Interaction of Nitromethane with Modified Paramagnetic Defects on a Thermochemically Activated Silica Surface

It was found that the interaction of the modified paramagnetic defects SiO(CH₂) _n H₂ (n = 0.1) with nitromethane on a thermochemically activated silica surface at 300 K results in the formation of the following nitroxyl radicals: SiO(CH₂) _n CH₂ON( )CH₃ and SiO(CH₂) _n CH₂N( )CH₃. It was suggested that these radicals are the products of two different reactions of the modified paramagnetic defects: the first results from a reaction with free nitromethane; the second, from a reaction with nitromethane bound as complexes with diamagnetic surface defects.     

Translational diffusion coefficient of a nitroxide radical in an ionic liquid, as determined via EPR spectroscopy, cyclic voltammetry, and chronoammetry

Values of the translational diffusion coefficient of a spin probe (2,2,6,6-tetramethyl-4-oxypiperidine-1-oxyl) are determined via cyclic voltammetry, chronoammetry, and EPR in ionic liquid (1-butyl-3methylimidazolium tetrafluoroborate) at 295 K. They are found to be (8 ± 3) × 10^?12, (9 ± 3) × 10^?12, and (11 ± 4) × 10^?12 m²/s, respectively.     

Electrochemical Biosensor Based on Nanosized Polymer-Enzyme Films Composed of Linear Poly(N,N-Dimethylaminoethyl Methacrylate) and Choline Oxidase

Moscow University Chemistry Bulletin - Nanosized polymer-enzyme films were fabricated on graphite surfaces via a sequential two-stage adsorption of the pH- and thermoresponsive polymer, viz.,...     

Radical chain photoreactions involving alkylperoxides grafted onto an activated surface of silicon dioxide

Photolysis of the alkylperoxy radicals ≡SiOCH₂OO and ≡SiOCH₂CH₂OO grafted onto an activated surface of silica was found to be accompanied by photochemical radical chain reactions.     

Phototransformations of azetidine radical cations stabilized in freonic matrices

It has been established that transformations of azetidine radical cations observed in freonic matrices under the action of light with λ = 436 nm (T = 77 K) are associated with C-N bond cleavage which corresponds to the cyclic form yielding a mixture of open distonic C-centered radical cations of the following structure: ·CH₂CH₂CH=NH ₂ ⁺      

Cage effect in the solid phase calculation of quantum yields of stabilized radicals on the basis of a free volume model

A method of evaluating the quantum yield of stabilized radicals in solid phase molecular homolytic photodecomposition is suggested. The calculation is based on a free volume model. It is assumed that the radical escape from the matrix cage occurs only where a free volume larger than the volume of the fragment coming out of the cage is concentrated near the decomposed molecule. The available experimental data on the quantum yields of the stabilized radicals are in good agreement with the calculated ones.     

Spontaneous Assembly of Miktoarm Stars into Vesicular Interpolyelectrolyte Complexes

Mixing a bis‐hydrophilic, cationic miktoarm star polymer with a linear polyanion leads to the formation of unilamellar polymersomes, which consist of an interpolyelectrolyte complex (IPEC) wall sandwiched between poly(ethylene oxide) brushes. The experimental finding of this rare IPEC morphology is rationalized theoretically: the star architecture forces the assembly into a vesicular shape due to the high entropic penalty for stretching of the insoluble arms in non‐planar morphologies. The transmission electron microscopy of vitrified samples (cryogenic TEM) is compared with the samples at ambient conditions (in situ TEM), giving one of the first TEM reports on soft matter in its pristine environment.

     

Conformation and rotational mobility ofэSiOĊH2 radicals grafted onto the silica surface

The conformation ofэSiOC·H₂ radicals was determined by comparison of the ESR data and results of quantum-chemical calculations. Based on the experimental data, the characteristic times τ_c of rotational mobility ofэSiOC·H₂ radicals grafted onto a silica surface were estimated over the temperature interval from 77 (τ_c = 15.8 · 10^-8 s) to 295 K (τ_c 1.3 · 10^-8 s). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2092–2095, November, 1999.     

Catalysis of carbon tetrachloride conversion by copper complexes with monoethanolamine immobilized on the surface of silica

The catalytic properties of silica-immobilized copper complexes with monoethanolamine in reactions of CCl₄ addition to 1-octene and combined metathesis of C-Cl and C-H bonds in the CCl₄-decane system were studied. The catalytic activity was found to be an extremal function of metal concentration. The increase of activity during the addition of CCl₄ to octene as the metal content was decreased to ~0.3 wt % can be explained by an increase in the fraction of mononuclear copper complexes of differing composition. Further changes in activity were due to the formation of metal complexes with various ligand environments. A comparison between EPR data and catalytic properties suggested that the most active catalysts contained a considerable number of divalent copper complexes with a coordination environment of four nitrogen atoms, which are more effective than oxygen at increasing electron density on copper ion; this facilitated the reduction of Cu(II) to Cu(I). The above complexes are unstable because the ligands are rigidly fixed on the surface and strained structures are formed. Ligands in the coordination sphere of the metal can be readily replaced by substrate molecules, which exhibit weak solvating power.Translated from Kinetika i Kataliz, Vol. 46, No. 1, 2005, pp. 73–79.Original Russian Text Copyright © 2005 by Smirnov, Tarkhanova, Kokorin, Pergushov, Tsvetkov.