title: Ab initio study on ultrafast excited-state decay of allopurinol keto-N9H tautomer from gas phase to aqueous solution.
abstract: The excited-state decay of the biologically relevant allopurinol keto-N9H tautomer populated at the optically bright S1((1)ππ*) state in the gas phase and in aqueous solution has been explored theoretically. In solution, the hybrid quantum-mechanical/molecular-mechanical simulations were performed, where the QM region (keto-N9H) was treated at the ab initio SA-CASSCF level, while the MM region (water) was described by the TIP3P model. Here we find that there exist four parallel relaxation pathways in the gas phase, but only two of them occur in aqueous solution. In addition, an ultrafast S1 → S0 internal conversion is found in vacuum, with an estimated excited-state lifetime of 104.7 fs, much faster than that in water (242.8 fs), showing reasonable agreement with the available experimental finding in aqueous solution (τ < 200 fs). Calculations indicate that the presence of water solvent plays an important role in the excited-state dynamics of DNA base, showing the pronounced environmental effects on its decay pathways and excited-state lifetimes.
authors.affiliation: State Key Laboratory for Physical Chemistry of Solid Surfaces and Fujian Provincial Key Lab of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering, Xiamen University , No. 422, South Siming Road, Xiamen 361005, P. R. China.
authors.forename: Xugeng
authors.initials: X
authors.lastname: Guo
authors.forename: Yuan
authors.initials: Y
authors.lastname: Zhao
authors.forename: Zexing
authors.initials: Z
authors.lastname: Cao
mesh_terms: D000493:Allopurinol / Q000737:chemistry*; D003198:Computer Simulation; D005740:Gases / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D011789:Quantum Theory; D012996:Solutions; D012997:Solvents / Q000737:chemistry*; D014618:Vacuum; D014867:Water / Q000737:chemistry*
chemical_list: D005740:Gases; D012996:Solutions; D012997:Solvents; D014867:Water; D000493:Allopurinol