Control of optical properties of gel-derived oxide coating films containing fine metal particles

Control of the optical properties of gel-derived oxide films containing fine metal particles is described. The duration of the aging of Si(OC₂H₅)₄-derived sols and the amount of water for hydrolyzing Si(OC₂H₅)₄ were found to greatly affect the size and the shape of Au particles formed in the silica matrix, and accordingly the optical absorption of the Au/SiO₂ composite films. Employing dielectric media with high refractive indices like TiO₂ was shown to shift the absorption peak of Au particles to longer wavelengths. Pd/TiO₂ and Pt/TiO₂ composite films showed absorption in the visible region.     

Determination of complex formation constants by phase sensitive alternating current polarography: Cadmium-polymethacrylic acid and cadmium-polygalacturonic acid

The use of phase sensitive alternating current polarography (ACP) for the evaluation of complex formation constants of systems where electrodic adsorption is present has been proposed. The applicability of the technique implies the previous selection of the phase angle where contribution of capacitive current is minimized. This is made using Multivariate Curve Resolution by Alternating Least Squares (MCR-ALS) in the analysis of ACP measurements at different phase angles. The method is checked by the study of the complexation of Cd by polymethacrylic (PMA) and polygalacturonic (PGA) acids, and the optimal phase angles have been ca. −10° for Cd-PMA and ca. −15° for Cd-PGA systems. The goodness of phase sensitive ACP has been demonstrated comparing the determined complex formation constants with those obtained by reverse pulse polarography, a technique that minimizes the electrode adsorption effects on the measured currents.     

The volume and compressibility change for the formation of transition metal sulfate ion pairs at 25°C

The apparent molal volume and adiabatic compressibilities of some transition metal (Mn²⁺, Co²⁺ Ni²⁺, Cu²⁺, Zn²⁺, and Cd²⁺) sulfates have been determined at 25°C. Values of to 11.4 cm³-mole^–1 and to 31.3 × 10^–4cm³-mole^–1-bar^–1 at 1 atm were found for the formation of the transition metal sulfate ion pairs. These results are in good agreement with the values obtained from the high-pressure conductance measurements of Fisher et al., Shimizu et al., and Taniguchi et al. The volume and compressibility data indicate that 3.1±0.7 water molecules are lost when transition metals form ion pairs with SO ₄ ^2– . The fractions of inner-sphere ion pairs (20%) estimated in this study are in good agreement with the values obtained from ultrasonic measurements.     

A quantum-chemical study of regioselectivity of indolization of some unsymmetrical ketone phenylhydrazones

The heat of formation (H _f) of unsymmetrical ketone phenylhydrazones and their enehydrazine tautomers was calculated by the semi-empirical quantum-chemical AM1 method. It is concluded that from H _f values it is possible to judge the regioselectivity of indolization of unsymmetrical ketone phenylhydrazones.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 220–221, January, 1993.     

Ultra-stable Ni catalysts for methane reforming by carbon dioxide

Methane reforming by carbon dioxide has been studied over ultra-stable Ni catalysts. The catalyst was characterized by XRD, IR and TEM and temperature programmed hydrogenation. The nickel–magnesia solid solution catalyst containing low nickel has shown excellent stability (>3000 h) and no carbon deposition in the methane reforming by carbon dioxide. It was also found that the small nickel metal particle interaction with support surface is effective for the inhibition of carbon formation.     

Formation at low surfactant concentrations and characterization of mesoporous MCM-41

At low concentrations of cetyltrimethylammonium bromide,all silica-based mesoporous materials with hexagonal phase have been synthesized via interactions between self-assembled surfactant molecule aggregates and aniomc silicate polymers.The resulting materials are characterized by XRD,FT-IR,solid state 29Si MAS NMR,thermal analysis and N2 adsorption-desorption measurements.After soluble ions are removed,the interactors between surfactant micelles and silicate polymers are reorganized and then form mesostructures 1 he hexagonal framework is sonsistent with amorphous silica gel.The structures of materials depend on the synthesis conditions Hydrothermal process improves the interactions between molecules and increases the degree of framework silicon atom polymerization The.surface area and the mesopore volume of the material prepared at 100℃ increase by 87% and 71 %,respectively,compared with those obtained at room temperature.     

Preparation and crystal structure of hydrated crystalline complex of ciprofloxacin and copper tetrachloride

Synthesis of a complex formed by ciprofloxacin (cfH) and copper(II) chloride is described; its crystal structure is reported and analyzed in comparison to related compounds. The obtained compound (cfH₃)CuCl₄·H₂O (cfH ₃ ²⁺ — double protonated cfH molecule) crystallizes as platelets of P2₁/c symmetry having the unit cell parameters a = 13.491(1) Å, b = 11.0459(7) Å, c = 16.299(1) Å; β = 111.392(7)°. Carbonyl oxygen O(1) is protonated, and hydrogen atom combined with it forms an intramolecular hydrogen bond with carboxylic O(2) oxygen (O(1)?O(2) = 2.642(5) Å). Terminal nitrogen atom N(3) of the piperazinyl group is also protonated, and two its hydrogen atoms participate in hydrogen bonds of N-H?Cl type. The structure also has hydrogen bonds O-H?O, O-H?Cl with the participation of water molecules which occupy hydrophilic channels. Molecular ions cfH ₃ ²⁺ make couples with intrapair π?π interactions.     

Determinations of combustion and formation enthalpies of C60 and C70

By using a micro-bomb calorimeter, the standard enthalpies of combustion of C₆₀ and C₇₀ have been determined to be - (25 947.1±8.5) and - (29 956.1 ± 8.9) kJ/mol respectively. A g. 1. c. analysis indicated that the amounts of residual organic solvents in the samples were very small, and their effects on the final results were negligible. The energy of combustion ofC60 determined in this work is in agreement in the uncertainty interval with that determined by means of traditional calorimeter using macro amount of sample. The enthalpies of formation of these two substances have been derived. The strain energies in the molecules of C₆₀ and C₇₀ were estimated by a bond energy scheme and by using corannulene as the model compound, the results estimated from different methods are very close. Project supported by the National Natural Science Foundation of China (Grant No. 29473143)     

Sedimentation and drying dissipative structures of colloidal silica (1.2 μm in diameter) suspensions in a glass dish and a polystyrene dish

Sedimentation and drying dissipative structural patterns formed in the course of drying colloidal silica spheres (1.2 μm in diameter) in aqueous suspension have been studied in a glass dish and a polystyrene dish. The broad ring patterns are formed within a short time in suspension state by the convection flow of water and colloidal spheres. The broad ring patterns are not formed when a dish is covered with a cap, which demonstrates the important role of the convectional flow of silica spheres and water accompanied with the evaporation of water on the air-suspension interface. The sedimentary spheres always move by the convectional flow of water, and the broad ring patterns became sharp with time. Broad ring and microscopic fine structures are formed in the solidification processes on the bases of the convectional and sedimentation patterns. Drying patterns of the colloidal suspensions containing sodium chloride are star-like ones, which strongly supports the synchronous cooperative interactions between the salt and colloidal spheres.     

Substituent Effects on the C-C Bond Strength, 15[1] Geminal Substituent Effects, 7[2]. Thermochemistry and Thermal Decomposition of Alkyl-substituted Tricyanomethyl Compounds

The thermolysis reactions of the tricyanomethyl compounds 10a-c were studied in solution. 2,2-Dicyano-3-methyl-3-phenylbutyronitrile ( 10a ) and 2,2-dicyano-3-methyl-3-(4-nitrophenyl)butyronitrile ( 10b ) decomposed heterolytically into carbenium ions and (CN)₃C⁻ anions, while 9-methyl-9-(tricyanomethyl)fluorene ( 10c ) underwent about 11% homolytic C-C bond cleavage into 9-methyl-9-fluorenyl- and tricyanomethyl radicals. The rates of the homolysis were determined by a radical scavenger procedure under conditions of pseudozero order kinetics. From the temperature effect on the rate constants the activation parameters were determined [ΔH ( 10c ) = 155· 2 kJ mol⁻¹, ΔS ( 10c ) = 58· 5 J mol⁻¹ K⁻¹]. Standard enthalpies of formation ΔH (g) were determined for 2,2-dicyanopropionitrile ( 2 ) (422.45 kJ mol⁻¹), 2,2-dicyanohexanenitrile ( 3 ) (349.74 kJ mol⁻¹), 2,2-dicyano-3-phenylpropionitrile ( 4 ) (540.75 kJ mol⁻¹), 2-butyl-2-methylhexanentrile ( 5 ) (-133.20 kJ mol⁻¹), 2,2-dimethylpentanenitrile ( 6 ) (-45.78 kJ mol⁻¹), and 2-methylbutyronitrile ( 7 ) (2.44 kJ mol⁻¹) from the enthalpies of combustion and enthalpies of sublimation/vaporization. From these data and known Δ (g) values for alkanenitriles and -dinitriles, thermochemical increments for ΔH (g) were derived for alkyl groups with one, two, or three cyano groups attached. The comparison of these increments with those of alkanes reveals a strong geminal destabilization, which is interpreted by dipolar repulsions between the cyano groups. - From ΔH (g) of 10c and ΔH of its homolytic decomposition the radical stabilization enthalpy for the tricyanomethyl radical 1 RSE ( 1 ) = -18 kJ mol⁻¹ was determined. Thus, 1 is destabilized, in comparison with the RSEs of tertiary α-cyanalkyl (23 kJ mol⁻¹) and α,α-dicyanoalkyl (27 kJ mol⁻¹) radicals, which were recalculated from bond homolysis measurements^[4] and the new thermochemical data. This change of RSE on increasing the number of α-cyano groups is discussed as the result of the additive contributions by resonance stabilization and increasing destabilization by dipolar repulsion. The amount of the dipolar energies was estimated by molecular mechanics (MM2).