Chemistry Program, NYU Shanghai, Pudong Xinqu, Shanghai Shi, China.
Chemistry Department, New York University, New York, NY.
Photochem Photobiol. 2019 Jan;95(1):244-251. doi: 10.1111/php.12926. Epub 2018 Jun 4.
The mechanistic aspects of one-electron oxidation of G-quadruplexes in the basket (Na ions) and hybrid (K ions) conformations were investigated by transient absorption laser kinetic spectroscopy and HPLC detection of the 8-oxo-7,8-dihydroguanine (8-oxoG) oxidation product. The photo-induced one-electron abstraction from G-quadruplexes was initiated by sulfate radical anions (SO ˙ ) derived from the photolysis of persulfate ions by 308 nm excimer laser pulses. In neutral aqueous solutions (pH 7.0), the transient absorbance of neutral guanine radicals, G(-H)˙, is observed following the complete decay of SO ˙ radicals (10 μs after the actinic laser flash). In both basket and hybrid conformations, the G(-H)˙ decay is biphasic with one component decaying with a lifetime of ~0.1 ms, and the other with a lifetime of 20-30 ms. The fast decay component (0.1 ms) in G-quadruplexes is correlated with the formation of 8-oxoG lesions. We propose that in G-quadruplexes, G(-H)˙ radicals retain radical cation character by sharing the N1-proton with the O -atom of G in the [G˙ : G] Hoogsteen base pair; this [G(-H)˙: H G G˙ : G] leads to the hydration of G˙ radical cation within the millisecond time domain, and is followed by the formation of the 8-oxoG lesions.
通过瞬态吸收激光动力学光谱和 HPLC 检测 8-氧代-7,8-二氢鸟嘌呤（8-oxoG）氧化产物，研究了篮式（Na 离子）和杂合（K 离子）构象中 G-四链体的单电子氧化的机理。G-四链体的光诱导单电子抽取是由 308nm 准分子激光脉冲光解过硫酸盐离子产生的硫酸盐自由基阴离子（SO ˙ ）引发的。在中性水溶液（pH 7.0）中，中性鸟嘌呤自由基（G(-H)˙）的瞬态吸收在 SO ˙ 自由基完全衰减后（光致激光闪光后约 10μs）观察到。在篮式和杂合构象中，G(-H)˙衰减呈双相，其中一个组件的衰减半衰期为0.1ms，另一个组件的衰减半衰期为 20-30ms。G-四链体中快衰减组件（0.1ms）与 8-oxoG 损伤的形成相关。我们提出，在 G-四链体中，G(-H)˙自由基通过与 G 中的 O 原子共享 N1-质子，保留自由基阳离子特征在 [G˙ : G] Hoogsteen 碱基对中；这[G(-H)˙: H G G˙ : G]导致 G˙ 自由基阳离子在毫秒时间域内水合，并随后形成 8-oxoG 损伤。
