Computational Study of Hydrogen-Bonded Complexes between the Most Stable Tautomers of Glycine and Uracil

Abstract

A total of 23 hydrogen bonded complexes between the lowest energy tautomers of uracil and glycine have been characterized at the density functional level of theory with a hybrid B3LYP exchange-correlation functional and 6-31++G** basis sets. The most stable complexes are formed when the carboxylic group of glycine is bound through two hydrogen bonds with a NH proton donor and an O proton acceptor of uracil, and stabilization energies for these cyclic structures span a range of 12.3−15.6 kcal/mol. Interplay between the topological match among proton donor and acceptor sites involved in cyclic structures and their preference to form single hydrogen bonds, measured by the values of proton affinity and deprotonation enthalpy, has been discussed. Upon formation of a uracil−glycine complex, the elongations of proton donor bonds and vibrational red shifts for proton donor stretching modes can reach 0.05 A and 650 cm-1, respectively. These perturbations of proton donor bonds correlate with the magnitude of two-bo...