- Substituent effect on the radical scavenging activity of 6-chromanol derivatives
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Several 6-chromanol derivatives with various substituents (one or two amino, acetylamino, chloro or nitro substituents at the 5-, 7-, 8- or 5,7-positions on the phenyl ring of 2,2-dimethyl-6-chromanol) were synthesized, and their second order rate constan
- Inami, Keiko,Suzuki, Mariko,Shimizu, Azusa,Furukawa, Miyuki,Morita, Mine,Mochizuki, Masataka
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- A QUESTION CONCERNING THE pK RANGE WITHIN WHICH AN ORGANIC FREE RADICAL EXHIBITS NORMAL RADICAL BEHAVIOUR. THE CASE OF GALVINOXYL
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Galvinoxyl (G.) reacts with a series of substituted acetic acids and forms hydrogalvinoxyl (GH) as the sole product.The kinetic data conform with a Bronsted type analysis.Hydrogalvinoxyl may dissociate to the relevant cation G+, in a
- Screttas, Constantinos G.,Heropoulos, Georgios A.,Karayannis, Miltiades I.
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- Antioxidant and antiproliferative activities of hydroxyl-substituted Schiff bases
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Eight hydroxyl-substituted Schiff bases with the different number and position of hydroxyl group on the two asymmetric aromatic rings (A and B rings) were prepared by the reaction between the corresponding aromatic aldehyde and aniline. Their antioxidant effects against the stable galvinoxyl radical (GO{radical dot}) in ethyl acetate and methanol, and 2,2′-azobis(2-amidinopropane hydrochloride) (AAPH)-induced DNA strand breakage, and their antiproliferative effects on human hepatoma HepG2 cells, were investigated. Structure-activity relationship analysis demonstrates that o-dihydroxyl groups on the aromatic A ring and 4-hydroxyl group attached to the aromatic B ring contribute critically to the antioxidant and antiproliferative activities.
- Cheng, Li-Xia,Tang, Jiang-Jiang,Luo, Hui,Jin, Xiao-Ling,Dai, Fang,Yang, Jie,Qian, Yi-Ping,Li, Xiu-Zhuang,Zhou, Bo
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- Galvinoxyl radicals: Synthesis of new derivatives, determination of low oxygen contents, and stability studies
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Two new derivatives of galvinoxyl (1), a perdeutered (2) and an adamantyl-analog (3) for potential applications as spin probes were synthesized. The synthesis with deuterated educts yielded 2 with 98% D. It exhibited an 18-line EPR spectrum in octanol wit
- Lampp, Lisa,Azarkh, Mykhailo,Drescher, Malte,Imming, Peter
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- Involvement of electron transfer in the radical-scavenging reaction of resveratrol
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Resveratrol (3,4′,5-trihydroxy-trans-stilbene) efficiently scavenges an oxygen radical via an electron transfer from resveratrol to the radical in deaerated acetonitrile, which is significantly accelerated by the presence of magnesium ion. Copyright
- Nakanishi, Ikuo,Shimada, Tomokazu,Ohkubo, Kei,Manda, Sushma,Shimizu, Takehiko,Urano, Shiro,Okuda, Haruhiro,Miyata, Naoki,Ozawa, Toshihiko,Anzai, Kazunori,Fukuzumi, Shunichi,Ikota, Nobuo,Fukuhara, Kiyoshi
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- Effect of methyl substitution on the antioxidative property and genotoxicity of resveratrol
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Resveratrol (trans-3,4′,5-trihydroxystilbene) is a natural phytoalexin with various biological activities including inhibition of lipid peroxidation and free radical scavenging properties. In addition to its beneficial effects, resveratrol also has significant genotoxicity that leads to a high frequency of chromosome aberration together with micronucleus and sister chromatid exchanges. To enhance the radical scavenging activities and to reduce the genotoxicity of resveratrol, we designed 4′-methyl resveratrol analogues where a methyl group was introduced at the ortho position relative to the 4′-hydroxy group, which is responsible for both antioxidative activities and genotoxicity of resveratrol. These synthesized methyl analogues of resveratrol showed increased antioxidative activities against galvinoxyl radical as an oxyl radical species. Furthermore, the methyl analogues also surprisingly showed reduced in vitro genotoxicities, suggesting that methyl substitution may improve resveratrol efficacy.
- Fukuhara, Kiyoshi,Nakanishi, Ikuo,Matsuoka, Atsuko,Matsumura, Tomohiro,Honda, Sachiko,Hayashi, Mikiko,Ozawa, Toshihiko,Miyata, Naoki,Saito, Shinichi,Ikota, Nobuo,Okuda, Haruhiro
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p. 282 - 287
(2008/12/22)
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- Electron-transfer mechanism in radical-scavenging reactions by a vitamin E model in a protic medium
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The scavenging reaction of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH*) or galvinoxyl radical (GO*) by a vitamin E model, 2,2,5,7,8-pentamethylchroman-6-ol (1H), was significantly accelerated by the presence of Mg(ClO4)2 in de-aerated methanol (MeOH). Such an acceleration indicates that the radical-scavenging reaction of 1H in MeOH proceeds via an electron transfer from 1H to the radical, followed by a proton transfer, rather than the one-step hydrogen atom transfer which has been observed in acetonitrile (MeCN). A significant negative shift of the one-electron oxidation potential of 1H in MeOH (0.63 V vs. SCE), due to strong solvation as compared to that in MeCN (0.97 V vs. SCE), may result in change of the radical-scavenging mechanisms between protic and aprotic media.
- Nakanishi, Ikuo,Kawashima, Tomonori,Ohkubo, Kei,Kanazawa, Hideko,Inami, Keiko,Mochizuki, Masataka,Fukuhara, Kiyoshi,Okuda, Haruhiro,Ozawa, Toshihiko,Itoh, Shinobu,Fukuzumi, Shunichi,Ikota, Nobuo
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p. 626 - 629
(2007/10/03)
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- Thermal decomposition of 2,6-di-tert-butyl-4-dimethylaminomethylphenol
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Products of thermolysis of 2,6-di-tert-butyl-4-dimethylaminomethylphenol were determined qualitatively and quantitatively by GLC, UV, and 1H NMR methods. The kinetics of the reaction was studied. The thermolysis products were studied as the inhibitors in thermopolymerization of monomers.
- Zakharova,Khismatullina,Ivanov
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p. 1787 - 1789
(2007/10/03)
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- 7-substituted quinone methides as inhibitors for unsaturated monomers
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Ethylenically unsaturated monomers are protected from premature polymerization during manufacture and storage by the incorporation therein of an effective stabilizing amount of a 7-substituted quinone methide compound.
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- SYNTHESIS OF 2,6-DI-tert-BUTYL-4-(3,5-DI-tert-BUTYL-4-HYDROXYBENZYLIDENE)-2,5-CYCLOHEXADIENONE
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2,6-Di-tert-butyl-4-(3,5-di-tert-butyl-4-hydroxybenzylidene)-2,5-cyclohexadienone has been prepared in 63-92percent yield by oxidative dehydrogenation of 4,4'-methylenebis(2,6-di-tert-butylphenol) with various quinones.The products of quinone reduction have been isolated.
- Mukmeneva, N. A.,Bukharov, S. V.,Kadyrova, V. Kh.,Zharkova, V. M.
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p. 1350 - 1351
(2007/10/02)
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- Etude du transfert monoelectronique entre des germylanions et des piegeurs de spin dia et paramagnetiques
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Reactions between organogermyllithium R3GeLi and several substrates favoring SET reactions (3,5-di-t-butyl-orthoquinone, fluorenone, tetracyanoquinodimethane, 2,4,6-tri-t-butylnitrosobenzene, etc.) lead mainly to the formation of digermanes and O- or N-germyl adducts.All these reactions seem to proceed principally by single-electron transfer.An ESR study of the reaction shows transient organic radical anion formation and germanium-centred radicals R3Ge.The prepondancy of this mechanism can be demonstrated by the reaction between R3GeLi and a paramagnetic quinonic species, the galvinoxyl radical: the latter is almost completely transformed into a diamagnetic anion.Digermanes mainly produced in these reactions are formed via radicalar duplication as well as lithiogermolysis of reaction adducts.
- Riviere, P.,Castel, A.,Desor, D.,Abdennadher, C.
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- ETUDE DE REACTIONS PAR TRANSFERT MONOELECTRONIQUE ENTRE DIVERS HYDROGERMANES A CARACTERE ACIDE ET DES SYSTEMES QUINONIQUES DIA- ET PARA-MAGNETIQUES
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The chlorogermanes PhnCl3-nGe-H (n = 0, 1, 2) were treated with diamagnetic (3,5-di-t-butylorthoquinone) 1 and the paramagnetic galvinoxyl 2.These reactions occur mainly by monoelectron transfer giving the corresponding adducts.In the case of 3,5-di-t-butylorthoquinone, the resulting 1-4 adducts decompose by two simultaneous processes (HCl elimination and redistribution) yielding germadioxolanes.The chlorogermadioxolanes prepared in this way easily cause halogenic redistribution leading to chlorogermanes and germylcatecholates having branched or spiranestructure.In the case of the galvinoxyl radical, the same chlorogermanes lead by monoelectron transfer to the corresponding quinophenol and an intermediate germanium-centered radical.The latter by recombination outside the solvent cage, gives digermane.However, its primary reaction, which occurs within the solvent cage, is with quinophenol to form two isomeric O- and C-germylated catechols.The C-isomer is by far predominant as it also formed in the secondary hydrogermylation of quinophenol produced in the initial stage of the reaction.We have been able to confirm these mechanisms by a comparative study of the reaction of germanium hydrides R3Ge?+-H?-, acidic germanes X3Ge?--H?+, and germanates X3Ge(-)N-H(+) with galvinoxyl and the corresponding quinophenol.Key words: SET reactions; germylations; quinones; chlorohydrogermanes; chlorogermanes; chlorogermanates.
- Riviere, P.,Castel, A.,Abdennadher, C.
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p. 181 - 194
(2007/10/02)
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- Temperature and Pressure Effects on the Reversible Reaction of a Parent Phenol (GH) Corresponding to Galvinoxyl with Aliphatic Amines
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The effects of temperature and pressure on the reversible reaction between GH and aliphatic amines in acetonitrile have been studied spectrophotometrically.The formation of the free ions rather than that of ion pairs has been confirmed by the modified Benesi-Hildebrand (B-H) plot.From the plot the equilibrium constants were estimated.From the temperature dependence of the equilibrium constant (K), the heat and entropy of reactions were estimated to be: (ΔH0)av=-44.5 kJ mol-1, and (ΔS0)av=-193 J K-1 mol-1.From the pressure dependence of K the reaction volume (ΔV0)av was estimated to be -40 dm3 mol-1.When unbranched primary amines were used, a side reaction took place for which an explanation has been given.
- Nishimura, Norio,Iga, Siroh,Satoh, Masahiro,Yamamoto, Shunzo
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p. 2437 - 2441
(2007/10/02)
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- Reinvestigation on the Reaction of 2,6-Di-tert-butylbenzoquinone Methide and 2,6-Di-tert-butylphenol
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The reaction of quinone methide 1 and phenol 2 in equimolar amounts was investigated in pentane at 30 deg C.Products were isolated by means of column chromatography on SiO2.There was a marked difference in product distribution between the reactions in the presence and absence of added Et3N.Dienones 3 and 10 were obtained only from the former reaction, while formation of 1,2-bis(4-hydroxyphenyl)ethane 18 and 4,4'-dihydroxybiphenyl 20 was overwhelming in the latter reaction.Other products from both reactions were relatively small quantities of 4,4'-stilbenequinone 17, 4,4'-diphenoquinone 21, and bis(4-hydroxyphenyl)methane 24, but dienone 4 was not obtained.Compounds 20 and 24 obtained from the latter reaction were formed by isomerization of dienones 19 and 23, respectively, during chromatography.The reaction is initiated by dimerization of 1 to generate biradical 11.Subsequent processes involving hydrogenation-dehydrogenation, coupling-dissociation, and dienone-phenol rearrangement account for the formation or the lack of formation of the products.The difference in product distribution is ascribed to capability of Et3N to catalyze the isomerization.Quinone methide 1 also adds to 2 to give 23.The decay of 1 in the presence of both 2 and phenol 6 gave dienone 8 additionally.The formation of 24 and 4 was facilitated by conducting the reaction of 1 and 2 in DMSO.Dehydrogenation of 10 and 3 with PbO2 afforded spirodienones 27 and 28, respectively.Compounds 27 and 28 were unstable, and their decay in solution was investigated in the presence or absence of added 2.The results show that the decay is initiated by homolytic scission of the C-C bond connecting the dienone rings in the cyclopentane (in 27) and cyclohexane (in 28) rings.Compound 28 is novel in that it bears two kinds of such C-C bonds.Reversibility of the dimerization of 1 is suggested.
- Omura, Kanji
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p. 306 - 312
(2007/10/02)
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- Molar Paramagnetic Solvent NMR Shifts of Galvinoxyl in Toluene. Kinetics of the Reaction Between Galvinoxyl and Tertiary Amines at High Radical Concentrations
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The molar paramagnetic solvent NMR shifts of galvinoxyl (1, G.) in toluene were measuredat 34 deg C and found to be 2.21 and 2.39 ppm mol-1 for the aliphatic and aromatic proton signals of toluene, respectively.The implications of the inequality of the two molar shifts are discussed.The paramagnetic solvent shift of G'in toluene in the presence of tertiary amines decays according to a first-order rate law.The apparent first-order rate constants were found to be linearly related to the initial concentration of the amine.The kobs vs. 0 regression lines in some cases exhibit a postivie intercept, indicating the involvement of the solvent in the reaction.The logarithms of the second-order rate contants are shown to be linear with respect to the ionization potentials of the amines.The reactions products of galvinoxyl with with n-Bu3N are hydrogalvinoxyl, GH and the enamine n-Bu2NCH=CHEt whereas, with N,N-dimethylaniline, the products are hydrogalvinoxyl and the hemiaminal ether of formaldehyde, derived from the combination of the radical PhN(Me)CH2. with G. through the oxygen of the latter.A mechanistic scheme is proposed involving a rate-determining electron-transfer step.
- Screttas, Constantinos G.,Heropoulos, Georgios A.
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p. 878 - 882
(2007/10/02)
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- A kinetic electron spin resonance study of the reaction of some oxy radicals with vanadyl acetylacetonate
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Reactions of phenyloxyl, iminoxyl, nitroxyl, peroxyl, and alkyloxyl radicals with VO(acac)2 in solution have been studied by kinetic esr spectroscopy.Rates of reaction are first-order with respect to each reactant and radical reactivity increases in the order galvinoxyl 2,4,6-tri-tert-butylphenoxyl di(1-adamantyl)methylene-iminoxyl tert-butylperoxyl.Rates of reaction are retarded by pyridine and accelerated by methanol and there is an isotope effect on the rate when the hydroxyl proton of CH3OH is replaced by deuterium.Vanadium-51 spectroscopy has demonstrated that several vanadium(V) products are formed while conventional product studies have indicated that, in the case of phenoxyl and alkoxyl, the radical is reduced almost exclusively to the parent phenol and alcohol and that VO(acac)2 is eventually regenerated in substantial yields.The net reaction is, therefore, catalytic reduction of the radical.Variable temperature esr studies have shown that phenoxyl and iminoxyl radicals and VO(acac)2 exist in equilibrium with diamagnetic reaction products.
- Howard, J. A.,Tait, J. C.,Yamada, T.,Chenier, H. B.
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p. 2184 - 2190
(2007/10/02)
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- Oxidation of Bisphenols. II. Some Compounds Related to Galvinoxyl
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The oxidation of a series of 4,4'-alkylidenebis(2,6-di-t-butylphenols) having increasing substitution of the central methylene carbon by alkyl groups is examined.In the monosubstituted compounds the stability of the monophenoxy radical increases with increase in the size of the substituent, while the stability of the galvinoxyl type radical decreases. β-Coupled products are only obtained from the ethylidene bisphenol, a result that can be correlated with e.s.r. hyperfine splitting constants.With increasing mono- or di-substitution bisspiroperoxides become the preferred oxidation products.The e.s.r. spectrum of an ethylenebisgalvinoxyl biradical is described
- Colegate, Steven M.,Hewgill, F. Richmond
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p. 351 - 369
(2007/10/02)
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