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SM ISO690:2012 BLONSCHI, Vladislav. Photochemical transformations of cysteine in the presence of humic acids. In: Achievements and perspectives of modern chemistry, 9-11 octombrie 2019, Chişinău. Chisinau, Republic of Moldova: Tipografia Academiei de Ştiinţe a Moldovei, 2019, p. 160. ISBN 978-9975-62-428-2. |
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Achievements and perspectives of modern chemistry 2019 | ||||||
Conferința "International Conference "Achievements and perspectives of modern chemistry"" Chişinău, Moldova, 9-11 octombrie 2019 | ||||||
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Pag. 160-160 | ||||||
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Thiolic substances (R-SH) are the class of biogenic organic compounds with multiple essential functions in biogeochemical systems. One of a biogenic nature thiols is cysteine (Cys), which, together with glutathione (GSH), is found in the large amounts in living organisms [1]. It is demonstrated that in the upper layers of aquatic objects R-SH suffer predominantly photochemical transformations, but the influence of humic acid (HA) in photochemical processes remains unclear [2]. According to recent research [3], humic acids are not only sensitizers in photochemical transformations. It was been demonstrated that HA can generate free radicals by the absorption of solar radiation by chromophore groups (-C=C-, -C=O, phenolic rings) of their structure, which gives them mixed properties, both photosensitizing and photoinitiating. An increase in the concentration of free radicals (1O2, OH ), generated by HA at high values of natural water mineralization and in the presence of transition metals [1-3] has been observed. However, under some conditions, HA may also act as antioxidants, regenerating photochemically oxidized aminoacid molecules, such as tryptophan [3]. The purpose of this paper is to identify some kinetic laws of Cys photolysis in the presence of humic acids, on model systems.Under laboratory conditions 4 systems were modeled, in each of them varying consecutively the concentration of one compound, while the other remained constant:(I) Cys-AH- hv;(II) Cys-AH- H2O2- hv;(III-IV) Cys-AH- H2O2- Men+ - hv, where Men+ are Cu (II) and Fe (III) ions.The experimental results confirmed that cysteine undergoes photochemical transformations in the presence of humic acids, the order of the photolysis constants experimentally calculated (10-4-10-5 M/s) is in line with literature data [1]. At addition of initiator and/or catalyst molecules to the system, the concentration of the -SH groups increases with time, which confirms the hypotheses proposed in literature that HA may behave as photosensitizers, photoinitiators, radical traps and antioxidants [4]. However, the chemical behaviour of HA remains a subject of research of photochemical transformations in natural waters. |
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