Guanine in water solution: Comprehensive study of hydration cage versus continuum solvation model

摘要

We report the results of computational investigation of structures and properties of deoxyribonucleic acid base guanine in the isolated and under heavily hydrated conditions. Heavily hydrated condition involves guanine inside the hydrated cage of 65 water molecules. For comparison, results of hydration of guanine with smaller water shells and that in bulk water solution are also presented. Ground state geometries were optimized at the Hartree-Fock and density functional theory (DFT) level using the B3LYP functional. Vertical electronic singlet transitions were computed at the time-dependent DFT level using the B3LYP optimized geometries. Geometries in the electronic lowest singlet ππ* excited state were optimized at the CIS level of the theory. Effect of bulk water solution was considered using the PCM approach. The standard 6-311G(d,p) basis set was used in all calculations. The similarity and differences between these two models (bulk water solvation and hydration) in describing the aqueous environment on guanine are also reported. It has been found that hydration with 65 water molecule and PCM solvation both produce similar ground and excited state geometry of guanine. In addition, the possible effect of selective hydration on the excited state dynamics is also discussed.