V. Yu. Tyurin

Comparative study of redox characteristics and antioxidant activity of porphyrins with 2,6-dialkylphenol groups

152 The oxidative stress of an organism is a result of the acceleration of lipid peroxidation (LPO) in cells and the formation of reactive oxygen species and free rad icals. This process leads to destruction of membranes, the emergence of numerous pathologies, and prema ture aging of the organism. The search for new antiox idants, as well as for methods to assess the antioxidant activity, is an important and interesting task [1]. Of particular interest are synthesis and study of properties of polyfunctional compounds with several pharma cophoric centers in the molecule, because such a com bination is able not only to enhance the known physi ological activity but also to cause the appearance of new types of physiological activity [2–4]. Ionol I (2,6 di tert butyl 4 methylphenol) is a known anti oxidant used in the manufacture of foodstuffs (food additive E321). 2,6 Diisobornyl 4 methylphenol (dibornol) IV is currently undergoing preclinical tri als as a promising drug [5]. CHEMISTRY

Electrochemical and antioxidant activity of 2,6-di- tert -butylphenols with phosphonate groups

ISSN 00125008, Doklady Chemistry, 2010, Vol. 432, Pa rt 2, pp. 165–167.

Effect of Organotin Compounds and Their Complexes with Phosphatidylcholine on Peroxide Oxidation of Lipid Structural Fragments

Oxidation of a lipid structural fragment, oleic acid, in the presence of a series of organotin compounds and their complexes with phosphatidylcholine was studied at 25, 37, 65, and 95°C. At a nearly physiological temperature, acceleration of hydroperoxide accumulation in the presence of these complexes was observed. At 65°C, addition of organotin derivatives leads to increase in the initial rate of hydroperoxide accumulation, but the kinetic curves acquire an S-like character as the reaction progresses. These data indicate that the rate of decomposition of hydroperoxides exceeds the rate of their accumulation. In the presence of 2,6-di-tert-butylphenol as antioxidant, the promoting effect of organotin compounds disappears. A possible reaction mechanism and the role of radical species arising from dissociation of the CÄSn bond are discussed.

Complexes of organotin compounds with bis- and trisphosphonate derivatives of 2,6-di-tert-butylphenol having antioxidant activity

Complexes of organotin compounds R2SnCl2 with bisand trisphosphonate derivatives of 2,6-di-tert-butyl-4-methylphenol (ionol) were synthesized. X-ray diffraction studies were carried out for some of them. The redox properties of the synthesized compounds were characterized by cyclic voltammetry. Antioxidant/prooxidant activity of the complexes was studied using a new electrochemical method based on measuring the rate of hydrogen atom transfer to the stable radical 2,2´-diphenyl-1-picrylhydrazyl (DPPH). The data obtained were compared with the results of studying activity of the compounds during lipid peroxidation (LP) in biological samples. A correlation is observed between the results on antioxidant activity obtained by electrochemical DPPH test and using biological samples. Unlike the initial organotin compounds, the synthesized complexes have antioxidant activity, whereas phosphorus-containing phenols exhibit the properties of efficient antioxidants and chelating agents.

Dual Effect of Organomercury Compounds on Peroxide Oxidation of Oleic Acid

Oxidation of oleic acid with atmospheric oxygen in the presence of HgCl2 and various organo- mercury compounds (methylmercury iodide, isopropylmercury bromide, n-hexylmercury bromide, phenylmercury bromide, diphenylmercury, p-tolylmercury bromide, bis-p-tolylmercury) was studied. Mercury compounds exert a dual effect on accumulation of oleic acid hydroperoxide in the temperature range 20-90°C. Below 50°C, the concentration of the hydroperoxides formed in the presence of mercury compounds is lower, and at higher temperatures, higher than in the experiments performed without mercury compounds. Comparison of the concentrations of oleic acid hydroperoxides with those of their transformation products, carbonyl compounds, determined spectrophotometrically, shows that actually organomercury compounds and HgCl2 accelerate peroxide oxidation at all the studied temperatures. Decreased accumulation of peroxides below 50°C is apparently due to the fact that the rate of their reaction with organomercury compounds is higher than the rate of their formation.

Ways of Decreasing the Oxidative Stress Promoted by Organomercury Compounds

The oxidative stress of an organism resulting in metabolism disorder is related to the peroxide oxidation of lipids (POL) and to changes in the structure of cell membranes [1]. Detailed studies of POL processes showed that a number of exogenous agents exist, for example, metal salts and organic radicals, which promote the formation of hydroperoxides or carbonyl compounds, which are products of their decomposition, and accumulation of these products in the cell [2]. In addition, assays carried out for the whole organism indicate that toxic organomercury compounds RHgX and R 2 Hg are accumulated in cell membranes due to their lipophilic properties and accelerate POL [3, 4]. However, scarcity of the available data on the mechanism of toxic action of RHgX and R 2 Hg at the molecular level do not allow one to propose a general concept for the choice of detoxifying agents. Currently, thio derivatives and complexones [5], for example, 2,3-dimercaptopropanol and calcium disodium ethylenediaminetetraacetate, are used most often as detoxifying agents against mercury poisoning. The action of these agents is based on the binding of Hg atoms to give Hg‐S or Hg‐O bonds; however, it does not imply the possibility of deactivation of the reactive C-centered organic radicals resulting from the homolytic cleavage of the Hg‐C bond, which inevitably accompanies the involvement of RHgX and R 2 Hg in biochemical redox and radical processes.