Formation of stable radicals during the reduction of fluoranil in alkaline alcoholic solutions

The magnetic-resonance parameters of a stable radical formed under anaerobic conditions during the reduction of fluoranil in alkaline alcohols were measured by the EPR, ENDOR and electron spin echo methods. It was concluded that a tetraethoxy-p-benzoquinone anion-radical is formed.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 26, No. 2, pp. 249–251, March–April, 1990.The authors wish to express their gratitude of I. I. Bil'kis for his participation in the discussions of the results of this work.     

The electronic absorption spectrum of the CrMo molecule

An absorption spectrum near 4800 Å was observed from flash photolysis of a mixture of Cr(CO)₆ + Mo(CO)₆ vapours, which is tentatively assigned to the CrMo molecule.     

Regulation of the sizes of silver nanoparticles stabilized with a maleic acid copolymer and the prospect of their biotechnological use

Methods of synthesizing silver nanoparticles (SNP) of various sizes stabilized with a maleic acid copolymer are proposed. The colloidal solutions of SNP are characterized by electron spectroscopy, static and dynamic light scattering, transmission electron microscopy. The stability of the obtained SNP in solutions of hydrogen peroxide and a hydrochloric acid salt is studied, their efficiency in antimicrobial activity tests is assessed.     

ESEEM Measurements of Local Water Concentration in D<Subscript>2</Subscript>O-Containing Spin-Labeled Systems

To calibrate electron spin echo envelope modulation (ESEEM) amplitudes with respect to the deuterium water content in spin-labeled biological systems, ESEEM of nitroxide TEMPO has been studied in frozen glassy D₂O-dimethylsulfoxide mixtures of different composition. The interaction between the unpaired electron of nitroxide and the deuterium nuclei manifests itself in a cosine Fourier transform spectrum as the sum of a narrow line with the doublet quadrupole splitting and of a broad one. The narrow line arises from interaction with distant deuterium nuclei, the broad one arises from interaction with nearby nuclei belonging to nitroxide-water molecule complexes. The dependence on water concentration was found to be nonlinear for the intensity of the narrow line and close to linear for the intensity of the quadrupole doublet. Therefore, the intensity of the quadrupole doublet is suggested as a measure of concentration of free water around a spin label in biological objects. Fourier transform line shape was theoretically simulated for different model distributions of water molecules around the spin label. Simulations confirm the linear dependence of the quadrupole doublet intensity on water concentration seen in the experiment. The suggested approach was applied to analyze data for spin-labeled dipalmitoylphosphatidylcholine (DPPC) and DPPC-cholesterol D₂O-hydrated model membranes. The concentration of free water near the spin-labeled fourth carbon atom along the lipid chain was estimated as 5.2 and 7.2 M for DPPC and DPPC-cholesterol membranes, respectively. Authors’ address: Sergei Dzuba, Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, Institutskaya 3, 630090 Novosibirsk, Russian Federation     

Microwave up-converter based on a nonlinear ferroelectric capacitor

An up-converter in which a capacitor with a nonlinear dielectric film is used as a nonlinear element is analyzed. Relationships between the conversion gain and capacitor parameters, such as loss tangent and the parameters of the C-V characteristic, which are of importance in converter design, are given. An up-converter using Ba_xSr_1−x TiO₃ capacitors is designed and tested. Experimental characteristics of this up-converter raising the frequency from 0.8 to 4.4 GHz are reported.     

Stabilization of silver nanoparticles with copolymers of maleic acid

Silver nanoparticles are obtained by reducing AgNO₃ with sodium borohydride in an aqueous solution in the presence of maleic acid copolymers with ethylene, N-vinylpyrrolidone, or styrene, as well as their octadecylamide group-containing hydrophobized derivatives, as dispersants. The influence of the structural features of the dicarboxylic acid copolymers on the silver nanoparticle formation process and the conditions for producing sols containing spherical nanoparticles with sizes of 1.5–3.5 nm (according to the data of transmission electron microscopy) are determined. It is shown that, at the equimolar copolymer/silver cation ratio, the morphology of resulting silver nanoparticles weakly depends on the nature of comonomers of maleic acid and the presence of hydrophobic fragments, which play an auxiliary role in the stabilization of dispersions of nanoparticles by increasing their stability with respect to ionic strength and oxidation. Evolution of the particle sizes in the system is monitored beginning with copolymer solutions to silver sols by the methods of light scattering, transmission electron microscopy, and atomic force microscopy. According to the light scattering data, copolymers and their complexes with silver ions in solutions are partly aggregated at concentrations corresponding to the conditions of nanosilver synthesis. Silver sols are shown to contain stabilized nanoparticles, which represent core-polyelectrolyte corona-type micelles and micellar clusters with polyelectrolyte coronas.     

Hyperfine Interaction Tensors of 13C Nuclei for Ring Carbons of Ubisemiquinone-10 Hydrogen Bonded in Alcohol Solvents

The anion radicals of ubiquinones-10 ¹³C chemically labeled at the C₅ or C₆ ring positions in alcohol have been studied by 1D and 2D ESEEM to define the hyperfine interaction tensors with the ¹³C nuclei. Analysis of the cross-peak line shapes and simulations of the spectra allowed us to conclude that the hyperfine tensors are characterized by an anisotropic component T ~6 MHz and an isotropic coupling a ~?3 MHz with support from DFT calculations. However, these values were found to be inconsistent with the shift of the sum combination harmonic in the four-pulse ESEEM spectra. Simulations resolve this apparent discrepancy by showing that the shift of the sum combination to lower frequency and its broadening can be accounted for by a distribution of the hyperfine couplings. A spread of the methoxy group conformations, as supported by previous experimental observations, is suggested as the mechanism influencing the distribution of the hyperfine couplings for the ring carbons.