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Biomedical subjects

S N Semenov

Publications and source records attributed to S N Semenov.

9 recordsLinked to original sources
PubMed2000

Kinetics of solid-phase extraction and solid-phase microextraction in thin adsorbent layer with saturation sorption isotherm.

The effects of sorbent saturation in thin adsorbent layers have been much overlooked in earlier research and should be taken into account in both the theory and practice of solid-phase extraction (SPE) and solid-phase microextraction (SPME). The adsorption kinetics of a single analyte into a thin adsorptive layer was modeled for several cases of agitation conditions in the analyzed volume. The extraction process in the adsorbent layer was modeled using a Langmuir isotherm approximated by the linear isotherm at low concentrations and by a saturation plateau at concentrations exceeding the critical saturation concentration. Laplace transformations were used to estimate the equilibration time and adsorbed analyte concentration profile for no agitation, practical and perfect agitation in the analyzed volume. The equilibration time may be significantly reduced at high degrees of oversaturation and/or agitation in the analyzed volume. The resulting models indicated that the adsorbent layer becomes saturated at some critical value of the oversaturation degree parameter. The critical value of the oversaturation parameter is affected by both the concentration of the analyte in the analyzed volume and the sorbent characteristics. It was also shown that the adsorption process is carried out via the propagation of the saturation adsorption boundary toward the inner boundary of the adsorbent layer. These new adsorption models should serve as "stepping stones" for the development of competitive adsorption kinetic models for both SPE and SPME, particularly in cases where fast sampling is used.

Chromatography, Liquid↗
PubMed1998

Hyphenated thermal field flow fractionation--capillary electrophoresis.

The possibility was considered to use the transverse thermophoresis of analytes in the capillary for capillary electrophoresis (CE) to control the separation process, decrease the peak width due to thermal effects and provide new separation parameters in CE. As the examination has shown, in non-aqueous buffers the Joule heating in the capillary for CE can provide transverse temperature gradients comparable with the temperature gradients in conventional devices for thermal field flow Fractionation (ThFFF). It was proposed to use the non-uniform velocity profile of analytes caused by the transverse temperature gradient and the temperature dependence of the buffer viscosity for the FFF-like separation of analytes besides CE separation. The expressions for the peak parameters have been derived, where the non-uniform transverse analyte concentration distribution due to the thermophoresis is taken into account, and the possibilities based on FFF-CE principles are discussed. As possible objects of this hyphenated technique, macromolecules and particles are considered.

Electrophoresis, Capillary↗
PubMedDate not supplied

[Usage of polymerase chain reaction in complex diagnosis of hepatitis B].

Sera from 926 patients were analyzed by PCR using universal primers to surface gene of hepatitis B virus (HBV). HBV DNA was detected in 195 specimens. There were no serological markers of HBV in 8.2% of these sera, but later they were detected in patients' sera. In patients without HBV DNA in the serum, specific HBV antigens and antibodies were detected in 62%. Only in 14% of them the clinical picture of the disease corresponded to acute viral hepatitis, although the blood for PCR analysis was collected during the late stages of the infection. The rest cases were referred to mixed hepatitis C + D. Comparison of the results of PCR test and detection of serological virus replication markers HBeAg and HBeAb showed the presence of HBV DNA in 28% cases without HBeAg.

DNA, Viral↗
PubMedDate not supplied

[Effect of low-frequency electromagnetic fields on the individual functional systems of the body].

This paper is a review of recent publications about the effects of low frequency electromagnetic fields (EMF) (constant and pulsed) on the cardiovascular, neuroendocrine, and blood systems of experimental animals and industrial workers exposed to them. It is reported that the regulatory systems (nervous and endocrine) are highly sensitive to EMF. It is obvious that investigations of hormone-receptor interactions can help better understand EMF effects on the endocrine system and the body as a whole. Published data about EMF effects on the cardiovascular system and blood are often contradictory, probably, because of different estimates of allowable limits recognized in various countries. It is hypothesized that circulatory changes are largely dependent on the central regulatory structures, particularly hypothalamus. White blood responses to the exposure, being most significant among hematological reactions, are also induced, to a certain extent, by regulatory mechanisms. The EMF effects may depend on the initial state and individual properties of the biological organism. It is postulated that the EMF effects on regulatory mechanisms may be related to primary disorders in cellular and mitochondrial membranes.

Animals↗
PubMedDate not supplied

[Magnetic sedimentation of protein molecules].

Usage of pondermotive interaction of protein molecules with heterogenous magnetic field for the studies of their physico-chemical properties is considered. Possibility is shown of creating spatial heterogenous concentration of macromolecules whose value is close to the equilibrium one near the slit edge of the magnetic system. Potentialities of magnetic sedimentation of macromolecules are compared with different variants of centrifugation. It is shown that by means of magnetic sedimentation the data on the shape, volume and molecular weight of the molecules, as well as on the change of these parameters, can be obtained. It is also possible to calculate the distribution parameters of macromolecules according to their magnetic sensitivity and partial volumes and to find correlation between these parameters. Conduction of macromolecule sedimentation in the media with different magnetic sensitivity allows to enlarge the scope of the information obtained.

Magnetics↗
PubMedDate not supplied

[Interaction of cardiotoxin from the venom of the cobra Naja naja oxiana with phospholipid membrane model systems].

Surface activity of cardiotoxin from the venom of cobra Naia naja oxiana and an acetylated analog of the cardiotoxin was investigated on the water-air interface. The interaction of these substances with lipid monolayers and bimolecular membrane was also studied. It was shown that on the water-air interface cardiotoxin can form two different types of monolayers with different conformations of molecules. Cardiotoxin is found to form complexes with phospholipids due to interaction of positive charges of amino groups of lysin with phosphate groups of lipid molecules. One molecule of toxin is able to complex up to 10 molecules of lipid. The complex formed has a high surface activity, much more than that of the pure protein. Cardiotoxin increases the anion conductivity of bimolecular membranes. The nature of this phenomen is studied. A hypothetical mechanism of biological activity of caridotoxin is offered. It is supposed that not cardiotoxin as that, but its complex with phospholipid is the active agent.

Animals↗