Alcoholic Proton Research Articles

Enhancement of Lithium-Mediated Nitrogen Reduction by Modifying Center Atom of Tetraalkyl-Type Ionic Liquids.

The lithium-mediated nitrogen reduction reaction (Li-NRR) offers a viable alternative to the Haber-Bosch process for ammonia production. However, ethanol, a common proton carrier in Li-NRR, exhibits electrochemical instability, leading to oxidation at the anode or byproduct formation at the cathode. This study replaces alcoholic proton carriers with ionic liquids (ILs), specifically tetrabutylphosphonium chloride (TBPCl) and tetrabutylammonium chloride (TBACl), to examine how the electronegativity differences between the central atom and adjacent carbon of the cation affect catalytic performance. The results show that switching the central atom in tetraalkyl-type ILs markedly enhances performance, specifically resulting in a 1.45-fold increase in Faradaic efficiency (FE) with the transition from phosphonium to ammonium cation of ILs. Additionally, optimal IL concentrations in the electrolyte are identified to maximize ammonia yield. TBACl, in particular, demonstrates enhanced ammonia production and operational stability, achieving an ammonia yield rate of 13.60 nmol/cm²/s, an FE of 39.5%, and operational stability for over 12 h under conditions of 10 mA/cm² and 10 atm. This research underscores the potential of precise IL modifications for more efficient and sustainable Li-NRR.

Enhancement of Lithium‐Mediated Nitrogen Reduction by Modifying Center Atom of Tetraalkyl‐Type Ionic Liquids

The lithium‐mediated nitrogen reduction reaction (Li‐NRR) offers a viable alternative to the Haber‐Bosch process for ammonia production. However, ethanol, a common proton carrier in Li‐NRR, exhibits electrochemical instability, leading to oxidation at the anode or byproduct formation at the cathode. This study replaces alcoholic proton carriers with ionic liquids (ILs), specifically tetrabutylphosphonium chloride (TBPCl) and tetrabutylammonium chloride (TBACl), to examine how the electronegativity differences between the central atom and adjacent carbon of the cation affect catalytic performance. The results show that switching the central atom in tetraalkyl‐type ILs markedly enhances performance, specifically resulting in a 1.45‐fold increase in Faradaic efficiency (FE) with the transition from phosphonium to ammonium cation of ILs. Additionally, optimal IL concentrations in the electrolyte are identified to maximize ammonia yield. TBACl, in particular, demonstrates enhanced ammonia production and operational stability, achieving an ammonia yield rate of 13.60 nmol/cm²/s, an FE of 39.5%, and operational stability for over 12 h under conditions of 10 mA/cm² and 10 atm. This research underscores the potential of precise IL modifications for more efficient and sustainable Li‐NRR.

A Solid‐Solution with Asymmetric Ni‐O‐Cr Sites for Boosting Protonation toward Anodic Oxidation

AbstractReplacing the slow protonation process of oxygen evolution reaction (OER) with the fast protonation of alcohol electro‐oxidation can decrease the driving potentials, thus improving overall efficiency of electrochemical devices. However, the formation of effective catalytic sites for alcohol oxidation remains challenging in accelerating protonation to inhibit metal leaching and improve catalyst stability. Herein, asymmetric Ni‐O‐Cr sites are constructed by alloying Cr into the NiO matrix to optimize coordination environments, showing significantly enhanced stability during alcohol electro‐oxidation. The asymmetric Ni‐O‐Cr can maintain constant valence states of Cr and Ni during alcohol oxidation, efficiently suppressing metal dissolution even at high oxidation potentials. In situ electrochemical characterizations combined with theoretical calculations indicate that asymmetric Ni‐O‐Cr can improve adsorption and activation of OH* and alcohol molecules compared to pure NiO, thus increasing anodic kinetics. The theoretical results also indicate that the smaller gap of Ni 3d‐O 2p in asymmetric Ni‐O‐Cr strengthens charge transfer, leading to fast protonation of catalytic sites with enhanced stability. This work gives insights into boosting anodic protonation using asymmetric sites‐enriched solid‐solution electrocatalysts.

The development of logic gate-based fluorescent probes that respond to intracellular hydrogen peroxide and pH in tandem

Logic gate-based fluorescent probes are powerful tools for the discriminative sensing of multiple signaling molecules that are expressed in concert during the progression of many diseases such as inflammation, cancer, aging, and other disorders. To achieve logical sensing, multiple functional groups are introduced to the different substitution sites of a single fluorescent dye, which increases the complexity of chemical synthesis. Herein, we report a simple strategy that incorporates just one responsive unit into a hemicyanine dye achieving the logic gate-based sensing of two independent analytes. We introduce boronic acid to hemicyanine to quench the fluorescence, and in the presence of hydrogen peroxide (H2O2), the fluorescence is recovered due to removal of the boronate. Interestingly, the subsequent decrease in pH turned the red fluorescence of hemicyanine to green emissive because of protonation of the phenolic alcohol. This unique feature of the probe enables us to construct “INHIBIT” and “AND” logical gates for the accurate measuring of intracellular H2O2 and acidic pH in tandem. This study offers insight into the simple construction of logic-gate based fluorescent probes for the tandem sensing of multiple analytes that are correlatively produced during disease progression.

Self-sustainable, self-healable sulfonated graphene oxide incorporated nafion/poly(vinyl alcohol) proton exchange membrane for direct methanol fuel cell applications

Nafion, a perfluorosulfonic acid polymer, has been the standard membrane material for direct methanol fuel cells (DMFCs) due to its proton-carrying capabilities, despite its shortcomings as a methanol barrier. To attain self-healing and methanol-blocking properties, the incorporation of poly(vinyl alcohol) (PVA) polymer into Nafion was pursued. However, this strategy resulted in low proton conductivity. Thus, acid functional groups were added to a secondary modifier to boost proton conductivity. In this work, sulfonated graphene oxide (SGO) was assembled with Nafion and PVA through a simple freezing-thawing method to demonstrate a self-healable proton exchange membrane (PEM) without compromising the proton conductivity of Nafion. The synergistic effect of SGO in methanol-blocking and proton transport successfully strode over recast Nafion by hampering 33.2 % of methanol permeation and increasing 19.5 % of proton conductivity. As a result, the selectivity of the best hybrid PEM (N/PVA/SGO1.0) was increased by 1.8 times in comparison to recast Nafion. A single cell passive DMFC made using the novel hybrid membrane exhibited a power density of 6.07 mW cm−2 at a current density of 26.48 mA cm−2, and an open circuit voltage of 0.55 V at room temperature using 4 M methanol. This performance was essentially higher than that achieved by recast Nafion and commercial Nafion 117. The N/PVA/SGO1.0 hybrid membrane also showed remarkable self-healing properties, with 89 % recovery of methanol blocking function through reversible hydrogen bonding, illustrating its tremendous sustainable potential for use in DMFCs.

Alcoholic Solvent-Mediated Excited-State Proton Transfer Dynamics of a Novel Dihydroxynaphthalene Dye.

The excited-state proton transfer (ESPT) reaction is an important primary photochemical process because it is closely related to photophysical properties. Although ESPT research in aqueous solutions is predominant, alcoholic solvent-mediated ESPT studies are also significant in terms of photoacid-based reactions. Especially, the research for dihydroxynaphthalenes (DHNs) has been largely neglected due to the challenging data interpretation of two hydroxyl groups. A novel fluorescent dye, resveratrone, synthesized by light irradiation of resveratrol, which is famous for its antioxidant properties, can be regarded as a type of DHN, and it has distinctive optical properties, including high quantum yield, a large two-photon absorption coefficient, a large Stokes shift, and very high biocompatibility. In this study, we investigate the overall kinetics of the optical properties of resveratrone and find evidence for alcoholic solvent-mediated ESPT involvement in the radiative properties of resveratrone with a large Stokes shift. Our investigation provides an opportunity to revisit the overlooked photophysical properties of intriguing photoacid behavior and the large Stokes shift of the dihydroxynaphthalene dye.

Investigating the Performance of a Zinc Oxide Impregnated Polyvinyl Alcohol-Based Low-Cost Cation Exchange Membrane in Microbial Fuel Cells.

The current study investigated the development and application of lithium (Li)-doped zinc oxide (ZnO)-impregnated polyvinyl alcohol (PVA) proton exchange membrane separator in a single chambered microbial fuel cell (MFC). Physiochemical analysis was performed via FT-IR, XRD, TEM, and AC impedance analysis to characterize thus synthesized Li-doped ZnO. PVA-ZnO-Li with 2.0% Li incorporation showed higher power generation in MFC. Using coulombic efficiency and current density, the impact of oxygen crossing on the membrane cathode assembly (MCA) area was evaluated. Different amounts of Li were incorporated into the membrane to optimize its electrochemical behavior and to increase proton conductivity while reducing biofouling. When acetate wastewater was treated in MFC using a PVA-ZnO-Li-based MCA, the maximum power density of 6.3 W/m3 was achieved. These observations strongly support our hypothesis that PVA-ZnO-Li can be an efficient and affordable separator for MFC.

Structures of lactaldehyde reductase, FucO, link enzyme activity to hydrogen bond networks and conformational dynamics.

A group-III iron containing 1,2-propanediol oxidoreductase, FucO, (also known as lactaldehyde reductase) from Escherichia coli was examined regarding its structure-dynamics-function relationships in the catalysis of the NADH-dependent reduction of (2S)-lactaldehyde. Crystal structures of FucO variants in the presence or absence of cofactors have been determined, illustrating large domain movements between the apo and holo enzyme structures. Different structures of FucO variants co-crystallized with NAD+ or NADH together with substrate further suggest dynamic properties of the nicotinamide moiety of the coenzyme that are important for the reaction mechanism. Modelling of the native substrate (2S)-lactaldehyde into the active site can explain the stereoselectivity exhibited by the enzyme, with a critical hydrogen bond interaction between the (2S)-hydroxyl and the side-chain of N151, as well as the previously experimentally demonstrated pro-(R) selectivity in hydride transfer from NADH to the aldehydic carbon. Furthermore, the deuterium kinetic isotope effect of hydride transfer suggests that reduction chemistry is the main rate-limiting step for turnover which is not the case in FucO catalysed alcohol oxidation. We further propose that a water molecule in the active site - hydrogen bonded to a conserved histidine (H267) and the 2'-hydroxyl of the coenzyme ribose - functions as a catalytic proton donor in the protonation of the product alcohol. A hydrogen bond network of water molecules and the side-chains of amino acid residues D360 and H267 links bulk solvent to this proposed catalytic water molecule.

Catalysis by [Ga4 L6 ]12- Metallocage on the Nazarov Cyclization: The Basicity of Complexed Alcohol is Key.

The Nazarov cyclization is investigated in solution and within K12 [Ga4 L6 ] supramolecular organometallic cage by means of computational methods. The reaction needs acidic condition in solution but works at neutral pH in the presence of the metallocage. The reaction steps for the process are analogous in both media: (a) protonation of the alcohol group, (b) water loss and (c) cyclization. The relative Gibbs energies of all the steps are affected by changing the environment from solvent to the metallocage. The first step in the mechanism, the alcohol protonation, turns out to be the most critical one for the acceleration of the reaction inside the metallocage. In order to calculate the relative stability of protonated alcohol inside the cavity, we propose a computational scheme for the calculation of basicity for species inside cavities and can be of general use. These results are in excellent agreement with the experiments, identifying key steps of catalysis and providing an in-depth understanding of the impact of the metallocage on all the reaction steps.

Effect of Substituents in Functional Bipyridonate Ligands on Ruthenium‐Catalyzed Dehydrogenative Oxidation of Alcohols: An Experimental and Computational Study

AbstractA series of hexamethylbenzene (HMB)–Ru complexes 2–5 bearing a 4,4’‐functionalized 2,2’‐bipyridine‐6,6’‐dionate (bpyO) ligand, which exhibits metal‐ligand cooperative catalysis, was prepared with the aim of developing excellent catalyst for dehydrogenative oxidation of alcohols. Interestingly, the catalytic activity increased in the order 3 (CF3) <4 (OMe)<2 (H) <5 (NMe2), where substituents at 4,4’‐positions of bpyO ligand are in parentheses. This is different from the order of simple electron‐donating ability. DFT calculations revealed that the rate‐limiting step is the concerted proton/hydride transfer from the alcohol to the complex. The activation energy decreases as the interaction between the alcoholic proton and the O atom of the bpyO ligand becomes stronger; hence, the introduction of the NMe2 group decreases the activation energy, whereas that of the CF3 group increases it. The unexpectedly lower catalytic ability of 4 than that of 2 results from the enthalpy–entropy compensation effect.

Conformational flexibility and hydrogen bonding in 5-aminopentanol

Rotational spectra of two conformers of 5-aminopentanol have been recorded using a Fourier-transform microwave spectrometer. For conformer C-1, eighty-two hyperfine components from the twenty-four a-, b-, and c-type transitions measured were fit to the quadrupole coupling constants, χaa = −2.954(2) MHz, χbb = 2.386(3) MHz. For conformer C-2, the fit of the seventy-six hyperfine components from the twenty-four a- and b-type transitions measured yielded χaa = −3.636(1) MHz and χbb = 2.087(2) MHz. Rotational and centrifugal distortion constants determined from fits of the resulting unsplit line centers to the Watson A-reduction Hamiltonian are A = 3322.169(1) MHz, B = 1958.7382(9) MHz, C = 1402.5957(8) MHz, ΔJ = 0.60(2) kHz, ΔJK = −0.21(8) kHz, ΔK = 0.99(3) kHz, δJ = 0.203(7) kHz, and δK = 1.1(1) kHz for conformer C-1 and A = 3249.2215(6) MHz, B = 2027.9327(3) MHz, C = 1432.5846(3) MHz, ΔJ = 0.545(6) kHz, ΔJK = 0.25(2) kHz, ΔK = 0.39(5) kHz, δJ = 0.18(4) kHz, and δK = 0.96(3) kHz for conformer C-2. The two experimental conformations are consistent with the two lowest energy ab initio MP2/6-311++G(d,p) structures. Both conformations of 5-aminopentanol are stabilized by an intramolecular hydrogen bond from the alcohol proton to amino nitrogen. The flexibility introduced by the five carbons in the alkyl group separating the amino and alcohol functional groups resulted in the first appearance of multiple low energy conformers being detected relative to the four, three, and two carbons in 4-aminobutanol, 3-aminopropanol, and 2-aminoethanol respectively in which only one experimental conformation was observed.

Dissertation Project for the Forensic Science Laboratory: Birch Reduction of Ephedrine and Analysis of Byproducts of Forensic Science Interest

This undergraduate dissertation project was designed to enhance organic and analytical chemistry skills of final year forensic science students. A modified Birch reaction method was employed to synthesize amphetamine from ephedrine and detect the most known byproduct of clandestine manufacture of amphetamines, e.g., 1-(1,4-cyclohexadienyl)-2-methylaminopropane (CMP). The use of this synthetic method led to simultaneous N-demethylation and dehydroxylation of the alkaloid. Harmful liquid ammonia and lithium metal, which are the typical reagents of the classic Birch reaction, were replaced by the safer sodium silica gel stage I (Na-SG-I) and an alcoholic proton source. Liquid chromatography–mass spectrometry (LC-MS) was used to monitor reaction progress and identify starting material, products, and byproducts, whereas proton and carbon nuclear magnetic resonance (1H and 13C NMR) and heteronuclear single-quantum correlation (HSQC) NMR spectroscopy experiments were employed to characterize amphetamine and the parent compound ephedrine. This multiweek project-based learning experience has been running for three years at De Montfort University (DMU), which offers a well-established Forensic Science BSc (Hons) undergraduate course. The students were guided with the help of an academic instructor through a research-like setting delving into synthesis, characterization, and analysis of a drug of abuse and its byproduct. As part of this learning experience, which culminated in a body of work that informed the content of final year dissertations, the students gained useful organic chemistry skills and consolidated previously acquired knowledge in trace analysis. A survey of the dissertations’ final grades and evaluation of end-of-project questionnaires revealed that students responded well to the challenges posed by the organic chemistry aspect of the lab and that the project topic and methods were engaging and very relevant to the forensic science course.

Метод определения констант образования межмолекулярной Н-связи по данным ИК-спектроскопии

An experimental method is proposed for determining the efficiency of the formation of intermolecular hydrogen bonds by determining the formation constant of the H-complex (K). The essence of the experiment to determine the value of K is that for one initial concentration of the proton donor, it is necessary to register the change in the optical density at the absorption wavelength of the monomers and the change in the optical density of the complexes of IR absorption bands at two concentrations of the proton acceptor. This approach was tested on the example of the interaction of butyl alcohol (proton donor) with 4-chloromethyl-1.3-dioxolane (proton acceptor). The obtained value of the equilibrium constant was 72.2 M-1. It is concluded that the proposed method for determining the value of K can be used not only in IR, but also in UV-visible spectroscopy.

Two-Substrate Glyoxalase I Mechanism: A Quantum Mechanics/Molecular Mechanics Study.

Glyoxalase I (GlxI) is an important enzyme that catalyzes the detoxification of methylglyoxal (MG) with the help of glutathione (H-SG). It is currently unclear whether MG and H-SG are substrates of GlxI or whether the enzyme processes hemithioacetal (HTA), which is nonenzymatically formed from MG and H-SG. Most previous studies have concentrated on the latter mechanism. Here, we study the two-substrate reaction mechanism of GlxI from humans (HuGlxI) and corn (ZmGlxI), which are Zn(II)-active and -inactive, respectively. Hybrid quantum mechanics/molecular mechanics calculations were used to obtain geometrical structures of the stationary points along reaction paths, and big quantum mechanical systems with more than 1000 atoms and free-energy perturbations were used to improve the quality of the calculated energies. We studied, on an equal footing, all reasonable reaction paths to the S- and R-enantiomers of HTA from MG and H-SG (the latter was considered in two different binding modes). The results indicate that the MG and H-SG reaction in both enzymes can follow the same path to reach S-HTA. However, the respective overall barriers and reaction energies are different for the two enzymes (6.1 and -9.8 kcal/mol for HuGlxI and 15.7 and -2.2 kcal/mol for ZmGlxI). The first reaction step to produce S-HTA is facilitated by a crystal water molecule that forms hydrogen bonds with a Glu and a Thr residue in the active site. The two enzymes also follow similar paths to R-HTA. However, the reactions reach a deprotonated and protonated R-HTA in the human and corn enzymes, respectively. The production of deprotonated R-HTA in HuGlxI is consistent with other theoretical and experimental works. However, our calculations show a different behavior for ZmGlxI (both S- and R-HTA can be formed in the enzyme with the alcoholic proton on HTA). This implies that Glu-144 of corn GlxI is not basic enough to keep the alcoholic proton. In HuGlxI, the two binding modes of H-SG that lead to S- and R-HTA are degenerate, but the barrier leading to R-HTA is lower than the barrier to S-HTA. On the other hand, ZmGlxI prefers the binding mode, which produces S-HTA; this observation is consistent with experiments. Based on the results, we present a modification for a previously proposed two-substrate reaction mechanism for ZmGlxI.

Sulfonated poly (arylene ether sulfone)-graft-sulfonated poly (vinyl alcohol) proton exchange membranes: Improved proton selectivity

Aldehyde terminated sulfonated poly (arylene ether sulfone) (SPAES-CHO) is prepared by a series of nucleophilic substitution reaction based on SPAES in this paper. Novel SPAES-graft-SPVA (SPAES-g-SPVA) membranes are fabricated by acetal reaction between SPAES-CHO and different amounts of sulfonated poly (vinyl alcohol) (SPVA). The 1H-NMR and FTIR indicate the successful preparation of SPAES-CHO and SPAES-g-SPVA membranes. With the introduction of SPVA, the SPAES-g-SPVA membranes have much lower methanol permeability than pure SPAES membrane and Nafion117 membrane. The methanol permeability coefficients of the SPAES-g-SPVA membranes decrease from 3.41 × 10−7 cm2 s−1 to 1.67 × 10−7 cm2 s−1 with the increase of SPVA content. And the proton conductivity of all the membranes is higher than 15 mS cm−1 at 25°C. Moreover, SPAES-g-SPVA membranes exhibit high proton selectivity. Especially, SPAES-g-SPVA-30% membrane has the highest proton selectivity, which is nearly five times higher than Nafion117.

Switching a HO···π Interaction to a Nonconventional OH···π Hydrogen Bond: A Completed Crystallographic Puzzle.

In this article, we present crystallographic and spectroscopic evidence of a tunable system wherein a HO···π interaction switches incrementally to a nonconventional OH···π hydrogen bonding (HB) interaction. More specifically, we report the synthesis of substituted forms of model system 1 to study the effects of aryl ring electronic density on the qualitative characteristics of OH···π hydrogen bonds therein. The OH stretch in experimental infrared data, in agreement with density-functional theory (DFT) calculations, shows continuous red-shifts as the adjacent ring becomes more electron rich. For example, the OH stretch of an amino-substituted analogue is red-shifted by roughly 50 cm-1 compared to the same stretch in the CF3 analogue, indicating a significantly stronger HB interaction in the former. Moreover, DFT calculations (ωB97XD/6-311+G**) predict that increasing electronic density on the adjacent top ring reduces the aryl π-OH σ* energy gap with a concomitant enhancement of the OH n-π* energy gap. Consequently, a dominant π-σ* interaction in the amino substituted analogue locks the system in the in-form while a favorable n-π* interaction reverses the orientation of the oxygen-bound hydrogen in its protonated form. Additionally, the 1H NMR data of various analogues reveal that stronger OH···π interactions in systems with electron-rich aromatic rings slow exchange of the alcoholic proton, thereby revealing coupling with the geminal proton. Finally, X-ray crystallographic analyses of a spectrum of analogues clearly visualize the three distinct stages of "switch"-starting with exclusive HO···π, to partitioned HO···π/OH···π, and finally to achieving exclusive OH···π forms. Furthermore, the crystal structure of the amino analogue reveals an interesting feature in which an extended HB network, involving two conventional (NH···O) and two nonconventional (OH···π) HBs, dimerizes and anchors the molecule in the unit cell.

Intramolecular hydrogen bond stabilized conformation of 3-aminopropanol

Rotational spectra of the most abundant, three 13C, and the 15N isotopologues of 3-aminopropanol have been recorded in natural abundance using a Fourier-transform microwave spectrometer. For the most abundant isotopologue, 54 hyperfine components from the thirteen a- and b-type transitions measured were fit to the quadupole coupling constants, χaa = −2.551(1) MHz, χbb = 1.248(1) MHz. Rotational and centrifugal distortion constants determined from fits of the resulting unsplit line centers to the Watson A-reduction Hamiltonian are A = 7405.303(1) MHz, B = 3868.1925(5) MHz, C = 2829.2615(7) MHz, ΔJ = 1.90(3) kHz, ΔJK = −0.5(3) kHz, ΔK = 2.7(3) kHz, δJ = 0.5(4) kHz, and δK = 4.0(4) kHz. Five to six transitions were measured for each of the 13C and 15N isotopologues and rotational constants were determined by fixing the distortion constants to the values found for the normal isotope. The five sets of moments of inertia were used to determine the 3-aminopropanol substitution structure as well to perform a least-squares fit. The heavy atom coordinates determined from these two methods are in good agreement. The newly measured moments of inertia of the heavy atoms has allowed for a refinement of the structure determined by an earlier microwave study. The conformation of 3-aminopropanol is stabilized by an intramolecular hydrogen bond from the alcohol proton to amino nitrogen. The experimental structure is consistent with the lowest energy ab initio [MP2/6-311++G(d,p)] structure.

Quantum Mechanics/Molecular Mechanics Study of the Reaction Mechanism of Glyoxalase I

Glyoxalase I (GlxI) is a member of the glyoxalase system, which is important in cell detoxification and converts hemithioacetals of methylglyoxal (a cytotoxic byproduct of sugar metabolism that may react with DNA or proteins and introduce nucleic acid strand breaks, elevated mutation frequencies, and structural or functional changes of the proteins) and glutathione into d-lactate. GlxI accepts both the S and R enantiomers of hemithioacetal, but converts them to only the S-d enantiomer of lactoylglutathione. Interestingly, the enzyme shows this unusual specificity with a rather symmetric active site (a Zn ion coordinated to two glutamate residues; Glu-99 and Glu-172), making the investigation of its reaction mechanism challenging. Herein, we have performed a series of combined quantum mechanics and molecular mechanics calculations to study the reaction mechanism of GlxI. The substrate can bind to the enzyme in two different modes, depending on the direction of its alcoholic proton (H2; toward Glu-99 or Glu-172). Our results show that the S substrate can react only if H2 is directed toward Glu-99 and the R substrate only if H2 is directed toward Glu-172. In both cases, the reactions lead to the experimentally observed S-d enantiomer of the product. In addition, the results do not show any low-energy paths to the wrong enantiomer of the product from neither the S nor the R substrate. Previous studies have presented several opposing mechanisms for the conversion of R and S enantiomers of the substrate to the correct enantiomer of the product. Our results confirm one of them for the S substrate, but propose a new one for the R substrate.

Effects of covalent bond interactions on properties of polyimide grafting sulfonated polyvinyl alcohol proton exchange membrane for vanadium redox flow battery applications

The preparation and characterization of novel carboxyl-containing polyimide (PID) grafting sulfonated polyvinyl alcohol (SPVA) copolymer membranes applied in vanadium redox flow batteries (VRFBs) are presented in this work. The microphase structures of the copolymer membranes are identified by TEM and XRD. Other basic properties are characterized, particularly the oxidative and water stability. The copolymer membranes exhibit better chemical stability than normal SPIs with five-numbered rings due to the covalent bonds between PI and SPVA as well as highly dispersed microphase separated structure. The physico-chemical properties of the copolymer membranes, including IEC, water uptake, swelling ratio, proton conductivity and vanadium ion permeability are evaluated and compared with Nafion 117. The PID30-g-SPVA membrane has the highest proton selectivity (1.33 × 105 S min cm−3), being much higher than that of Nafion 117 (0.41 × 105 S min cm−3). In VRFB single cell tests, the cells assembled with copolymer membranes show higher coulombic efficiency (CE), higher energy efficiency (63.3% vs 74.3% at 90 mA cm−2) and much lower self-discharge rate than with Nafion 117. In addition, the copolymer membranes retain excellent stability after 100 cycles. All the results show that the copolymer membranes have promising prospects for VRFB applications.

Cooperation between an alcoholic proton and boryl species in the catalytic gem-hydrodiborylation of carboxylic esters to access 1,1-diborylalkanes

Cooperation between an alcoholic proton and boryl species in the selective gem-hydrodiborylation of carboxylic esters is described.