Görner Helmut
Max-Planck-Institut für Bioanorganische Chemie, D-45413 Mülheim an der Ruhr, Germany.
Photochem Photobiol Sci. 2004 Oct;3(10):933-8. doi: 10.1039/b410386f. Epub 2004 Sep 28.
The photoreduction of 1,4-benzoquinone (BQ), 1,4-naphthoquinone (NQ), 9,10-anthraquinone (AQ) and several derivatives, e.g. dimethylBQ, trimethylBQ, duroquinone, bromoNQ, methoxyNQ, methylAQ and dimethylAQ in acetonitrile-water by ascorbate was studied by time-resolved UV-vis spectroscopy using 20 ns laser pulses at 308 nm and continuous 254 nm irradiation. The semiquinone radical (QH/Q(-)) is formed after H-atom transfer from ascorbate to the quinone triplet state. The rate constant for quenching is k(q)=(2-9) x 10(9) M(-1) s(-1). Termination of the radicals takes place in the micros-ms range. The results are compared with those initiated by electron transfer from DABCO under similar conditions, where the k(q) values are similar, but the termination of Q*(-) takes place by electron back transfer not yielding hydroquinones. Specific properties of the quinone triplet state, e.g. self-quenching, nucleophilic water addition and the effects of structure are discussed.
采用时间分辨紫外可见光谱法，使用308nm的20ns激光脉冲和254nm的连续照射，研究了抗坏血酸盐在乙腈 - 水中对1,4 - 苯醌（BQ）、1,4 - 萘醌（NQ）、9,10 - 蒽醌（AQ）及其几种衍生物（如二甲基BQ、三甲基BQ、杜醌、溴代NQ、甲氧基NQ、甲基AQ和二甲基AQ）的光还原作用。在氢原子从抗坏血酸盐转移到醌三重态后形成半醌自由基（QH/Q(-)）。猝灭速率常数为k(q) = (2 - 9)×10(9) M(-1) s(-1)。自由基的终止发生在微秒 - 毫秒范围内。将结果与在类似条件下由DABCO的电子转移引发的结果进行比较，其中k(q)值相似，但Q*(-)的终止是通过电子反向转移发生的，不会生成对苯二酚。讨论了醌三重态的特殊性质，如自猝灭、亲核水加成和结构效应。
