The meyer-schuster rearrangement and hydrohalide addition of 3-alkynyl-3-hydroxy-1H-isoindol-1-ones

Treatment of N-methyl and N-phenylphthalimide with appropiate lithium acetylides in tetrahydrofuran obtained the acetylenic alcohols 2a through 2h . These compounds, when subjected to mildly acidic hydrolysis conditions in aqueous organic solvents, underwent Meyer-Schuster rearrangement to yield the α,β-unsaturated carbonyl compounds 4a through 4h which were determined to have the E configuration. The phenyl ethynyl analogs of series 4 underwent hydrohalide addition when treated with hydrogen halides in water solution.     

Oxygen reduction reaction on polycrystalline gold. Pathways of hydrogen peroxide transformation in the acidic medium

The mechanism of oxygen electroreduction on polycrystalline gold is studied in the acidic medium. Hydrogen peroxide is the main reaction product. However, two potential regions can be singled out in which the oxygen electroreduction reaction proceeds by different pathways. The first region is the potential interval close to the steady-state potential. Here, the oxygen electroreduction virtually completely produces peroxide. The second interval is the potential range of considerable cathodic polarization values. In this case, peroxide can be reduced to water. The low energy of hydrogen peroxide adsorption on gold determines the considerable overpotential of peroxide reduction. It is shown that on the gold electrode surface, the catalytic decomposition of peroxide occurs. The use of the method of electrochemical impedance spectroscopy allows the peculiarities of the oxygen reaction associated with hydrogen peroxide transformations to be revealed. In the acidic medium, the reactions of consecutive reduction of oxygen through the intermediate formation of hydrogen peroxide and the catalytic decomposition of the intermediate product are shown to proceed simultaneously. The ratio of rate constants of electrochemical stages depends on the potential. The chemical decomposition is observed both near the steady-state potential and in the cathodic region where considerable electrochemical reduction of peroxide occurs.     

Bioelectrocatalysis by Hydrogenase Th. Roseopersicina Immobilized on Carbon Materials

Application of various carbon materials as substrates for immobilizing hydrogenase and creating a hydrogen enzyme electrode is studied. A stable, highly-active electrocatalyst for mediatorless oxidation–evolution of hydrogen is obtained. The electrocatalyst uses hydrogenase from Th. roseopersicina immobilized on an inactive carbon material (based on carbon cloth TVSh-300M) and retains more than 50% of its initial activity after a half year in storage. An equilibrium hydrogen potential is established on enzyme electrodes made of a graphitized cloth and graphite rods with hydrogenase immobilized on them.     

Researches on chemically modified electrode: V. Catalytic reduction of oxygen on iron porphyrin modified electrode

By surface organic synthesis a Fe (III) tetra-o-aminophenyl porphyrin modified electrode was successfully prepared on glassy carbon electrode surface through amidization. The preparative conditions were investigated in detail. Using cyclic voltammetry and semidifferential neo-polarography in an acidic aqueous solution the behavior of the catalytic reduction of oxygen on iron porphyrin modified electrode was studied. Based on experimental results it was shown that the irreversible process of 2-electron-reduction to hydrogen peroxide belongs to EC parallel catalytic process.     

Nucleophilic character of alkyl radicals. XIV. Homolytic δ-aminoalkylation of protonated quinoxaline

A new general reaction of wide synthetic interest, involving homolytic δ-aminoalkylation of quinoxaline in acidic medium, is described. Primary and secondary alkylamines, through the corresponding N-chloroamines, and tertiary alkylamines, through the corresponding N-oxides, are used. The mechanism of the reaction, involving intramolecular hydrogen abstraction by amino radical cations, and the unusual selectivity are discussed in terms of nucleophilic character of the alkyl radicals and of polar effects in the aromatic substitution.     

Hydrogen-bonded liquid crystals built from hydrogen-bonding donors and acceptors. Infrared study on the stability of the hydrogen bond between carboxylic acid and pyridyl moieties

Abstract

The stability of a hydrogen-bonded complex built through inter-molecular hydrogen bonding between carboxylic acid and pyridine fragments has been examined using infrared spectroscopy. Infrared spectra as a function of temperature have been recorded for the 1:1 complex of 4-hexyloxybenzoic acid and trans-4-propoxy-4′-stilbazole from the crystalline state to the isotropic state. A dependence of the stability of the hydrogen bond on molecular orientation is observed clearly in the infrared spectra. The spectra also suggest that the hydrogen bond is an unionized type with a double minimum potential energy.     

Rhodium-Catalyzed ortho-Bromination of O-Phenyl Carbamates Accelerated by a Secondary Amide-Pendant Cyclopentadienyl Ligand

It has been established that a newly developed cyclopentadienyl rhodium(III) [Cp^ARh^III] complex, bearing an acidic secondary amide moiety on the Cp ring, is able to catalyze the ortho-bromination of O-phenyl carbamates with N-bromosuccinimide (NBS) at room temperature. The presence of the acidic secondary amide moiety on the Cp^A ligand accelerates the bromination by the hydrogen bond between the acidic NH group of the Cp^A ligand and the carbonyl group of NBS.     

Kinetics of the Decomposition of Hydrogen Peroxide in the Presence of Aqua-Pentacyanoferrate (II)

The decomposition of hydrogen peroxide has been studied in the presence of a large number of metal ions and their complexes^1,2). Interest in radiation chemistry of aqueous solutions where hydrogen peroxide is one of the products and the use of acidic ferrous sulphate solutions as dosimeter in these studies has particularly stimulated the investigation on the kinetics of decomposition of hydrogen peroxide in the presence of Fe⁺², Fe⁺³ and their complexes^1,2). Ferrous sulphate solution can be used as a dosimeter under acidic conditions only, as at higher pH the hydrolysis of Fe⁺² and Fe⁺³ interferes. Recent studies^3-6) have shown the possibility of using the aqueous solutions of ferro- and ferri-cyanides over a range of pH as dosimeter. In the studies of ferrocyanide and ferricyanide catalysed decomposition of hydrogen peroxide^7-11), it is suggested that the catalytic properties of hexacyano ferrates are through their hydrated products. The present study aims at studying the interaction of aquapentacyanoferrate¹¹) with hydrogen peroxide over a range of pH, concentration and temperature.     

Hydrogen bonding in butadiene copolymers. I. Network formation

The incorporation of comonomers bearing functional groups yields butadiene copolymers capable of hydrogen bonding. Three such butadiene-based materials were studied: methacrylic acid copolymers, 2-methyl-5-vinylpyridine copolymers, and stoichiometric mixtures of the acidic and basic copolymers. The elastic effects of intermolecular hydrogen bonding were determined by comparing the simple weighted average of the moduli of the parent copolymers with the observed modulus of their stoichiometric mixture. The results show that measurable increases in the moduli of the mixtures persist even above the glass temperature T_g, which is itself elevated in the mixtures. These increases may be treated as temperature-dependent temporary crosslinks.     

Synthesis and in solution and solid state structural study of intramolecular Pt...H interactions in pentafluorophenyl platinum(II) complexes containing the ligands triazene, formamidine, and 2-aminopyridine

The preparation of the [NBu4][Pt(C6F5)3L] complexes (L=triazene, formamidine, 2-aminopyridine,) have been carried out. These ligands contain a hydrogen atom, with more or less acidic character, in a position suitable for establishing an intramolecular hydrogen bonding interaction with the metal center. This interaction has been detected in solution for; its 1H NMR spectrum shows that the resonance assignable to this hydrogen has platinum satellites. For, this coupling is not observed, and the interaction, if it exists, has to be weaker because of the less acidic character of the hydrogen atom. The 2-aminopyridine ligand is more flexible than the triazene or formamidine, and also in this case, no evidence of the interaction in solution is obtained. Nevertheless, if another potential proton acceptor is present, such as ClO4- in [NBu4]2[Pt(C6F5)3(C5H6N2)](ClO4), a conventional N-H...O-Cl hydrogen bond is formed. The crystal structures of complexes have been determined by X-ray diffraction.     

片状碳载金属纳米颗粒复合物的制备及其氧还原电活性

将双氰胺、蔗糖与酞菁铁(钴)的混合物通过简单热解法,制备出Co/C-N、Fe/C-N和Fe-Co/C-N纳米复合物。随后利用热还原法,将少量铂沉积于Co/C-N上得到片状碳负载的Co-Pt纳米颗粒Co-Pt/C-N。对样品进行了详细表征,并研究了其在全域pH范围内(酸性、中性与碱性溶液)中的氧还原反应(ORR)活性。结果表明,Co/C-N具有比Fe/C-N和Fe-Co/C-N更高的ORR起始电位和半波电位,并且在碱性和中性溶液中,Co/C-N表现出比Pt/C更强的ORR电活性;在酸性溶液中,铂负载量(质量分数)8.1%的Co-Pt/C-N表现出与Pt/C相近的ORR起始与半波电位。催化剂优异的电活性主要归因于片状碳形成的三维结构、金属纳米颗粒的均匀分布以及丰富的吡啶氮。     

Hydrogen bonding in butadiene copolymers. II. Network relaxation

The mechanical lability of intermolecular hydrogen bonds in stoichiometric mixtures of acidic and basic butadiene copolymers has been studied by both infrared and mechanical methods. Comparison is made between the weight-averaged E(t) and H(τ) spectra of the parent copolymers and those of the mixed copolymers. The results indicate that the maximum contributions of bond-interchange relaxation migrate to shorter times as the concentration of bonding groups increases.     

Electrosynthesis of Н<Subscript>2</Subscript>О<Subscript>2</Subscript> from О<Subscript>2</Subscript> in a Gas-Diffusion Electrode Based on Mesostructured Carbon CMK-3

Mesostructured carbon CMK-3 (Carbon Mesostructured by KAIST) synthesized by the template method is studied as the electrocatalyst for electrosynthesis of Н₂О₂ from О₂ in a gas-diffusion electrode (GDE) in alkaline and acidic solutions. The texture characteristics of the original material and its mixture with hydrophobizer (polytetrafluoroethylene) are studied by the method of low-temperature nitrogen adsorption. The rate constants for hydrogen peroxide decomposition on these materials in alkaline and acidic solutions are calculated. Kinetic parameters of oxygen reduction in alkaline and acidic solutions are determined as well as the capacitance of gas-diffusion electrodes based on mesocarbon. The selectivity of the electrocatalyst is estimated by finding the current fracture γ consumed in oxygen reduction to hydrogen peroxide. Data on the kinetics of hydrogen peroxide accumulation during electrosynthesis of Н₂О₂ from О₂ are obtained. The acidic solution of hydrogen peroxide with the concentration more than 3 M is obtained with the current efficiency higher than 80%.     

Photoelectrochemical Hydrogen Production in Alkaline Solutions Using Cu2O Coated with Earth‐Abundant Hydrogen Evolution Catalysts

The splitting of water into hydrogen and oxygen molecules using sunlight is an attractive method for solar energy storage. Until now, photoelectrochemical hydrogen evolution is mostly studied in acidic solutions, in which the hydrogen evolution is more facile than in alkaline solutions. Herein, we report photoelectrochemical hydrogen production in alkaline solutions, which are more favorable than acidic solutions for the complementary oxygen evolution half‐reaction. We show for the first time that amorphous molybdenum sulfide is a highly active hydrogen evolution catalyst in basic medium. The amorphous molybdenum sulfide catalyst and a Ni–Mo catalyst are then deposited on surface‐protected cuprous oxide photocathodes to catalyze sunlight‐driven hydrogen production in 1 M KOH. The photocathodes give photocurrents of ?6.3 mA cm^?2 at the reversible hydrogen evolution potential, the highest yet reported for a metal oxide photocathode using an earth‐abundant hydrogen evolution reaction catalyst.     

Electrochemical deposition and mechanism investigation of Prussian blue on graphic carbon paste electrode from an acidic ferricyanide solution

Prussian blue (PB) films were electrochemically deposited on graphite carbon paste electrodes (GCPEs) from an acidic solution of ferricyanide using the potentiodynamic and potentiostatic techniques. Interestingly, we, for the first time, observed that on the surface of GCPE, the electrochemistry of PB films strongly depended on the deposition potential. A maximum formation rate of PB was obtained at a more positive deposition potential (0.4 V vs saturated calomel electrode) on GCPE than that on Au or Pt electrode. The ratio of peak current at ca 0.75 V to the one at 0.19 V varied with the deposition potential. In addition, the electrocatalytic activity of the modified GCPEs towards the reduction of hydrogen peroxide considerably changed with the formation potentials of the PB films. These phenomena can be due to the different formation mechanism of PB at different deposition potentials. Dedicated to Prof. Dr. Teresa Iwasita on the occasion of her 65th birthday in recognition of her numerous contributions to interfacial electrochemistry.     

An analytic potential energy function for the amide–amide and amide–water intermolecular hydrogen bonds in peptides

An analytic potential energy function is proposed and applied to evaluate the amide–amide and amide–water hydrogen‐bonding interaction energies in peptides. The parameters in the analytic function are derived from fitting to the potential energy curves of 10 hydrogen‐bonded training dimers. The analytic potential energy function is then employed to calculate the N? H…O?C, C? H…O?C, N? H…OH₂, and C?O…HOH hydrogen‐bonding interaction energies in amide–amide and amide–water dimers containing N‐methylacetamide, acetamide, glycine dipeptide, alanine dipeptide, N‐methylformamide, N‐methylpropanamide, N‐ethylacetamide and/or water molecules. The potential energy curves of these systems are therefore obtained, including the equilibrium hydrogen bond distances R(O…H) and the hydrogen‐bonding energies. The function is also applied to calculate the binding energies in models of β‐sheets. The calculation results show that the potential energy curves obtained from the analytic function are in good agreement with those obtained from MP2/6‐31+G** calculations by including the BSSE correction, which demonstrate that the analytic function proposed in this work can be used to predict the hydrogen‐bonding interaction energies in peptides quickly and accurately. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Modeling the H bond donor strength of ?OH, ?NH,and ?CH sites by local molecular parameters

A quantum chemical model is introduced to predict the H‐bond donor strength of monofunctional organic compounds from their ground‐state electronic properties. The model covers ? OH, ? NH, and ? CH as H‐bond donor sites and was calibrated with experimental values for the Abraham H‐bond donor strength parameter A using the ab initio and density functional theory levels HF/6‐31G** and B3LYP/6‐31G**. Starting with the Morokuma analysis of hydrogen bonding, the electrostatic (ES), polarizability (PL), and charge transfer (CT) components were quantified employing local molecular parameters. With hydrogen net atomic charges calculated from both natural population analysis and the ES potential scheme, the ES term turned out to provide only marginal contributions to the Abraham parameter A, except for weak hydrogen bonds associated with acidic ? CH sites. Accordingly, A is governed by PL and CT contributions. The PL component was characterized through a new measure of the local molecular hardness at hydrogen, η(H), which in turn was quantified through empirically defined site‐specific effective donor and acceptor energies, EE_occ and EE_vac. The latter parameter was also used to address the CT contribution to A. With an initial training set of 77 compounds, HF/6‐31G** yielded a squared correlation coefficient, r², of 0.91. Essentially identical statistics were achieved for a separate test set of 429 compounds and for the recalibrated model when using all 506 compounds. B3LYP/6‐31G** yielded slightly inferior statistics. The discussion includes subset statistics for compounds containing ? OH, ? NH, and active ? CH sites and a nonlinear model extension with slightly improved statistics (r² = 0.92). © 2008 Wiley Periodicals, Inc. J Comput Chem 2009     

Solvation of 4-nitropyrazoles according to UV spectroscopy data

The dependence of the energies of intramolecular charge-transfer electron transitions in 1,3,5-trimethyl-4-nitropyrazole, 4-nitropyrazole, and its anion on the dielectric and acidbase properties of solvents was analyzed. The dipole moments of these species in the excited state are larger than those in the ground state. The nonspecific solvation is accomplished through dipole-dipole interactions. 4-Nitropyrazole, which possesses acidic properties, is also solvated by the mechanism of hydrogen bonding with the solvent, which acts as a base. The strength of the hydrogen bond increases on going from the ground to the electron-excited state. The 4-nitropyrazole anion is a base, and its hydrogen bonds with the solvent are stronger in the ground state. The mechanism of specific solvation of the molecule and the anion of 4-nitropyrazole during electronic excitation is discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 867–869, April, 1997.     

A Reference Electrode System for Electrochemical Measurements in Pure Water

A reference hydrogen electrode systems is constructed by employing a strip of proton‐type Nafion membrane as an ion‐conducting “bridge” to connect a reversible hydrogen electrode (RHE) in an acidic solution to an electrochemical system using pure water as electrolyte, in which the working electrode (WE) is placed. Using such a reference electrode system, the potential at the “WE/pure water” interface is equal to the equilibrium hydrogen electrode potential in pure water when the potential difference between RHE and WE is zero, irrespective of the pH value of the acidic solution in the RHE compartment. The accuracy and reproducibility of the WE potential measurements are within 1–2 mV.     

An ab initio theoretical prediction: an antiaromatic ring pi-dihydrogen bond accompanied by two secondary interactions in a "wheel with a pair of pedals" shaped complex FH . . . C4H4 . . . HF

By the counterpoise-correlated potential energy surface method (interaction energy optimization), the structure of the pi H-bond complex FH cdots, three dots, centered FH . . . C4H4 . . . HF has been obtained at the second-order M?ller-Plesset perturbation theory (MP2/aug-cc-pVDZ) level. Intermolecular interaction energy of the complex is calculated to be -7.8 kcal/mol at the coupled-cluster theory with single, double substitutions and perturbatively linked triple excitations CCSD (T)/aug-cc-pVDZ level. The optimized structure is a "wheel with a pair of pedals" shaped (1mid R:1) structure in which both HF molecules almost lie on either vertical line passing through the middle-point of the C[Double Bond]C bond on either side of the horizontal plane of the C4 ring for cyclobutadiene. In the structure, an antiaromatic ring pi-dihydrogen bond is found, in which the proton acceptor is antiaromatic 4 electron and 4 center pi bond and the donors are both acidic H atoms of HF molecules. In accompanying with the pi-dihydrogen bond, two secondary interactions are exposed. The first is a repulsive interaction between an H atom of HF and a near pair of H atoms of C4H4 ring. The second is the double pi-type H bond between two lone pairs on a F atom and a far pair of H atoms.