Fiebig Torsten, Wan Chaozhi, Zewail Ahmed H
Laboratory for Molecular Sciences, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, CA 91125, USA.
Chemphyschem. 2002 Sep 16;3(9):781-8. doi: 10.1002/1439-7641(20020916)3:9<781::AID-CPHC781>3.0.CO;2-U.
As a fluorescent isomer of adenine, 2-aminopurine (Ap) is a powerful probe of DNA dynamics and DNA-mediated charge transfer processes. Here, we report studies with femtosecond resolution of the excited-state dynamics of Ap in various solvents and in bimolecular complexes with nucleotides. Using time-resolved transient absorption and fluorescence up-conversion methods we identify charge transfer as the origin for the quenching of the Ap fluorescence by all four DNA nucleotides. The direction of the redox process is, however, dependent on the base, and from the rates we deduce the nature of the transfer, hole versus electron transfer. The pH and the kinetic isotope effects of these charge transfer reactions revealed no evidence for proton transfer involvement in the rate-determining step. From the measured rates and using electron transfer theory we estimate the driving force for charge transfer between all four nucleobases and Ap. The results are important for the studies of dynamics using Ap in DNA assemblies.
作为腺嘌呤的一种荧光异构体，2-氨基嘌呤（Ap）是研究DNA动力学和DNA介导的电荷转移过程的有力探针。在此，我们报告了对Ap在各种溶剂中以及与核苷酸形成的双分子复合物中的激发态动力学进行的飞秒分辨率研究。使用时间分辨瞬态吸收和荧光上转换方法，我们确定电荷转移是所有四种DNA核苷酸淬灭Ap荧光的原因。然而，氧化还原过程的方向取决于碱基，并且从速率我们推断出转移的性质，即空穴转移与电子转移。这些电荷转移反应的pH值和动力学同位素效应表明，在速率决定步骤中没有质子转移参与的证据。根据测量的速率并使用电子转移理论，我们估计了所有四种核碱基与Ap之间电荷转移的驱动力。这些结果对于使用Ap研究DNA组装体中的动力学具有重要意义。
