SPECTRAL, THERMAL, AND PHOTOCHEMICAL STUDIES ON CERTAIN FIRST, SECOND, AND THIRD GENERATION CEPHALOSPORIN ANTIBIOTICS AND THEIR CD(II) COMPLEXES

Abstract

ABSTRACT The reactions of six cephalosporin antibiotics with cadmium chloride afforded the corresponding Cd(II) complexes. The antibiotics are: cephalexin, cephapirin, cefamandole, cefuroxime, cefotaxime, and ceftazidime. Their Cd(II) complexes are of the general formulas Cd(ATB)ClċxH2O, Cd(ATB)2ċ-xH2O and Cd2(ATB)Cl2ċxH2O where ATB=the respective antibiotic, x=1–3. The complexes have been characterized on the basis of elemental analyses, IR, electronic and 1H NMR spectroscopy, thermal decomposition and photochemical behaviour. Thermogravimetry and derivative thermogravimetry (TG-DTG) have been used to study the stabilities and the thermal decomposition processes of the antibiotics and their Cd(II) complexes. In some cases, the decomposition steps could be correlated with the proper decomposition products, where possible activation energies and order of the decomposition reaction have been calculated from the thermal data. The photochemical behaviour of the antibiotics under investigation and their Cd(II) complexes have been studied. Cephalexin and cefamandole show similar behaviour upon irradiation with light of 298 nm, i.e., an appearance of a new band at long wavelength attributable to the formation of a photocyclization product. The Cd(II) complex of cephalexin exhibits high light sensitivity. Mechanisms of the photolysis of the free antibiotics and Cd-complexes are suggested.