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Photochemical relaxation pathways of S6-methylthioinosine and O6-methylguanosine in solution
Faraday Discussions ( IF 3.4 ) Pub Date : 2017-11-07 , DOI: 10.1039/c7fd00193b
Brennan Ashwood 1, 2, 3, 4, 5 , Luis A. Ortiz-Rodríguez 1, 2, 3, 4, 5 , Carlos E. Crespo-Hernández 1, 2, 3, 4, 5
Affiliation  

S6-Methylthioinosine and O6-methylguanosine are byproducts resulting from the enzymatic reactions of sulfur-substituted prodrugs in cells and from the interaction of alkylating agents with cellular DNA, respectively. Their photochemistry has not been investigated, and it is currently unknown whether light absorption by these byproducts may pose any threat to the cell. In this contribution, their photoinduced processes upon absorption of UVB radiation are reported using broadband transient absorption spectroscopy. Plausible electronic relaxation mechanisms are proposed for both biological molecules, which are supported by steady-state absorption and emission measurements, and by singlet and triplet vertical excitation energies performed on a large subset of ground-state optimized conformational isomers in solution. The results are compared to the body of knowledge gathered in the scientific literature about the light-induced processes in the sulfur-substituted and canonical purine monomers. In particular, it is shown that S6-methylation decreases the rate to populate the lowest-energy triplet state and blueshifts the ground-state absorption spectrum compared to those for the sulfur-substituted prodrugs and for the 6-thioguanosine metabolite. Similarly, O6-methylation decreases the rate of internal conversion to the ground state observed in the guanine monomers by more than 10-fold in acetonitrile and 40-fold in aqueous solution, while it redshifts the ground-state absorption spectrum. Collectively, this investigation provides relevant new insights about the relationship between structural modifications of the purine chromophore and the electronic relaxation mechanisms in this important group of biological molecules.

中文翻译:

溶液中S 6-甲基硫代肌苷和O 6-甲基鸟苷的光化学弛豫途径

S 6-甲基硫代肌苷和O 6-甲基鸟苷是分别由硫取代的前药在细胞中的酶促反应以及烷基化剂与细胞DNA相互作用产生的副产物。尚未对其光化学性质进行研究,目前尚不清楚这些副产物的光吸收是否可能对细胞构成威胁。在这种贡献中,使用宽带瞬态吸收光谱法报道了它们在吸收UVB辐射后的光诱导过程。两种生物分子均提出了合理的电子弛豫机制,这两种稳态分子均受稳态吸收和发射测量以及在溶液中对一大批基态优化构象异构体进行的单重态和三重态垂直激发能的支持。将结果与科学文献中收集的有关硫取代的和规范的嘌呤单体中的光诱导过程的知识进行了比较。特别地,表明S与硫取代的前药和6-硫代鸟苷代谢物相比, 6-甲基化降低了填充最低能量三重态的速率,并使基态吸收光谱蓝移。类似地,O 6-甲基化将鸟嘌呤单体中观察到的内部转化为基态的速率降低,在乙腈中提高10倍以上,在水溶液中降低40倍以上,同时使基态吸收光谱发生红移。集体,这项调查提供有关嘌呤发色团的结构修饰和这一重要的生物分子组中的电子弛豫机制之间的关系的相关新见解。
更新日期:2018-04-17
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