title: Kinetics and mechanism of zinc ion-mediated degradation of cephalosporins in tromethamine solution.
abstract: Earlier studies of the hydrolysis and aminolysis of penicillin, in the presence of zinc ion and tromethamine (Tris), revealed a very rapid catalysis mediated by a ternary complex in which the metal ion brought the reactants into close proximity in a suitable configuration for reaction. In the present work similar studies with a group of cephalosporins show not only much slower rates of reaction but a different mechanism in which the zinc ion-tromethamine complex functions as a nucleophile in a bimolecular reaction. Evidence for the differences in mechanism includes not only the different dependence of rate upon tromethamine concentration, but comparable rates of reaction of methyl esters of a penicillin and a cephalosporin and the reaction products observed by high-performance liquid chromatography.
mesh_terms: D002384:Catalysis; D002511:Cephalosporins / Q000032:analysis*; D002851:Chromatography, High Pressure Liquid; D006868:Hydrolysis; D007700:Kinetics; D008433:Mathematics; D012996:Solutions; D013053:Spectrophotometry / Q000379:methods; D014325:Tromethamine / Q000032:analysis*; D015032:Zinc / Q000032:analysis*
chemical_list: D002511:Cephalosporins; D012996:Solutions; D014325:Tromethamine; D015032:Zinc