One-Electron Oxidation Reactions of Some Purine and Pyrimidine Bases in Aqueous Solutions. Electrochemical and Pulse Radiolysis Studies

Abstract

The reduction potentials of some purine and pyrimidine bases and the guanine nucleoside and nucleotide at pH values between 7 and 13 were investigated using the techniques of cyclic voltammetry, differential pulse polarography, and pulse radiolysis. The results clearly show that the lowest reduction potentials, in volts vs NHE, at pH 7 are those of xanthine, 0.88 V, and 1-methylguanine, 1.06 V (NHE). The extrapolated value of guanine is ca. 1.0 V. We also studied the one-electron oxidation reaction of the azide radical with the above compounds. We monitored their transient absorption spectra and determined their formation secondorder rate constants. The decay kinetics of these radicals was followed. Radicals derived from the bases decayed via a radical-radical mechanism with a second-order rate constant. However, the guanine nucleosides and nucleotide radicals have shown at all pHs two consecutive processes (first order followed by a second order). The first-order reaction is pH dependent. Formation of a new transient was observed at pH g9 for guanosine, pH g11 for 2′-deoxyguanosine, and at pH 13 for 5′-GMP. The observed new transient spectra were similar to that observed for the oxidized guanine radical. Therefore, we suggest that in these oxidized guanine nucleosides and nucleotide the oxidized guanine radical has been released. As previously suggested our results imply that the radiation-induced base release from nucleosides in alkaline solution is due to the preferred reaction of the nucleoside sugar with O •-Using our results, those of Steenken et al.

A Century of Organic Electrochemistry

“…218 It has been suggested that the high ability to conduct holes is developed to protect essential parts of DNA against oxidation by transferring the attacking hole to a less essential part of the genome. Of the four bases guanine is more easily oxidized than the three others ͓E ͑pH 7͔: G 1.04 V, T 1.29 V, A 1.32 V, and C 1.44 V vs. NHE͒ 219,220 and by having long stretches of GC without essential function in the cell and good conductivity, the damaging hole may be transferred to the more easily oxidized part of the genome, and the hole may end by oxidizing guanine to 7,8-dihydro-8-oxoguanine. G is not only the most easily oxidizable base, but its catalytic one-electron oxidation in poly-G sequences is particular fast.…”

Site‐Selective Blocking of PCR by a Caged Nucleotide Leading to Direct Creation of Desired Sticky Ends in The Products

“…However, a high pH is not favorable for this system, because it elevates the risk of oxidative base damage. [28] Use of LACE-PCR to provide products possessing restriction enzyme termini…”

Deprotonation of Guanine Radical Cation in G-Quadruplex: A Combined Experimental and Theoretical Study

“…通常 认为, 空穴沿着 DNA 链传递是空穴通过鸟嘌呤碱基(G) 而发生的多步短距离跳跃过程 [9] . 在形成 DNA 链的所 有四个碱基中, 由于 G 碱基具有最低的氧化还原电 势 [10] , 因此空穴最终会被 G 碱基捕获, 产生鸟嘌呤自由 3) [15,16] , 因此双链 DNA 中的 G 碱 基被单电子氧化为 G •＋ 后, 质子会首先从 G •＋ 的 N(1)位 点通过氢键转移到 C 碱基的 N(3)位上, 最终在 C 碱基上 被水分子捕获 [17～19] . 这一脱质子过程的速率常数约为 10 6 到 10 7 s -1 , 完全可以与空穴传递过程竞争, 因而导 致空穴在双链 DNA 中只能传递大约 200 Å [20] .…”