Abstract

REVIEW ON COMPUTATIONAL STUDY OF ZWITTERIONS IN PHENETHICILLIN TAUTOMERS BY AUSTIN MODEL-1 METHOD

Bojja Rajeshwar Rao*

ABSTRACT

Phenethicillin is one of the penicillin derivatives most widely used against gram-positive bacteria. It is partially bound to plasma due to their favourable absorption patterns and reduced undesirable side effects particularly in the treatment of gonorrhoea. The tautomerism of phenethicillin reveals with the shifting of hydrogen atom from α-carbon atom of β-lactam (-HC-C=O) group to the oxygen atom for the formation of enol (-C=C-O-H) group or shifting of hydrogen atom from nitrogen atom of lactam (-HN-C=O) group to the oxygen atom for the formation of lactim (-N=C-O-H) group. The molecular geometry, conformations and electronic properties of phenethicillin (1) with its enol (2), lactim (3) and lactim-enol (4) systems and their zwitterions were optimized and calculated by semi-empirical molecular orbital AM1 method which includes experimental parameters and extensive simplification of the Schrodinger’s equation (HΨ=EΨ) for calculation of various properties in the gas phase. The formation of zwitterions (N12H+) & (N7H+) of phenethicillin tautomers (1 to 4) has been studied by comparison of the heats of formation (ΔHfo), dipole moment (μ), full atomic charges and energies of frontier molecular orbitals (EHOMO and ELUMO). The dipolar characters of the molecule, conformational changes and their stabilities have been discussed.

Keywords: Phenethicillin, -lactim, -enol, -lactim-enol, zwitterions, HOMO, LUMO, frontier molecular orbitals, quantum chemical descriptors.