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Legalities of some thiol substances photochemical transformation in aquatic systems


Author: Lis Angela
Degree:doctor of chemistry
Speciality: 02.00.20 - Ecological chemistry
Year:2022
Scientific adviser: Viorica Gladchi
doctor, associate professor (docent), Moldova State University
Scientific consultant: Gheorghe Duca
doctor habilitat, professor, Moldova State University
Institution: Moldova State University

Status

The thesis was presented on the 12 July, 2022 at the meeting of the Scientific Council and now it is under consideration of the National Council.

Abstract

Adobe PDF document1.13 Mb / in romanian

Thesis

CZU C.Z.U.: 574.5:544.52:547.367(043)

Adobe PDF document 4.81 Mb / in romanian
226 pages


Keywords

cysteine (Cys), glutathione (GSH), thioglycolic acid (ATG), thiourea (TU), thiol, direct photolysis, induced photolysis, sensitized photolysis, quantum yield, chemical actinometer, self-purification capacity

Summary

Thesis structure: introduction, six chapters, general conclusions and recommendations, bibliography of 261 titles, 133 pages of basic text, 26 tables, 52 figures and 43 annexes. The results are published in 28 scientific papers.

Field of investigation: 145.02 - ecological chemistry of water.

The purpose of the paper: consists in the research of photochemical transformations of some thiol substances, and their role in the formation of the quality of the aquatic environment.

Research objectives: synthesis of research results on the place and role of thiol substances in the aquatic environment; determination of the intensity, light flux and energy of the irradiation sources used in the study; studying the legalities and establishing the mechanisms of photochemical transformation of some thiol substances in the aquatic environment; determination of the kinetic parameters of the photochemical reactions with the participation of thiols; establishing the influence of thiols on the process of radical self-purification of aquatic systems; monitoring the content of thiol compounds in some aquatic objects on the territory of the Republic of Moldova.

Scientific novelty and originality lie in elucidating the kinetic laws of the thiols photolysis processes: TU, Cys, GSH and TGA. Were determined the light intensity, light flux and energy of the irradiation sources used in the study. Were determined the quantum yields of the photochemical transformation reactions of TU, Cys and GSH. It was found that the rates of photochemical processes in aquatic systems are influenced by several factors: the concentrations of components, hydrogen peroxide, of metal ions with variable valence (on the Cu(II) and Fe(III) ions example), radiation quality and quantity, season, temperature, cloudiness, etc. For the first time, the kinetic parameters of the direct, induced and sensitized photolysis processes for TU, Cys, GSH and TGA were determined. Were monitored the thiol concentrations in some surface aquatic objects in the Republic of Moldova. Was established the influence of the investigated thiols on the processes of radical self-purification of the aquatic systems.

The results obtained that contribute to solving the important scientific problem consists in establishing of the photochemical transformations legalities, determining the kinetic parameters of direct, induced and sensitized photolysis and evaluating the influence of some thiol substances in the aquatic systems on the intensity of their radical self-purification processes. In practical terms, these results contribute to solving one of the three main problems of ecological chemistry, related to the influence of pollutants on the environment and evaluation of the photochemical transformation rate of pollutants according to environmental factors by using kinetic parameters to predict their behavior in natural waters.

Theoretical significance consists in substantiating the knowledge in the ecological chemistry field regarding the photochemical transformations of some thiol substances for the formation of a chemical composition suitable for a habitat value and the improvement of the chemical self-purification process. The results has confirmed the effectiveness of the kinetic principle in in researching photochemical processes in aquatic systems. A database on the photochemical transformations of thiols (Cys, GSH, TU, ATG) has been completed.

Applicable value refers to the use of experimental data for the determination of redox toxicity and self-purification processes of natural waters, as well as the prevention of pollution of aquatic systems with thiol substances.

Implementation of scientific results. The experimental results were used to determine the self-purification capacity of natural waters, monitoring of thiol concentration, assessment of the pollution and prediction of consequences for aquatic systems. The results obtained are used in the teaching process of students by training the skills of aquatic systems treatment in the course “Wastewater treatment technologies”. Also, the obtained results are confirmed by three acts of implementation of the scientific activity in practice, place of implementation: Ustia village, Dubasari district, 17.05.2019; Danceni village, Ialoveni district, 25.05.2019; Customer group, Hagimus village, Causeni district, 15.06.2021.