Brunmark A
Department of Pathology II, University of Linköping, Sweden.
J Biolumin Chemilumin. 1989 Jul;4(1):219-25. doi: 10.1002/bio.1170040131.
The reaction between p-benzoquinone and H2O2 in slightly alkaline solutions yields three major quinoid products that accumulate in the reaction mixture: (a) 2,3-epoxy-p-benzoquinone, (b) 2-hydroxy-p-benzoquinone and (c) p-benzohydroquinone. The reaction is accompanied by photoemission, probably originating from excited triplet 2-hydroxy-p-benzoquinone. These products originate from hydrogen peroxide and hydroxide nucleophilic addition to the C2 = C3 double bond, as well as secondary redox interactions. The hydroxy substituent and the epoxide ring exert a substantial influence on the electronic distribution in the p-benzoquinone molecule leading to a decrease in the half-wave potential, as compared to the parent p-benzoquinone. The generation of electronically excited states is the result of reactions secondary to the nucleophilic additions involving 2-hydroxy-p-benzosemiquinone, H2O2 and hydroxyl radical. The process involves the primary oxidation of 2-hydroxy-p-benzosemiquinone by hydrogen peroxide, followed by oxidation of the semiquinone by hydroxyl radical leading to the formation of the electronically excited quinone. The decay of the excited triplet to the ground state is accompanied by photoemission with maximal intensity at 485-530 nm. Thermodynamic calculations along with an observed increase of photoemission intensity in anaerobiosis point to the triplet (n, pi*) multiplicity of the excited state. The efficiency of chemiluminescence could be calculated as 10(-8) photons/2-hydroxy-p-benzoquinone molecule formed. Photoemission arising from the p-benzoquinone/H2O2 reaction was inhibited efficiently by addition of GSH to the reaction mixture. This may be due to deactivation of the triplet quinone by a 2-glutathionyl-p-benzohydroquinone adduct, involving thioether alpha-hydrogen atom-transfer to the triplet ketone.
对苯醌与过氧化氢在弱碱性溶液中的反应会产生三种主要的醌类产物，它们会在反应混合物中积累：(a) 2,3-环氧对苯醌，(b) 2-羟基对苯醌和(c) 对苯二酚。该反应伴随着光发射，可能源于激发态三重态的2-羟基对苯醌。这些产物源自过氧化氢和氢氧根对C2 = C3双键的亲核加成，以及二级氧化还原相互作用。与母体对苯醌相比，羟基取代基和环氧环对苯醌分子中的电子分布有显著影响，导致半波电位降低。电子激发态的产生是涉及2-羟基对苯半醌、过氧化氢和羟基自由基的亲核加成的二级反应的结果。该过程包括过氧化氢对2-羟基对苯半醌的初次氧化，随后羟基自由基对半醌的氧化，导致电子激发醌的形成。激发态三重态衰变回基态伴随着在485 - 530 nm处具有最大强度的光发射。热力学计算以及在厌氧条件下观察到的光发射强度增加表明激发态的三重态(n, π*)多重性。化学发光效率可计算为每形成一个2-羟基对苯醌分子产生10(-8)个光子。向反应混合物中添加谷胱甘肽可有效抑制对苯醌/过氧化氢反应产生的光发射。这可能是由于2-谷胱甘肽基对苯二酚加合物使三重态醌失活，涉及硫醚α-氢原子转移到三重态酮上。
