Excited-State Dynamics of DNA Duplexes with Different H-Bonding Motifs

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• 作者：Yuyuan Zhang ; Kimberly de La Harpe ; Ashley A. Beckstead ; Lara Martínez-Fernández ; Roberto Improta ; Bern Kohler
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2016
• 出版时间：March 17, 2016
• 年：2016
• 卷：7
• 期：6
• 页码：950-954
• 全文大小：386K
• ISSN：1948-7185

文摘

The excited-state dynamics of three distinct forms of the d(GC)₉·d(GC)₉ DNA duplex were studied by combined time-resolved infrared experiments and quantum mechanical calculations. In the B- and Z-forms, bases on opposite strands form Watson–Crick (WC) base pairs but stack differently because of salt-induced changes in backbone conformation. At low pH, the two strands associate by Hoogsteen (HG) base pairing. Ultraviolet-induced intrastrand electron transfer (ET) triggers interstrand proton transfer (PT) in the B- and Z-forms, but the PT pathway is blocked in the HG duplex. Despite the different decay mechanisms, a common excited-state lifetime of ∼30 ps is observed in all three duplex forms. The ET–PT pathway in the WC duplexes and the solely intrastrand ET pathway in the HG duplex yield the same pair of π-stacked radicals on one strand. Back ET between these radicals is proposed to be the rate-limiting step behind excited-state deactivation in all three duplexes.