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a sulfonamide fragment but also conformational equilibrium among these types of intramolecular interactions are essential for the manifestation of high efficiency in suppressing HIV-infection in cell culture.Introduction. Many derivatives of aminophenols (AP) are known to be effective antioxidants that are capable of changing the course of free-radical processes [1]. These compounds also have traditional applications as stabilizers of industrial organic materials and as food preservatives [2,3]. They exhibit high efficiency for prevention and treatment of pathologies due to disorders in the human antioxidant system [4] and as antiviral agents against herpes simplex and flu A virus [5][6][7][8][9]. AP derivatives that suppress HIV-infection in cell culture were recently synthesized [10].The pharmacological properties of AP are related to their effect on the course of free-radical processes in biological systems. Steady-state radiolysis and IR spectroscopic methods found that the antioxidant properties of AP are enhanced when the hydroxyls in the molecules are free and diminished upon forming various types of intramolecular hydrogen-bonds (IHB) [11]. As a rule, reactions involving active oxygen species occur nonselectively. Their occurrence in biological systems can damage both the cells themselves and viruses incorporated into them if highly active antioxidants are used.The question of which AP derivatives that are added to biological systems can change the course of free-radical reactions so that an effective and stable antiviral effect is obtained remains open. Therefore, it is important in principle to study properties of individual molecules such as the ability to form IHB because the type of IHB found in the AP is frequently related to their antiradical and antiviral activity [12,13].Herein IR-Fourier spectroscopy is used to study intramolecular interactions (IMI) in CCl 4 solutions of five structurally similar AP derivatives, 4,6-di-tert-butyl-2-(phenylamino)phenol (AP I), N-(3,5-di-tert-butyl-2-hydroxyphenyl)acetamide (AP II), N-(2-hydroxy-3,5-di-tert-butylphenyl)-4-methylbenzenesulfonamide (AP III), N-(2-methoxy-3,5-di-tert-butylphenyl)-4-methylbenzenesulfonamide (AP IV), and N-(2-hydroxy-3,5-di-tert-butylphenyl) methanesulfo-namide (AP V):

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Background: In this review article a brief overview of novel metallotherapeutic agents (with an emphasis on the complexes of essential biometals) promising for medical application is presented. We have also focused on recent work carried out by our research team, specifically the development of redox-active antimicrobial complexes of sterically hindered diphenols with some essential biometals (copper, zinc, nickel). Results: The complexes of essential metals (manganese, iron, cobalt, nickel, copper, zinc) described in the review show diverse in vitro biological activities, ranging from antimicrobial and anti-inflammatory to antiproliferative and enzyme inhibitory. It is necessary to emphasize that the type of organic ligands in these metal complexes seems to be responsible for their pharmacological activities. In the last decades there has been a significant interest in synthesis and biological evaluation of metal complexes with redox-active ligands. A substantial step in the development of these redox-active agents is the study of their physico-chemical and biological properties, including investigations in vitro of model enzyme systems, which can provide evidence on a plausible mechanism underlying the pharmacological activity. When considering the peculiarities of the pharmacological activity of the sterically hindered diphenol derivatives and their nickel(II), copper(II) and zinc(II) complexes synthesized, we took into account their being potential antioxidants, their antimicrobial activity possibly resulting from their affecting the electron-transport chain. Conclusion: We have obtained novel data demonstrating that the level of antibacterial and antifungal activity in the series of the above-mentioned metal-based antimicrobials depends not only on the nature of the phenolic ligands and complexing metal ions, but also on the lipophilicity and reducing ability of the ligands and metal complexes, specifically regarding the potential biotargets of their antimicrobial action – ferricytochrome c and the superoxide anion radical. The combination of antibacterial, antifungal and antioxidant activity allows one to consider these compounds as promising substances for developing therapeutic agents with a broad spectrum of activity.

Effects of a number of quinones and diphenols of various structures on free-radical fragmentation processes taking place in alpha-diols, glycerol, 2-aminoethanol, glycero-1-phosphate, ethylene glycol monobutyrate, maltose, and some lipids were investigated. Quinone additions have been found to change the direction of free-radical transformations of the compounds cited above by inhibiting formation of the respective fragmentation products owing to oxidation of radicals of the starting compounds. The results obtained and literature data available allow a suggestion to be made that the system quinone/diphenol is able to not only deactivate or generate such active species as O2.- but also control the realization probability of free-radical processes of peroxidation and fragmentation in biologically important molecules.