Proton Binding Research Articles

Carboxyl-Group-Bearing Metal Corroles of Cobalt, Manganese and Copper for Electrocatalytic Hydrogen Evolution.

5,15-bis(perfluorophenyl)-10-(4-carboxyphenyl) corrole and its Co(III), Mn(III), and Cu(III) corrole complexes were synthesized. The electrocatalytic hydrogen evolution reaction (HER) of these metal corrole complexes was investigated using different proton sources (AcOH, trifluoroacetic acid, and TsOH) in an organic dimethylformamide solvent. The electrocatalytic HER may proceed through EECC, EECEC, or EEECEC pathways (where E represents electron transfer and C represents proton binding) depending on the acidity and concentration of the proton source used. The Co corrole complex exhibits remarkable hydrogen production performance, achieving a turnover frequency of 201 s-1 and a catalytic efficiency of 1.00. The examined metal corrole complexes also exhibit good HER activity in aqueous solution, with their catalytic activity following an order of 1-Co > 1-Cu > 1-Mn in both organic and aqueous phases.

Using physicochemical properties to predict the impact of natural dissolved organic carbon on transepithelial potential in the freshwater rainbow trout (Oncorhynchus mykiss) at neutral and acidic pH.

Dissolved organic carbon (DOC) is a complex mixture of molecules that varies in composition based on origin as well as spatial and temporal factors. DOC is an important water quality parameter as it regulates many biological processes in freshwater systems, including the physiological function of the gills in fish. These effects are often beneficial, especially at low pH where DOCs mitigate ion loss and protect active ion uptake. DOCs of different compositions and quality have varied ionoregulatory effects. The molecular variability of DOCs can be characterized using optical and chemical indices, but how these indices relate to the physiological effects exerted by DOCs is not well understood. We tested the effects of five naturally sourced DOCs, at both pH 7 and pH 4, on transepithelial potential (TEP) (a diffusion potential between the blood plasma and the external water) in rainbow trout. The five chosen DOCs have been well characterized and span large differences in physicochemical characteristics. Each of the DOCs significantly influenced TEP, although in a unique manner or magnitude which was likely due to their physicochemical characteristics. These TEP responses were also a function of pH. With the goal of determining which physicochemical indices are predictive of changes in TEP, we evaluated correlations between various indices and TEP at pH 7 and pH 4. The indices included: specific absorbance coefficient at 340nm, molecular weight index, fluorescence index, octanol-water partition coefficient, molecular charge, proton binding index, % humic acid-like, % fulvic acid-like, and % protein-like components by parallel factor analysis on fluorescence data (PARAFAC). Our results demonstrate the novel finding that there are three particularly important indices that are predictors of changes in TEP across pHs in rainbow trout: specific absorbance coefficient at 340nm, octanol-water partition coefficient; and proton binding index.

Finding the E-channel proton loading sites by calculating the ensemble of protonation microstates

The aerobic electron transfer chain builds a proton gradient by proton coupled electron transfer reactions through a series of proteins. Complex I is the first enzyme in the sequence. Here transfer of two electrons from NADH to quinone yields four protons pumped from the membrane N- (negative, higher pH) side to the P- (positive, lower) side. Protons move through three linear antiporter paths, with a few amino acids and waters providing the route; and through the E-channel, a complex of competing paths, with clusters of interconnected protonatable residues.Proton loading sites (PLS) transiently bind protons as they are transported from N- to P-compartments. PLS can be individual residues or extended clusters of residues. The program MCCE uses Monte Carlos sampling to analyze the E-channel proton binding in equilibrium with individual Molecular Dynamics snapshots from trajectories of Thermus thermuphillus Complex I in the apo, quinone and quinol bound states. At pH 7, the five E-channel subunits (Nqo4, Nqo7, Nqo8, Nqo10, and Nqo11) take >25,000 protonation microstates, each with different residues protonated. The microstate explosion is tamed by analyzing interconnected clusters of residues along the proton transfer paths. A proton is bound and released from a cluster of five coupled residues on the protein N-side and to six coupled residues in the protein center. Loaded microstates bind protons to sites closer to the P-side in the forward pumping direction. MCCE microstate analysis identifies strongly coupled proton binding amongst individual residues in the two PLS clusters.

Theoretical investigation for the proline effect on peptide fragmentation induced by matrix-assisted laser desorption/ionization in-source decay with an oxidizing matrix

The use of an oxidizing matrix for matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) specifically induces the cleavage of Cα-C bonds on the peptide backbone, except for bonds located on the N-terminal side of proline residues. To examine the effect of Pro residues on bond cleavage induced by MALDI-ISD with an oxidizing matrix, the small dipeptides AcAA-NH2 and AcAP-NH2 were used as models. As the fragmentation is initiated by electron transfer from the peptide to the oxidizing matrix, the dissociation chemistry of the cation radical forms of the model peptides [AcAA-NH2]+• and [AcAP-NH2]+• was investigated using quantum chemistry calculations. The [AcAA-NH2]+• can produce fragment ions not only due to Cα–C bond cleavage, but also peptide bond cleavage. Quantum chemistry calculations indicated that peptide bond cleavage of [AcAA-NH2]+• occurs more slowly compared to Cα–C bond cleavage. Instead of Cα–C bond cleavage, the bond on the N-terminal side of Pro residue undergoes peptide bond cleavage during MALDI-ISD with an oxidizing matrix, due to the lack of an amide hydrogen in the Pro residue. The [AcAP-NH2]+• undergoes proton migration from the δ-carbon of the Pro residue. Depending on the proton binding site in the peptide cation radical, the peptide bond cleavage of [AcAP-NH2]+• results in the formation of either [b1]+, and [y1]•, or [a1]• and [y1]+. These theoretical results are consistent with experimental findings, and the newly proposed mechanism involving peptide cation radical formation followed by proton migration provides a more accurate model for the MALDI-ISD processes.

Heterometallic Transition Metal Oxides Containing Lewis Acids as Molecular Catalysts for the Reduction of Carbon Dioxide to Carbon Monoxide with Bimodal Activity.

Electrocatalytic CO2 reduction (e-CO2RR) to CO is replete with challenges including the need to carry out e-CO2RR at low overpotentials. Previously, a tricopper-substituted polyoxometalate was shown to reduce CO2 to CO with a very high faradaic efficiency albeit at -2.5 V versus Fc/Fc+. It is now demonstrated that introducing a nonredox metal Lewis acid, preferably GaIII, as a binding site for CO2 in the first coordination sphere of the polyoxometalate, forming heterometallic polyoxometalates, e.g., [SiCuIIFeIIIGaIII(H2O)3W9O37]8-, leads to bimodal activity optimal both at -2.5 and -1.5 V versus Fc/Fc+; reactivity at -1.5 V being at an overpotential of ∼150 mV. These results were observed by cyclic voltammetry and quantitative controlled potential electrolysis where high faradaic efficiency and chemoselectivity were obtained at -2.5 and -1.5 V. A reaction with 13CO2 revealed that CO2 disproportionation did not occur at -1.5 V. EPR spectroscopy showed reduction, first of CuII to CuI and FeIII to FeII and then reduction of a tungsten atom (WVI to WV) in the polyoxometalate framework. IR spectroscopy showed that CO2 binds to [SiCuIIFeIIIGaIII(H2O)3W9O37]8- before reduction. In situ electrochemical attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) with pulsed potential modulated excitation revealed different observable intermediate species at -2.5 and -1.5 V. DFT calculations explained the CV, the formation of possible activated CO2 species at both -2.5 and -1.5 V through series of electron transfer, proton-coupled electron transfer, protonation and CO2 binding steps, the active site for reduction, and the role of protons in facilitating the reactions.

Sludge-derived hydrochar modulates complete nonradical electron transfer in peroxydisulfate activation via pyrrolic-N and carbon defect: Implication for degrading electron-rich ionizable anilines compounds

Nonradical electron transfer process (ETP) is a promising pathway for pollutant degradation in peroxydisulfate-based advanced oxidation processes (PDS-AOPs). However, there is a critical bottleneck to trigger ETP by sludge-derived hydrochar due to its negatively charged surface, inferior porosity and electrical conductivity. Herein, pyrrolic-N doped and carbon defected sludge-derived hydrochar (SDHC-N) was constructed for PDS activation to degrade anilines ionizable organic compounds (IOC) through complete nonradical ETP oxidation. Degradation of anilines IOC was not only affected by the electron-donating capacity but also proton concentration in solution because of the ionizable amino group (−NH2). Diverse effects including proton favor, insusceptible and inhibition were observed. Impressively, addition of HCO3 with strong proton binding capacity boosted aniline degradation nearly 10 times. Moreover, characterizations and theoretical calculations demonstrated that pyrrolic-N increased electron density and created positively charged surface, profoundly promoting generation of SDHC-N-S2O82−* complexes. More delocalized electrons around carbon defect could enhance electron mobility. This work guides a rational design of sludge-derived hydrochar to mediate nonradical ETP oxidation, and provides insights into the impacts of proton on anilines IOC degradation.

The mechanism of mammalian proton-coupled peptide transporters.

Proton-coupled oligopeptide transporters (POTs) are of great pharmaceutical interest owing to their promiscuous substrate binding site that has been linked to improved oral bioavailability of several classes of drugs. Members of the POT family are conserved across all phylogenetic kingdoms and function by coupling peptide uptake to the proton electrochemical gradient. Cryo-EM structures and alphafold models have recently provided new insights into different conformational states of two mammalian POTs, SLC15A1, and SLC15A2. Nevertheless, these studies leave open important questions regarding the mechanism of proton and substrate coupling, while simultaneously providing a unique opportunity to investigate these processes using molecular dynamics (MD) simulations. Here, we employ extensive unbiased and enhanced-sampling MD to map out the full SLC15A2 conformational cycle and its thermodynamic driving forces. By computing conformational free energy landscapes in different protonation states and in the absence or presence of peptide substrate, we identify a likely sequence of intermediate protonation steps that drive inward-directed alternating access. These simulations identify key differences in the extracellular gate between mammalian and bacterial POTs, which we validate experimentally in cell-based transport assays. Our results from constant-PH MD and absolute binding free energy (ABFE) calculations also establish a mechanistic link between proton binding and peptide recognition, revealing key details underpining secondary active transport in POTs. This study provides a vital step forward in understanding proton-coupled peptide and drug transport in mammals and pave the way to integrate knowledge of solute carrier structural biology with enhanced drug design to target tissue and organ bioavailability.

The mechanism of mammalian proton-coupled peptide transporters

Proton-coupled oligopeptide transporters (POTs) are of great pharmaceutical interest owing to their promiscuous substrate binding site that has been linked to improved oral bioavailability of several classes of drugs. Members of the POT family are conserved across all phylogenetic kingdoms and function by coupling peptide uptake to the proton electrochemical gradient. Cryo-EM structures and alphafold models have recently provided new insights into different conformational states of two mammalian POTs, SLC15A1, and SLC15A2. Nevertheless, these studies leave open important questions regarding the mechanism of proton and substrate coupling, while simultaneously providing a unique opportunity to investigate these processes using molecular dynamics (MD) simulations. Here, we employ extensive unbiased and enhanced-sampling MD to map out the full SLC15A2 conformational cycle and its thermodynamic driving forces. By computing conformational free energy landscapes in different protonation states and in the absence or presence of peptide substrate, we identify a likely sequence of intermediate protonation steps that drive inward-directed alternating access. These simulations identify key differences in the extracellular gate between mammalian and bacterial POTs, which we validate experimentally in cell-based transport assays. Our results from constant-PH MD and absolute binding free energy (ABFE) calculations also establish a mechanistic link between proton binding and peptide recognition, revealing key details underpining secondary active transport in POTs. This study provides a vital step forward in understanding proton-coupled peptide and drug transport in mammals and pave the way to integrate knowledge of solute carrier structural biology with enhanced drug design to target tissue and organ bioavailability.

Rapid and ultra-sensitive trace water determination in organic solvents utilizing nitrobenzoxadiazole (NBD)-based fluorescent sensing system

The presence of minute quantities of water in organic solvents can affect the progress of many reactions and cause unnecessary losses and even safety accidents in the chemical industry, especially in the productions process of organic fine chemicals. Therefore, it is necessary to carry out high-performance strategies for trace water detections in commonly used organic solvents. In this work, a fluorescent sensing system based on competitive binding of protons has been developed, demonstrating remarkable responses by UV–vis absorption and fluorescence two-modes toward a trace amount of water in organic solvents including 1,4-dioxane (Diox), tetrahydrofuran (THF), acetonitrile (MeCN), acetone (ACE), dimethylsulfoxide (DMSO) and mixed organic solvents (THF: MeCN=1: 1). The key component of the sensing system is a newly designed fluorophore NBD-PMA, which can be deprotonated to form a dynamic non-luminescent adduct, namely NBD-PMA-F, by an organic fluoride salt tetrabutylammonium fluoride (TBAF). NBD-PMA-F can be reprotonated via using trace water, exhibiting fluorescence turn on of the system. The as-prepared sensing system shows superior sensitivity, low detection limits (v/v, 0.0007 %), quick response speed (≤1.2 s) and good reversibility. Moreover, naked-eye visual rapid detection has also been successfully realized at ambient temperature, which demonstrated their practical applications value for trace water determinations.

Enhancing dewaterability of water resource recovery facility solids with electrochemical treatment through synergetic effects of acidification and cation removal

Solids dewaterability is vital for water resource recovery facilities to effectively manage and dispose treatment residuals, and current methods for improving dewaterability is at the expense of chemical consumption. Herein, an electrochemical approach that integrates anodic acidification, electrooxidation, and cation removal was investigated to enhance solids dewaterability. The results show that the specific resistance to filtration (SRF) was decreased by > 97 % for raw solids before anaerobic digestion, anaerobically digested solids (ADS), and primary solids. ADS exhibited the highest conductivity and required the least energy (34.9 ± 1.3 kWh m−3 treated solids). Increasing the applied current density reduced treatment time but demanded greater energy consumption. Both acidification and cation removal were critical to dewaterability enhancement: acidification facilitated the flocculation of solids flocs through protonation of functional groups and the leaching of divalent ions, while cation removal reduced competition for proton binding, leading to improved dewaterability. The input of electrical energy for the electrochemical treatment can potentially be offset by revenue from recovered nutrient products and use of renewable energy. This study has demonstrated the feasibility of using electrochemical processes for solids treatment and resource recovery.

Installing Quinol Proton/Electron Mediators onto Non-Heme Iron Complexes Enables Them to Electrocatalytically Reduce O2 to H2O at High Rates and Low Overpotentials.

We prepare iron(II) and iron(III) complexes with polydentate ligands that contain quinols, which can act as electron proton transfer mediators. Although the iron(II) complex with N-(2,5-dihydroxybenzyl)-N,N',N'-tris(2-pyridinylmethyl)-1,2-ethanediamine (H2qp1) is inactive as an electrocatalyst, iron complexes with N,N'-bis(2,5-dihydroxybenzyl)-N,N'-bis(2-pyridinylmethyl)-1,2-ethanediamine (H4qp2) and N-(2,5-dihydroxybenzyl)-N,N'-bis(2-pyridinylmethyl)-1,2-ethanediamine (H2qp3) were found to be much more active and more selective for water production than a previously reported cobalt-H2qp1 electrocatalyst while operating at low overpotentials. The catalysts with H2qp3 can enter the catalytic cycle as either Fe(II) or Fe(III) species; entering the cycle through Fe(III) lowers the effective overpotential. On the basis of their TOF0 values, the successful iron-quinol complexes are better electrocatalysts for oxygen reduction than previously reported iron-porphyrin compounds, with the Fe(III)-H2qp3 arguably being the best homogeneous electrocatalyst for this reaction. With iron, the quinol-for-phenol substitution shifts the product selectivity from H2O2 to water with little impact on the overpotential, but unlike cobalt, this substitution also greatly improves the activity, as assessed by TOFmax, by hastening the protonation and oxygen binding steps. The addition of a second quinol further enhances the activity and selectivity for water but modestly increases the effective overpotential.

Understanding Microscopic Interactions in Binding Reactions: The pH Titration of EDTA

ABSTRACT Students beginning the study of biochemistry or biophysics at the undergraduate or even early graduate level are often overwhelmed by the complexity of the systems and the nomenclature. By comparison, chemical systems appear simple, as students can more easily relate to introductory chemistry courses, where the molecules are smaller and bind yet smaller ions. This allows students to write the structure of the entire molecule on a piece of paper and see exactly to which functional groups an ion, such as a proton (H+) in the simplest case, binds. Yet, concepts that are fundamental in biochemical macromolecules, namely proteins, can perfectly well be taught at the undergraduate or beginning graduate level, and probably be more easily understood, by using simpler, familiar chemical examples. The concept of interacting binding sites, which is at the root of cooperativity in protein binding reactions and conformational changes, is already present in simple molecules, such as ethylenediaminetetraacetic acid (EDTA). In this article, we show how to teach these topics by using the idea of the partition function, rather than a formal algebraic approach, to treat the binding of protons to EDTA. Profound concepts, such as that of interacting sites, appear naturally in a small molecule, where the origin can be easily ascribed, in this case, mainly to electrostatic interactions. Equipped with this understanding and this approach, students will be able to tackle more complicated biochemical systems, in which the molecules are larger, but the concepts are the same.

Synergistic Mo and W single atoms co-doped surface hydroxylated NiFe oxide as bifunctional electrocatalysts for overall water splitting

Two novel defect engineering strategies, surface hydroxylation and single atom (SA) doping, are explored to fabricate a high performance bifunctional water electrolysis catalyst, synergistic Mo and W SAs co-doped surface hydroxylated NiFe oxide (FN-MoWact). The product catalyst achieves ultralow overpotentials of 196 and 246 mV for oxygen evolution reaction (OER) and decent overpotentials of 79 and 246 mV for hydrogen evolution reaction (HER) at current densities of 10 and 500 mA cm−2, respectively. For overall water splitting, the FN-MoWact//FN-MoWact couple requires ultralow cell voltages of 1.504 and 1.729 V to deliver current densities of 10 and 500 mA cm−2, respectively, and remains stable after a 100-hour operation at an initial current density of 534 mA cm−2. The enhanced electrocatalytic activities are attributed to surface hydroxylation and doping of synergistic Mo and W SAs. The two defect engineering modifications, as supported by analyses of density functional theory calculations and in-situ X-ray absorption spectroscopy, lead to a proper reduction in metal-oxygen covalency, thus minimizing the energy difference of the rate-determining step of the OER process, and create surface active sites with a d-band center located closer to the Fermi level, thus properly strengthening proton binding to enhance HER activities.

ANC and SF of bound states in 15N→14C+p, 16O→15N+p, 19F→18O+p, 32S→31P+p

Asymptotic normalization coefficients (ANCs) and spectroscopic factors (SFs) for proton binding in the ground states of the [Formula: see text]N, [Formula: see text]O, [Formula: see text]F and [Formula: see text]S nuclei were extracted from an analysis of available literature data on the (3He[Formula: see text]) and ([Formula: see text]) reactions. Modified DWBA and ADWA analyses showed that the proton transfer process is more peripheral in (3He,d) reactions and therefore more reliable for determining the ANCs. As a result of the comparative analysis of peripheral (3He,d) and nonperipheral ([Formula: see text]) reactions, the uncertainties in the extracted values of SFs were reduced. The data obtained are to be used in calculating astrophysical S-factors for radiative proton capture.

Proton-coupled transport mechanism of the efflux pump NorA.

Efflux pump antiporters confer drug resistance to bacteria by coupling proton import with the expulsion of antibiotics from the cytoplasm. Despite efforts there remains a lack of understanding as to how acid/base chemistry drives drug efflux. Here, we uncover the proton-coupling mechanism of the Staphylococcus aureus efflux pump NorA by elucidating structures in various protonation states of two essential acidic residues using cryo-EM. Protonation of Glu222 and Asp307 within the C-terminal domain stabilized the inward-occluded conformation by forming hydrogen bonds between the acidic residues and a single helix within the N-terminal domain responsible for occluding the substrate binding pocket. Remarkably, deprotonation of both Glu222 and Asp307 is needed to release interdomain tethering interactions, leading to opening of the pocket for antibiotic entry. Hence, the two acidic residues serve as a "belt and suspenders" protection mechanism to prevent simultaneous binding of protons and drug that enforce NorA coupling stoichiometry and confer antibiotic resistance.

Pt-Modified High Entropy Rare Earth Oxide for Efficient Hydrogen Evolution in pH-Universal Environments.

The development of efficient and stable catalysts for hydrogen production from electrolytic water in a wide pH range is of great significance in alleviating the energy crisis. Herein, Pt nanoparticles (NPs) anchored on the vacancy of high entropy rare earth oxides (HEREOs) were prepared for the first time for highly efficient hydrogen production by water electrolysis. The prepared Pt-(LaCeSmYErGdYb)O showed excellent electrochemical performances, which require only 12, 57, and 77 mV to achieve a current density of 100 mA cm-2 in 0.5 M H2SO4, 1.0 M KOH, and 1.0 M PBS environments, respectively. In addition, Pt-(LaCeSmYErGdYb)O has successfully worked at 400 mA cm-2 @ 60 °C for 100 h in 0.5 M H2SO4, presenting the high mass activity of 37.7 A mg-1Pt and turnover frequency (TOF) value of 38.2 s-1 @ 12 mV, which is far superior to the recently reported hydrogen evolution reaction (HER) catalysts. Density functional theory (DFT) calculations have revealed that the interactions between Pt and HEREO have optimized the electronic structures for electron transfer and the binding strength of intermediates. This further leads to optimized proton binding and water dissociation, supporting the highly efficient and robust HER performances in different environments. This work provides a new idea for the design of efficient RE-based electrocatalysts.

Deep neural network surrogate for surface complexation model of metal oxide/electrolyte interface

HypothesisSurface Complexation Models (SCM) are one of the most successful geochemical thermodynamics models of the speciation and charging of the mineral/electrolyte interface. However, finding unique and transferable SCM parameter values by fitting experimental data using existing numerical solvers is often challenging. We hypothesized that SCM surrogates built using Artificial Intelligence algorithms provide an alternative strategy for determining model parameter values and thus offer an ultrafast prediction of electrical double layer characteristics of metal oxide/electrolyte interface. ExperimentsWe generated synthetic datasets of surface charge and electrokinetic potential as a function of pH, ionic strength, varying site densities, acidity, and ion-affinities of mineral surfaces using the 2-pK Triple Layer Model - one of the most used generic SCM. We explored a wide range of types of mineral surfaces using random walks in the parameter space. Next, we trained and validated two AI surrogates using our synthetic SCM data. FindingsWe showed that AI-SCM surrogates for oxide/electrolyte interfaces are possible and cost-effective. They allow ultrafast and accurate SCM parametrization using synthetic data. AI-SCM can predict thermodynamic parameters from just a few titration data points, such as ion affinities and proton binding constants. What is more, the computational strategy we presented here to surrogate geochemical models by pre-trained AI architectures is more universal and can be applied to other geochemical/thermodynamic models – replacing the computationally expensive solvers with trained AI, thus minimizing computing costs and speeding up data analysis.

Vibrational signatures of dynamic excess proton storage between primary amine and carboxylic acid groups.

Ammonium and carboxylic moieties play a central role in proton-mediated processes of molecular recognition, charge transfer or chemical change in (bio)materials. Whereas both chemical groups constitute acid-base pairs in organic salt-bridge structures, they may as well host excess protons in acidic environments. The binding of excess protons often precedes proton transfer reactions and it is therefore of fundamental interest, though challenging from a quantum chemical perspective. As a benchmark for this process, we investigate proton storage in the amphoteric compound 5-aminovaleric acid (AV), within an intramolecular proton bond shared by its primary amine and carboxylic acid terminal groups. Infrared ion spectroscopy is combined with abinitio Molecular Dynamics (AIMD) calculations to expose and rationalize the spectral signatures of protonated AV and its deuterated isotopologues. The dynamic character of the proton bond confers a fluxional structure to the molecular framework, leading to wide-ranging bands in the vibrational spectrum. These features are reproduced with remarkable accuracy by AIMD computations, which serves to lay out microscopic insights into the excess proton binding scenario.

Novel nanocomposite systems based on cesium dihydrogen phosphate: Electrotransport structural, morphological and mechanical characteristics

CsH2PO4 is a proton conductor belonging to the family of acidic salts and exhibits a monoclinic to cubic phase transition at 230 ± 2 °C with the conductivity jump of four orders of magnitude. To change the electrotransport and mechanical characteristics the non-oxide additives, such as detonation nanodiamonds, were firstly used as a dopant for proton nanocomposites based on cesium dihydrogen phosphate. The use of carbon containing materials has made it possible to create a new type of medium-temperature, highly conductive proton electrolytes. Influence of nanodiamonds (NDs) on the electrotransport, structural and thermodynamic properties of (1-x)CsH2PO4-xNDs (x-mole fraction, x = 0–0.99) electrolytes have been firstly investigated in detail by X-ray diffraction method, electrochemical impedance, FTIR-spectroscopy and differential scanning calorimetry. The CsH2PO4 (P21/m) exists in nanocomposites in the dispersed (up to 300 nm) and partially amorphous state resulting in the strong changes of the salt thermodynamic properties with increase of x mole fraction. The heterogeneous doping by non-oxide dopant resulted in the significant increase of the low temperature conductivity of 3.5 orders of magnitude due to interface interaction, while the superionic conductivity of nanocomposites remains close to the individual CsH2PO4 (∼10-2 S/cm) up to x = 0.7 (fvNDs = 11.7 %). The jump in the conductivity during the phase transition decreases significantly and almost disappears. The conductivity of nanocomposites decreases significantly only at x > 0.95 (fvNDs = 51.8 %) due to the percolation effect. The mechanical properties of CsH2PO4-NDs were shown to be much higher than of the individual CsH2PO4 even with small NDs content. Mechanism of nanocomposites formation is associated with the partial binding of CsH2PO4 protons by surface OH– groups of nanodiamonds. The results are important for the establishing and design the next generation membrane of fuel cells and nanocomposite electrodes for medium-temperature electrochemical devices.

Constant-pH Simulations of a Coarse-Grained Model of Polyfunctional Weak Charged Biopolymers

A coarse-grained model of linear polyfunctional weak charged biopolymers was implemented, formed of different proportions of acid-base groups resembling the composition of humic substances. These substances are mainly present in dissolved organic matter in natural water. The influence of electrostatic interactions computing methods, factors concerning the structure of the chain, different functional groups, and the ionic strength on polyelectrolytes were studied. Langevin dynamics with constant pH simulations were performed using the ESPResSO package and the Python-based Molecule Builder for ESPResSo (pyMBE) library. The coverage was fitted to a polyfunctional Frumkin isotherm, with a mean-field interaction between charged beads. The composition of the chain affects the charge while ionic strength affects both the charge and the radius of gyration. Additionally, the parameters intrinsic to the polyelectrolyte model were well reproduced by fitting the polyfunctional Frumkin isotherm. In contrast, the non-intrinsic parameters depended on the ionic strength. The method developed and applied to a polyfunctional polypeptide model, that resembles a humic acid, will be very useful for characterizing biopolymers with several acid-base functional groups, where their structure, the composition of the different functional groups, and the determination of the main intrinsic proton binding constants and their proportion are not exactly known.