19021-48-8Relevant articles and documents
Afanas'ev,Polozova
, (1979)
Involvement of semiquinone radicals in the in vitro cytotoxicity of cigarette mainstream smoke
Chouchane, Salem,Wooten, Jan B.,Tewes, Franz J.,Wittig, Arno,Mueller, Boris P.,Veltel, Detlef,Diekmann, Joerg
, p. 1602 - 1610 (2008/12/22)
Free radicals in cigarette smoke have attracted a great deal of attention because they are hypothesized to be responsible in part for several of the pathologies related to smoking. Hydroquinone, catechol, and their methyl-substituted derivatives are abundant in the particulate phase of cigarette smoke, and they are known precursors of semiquinone radicals. In this study, the in vitro cytotoxicity of these dihydroxybenzenes was determined using the neutral red uptake (NRU) assay, and their radical-forming capacity was determined by electron paramagnetic resonance (EPR). All of the dihydroxybenzenes studied were found to generate appreciable amounts of semiquinone radicals when dissolved in the cell culture medium employed in the NRU assay. Hydroquinone exhibited by far the highest capacity to form semiquinone radicals at physiological pH, even though it is not the most cytotoxic dihydroxybenzene. Methyl-substituted dihydroxybenzenes were found to be more cytotoxic than either hydroquinone or catechol. The formation of semiquinone radicals via auto-oxidation of the dihydroxybenzenes was found to be dependent on the reduction potential of the corresponding quinone/semiquinone radical redox couple. The capacity to generate semiquinone radicals was found to be insufficient to explain the variance in the cytotoxicity among the dihydroxybenzenes in our study; consequently, other mechanisms of toxicity must also be involved. The observed interactions between 2,6-dimethylhydroquinone and hydroquinone in the cytotoxicity assay and EPR analysis suggest that care needs to be taken when the bioactivity of cigarette smoke constituents is evaluated, i.e., the effect of the cigarette smoke complex matrix on the activity of the single constituent studied must be taken into consideration.
Kinetics and mechanisms of the oxidaton of ascorbic acid and benzene diols by nickel(III)tetraazamacrocycles in aqueous perchloric acid
McAuley, A.,Oswald, T.,Haines, R. I.
, p. 1120 - 1125 (2007/10/02)
The kinetics of reaction of ascorbic acid, hydroquinone, and catechol (H2A) with nickel(III) macrocycles (NiL3+) (L=cyclam, meso-(5,12)-7,7,14,14-Me6-14-ane-1,4,8,11-N4 (tet-a), and rac-(5,14)-7,7,12,12-Me6-14-ane-1,4,8,11-N4 (tet-c): 2NiL3+ + H2A -> 2NiL2+ + A + 2H+ have been investigated in aqueous perchloric acid solution using the stopped-flow technique.The data are consistent with a rate-determining one-electron transfer reactions: NiL3+ + H2A -> NiLi2+ + H2A+; NiL3+ + HA- -> NiLi2+ + HA; H2A HA- + H+ (Ka) followed by a rapid oxidation of the radical formed.In the reaction with ascorbic acid, for Ni(cyclam)3+, k1=250 M-1 s-1 (25 deg C), k4Ka=680 s-1, Ni(tet-c)3+, ka=2.52 * 103 M-1 s-1, k4Ka=1.06 * 104 s-1; and Ni(tet-a)3+, ka=2.85 * 103 M-1 s-1 (21.95 deg C), k4Ka=1.26 * 104 s-1.With catechol, k1=6.98 * 102 M-1 s-1, 1.73 * 104 M-1 s-1, and 3.3 * 104 M-1 s-1 respectively in reactions with Ni(cyclam)3+, Ni(tet-c)3+, and Ni(tet-a)3+).With hydroquinone, k1=1.09 *10k4 M-1 s-1 (Ni(cyclam)3+) and 2.49 * 105 M-1 s-1 (20.09 deg C) (Ni(tet-c)3+).The reactions are considered to take place via an outer-sphere mechanism rate constants are discussed in terms of the Marcus cross correlations.Use has been made of predicted rate constants to identify reaction pathways in the hydrogen-ion dependent systems.
