Theoretical study on the relative energies of neutral pterin tautomers

Abstract

Current literature lists the lactam and lactim tautomers as the only major contributors to aqueous pterin structures. Density functional theory calculations were used to determine whether there are other significant neutral tau- tomers of pterin participating in photochemical and biological systems other than the lactam and lactim forms in aqueous media. Calculations showed that the lactam tautomer is the lowest energy structure while the lactim structure is higher in energy than expected (∼6 kcal/mol) compared to the lactam structure. Three other neutral pterin structures were calculated to be less than ∼4 kcal/mol above the most stable lactam and therefore should also be considered as structures which possibly play an important role in chemical and biological pterin systems.