Young T, Nieman R, Rose S D
Department of Chemistry, Arizona State University, Tempe 85287-1604.
Photochem Photobiol. 1990 Oct;52(4):661-8. doi: 10.1111/j.1751-1097.1990.tb08664.x.
Anthraquinone-2-sulfonate (AQS) photosensitizes pyrimidine dimer splitting. Electron abstraction from the dimer is thought to induce dimer splitting, but direct evidence for the existence and intermediacy of dimer radical cations has been lacking. By employing photochemically induced dynamic nuclear polarization, we have found emission signals in the NMR spectra of dimers upon photolysis of dimers in the presence of anthraquinone-2-sulfonate. The two dimers employed were cis, syn-thymine dimer in which the N(1)-positions were linked by a three-carbon bridge and the N(3), N(3')-dimethyl derivative of that compound. The anthraquinone-2-sulfonate sensitized photochemically induced dynamic nuclear polarization spectrum of the methylated derivative exhibited an emission signal from the dimer-C(6) hydrogens. This result implied the existence of a dimer radical cation (mD+.) formed by electron abstraction by excited anthraquinone-2-sulfonate and nuclear spin sorting within a solvent caged radical ion pair [mD+. AQS-.]. Product pyrimidine photochemically induced dynamic nuclear polarization signals were also seen [enhanced absorption by C(6)-hydrogens and emission by C(5)-methyl groups]. Nuclear spin polarization in the product resulted from spin sorting in one or more of its precursors, including mD+. The results support the conclusion that dimer radical cations not only exist but are intermediates in the photosensitized splitting of pyrimidine dimers by anthraquinonesulfonate.
蒽醌 - 2 - 磺酸盐（AQS）可使嘧啶二聚体的分裂产生光致敏作用。人们认为从二聚体中夺取电子会诱导二聚体分裂，但一直缺乏关于二聚体自由基阳离子存在及其作为中间体的直接证据。通过采用光化学诱导动态核极化技术，我们发现在蒽醌 - 2 - 磺酸盐存在下二聚体光解时，二聚体的核磁共振谱中出现了发射信号。所使用的两种二聚体分别是顺式、syn - 胸腺嘧啶二聚体（其中N(1) - 位通过一个三碳桥相连）及其N(3), N(3') - 二甲基衍生物。甲基化衍生物的蒽醌 - 2 - 磺酸盐敏化光化学诱导动态核极化谱显示出二聚体 - C(6)氢的发射信号。这一结果表明存在由激发态的蒽醌 - 2 - 磺酸盐夺取电子形成的二聚体自由基阳离子（mD +.），以及在溶剂笼状自由基离子对[mD +. AQS -.]内的核自旋分选。还观察到了产物嘧啶的光化学诱导动态核极化信号[C(6) - 氢的吸收增强和C(5) - 甲基的发射增强]。产物中的核自旋极化是由其一种或多种前体（包括mD +.）中的自旋分选导致的。这些结果支持了这样的结论：二聚体自由基阳离子不仅存在，而且是蒽醌磺酸盐使嘧啶二聚体光致敏分裂过程中的中间体。
