title: Solvent effects on the photochemistry of 4-aminoimidazole-5-carbonitrile, a prebiotically plausible precursor of purines.
abstract: 4-Aminoimidazole-5-carbonitrile (AICN) was suggested as a prebiotically plausible precursor of purine nucleobases and nucleotides. Although it can be formed in a sequence of photoreactions, AICN is immune to further irradiation with UV-light. We present state-of-the-art multi-reference quantum-chemical calculations of potential energy surface cuts and conical intersection optimizations to explain the molecular mechanisms underlying the photostability of this compound. We have identified the N-H bond stretching and ring-puckering mechanisms that should be responsible for the photochemistry of AICN in the gas phase. We have further considered the photochemistry of AICN-water clusters, while including up to six explicit water molecules. The calculations reveal charge transfer to solvent followed by formation of an H3O(+) cation, both of which occur on the (1)πσ* hypersurface. Interestingly, a second proton transfer to an adjacent water molecule leads to a (1)πσ*/S0 conical intersection. We suggest that this electron-driven proton relay might be characteristic of low-lying (1)πσ* states in chromophore-water clusters. Owing to its nature, this mechanism might also be responsible for the photostability of analogous organic molecules in bulk water.
authors.affiliation: Institute of Biophysics, Academy of Sciences of the Czech Republic, Královopolská 135, 61265, Brno, Czech Republic. rafal.szabla@gmail.com.
authors.forename: Rafał
authors.initials: R
authors.lastname: Szabla
authors.forename: Judit E
authors.initials: JE
authors.lastname: Sponer
authors.forename: Jiří
authors.initials: J
authors.lastname: Sponer
authors.forename: Andrzej L
authors.initials: AL
authors.lastname: Sobolewski
authors.forename: Robert W
authors.initials: RW
authors.lastname: Góra
mesh_terms: D003198:Computer Simulation; D007093:Imidazoles / Q000737:chemistry* / Q000528:radiation effects; D008027:Light; D008422:Materials Testing; D008956:Models, Chemical; D008958:Models, Molecular; D009570:Nitriles / Q000737:chemistry* / Q000528:radiation effects; D010777:Photochemistry / Q000379:methods; D056692:Prebiotics; D011687:Purines / Q000737:chemistry* / Q000528:radiation effects; D012997:Solvents / Q000737:chemistry* / Q000528:radiation effects
chemical_list: D007093:Imidazoles; D009570:Nitriles; D056692:Prebiotics; D011687:Purines; D012997:Solvents; C098330:4-aminoimidazole