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Radical Reactions (radical + reaction)
Selected AbstractsDimethylzinc-Initiated Radical Reaction of Cyclic Ethers with Arylamines, Alkoxyamines, and Dialkylhydrazines.CHEMINFORM, Issue 21 2005Yasutomo Yamamoto Abstract For Abstract see ChemInform Abstract in Full Text. [source] Triethylborane Induced Radical Reaction of Gallium Enolates with ,-Halo Esters.CHEMINFORM, Issue 1 2003Shin-ichi Usugi Abstract For Abstract see ChemInform Abstract in Full Text. [source] Free Radical Reaction of Sodium Arenesulfinates with Acetylenes: New Regio- and Stereoselective Preparation of (E)-,-(Phenylseleno)vinyl Sulfones.CHEMINFORM, Issue 38 2002Xian Huang Abstract For Abstract see ChemInform Abstract in Full Text. [source] 2,5-Disubstituted Pyrrolidines as Chiral Auxiliaries in Radical Reactions: A Theoretical ApproachEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2010Miglena K. Georgieva Abstract The radical addition to amides derived from chiral 2,5-disubstituted pyrrolidines has been theoretically studied by the use of density functional methods and the results compared with known experimental data. The results agree quite well with those obtained experimentally and allow the full rationalization of the factors influencing the diastereoselectivity. Steric effects are the main factors determining the selectivity, but electronic interactions can also be very important when the attacking alkene is ,,,-conjugated, as in acrylic esters or acrylamides. Additions at the ,- and ,-positions of the amide chain in the auxiliary are subject to different rules, with the former usually yielding high diastereoselectivities both experimentally and theoretically, whereas the latter is theoretically predicted to occur with low selectivity. We fully rationalize these two opposite behaviours and suggest several ways to circumvent this limitation, thus strongly increasing the interest of this type of structure as chiral auxiliaries in radical reactions. [source] Investigations into the Chemical Modification of Polyolefin Surfaces by Radical Reactions during MoldingMACROMOLECULAR REACTION ENGINEERING, Issue 4 2007Jürgen Nagel Abstract The surfaces of polyolefin parts are usually modified by separate processing steps. In this paper, we investigate how an in situ surface modification of polyolefins could be realized during molding, based on radical reactions, by which a macromolecule with functional groups is grafted to the polyolefin surface. The temperature of the melt is used to initialize the reactions. The different steps of the radical reaction chain were analyzed using model reactions. A modifier composition consisting of dibenzoylperoxide, potassium persulfate and poly(vinyl alcohol) revealed to be suitable. This composition was used for injection molding experiments. The bondability of the injection molded parts was largely enhanced. [source] AIBN-Initiated Radical Reactions of Ethyl Phosphinate.CHEMINFORM, Issue 5 2007Monika I. Antczak Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Enantioselective Radical Reactions: Formation of Chiral Quaternary Centers.CHEMINFORM, Issue 30 2006Mukund P. Sibi Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Synthesis of Highly Substituted Pyrroles via Oxidative Free Radical Reactions of ,-Aminocinnamates.CHEMINFORM, Issue 26 2006An-I Tsai Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Development of Radical Reactions with Zirconocene Complexes as Electron Transfer Reagents.CHEMINFORM, Issue 52 2004Kazuya Fujita Abstract For Abstract see ChemInform Abstract in Full Text. [source] Zinc-Mediated Radical Reactions of Per- (or Poly)fluorophenyl Aromatic Aldimines in Aqueous Media.CHEMINFORM, Issue 33 2004Xinyuan Liu Abstract For Abstract see ChemInform Abstract in Full Text. [source] Radical Reactions on Enol-Esters: Facile Synthesis of 3-Ulosonic Acid Derivatives and Chiral Spiroacetals.CHEMINFORM, Issue 7 2004G. V. M. Sharma Abstract For Abstract see ChemInform Abstract in Full Text. [source] Enantioselective Radical Reactions: The Use of Metal Triflimides as Lewis Acids.CHEMINFORM, Issue 6 2004Mukund P. Sibi Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Triethylborane-Induced Radical Reactions with Gallium Hydride Reagent HGaCl2.CHEMINFORM, Issue 52 2001Satoshi Mikami Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Nitroxyl Radical Reactions with 4-Pentenyl- and Cyclopropylketenes: New Routes to 5-Hexenyl- and Cyclopropylmethyl Radicals.CHEMINFORM, Issue 50 2001Annette D. Allen Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Regioselectivity in Radical Reactions of C60 Derivatives.CHEMINFORM, Issue 36 2001Benoit de La Vaissiere Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Stereoselective Synthesis of 24-Alkyl-22-hydroxysterols Based on Chelation-Controlled Radical Reactions.CHEMINFORM, Issue 19 2001Hajime Nagano Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Contact allergy caused by air oxidation of common materials , diagnosis and preventionCONTACT DERMATITIS, Issue 3 2004Ann-Therese Karlberg When considering the allergenic activity of a compound not only the possibility of bioactivation by skin metabolism but also air activation by autoxidation must be taken into account. Natural compounds (terpenes) easily oxidize at air exposure. They are found in products that are common causes of allergic contact dermatitis (ACD) i.e. colophony and fragrances. The introduction of oxygen enables the molecules to form antigens with skin proteins via a nucleophilic- electrophilic interaction or via a radical reaction. The latter mechanism seems to be important since the primary oxidation products, the hydroperoxides, are the most potent sensitizers formed. Oxidative decomposition at air exposure resulting in allergenic oxidation products is observed also for other common compounds e.g. ethoxylated fatty alcohols used as surfactants. It is important to test the patient with the offending compounds for diagnosis of ACD. A negative diagnosis can be due to failure in testing with the correct substances. In the case of air activated compounds, testing should not be performed with the pure substances but rather with the oxidation mixture or the most sensitizing oxidation products (the hydroperoxides). We have in multicenter-studies shown that the common fragrance terpenes, limonene and linalool, are frequent sensitizers when oxidized. This is a challenge in clinical practice since such patch test materials are not easily standardized. Compounds, easily activated at air exposure, should be prevented from oxidative decomposition by addition of antioxidants and proper handling and storage. More research is needed in this area. [source] Metal-Free, Selective Alkane FunctionalizationsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9-10 2003Andrey Abstract The present overview of alkane functionalization reactions presents comparisons between radical and metal-initiated (sometimes metal-catalyzed) methodologies. While metal-catalyzed processes are excellent approaches to this problem, metal-free alternatives are equally if not, at least from an environmental and cost perspective, more useful. This conclusion is supported by the fact that many so-called metal-catalyzed reactions also work without the metal present, and the large variety of metals showing the same product distributions emphasizes that the metal often just aids in the generation of the active species, i.e., the metal itself is not participating in the crucial CH activation step. Highly selective alkane functionalization reactions such as those derived from nitroxyl and related radicals as well as through radical reactions conducted in phase-transfer catalyzed systems are available but generally underutilized. These systems, in contrast to typical metal-catalyzed approaches, are also applicable to highly strained alkanes and offer the highest 3°/2° CH selectivities reported to date in a radical reaction. The article closes with representative experimental protocols for the PTC bromination of cubane as an example of the applicability of this method to strained hydrocarbons and the direct iodination of cyclohexane as well as adamantane as typical alkanes bearing secondary and tertiary CH bonds. [source] Determination of primary bond scissions by mass spectrometric analysis of ultrasonic degradation products of poly(ethylene oxide- block -propylene oxide) copolymersJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2010Takehiro Watanabe Abstract Ultrasonic degradation of poly(ethylene oxide- block -propylene oxide) copolymers consisting of a hydrophilic and a hydrophobic portion was studied with the aim to determine the location of bonds involved in the initial scission of the copolymers. LC,APCI-IT-MS and LC,APCI-orbitrap-MS were used for the detailed structural analysis of degradation products. The results indicated that initial bond scissions occurred principally at the boundary regions between backbones of polyethylene oxide (PEO) and polypropylene oxide (PPO) chains. Further structural analysis revealed the presence of oxygen adducts in the degradation products. Comparison with a thermal degradation carried out in helium atmosphere, one can conclude that the oxygen adducts are formed by radical reaction with water or dissolving oxygen molecules. The study demonstrated that chemical reactions as well as physical bond stress scissions are involved in the ultrasonic degradation of the copolymers. Copyright © 2010 John Wiley & Sons, Ltd. [source] Poly(vinyltriethoxysilane) modified MWCNT/polyimide nanocomposites,Preparation, morphological, mechanical, and electrical propertiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2008Siu-Ming Yuen Abstract Multi-walled carbon nanotube (MWCNT) modified by vinyltriethoxysilane (VTES) via free radical reaction has been prepared (poly (vinyltriethoxysilane) modified MWCNTs, PVTES-MWCNT). Precursor of polyimide, polyamic acid has been synthesized by reacting 4,4,-oxydianiline with 3,3,,4,4,-benzophenone tetracarboxylic dianhydride. PVTES-MWCNT were then mixed with polyamic acid and heated to 300 °C to form CNT/polyimide composite. During the imidization processes, the silanes on CNT surface reacted with each other and may be connected together by covalent bond (SiOSi). The PVTES-MWCNT was analyzed by Fourier transform infrared and X-ray photoelectron spectroscopy. The PVTES-MWCNT/polyimide composites were analyzed by CP/MAS solid state 29Si nuclear magnetic resonance (NMR) spectroscopy. Morphological properties of the PVTES-MWCNT/polyimide composites were investigated by scanning electron microscope and transmission electron microscope. Electrical conductivity increased dramatically comparing to the unmodified MWCNT/polyimide composites. Mechanical properties of nanocomposite were enhanced significantly by PVTES-MWCNT. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 803,816, 2008 [source] Synthesis of a [60]fullerene-functionalized poly(vinyl chloride) derivative by stereospecific chemical modification of PVCJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2007Gerardo Martínez Abstract The covalent attachment of [60]fullerene (C60) to two poly(vinyl chloride) (PVC) samples with different isotactic content is achieved by direct reaction in o -dichlorobenzene (o -DCB) solution in the presence of AIBN. The extent of fullerenation is controlled by varying the C60 feed ratio. The pendant C60 -chemically modified PVC polymers are soluble in tetrahydrofuran (THF) and have been characterized by UV,vis, NMR, FTIR, DSC, TGA, cyclic voltammetry, and SEM. The quantitative microstructural analysis after covalent attachment of the bulky C60 moiety to the PVC has been followed by 13C NMR spectroscopy. From the results it can be concluded that the modification of PVC by graft reaction through free radical reaction proceeds by a stereoselective mechanism. This conclusion has been confirmed on the basis of the increase of the glass-transition temperature (Tg) and the thermal stability of the C60 -chemical modified PVC samples. The fullerenated PVCs obtained show good electron acceptor properties, as evidenced by electrochemical investigations. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5408,5419, 2007 [source] Investigation on the interaction between dihydroxybenzene and Fe3+,H2O2,Rh6G system based on enhancing chemiluminescenceLUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 1 2006Deyong He Abstract A highly sensitive flow-injection chemiluminescence (FI,CL) method has been developed for the determination of dihydroxybenzene, based on the hydroxyl radical reaction. Hydroxyl radical (·OH) produced by the reaction of Fe3+ and H2O2 oxidize rhodamine 6G to produce weak CL. It was observed that catechol and hydroquinone greatly enhanced the weak CL reaction. However, the proposed CL system is not suitable for determination of resorcinol because the enhancement reaction is very slow. The proposed procedure has a linear range of 0.01,2 mg/L for catechol, with a detection limit of 0.006 mg/L, and 0.008,1 mg/L for hydroquinone, with a detection limit of 0.004 mg/L. The possible mechanism of the CL system is discussed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Water-Soluble Carbon Nanotubes by Redox Radical PolymerizationMACROMOLECULAR RAPID COMMUNICATIONS, Issue 15 2007Dimitrios Tasis Abstract Water-soluble single- and multi-walled carbon nanotubes (CNTs) were prepared by grafting polyacrylamide chains from the graphitic surface via ceric ion-induced redox radical polymerization. The reducing functionalities were covalently attached to the tubes by peroxide-assisted radical reaction. The results showed that polymer chains were grafted onto CNTs by the redox process. The redox radical polymerization initiated by carbon nanotube-bearing functionalities not only provides a powerful strategy for modifying the carbon nanostructures but also gives us the knowledge of their sidewall chemistry. [source] 2,5-Disubstituted Pyrrolidines as Chiral Auxiliaries in Radical Reactions: A Theoretical ApproachEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2010Miglena K. Georgieva Abstract The radical addition to amides derived from chiral 2,5-disubstituted pyrrolidines has been theoretically studied by the use of density functional methods and the results compared with known experimental data. The results agree quite well with those obtained experimentally and allow the full rationalization of the factors influencing the diastereoselectivity. Steric effects are the main factors determining the selectivity, but electronic interactions can also be very important when the attacking alkene is ,,,-conjugated, as in acrylic esters or acrylamides. Additions at the ,- and ,-positions of the amide chain in the auxiliary are subject to different rules, with the former usually yielding high diastereoselectivities both experimentally and theoretically, whereas the latter is theoretically predicted to occur with low selectivity. We fully rationalize these two opposite behaviours and suggest several ways to circumvent this limitation, thus strongly increasing the interest of this type of structure as chiral auxiliaries in radical reactions. [source] Studies on low-coordinated nitrogen, phosphorus, sulfur, and selenium compoundsHETEROATOM CHEMISTRY, Issue 4 2001Naoki Inamoto The major studies of my laboratory on heteroatom chemistry are briefly outlined and include the following topics: (1) novel radical reactions to kinetic stabilization of organosulfur and selenium compounds, (2) novel reactions of organophosphorus compounds, (3) reaction of the S atom to stabilization of o-thioquinonemethides, (4) N-nitrosoimines stabilized by heterocycles to hypervalent sulfur compounds, and (5) phosphinidenes (R-P) to kinetic stabilization of low-coordinated organophosphorus compounds. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:183,194, 2001 [source] Kinetics of the gas-phase reactions of cyclo-CF2CFXCHXCHX , (X = H, F, Cl) with OH radicals at 253,328 KINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2009L. Chen Rate constants were determined for the reactions of OH radicals with halogenated cyclobutanes cyclo-CF2CF2CHFCH2(k1), trans -cyclo-CF2CF2CHClCHF(k2), cyclo-CF2CFClCH2CH2(k3), trans -cyclo-CF2CFClCHClCH2(k4), and cis -cyclo-CF2CFClCHClCH2(k5) by using a relative rate method. OH radicals were prepared by photolysis of ozone at a UV wavelength (254 nm) in 200 Torr of a sample reference H2OO3O2He gas mixture in an 11.5-dm3 temperature-controlled reaction chamber. Rate constants of k1 = (5.52 ± 1.32) × 10,13 exp[,(1050 ± 70)/T], k2 = (3.37 ± 0.88) × 10,13 exp[,(850 ± 80)/T], k3 = (9.54 ± 4.34) × 10,13 exp[,(1000 ± 140)/T], k4 = (5.47 ± 0.90) × 10,13 exp[,(720 ± 50)/T], and k5 = (5.21 ± 0.88) × 10,13 exp[,(630 ± 50)/T] cm3 molecule,1 s,1 were obtained at 253,328 K. The errors reported are ± 2 standard deviations, and represent precision only. Potential systematic errors associated with uncertainties in the reference rate constants could add an additional 10%,15% uncertainty to the uncertainty of k1,k5. The reactivity trends of these OH radical reactions were analyzed by using a collision theory,based kinetic equation. The rate constants k1,k5 as well as those of related halogenated cyclobutane analogues were found to be strongly correlated with their CH bond dissociation enthalpies. We consider the dominant tropospheric loss process for the halogenated cyclobutanes studied here to be by reaction with the OH radicals, and atmospheric lifetimes of 3.2, 2.5, 1.5, 0.9, and 0.7 years are calculated for cyclo-CF2CF2CHFCH2, trans -cyclo-CF2CF2CHClCHF, cyclo-CF2CFClCH2CH2, trans -cyclo-CF2CFClCHClCH2, and cis -cyclo-CF2CFClCHClCH2, respectively, by scaling from the lifetime of CH3CCl3. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 532,542, 2009 [source] Hydroxyl radical reactions with halogenated ethanols in aqueous solution: Kinetics and thermochemistryINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2008I. Morozov Laser flash photolysis combined with competition kinetics with SCN, as the reference substance has been used to determine the rate constants of OH radicals with three fluorinated and three chlorinated ethanols in water as a function of temperature. The following Arrhenius expressions have been obtained for the reactions of OH radicals with (1) 2-fluoroethanol, k1(T) = (5.7 ± 0.8) × 1011 exp((,2047 ± 1202)/T) M,1 s,1, (2) 2,2-difluoroethanol, k2(T) = (4.5 ± 0.5) × 109 exp((,855 ± 796)/T) M,1 s,1, (3) 2,2,2-trifluoroethanol, k3(T) = (2.0 ± 0.1) × 1011 exp((,2400 ± 790)/T) M,1 s,1, (4) 2-chloroethanol, k4(T) = (3.0 ± 0.2) × 1010 exp((,1067 ± 440)/T) M,1 s,1, (5) 2, 2-dichloroethanol, k5(T) = (2.1 ± 0.2) × 1010 exp((,1179 ± 517)/T) M,1 s,1, and (6) 2,2,2-trichloroethanol, k6(T) = (1.6 ± 0.1) × 1010 exp((,1237 ± 550)/T) M,1 s,1. All experiments were carried out at temperatures between 288 and 328 K and at pH = 5.5,6.5. This set of compounds has been chosen for a detailed study because of their possible environmental impact as alternatives to chlorofluorocarbon and hydrogen-containing chlorofluorocarbon compounds in the case of the fluorinated alcohols and due to the demonstrated toxicity when chlorinated alcohols are considered. The observed rate constants and derived activation energies of the reactions are correlated with the corresponding bond dissociation energy (BDE) and ionization potential (IP), where the BDEs and IPs of the chlorinated ethanols have been calculated using quantum mechanical calculations. The errors stated in this study are statistical errors for a confidence interval of 95%. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 174,188, 2008 [source] Theory of chemical bonds in metalloenzymes.INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2010Abstract Reaction mechanisms of oxygen evolution in native and artificial photosynthesis II (PSII) systems have been investigated on the theoretical grounds, together with experimental results. First of all, our previous broken-symmetry (BS) molecular orbitals (MO) calculations are reviewed to elucidate the instability of the d,-p, bond in high-valent (HV) Mn(X)O systems and the d,-p,-d, bond in HV MnOMn systems. The triplet instability of these bonds entails strong or intermediate diradical characters: ,Mn(IV)O, and ,MnOMn,; the BS MO resulted from strong electron correlation, leading to the concept of electron localizations and local spins. The BS computations have furthermore revealed guiding principles for derivation of selection rules for radical reactions of local spins. As a continuation of these theoretical results, the BS MO interaction diagrams for oxygen-radical coupling reactions in the oxygen evolution complex (OEC) in the PSII have been depicted to reveal scope and applicability of local singlet diradical (LSD) and local triplet diradical (LTD) mechanisms that have been successfully utilized for theoretical understanding of oxygenation reactions mechanisms by p450 and methane monooxygenase (MMO). The manganese-oxide cluster models examined are London, Berlin, and Berkeley models of CaMn4O4 and related clusters Mn4O4 and Mn3Ca. The BS MO interaction diagrams have revealed the LSD and/or LTD mechanisms for generation of molecular oxygen in the total low-, intermediate and high-spin states of these clusters. The spin alignments are found directly corresponding to the spin-coupling mechanisms of oxygen-radical sites in these clusters. The BS UB3LYP calculations of the clusters have been performed to confirm the comprehensive guiding principles for oxygen evolution; charge and spin densities by BS UB3LYP are utilized for elucidation and confirmation of the LSD and LTD mechanisms. Applicability of the proposed selection rules are examined in comparison with a lot of accumulated experimental and theoretical results for oxygen evolution reactions in native and artificial PSII systems. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Modeling formation of molecules in the interstellar medium by radical reactions with polycyclic aromatic hydrocarbonsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2010Yenner Bentarcurt Abstract Adsorptions of CH°2, CH°3, NH°2, and OH° radicals and molecule formation on a partially hydrogenated surface of a polycyclic aromatic hydrocarbon (PAH) (C24H27+) were modeled. It was found that radical adsorptions are feasible with important modifications of surface bond strengths and bond distances. Adsorbed hydrogen may diffuse due to adsorbate-surface interactions. Formations of CH4, NH3, H2O, CH3NH2, and CH3OH were studied by Eley-Rideal (ER) and Langmuir-Hishelwood (LH) mechanisms. Potential energetic surfaces were performed for both mechanisms and the ER presents lower reaction energy barriers than the LH one, in all cases. Parametric quantum program (CATIVIC) was employed and comparisons with DFT results were performed. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2560,2572, 2010 [source] Mitochondrial Oxidative Stress Plays a Key Role in Aging and ApoptosisIUBMB LIFE, Issue 5 2000Juan Sastre Abstract Harman first suggested in 1972 that mitochondria might be the biological clock in aging, noting that the rate of oxygen consumption should determine the rate of accumulation of mitochondrial damage produced by free radical reactions. Later in 1980 Miquel and coworkers proposed the mitochondrial theory of cell aging. Mitochondria from postmitotic cells use O2 at a high rate, hence releasing oxygen radicals that exceed the cellular antioxidant defences. The key role of mitochondria in cell aging has been outlined by the degeneration induced in cells microinjected with mitochondria isolated from fibroblasts of old rats, especially by the inverse relationship reported between the rate of mitochondrial production of hydroperoxide and the maximum life span of species. An important change in mitochondrial lipid composition is the age-related decrease found in cardiolipin content. The concurrent enhancement of lipid peroxidation and oxidative modification of proteins in mitochondria further increases mutations and oxidative damage to mitochondrial DNA (mtDNA) in the aging process. The respiratory enzymes containing the defective mtDNA-encoded protein subunits may increase the production of reactive oxygen species, which in turn would aggravate the oxidative damage to mitochondria. Moreover, superoxide radicals produced during mitochondrial respiration react with nitric oxide inside mitochondria to yield damaging peroxynitrite. Treatment with certain antioxidants, such as sulphur-containing antioxidants, vitamins C and E, or the Ginkgo biloba extract EGb 761, protects against the ageassociated oxidative damage to mtDNA and the oxidation of mitochondrial glutathione. Moreover, the EGb 761 extract also prevents changes in mitochondrial morphology and function associated with aging of the brain and liver. [source] | ||||||||||||||||