Solvent Effects in Halogen and Hydrogen Bonding Mediated Electrochemical Anion Sensing in Aqueous Solution and at Interfaces

Sensing anionic species in competitive aqueous media is a well-recognised challenge to long-term applications across a multitude of fields. Herein, we report a comprehensive investigation of the electrochemical anion sensing performance of novel halogen bonding (XB) and hydrogen bonding (HB) bis-ferrocene-(iodo)triazole receptors in solution and at self-assembled monolayers (SAMs), in a range of increasingly competitive aqueous organic solvent media (ACN/H₂O). In solution, the XB sensor notably outperforms the HB sensor, with substantial anion recognition induced cathodic voltammetric responses of the ferrocene/ferrocenium redox couple persisting even in highly competitive aqueous solvent media of 20 % water content. The response to halides, in particular, shows a markedly lower sensitivity to increasing water content associated with a unique halide selectivity at unprecedented levels of solvent polarity. The HB sensor, in contrast, generally displayed a preference towards oxoanions. A significant surface-enhancement effect was observed for both XB/HB receptive films in all solvent systems, whereby the HB sensor generally displayed larger responses towards oxoanions than its halogen bonding analogue.     

The Molecular Structure of Alzheimer β‐Amyloid Fibrils Formed in the Presence of Phospholipid Vesicles

β‐amyloid (Aβ) fibrils are the major species involved in Alzheimer’s disease (AD). An atomic‐resolution molecular structure of Aβ40 fibrils formed in the presence of lipid vesicles was obtained by using magic angle spinning (MAS) solid‐state NMR spectroscopy. The fibril structures formed in the presence of the lipid vesicles are remarkably different from those formed in solution. These results provide insights into the molecular mechanism of Aβ aggregation in the presence of lipid vesicles.     

The Structure Formation of Zirconium Oxide Gels in Alcoholic Solution

Zirconium oxide gels were prepared by controlled hydrolysis and condensation of zirconium-n-propoxide in alcoholic solution. After completion of the gelation the aging and drying of the alcogel was observed in situ by Small and Wide Angle X-ray Scattering experiments at room temperature. The xerogels obtained have been annealed at different temperatures to crystallization. The structural changes were observed by using SAXS and WAXS. Structural models reproducing the experimental WAXS data have been simulated by the reverse Monte Carlo method. A comparison between zirconium oxide xerogels obtained under different thermal treatments was made and evidence was found that thermal treatment at higher temperatures and preparation conditions affect the atomic arrangement of these amorphous gels.     

Interaction of Sodium Dodecyl Sulfate with Poly(ethyleneimine) in Bulk Solution and at the Air-Solution Interface

Interaction of sodium dodecyl sulfate (SDS) with the cationic polyelectrolyte poly(ethyleneimine) (PEI) was investigated in this study. Turbidity measurements were performed in order to analyze the interaction and complex formation in bulk solution as a function of polymer concentration and pH. Surface tension measurements were made to investigate the properties of SDS/PEI/water mixtures at air/solution interface. Results revealed that SDS/PEI complexes form in solution depending on the surfactant and polymer concentration. A decrease was observed in surface tension values in the presence of SDS/PEI mixtures compared to the values of pure SDS solutions. Both solution and interfacial properties exhibited pH dependent behavior. A shift was seen in the critical micelle concentration of SDS solutions as a function of PEI concentration and solution pH. Monovalent and divalent salt additions showed some influence on the interfacial properties of SDS solutions in the presence of PEI.     

Theoretical Analysis of the Effect of Ion Concentration in Solution Bulk and at Membrane Surface on the Mass Transfer at Overlimiting Currents

Overlimiting current modes are of considerable interest for the practice of electrodialysis (ED). However, the economical expedience of such ED modes is evident only for desalination of dilute solutions. Here, we show the theoretical analysis of the effect of concentration on the behavior of an ED cell with homogeneous ion-exchange membranes. The study is based on numerical solution of the two-dimensional system of coupled equations of Nernst–Planck–Poisson–Navier–Stokes. It is shown that as the electrolyte concentration in solution that enters the ED desalination chamber increases, the intensity of electroconvection decreases, which induces a decrease in the relative mass-transfer rate (the decrease in the ratio of current density to its limiting value). This effect is stronger in the region of high potential differences where the electroconvective instability of Rubinstein–Zaltzman is realized under the conditions of a nonuniform concentration field caused by solution desalination. In contrast, the increase in the counterion concentration at the membrane surface (associated with the increase in the surface charge) intensifies the electroconvection.     

两亲嵌段共聚物溶液内胶束形成的温度效应

合成了一系列具有两亲嵌段结构的聚（乙二醇）（PEO）一聚（丙二醇）（PPO）共聚物．利用荧光探针及示差量热法测定了共聚物水溶液的临界胶束形成温度（CMT）值．发现二嵌段共聚物（PEO－PPO）和三嵌段共聚物（PEO－PPO－PEO）有着类似的变化规律，即随共聚物分子中疏水链（PPO）长度的增大，其CMT值降低．但三嵌段共聚（PPO－PEO－PPO）则因疏水链段处于共聚物分子的两端，因而在溶液中有可能形成立体网状交联结构．此外，利用探针分子在不同极性溶剂中荧光峰值波长发生位移的现象可以对形成胶束内核的组织程度、极性大小进行估测．     

化学发光演示实验──水溶液中单线态氧的生成

氧气是生命过程必不可少的,人们侮天呼吸的氧气是能量最低的一种基态氧分子。经测定它有顺磁性,证明该氧分子中有自旋平行的两个电子在分开的轨道上。     

The Formation of Imidazolium Salt Intimate (Contact) Ion Pairs in Solution

1‐n‐Butyl‐2,3‐dimethylimidazolium (BMMI) ionic liquids (ILs) associated with different anions undergo H/D exchange preferentially at 2‐Me group of the imidazolium in deuterated solvents. This process is mainly related to the existence of ion pairs rather than the anion basicity. The H/D exchange occurs in solvents (CDCl₃ and MeCN for instance) in which intimate contact ion pairs are present and the anion possesses a labile H in its structure, such as hydrogen carbonate and prolinate. In D₂O, separated ion pairs are formed and the H/D exchange does not occur. A plausible catalytic cycle is that the IL behaves as a neutral base in the course of all H/D exchange processes. NMR experiments, density functional calculations, and molecular dynamics simulations corroborate these hypotheses.     

The Molten Globule State of a Globular Protein in a Cell Is More or Less Frequent Case Rather than an Exception

Quite a long time ago, Oleg B. Ptitsyn put forward a hypothesis about the possible functional significance of the molten globule (MG) state for the functioning of proteins. MG is an intermediate between the unfolded and the native state of a protein. Its experimental detection and investigation in a cell are extremely difficult. In the last decades, intensive studies have demonstrated that the MG-like state of some globular proteins arises from either their modifications or interactions with protein partners or other cell components. This review summarizes such reports. In many cases, MG was evidenced to be functionally important. Thus, the MG state is quite common for functional cellular proteins. This supports Ptitsyn’s hypothesis that some globular proteins may switch between two active states, rigid (N) and soft (MG), to work in solution or interact with partners.     

浓碱溶液中生成高铁酸盐的玻碳电极循环伏安法表征(英文)

用玻碳电极研究了与Fe(Ⅵ)／Fe(Ⅲ)电对氧化还原有关的循环伏安曲线.所研究的体系是13mol·L-1NaOH中浓度范围分别为0.015～0.06mol·L-1的Na2FeO4和0.01～0.025mol·L-1的NaFeO2溶液。另一类研究体系是胶体石墨分别与固体K2FeO4、固体KFeO2组成的混合物,将这些混合物粘附于玻碳电极表面后在13mol·L-1KOH中进行循环伏安曲线的测定。结果证明了峰电位在0.7～1.0V的阳极电流峰与峰电位在0.15～0.2V(均相对于13mol·L-1NaOH或13mol·L-1KOH溶液中的Hg／HgO参比电极)的阴极电流峰,分别与高铁酸盐的生成与还原相对应。确定了将高铁酸盐的阳极生成电流峰与阳极析氧电流峰区别开来的条件。     

The Dipole Moment and Molecular Mobility of Cholesteryl-Containing Monomers in Solution: Association and Gel Formation

The permittivity, molecular dipole moment, and dielectric relaxation parameters (relaxation time and activation energy) of cholesteryl esters of alkyl-, methacryloyl-ω-oxy-, and aminocarboxylic acids were studied in dilute solutions in toluene. The influence of the chemical structure of molecules on these characteristics was considered. The presence of NH groups and cholesteryl radicals (responsible for H-bonding and specific dispersion interactions) and an increase in the length of methylene chains in molecules substantially influenced dipole moments and dipole polarization relaxation times and contributed to the development of structuring processes (association and gel formation) in solutions of these compounds.     

The Enthalpies of Solution and Solvation of L-Serine in Aqueous Alcoholic Solutions at 298.15 K

The integral enthalpies of solution (Δ_sol H ^m ) of L-serine in water-alcohol (ethanol, n-propanol, isopropanol) mixtures were measured over the range of alcohol concentrations up to 0.32 mole fractions. The standard enthalpy of solution (Δ_sol H°), enthalpy of transfer of L-serine from water into a mixed solvent (Δ_tr H°), and enthalpy of solvation (Δ_solv H°) were calculated. The dependences of Δ_sol H°, Δ_solv H°, and Δ_tr H° on the composition of mixtures had extrema. The calculated enthalpy coefficients of the pair interactions of L-serine with alcohol molecules were positive and increased along the series ethanol, n-propanol, isopropanol. The data obtained were interpreted in terms of different types of interactions in solutions and the influence of the nature of amino acid residues on the thermochemical solution characteristics. Original Russian Text ? I.N. Mezhevoi, V.G. Badelin, 2008, published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 4, pp. 789–791.     

电极/溶液界面单分子吸附层的统计力学处理 I. 非水溶液中汞电极的内层微分电容

本文提出电极/溶液界面溶剂化层偶极取向分布模型, 应用统计力学方法及热力学平衡条件导出普遍化的单层吸附等温方程, 其电解质溶液的溶剂组成可以是纯态的或混合物(多组份)的. 文中分别以甲酰胺、碳酸亚乙酯和甲醇等三种纯溶剂的汞/溶液界面为例, 采用曲线拟合计算内层微分电容随表面电荷变化关系。预计本模型处理对汞/水溶液或汞/(混合溶剂)溶液界面仍可适用。     

Multistep Electrochemical Reactions Involving Transport of Intermediates between the Near-electrode Layer and the Bulk Solution: The Kinetics of Two-Step Processes in Conditions of Non-steady-state Diffusion

Results of numerical simulation of the kinetics of a two-stage electrochemical reaction with partial transport of intermediates between the near-electrode layer and the bulk solution in conditions of linear nonsteady-state diffusion of reactants are analyzed with use made of a theory of generalized variables. Dimensionless complexes (similitude criteria) that characterize the electrochemical reaction under consideration are obtained. Combinations of kinetic parameters of the first and second steps of the reaction, at which the reaction proceeds in a quasi-steady-state regime, are established. The conditions, at which rates of individual steps of electrochemical conversion are equal, are determined.     

The influence of an intermediate on reaction kinetics in organometallic systems: Formation of products apparently faster than the disappearance of reactants

In a spectrophotometric study of the kinetics of reactions in solution it is possible to find that products are apparently formed faster than the reactants are used up. This can arise when reaction proceeds via an intermediate in a two-step mechanism as found in many organometallic systems.     

电极/溶液界面单分子吸附层的统计力学处理 IV. 水溶液中银单晶电极的内层微分电容

根据本文系列I~[6]提出的电极/溶液界面溶剂化层偶极取向分布模型, 拟合计算Ag(111)、Ag(100)及Ag(110)/水溶液界面的内层微分电容(C_1)～表面电荷密度(σ)变化关系。表明在银电极上, 吸附水分子似分别稳定在金属原子点阵的顶位(111)或穴位(100)及(110)。讨论了溶剂化层的结构与性质对C_1～σ曲线可能产生的影响。     

The Partial Molar Volume and Heat Capacity of the Glycyl Group in Aqueous Solution at 25^C

The partial molar volumes, V₂ ^{^}, and the partial molar heat capacities, C_p,2 ^{^}, at infinite dilution have been determined for three new peptides of sequence seryl(glycyl)_xglycine, where x=0 to 2, in aqueous solution at 25^{^}C. Values for V₂ ^{^} at 25^°C have also been determined for two neutral peptide derivatives N-acetylglycylglycinamide and N-acetylglycylglycylglycinamide. These V₂ ^°; and C_p,2 ^°; results were used to estimate the partial molar volume and heat capacity of the backbone glycyl group, CH₂CONH, of proteins in aqueous solution at 25^°;C. The results obtained are compared with those calculated using partial molar data for alternative model compounds. The new glycyl group contributions are in excellent agreement with those currently used in our group additivity schemes for the calculation of the partial molar volumes and heat capacities of unfolded proteins.     

The Formation and Structural and Phase Transformations of Aluminum Hydroxy Species in Hydrothermal Synthesis under Conditions of Homogeneous Precipitation from Sulfate Solution

By X-ray powder diffraction analysis, Raman spectroscopy, scanning and transmission electron microscopy, and low-temperature nitrogen adsorption method, it was studied how the temperature of hydrothermal synthesis affects the phase composition of precursor species and the structure and morphology of alumina obtained under conditions of low-temperature hydrothermal synthesis at 90–130°C in the system 0.5Al₂(SO₄)₃ · 18H₂O∥0.2C₁₆H₃₃(CH₃)₃NBr∥5i-PrOH∥85H₂O∥2CO(NH₂)₂. It was found that, at T_HTS = 90–110°C, alumina microspheres with globular structure form from X-ray amorphous hydrated alumina with an admixture of NH₄Al₃(SO₄)₂(OH)₆. It was shown that needle-like alumina particles with slitlike pores form from NH₄Al(OH)₂CO₃ obtained at T_HTS = 110–120°C. At T_HTS = 130°C, under conditions of the formation of γ-AlOOH, alumina spherulites constituted by needle-like particles with block–layer structure form. It was determined that the temperature range of the formation of metastable crystalline modifications of alumina is controlled by the phase composition of hydrothermal synthesis products.     

The Enthalpies of Solution of Tetraethyl- and Tetrabutylammonium Bromides in Aqueous Solutions of Hexamethylphosphorus Triamide at 328.15 K

The heats of solution of Et₄NBr and Bu₄NBr in water and aqueous solutions of hexamethylphosphorus triamide (HMPT) at 328.15 K were measured in a variable-temperature isothermic-shell calorimeter. The standard enthalpies of solution were calculated using the Debye-Hückel second-order theory. The enthalpy parameter of electrolyte—amide pair interactions was determined in terms of the McMillan-Mayer formalism. The processing of the data obtained in this work and previously led us to conclude that heat capacity changes caused by pair interactions of Et₄NBr and Bu₄NBr with HMPT were negative and independent of temperature over a wide temperature range. The methyl and methylene groups interacted with HMPT without heat capacity changes and, consequently, the enthalpies and entropies of their interactions with HMPT were constant over a wide temperature range.