Volume 224, Issue 9 -

The properties and advantages of microelectrodes and arrays are reviewed and mass transfer to these microstructures detailed. Various methods for the solution of the mass transfer equations are described, and an overview of analytical and numerical techniques mentioned, including discrete methods, methods of weighted residuals, and finite element methods. Applications in the simulation of electrochemical systems are reported.

Fluorescence quenching of phycoerythrin (PE) by a series of anthraquinone dyes has been investigated using steady state fluorescence technique in water medium. The dyes used were Uniblue, Acid blue 129, Alizarin and Alizarin red S. The quenching of PE was found to obey the Stern-Volmer equation and the corresponding Stern-Volmer plots were linear indicating the dynamic quenching. The quenching rate constants ( k q ) were calculated by using fluorescence data. The mechanism of quenching is discussed on the basis of quenching rate constants as well as the reduction potential of dyes. The electron transfer mechanism has been proved by the calculation of free energy change (ΔG et ) by applying Rehm-Weller equation.

The analogy between the principle of least time in optics (Fermat’s principle) and Ostwald’s rule of intermediate steps made it possible to set up the principle of least time for first-order phase transitions. In its turn, the analogy between first-order phase transitions and chemical reactions allows assume that the principle of least time is also valid in chemical kinetics. This assumption is substantiated in the given work. Also proposed is a different derivation of the indicated principle based on generalization of empirical data.

A novel anionic Gemini surfactant, sodium dialkylbenzene disulfonate with spacer of -C 3 H 6 -, was synthesized and confirmed by 1 HNMR, MS and IR. Such Gemini surfactant in dilute aqueous solution without additives was researched by rotational rheometer and exhibited special viscoelastic behaviors and shear-thinning properties like entangled polymer solution. The influence of concentration and shear rate on viscosity and shear modulus has been studied and the reason of enhancing viscosity has also been discussed.

The relationship between the hydrophobic characteristic of supports and the reactivity of the liquid oxidation of cyclohexane using oxygen as oxidant was investigated. Co 3 O 4 supported on amorphous silica was silylated with organosilane and characterized by FT-IR, contact angle testing and the retention of cyclohexane and cyclohexanone tesing on GC. Compared with unsilylated catalyst, the conversion of cycloheaxane was greatly enhanced with the silylated catalyst. And the correlation of reactivity and hydrophobicity of was observed.

1-dodecylamine hydrobromide was synthesized. The crystal structure of the compound was determined by X-ray crystallography. Low-temperature heat capacities of the title compound were measured by an adiabatic calorimeter over the temperature range from 78 to 390 K. Three solid–solid phase transitions were observed at the peak temperatures of (329.278±0.234), (337.805±0.326), and (347.371±0.154) K. The molar enthalpies and entropies of the three phase transitions of the substance were calculated based on the analysis of heat capacity curves. Experimental values of heat capacities for the title compound were fitted to two polynomial equations. Three solid–solid phase transitions and a melting process of 1-dodecylamine hydrobromide were verified by DSC technique. In addition, the reversibility and repeatability of the three phase transitions were discussed.

Absolute values of enthalpy and Gibbs free energy of hydration (h) or solvation (s) of H + ion, ΔH 0 (H + ) h or s and ΔG 0 (H + ) h or s in aqueous and non-aqueous solvents (methanol, ethanol, n-propanol, iso-propanol, n-butanol, t-butanol, ethylene glycol, propylene carbonate, n-methyl formamide, acetone, tetrahydro furan, 1,4-dioxan, acetonitrile) were determined directly using a single standard state [i.e.H 2 (g) at 1bar and 298.15K]. A comparative study of the methods of Tissandier et al. and the present one has been made. The values −1299.4 kJ mol −1 (−1303.9 kJ mol −1 ) and −1284.5 kJ mol −1 (−1288.9 kJ mol −1 ) for the absolute enthalpy [∆H 0 h (H + )] and Gibbs free energy [∆G 0 h (H + )] of hydration determined in the present work have been found to be much lower than the corresponding values −1150.1±0.9 kJ mol −1 and −1104.5±0.3 kJmol −1 determined by Tissandier et al. using cluster-ion solvation data. The values of Tissandier et al. have been acclaimed to be the most accurate values of these quantities by most of the workers. However, the method is based on approximations and assumptions and uses a number of conventional standard states. The calculations use the principle of ionic additivity and Klot’s equation which are open to question. The equations, based on the difference between several sets of energy values of different ion-pairs of similar magnitude, have been used. Thus, the method is insensitive and many of the important energy terms characterizing the ions and the structure of the solvents are eliminated. Thus the accuracy of the energy values are not without question.Our method, on the other hand, is a direct one using a single standard state. The most important contributory factor for the determination of ΔG 0 h (H + ) is the Gibbs free energy of charging and the value is accurately known. Thus, the values for ΔH 0 h (H + ) and ΔG 0 h (H + ) determined by us though much lower than those of Tissandier et al. can be regarded to be reasonable.