AM1 study of the electronic structure of 7-aminodeacetoxycephalosporanic acid (7-ADCA)

The geometry and electronic structure of 7-aminodeacetoxycephalosporanic acid (7-ADCA) have been fully optimized and calculated by semi-empirical molecular orbital AM I method. The mechanism of protonation at nitrogen atoms of the molecule has been studied by the comparison of net charges in the different positions. Further, the effect of conformational changes on the electronic properties has been studied. In this connection, the heats of formation (H?), dipole moments (p), full atomic charges. and energies of frontier molecular orbitals (E-HOMO and E-LUMO) have been calculated and discussed. The conformational analyses of mono- and di-protonated species have also been performed by AM1 method and their stable conformations determined.