Protonation Behavior Research Articles

Oscillating behavior of proton scattering amplitude on an electron-stimulated-desorbed surface of KBr by keV electrons

Specular yields of 15 keV protons scattered from a KBr(001) electron-stimulated desorbed surface for 1.5–5 keV electron irradiation have been measured, whose periodic oscillations are resulting from the layer-by-layer removal by surface erosion. In each oscillation, the first half-period is found to elongate compared with subsequent half-periods. This elongation indicates that extra electron fluence is needed for the initiation of the surface erosion. The elongation depends on the irradiation electron energy and decreases with the elevating temperature of the sample. From the extra electron fluence irradiated during the elongation, the amount of F centers accumulated in the thin surface layers rise to 30% of the number of alkalis on the topmost layer. This high number of F centers indicates that, before the initiation, the growth of aggregated F centers takes place in numerous heaped F centers under the flat surface, as though the X centers are sinks of F center-diffusion.

Large Changes in Protonation of Weak Polyelectrolyte Brushes with Salt Concentration-Implications for Protein Immobilization.

We report for the first time that the protonation behavior of weak polyelectrolyte brushes depends very strongly on ionic strength. The pKa changes by one pH step per order of magnitude in salt concentration. For low salt concentrations (∼1 mM), a very high pH is required to deprotonate a polyacidic brush and a very low pH is required to protonate a polybasic brush. This has major consequences for interactions with other macromolecules, as the brushes are actually almost fully neutral when believed to be charged. We propose that many previous studies on electrostatic interactions between polyelectrolytes and proteins have, in fact, looked at other types of intermolecular forces, in particular, hydrophobic interactions and hydrogen bonds.

Neutron crystallography of copper amine oxidase reveals keto/enolate interconversion of the quinone cofactor and unusual proton sharing

Recent advances in neutron crystallographic studies have provided structural bases for quantum behaviors of protons observed in enzymatic reactions. Thus, we resolved the neutron crystal structure of a bacterial copper (Cu) amine oxidase (CAO), which contains a prosthetic Cu ion and a protein-derived redox cofactor, topa quinone (TPQ). We solved hitherto unknown structures of the active site, including a keto/enolate equilibrium of the cofactor with a nonplanar quinone ring, unusual proton sharing between the cofactor and the catalytic base, and metal-induced deprotonation of a histidine residue that coordinates to the Cu. Our findings show a refined active-site structure that gives detailed information on the protonation state of dissociable groups, such as the quinone cofactor, which are critical for catalytic reactions.

Study of impedance and solid-state double-layer capacitor behavior of proton (H+)-conducting polymer blend electrolyte-based CS:PS polymers

A series of proton-conducting polymer blend electrolytes (PBEs) were prepared using solution casting techniques. Chitosan (CS) and starch of potato (PS) were blended and doped with various amounts of ammonium fluoride (NH4F). The highest DC conductivity was found to be 1.38 × 10−3 S/cm for the sample incorporated with 40 wt.% NH4F salt using electrical impedance spectroscopy (EIS). A good complex formation between the polymer blends and the doped salt was confirmed from the morphology of the sample’s surface using field emission scanning electron microscope (FESEM). The crystalline peak broadening and intensity reduction of CS:PS polymer blend with the increasing salt concentration was observed in the X-ray diffraction (XRD) analysis. The type of charge carrier in the PBEs was examined via transference number measurements (TNM), and the dominancy of ion was approved. The extent of electrochemical stability of electrolyte was determined to be up to 1.78 V using linear sweep voltammetry (LSV). The specific capacitance of 6.85 F/g was obtained from cyclic voltammetry (CV) measurement. The rechargeability of the electric double-layer capacitor (EDLC) exhibited stability up to 100 cycles with average specific capacitance of 4.1 F/g. Three criteria were determined, which are internal resistance, energy density, and power density (550 Ω, 0.57 Wh/kg, and 155 W/kg, respectively) of the EDLC at the first cycle.

(Invited) Equivalent Circuit Analysis of Mass Transport of Proton- Oxide Ion- Electron Mixed Conductors for Fuel Cells and Electrolysis Cells

Recently proton conducting ceramics have been intensively developed for proton ceramic cells (PCCs) for fuel cell and electrolyzer. There are potentially three conduction carriers (proton, oxide-ion, electron hole) in a proton conducting electrolyte, whose partial conductivities vary drastically with change in chemical potential and temperature. Therefore the complicated mass transport phenomena in proton conducting electrolyte must be fully understood to develop the fuel cell and electrolysis cell. While a couple of papers have reported the analysis results of behavior of proton, oxide-ion, and electron hole in the electrolyte [1, 2], the cell behavior including electrode materials are not yet fully understood. In this paper, we analyze complex impedance response of PCCs under the operation conditions of fuel cell and electrolysis cell by equivalent circuit analysis using universal circuit simulator.[1] H. Zhu, R. J. Kee, Int. J. Hydrogen Energy, 41 (2016) 2931.[2] D. Poetzsch, R. Merkle, J. Maier, Adv. Func. Mater., 25 (2015) 1542.

Electrochemistry of Nanoscale Hybrid Materials (NOHM) Complexes

Nanoparticle organic hybrid materials, also known as NOHMs, are composite particles formed by polymers grafted (either ionically or covalently) onto surface-modified inorganic nanoparticles. The unique structure and liquid-like properties of such material have promoted the interest on its application as an electrolyte with the potential to capture and carry nonpolar electroactive species.In this work two types of NOHMs are considered. Both systems comprise silica cores ionically grafted with polymer tails. The polymer tails correspond to polyethylimine for the NOHM-I-PEI, and to polyetheramine with a sulfonic acid linker for the NOHM-I-HPE.Cyclic voltammetry was used to investigate the interaction of NOHM-I-PEI and NOHM-HPE with copper. NOHM-I-PEI showed a significant pH influence, with peak inhibition occurring at high pH. The protonation behavior of PEI and NOHM-I-PEI was explored (Figure 1). CV results suggest a strong binding of the copper ions and a potential competition between protons and metal ions. Copper hydroxide formation can also occur at higher pH. In contrast, onset potential shift was observed in presence of NOHM-I-HPE.These studies are complemented by exploration through Electron Paramagnetic Resonance (EPR) and Nuclear Magnetic Resonance (NMR). Through EPR, the nature of the ion in solution can be explored. On the other hand, 13C T1 relaxation of the NOHM-based electrolyte at different compositions provide information on the dynamics of the grafted polymers in solution Figure 1

A first-principles study of the proton and oxygen migration behavior in the rare-earth perovskite SmNiO3

Transition-metal oxide perovskites usually exhibit mixed ionic and electronic conductivity and have been widely investigated as electrode materials for use in solid-oxide fuel cells. Recently, samarium nickelate SmNiO3 was found experimentally to show promising potential for use in proton-conducting fuel cells. To understand the ionic conductivity of SmNiO3, the oxygen and proton diffusion therein are investigated via density functional theory calculations in this work. Based on the vacancy hopping mechanism, oxygen diffusion in SmNiO3 shows a migration barrier of 0.84 eV. The proton diffusion is studied in terms of different diffusion mechanisms, including reorientation, intraoctahedral, and interoctahedral hopping. The migration barrier for intraoctahedral migration is calculated to be lower than that for interoctahedral hopping. To realize long-range diffusion, the proton is predicted to exhibit reorientation and intraoctahedral hopping. These findings provide a theoretical guide for the development of mixed ionic and electronic perovskite conductors.

Investigation of the Electrooxidation of Thymine on Screen-Printed Carbon Electrodes by Hyphenation of Electrochemistry and Mass Spectrometry.

The electrooxidation of thymine on screen-printed carbon electrodes was investigated utilizing different complementary instrumental approaches. The potential-dependent product profile was obtained by recording real-time mass voltammograms. Electrochemical flow cells with integrated disposable electrodes were directly coupled with mass spectrometry to facilitate a very fast detection of electrogenerated species. Thymine dimers were found at a potential of about 1.1 V in ammonium acetate (pH 7.0) and 1.25 V in ammonium hydrogen carbonate electrolyte (pH 8.0). Electrochemistry-capillary electrophoresis-mass spectrometry measurements revealed that two isobaric isomers of a dimeric oxidation product were formed. Separations at different time intervals between end of oxidation and start of separation showed that these were hydrated over time. An investigation of the pKa values by changing the separation conditions in electrochemistry-capillary electrophoresis-ultraviolet-visible spectroscopy measurements allowed for further characterization of the primary oxidation products. The results showed that both isomers exhibited two deprotonation steps. The oxidation products were further characterized by high-performance liquid chromatography-tandem mass spectrometry. Based on the obtained data, the main oxidation products of thymine in aqueous solution could most likely be identified as N(1)-C(5') and N(1)-C(6') linked dimer species evolving into the corresponding dimer hydrates over time. The presented methods for online characterization of electrochemically pretreated samples showed that not only mass spectrometric data can be obtained by electrochemistry-mass spectrometry but also further characterizations such as the investigation of product stability and the pH-dependent protonation or deprotonation behavior are possible. This is valid not only for stable oxidation products but also for intermediates, as analysis can be carried out within a short time scale. Thus, a vast amount of valuable experimental data can be acquired, which can help in understanding electrooxidation processes.

Performance of Polymer Electrolyte Membrane for Direct Methanol Fuel Cell Application: Perspective on Morphological Structure.

Membrane morphology plays a great role in determining the performance of polymer electrolyte membranes (PEMs), especially for direct methanol fuel cell (DMFC) applications. Membrane morphology can be divided into two types, which are dense and porous structures. Membrane fabrication methods have different configurations, including dense, thin and thick, layered, sandwiched and pore-filling membranes. All these types of membranes possess the same densely packed structural morphology, which limits the transportation of protons, even at a low methanol crossover. This paper summarizes our work on the development of PEMs with various structures and architecture that can affect the membrane’s performance, in terms of microstructures and morphologies, for potential applications in DMFCs. An understanding of the transport behavior of protons and methanol within the pores’ limits could give some perspective in the delivery of new porous electrolyte membranes for DMFC applications.

Electrochemical behavior of protons and cupric ions in water in salt electrolytes with alkaline metal chloride

The proton reduction and copper deposition in water-in-salt electrolytes with LiCl were studied. Cyclic voltammetry on stationary electrode with various scan rates and linear sweep voltammetry on disk electrodes with different rotation rates were used to determine not only the diffusion coefficients but also the effective concentrations of protons and cupric cations. The suppression of hydrogen evolution limiting current observed in water-in-salt electrolyte was determined to result from the inhibition of proton diffusion. This diffusion inhibition was mainly related to the structural diffusion across hydrogen bond network and is not observed for cupric cations. The effects of alkaline metal cations on the acidity of electrolytes, the diffusivity of protons as well as the copper deposition rate were also studied using various super high concentrations of LiCl, NaCl and KCl.

Proton belt variations traced back to Fengyun-1C satellite observations

We used historical data to trace trapped protons observed by the Fengyun-1C (FY-1C) satellite at low Earth orbits (~800 km) and chose data at 5–10 MeV, 10–40 MeV, 40–100 MeV, and ~100–300 MeV from 25 March to 18 April 2000 to analyze the proton variations. Only one isolated strong storm was associated with a solar proton event during this period, and there was no influence from previous proton variations. Complex dynamic phenomena of proton trapping and loss were affected by this disturbance differently depending on the energy and L location. The flux of 5–10 MeV protons increased and created new trapping with a maximum at L ~2.0, and the peak flux was significantly higher than that at the center of the South Atlantic Anomaly. However, at higher L, the flux showed obvious loss, with retreat of the outer boundary from L ~2.7 to L ~2.5. The increase in the 10–40 MeV proton flux was similar to that of the 5–10 MeV flux; however, the peak flux intensity was lower than that at the center of the South Atlantic Anomaly. The loss of the 10–40 MeV proton flux was closer to the Earth side, and the outer boundary was reduced from L ~2.3 to L ~2.25. For the higher energy protons of 40–100 MeV and 100–300 MeV, no new trapping was found. Loss of the 40–100 MeV protons was observed, and the outer boundary shifted from L ~2.0 to L ~1.9. Loss was not obvious for the 100–400 MeV protons, which were distributed within L < 1.8. New proton trapping was more likely to be created at lower energy in the region of solar proton injection by the strong magnetic storm, whereas loss occurred in a wide energy range and reduced the outer boundary on the Earth side. Similar dynamic changes were observed by the NOAA-15 satellite in the same period, but the FY-1C satellite observed more complex changes in lower energy protons. These results revealed that the dynamic behavior of protons with different L-shells was due to differences in the pitch angle. Possible mechanisms related to new trapping and loss are also discussed. These mechanisms are very important for understanding the behavior of the proton belt in the coming solar cycle.

1D and 2D Nuclear magnetic resonance (NMR) relaxation behaviors of protons in clay, kerogen and oil-bearing shale rocks

Abstract Few 1D T2 and 2D T1-T2 Nuclear magnetic resonance (NMR) studies have focused on oil-bearing shales with complex constituents and a deeper understanding of the NMR relaxation behaviors of oil confined in shale is needed. In this paper, a series of T2 and T1-T2 NMR experiments were performed on oil-bearing shale and its components (clay minerals and kerogen) to obtain the T1-T2 fluid typing chart and analyze the adsorbed and free oil in shale. The results were as follows: five types of water (bound, adsorbed, free, crystal and structural water) in clay minerals were qualitatively identified and described by the specific T2 to T1/T2 ratio values, and T1-T2 maps were used to qualitatively indicate the clay type. The T1-T2 fluid typing chart containing the signatures of 8 proton populations in oil-bearing shale was defined and included bulk liquid, macropore (>1000 nm) oil, nanopore (

Surface complexation model of rare earth element adsorption onto bacterial surfaces with lanthanide binding tags

Lanthanide binding tags (LBTs) have been engineered onto the cell surface of E. coli to enhance biosorption and recovery of rare earth elements (REEs). The protonation behavior of the bacterial surfaces before and after LBT-display was compared by modeling acid-base titration data. A multiple discrete site, constant capacitance surface complexation model was constructed to examine rare earth (Tb) binding to cell surface functional groups, comparing wild type and LBT-engineered surfaces. Our acid-base titrations show similar pKa values between the two strains, suggesting induction of LBTs does not significantly alter cell surface protonation behavior. Tb sorption onto the wild type cell surface can be captured by a one-site carboxyl model. The LBT strain exhibited a higher metal loading that can be explained by the increase of sorption sites in the form of lanthanide binding tags. Furthermore, carboxyl site concentrations between wild type and LBT-induced cells were statistically indistinguishable. We thus attribute the engineered strains’ increase in Tb adsorption capacity and affinity to the addition of lanthanide binding tags to the cell surface. The Tb stability constant with the LBT site is two orders of magnitude higher than that with the carboxyl functional group. As a result, at low metal loading <10 μM, the Tb binding to the cell surface of the LBT-strain is controlled by the presence of high-affinity, but lower capacity, LBT sites. At higher metal loadings >10 μM, a more abundant but low affinity functional group becomes the main source of adsorption that results in an overall higher sorption capacity. This work demonstrates how surface complexation modeling can be implemented for bacterial surfaces engineered with a known protein tag to optimize REE recovery from fluids with variable pH and metal loadings.

Thermodynamic anomalies and three distinct liquid-liquid transitions in warm dense liquid hydrogen

The properties of hydrogen at high pressure have wide implications in astrophysics and high-pressure physics. Its phase change in the liquid is variously described as a metallization, H2-dissociation, density discontinuity or plasma phase transition. It has been tacitly assumed that these phenomena coincide at a first-order liquid-liquid transition (LLT). In this work, the relevant pressure-temperature conditions are thoroughly explored with first-principles molecular dynamics. We show there is a large dependency on exchange-correlation functional and significant finite size effects. We use hysteresis in a number of measurable quantities to demonstrate a first-order transition up to a critical point, above which molecular and atomic liquids are indistinguishable. At higher temperature beyond the critical point, H2-dissociation becomes a smooth cross-over in the supercritical region that can be modelled by a pseudo-transition, where the H2-2H transformation is localized and does not cause a density discontinuity at metallization. Thermodynamic anomalies and counter-intuitive transport behavior of protons are also discovered even far beyond the critical point, making this dissociative transition highly relevant to the interior dynamics of Jovian planets. Below the critical point, simulation also reveals a dynamic H2-2H chemical equilibrium with rapid interconversion, showing that H2 and H are miscible. The predicted critical temperature lies well below the ionization temperature. Our calculations unequivocally demonstrate that there are three distinct regimes in the liquid-liquid transition of warm dense hydrogen.

The Chromic Response to Environment of some Imine-Based Oligomers

Among the organic materials widely studied for applications in advanced techniques, imine-based compounds (or azomethines) have received considerable attention due to their ability to reversibly change the color under the action of an external stimulus. The halochromic or photochromic behavior of imines is based on the protonation or photoizomerization ability of the imine linkage, the color changing effect occurring in response to the change in pH of the surrounding medium or electromagnetic radiation absorption. Starting from these aspects, three imine-based oligomers with a donor-acceptor-donor topology containing phenoxazine as the donor unit and diphenyl-1,3,4-oxadiazole, 9,9-diphenylfluorene or fluorene as an acceptor moiety were thoroughly investigated with respect to their protonation and photoiradiation behavior, evaluated by means of photo-physics analysis.

Electrolytes Based on Nanoscale Organic-Inorganic Hybrid Materials (NOHMs)

The potential use of nanoparticle organic hybrid materials (NOHM) as electrolytes in redox flow batteries is being explored. NOHMs are composite particles formed by polymers grafted (either ionically or covalently) onto surface-modified inorganic nanoparticles. Such structure has great potential to capture and carry nonpolar electroactive species.1 In this work, the protonation behavior, and the effect NOHM structures have on metal cation uptake is evaluated. Both NOHMs considered in this analysis comprise silica cores ionically grafted with polymer tails. The polymer tails correspond to polyethylimine for the NOHM-I-PEI, and to polyetheramine with a sulfonic acid linker for the NOHM-I-HPE. Cyclic voltammetry was used to investigate the interaction of the copper species as the concentration of the NOHM of interest increases (Figure 1). NOHM-I-PEI showed inhibition of the oxidation and reduction peaks as the NOHM concentration increased, suggesting the formation of the cuprammonium complex. The formation of this complex was also explored via acid-base titration and UV-Vis. On the other hand, the dynamics of neat and NOHM-based fluids was explored via NMR. DOSY was used to explore the diffusion coefficients of the pure polymers and the NOHMs.

Unique protonation behavior of cationic free-base porphyrins in the interlayer space of transparent solid films comprising layered α-zirconium phosphate

The protonation behavior of α,β,γ,δ-tetrakis(1-methylpyridinium-4-yl)porphyrin (H2TMPyP) in the interlayer space of transparent solid films comprising layered α-zirconium phosphate was investigated. It was found that the exposure of H2TMPyP-impregnated films to aqueous HCl resulted in pyrrole group protonation and induced a color change from yellow to greenish yellow. The two pKa values of H2TMPyP, determined as 2.4 and 2.6, exceeded those determined in aqueous solution (0.80 and 2.06), which was attributed to the condensation of H+ in the interlayer space caused by the cation exchange reaction between H+ in the aqueous solution and n-butylamine intercalated in the interlayer space.

Molecularly defined graphitic interface toward proton manipulation

Abstract Proton plays a critical role in electrochemical systems to control electrochemical reactivity or isotopic enrichment. Graphene is intensively investigated owing to its unique electronic structure and device fabrication. Through the structural tunability of graphitic materials by chemical or physical modification of the surface, graphene is revealed to be an ideal material for proton manipulation. Here, we review the use of graphene or graphitic materials toward the manipulation of proton with regard to the following three points. (1) Electronic properties of graphene: The electronic band structure of graphene can be modified by metal contacts owing to the interaction with a metal surface. (2) Molecular control of graphitic interface: The chemical structure of graphene can be modified, as is done in molecular chemistry, and can be used as a catalytic platform. (3) Proton conduction by graphene: Proton transport through a graphene layer occurs with a unique mechanism such as tunneling. We provide a perspective on the use of graphitic materials toward controlling the behavior of protons on the basis of the aforementioned points. From the above, graphene can be used as a platform for proton manipulation.

Protonation behavior of dextran amino acid esters

Dextran esters of different amino acids (glycine, -alanine, L-ornithine, L-lysine) are investigated regarding their pKa values by potentiometric titration. The pKa values of the dextran derivatives are generally dependent on the position of the amino group in relation to the ester group, i.e. the nearer they are located in the molecule, the lower the resulting pKa values are, L-ornithine ester being the exception. An influence of the polymer backbone is ruled out. Stability against hydrolysis at different pH values and over longer periods at constant pH value is measured by potentiometric and polyelectrolyte titration. The -alanine ester shows slowest hydrolysis at alkaline pH values, starting at a pH value of 8. The esters investigated are polycations at physiological pH values; thus, the charging properties are essential for using these esters as nonviral vectors in gene delivery.

In situ investigation of intrinsic relationship between protonation behavior and HA characteristics in sediments

Proton-binding study of humic acid (HA) is critical for describing and modeling the binding mechanism of HA with heavy metals. However, little is known about the intrinsic relationship between protonation behavior and HA characteristics, especially in sediments. In this study, HA was extracted from sediments and combination of spectrographic titration with parallel factor analysis, Gaussian fitting model and two-dimensional correlation spectroscopy analysis was developed as a novel in-situ tool. Results indicated that the intensity changes of fluorophores of sediment HA might be dependent on the structure characteristics (fused or non-fused ring) of phenolic species in the protonation process. Compared with phenolic groups (A1, 5.27 ± 0.05 eV; A3, 3.91 ± 0.02 eV), the carboxyl groups (A2, 4.65 ± 0.03 eV) exhibited greater contribution in the response of chromophores to the protonation process of sediment HA. Furthermore, proton binding to sediment HA first occurred in carboxyl groups and then in phenolic groups. The combined technique is a promising approach for the examination of the binding sites, binding capacities, and binding order in proton-HA binding process under environmental concentrations. Importantly, this method is a sensitive, effective and non-destructive technique without any need pre-concentrate.