Proton Migration Research Articles

Membrane composition may regulate proton wave propagation.

Lateral proton diffusion along membrane surfaces, specifically between a proton source and a sink, is a fundamental process in many biological systems. It may play a significant part in the uptake of cations, sugars, amino acids, and ATP synthesis. Fast interfacial diffusion cannot rely on titratable membrane residues, as a comparison with the relatively slow proton release reaction shows [1]. Yet, an entropy-dominated free energy barrier prevents surface protons from equilibrating with bulk protons [2]. The dependence of barrier height on membrane compositions thus far remained enigmatic. To establish the barrier-modulating role of glycolipids, we released protons to a small spot on the surface of planar lipid bilayers by Ca2+ microinjection. The membranes contained a calcium ionophore (A23187) which facilitated the transmembrane transport of Ca2+ ions in exchange for protons [3]. A lipid-anchored pH-sensor allowed detection of the arrival of the locally triggered proton wave on a distant membrane patch as a change in fluorescence intensity. Our results indicated that interfacial sugar moieties might be potent regulators of proton migration between membrane-embedded proton sources and sinks. This project was supported by the Marie Skłodowska-Curie grant 860592 (Horizon 2020). [1] Springer, et al. Proc. Natl. Acad. Sci. U.S.A, 2011, 108, 14461-14466. [2] Weichselbaum, et al. Scientific Reports, 2017, 7, 4553. [3] Peter Pohl, Yuri N. Antonenko, Lev S. Yaguzhinsky, Biochimica et Biophysica Acta, 1990, 1027, 295-300.

Molecular origin of the proton selectivity in the human voltage-gated proton channel.

The human voltage-gated proton channel hHv1 is a ubiquitous membrane protein involved in a large range of cellular processes including proton extrusion, pH regulation, reactive oxygen species production and cancer cell proliferation. The proton channel, once activated, conducts a drastic shift in one of the four transmembrane helices aligned with the direction of the membrane potential. Mutagenesis studies have suggested that the proton selectivity of this channel is directly related to a key residue, Asp112, but the mechanism by which Asp112 controls proton selectivity remains elusive. The goal of this study is to understand the proton permeation mechanism and the associated proton selectivity of hHv1 via quantum-mechanics-based simulations of explicit proton migration over the whole channel. We computed a quantitative free energy profile characterizing the proton transport process, which, when paired with Markov state kinetics modeling, clarifies the critical involvement of Asp112 in proton selectivity.

Electronic and magnetic properties of TATA-DNA sequence driven by chemical functionalization.

The TATA box is a promoter sequence able to interact directly with the components of the basal transcription initiation machinery. We investigate the changes in the electronic and magnetic properties of a TATA-DNA sequence when functionalized with different chemical groups; using the first-principles density functional theory specifically, the TATA-DNA sequences were functionalized with methyl groups (CH3 , methylation), amino groups (NH2 , amination), imine groups (NH, imination), chloroamine groups (NCl2 , chloramination), H-adatom (hydrogenation), and Cl-adatom (chlorination). The functional groups were anchored at nitrogen atoms from adenine and oxygen atoms from thymine at sites pointed as reactive regions. We demonstrated that chemical functionalization induces significant changes in charge transfer, hydrogen bond distance, and hydrogen bond energy. The hydrogenation and imination increased the hydrogen bond energy. Results also revealed that the chemical functionalization of DNA molecules exhibit a ferromagnetic ground state, reaching magnetization up to 4.665 μB and complex magnetic ordering. We further demonstrated that the functionalization could induce tautomerism (proton migration in the base pair systems). The present study provides a theoretical basis for understanding the functionalization further into DNA molecules and visualizing possible future applications.

Constructing highly active surface-nanostructured core/bi-shell La1.2Sr0.8Ni0.5Mn0.5O4+δ cathode for protonic ceramic fuel cells

Development of highly-active electrodes is essential yet challenging for the designs of low-temperature protonic ceramic fuel cells (LT-PCFCs). Herein, a core/bi-shell surface-nanostructure on base of K2NiF4-type La1.2Sr0.8Ni0.5Mn0.5O4+δ (LSNM) is developed. With the occurence of dopant segregation during atom arrangement in powder calcination process, the core/bi-shell is formed, accompanied by the formations of B-site deficient K2NiF4 phase and perovskite separately existing in two shell-regions, which could promote oxygen reduction and proton migration, thus extending the cathode reaction. The DFT simulation also provides further evidence of easily proton transfer for facilely rotating and jumping. This unique LSNM cathode attains an impressive power approaching 1.1 W cm−2 at 650 °C, outperforming other Ln2NiO4-based cathodes in the literature. On balance, the predominant cell performance coupled with good durability suggests that the core/bi-shell LSNM is a preferential alternative for LT-PCFCs. This work provides a new strategy to design highly-active electrode materials via decorating surface structure, which would be beneficial to the related electrocatalytic fields.

Proton transfer in layered hydrogen-bonded system γ-MOOH (M = Al, Sc): Robust bi-mode ferroelectricity and 1D superionic conductivity

Layered γ-MOOH, such as synthetic boehmite γ-AlOOH and γ-ScOOH, has been explored for various applications since 1950s. In this paper, based on first-principles calculations, we show the evidence of two proton transfer modes in their hydrogen-bonded network that give rise to extraordinary properties: (1) they, respectively, result in two distinct types of ferroelectricity with different switching mechanisms and polarizations, while the exhibiting mode under an electric field depends on various factors, including the field intensity and direction, the existence of vacancies, and temperature; and (2) the combination of two modes can lead to ultra-high proton conductivity along 1D channels. Their proton migration barriers ensure high ferroelectric Curie temperature, while still much lower compared with current proton conductors, giving rise to 1D superionicity with unprecedented protonic conductivity over 24 mS/cm. Those light weight nontoxic layered materials with high polarizations, Curie temperature, and ultra-high protonic conductivity should provide vast opportunities for various applications.

Conjugated Coordination Polymer as a New Platform for Efficient and Selective Electroreduction of Nitrate into Ammonia.

Electroreduction of nitrate into ammonia (NRA) provides a sustainable route to convert the widespread nitrate pollutants into high-value-added products under ambient conditions, which unfortunately suffers from unsatisfactory selectivity due to the competitive hydrogen evolution reaction (HER). Previous strategies of modifying the metal sites of catalysts often met a dilemma for simultaneously promoting activity and selectivity toward NRA. Here, a general strategy is reported to enable an efficient and selective NRA process through coordination modulation of single-atom catalysts to tailor the local proton concentration at the catalyst surface. By contrast, two analogous Ni-single-atom enriched conjugated coordination polymers (NiO4 -CCP and NiN4 -CCP) with different coordination motifs are investigated for the proof-of-concept study. The NiO4 -CCP catalyst exhibits an ammonia yield rate as high as 1.83mmol h-1 mg-1 with a Faradaic efficiency of 94.7% under a current density of 125mA cm-2 , outperforming the NiN4 -CCP catalyst. These experimental and theoretical studies both suggest that the strategy of coordination modulation can not only accelerate the NRAby adjusting the adsorption energies of NRA intermediates on the metal sites but also inhibit the HER through regulating the proton migration with contributions from the metal-hydrated cations adsorbed at the catalyst surface, thus achieving simultaneous enhancement of NRA selectivity and activity.

First Principles Calculations of Hydrogen Evolution Reaction and Proton Migration on Stepped Surfaces of SrTiO3

AbstractRecent research suggests that photocatalytic activity toward water splitting of strontium titanate SrTiO3 (STO) is enhanced by creating multifaceted nanoparticles. To better understand the source of this activity, a previously designed model is used for two types of surfaces of this nanoparticle, flat and double‐stepped. Density functional theory calculations of water adsorption on these surfaces are performed to gain insight into water adsorption and proton migration processes, as well as thermodynamics of hydrogen evolution reaction within the framework of computational hydrogen electrode. It is concluded that ridges of single‐ and double‐stepped surfaces are nearly identical in terms of adsorption configurations and energetics. Also, it is demonstrated that protons have migration barriers lower than 0.7 eV and that surface morphology impacts catalytic activity toward hydrogen evolution reaction, with flat surface demonstrating higher catalytic activity.

Improved oxygen reduction reaction response of novel spinel structured LaFe2O4 and its heterostructure with Gd-doped-ceria-oxide by Ni foam support for PCFCs cathode

Low-temperature operation of ceramic fuel cells (LT-CFCs; 350° to 550 °C) holds grand promise for abundant large and small scaled applications; if suitable, oxygen reduction electrocatalysts can be developed to hinder sluggish redox reaction at low operating temperature. Herein, we have developed a novel spinal structured cobalt-free LaFe2O4-Gd-doped-CeO2 (LFO-GDC) heterostructure composite as an efficient electrocatalyst for solid oxide fuel cells. The designed LaFe2O4-GDC heterostructure composite exhibits low-area-specific resistance and high oxygen reduction reaction (ORR) activity at low operating temperatures. We have demonstrated high-power densities of 835 mW-cm-2 and a current density of 2216 mA-cm2 at 550 °C for button-sized SOFC with H2 and atmospheric air fuels, and even possible operation at 400 °C. Moreover, the LaFe2O4-GDC heterostructure composite shows minimal proton migration energy and activation energy compared to individual LaFe2O4 and GDC, which help promote ORR activity. Various transmission and spectroscopic measurements such as X-ray diffraction and photoelectron spectroscopy, U-visible, Raman, and density functional theory (DFT) calculations were employed to understand the improved ORR electrocatalytic activity of LaFe2O4-GDC heterostructure composite. The results can further help to develop functional cobalt-free electro-catalysts for LT-SOFCs.

Dual molecules engineered carbon nitride for achieving outstanding photocatalytic H2O2 production

Molecular engineering of carbon nitride (CN) was considered as a suitable and compelling strategy to overcome the intrinsic imperfections and enhance photocatalytic H2O2 production. However, the photocatalytic H2O2 production of conventional single molecular engineering is still unsatisfactory, and the comprehension of photogenerated carrier migration and separation is still indistinct. Herein, dual molecules were engineered on CN molecular skeleton for achieving an outstanding photocatalytic rate of H2O2 production. The photocatalytic H2O2 production rate of the dual molecules engineered CN was up to 3320 μmol g−1 h−1, which was approximately 25 times than that of the pristine CN. After the dual-molecular engineering, pyrimidine and cyano group were co-grafted. Synchronously, K ion and Na ion were co-embedded near the interlamination of CN layers. The synergistic effect of the dual molecules in CN not only restrained photogenerated carrier recombination and broadened visible light response by modulating the intrinsic energy band structure, but also enhanced the capture of the photogenerated electrons and accelerated the migration of proton. Hence, the photocatalytic 2e- oxygen reduction reaction, the rate-determining step, was significantly strengthened. Additionally, caused by the positive valence band potential, the H2O oxidation reaction became an indispensable role in photocatalytic H2O2 production. This work provided a viable route to modulate the molecular skeleton of organic semiconductors and presented a promising strategy to obtain high-efficient photocatalytic H2O2 production.

Enhancing protonic movement in meta-polyaniline thin films by chemical functionalization

We investigate proton diffusion in chemically functionalized meta-polyaniline thin films by ab initio molecular dynamics (AIMD) simulations. Our results show that protonic movement in unfunctionalized meta-polyaniline is hindered by proton migration to the polymer amine sites. Functionalization of the meta-polyaniline backbone with small chemical groups enhances protonic movement through the thin film water channels by reducing protonation of the amines. Additionally, the path of proton diffusion is influenced by the choice of chemical group.

Long-range hydrogen-bond relay catalyses the excited-state proton transfer reaction.

Solvent (e.g., water)-catalyzed proton transfer (SCPT) via the relay of hydrogen (H)-bonds plays a key role in proton migration. In this study, a new class of 1H-pyrrolo[3,2-g]quinolines (PyrQs) and their derivatives were synthesized, with sufficient separation of the pyrrolic proton donating and pyridinic proton accepting sites to probe excited-state SCPT. There was dual fluorescence for all PyrQs in methanol, i.e., normal (PyrQ) and tautomer 8H-pyrrolo[3,2-g]quinoline (8H-PyrQ) emissions. The fluorescence dynamics unveiled a precursor (PyrQ) and successor (8H-PyrQ) relationship and the correlation of an increasing overall excited-state SCPT rate (kSCPT) upon increasing the N(8)-site basicity. kSCPT can be expressed by the coupling reaction kSCPT = Keq × kPT, where kPT denotes the intrinsic proton tunneling rate in the relay and Keq denotes the pre-equilibrium between randomly and cyclically H-bonded solvated PyrQs. Molecular dynamics (MD) simulation defined the cyclic PyrQs and analyzed the H-bond and molecular arrangement over time, which showed the cyclic PyrQs incorporating ≧3 methanol molecules. These cyclic H-bonded PyrQs are endowed with a relay-like proton transfer rate, kPT. MD simulation estimated an upper-limited Keq value of 0.02-0.03 for all studied PyrQs. When there was little change in Keq, the distinct kSCPT values for PyrQs were at different kPT values, which increased as the N(8) basicity increased, which was induced by the C(3)-substituent. kSCPT was subject to a deuterium isotope effect, where the kSCPT of 1.35 × 1010 s-1 for PyrQ-D in CH3OD was 1.68 times slower than that (2.27 × 1010 s-1) of PyrQ in CH3OH. MD simulation provided a similar Keq for PyrQ and PyrQ-D, leading to different proton tunneling rates (kPT) between PyrQ and PyrQ-D.

Enhancing proton mobility and thermal stability in phosphate glasses with WO3: the mixed glass former effect in proton conducting glasses.

This study aimed to investigate the impact of WO3 on the thermal stability of glass, as measured by the glass transition temperature (Tg), as well as the activation energy (Ea) of proton conduction and proton mobility (μH). These parameters were analyzed based on variations in the glass network structure and the nature of the P-O and O-H bonds in 35HO1/2-xWO3-8NbO5/2-5LaO3/2-(52 - x) PO5/2 (x = 2, 4, 6, and 8) glasses. As previously predicted by a linear regression model, replacing PO5/2 with WO3 resulted in an increase in Tg and μH at Tg. The observed enhancement rates were +9.1 °C per mol% of WO3 for Tg and 0.09 per mol% of WO3 for log(μH at Tg [cm2 V-1 s-1]), which aligned with the predicted values of +6.5 °C and 0.08, respectively, validating the linear regression model. The increased Tg was attributed to the formation of heteroatomic P-O-W linkages that tightly cross-linked the phosphate chains. The decrease in Ea and increase in μH at Tg with increasing WO3 content were attributed to the reduction of the energy barrier for inter-phosphate chain proton migration owing to the increasing proton migration paths through P-O-W linkages. This μH enhancement is distinct from previously reported ones due to the reduction of the energy barrier for proton dissociation from OH groups. This phenomenon can be attributed to the mixed glass former effect in proton conducting glass.

Nuclear quantum and H/D isotope effects on intramolecular hydrogen bond in curcumin.

Curcumin and its derivatives possess intramolecular low-barrier hydrogen bonds for intramolecular proton transfer. The π-delocalization in the OCCCO framework of the hydrogen bond in these compounds is reorganized concomitantly with the proton transfer. To characterize the hydrogen bond and π-delocalization, we performed path integral molecular dynamics simulations, revealing that although the proton migration and reorganization of the π-delocalized structure showed a positive correlation, the correlation was weak.

Proton transfer reactions: From photochemistry to biochemistry and bioenergetics

The present Review is an attempt by projecting the basic knowledge on photochemical proton transfer to achieve consistent understanding of proton motions in biocatalysis, photobiocatalysis, operation of selective proton channels and systems of photosynthesis and cellular respiration. The basic mechanisms of proton transfer are in active research in the electronic excited states of organic molecules. This allows observing the reactions directly in real time, providing their dynamic and thermodynamic description and coupling with structural and energetic variables. These achievements lay the background for understanding the proton transfers in biochemical reactions, where such ultrafast events are not only ‘optically silent’ but are hidden under much slower rate-limiting steps, such as protein conformational changes, substrate binding and product release. The mechanistic description of biocatalytic and transmembrane proton transport is shown as a multi-step proton migration that is available for modeling in photochemical reactions. For explaining the formation of transmembrane proton gradients, a simple ‘proton lift’ concept is presented that may be the basis of further research and analysis.

Strain effect on proton-memristive NdNiO3 thin film devices

We investigate resistance switching in proton-memristive NdNiO3 film devices via the diffusional migration of a proton dopant by using electric field control. Lattice strain is found to play a significant role in determining proton migration within NdNiO3 thin film. Compressive strain can accelerate the migration, resulting in a switching efficiency of 28.22% which is significantly higher than 0.21% on a tensile-strained device. The results demonstrate the significance of strain engineering and will guide the development of the design of multifunctional perovskite devices for emerging iontronics memory and computing applications.

Proton migration barriers in BaFeO3−δ – insights from DFT calculations

O–O and O–H distances co-determine the proton migration barrier in triple conducting BaFeO3−δ.

Biocompatible Potato-Starch Electrolyte-Based Coplanar Gate-Type Artificial Synaptic Transistors on Paper Substrates.

In this study, we propose the use of artificial synaptic transistors with coplanar-gate structures fabricated on paper substrates comprising biocompatible and low-cost potato-starch electrolyte and indium-gallium-zinc oxide (IGZO) channels. The electrical double layer (EDL) gating effect of potato-starch electrolytes enabled the emulation of biological synaptic plasticity. Frequency dependence measurements of capacitance using a metal-insulator-metal capacitor configuration showed a 1.27 μF/cm2 at a frequency of 10 Hz. Therefore, strong capacitive coupling was confirmed within the potato-starch electrolyte/IGZO channel interface owing to EDL formation because of internal proton migration. An electrical characteristics evaluation of the potato-starch EDL transistors through transfer and output curve resulted in counterclockwise hysteresis caused by proton migration in the electrolyte; the hysteresis window linearly increased with maximum gate voltage. A synaptic functionality evaluation with single-spike excitatory post-synaptic current (EPSC), paired-pulse facilitation (PPF), and multi-spike EPSC resulted in mimicking short-term synaptic plasticity and signal transmission in the biological neural network. Further, channel conductance modulation by repetitive presynaptic stimuli, comprising potentiation and depression pulses, enabled stable modulation of synaptic weights, thereby validating the long-term plasticity. Finally, recognition simulations on the Modified National Institute of Standards and Technology (MNIST) handwritten digit database yielded a 92% recognition rate, thereby demonstrating the applicability of the proposed synaptic device to the neuromorphic system.

Valorisation of Corncob Residue towards the Sustainable Production of Glucuronic Acid

The production of glucuronic acid (GA) directly from actual biomass via chemocatalysis is of great significance to the effective valorisation of biomass for a sustainable future. Herein, we have developed a one-step strategy for the conversion of cellulose in corncob residue into GA with the cooperation of Au/CeO2 and maleic acid, achieving a 60.3% yield. Experimental and density functional theory (DFT) results show that maleic acid is effective in the fractionation of cellulose from corncob residue and the depolymerisation of cellulose fragments to glucose, on account of the good capacity for proton migration. Au/CeO2 is responsible for the selective oxidation of glucose to GA, in which the formation of glucaric acid is restrained, due to the weak capacity of Au/CeO2 on the proton transfer without the occurrence of the ring-opening reaction of glucose. Therefore, the relay catalysis of Au/CeO2 and maleic acid enables the production of GA via the complex cascade reactions. This work may provide insight regarding the conversion of actual biomass to targeted products.

Performance optimization for proton conducting SOFCs by impregnating triple-conducting NBSCF to form composite cathode

• Triple-conducting NBSCF was evaluated as impregnating material. • H-SOFCs with NBSCF modified LSCF composite cathode achieved a relatively high performance. • Migration of protons and oxygen ions were highly enhanced. Considering the sluggish cathode reaction rate, this work applied a triple conducting coating of NdBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5+δ (NBSCF) on a state-of-the-art La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3+δ (LSCF) cathode via a common infiltrating method. The electrical measurement revealed that the polarization resistance decrease from 0.44 to 0.14Ω·cm 2 and maximum power density increase from 486 to 696mW cm -2 at 700°C. Moreover, the analysis of distribution of relaxation time method (DRT) and impedance spectrums revealed that the migration rate of proton and oxygen ion was enhanced, indicating that the impregnation of triple-conducting materials could promote oxygen adsorption and ion migration.

A dibutylhydroquinone/dibutylbenzoquinone-Cd2+/Cd self-stratified Battery

Self-stratified battery is a new type of rechargeable battery potentially applicable for large-scale energy storage. It has a thermodynamically stable membrane-free self-stratified architecture which endows the battery with low cost, high cycling stability and excellent safety. In this paper, a novel self-stratified battery based on quinone cathode is reported. 2,5-di-tert-butyl-1,4-hydroquinone (DBHQ) is studied as the reversible redox active material at the cathode side. It is dissolved in an organic solvent to form the catholyte which is immiscible with the aqueous electrolyte. The aqueous electrolyte is composed of sulfuric acid/magnesium sulfate/cadmium sulfate mixed aqueous solution. Cadmium metal is used as the anode material. Due to density difference, the organic catholyte, aqueous electrolyte and cadmium metal anode are automatically stratified and forms a thermodynamically stable cell structure. The charge/discharge process of the battery is accompanied with the migration of proton between the organic and aqueous phases. Interestingly, we found that adding bis trifluoromethyl sulfonimide anion (TFSI − ) in the organic phase would effectively reduce the battery polarization and improve the cycle performance. Through spectroscopic analysis, we ascribe such performance improvement to the increase of proton concentration in the organic layer and the solvation structure change of DBHQ molecules. Our work extends the active materials system of self-stratified cells to quinone compounds and demonstrates novel performance influencing mechanism based on catholyte solvation structure.