Study of binding energies using DFT methods, vibrational frequencies and solvent effects in the interaction of silver ions with uracil tautomers

Abstract

Relative energies and optimized structures of uracil tautomers and their complexes with silver ions were obtained using B3LYP calculations and more properties were investigated using AIM and NBO calculations. The interactions between all uracil tautomers and silver ions in different ways were investigated. Nine tautomers for uracil (U) and twenty U-Ag+ complexes were considered in this study. The IR spectra for three most stable tautomers and complexes were graphically presented, showing significant differences between their spectra. Analyzing the IR spectra of tautomers and complexes revealed that the frequency of C[dbnd]O π-bond near the silver ion increases and it decreased while being away from the silver ion. The di-keto tautomer (pyrimidine-2,4(1H,3H)-dione) is the most stable tautomer but their complexes with silver ions are not the most stable because they are coordinated to silver ions only via oxygen atom. Moreover, binding energies in the gas phase and different solvents were obtained. In all solvents except water, with the increase of the solvent's dielectric constant, the binding energy decreased. A linear-like relationship was found between the binding energies in all solvents and in the gas phase and the frequency of stretching vibrations of U-Ag+. AIM (based on atom in molecular theory) values at the critical points confirm the effective interaction between silver ions and oxygen or nitrogen atoms of uracil tautomers. Natural bond orbital (NBO) calculations were employed to obtain the interaction energies for the charge transfer between uracil tautomers and silver ions. At last, UV–Vis absorptions and NMR chemical shifts of two most stable tautomers and complexes were calculated and compared with experimental data.