DNA Effect on Cis–Trans Equilibrium and Fluorescent Properties of 3,3′-Diethyl-9-thiomethylthiacarbocyanine Iodide in Aqueous Solution

The influence of DNA on the cis–trans equilibrium and fluorescent properties of 3,3-diethyl-9-thiomethylthiacarbocyanine iodide (DTTC) in a phosphate buffer (pH 7) was studied by various photochemical techniques. The interaction of dye molecules with DNA leads to the formation of stable noncovalently bonded complexes. Data obtained from DTTC absorption and fluorescence spectra suggest that complexation proceeds primarily through the cis-form of the dye. Complexation with DNA leads to a substantial increase in the quantum yield of the triplet state of DTTC molecules. The rate constant for quenching the dye triplet state by oxygen turned out to be significantly lower than the diffusion-controlled value.     

Electrocatalytic properties of Au(111)-Pd quasi-single-crystal film electrodes as probed by ATR-SEIRAS

Electrochemical and electrocatalytic properties of thin films Au(111-25 nm), which are quasi-single-crystal electrodes 25 nm thick made of gold with the (111) preferential orientation, and same electrodes modified with a monolayer (ML) of palladium are studied in 0.1 M solutions of HClO₄ and H₂SO₄ employing voltammetric techniques and surface enhanced infrared reflection absorption spectroscopy (ATR-SEIRAS). Spectroscopic experiments demonstrate strong adsorption of electrolyte species (H₂O, OH_ads, anions) on the Pd surface. The weak and reversible adsorption of CO on Au(111-25 nm) does not change the interfacial-water structure. Adsorption of CO on the Pd-modified film results in an irreversibly adsorbed CO adlayer stabilized by co-adsorbed isolated water species. Various electrooxidation mechanisms are discussed. Electrochemical and spectroscopic investigations on the adsorption and electrooxidation of HCOOH on bare and 1 ML Pd-Au(111-25 nm) electrodes reveal that electrooxidation proceeds in both cases via a direct or dehydrogenation pathway. This mechanism involves the formation of formate as intermediate, which is detected by in situ ATR-SEIRAS. The reactivity on Pd-modified surfaces is higher than on bare gold. The specifically adsorbed anions (sulfate/bisulfate) and the oxide formation on the substrate surface lower the reactivity for CO and HCOOH on both surfaces. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 11, pp. 1312–1329. Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes,” October 18–22, 2005, Moscow. The text was submitted by the authors in English.     

Phase Equilibria in the Fullerene C60-Fullerene C70-Hexane-o-Xylene-Dimethylformamide System

The phase diagram of the hexane-o-xylene-dimethylformamide ternary liquid system was studied at T= 298.15 K. The diagram contained the regions of homogeneous solutions and two-phase liquid systems (systems with stratification), phase I being enriched in dimethylformamide and phase II, in hexane. The distribution of fullerenes C⁶⁰ and C⁷⁰ was considered at various concentrations and simultaneous presence in sections at variable phase compositions. The extraction isotherms of fullerenes C⁶⁰ and C⁷⁰ under various conditions were found to be close to linear, and the C⁷⁰/C⁶⁰ separation factor depended on the composition of the coexisting phases and ranged from 1.25 to 1.8. Fullerene C⁷⁰ was predominantly distributed in phase I.     

Solubility in the Fullerene C6 0-Fullerene C7 0-o-C6H1 4(CH3)2 System

The solubility diagram of the ternary fullerene-containing system C₆₀-C₇₀-o-xylene at 25 and -20°C was studied.     

Photochemical properties of meso-substituted thiacarbocyanine dyes in solutions and in complexes with DNA

The processes of cis-trans photoisomerization and thermal back isomerization as well as the effect of DNA on the spectral and kinetic characteristics of the triplet state of a number of meso-substituted thiacarbocyanine dyes: 3,3’-diethyl-9-methoxythiacarbocyanine iodide (K1), 3,3’,9-triethylthiacarbocyanine iodide (K2), 3,3’-diethyl-9-methylthiacarbocyanine iodide (K3), and 3,3’-diethyl-9-chlorothiacarbocyanine perchlorate (K4), were studied by the flash photolysis method. Upon flash photoexcitation, the processes of trans-cis and cis-trans photoisomerization were observed for dye K1; the data on the structure of the absorption bands of the photoisomers were obtained. Complexation with DNA leads to an increase in the quantum yield of the triplet state of the dyes, which is explained by growing rigidity of the bound molecules. In the presence of DNA, triplet state deactivation follows the two-exponential law, thus showing that the dyes form complexes of two different types. The processes of quenching of the dye triplet state by oxygen were studied in solutions and in complexes with DNA. The rate constants for oxygen quenching of the triplet state of the dyes in complexes with DNA were found to be much lower than the values expected for the diffusion-controlled reactions (with allowance for the spin statistical factor, $k_{qO_2 } < 1/9k_{dif} $ ), which is explained by the steric factor of the complexation.     

Study of cis-trans equilibrium of oxacarbocyanine dyes in solution and in a complex with DNA

Cis-trans equilibrium for a number of meso-substituted oxacarbocyanine dyes, 3,3′-diethyloxacarbocyanine iodide (K1), 3,3′-diethyl-9-methyloxacarbocyanine iodide (K2), 3,3′-dimethyl-9-ethyloxacarbocyanine iodide (K3), 3,3′,9-triethyl-6,6′-dimethoxyoxacarbocyanine iodide (K4), and 3,3′,9-triethyl-5,5′-dimethyloxacarbocyanine iodide (K5), has been studied in solutions and in a complex with DNA by spectral and fluorescent methods. A shift of the cis-trans isomer equilibrium toward the formation of the trans-isomer was observed in the presence of DNA, which determined in many respects the spectral effects observed upon the complexation of the oxacarbocyanine dyes. A steep rise of fluorescence (due to binding of the trans-isomer) in a complex with DNA is favorable for using oxacarbocyanine dyes to determine DNA.     

Quenching of the triplet state of meso-substituted thiacarbocyanine dyes by nitroxyl radicals, iodide ions, and oxygen in solutions and in complexes with DNA

Using the flash photolysis method, the spectral and kinetic characteristics of triplet states of a number of meso-substituted thiacarbocyanine dyes (3,3′-diethyl-9-methoxythiacarbocyanine iodide, 3,3′,9-triethylthiacarbocyanine iodide, 3,3′-diethyl-9-methylthiacarbocyanine iodide, and 3,3′-diethyl-9-thiomethylthiacarbocyanine iodide) were studied, and the rate constants of triplet quenching by a stable nitroxyl radical, iodide ion, and oxygen were determined in solutions and in complexes with DNA. The results obtained show the formation of two types of dye-DNA complexes: formed by binding of the dye in the groove of a DNA molecule and by intercalation of the dye between base pairs. The complexation creates steric hindrances upon quenching of the triplet states of the ligands and causes great differences between the rate constants of the quenching processes.     

Structure and Electric Properties of Lithium Phosphate Glasses

The temperature-concentration dependence of the conductivity in glasses of the system Li₂O-P₂O₅ was studied. The content of extrinsic hydrogen in the structure of glasses was estimated by IR transmission spectra. The effect of hydrogen on the electrical properties and structure of the glasses studied was considered.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 5, 2005, pp. 755–760.Original Russian Text Copyright © 2005 by Sokolov, Tarlakov, Ustinov, Pronkin.