IL, 1-butyl-3-methylimidazolium tetrafluoroborate [bmim][BF4] or hydrophobic IL, 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6] into PNP dissolved in high pH water causes protonation of the already present p-Nitrophenolate anion. Protonation of p-Nitrophenolate is attributed due to presence of acidic C2-H protons in [bmim]+ cations associated with both ILs. Furthermore, the extent of protonation induced by addition of [BF4]− based IL is found to be much pronounced as compared to [PF6]− based IL having same cation due to difference in hydrolytic properties of [BF4]− based ILs when compared with [PF6]− based ILs. These findings could contribute to the technological applications for detection, removal and sensing of environmentally hazardous p-Nitrophenol and its ionic forms from water. The results presented in this work lead to a better understanding of prototropic behavior of PNP in IL based media as well as different organic solvents based media.

In this review, we have attempted to briefly summarize the influence of an external electric field on an assembly of tautomeric molecules and to what experimentally observable effects this interaction can lead to. We have focused more extensively on the influence of an oriented external electric field (OEEF) on excited-state intramolecular proton transfer (ESIPT) from the studies available to date. The possibilities provided by OEEF for regulating several processes and studying physicochemical processes in tautomers have turned this direction into an attractive area of research due to its numerous applications. [ABSTRACT FROM AUTHOR]

Using hydrogen as a fuel is an effective way to combat energy crisis and at the same time reduce greenhouse gas emission. Alkaline hydrogen evolution reaction (HER) is one important way to obtain green hydrogen, which however is energy intensive and is difficult to obtain high efficiencies even when using state-of-the-art noble metal catalysts. Here, we report a three-component catalytic system using only non-noble elements, consisting of cobalt oxide clusters and single molybdenum atoms supported on oxyanion-terminated two-dimensional MXene, which enabled the unusual generation of hydrogen by a kinetically fast Volmer-Tafel process in an alkaline electrolyte. The key feature of this catalyst is that the three components are connected by bridging oxygen, which serves to immediately adsorb H* produced during water dissociation on cobalt oxide and relay it to the molybdenum single-atom catalyst. On the Mo atom, due to this unique coordination environment, the relayed H* intermediates directly combine and desorb, realizing H2 generation through an unusual Tafel pathway. The presence of bridging oxygen increases the acidity of the catalyst as Brønsted acid with the reversible adsorption and donation of a proton, thus eliminating the need for acid addition and ensuring excellent and sustainable alkaline HER performance. The performance of our catalyst is comparable to that of the commercial noble metal catalyst PtRu/C. Our work makes a significant contribution to designing efficient non-noble catalysts for alkaline HER electrocatalysis. [ABSTRACT FROM AUTHOR]

Deprotonation of a bis(amino)phosphane H2L = PhP(HNBtd)2 bearing a heterocyclic Btd = 2,1,3-benzothiadiazol-4-yl substituents at nitrogen atoms by silylamides LiNTms2 and Y(NTms2)3 (Tms = trimethylsilylamide) results in lithium and yttrium complexes with the deprotonated HL– and L2– forms as κ2-N and κ4-N chelating ligands. A binuclear complex [LiHL]2 was crystallized from Et2O, and was shown to reversibly dissociate in thf (tetrahydrofuran) with the NH(soln)–PH(crystal) tautomeric shift; the compound [Li2L] was spectroscopically characterized. Yttrium readily forms stable bis-ligand complexes [YL2]– and [YL(HL)]. In the latter, the H atom in HL resides on phosphorus; the coordination sphere remains accessible to another ligands, and it was crystallized as [{YL(HL)}2(µ-dioxane)] species (YN8O coordination). In the former complex, the coordination sphere was saturated (YN8) by closer bound ligands; it was crystallized as a salt with [Li(thf)4]+. The monoligand complex could not be cleanly obtained in a 1:1 reaction of H2L and Y(NTms2)3, and was only crystallographically characterized as a dimer [YL(NTms)2]2. Partial oxidation of the central P atom with the formation of phosphine-oxide ligands PhP(O)(NBtd)2– was observed. They co-crystallize in the same position as non-oxidized ligands in [YL2]– and [YL(NTms2)]2 species and participate in bonding between two units in the latter. TD-DFT calculations reveal that main transitions in the visible region of electronic spectra correspond to the charge transfer bands mostly associated with the orbitals located on Btd fragments. [ABSTRACT FROM AUTHOR]

An organic–inorganic cation–anion manganese(II) tetrabromide compound with diprotonated 1-hydroxy-2-(pyridin-2-yl)-4,5,6,7-tetrahydrobenzimidazole, [H3L][MnBr4][H2O], has been synthesized and investigated. The compound has a few possible pathways for proton transfers, which play an important role in the observed luminescence, optical, and magnetic properties. The proton transfers result in the appearance of two-band luminescence. One band is caused by the Mn(II) d-d transitions. The other band is caused by the transition from the triplet state of organic cation and the d-d transition of manganese(II) coupled through {[H3L]}-{[MnBr4]}-{[H2O]} vibrations. The optical absorption spectra of [H3L][MnBr4][H2O] indicate the presence of two direct and one indirect band transitions. The reason for the two-band luminescence and complex optical absorption in [H3L][MnBr4][H2O] were additionally considered using the DFT calculations. [ABSTRACT FROM AUTHOR]

The affinity of [β-Mo8O26]4− toward different proton sources has been studied in various conditions. The proposed sites for proton coordination were highlighted with single crystal X-ray diffraction (SCXRD) analysis of (Bu4N)3[β-{Ag(py-NH2)Mo8O26]}] (1) and from analysis of reported structures. Structural rearrangement of [β-Mo8O26]4− as a direct response to protonation was studied in solution with 95Mo NMR and HPLC-ICP-AES techniques. A new type of proton transfer reaction between (Bu4N)4[β-Mo8O26] and (Bu4N)4H2[V10O28] in DMSO results in both polyoxometalates transformation into [V2Mo4O19]4−, which was confirmed by the 95Mo, 51V NMR and HPLC-ICP-AES techniques. The same type of reaction with [H4SiW12O40] in DMSO leads to metal redistribution with formation of [W2Mo4O19]2−. [ABSTRACT FROM AUTHOR]

CoFe 2 O 4 is a promising catalytic material for many chemical reactions. We used ab initio molecular dynamic simulations to study the structure and reactivity of the A- and B-terminations of the low-index CoFe 2 O 4 (001) surfaces to water adsorption at room temperature. Upon adsorption, water partly dissociates on both termination with a higher dissociation degree on the A-termination (30% versus 19%). The 2-fold coordinated Fe3+(tet) in the tetrahedral voids and the 5-fold coordinated Fe3+(oct) in the octahedral voids are the main active sites for water dissociation on the A- and B-termination, respectively. Molecular water, hydroxydes, and surface OH resulting from proton transfer to surface oxygens are present on the surfaces. Both water-free surface terminations undergo reconstruction. The outermost Fe3+(tet) on the A-termination and B-termination move towards the nearby unoccupied octahedral voids. In the presence of a thin film of 32 water molecules, the reconstructions are partially and completely lifted on the A- and B-termination, respectively. [ABSTRACT FROM AUTHOR]

Cytochrome c oxidase is a membrane protein of the respiratory chain that consumes protons and molecular oxygen to produce water and uses the resulting energy to pump protons across the membrane. Our molecular dynamics simulations with an excess proton located at different positions in one of the proton-conducting channels, the K-channel, show a clear dependence of the number of water molecules inside the channel on the proton position. A higher hydration level facilitates the formation of hydrogen-bonded chains along which proton transfer can occur. However, a sufficiently high hydration level for such proton transport is observed only when the excess proton is located above S365, i.e., the lower third of the channel. From the channel entrance up to this point, proton transport is via water molecules as proton carriers. These hydronium ions move with their surrounding water molecules, up to K362, filling and widening the channel. The conformation of K362 depends on its own protonation state and on the hydration level, suggesting its role to be proton transport from a hydronium ion at the height of K362 to the upper part of the channel via a conformational change. The protonation-dependent conformational dynamics of E101 at the bottom of the channel renders proton transfer via E101 unlikely. Instead, its role is rather that of an amplifier of H96's proton affinity, suggesting H96 as the initial proton acceptor. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel strategy was used in superior pRTP properties in highly polar polymer matrix. • A consecutive proton transfer and photo-induced charge transfer strategy to achieve 3CT emission. • The doped films are successfully employed for inkjet printings of information encryption. The intermolecular interactions between small molecules and the matrix in a highly polar environment could easily lead to non-radiative transitions, which significantly hampers the development of high-performance persistent room-temperature phosphorescence (pRTP) materials in such condition. Herein, we introduce a novel strategy that integrates consecutive proton transfer and photo-induced charge transfer to facilitate triplet charge transfer emission in highly polar polymer matrix. In particular, doping aza-arene guests including 1,10-phenanthroline (1,10-Phen), 2,9-dimethyl-1,10-phenanthroline (DM-Phen), and 7,8-benzoquinoline (7,8-BQ) into polyacrylic acid (PAA) resulted in superior pRTP properties compared to other polymer hosts. Spectroscopic investigations and theoretical calculations elucidate that this is attributed to the proton transfer and triplet charge transfer characteristics between the host and guest. Moreover, due to the rigid environment and space confinement provided by PAA, pRTP with the lifetime up to 841 ms is achieved. Capitalizing on the excellent water solubility of the doped PAA films, the inkjet printings have been executed, and showcasing the promising the potential applications of these pRTP materials in the field of information encryption. [ABSTRACT FROM AUTHOR]

[Display omitted] • Introducing "bisartans, novel sartan-like ARBs • ACC519T has promising antiviral abilities by strongly binding to the centre of ACE2 • BV6(K+) 2 markedly increases ACE2 activity by decreased AngII and increased Ang(1-7) • Bisartans are appealing COVID-19 treatment due to anti-viral and -hypertensive effects The binding affinities and interactions between eight drug candidates, both commercially available (candesartan; losartan; losartan carboxylic acid; nirmatrelvir; telmisartan) and newly synthesized benzimidazole- N -biphenyltetrazole (ACC519T), benzimidazole bis-N,Nʹ-biphenyltetrazole (ACC519T(2) and 4-butyl-N, N -bis([2-(2H-tetrazol-5-yl)biphenyl-4-yl]) methyl (BV6), and the active site of angiotensin-converting enzyme-2 (ACE2) were evaluated for their potential as inhibitors against SARS-CoV-2 and regulators of ACE2 function through Density Functional Theory methodology and enzyme activity assays, respectively. Notably, telmisartan and ACC519T(2) exhibited pronounced binding affinities, forming strong interactions with ACE2′s active center, favorably accepting proton from the guanidinium group of arginine273. The ordering of candidates by binding affinity and reactivity descriptors, emerged as telmisartan > ACC519T(2) > candesartan > ACC519T > losartan carboxylic acid > BV6 > losartan > nirmatrelvir. Proton transfers among the active center amino acids revealed their interconnectedness, highlighting a chain-like proton transfer involving tyrosine, phenylalanine, and histidine. Furthermore, these candidates revealed their potential antiviral abilities by influencing proton transfer within the ACE2 active site. Furthermore, through an in vitro pharmacological assays we determined that candesartan and the BV6 derivative, 4-butyl-N,N0-bis[20-2 Htetrazol -5- yl) bipheyl -4- yl ]methyl)imidazolium bromide (BV6(K+) 2) also contain the capacity to increase ACE2 functional activity. This comprehensive analysis collectively underscores the promise of these compounds as potential therapeutic agents against SARS-CoV-2 by targeting crucial protein interactions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Effect of Twisted Structure on Properties. • Novel salicylaldehyde Schiff bases with progressive thermochromic behavior and AIE properties. • Probed its proton transfer process. Great attention has been attracted to the salicylaldehyde Schiff base due to its thermochromic and photochromic characteristics in the solid state. However, the boundary between photochromic and thermochromic salicylaldehyde Schiff base structures is still unclear, and few studies have been conducted to investigate their thermochromic behavior and structures in depth and systematically. In the present work, we have synthesized a novel salicylaldehyde Schiff base derivative (2,2′-((1E,1′E)-((2,2′-bis(trifluoromethyl)-[1,1′-biphenyl]-4,4′-diyl)-bis(azaneylylidene))bis(methaneylylidene))diphenol, BTB) with twisted structure, which possesses both thermochromic and aggregation-induced emission (AIE) characteristics, and systematically investigated its thermochromic properties, enol-keto isomerization, AIE properties, aggregated state, and excited state intramolecular proton transfer (ESIPT) process. Interestingly, in our study, we found that the color of the BTB molecule changed gradually during the heating process, and it can be found that the thermochromism of BTB is produced by the reversible equilibrium shift of the enol form and the keto forms due to the temperature change by the color difference test, the in-situ IR spectra and the DSC curves. Finally, the pathway of BTB proton transfer was analyzed through quantum chemical calculations, and it was found that enol ketone isomerization is achieved through single excited state intramolecular proton transfer, rather than the expected double excited state intramolecular proton transfer. [ABSTRACT FROM AUTHOR]

A recently proposed reaction mechanism of soluble Δ9 desaturase (Δ9D) allowed us to identify auxiliary residues His203, Asp101, Thr206 and Cys222 localized near the di-iron active site that are supposedly involved in the proton transfer (PT) to and from the active site. The PT, along with the electron transfer (ET), seems to be crucial for efficient desaturation. Thus, perturbing the major PT chains is expected to impair the native reaction and (potentially) amplify minor reaction channels, such as the substrate hydroxylation. To verify this hypothesis, we mutated the four residues mentioned above into their counterparts present in a soluble methane monooxygenase (sMMO), and determined the reaction products of mutants. We found that the mutations significantly promote residual monohydroxylation activities on stearoyl-CoA, often at the expense of native desaturation activity. The favored hydroxylation positions are C9, followed by C10 and C11. Reactions with unsaturated substrate, oleoyl-CoA, yield erythro-9,10-diol, cis-9,10-epoxide and a mixture of allylic alcohols. Additionally, using 9- and 11-hydroxystearoyl-CoA, we showed that the desaturation reaction can proceed only with the hydroxyl group at position C11, whereas the hydroxylation reaction is possible in both cases, i.e. with hydroxyl at position C9 or C11. Despite the fact that the overall outcome of hydroxylation is rather modest and that it is mostly the desaturation/hydroxylation ratio that is affected, our results broaden understanding of the origin of chemo- and stereoselectivity of the Δ9D and provide further insight into the catalytic action of the NHFe2 enzymes.

The e-donor 2, 3-Diamino-5-bromopyridine (5BPY) and the e-acceptor 2, 4-Dinitrophenol (DNP) were both involved in the synthesis of a new charge transfer complex, which was then characterized experimentally as well as theoretically. Several spectroscopic techniques were used to analyze the produced solid compound. 1H NMR, FT-IR, P-XRD and SEM-EDX analyses all confirmed the presence of charge and proton transfers in the resulting complex. Analysis of the complex DNA binding ability was carried out using electron absorption spectroscopy; the CT complex binding mechanism was determined to be intercalative, and the intrinsic binding constant (Kb) value was determined to be 7.2 × 106 M−1. To corroborate the results of the experiments, theoretical calculations were performed using DFT with a basis set of CAM-B3LYP/6-31 G (d, p). In accordance with the experimental findings, we calculated and analyzed the molecular electrostatic potential maps (MEPs), geometrical parameters and Mullikan atomic charges. The presence of an H-bond also affects the stability of the complex, in addition to e-transfer. The experimental findings are in agreement with the DFT calculations.

A charge transfer hydrogen bonded complex between the electron donor 4-dimethylaminopyridine (4-DMAP) and the electron acceptor Chloranilic acid (CLA) has been synthesized. The complex was studied experimentally and theoretically. A chemical reaction developed due to strong H-bonding, followed by proton transfer from the CLA to the 4-DMAP in acetonitrile medium (ACN). The straight line approach was employed to verify the 1:1 M ratio of the synthesised CT complex. The Benesi-Hildebrand equation was employed to compute the association constant (KCT), molar absorptivity (εCT), and other physical parameters. The synthesized complex was characterized spectroscopically. The presence of proton and charge transfers in the resultant complex was supported by 1H NMR, FT-IR and SEM-EDX investigations. The complex DNA binding ability of complex was investigated using electron absorption spectroscopy to reveal that the CT complex binding mechanism is intercalative and the intrinsic binding constant (Kb) value is 6.7 × 104 M−1. Theoretical calculations using DFT at the basis set CAM-B3LYP/6–31 G (d, p) were used to validate the experimental outcomes. The Mullikan atomic charges, geometrical parameters, and molecular electrostatic potential maps (MEPs) were computed and interpreted in conformity with the experimental results. In addition to e-transfer, the presence of an H-bond influences complex stability. There is good agreement between experimental results and DFT calculations.

Calculations of level energies in the shell model of deformed and spherical nuclei are performed for 14N nuclei. The present theoretical analysis of the 12C(14N,13 C)13N reaction at 116 MeV was performed by means of the FRESCO code. Our theoretically calculated di erential cross sections give a fair description of the experimental data for the proton transfer reaction. Based on calculation for 116 MeV predicted calculations for region from Coulomb barrier to a maximum energy available at the DC-60 heavy ion accelerator were made.

Quantum mechanics revolutionized chemists' understanding of molecular structure. In contrast, the kinetics of molecular reactions in solution are well described by classical, statistical theories. To reveal how the dynamics of chemical systems transition from quantum to classical, we study femtosecond proton transfer in a symmetric molecule with two identical reactant sites that are spatially apart. With the reaction launched from a superposition of two local basis states, we hypothesize that the ensuing motions of the electrons and nuclei will proceed, conceptually, in lockstep as a superposition of probability amplitudes until decoherence collapses the system to a product. Using ultrafast spectroscopy, we observe that the initial superposition state affects the reaction kinetics by an interference mechanism. With the aid of a quantum dynamics model, we propose how the evolution of nuclear wavepackets manifests the unusual intersite quantum correlations during the reaction. [ABSTRACT FROM AUTHOR]