I. A. Veselova

Mechanisms of peroxidase oxidation of o-dianisidine, 3,3’,5,5’-tetramethylbenzidine, and o-phenylenediamine in the presence of sodium dodecyl sulfate

Peroxidase oxidation of o-dianisidine, 3,3′,5,5′-tetramethylbenzidine, and o-phenylenediamine in the presence of sodium dodecyl sulfate (SDS), an anionic surfactant, was spectrophotometrically studied. It was found that 0.1–100 mM SDS concentrations stabilize intermediates formed in the peroxidase oxidation of these substrates. The cause of the stabilization is an electrostatic interaction between positively charged intermediates and negatively charged surfactant.

Catalytic activity and the stability of horseradish peroxidase increase as a result of its incorporation into a polyelectrolyte complex with chitosan

The incorporation of horseradish peroxidase into polyelectrolyte complexes with chitosans of different molecular weights (MW 5–150 kDa) yielded highly active and stable enzyme preparations. As a result of the selection of optimal conditions for the formation of peroxidase-chitosan complexes, it was found that 0.1% chitosan with a MW of 10 kDa had the strongest activatory effect on peroxidase (activation degree, >70%) in the reaction of o-dianisidine oxidation by hydrogen peroxide. The complex formed by 0.001% chitosan with a molecular weight of 150 kDa was most stable: when immobilized on foamed polyurethane, it retained at least 50% of the initial activity for 550 days. The highest catalytic activity was exhibited in a 0.05 M phthalate buffer (pH 5.9–6.2) by the complex containing 0.006–0.009% chitosan in the indicator reaction. The activatory effect of the polysaccharide on the enzyme was determined by its influence on the binding and conversion of the reducting substrate peroxidase.

Properties and analytical applications of the self-assembled complex {peroxidase-chitosan}.

A novel promising approach to the improvement of analytical properties of horseradish peroxidase based on its inclusion into self-assembled structures of chitosan is discussed. It is shown that the reasonable choice of a polyelectrolyte, a detailed investigation of its interaction with the enzyme and the conditions of the {peroxidase-polyelectrolyte} complex formation allow for stabilizing the biocatalyst in aqueous and aqueous-organic media without a substantial loss in its activity and developing corresponding analytical procedures and biosensors. The latter provides highly selective determination of a number of organic compounds and sensitive determination of heavy metal ions that becomes possible due to the specific interactions of the analytes with the polymer matrix. Besides, the application of the proposed analytical systems and biosensors provides the expansion of the range of the compounds, and poorly water soluble and slowly oxidized substrates of peroxidase as well, which could be determined and real samples which could be analyzed by enzymatic methods. Analytical performance of the developed spectrophotometric indicator procedures and biosensors based on the self-assembled complex {peroxidase-chitosan} is demonstrated in the determination of metal ions (Hg(II), Cd(II), and Pb(II)), phenothiazines (promazine, chloropromazine, and trifluoroperazine), phenolic compounds (phenol, hydroquinone, catechol, pyrogallol, quercetin, rutin, and esculetin), organic peroxides (tert-butyl peroxide, 2-butanone peroxide, and benzoyl peroxide) in various samples, including water-insoluble matrices.

A solid-phase fluorescent biosensor for the determination of phenolic compounds and peroxides in samples with complex matrices

A solid-phase fluorescent biosensor for the determination of phenolic compounds (simple substituted phenols and catecholamines) and peroxides has been developed. The biosensor has a simple construction and the analytical signal is measured directly in a biosensitive layer {peroxidase-chitosan} on the sensor surface. This approach allowed analyzing samples with complex matrices (including water-insoluble samples and nontransparent solutions) without their preliminary pretreatment. Two novel fluorescent indicator reactions for the determination of the above-mentioned analytes in wide concentration ranges (from nmol l−1 to mm l−1) which provided an analytical signal registration on a solid phase were proposed. The developed sensor was applied successfully for the analysis of urine, cosmetics, pharmaceuticals preparations, etc.

Determination of fluoride, cyanide, and thiocyanate using horseradish peroxidase immobilized on modified silica gel

Abstract Silica gels modified with different functional groups (amino, epoxy, cycloepoxy, isocyanate, and thiocyanate) were used for the covalent immobilization of horseradish peroxidase (HRP). The catalytic activity and stability of the obtained enzyme preparations were studied using the reaction of o‐dianisidine oxidation with hydrogen peroxide as an indicator. The covalent immobilization of horseradish peroxidase using silica gel modified with thiocyanate groups provided not only the improvement of the enzyme stability, but also the development of the sensitive, rapid, and simple procedures for the determination of fluoride, cyanide, and thiocyanate. Enzymatic determination of inorganic anions is based on their inhibitory effect on the enzyme as the ligands capable to form stable complexes with Fe(III)‐HRP cofactor. The proposed procedures were applied for the determination of F− in mineral and drinking waters; CN− and SCN−—in biological fluids (blood and saliva).

Biochemical methods of crude hydrocarbon desulfurization

Up-to-date information on the microbiological method of fuel desulfurization has been systematized and the ways of increasing the efficiency of this method have been considered. The prospective uses of biochemical methods for the specific elimination of sulfur from petroleum and the production of fuel conforming to modern standards are discussed. Reports on the novel desulfurization procedure that employs commercial preparations of enzymes and proteins are analyzed in detail.

Enzymatic methods of analysis: Novel approaches and applications

The results of a series of investigations dealing with the development of enzymatic methods for determination of biologically active compounds, viz., inhibitors, activators, and substrates of native and immobilized enzymes of the oxidoreductase (peroxidases, alcohol dehydrogenases) and hydrolase (alkaline and acid phosphatases) classes isolated from diverse sources are summarized. Novel original approaches, proposed by the authors, for improving the sensitivity, selectivity, and rapidity of the methods are discussed. Numerous examples of application of the developed enzymatic procedures for the analysis of a wide range of samples are given.

Determination of Zinc(II) Using Native and Immobilized Alkaline Phosphatases of Different Origin

The effect of zinc(II) and other metal ions on the catalytic activity of native and immobilized alkaline phosphatases isolated from three different sources (Escherichia coli, chicken intestine, and small intestine of Greenland seal) was studied. Zinc(II) inhibits the catalytic activity of all native alkaline phosphatases to different extents. Zinc(II) produces the most significant and selective effect only on the alkaline phosphatase from seal intestine. As for alkaline phosphatases immobilized on polyurethane foam, zinc(II) hardly affects the activity of the enzyme from chicken intestine and inhibits the phosphatases from E. coli and seal intestine in concentrations from 2.5 to 50 μg/mL and 0.1 ng/mL to 50 μg/mL, respectively. With the use of native and immobilized alkaline phosphatase from the small intestine of the seal, selective procedures were developed for the determination of Zn(II) with spectrophotometric and visual control of the reaction rate. The detection limits are 1 μg/mL and 0.1 ng/mL, respectively.

Novel Multilayer Nanostructured Materials for Recognition of Polycyclic Aromatic Sulfur Pollutants and Express Analysis of Fuel Quality and Environmental Health by Surface Enhanced Raman Spectroscopy

A novel concept of advanced SERS (surface enhanced Raman spectroscopy) planar sensors is suggested for fast analysis of sulfur-containing hazardous oil components and persistent pollutants. The main advantage of the proposed sensors is the utilization of an additional preconcentrating layer of optically transparent chitosan gel, which is chemically modified with appropriate π-acceptor compounds to selectively form charge-transfer complexes (CTCs) at the interface with nanostructured silver coatings. The CTCs shift absorption bands of polycyclic aromatic sulfur heterocycles (PASHs) and other important analytes in a controllable way and thus provide a surplus enhancement of vibration modes due to resonant Raman scattering. This novel indicator system provides multiplex determination of PASHs in different forms in a small volume of oil without any tedious sample pretreatment steps. This approach opens new possibilities of increasing either spectral and concentration sensitivity or specificity of SERS-based sensors, allowing for new developments in the fields of ecology, advanced fuel analysis, and other prospective applications.

Methods for determining neurotransmitter metabolism markers for clinical diagnostics

Published data describing the current status and prospects for the development of clinical diagnostics of a number of neurodegenerative and neuroendocrine diseases associated with neurotransmitter balance disorders in a human body are generalized, systematized, and assessed in the review. Characteristics, advantages, and limitations of neuroimaging techniques and different diagnostic methods based on measuring concentrations of protein markers, catecholamines, and their metabolites are discussed. Prospects of the application of optical methods, such as fluorimetry and surface-enhanced Raman spectroscopy, to the development of sensor systems for the diagnosis of these diseases by the concentration of catecholamines and their metabolites in biological fluids are demonstrated.