Abstract

A CRITICAL REVIEW ON THE COMPUTATIONAL STUDY OF ZWITTERIONS IN BENZYLPENICILLIN TAUTOMERS BY AUSTIN MODEL-1 METHOD

Dr. Bojja Rajeshwar Rao*

ABSTRACT

Antibiotics can be organized into different classes according to their effect and mode of action. Benzylpenicillin has been recognized as first antibiotic in chemotherapy for the treatment of infections caused by most species of Gram-positive bacteria. The tautomerism of benzylpenicillin 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 benzylpenicillin (1) with its enol (2), lactim (3) and lactim-enol (4) systems and their zwitterions were optimized and calculated in the gas phase by semi- empirical molecular orbital AM1 method usually considering an isolated molecule surrounded by vacuum. The formation of zwitterions of benzylpenicillin 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 character of the molecule has been expected to influence selective penetration through the porin channels of the cell membrane. The effect of conformational changes and their stabilities have been discussed.

Keywords: .