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Department of Chemical and Biological Engineering, Physical Chemistry, Chalmers University of Technology, SE-41296 Göteborg, Sweden
; Fax: +46 31 772305
; Tel: +46 31 7723055
School of Chemistry, Bedson Building, Newcastle upon Tyne NE1 7RU, United Kingdom
; Fax: +44 (0) 191 2226929
; Tel: +44 (0) 191 2225523
Dalton Trans., 2013,42, 4081-4090
24 Oct 2012,
11 Jan 2013
First published online
14 Jan 2013
The luminescence of DNA-bound [Ru(phen)2dppz]2+ is shown to be highly sensitive to environmental conditions such as ionic strength, temperature, and the sequence and secondary structure of the nucleic acid, although not to bulky DNA substituents in the major groove. Each enantiomer has two characteristic lifetimes with any polynucleotide and their relative amplitudes vary as a function of binding ratio. For [poly(dA-dT)]2 as a model sequence, the longer lifetime for Δ-[Ru(phen)2dppz]2+ has been assigned to canted intercalation of the complex and the shorter lifetime is ascribed to symmetric intercalation. At a fixed binding ratio, the longer lifetime amplitude increases with increasing ionic strength, without significant change in lifetimes. Increasing temperature has a similar effect, but also affects lifetimes. In general, emission is strongest with AT-rich polynucleotides and with higher-order secondary structures, with intensity increasing as single-stranded < duplex < triplex. However, sequence-context and secondary duplex structure also influence the photophysics since emission with [poly(dA)]·[poly(dT)] is significantly higher than with [poly(dA-dT)]2 or [poly(rA)]·[poly(rU)]. The strong influence of different environmental conditions on the emission of nucleic acid-bound [Ru(phen)2dppz]2+ reflects subtle heterogeneities that are inherent elements of DNA recognition by small molecules, amplified by large changes in photophysics caused by differential exposure of the dppz nitrogens to groove hydration.
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