Issue 22, 2012

Nonadiabatic decay dynamics of 9H-guanine in aqueous solution

Abstract

The nonadiabatic decay of the biologically relevant guanine tautomer (9H-guanine) in aqueous solution has been investigated by trajectory surface hopping simulations in a quantum mechanical–molecular mechanical (QM–MM) framework. The QM part (9H-guanine) was treated at the semiempirical OM2/MRCI level, while the MM part (water) was described by the TIP3P force field. The optimized geometries for the relevant minima and conical intersections are qualitatively similar for 9H-guanine in the gas phase and in aqueous solution, while there are notable solvent-induced shifts in the computed vertical excitation energies (up to about 0.4 eV). Overall, the results from the static OM2/MRCI-based calculations are in reasonable agreement with the available ab initio and experimental data. The dynamics simulations show ultrafast nonradiative decay for 9H-guanine in water that is even slightly faster than in the gas phase, with time constants of 20 fs and around 0.3 ps for the S2 → S1 and S1 → S0 internal conversions, respectively. They predict a change in the S1 → S0 decay mechanism when going from the gas phase to aqueous solution: the major pathway for 9H-guanine in water involves a conical intersection with an out-of-plane distortion of the carbonyl oxygen atom, which does not play any significant role in the gas phase, where the decay mainly proceeds via two other conical intersections characterized by ring distortions and out-of-plane displacement of the amino group, respectively. Possible reasons for this change in the mechanism are analyzed.

Graphical abstract: Nonadiabatic decay dynamics of 9H-guanine in aqueous solution

Supplementary files

Article information

Article type
Paper
Submitted
31 Jan 2012
Accepted
10 Apr 2012
First published
10 Apr 2012

Phys. Chem. Chem. Phys., 2012,14, 8137-8146

Nonadiabatic decay dynamics of 9H-guanine in aqueous solution

B. Heggen, Z. Lan and W. Thiel, Phys. Chem. Chem. Phys., 2012, 14, 8137 DOI: 10.1039/C2CP40300E

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