Valery Kochev

Interaction of solid supported thin lipid films with saponin

Abstract The interaction of solid supported liquid films of lipids with saponin is investigated in the present work by impedimetric analysis. It is shown that the specific reaction of saponin with the cholesterol molecules present in the modified films can readily be distinguished by the impedance data. In this respect, possibilities for the realization of sensor devices based on solid supported lipid films are briefly discussed.

Voltammetric study of levomepromazine induced ionic permeability in a model lipid membrane system

The interaction of solid supported liquid films of lipids with levomepromazine is investigated in the present work by voltammetry. It is shown that the levomepromazine penetrates into the films, which results in a readily detectable change of the film permeability to electroactive species. In this respect, possibilities for the employment of supported lipid films as model systems in the research of biomembrane active compounds are briefly discussed.

Probing the “interfacial” and “bulk” characteristics of solid-supported thin liquid films

Abstract The conversion of relatively “thick” (on the order of 100 A) solid-supported liquid films of lipids to mono- or bilayer molecular structures by the aid of electrostriction is considered in the present work. Technique based on the concept of impedance is used for the investigation of the parameters of these different types of films. It is shown that the “thick” films could structurally be regarded as composed of “bulk” and “interfacial” parts with readily distinguished characteristics. Some possibilities of using this information for the realization of sensor devices based on solid-supported thin liquid films of lipids are discussed.

An improvement of the diffusion model for assessment of drought stress in plant tissues

The article discusses an improvement of a previously developed method for assessment of ion leakage from plant tissues as a gauge of membrane and cell wall performance under stressful environment. It employs conductometric measurements of the ion efflux from leaves and their quantitative interpretation by a theoretical model based on the laws of diffusion. Experimental data are readily fit with the model and results are in accordance with relative water content of dehydrated barley (Hordeum vulgare) seedlings of two distinct cultivars. Some new parameters obtained from fitting are proposed as reliable indicators of the leaf status. They appear to be helpful in further distinguishing the behavior of two separate cellular structures with respect to their electrolyte permeability. It is concluded that the established method based on the kinetics of ion leakage is adequate for evaluation of contrasting genotypes under normal and stress conditions. Furthermore, it could be used as a simple and powerful tool for routine analysis and screening for drought tolerance in crops.

Preparation of extremely thin solid supported films of lipids by the method of electrostriction

Preparation of stable ultra thin lipid layers onto polished glassy carbon (GC) surface is reported in this work. The method of formation relies on additional thinning of wetting films by electrostriction. The possible final structure of the films, as well as, their relevance for sensor development are discussed.

From 'bulk' to 'interfacial' types of sensors

Abstract The advantages of a two-dimensional design for the receptor part of a biosensor are discussed in the light of a compromise between stability and sensitivity. Some further prospects for a promising novel biosensor technology, based on solid-supported thin liquid films, are described.

Mn2+ as a mediator for the electron transfer across thin wetting films of lecithin

Abstract The employment of manganese (Mn 2+ ) as a mediator for the electron transfer across glassy carbon-supported thin lecithin films in contact with electrolyte is described in the present work. The results suggest, that the ascorbate oxidation, which is normally hampered by the film, can proceed through the incorporated manganese. In this respect, the potential of Mn for modification of lipid wetting films in construction of sensitive interfaces is briefly outlined.

Potentiometric assessment of iron release during ferritin reduction by exogenous agents.

This work studied the possibilities for quantitative determination of iron mobilization in connection with ferritin reduction by ascorbic acid (vitamin C) and sodium dithionite in vitro. The iron storage protein was incubated with an excess of reductant in aerobic conditions in the absence of complexing agents in the medium. The release of Fe(2+) was let to go to completion, and the overall content of Fe(2+) in the solution was evaluated with the aid of potentiometric titration using Ce(4+) as an oxidizing titrant. Results suggest a moderate iron efflux under the influence of the chosen reducing agents. Although such a reduction of the protein mineral core by dihydroxyfumarate contributes greatly to the iron mobilization, ferritin behavior with vitamin C and dithionite seems to be different. Although redox properties of dihydroxyfumarate are determined by hydroxyl groups similar to those of ascorbic acid, the two compounds differ significantly in structure, and this could be the basis for an explanation of the specificities in their interaction with ferritin. As revealed by the study, potentiometric titration promises to be a reliable tool for evaluation of the amount of Fe(2+) present in the solution as a result of the reduction of the ferritins mineral core.

A SIMPLE IMPEDIMETRIC DEVICE FOR IN SITU ANALYSIS OF PLANT TISSUES

Construction and major features of a set-up suitable for impedance analysis of plant tissues are disclosed in the paper. The measuring device is based on a simple scheme operating in conjunction with the PC sound card. While many programmes running directly on sound card are capable of simulating impedance analyzer, their performance is not consistent when chemical or biological systems are explored. The main reason is a relatively low input impedance of the card itself. An addition of coordinating preamplifier between the sample and the audio input of the PC drastically improves the implementation of the set-up. On the other hand, a specially designed measuring head gives possibilities for straightforward assessment of plant tissue’s electrical parameters in situ at various ambient conditions. Some examples of impedance analysis of intact leaves are given and their behaviour in regard to a preliminary imposed desiccation is briefly discussed.