Molecular Structure Investigation of Penicillins and Cephalosporins Antibiotics by DFT Method

The class of β-lactam antibiotics are the most successful medicines. They have a β-lactam reaction ring opening.1 Penicillins and cephalosporins are both β-lactam antibiotics that interfere with the synthesis of peptidoglycan, which it is the main component of the bacterial cell membrane.2 The molecular structures and the activities of β-lactam antibiotics are particularity importance in the emerging bacterial resistance to these medicines.3 Here, some selected medicines from penicillin and cephalosporin antibiotics were discussed and the effect of pyramidality, carboxylate orientation and amide resonance (changes in the C-N and C=O length bond) have measured with quantum mechanics DFT/B3LYP/6-31G* method. The obtained values show that distance of the carboxyl with the carbonyl of the β-lactam is shorter in the active structures (Cohen distance between 3.0 to 3.9Å) as compared to those observed on the inactive geometries (more than 4.1Å Cohen distance). Also, the compared structural data of selected penicillins and cephalosporins were considered. The results show that the reduction of pyramidality values in cephalosporins is one of the reasons related to the acylation reaction by β-lactamase enzyme.

کلیدواژه ها:

Penicillin ، Cephalosporin ، β-lactamas ، Acylation ، β-lactam ، pyramidality