Reactions of 7-nitropyrido[1,2-<Emphasis Type="Italic">a</Emphasis>]benzimidazolium salts with hydrazines and hydroxylamine

We are the first to show that quaternary 7-nitropyrido[1,2-a]benzimidazolium salts are cleaved by hydrazine, phenylhydrazine, and hydroxylamine to form 2-pyrazolinemethyl- and 2-isoxazoline-methyl-6-nitrobenzimidazoles.     

Conversion of 2-ethyl-3,3,5,5-tetramethyl- and 2-ethyl-1,3,3,5,5-pentamethyl-1,2,4,5-tetra-hydro-3h-benz-2-azepines by the action of ethyl propiolate

It has been shown that, on interacting 2-ethyl-3,3,5,5-tetramethyl- and 2-ethyl-1,3,3,5,5-pentamethyl-1,2,4,5-tetrahydro-3H-benz-2-azepines with ethyl propiolate in methanol, fission of the azepine ring occurs at the C(1)–N(2) bond involving a molecule of solvent. The indicated azepines do not react with acetylenedicarboxylic acid ester under these conditions.     

Interaction between blood plasma proteins and magnetite nanoparticles

Spin label EPR spectroscopy and dynamic and Rayleigh light scattering are employed to study the interaction between magnetite nanoparticles with a diameter of 17 nm and plasma proteins (fibrinogen and albumin). Protein molecules are shown to be adsorbed on nanoparticle surface with the formation of multilayer shells. When a buffer solution (pH 8.5) contains 0.01 vol % nanoparticles, 90–100 fibrinogen molecules are adsorbed per one particle and the thickness of an adsorbed layer is 30–40 nm. For albumin, the layer thickness is 10–15 nm. In a constant magnetic field, large linear microsized aggregates oriented parallel to field lines are formed in dispersions of nanoparticles covered with adsorbed protein molecules. The study of fibrin gel formation resulting from the action of thrombin enzyme on fibrinogen suggests that, in the presence of nanoparticles, the rate of gelation decreases by a factor of approximately two, while the ratio between the average mass and average length of fibrin polymer fibers rises.     

Structural organization of films based on polyaniline/polysulfonic acid complexes depending on the synthesis method

The optical properties and morphology of complexes based on polyaniline (PANI) and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS), depending on their synthesis conditions, have been characterized by UV-visible spectroscopy and atomic force microscopy. The dependence of the electron absorption spectra of PANI/PAMPS complexes and the surface topography of their films on the initiation way of PANI formation (chemical and enzymatic) and the use of promoters of aniline polymerization has been investigated. The aniline polymerization kinetics with and without polymerization promoters has been studied. All PANI/PAMPS complexes are found to have a nanocomposite time-stable structure.     

Dispersion-dominated nonlinear fiber-optic channel

We propose to apply a large predispersion (having the same sign as the transmission fiber) to an optical signal before the uncompensated fiber transmission in coherent communication systems. This technique is aimed at simplification of the following digital signal processing of nonlinear impairments. We derive a model describing pulse propagation in the dispersion-dominated nonlinear fiber channel. In the limit of very strong initial predispersion, the nonlinear propagation equations for each Fourier mode become local and decoupled. This paves the way for new techniques to manage fiber nonlinearity.     

Photoacoustic monitoring of gases using a novel laser source tunable around 2.5 μm

We present the first spectroscopic measurements using a tunable solid state Cr²+:ZnSe laser emitting at wavelengths between 2.2 μm and 2.8 μm. Photoacoustic measurements on various gases such as methane, carbon monoxide, carbon dioxide, water vapour, nitrous oxide, and ambient air were carried out. In this paper, we present measurements on methane, nitrous oxide, and ambient air. The deduced detection limits are in the low ppm or sub-ppm range, e.g., 0.2 ppm for carbon dioxide, 0.8 ppm for methane and 2.7 ppm for carbon monoxide.     

Reaction of 1,2,3,4-tetrahydro-2,4,5-trimethylpyrrolo[1,2-c]pyrimidine and its 7-formyl-substituted derivative with nitric acid

1,2,3,4-Tetrahydro-2,4,5-trimethylpyrrolo[1,2-c]pyrimidine and its 7-formyl derivative when treated with nitric acid are converted to substituted tetrahydropyrrolo-[1,2-c]pyrimidine-7-carboxylic acid. Conversion occurs through opening of the aminal moiety and formylation of the second molecule of tetrahydropyrrolo[1,2-c]pyrimidine by formaldehyde formed to the 7-formyl-substituted derivative.Russian University of International Friendship, Moscow 117198. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp 219–222, February, 1999.     

X-ray fluorescence determination of the molar ratio of metals in heterobimetallic complexes

A method was developed for the X-ray fluorescence determination of the molar ratio of metals in heterobimetallic complexes. The procedure includes simple rapid sample preparation and a novel algorithm of measurements and data processing. It was demonstrated that the procedure can be also used for the determination of the metal ratio in films of complexes applied to oxide supports.     

Effect of the fields of randomly spaced charged centers on the luminescence polarization

This paper considers the effect produced by randomly spaced charged centers in a crystal on the luminescence polarization associated with Jahn-Teller centers under conditions of uniaxial strain.     

Sub-20 fs pulse generation from the mirror dispersion controlled Cr:LiSGaF and Cr:LiSAF lasers

Received: 21 March 1997/Revised Version: 9 May 1997