Post Hartree–Fock and density functional theory studies on tautomerism of 6-thioxanthine in gas phase and in solution

Investigation of tautomerism of 1,3,5-triazine derivative, stability, and acidity of its tautomers from density functional theory

Recent studies have identified N2,N4-bis(4-fluorophenethyl)-N6-(3-(dimethylamino)propyl)-1,3,5-triazine-2,4,6-triamine (1TZ(7,8,9)) as a potent, pure antagonist that inhibits thermosensory transient receptor potential vanilloid 1 channel (TRPV1) channel activity. This study provides theoretical data on the stability and acidity of the tautomers of this molecule. We show that this triazine can exist as three predominant tautomers (2TZ(5,7,8), 4TZ(3,7,9), 7TZ(1,8,9)). In the aqueous phase, equilibrium constants calculations show that only the tautomeric equilibria between 1TZ(7,8,9) and the three most stable triazines can be present which suggests that these three tautomeric equilibria would be the basis of 1TZ(7,8,9)'s biological activity.

DFT study on tautomerism and natural bond orbital analysis of 4-substituted 1,2,4-triazole and its derivatives: solvation and substituent effects

Density functional theory investigations at the DFT-B3LYP/6-311++G^** theoretical level employed to determine the tautomerism, substituent effects of 4-substituted 4-amino-5-methyl-2,4-dihydro-3H-1,2,4-triazole-3-thione, and its derivatives (4-R-H, 4-R-CH₃, 4-R-F, 4-R-NO₂) in the selected solvent (acetone, acetonitrile, and dichloromethane) and gas phases using the polarizable continuum method (PCM) model. The substituted 1,2,4-triazoles have two main different tautomers namely N₂-H and S₇-H. For considered derivatives, thione forms are more energetically stable and dominant form in the studied solvent and gas phases. In addition, geometrical parameters, charges on atoms, dipole moments, energetic properties, and the nucleus-independent chemical shifts (NICS) are investigated. It has been seen that these molecular features of the studied compound and its derivatives are mostly solvent dependent. For electron-releasing and -withdrawing derivatives in the solution and gas phases, 2-H forms are the more stable and dominant form. The relative stability of the C₄-substituted 1,2,4-triazole tautomerism is influenced by the possibility for intramolecular interactions between substituent and electron-donor or electron-acceptor centers of the triazole ring.

Molecular modeling of some 1H-benzimidazole derivatives with biological activity against Entamoeba histolytica: a comparative molecular field analysis study

Comparative molecular field analysis (CoMFA) was performed on a set of 1H-benzimidazole derivatives. Molecular modeling and 3D-QSAR were employed to determine the tautomeric form that would probably fit a target receptor in Entamoeba histolytica. CoMFA results suggest that the antiamoebic activity is favored with steric bulk at position 5 of the benzimidazole ring and low electron density on the group at position 2. To the best of our knowledge this is the first 3D-QSAR study performed for benzimidazoles as antiamoebic agents. The CoMFA models derived will be very valuable to design new and more potent compounds against E. histolytica.