Shkrob Ilya A, Marin Timothy M, Adhikary Amitava, Sevilla Michael D
Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 S. Cass Ave, Argonne, IL 60439.
J Phys Chem C Nanomater Interfaces. 2011 Feb 7;115(8):3393-3403. doi: 10.1021/jp110682c.
Photocatalytic oxidation of nucleic acid components on aqueous metal oxides (TiO(2), α-FeOOH, and α-Fe(2)O(3)) has been studied. The oxidation of purine nucleotides results in the formation of the purine radical cations and sugar-phosphate radicals, whereas the oxidation of pyrimidine nucleotides other than thymine results in the oxidation of only the sugar-phosphate. The oxidation of the thymine (and to a far less extent for the 5-methylcytosine) derivatives results in deprotonation from the methyl group of the base. Some single stranded (ss) oligoribonucleotides and wild-type ss RNA were oxidized at purine sites. In contrast, double stranded (ds) oligoribonucleotides and DNA were not oxidized. These results account for observations suggesting that cellular ds DNA is not damaged by exposure to photoirradiated TiO(2) nanoparticles inserted into the cell, whereas ss RNA is extensively damaged. The astrobiological import of our observations is that the rapid degradation of monomer nucleotides make them poor targets as biosignatures, whereas duplex DNA is a better target as it is resilient to oxidative diagenesis. Another import of our studies is that ds DNA (as opposed to ss RNA) appears to be optimized to withstand oxidative stress both due to the advantageous polymer morphology and the subtle details of its radical chemistry. This peculiarity may account for the preference for DNA over RNA as a "molecule of life" provided that metal oxides served as the template for synthesis of polynucleotides, as suggested by Orgel and others.
研究了核酸成分在水性金属氧化物（TiO₂、α-FeOOH和α-Fe₂O₃）上的光催化氧化。嘌呤核苷酸的氧化导致嘌呤自由基阳离子和糖磷酸自由基的形成，而除胸腺嘧啶外的嘧啶核苷酸的氧化仅导致糖磷酸的氧化。胸腺嘧啶（以及程度远低于5-甲基胞嘧啶）衍生物的氧化导致碱基甲基的去质子化。一些单链（ss）寡核糖核苷酸和野生型ss RNA在嘌呤位点被氧化。相比之下，双链（ds）寡核糖核苷酸和DNA未被氧化。这些结果解释了一些观察结果，即细胞双链DNA不会因暴露于插入细胞中的光照射TiO₂纳米颗粒而受损，而单链RNA则会受到广泛损伤。我们观察结果的天体生物学意义在于，单体核苷酸的快速降解使其作为生物特征的目标不佳，而双链DNA是更好的目标，因为它对氧化成岩作用具有弹性。我们研究的另一个意义在于，双链DNA（与单链RNA相对）似乎由于有利的聚合物形态及其自由基化学的细微细节而被优化以承受氧化应激。如果如奥格尔等人所建议的那样，金属氧化物作为多核苷酸合成的模板，那么这种特殊性可能解释了为什么DNA比RNA更受青睐作为“生命分子”。
