Free Radical Transformations Research Articles

Dopamine and iron mediated fragmentation of galactocerebroside and cardiolipin in micelles

AbstractMatrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and thin-layer chromatography (TLC) have been used to study dopamine and iron mediated free-radical transformation of lipids in their hydrophilic parts. It has been shown that the action of the dopamine/Fe2+ system on galactocerebroside or cardiolipin, which are the components of mixed micelles, results in formation of ceramide or phosphatidic acid and phosphatidylhydroxyacetone, respectively. These data, when combined with results obtained using the ascorbate/Fe2+/H2O2 oxidizing system with the same substrates, demonstrate that the formation of these products proceeds via an OH-radical induced fragmentation taking place in polar moiety of the starting lipids.

Effect of nature and surface density of oxygen species on product distribution in the oxidative dehydrogenation of propane over oxide catalysts

Catalytic performance of non-reducible (rare-earth/alkaline-earth oxides) and reducible (vanadium-based oxides) metal oxides in auto-thermal oxidative dehydrogenation (ODH) of propane differs strongly regarding to the ratio of C3H6/C2H4. In contrast to the latter materials, ethylene is the main olefin over the former ones. In order to elucidate factors influencing the catalytic performance, a kinetic analysis of the oxidative dehydrogenation (ODH) of propane was performed. In this analysis, the ODH reaction is assumed to occur via formation and further transformations of free propyl radicals. It was demonstrated that the overall reaction rate of these both processes is affected by both strength and density (surface concentration) of oxidising active sites. However, the ratio of propene-to-ethylene is mostly affected by the density of oxidising sites (DOS), and to much less extent by their strength. High DOS is essential for further ODH of propyl radicals to propene and, therefore, for suppression of concurrent cracking reaction channel yielding ethylene.

The effect of α-tocopherol on the oxidation and free radical decay in irradiated UHMWPE

We developed a radiation cross-linked ultra-high molecular weight polyethylene (UHMWPE) stabilized with alpha-tocopherol (Vitamin E) as a bearing material in total joint replacements. The stabilizing effect of alpha-tocopherol on free radical reactions in UHMWPE is not well understood. We investigated the effect of alpha-tocopherol on the oxidation and transformation of residual free radicals during real-time aging of alpha-tocopherol-doped, irradiated UHMWPE (alphaTPE) and irradiated UHMWPE (control). Samples were aged at 22 degrees C (room temperature) in air, at 40 degrees C in air and at 40 degrees C in water for 7 months. During the first month, alphaTPE showed some oxidation at the surface, which stayed constant thereafter. Control exhibited substantial oxidation in the subsurface region, which increased with time. The alkyl/allyl free radicals transformed to oxygen centered ones in both materials; this transformation occurred faster in alpha-TPE. In summary, the real-time oxidation behavior of alpha-TPE was consistent with that observed using accelerated aging methods. This new UHMWPE is oxidation resistant and is expected to maintain its properties in the long term.

The use of low-temperature plasmas in wool finishing

Processes that occur in wool fiber under the action of a glow-discharge plasma were considered. The kinetics of plasma etching, the amino acid compositions of whole fiber and separated cuticle elements, the surface of fiber (using scanning electron microscopy and attenuated total multiple internal reflection IR spectroscopy), as well as the electrosurface, friction, and other properties, were studied. These studies demonstrated that undergoing degradation and modification were primarily the fiber cuticle and its proteins and, particularly, lipids. Important reaction paths were processes involving the transformations of free radicals. Cystine, peptide, alanine, and glycine radicals were identified on the basis of EPR spectra. Plasma treatment enhanced the wettability of wool and the diffusion of dyes into fibers upon dyeing and printing and decreased the felting ability. This treatment did not impair the physicomechanical, heat-insulation, and thermal properties of wool. However, the resulting changes somewhat decreased the hydrophilicity of wool after plasma treatment.

Free radicals as intermediates in catalytic oxidation of light alkanes: new opportunities

The analysis of catalytic partial oxidation of light alkanes indicates that processes involving this group proceed via the formation and consecutive transformations of free radicals. Depending on the properties of the catalytic system and reaction conditions the same primary radical can give different final products, olefins, oxygenated organic substances and carbon oxides. An approach to design a complex catalytic system for efficient alkane partial oxidation based on separation of zones where free radicals are formed and where they are transformed into desired products is suggested and examples of its implementation are presented.

Effects of various vitamins and coenzymes Q on reactions involving α-hydroxyl-containing radicals

Effects of vitamins B, C, E, K and P, as well as coenzymes Q, on formation of final products of radiation-induced free-radical transformations of ethanol, ethylene glycol, α-methylglycoside and glucose in aqueous solutions were studied. Based on the obtained results, it can be concluded that there are substances among vitamins and coenzymes that effectively interact with α-hydroxyl-containing radicals. In the presence of these substances, recombination reactions of α-hydroxyalkyl radicals and fragmentation of α-hydroxy-β-substituted organic radicals are suppressed. It has been established that the observed effects are due to the ability of the vitamins and coenzymes under study to either oxidize α-hydroxyl-containing radicals yielding the respective carbonyl compounds or reduce them into the initial molecules.

Reaction of Sterically Congested Phenols and Quinones with Organic Radicals

In the course of radiation-induced free-radical transformations of hexane and ethanol, pyrocatechol and hydroquinone derivatives, as well as their respective quinones, are more effective than phenol and resorcinol derivatives in controlling reactions that involve alkyl and hydroxyalkyl radicals. The opposite result takes place in the inhibition by phenols of hexane oxidation in which the key role belongs to the peroxyl radicals generated from the starting compounds.

Radiation-induced free-radical transformation of phospholipids: MALDI-TOF MS study

Under the action of free-radical reaction initiators on membrane phospholipids, complex processes are taking place in both hydrophobic and hydrophilic parts of the phospholipids. Realization of these processes results in a mixture consisting of the initial lipids and their peroxidation and fragmentation products. Identification of compounds in such mixtures requires analytical methods of high sensitivity, reproducibility and accuracy to be applied. These properties are characteristic of the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) method. In the studies of radiation-induced free-radical transformations of phosphatidylglycerol, the MALDI-TOF MS in combination with thin layer chromatography (TLC) has been shown to be able to detect and identify products of free-radical transformations taking place in both hydrophilic and hydrophobic parts of the phospholipid. Thus, the MALDI-TOF MS can serve as a suitable analytical tool to investigate free-radical transformations of lipids.

EPR study of light illumination effects on radicals in gamma-irradiated l-alanine

Exposure of γ-irradiated l-alanine samples to sunlight and to light from a regular, fluorescent lamp resulted in significant changes in their EPR resonance patterns, both to spectral shapes and intensities. The experimental EPR spectra were numerically decomposed into three components reflecting contributions of three different radicals (R1–R3) generated by ionizing radiation in alanine. The light exposure caused a decay of the measured EPR signal intensity. For similar light intensities and exposure times the decay was much more pronounced in samples illuminated by sunlight than in samples illuminated by the fluorescent lamp. In both cases light-induced decay of R1 radicals was observed. Sunlight illumination resulted in a moderate decay of R2 radicals and in a doubling of the R3 radical population. On the other hand, fluorescent light caused a significant increase of R2 radicals and did not change the amount of R3 radicals. A quantitative analysis of the variations of the three radical contributions to the total EPR spectra upon fluorescent light exposure suggests a net R1→R2 free radical transformation. These effects of light on the alanine dosimetric signal should be taken into account in dosimetry protocols, assuring protection of alanine dosimeters from extended exposure to light.

Radiation Chemistry of Polysaccharides: 2. Free-Radical Mechanisms of Formation of Citric Acid and Dicarboxylic Acids

Based on experimental data on the buildup of citric acid and dicarboxylic (succinic, malic, fumaric, tartaric, and malonic) acids in native starches, low-temperature ESR measurement results, and reaction rate- or reaction yield-detected magnetic resonance data (room temperature, cellulose), the sequences of elementary events (mechanisms) of transformation of free radicals in the anhydroglucose ring of glucose high polymers up to the formation of these acids were determined. Time ranges for the generation of radicals in reactions, such as dehydration (Н2О β-elimination), oxygenation, isomerization involving C–C and C–O bond cleavage, and rearrangement of C–H bonds, were estimated at (3–7) × 10–9 to (8–10) × 10–8 s.

Quinones as Free-radical Fragmentation Inhibitors in Biologically Important Molecules

Effects of a number of quinones and diphenols of various structures on free-radical fragmentation processes taking place in f -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 O 2 ” m but also control the realization probability of free-radical processes of peroxidation and fragmentation in biologically important molecules.

Radical translocation reactions in synthesis

This review highlights synthetically useful transformations of organic free-radicals in which a key step is relocation of the radical site by intramolecular abstraction either of a hydrogen atom or a group (e.g. phenyl, cyano, trialkylsilyl). The material is organised around the nature of the radical that initiates translocation and coverage is largely confined to reports that have appeared within the past decade, reference to earlier work only being made in order to establish a context for more recent results.

ESR Study of Stable N,N,N",N"-Tetramethyl-4,4"-diaminodiphenylmethane Radicals in Solid Solutions

The ESR spectra of γ-irradiated N,N,N",N"-tetramethyl-4,4"-diaminodiphenylmethane (Am) in solid solutions of poly(vinyl chloride), poly(methyl methacrylate), and benzene were studied. The formation mechanism of the free radical Am·in these solutions was discussed. Along with Am·, the formation of radicals with the cyclohexadienyl structure was shown to be possible in Am irradiation. The influence of the matrix structure on the radiation-chemical yield of Am·radicals and their thermal stability was established. The radiation-induced chemical transformations of free radicals and transient ionic species resulting in the formation of terminal alkyl radicals in poly(methyl methacrylate) were investigated. Data on the mechanism of the protective action of the Am additive during PMMA radiolysis were obtained.

97/03621 Free radical transformations in the Irati oil shale due to diabase intrusion

The synthesis of 2,3-dihydro-1H-indeno[5,4-a]anthracene (2), the fluoreno[a]anthracenes 3 and 4, 2,3-dihydro-1H-cyclopenta[a]chrysene (6), 3,4-dihydro-2-vinylphenanthrene (10) and cyclopenta[c]chrysenes 11, 12 has been described. Structure analysis of the new products by 1H and 13C NMR spectroscopy is presented. Estimates of the mutagenic activity of compounds 2–4, 6 and 11–14 in Salmonella typhimurium determined by Ames' test indicate that all products are inactive for both TA 98 and TA 100 strains except 4,5-dihydro-3H-cyclopenta[c]chrysene (12). The mutagenic properties of these compounds have been compared with those shown by previously studied benzo[g]cyclopenta[a]phenanthrenes and cyclopenta[c]phenanthrenes and discussed. Some conclusions have been drawn about the effects of benzoannulation and of the carbonyl function on the mutagenicity of this class of compounds.

Heterophase Features of Chain Reactions of Macromolecules in Noncrystalline Polymer Matrix with Participation of Antioxidants

Principles of kinetic model composition of initiated free radical transformations in an amorphous polymer matrix are discussed. Micellar-sponge model of supermolecular structure which takes into account character of inhomogeneous zone functioning different by sizes and fluctuation dynamics of micropores composing them are put to the base of the chemical modelling. Features of antioxidant effects on chain processes are connected with the existence of conjugated reaction chains localized in separate zones of polymer chain-sponge micelles. Special attention is paid to the mechanism of the process proceeding during the induction period of polyolefine autoxidation which contain sterically hindered alkylated phenols. The induction period precedent to the stage of direct polymer oxidation is characterized as a stage of chain co-oxidation of an antioxidant and a polymer. This chain stage is the steady state order zero or one reaction by alkylphenol in dependence on its molecular structure.

Free radical transformations in the Irati oil shale due to diabase intrusion

Electron spin resonance (ESR) spectroscopy was used to evaluate the effect of a diabase intrusion on the production and decomposition of free radicals in the Irati oil shale (Paraná Basin, Brazil). Free radical concentration measurements on the stratigraphic column CERI-2 indicated that the ratio between the extent of thermal alteration on sedimentary organic matter and the intrusive thickness was 1.14. Kinetics of free radical transformation obtained from laboratory pyrolysis of Irati oil shale can be described by first-order production and decomposition reactions of distinct species. Although these species present different kinetic parameters, they are not resolved and lie inside the envelope of the “single line” ESR spectrum. The activation energies for parallel first-order production reactions of two main species of free radicals, in the temperature range of 360–420°C, were found to be 54 ± 2 kcal mol −1 and 36 ± 9 kcal mol −1.

Modulation of neuronal and glial cell function by adenosine and neuroprotection in vascular demential

Dementia is one of the major medical challenges in the industrialized countries. An increasing number of demented patients shows ischemic brain lesions. One strategy to treat dementia could be the reinforcement of the multifarious neuroprotective actions of the endogenous cell modulator adenosine. This involves the modulation of neuronal and glial cell functions. Adenosine appears to raise the threshold for the initiation of the pathophysiological cascade of ischemic neuronal death by counteracting ischemic membrane depolarization and the successive disturbance of intracellular Ca2+ homeostasis. When this threshold is overcome, adenosine seems to stimulate astrocyte differentiation and reinforce important protective astrocyte functions, e.g., synthesis and release of neurotrophic factors such as NGF and the clearance of abnormal neurotoxic levels of K+ and glutamate from the extracellular space. Propentofylline, a combined inhibitor of adenosine reuptake and cAMP phosphodiesterases, reinforces the actions of endogenous adenosine and cAMP. One important action of propentofylline is the inhibition of potentially neurotoxic functions of activated microglia (free radical formation and transformation into brain macrophages). Such drugs may help to inhibit the progressive neurodegenerative process in dementia.

The damage to phospholipids caused by free radical attack on glycerol and sphingosine backbone

The effect of gamma -radiation on aqueous solutions of saturated phospholipids, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG), 1-palmitoyl-2-lyso-sn-glycero-3-phosphocholine (lysoPC), and bovine brain sphingomyelin (SM) has been investigated. It is shown that the phospholipids with an OH group in beta -position to the P-O bond (DPPG and lysoPC), or to the amide bond (SM), undergo a free radical fragmentation. As a result of such fragmentation, stearoylamide, palmitoxyacetone and phosphatidic acid are formed from SM, lysoPC and DPPG, respectively. In parallel with the formation of hydrophobic fragments, an accumulation of hydrophilic species such as oxyacetone and phosphocholine in the irradiated DPPG and lysoPC dispersions was observed. On the basis of the data obtained for free radical transformation of phospholipids and their simplest analogs, such as glycero-1-phosphate, triacetin and 1,2-isopropylidene glycerol, it is suggested that the fragmentation of the radicals derived from the above compounds proceed by a concerted mechanism through a five-membered transition state. The accumulation of hydrophobic fragments in phospholipid membranes is shown to influence the temperature and co-operativity of the 'gel-to-liquid crystal' phase transition. An assumption is made that the fragmentation of phospholipids caused by free radical attack on the hydrophilic moiety, along with lipid peroxidation, may constitute principal mechanisms of radiation-induced damage of biological membranes.

Mechanisms of processes involving ?-substituted cyclopropyl radicals. Ring expansion in the reaction with CO

The reaction of β-substituted cyclopropyl radicals with CO was studied by ESR. Tile acyl radical resulting from the addition of CO to the cyclopropyl radical was detected. At temperatures near 270 K, an intramolecular rearrangement of the acyl radical affords substituted 2-oxocyclobutyl radicals (ring expansion reaction). Mechanisms for the free-radical transformations studied were suggested.

β-carotene as an interceptor of free radicals

Kinetics of nonenzymic and nonphotochemical oxidation of β-carotene have been studied. The rate constants for the reactions of β-carotene with initiator-derived C-centered and peroxyl radicals in solution were measured as ∼ 10 4 and 5 × 10 5 − 1 × 10 4 M −1s −1, respectively. β-Carotene-derived free radicals have been shown to be less reactive toward polyene than initiator-derived radicals. This suggests that β-carotene might behave as an interceptor of free radical species regardless of the oxygen pressure in the environment. The mechanism for β-carotene oxidation covering the main pathways for formation, transformation, and decay of free radicals has been formulated. In combination with experimental kinetic parameters and their temperature correlation, computer modeling has been used to solve the reaction kinetics numerically. The model proposed enables analysis of the kinetics of β-carotene consumption and oxygen uptake under various conditions, as well as the influence of β-carotene on oxidation of polyunsaturated fatty acids and their esters.