Abstract

COMPUTATIONAL STUDY ON THE PROTONATION OF PHENOXYMETHYLPENICILLIN-LACTIM-ENOL BY AM1 METHOD

Thandra Karunakar, Boda Mahipal Reddy and Bojja Rajeshwar Rao*

Abstract

The geometry, conformation and electronic structure of phenoxymethylpenicillin-lactim-enol tautomer has been optimized and calculated in the gas phase, usually considering an isolated molecule surrounded by vacuum, using semi-empirical molecular orbital AM1 method. In this connection, the mechanism of lactam-lactim and ketoenol tautomerism and protonation on phenoxymethylpenicillin-lactimenol has been studied with the different positions of net charges at nitrogen atoms in the molecule. It is observed that the net charges on N7- and N13- atoms are respectively -0.1340 and -0.1609 in the case of phenoxymethylpenicillin-lactim-enol and also investigated that the stability of mono-protonated phenoxymethylpenicillin-lactim-enols are discussed. Further, the heats of formation (ΔHf o), dipole moment (μ), ionization potential (IP), full atomic charges and energies of frontier molecular orbitals (EHOMO and ELUMO) have been performed. The conformational analyses of mono- and diprotonated phenoxymethylpenicillin-lactim-enol and their stable conformations have also been evaluated.

Keywords: AM1, Lactam-lactim, keto-enol tautomerism, phenoxymethylpenicillin, induction effect, frontier molecular orbitals.