The effect of water-mediated catalysis on the intramolecular proton-transfer reactions of the isomers of 5-chlorouracil: a theoretical study

Abstract

The geometrical structures and thermal energies (E), enthalpies (H) and Gibbs free energies (G) of 13 isomers of 5-chlorouracil (5ClU) in the gas and water phases were investigated using the density functional theory (DFT) method at the M06-2X/6-311++g(3df,3pd) level. The isomers of 5ClU can be microhydrated at different molecular target sites. The mono-and dihydrated forms are the most stable in both the gas and water phases, and, because of the intermolecular interactions, the hydrations lead to a degree of change in the stability trend. Two types of isomerizations were considered: the internal H-O bond rotations in which the H atom rotates 180 around the C-O bond and the intramolecular proton-transfer reactions in which an H atom is transferred between an O atom and a neighbouring N atom. The forward and backward energy barriers for isomerizations of nonhydrated 5ClU were calculated. In addition, 16 optimized transition-state structures for water-mediated catalysis on isomerizations of 5ClU were investigated. The forward and backward protontransfer energy barriers of water-mediated catalysis on isomerizations of 5ClU were obtained. The results indicate that the catalytic effect of two H 2 O molecules is much greater than that of one H 2 O molecule in isomerizations of 5ClU.

Proton transfer theoretical study catalyzed by 5‐chlorouracil

“…19 Zhang employed density functional theory at the M06-2X/6-311++G(3df,3pd) level to investigate the geometric structures and thermodynamic properties (energy, enthalpy, and Gibbs free energy) of 13 isomers of 5-ClU in the gas and aqueous phases. 20 However, most studies primarily focus on examining the tautomers of 5-ClU molecules in the gas or aqueous phases.…”

“…Wieczorkiewicz investigated the impact of solvents on the intramolecular interactions of 5‐ or 6‐substituted nitro and amino derivatives of uracil in its six tautomeric forms 19 . Zhang employed density functional theory at the M06‐2X/6‐311++G(3df,3pd) level to investigate the geometric structures and thermodynamic properties (energy, enthalpy, and Gibbs free energy) of 13 isomers of 5‐ClU in the gas and aqueous phases 20 . However, most studies primarily focus on examining the tautomers of 5‐ClU molecules in the gas or aqueous phases.…”