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Excited State Dynamics of Mononucleotides and DNA Strands in a Deep Eutectic Solvent

Abstract

The photophysics of several mono- and oligonucleotides were investigated in a deep eutectic solvent for the first time. The solvent glyceline, prepared as a 1:2 mole ratio mixture of choline chloride and glycerol, was used to study excited-state deactivation in a non-aqueous solvent by steady-state and time-resolved spectroscopy. DNA strands in glyceline retain the secondary structures present in aqueous solution to some degree, enabling study of the effects of solvent properties on excited states of stacked bases and stacked base pairs. The excited-state lifetime of the mononucleotide 5’-AMP in glyceline is 630 fs, or twice as long as in aqueous solution. Even slower relaxation is seen for 5’-TMP in glyceline, and a possible triplet state with a lifetime greater than 3 ns is observed. Circular dichroism spectra show that the single strand (dA)18 and the duplex d(AT)9⋅d(AT)9 adopt similar structures in glyceline and in aqueous solution. Despite having similar conformations in both solvents, femtosecond transient absorption experiments reveal striking changes in dynamics. Excited-state decay and vibrational cooling generally take place more slowly in glyceline than in water. Additionally, the fraction of long-lived excited states in both oligonucleotide systems is lower in glyceline than in aqueous solution. For a DNA duplex, water is suggested to favor decay pathways involving intrastrand charge separation, while the deep eutectic solvent favors interstrand deactivation channels involving neutral species. Slower solvation dynamics in the viscous deep eutectic solvent may also play a role. These results demonstrate that the dynamics of excitations in stacked bases and stacked base pairs depend not just on conformation, but are also highly sensitive to the solvent.

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Publication details

The article was received on 19 Oct 2017, accepted on 06 Nov 2017 and first published on 06 Nov 2017


Article type: Paper
DOI: 10.1039/C7FD00205J
Citation: Faraday Discuss., 2017, Accepted Manuscript
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    Excited State Dynamics of Mononucleotides and DNA Strands in a Deep Eutectic Solvent

    Y. Zhang, K. deLaHarpe, M. Hariharan and B. Kohler, Faraday Discuss., 2017, Accepted Manuscript , DOI: 10.1039/C7FD00205J

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