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The regeneration of a series of 2,3-dihydrobenzo[b]selenophene-5-ol derivatives by water-soluble N-acetylcysteine in a two-phase model system for lipid peroxidation is investigated. The results have shown that the regeneration and catalytic performance is dictated by the number and position of methyl substituents present in the phenolic ring of the antioxidant.

A kinetic and thermodynamic investigation of phenols para-substituted with thiyl (SR), sulfinyl (SOR) and sulfonyl (S[O.sub.2]R) groups and ortho-substituted with thiyl groups is presented. The ESI-MS analysis of the products that are formed by reacting the sulfides with peroxyl radicals from the azoinitiator AIBM has revealed the formation of a complex mixture of products that might play a vital role in determining the overall antioxidant activity of the parent compounds.

Oxidative stress is a contributing factor in many of the diseases of aging, which include conditions such as atherosclerosis and Alzheimer's disease. Bodies have an endogenic arsenal of enzymatic and nonenzymatic antioxidants to combat oxidative degradation, but as it is apparent that these defenses are sometimes breached, there is an interest in the development and application of new synthetic antioxidants for antioxidant therapy.

The synthesis and study of a series of 6-substituted-2,4-dimethyl-3-pyridinols having interesting antioxidant properties is discussed. The experiments revealed that some of the newly synthesized pyridinols are the most effective phenolic chain-breaking antioxidants reported.

The antioxidant activity of the cis and trans isomers of several analogues of resveratrol and pterostilbene is investigated, especially with regard to the effect to the stereochemistry about the olefinic double bond. The antioxidant power of these compounds is estimated by measuring the rate constants for their reactions with peroxyl radicals and, with two of them, the bond dissociation enthalpy of the phenolic O-H bond which is cleaved in the inhibition reaction.

The interaction of para-substituted benzyl hydroxyalkyl nitroxide with the monolayer of water-soluble protected gold cluster made by a short alkyl chain and a triethylene glycol monomethyl ether unit is studied by using EPR spectroscopy. The inclusion of nitroxide probes in the more hydrophobic environment of the monolayer gave rise to a reduction of the value of both nitrogen and Beta-proton hyperfine splittings.

The experimental and computational study presented demonstrates that hydrogen bond donors can significantly change the spectroscopic and thermochemical properties of phenoxyl radicals. A strong H-bond donor such as hexafluoropropanol produces large variations of the hyperfine splitting constants indicative of a large redistribution of electron spin density which can be accounted for by the increased importance of the mesomeric structures (E-H) with electric charge separation.

Bond dissociation enthalpy differences, Z-X deltaBDA = BDE(4-YC6H4Z-X) - BDE(C6H5Z-X), for Z = CH(sub 2) and O are largely independent of X and are determined mainly by the stabilization/destabilization effect of Y on the 4-YC6H4Z radicals. For validating theory by connecting it to experiment, the N-H deltaBDEs of four 4,4'-disubstituted diphenylamines and five 3,7-disubstituted phenothiazines are both calculated and measured by the radical equilibrium EPR technique.

An octyltelluro group ortho was introduced to the phenolic moiety in 3-tert-butyl-4-hydroxyanisole (BHA) to significantly enhance the antioxidant characteristics of the material. The findings recommended considering the ortho-arrangement of an alkyltelluro group and hydroxyl as a privileged structure for phenolic antioxidants.

The impact of remote intramolecular hydrogen bonds (HBs) in phenols and benzylammonium cations on the dissociation enthalpies of their O-H and C-N bonds is studied. The thermochemistries of the HBs and hydrogen bond acceptors (HBAs) are reflected in the transition states for hydrogen atom abstraction from phenols by free radicals and the fragmentation of ring-substituted ions to form the benzyl cations has shown similar intramolecular HB effects.

The preparation of 3-pyridinols carrying alkyltlluro, alkylseleno and alkylthio groups is described along with kinetic, thermodynamic and mechanistic study of their antioxidant activity. The tellurium-containing 3-pyridinols have catalyzed reduction of hydrogen peroxide in the presence of thiol reducing agents, thereby acting as multifunctional catalytic antioxidants.

Synthesis and characterization of a series of amino acids analogous to tyrosine which differ in the physicochemical properties of the aryl alcohol side chain is described. The obtained compounds could be potentially useful to understand the the relationships between structure, thermodynamics, and kinetics in long-range proton-coupled electron transfer processes in peptides and proteins.

Stability constants, rates of association and dissociation, and thermodynamic and activation parameters for the formation of inclusion complexes between the radical guest, N-benzyl-tert-butyl-[d.sub.9]-nitroxide and [beta]- or 2,6-O-dimethyl-[beta]-cyclodextrin (CDs), are determined by EPR spectroscopy in water in the presence of different alcohols, differing in size and lipophilicity. EPR spectroscopy is considered as a rapid and accurate technique in order to examine the CDs binding behavior toward different nonradical guest.

Sulfur containing heterocycles are synthesized in order to examine the effect of the conformation of the ortho-SR groups on the phenolic O-H bond dissociation enthalpy (BDE(O-H)) and on the reactivity of the hydroxyl group toward free radicals. The results have helped in understanding the role of the tyrosine-cysteine link in the active site of galactose oxidase and have shown that switching of the ortho-SR substituent between perpendicular and planar conformations have attributed to the efficiency of this enzyme.

A demonstration that the core size of metallic nanoparticles passes on to the protective organic monolayer that has various water soluble properties could be measured with the help of ESR spectroscopy is presented. Results confirmed that ESR spectroscopy is an effective tool to check the properties of nanoparticles that binds them.

The effect of water on the O-H bond dissociation enthalpy (BDE) of para-substituted phenols using DFT calculations is examined. The experimental BDE values are fairly well reproduced by simple calculations carried out on the phenol/phenoxyl-water complexes, taking into account only hydrogen-bonding (HB) interactions of water molecules with molecular sites (HB model).

The complexity between heptakis-2,6-di-O-methyl-beta-cyclodextrin and different enantiomeric pairs of chiral nitroxides of general structures can be investigated by the EPR spectroscopy. The analysis of the mass spectra is done and the outcome is investigated.

The phenolic co-antioxidants in homogeneous hydrocarbon solution, is used for the study of the regeneration of alpha tocopherol (vitamin E). A model based on the knowledge of kinetic and thermochemical data concerning the various reactants, predicts the behavior of some relevant phenols.

Research has been conducted on 2,2'-methylenebis(6-tert-butyl-4-methylphenol), 2,2'-ethylidenebis(4,6-di-tert-butylphenol) and 4,4'-methylenebis(2,6-di-tert-butylphenol). The authors have studied the kinetics and thermodynamics of the antioxidant activity of these compounds, and present the results.