Formation of semiquinone radical in the reaction of embelin (2,5-dihydroxy-3-undecyl-1,4-benzoquinone) with reductants as well as oxidants. Characterization by pulse radiolysis and structure investigation by quantum chemical study

被引:12
作者
Joshi, Ravi [1 ]
Ghanty, Tapan K. [2 ]
Mukherjee, Tulsi
机构
[1] Bhabha Atom Res Ctr, Chem Grp, Radiat & Photochem Div, Bombay 400085, Maharashtra, India
[2] Bhabha Atom Res Ctr, Chem Grp, Theoret Chem Sect, Bombay 400085, Maharashtra, India
关键词
Embelin; Semiquinone radical; Pulse radiolysis; Density functional theory; ONE-ELECTRON REDUCTION; QUINONES; SOLVENT; BENZOQUINONE; COMPLEXES; DYE;
D O I
10.1016/j.molstruc.2009.03.010
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Embelin, 2,5-dihydroxy-3-undecyl-1,4-benzoquinone, has two intra-molecular hydrogen bonds between the quinone and hydroquinone groups present on the same ring. Therefore, it is expected to produce semiquinone radical in the oxidation as well reduction reactions. To investigate this aspect, kinetics and mechanism of reduction reactions of embelin have been studied using nanosecond electron pulse radiolysis technique and compared with the oxidation process. Two distinct transients observed in the reduction (lambda(max)=450 nm) and the oxidation (lambda(max)=410 nm) processes with various free radicals have been characterized and assigned to two different embelin semiquinone radicals on the basis of pulse radiolysis studies. The structures of these transients have been further ascertained using density functional theory with B3LYP functional and 6-31+G(d,p) basis set. Reduction reaction of embelin has been found to produce delocalized semiquinone anion radical. On the other hand, oxidation of embelin is expected to produce several transient species. However, the calculations suggest that oxidation of hydroquinone group is the first step, which is followed by transformation into carbon-centered radical. (C) 2009 Elsevier B.V. All rights reserved.
引用
收藏
页码:46 / 53
页数:8
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