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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.

Research has been conducted on alpha-tocopherol. The regeneration of this compound carried out in homogeneous solution by means of coantioxidants in investigating the mechanism responsible for this process is described.

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.

Research has been conducted on the phenolic compounds. The determination of the phenols' bond dissociation enthalpies has been carried out via the use of EPR radical equilibration technique and the results indicate that CN, NO (sub)2 CHO, COOR and COOH induce the enthalpy value of the O-H bond.

Research has been conducted on N-hydroxyphthalimide which is combined with cobalt salts. The oxidation of N-alkylamides by O (sub)2 catalyzed by N-hydroxyphthalimide has been examined and the results indicate that this oxidation allows alkylamine reverse transformation to carbonyl compounds via intermediate amides.

Research has been conducted on the homolytic reactivity of 3,3'-di--tert-butyl-5,5'-dimethyl(1,1'-biphenyl)-2,2'-diol. The thermodynamics and kinetics of this reactivity have been investigated and the results are described.

Research is presented describing kinetic and thermodynamic investigations on the homolytic reactivity of phenoselenazine, phenoxazine, phenothiazine, substituted phenothiazines and related tricyclic aromatic amines. Electron paramagnetic resonance spectroscopy is used.

The synthesis of 2-methyl-2-(1-naphthyl)-1-bromopropane and of 2-methyl-2-(2 naphthyl)-1-bromopropane that can generate the radicals 2-methyl-2-(1-naphthyl)-1-propyl and 2-methyl-2-(2-naphthyl)-1-propyl and the calibration of their rearrangement reactions was described. The rearrangement of the radicals at room temperature with rate constants of 6.4 x 10 to the third power and 1.4 x 10 to the fourth power M-1s-1, respectively, can be valuable in determining rate constants for hydrogen abstraction by primary alkyl radicals.

The kinetics of hydrogen atom transfer from substituted phenols to primary alkyl radicals were studied. It was established that hydrogen atom shift from a phenolic antioxidant resulted in a hydroperoxide and an aryloxyl radical. It was observed that the rate constants for the hydrogen atom abstraction from 18 phenols were greater in phenols having electron-donating para substituents and lesser in phenols substituted with electron-withdrawing groups.

The spontaneous reactions of [Et.sub.3]SiH, [Ph.sub.3]GeH, [Bu.sub.3]SnH, and [([Me.sub.3][Si).sub.3]SiH with 2,2,6,6-tetramethyl-1-piperidinoxy] (TEMPO) and related nitroxides have been investigated. Metal hydrides characterized by relatively weak metal-hydrogen bonds, like [Ph.sub.3]GeH and [Bu.sub.3]SnH, reduce TEMPO to the corresponding hydroxylamine while no reaction is observed with [Et.sub.3]SiH and [Ph.sub.3]SiH. Tris(trimethy]silyl)silane, on the other hand, is able to reduce the nitroxide to the corresponding hydroxylamine and amine in a ca. 1:1 ratio. By repeating the above reactions in the presence of thermal or photochemical radical initiators, deoxygenation of TEMPO was obtained in high yield with [([Me.sub.3]Si).sub.3]SiH and [([Me.sub.3]Si).sub.2]Si(H)Me, but not with other silanes, germanes, and stannanes. A mechanism for the reduction of TEMPO by the two trimethylsilyl-substituted silanes is proposed, and kinetic data for the various steps of the overall reaction are reported. In particular rate constants and activation parameters have been measured for the hydrogen transfer reaction from several silanes to the hindered aminyl radical 2,2,6,6-tetramethylpiperidinyl.

The equilibration couples of several phenolic compounds and their phenoxy radicals were analyzed by electron paramagnetic resonance (EPR) spectroscopy to determine their bond dissociation energies (BDE). EPR analysis of phenolic compounds indicated the role of the phenolic hydroxylic group in reducing the reactivity of the phenols toward peroxy radicals. Furthermore, substituted phenols exhibited a constant decrease in bond strength due to a given substituent.

Electron paramagnetic resonance (EPR) spectroscopy was used to analyze reactions between tris(trimethylsilyl)germyl radicals and a number of unsaturated compounds. Results show that, with the exception of 4-vinylpyridine, no additional products are developed in analogous reactions with alkenes. Moreover, the intensity of the spectra was quite weak and no EPR signals were identified.

EPR spectroscopy was used to detect the radical anions from thiobenzophenone, thiobenzoyltriphenylsilane and 3,5-di-tert-butylthiobenzoyltriphenylsilane, on reaction with several Grignard reagents. The addition of R. radicals to the thiones led to radical adducts. The occurrence of a SET process is indicated.

The equilibration couples of several phenolic compounds and their phenoxy radicals were analyzed by electron paramagnetic resonance (EPR) spectroscopy to determine their bond dissociation energies (BDE). EPR analysis of phenolic compounds indicated the role of the phenolic hydroxylic group in reducing the reactivity of the phenols toward peroxy radicals. Furthermore, substituted phenols exhibited a constant decrease in bond strength due to a given substituent.

Ligated boranes are inefficient reducing agents for aliphatic nitro compounds under free radical conditions. The attempt to reduce tertiary nitroalkanes to the corresponding hydrocarbons is hampered due to the fragmentation of the resulting boroxy nitroxides through the cleavage of the nitrogen-oxygen bond. The radical-initiated reaction of phosphine-boranes and amine-boranes with aliphatic nitro compounds is examined, and the boroxy nitroxides are detected and characterized using EPR spectroscopy. The Arrhenius parameters for the boroxy nitroxide fragmentation are determined.

The kinetics for the generation of ligated boryl radicals by reactions with a primary alkyl radical, with t-BuO and with peroxy radicals have been investigated. The results showed ligated boranes exhibited hydrogen transfer reaction which is slow with alkyl radicals but very fast with alkoxy radicals. Hydrogen transfer to tert-butoxyl radicals was very fast and is scarcely affected by the nature of the ligand. The rate constants for the hydrogen transfer to peroxy radicals could not be determined but showed a behavior intermediate between the reactions with alkyl and alkoxy radicals.

EPR spectroscopic studies help determine equilibrium constants for reactions between galvinoxyl and various phenolic antioxidants. The known bond dissociation enthalpy (DH) of 2,4, 6-tri-tert-butylphenol helps calculate DH for the ArO-H bond of various phenols. Conformation of para alkylthio group in Probucol explains the high DH value of probucol. The alpha-tocopherol DH value is close to that of the phenolic precursor of galvinoxyl and is higher than that of 2, 6-di-tert-butyl-4-methoxyphenol.

N-(9H-carbazol-9-yl)arylaminyl radicals were derived from 2-(arylazo)-2'-iodobiphenyls using the tin hydride method. The radical was reduced by a hydride to produce N-(9H-carbazol-9-yl)arylamine. Alternatively, it can attack the carbonyl moiety by a 5-exo cyclization to pproduce an intermediate. This led to an arlozy radical by ring opening and ultimately to the rearranged product by hydrogen abstraction. Evidences of this mechanism was determined by EPR spectroscopy.

Studies on the oxynitroxide decomposition at different temperatures reveal that the first nitroxide cleaves at the nitrogen-oxygen bond more easily than the nitrogen-carbon bond. The organometallic nitroxides breakdown, eliminating a tert-butyl radical. The fragmentation increases along the sequence Ph3G3 < Ph3Si < Pi3Sn and depend on the balance between the nitroxide adduct and the dimer.

Tris(trimethylsilyl)silane (TTMSS) fails to yield the expected hydrocarbons in its reactions with nitroalkanes. TTMSS is a potential alternative for tributyltin hydride, which reacts with nitroalkanes to produce hydrocarbons. Spectral, kinetic and productstudies trace this failure to preferential cleavage at the N-O bond rather thanthe C-N bond, giving a silyoxy radical that rearranges and attaches to the nitro radical to produce a secondary nitroxide. The primary and secondary adducts are studied kinetically as they decay to nitromethane and nitrosomethane under various thermal conditions.

Tributyltin hydride causes the reduction of azoarenes giving substituted hydrazyls in desired amounts and selectivity. Reactions involving the reduction of azoarenes with ortho substituents to the azo function, produce heterocyclic compounds of low selectivity. Whereas, reactions involving stannyl free radicals and azoarenes require the presence of a radical initiator such as alpha,alpha'-azobis(isobutyronitrile), so that reactions follow a radical chain mechanism.

Research was conducted to determine whether peroxyl radicals follow the rule that the effects of kinetic solvent on H-atom abstraction do not depend on the abstracting radical. The oxidizability values obtained demonstrated that they are affected by solvent. The smaller values were obtained from tert-butyl alcohol, while the larger ones are from isooctane. Moreover, the values of 2kt derived by following the decay of the electron paramagnetic resonance showed that the traces agree with second-order kinetics for all conditions examined.

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.

Research has been conducted on hydroxylamines containing aryl, vinyl, alkyl and carbonyl substituents at the nitrogen atom. The authors demonstrate that these compounds have been determined via the use of EPR radical equilibration technique in investigating the role of substituents in the compounds' O-H bond strength.

5-pyrimidonils were studied to consider their chain breaking activities in relation to phenols.

Examines the synthesis of morpholin-4-ylphosphoramidic acid diethyl ester (1a) and (2,2,6,6-tetramethylpiperidin-1-yl)phosphoramidic acid diethyl ester (2a). Characterization of formed hydrazyl radicals 1b and 2b by electron paramagnetic resonance spectroscopy; Dependence of 1b radical spectra on temperature; Determination of constants for cyclodextrins.

Oxidizes the E geometrical isomers of benzaldoxime, p-chlorobenzaldoxime and p-methylbenzaldoxime to the corresponding iminoxyl radicals within the cavity of an EPR spectrometer by using photolytically produced tert-butoxy radicals. Geometry of iminoxyls at low temperature; Notion of Molecular Orbital theory.

The effect of 1,1,1,3,3,3-hexafluoropropan-2-ol (HFP) on the properties of phenoxyl radicals has been investigated. HFP produces large variations of the phenoxyl 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 with electric charge separation. The conformational rigidity of phenoxyl radicals with electron-releasing substituents is also greatly enhanced in the presence of HFP, as demonstrated by the 2 kcal/mol increase in the activation energy for the internal rotation of the p-OMe group in the p-methoxyphenoxyl radical. By using the EPR equilibration technique, we have found that in phenols the O-H bond dissociation enthalpy (BDE) is lowered in the presence of HFP because it preferentially stabilizes the phenoxyl radical. In phenols containing groups such as OR that are acceptors of H-bonds, the interaction between HFP and the substituent is stronger in the phenol than in the corresponding phenoxyl radical because the radical oxygen behaves as an electron-withdrawing group, which decreases the complexating ability of the substituent. In phenols containing OH or NH[sub 2] groups, EPR experiments performed in H-bond accepting solvents showed that the interaction between the solvent and the substituent is much stronger in the phenoxyl radical than in the parent phenol because of the electron-withdrawing effect of the radical oxygen, which makes more acidic, and therefore more available to give H-bonds, the OH or NH[sub 2] groups. These experimental results have been confirmed by DFT calculations. The effect of HFP solvent on the reactivity of phenols toward alkyl radicals has also been investigated. The results indicated that the decrease of BDE observed in the presence of HFP is not accompanied by a larger reactivity. The origin of this unexpected behavior has been shown by DFT computations. Finally, a remarkable increase in the... [ABSTRACT FROM AUTHOR]