Proton Carrier Research Articles

Polyallylamine-Functionalized Platinum Tripods: Enhancement of Hydrogen Evolution Reaction by Proton Carriers

Tailoring the size, controlling the morphology, and designing the metal–organic interface are three promising strategies to improve the catalytic performance of monometallic noble-metal nanocrystals. In the “hydrogen economy” society, water electrolysis is viewed as one of the most promising technologies for hydrogen production. The design and synthesis of highly active and durable electrocatalysts for the hydrogen evolution reaction (HER) is vitally important for the development of the hydrogen economy. In this work, we successfully synthesized polyallylamine (PAA)-functionalized Pt tripods (Pttripods@PAA) with ultrathin and ultralong branches through a facile chemical reduction method in an aqueous solution of PAA. The morphology, structure, and composition of Pttripods@PAA were fully investigated by various physical techniques. The characterization results reveal that ultrathin and ultralong branches of Pttripods@PAA have a concave structure with high-index facets and that PAA strongly binds on the Pt ...

Metal Loading Affects the Proton Transport Properties and the Reaction Monitoring Performance of Fe-ZSM-5 and Cu-ZSM-5 in NH3-SCR

Metal-promoted zeolites are widely applied as catalysts for the selective catalytic reduction of nitrogen oxide by NH3 (NH3-SCR). Here, we describe a systematic study on the proton transport properties of Fe-ZSM-5 and Cu-ZSM-5 NH3-SCR catalysts with different metal loadings. By means of in situ impedance spectroscopy (IS), we revealed the different influence of exchanged Fe and Cu on the NH3-supported proton transport in different atmospheres (N2 and NO/O2) and, consequently, on the monitoring of the NH3-SCR reaction using the zeolite catalysts directly as sensors. On the one hand, the mobility of adsorbed NH3 species as proton carriers, determined by the NH3–zeolite interaction, was influenced differently by Fe and Cu and their loadings. While the increase of Fe loading weakened slightly the NH3–zeolite interaction, a higher Cu loading enhanced significantly the NH3–zeolite interaction. On the other hand, highly proton-conducting ammonium ion (NH4+) intermediates, as unveiled by IS combined with DRIFTS, ...

Mechanism of pH-dependent activation of the sodium-proton antiporter NhaA.

Escherichia coli NhaA is a prototype sodium-proton antiporter, which has been extensively characterized by X-ray crystallography, biochemical and biophysical experiments. However, the identities of proton carriers and details of pH-regulated mechanism remain controversial. Here we report constant pH molecular dynamics data, which reveal that NhaA activation involves a net charge switch of a pH sensor at the entrance of the cytoplasmic funnel and opening of a hydrophobic gate at the end of the funnel. The latter is triggered by charging of Asp164, the first proton carrier. The second proton carrier Lys300 forms a salt bridge with Asp163 in the inactive state, and releases a proton when a sodium ion binds Asp163. These data reconcile current models and illustrate the power of state-of-the-art molecular dynamics simulations in providing atomic details of proton-coupled transport across membrane which is challenging to elucidate by experimental techniques.

Correction to "Encapsulating Mobile Proton Carriers into Structural Defects in Coordination Polymer Crystals: High Anhydrous Proton Conduction and Fuel Cell Application".

We describe the encapsulation of mobile proton carriers into defect sites in nonporous coordination polymers (CPs). The proton carriers were encapsulated with high mobility and provided high proton conductivity at 150 °C under anhydrous conditions. The high proton conductivity and nonporous nature of the CP allowed its application as an electrolyte in a fuel cell. The defects and mobile proton carriers were investigated using solid-state NMR, XAFS, XRD, and ICP-AES/EA. On the basis of these analyses, we concluded that the defect sites provide space for mobile uncoordinated H3PO4, H2PO4–, and H2O. These mobile carriers play a key role in expanding the proton-hopping path and promoting the mobility of protons in the coordination framework, leading to high proton conductivity and fuel cell power generation.

Proton Conducting Nanocomposites Using Phosphonic Acid Grafted Polyhedral Oligomeric Silsesquioxane (POSS)

In PEMFC, nanocomposites are drawing attention as the alternative membrane because of selected various acid moiety functionalized additives, increased water retention and improved mechanical and thermal properties. But in modification of nanocomposites, when more than 100 nm-sized particles are introduced in ion channel, ion channel development is affected and hydrogen ion movement is reduced. So this study explores the concept of improving fuel cell membrane performance without compromising proton conductivity by using a 1 ~ 3 nm sized polyhedral oligomeric silsesquioxane (POSS). Polyhedral oligomeric silsesquioxane (POSS) is a molecule that has a spatially defined, rigid and hydrophobic cube-octameric siloxane skeleton (about 1 ~ 3 nm in size) with eight organic vertex groups, one or more of which are reactive or polymerizable. [1 ~ 3]. These particular structural features render POSS be a versatile additive for acquiring enhanced thermomechanical properties, better thermal stability, atom oxygen resistance, abrasion resistance and low water uptake [4 ~ 6]. Only one POSS-based nanocomposite for PEMFC h as been reported [7]. An open-cage POSS carrying three glycidyl epoxy groups was reacted with 4-hydroxybenzenesulfonic acid, the resulting sulfonated POSS was blended with polyvinylalcohol and the blend was crosslinked using ethylenediaminetetracetic dianhydride (EDTAD). This system differs considerably from the system described in this study (open-cage versus closed-cage POSS, crosslinked versus noncross-linked structure and aliphatic versus aromatic composition) and also has several disadvantages as follows: it requires a multistep fabrication process and it contains chemically unstable methylene groups. Additionally, the mechanical and chemical stability was not reported. In this study, POSS nanoadditives carrying phosphonic acid moieties were synthesized, characterized and formulated into Nafion®. As mention in the ref. [8 ~ 12], phosphonic acid groups are good candidate for high temperature proton carriers with the relatively high proton conductivity without water due to its self-dissociation natures. Also we developed Nafion®/3-aminopropyl triethoxysilane (APTES) hybrid membranes with phosphonic acid groups in the previous work in order to improved high temperature performances [11]. These hybrid membranes show high proton conductivities (0.028 S/cm) at 120 oC and 40% RH, so we can confirm the strong influence of phosphonic acid groups in low humid conditions. Also, in contrast to common additives, it can be possible to progressive improvement of proton conductivity because of eight vertex groups which substitute by phosphonic acid groups. We expect to innovatively improve proton conductivities by molecular-closed particle size and many vertex groups of POSS. The phosphonic acid grafted POSS prepared were characterized for particle size and chemical structure. Also Nafion®/POSS-PA nanocomposites were characterized for morphologies, mechanical strength, proton conductivities at different temperatures and humid conditions, and the cell performances at different temperatures.

1000-fold enhancement in proton conductivity of a MOF using post-synthetically anchored proton transporters.

Pyridinol, a coordinating zwitter-ionic species serves as stoichiometrically loadable and non-leachable proton carrier. The partial replacement of the pyridinol by stronger hydrogen bonding, coordinating guest, ethylene glycol (EG), offers 1000-fold enhancement in conductivity (10−6 to 10−3 Scm−1) with record low activation energy (0.11 eV). Atomic modeling coupled with 13C-SSNMR provides insights into the potential proton conduction pathway functionalized with post-synthetically anchored dynamic proton transporting EG moieties.

Structural transformation of an imidazolium-templated two-dimensional aluminophosphate and its proton conduction under anhydrous conditions

We focused on an imidazolium-templated two-dimensional aluminophosphate (C3N2H5)[Al(HPO4)2(H2O)2] (denoted as AlPO-PC-1) with complex hydrogen bonding network to show inherent proton conductivity under anhydrous conditions. Inherent proton conductivity was studied under a N2 atmosphere (zero-humidity conditions). Notably, the AlPO-PC-1 suffers the ordered-to-disordered structural transformation induced by the increase of temperature, which influences the proton conduction process and conduction mechanism. The resulting material shows a proton conductivity of 1.1×10−4Scm−1 at 150°C. At 25–100°C, the proton conduction is controlled by Grotthuss mechanism. While at 115–150°C, the transformation of the structure affords highly mobile proton carriers and both vehicle and Grotthuss mechanism contribute to the proton conduction.

Encapsulating Mobile Proton Carriers into Structural Defects in Coordination Polymer Crystals: High Anhydrous Proton Conduction and Fuel Cell Application.

We describe the encapsulation of mobile proton carriers into defect sites in nonporous coordination polymers (CPs). The proton carriers were encapsulated with high mobility and provided high proton conductivity at 150 °C under anhydrous conditions. The high proton conductivity and nonporous nature of the CP allowed its application as an electrolyte in a fuel cell. The defects and mobile proton carriers were investigated using solid-state NMR, XAFS, XRD, and ICP-AES/EA. On the basis of these analyses, we concluded that the defect sites provide space for mobile uncoordinated H3PO4, H2PO4(-), and H2O. These mobile carriers play a key role in expanding the proton-hopping path and promoting the mobility of protons in the coordination framework, leading to high proton conductivity and fuel cell power generation.

Application of modified chitosan membrane for microbial fuel cell: Roles of proton carrier site and positive charge

Modified chitosan membrane was synthesized as a proton exchange membrane for microbial fuel cell application. Glutaraldehyde and sulfosuccinic acid were used as crosslinking agents in order to improve its ultimate tensile strength and proton conductivity. 3-Chloro-2-hydroxypropyl trimethylammonium chloride was employed for quaternization to develop its antimicrobial activity. The results showed that the proton conductivity of the membrane was enhanced with the content of sulfosuccinic acid, as a result of proton carrier sites, until a certain value was reached. The additional positive charge from quaternization increased with the reaction time. The morphological change of microorganisms in contact with the surface of the quaternized chitosan membrane exhibited damage and the number of damaged microorganisms increased with the positive charge density; nevertheless, the high positive charge density resulted in not only a high antimicrobial property, but also in significant water uptake of the quaternized chitosan membrane. As a consequence, the strength of the membrane was lost. Additionally, the positive charge also accelerated the adhesion of microorganisms at the membrane surface, but the surface growth could be retarded due to the high number of microorganisms being damaged.

The Flip-Flop Diffusion Mechanism across Lipids in a Hybrid Bilayer Membrane

In this study, we examine the mechanism of flip-flop diffusion of proton carriers across the lipid layer of a hybrid bilayer membrane (HBM). The HBM consists of a lipid monolayer appended on top of a self-assembled monolayer containing a Cu-based O2 reduction catalyst on a Au electrode. The flip-flop diffusion rates of the proton carriers dictate the kinetics of O2 reduction by the electrocatalyst. By varying both the tail lengths of the proton carriers and the lipids, we find the combinations of lengths that maximize the flip-flop diffusion rate. These experimental results combined with biophysical modeling studies allow us to propose a detailed mechanism for transmembrane flip-flop diffusion in HBM systems, which involves the bending of the alkyl tail of the proton carrier as the rate-determining step. Additional studies with an unbendable proton carrier further validate these mechanistic findings.

The First Demonstration of the Gyroid in a Polyoxometalate-Based Open Framework with High Proton Conductivity.

The fabrication of extended open frameworks with crystalline ordering on the atomic level by following peculiar mathematical geometry (e.g. Möbius band, Klein bottle, periodic minimal surfaces, etc.) is challenging, but extremely beneficial for discovering non-trivial structure-dependent properties. In light of this, we herein report the first polyoxometalate-based open framework (POM-OF) that definitely lies on the gyroid (G)-minimal surface, which was constructed by a rare pair of chiral POM enantiomers and zinc ions. Due to the presence of the proton carriers (i.e., water, Na(+) , [(Bu)4 N](+) , etc.) in the resultant gyroidal channels, with pore dimensions on the order of the quasi-mesoporous scale, this compound shows a high proton conductivity of 1.04×10(-2) S cm(-1) at a relative humidity of 75 % (80 °C), and also exhibits enormous potential in the application of electrochemical catalysis.

Synthesis of a novel proton exchange membrane for high-temperature applications

A novel proton exchange membrane based on Polyvinylidene Fluoride (PVDF)-CsAl(SO4)2·12H2O suitable for high-temperature applications is synthesised. The proton conductivity and the methanol permeability of the membranes are studied. Results show that the novel membrane holds the proton conductivity in a wide range of temperature (30–200 °C). The water of crystallisation in the CsAl(SO4)2·12H2O is the proton carrier in the membrane, which leads to the proton conductivity. The PVDF-CsAl(SO4)2·H2O membrane also shows a better performance in restraining the methanol permeability. The good conductivity and methanol permeability properties of the novel membrane make it as a candidate material for the high-temperature proton exchange membrane fuel cells (PEMFC).

Anhydrous proton conducting poly(vinyl alcohol) (PVA)/ poly(2-acrylamido-2-methylpropane sulfonic acid) (PAMPS)/1,2,4-triazole composite membrane

The design and fabrication of anhydrous proton exchange membranes are critically important for high temperature proton exchange membrane fuel cell (HT-PEMFC) operating between 100 and 200 °C. Herein, we demonstrate a novel proton conducting membrane consisting of poly(vinyl alcohol) (PVA), poly (2-acrylamido-2-methylpropane sulfonic acid) (PAMPS) and 1,2,4-triazole, which was fabricated by physical blending, casting and solvent evaporation techniques. The in-situ chemical cross-linking was performed by glutaraldehyde (GA) to improve the water management of the membranes. The molecular structure of the membranes and intermolecular interactions between the constituents were confirmed by Fourier-transform infrared spectroscopy (FT-IR). The surface and cross-section morphologies of the membranes were observed by scanning electron microscopy (SEM). The thermal stability performance of the membranes was studied with thermogravimetric analysis (TGA). In order to determine the physico–chemical properties of the membranes, water uptake (WU), dimensional change and ion exchange capacity (IEC) tests were carried out. The proton conductivities of composite membranes increase with the temperature and the temperature dependencies exhibit an Arrhenius behavior. Proton conductivity measurements revealed an optimum ratio between PAMPS and 1,2,4-triazole content to achieve higher proton conductivity. In anhydrous state at 150 °C, the highest proton conductivity measured was 0.002 S/cm for PVA:PAMPS:1,2,4-triazole (1:1:1) composition. Overall, our investigation showed that 1,2,4-triazole is a promising proton carrier reagent above 100 °C when it is embedded into appropriate host polymers.

Proton conduction in crystalline and porous covalent organic frameworks.

Progress over the past decades in proton-conducting materials has generated a variety of polyelectrolytes and microporous polymers. However, most studies are still based on a preconception that large pores eventually cause simply flow of proton carriers rather than efficient conduction of proton ions, which precludes the exploration of large-pore polymers for proton transport. Here, we demonstrate proton conduction across mesoporous channels in a crystalline covalent organic framework. The frameworks are designed to constitute hexagonally aligned, dense, mesoporous channels that allow for loading of N-heterocyclic proton carriers. The frameworks achieve proton conductivities that are 2-4 orders of magnitude higher than those of microporous and non-porous polymers. Temperature-dependent and isotopic experiments revealed that the proton transport in these channels is controlled by a low-energy-barrier hopping mechanism. Our results reveal a platform based on porous covalent organic frameworks for proton conduction.

New Opportunities Offered By Lipid-Modified Electrodes to Interrogate Transmembrane Diffusion Mechanisms and Kinetics

Diffusion of small molecules between intra- and extra-cellular spaces across lipid layers is instrumental to the understanding of fundamental biological transport processes and the improvement in drug delivery schemes. In natural systems, organisms develop intricate ion channels and stimuli-responsive gating machineries for signal transduction, cell identification, and toxin removal, while still allowing the selective and proficient uptake of vital nutrients that are critical to survival, growth, and reproduction. Understanding membrane function is a colossal step in developing cutting-edge drug therapies in a rational way. Lipinski’s rule of five describes the molecular properties essential for the bioavailability and pharmacokinetics of candidate drugs inside human bodies and thus serves as a first-order consideration for drug design.Altering the length of an alkyl tail is thus a viable method to tune the lipophilicity of a compound, thus modulating the transport properties of the drug. In this presentation, we report on our efforts to interrogate the “flip-flop” diffusion mechanism of alkyl proton carriers traversing the lipid layer of a hybrid bilayer membrane (HBM) using electrochemical techniques including but not limited to electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and pulse techniques. The 4-nm thick HBM electrochemical platform consists of a lipid monolayer appended on top of a self-assembled monolayer (SAM) containing a dinuclear Cu-triazole complex for O2 reduction reaction (ORR) on a Au electrode prepared using electron-beam evaporation (Scheme 1a). The “flip-flop” diffusion rates of the proton carriers dictate the O2 reduction turnover frequency by the Cu-based electrocatalyst. By varying both the tail lengths of the proton carriers and the lipids, we find that a difference between the lipid tail lengths and the proton carrier tail lengths of approximately 6-10 Å results in a maximum “flip-flop” diffusion rate. We evaluate these empirical findings using a biophysical model that contains parameters considering changes in Coulombic interactions, stress buildup, surface tension, and dielectric constants across the lipid-water interface. The model correctly mimics the relative alterations in the energy barriers associated with the rate-determining step (RDS) for the “flip-flop” diffusion process (Scheme 1b). Studies with a rigid proton carrier further substantiate findings that the RDS involves the bending of the alkyl tail of the proton carrier as it moves across the hydrophobic interior of the lipid layer. We envision that the methodologies developed here will ultimately lead to improved understanding of the mechanismof “flip-flop” diffusion in lipid bilayers and aid in the development of next-generation targeted drug delivery schemes. Acknowledgements. E.C.M.T. acknowledges a Croucher Foundation Scholarship. We thank the US Department of Energy (DE-FG02-95ER46260) for support of this research. Scheme 1 is presented here. Figure 1

Bio-Inspired Photoresponsive Regulator for Proton Cross-Membrane Transport

Proton-Coupled Electron Transfer (PCET) is ubiquitous in nature, essential to life but particularly difficult to study because of the complexity of natural systems. We recently developed a new experimental framework to permit fine-tuning of proton-transfer kinetics without perturbing the thermodynamics. The regulation took advantage of the “flip-flop” diffusion of proton carriers inside lipid membranes. Unfortunately, the diffusion happens spontaneously and more precise control could be beneficial. As a result, we designed the first synthetic photoresponsive proton gate incorporated in a lipid layer. The new proton carrier features a boronic acid head-group for proton transfer, a stiff stilbene body for photoresponsiveness, and an alkyl tail for lipid incorporation. The light-induced cross-membrane proton transfer was quantified by the activity of an O2 reduction catalyst buried under the lipid layer by electrochemistry. This molecular switch mimics the natural system to precisely control proton relocation without perturbing the proton thermodynamics (Scheme 1). Scheme 1. Illustration of photoresponsive transmembrane proton transfer. Figure 1

Coenzyme Q10 and its Effective Sources

Coenzyme Q10 (2,3-dimethoxy, 5-methyl, 6-decaprenyl benzoquinone, CoQ10) is naturally present in many organisms. It has key roles in several biochemical pathways. CoQ10, as an electron and proton carrier for energy coupling leads to Adenosine Triphosphate (ATP) formation. Furthermore, in medicine, the pharmacological use of CoQ10 has attracted more attention due to its benefits in treating cardiovascular and degenerative neurologic diseases. CoQ10 can be produced by chemical synthesis, extraction from biological tissues and microbial fermentation. It is found in plants such as soya bean, peanut, palm oil and litchi pericarp and in animals such as pelagic fish, beef and pork hearts. Various analytical methods have been published for the extraction and analysis of CoQ10 from different matrices. Biological production of CoQ10 offers an environmentally benign option based on the enzymatic catalysis at the cellular level. Moreover, this process due to ease of control and low production costs offers more advantages over the existing technologies.

Interplaying Intrinsic and Extrinsic Proton Conductivities in Covalent Organic Frameworks

A sulfonic-acid-based covalent organic framework (TpPa-SO3H) has been synthesized that exhibits intrinsic proton conductivity under anhydrous conditions. The sulfonic acid groups are aligned on the two-dimensional (2D) layers at periodic intervals and promote the proton hopping inside the hexagonal one-dimensional channel. The intrinsic proton conductivity of TpPa-SO3H was measured as 1.7 × 10–5 S cm–1 at 120 °C under anhydrous conditions. To enhance the proton conductivity, we have synthesized a hybrid COF TpPa-(SO3H-Py) by a ligand-based solid-solution approach that contains sulfonic acid as the acidic site, as well as pyridine as the basic site, in order to immobilize acidic proton carrier molecules. Impregnation of phytic acid molecules inside the framework increases the anhydrous proton conductivity up to 5 × 10–4 S cm–1 at 120 °C. Such an approach highlights the advantage and first-time use of hybrid COF for interplaying intrinsic to extrinsic proton conductivity.

Effect of end-group cross-linking on transport properties of sulfonated poly(phenylene sulfide nitrile)s for proton exchange membranes

A series of end-group cross-linked membranes (Az-XESPSN) were prepared by click reaction to investigate the effects of cross-linking on the morphology and proton transport properties of proton exchange membranes. The morphological transformations resulting from thermal annealing and cross-linking were observed by means of atomic force microscopy (AFM) and transmission electron microscopy (TEM). Compared to the non-cross-linked ESPSN membranes, the Az-XESPSN membranes exhibited lower water uptake and improved mechanical and chemical stabilities. In addition, the Az-XESPSN membranes exhibited higher proton conductivities (0.018–0.028 S cm−1) compared to those of the ESPSN membranes (0.0044–0.0053 S cm−1) and Nafion 212 (0.0061 S cm−1), particularly in conditions of elevated temperature (120 °C) and low relative humidity (35%). Such enhancements can be attributed to a synergistic effect of well-defined hydrophilic ionic clusters and triazole groups that function as proton carriers under anhydrous conditions. Furthermore, the Az-XESPSN membranes exhibited significantly enhanced single cell performance and long-term stability compared to those of ESPSN membranes.

Untargeted Metabolomics To Ascertain Antibiotic Modes of Action.

Deciphering the mode of action (MOA) of new antibiotics discovered through phenotypic screening is of increasing importance. Metabolomics offers a potentially rapid and cost-effective means of identifying modes of action of drugs whose effects are mediated through changes in metabolism. Metabolomics techniques also collect data on off-target effects and drug modifications. Here, we present data from an untargeted liquid chromatography-mass spectrometry approach to identify the modes of action of eight compounds: 1-[3-fluoro-4-(5-methyl-2,4-dioxo-pyrimidin-1-yl)phenyl]-3-[2-(trifluoromethyl)phenyl]urea (AZ1), 2-(cyclobutylmethoxy)-5′-deoxyadenosine, triclosan, fosmidomycin, CHIR-090, carbonyl cyanide m-chlorophenylhydrazone (CCCP), 5-chloro-2-(methylsulfonyl)-N-(1,3-thiazol-2-yl)-4-pyrimidinecarboxamide (AZ7), and ceftazidime. Data analysts were blind to the compound identities but managed to identify the target as thymidylate kinase for AZ1, isoprenoid biosynthesis for fosmidomycin, acyl-transferase for CHIR-090, and DNA metabolism for 2-(cyclobutylmethoxy)-5′-deoxyadenosine. Changes to cell wall metabolites were seen in ceftazidime treatments, although other changes, presumably relating to off-target effects, dominated spectral outputs in the untargeted approach. Drugs which do not work through metabolic pathways, such as the proton carrier CCCP, have no discernible impact on the metabolome. The untargeted metabolomics approach also revealed modifications to two compounds, namely, fosmidomycin and AZ7. An untreated control was also analyzed, and changes to the metabolome were seen over 4 h, highlighting the necessity for careful controls in these types of studies. Metabolomics is a useful tool in the analysis of drug modes of action and can complement other technologies already in use.