Modeling of stability and properties of anionic and cationic tautomers of the 3-hydroxypyridin-4-one system

Theoretical study on the origins of sildenafil tautomers’ relative stability

Tautomers of sildenafil (5-{2-Ethoxy-5-[(4-methylpiperazin-1-yl)sulfonyl]phenyl}-1-methyl-3-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one), a drug commonly used for treating the erectile dysfunction and pulmonary arterial hypertension were studied computationally at the DFT (B3LYP/6-311++G**) level. Four possible structures of sildenafil tautomers structures were considered. The geometries and chemical shifts of carbon and nitrogen nuclei were calculated and compared with available experimental data. The theoretical calculations proved to be consistent with experimental data and indicate the same lowest energy sildenafil structure. The energies of the all considered sildenafil tautomers were determined and ranked according to their energy values. This article presents calculations of several properties (aromaticity, atomic charges, atomic energies, intramolecular hydrogen bonding) and discusses their influence on the relative energies of sildenafil tautomers.

A Comparative DFT Study on the Antioxidant Activity of some Novel 3-hydroxypyridine-4-one Derivatives

The current study on the antioxidant activity of Kojic acid and 3-hydroxypyridine-4-one derivatives was performed by implementation of density functional theory calculations with the B3LYP hybrid functional and the 6-311++ G** basis set in Polarizable Continuum Model. Compounds under evaluation were previously synthesized by our research group. The DPPH scavenging effect and IC 50 values of them in mM concentrations were evaluated. Subsequently, various electronic and energetic descriptors such as HOMO and LUMO energy gaps, bonding dissociation enthalpy of OH bond, ionization potential, electron affinity, hardness, and softness, NBOs and spin density of radical and neutral species were used to study antioxidant properties of investigated compounds. The computations detected two compounds, HP3 and HP4 , with significant antioxidant activity. Energetic descriptors indicated that SPLET mechanism is preferred over than other antioxidant mechanism and computational results were in accordance with the experimental results.

Solvent and temperature effects on the tautomerization of a carbonitrile molecule: A conductor-like polarizable continuum model (CPCM) study

This research examined the effects of solvent polarity and temperature on the tautomerization of a carbonitrile molecule at CAM-B3LYP/6-311G (d,p) level of theory. The selected solvents were n-hexane, diethyl ether, pyridine, ethanol, methanol, and water. The solvent effects were examined by the self-consistent reaction field theory (SCRF) based on conductor-like polarizable continuum model (CPCM). The solvent effects were explored on the energy barrier, frontier orbitals energies, and HOMO-LUMO gap. Dependencies of thermodynamic parameters (ΔG and ΔH) on the dielectric constants of solvents were also tested. Specifically, the temperature dependencies of the thermodynamics parameters were studied within 100–1000 K range. The rate constant of the tautomerism reaction was computed from 300 to 1200 K, in the gas phase.