title: Thermodynamics of the hydrolysis of penicillin G and ampicillin.
abstract: Apparent equilibrium constants and calorimetric enthalpies of reaction have been measured for the beta-lactamase catalyzed hydrolysis of penicillin G(aq) and ampicillin(aq) to penicillinoic acid(aq) and to ampicillinoic acid(aq), respectively. High-pressure liquid-chromatography and microcalorimetry were used to perform these measurements. The results for the reference reactions at T = 298.15 K and Im = 0 are: Ko = (9.4 +/- 3.1) x 10(-7), delta rGo = (34.4 +/- 1.0)kJ mol-1, delta rHo = -(73.7 +/- 0.4)kJ mol-1, and delta rSo = -(363 +/- 4) J K-1 mol-1 for penicillin G-(aq) + H2O(1) = penicillinoic acid2-(aq) + H+(aq); Ko = (6.0 +/- 3.0) x 10(-6), delta rGo = (29.8 +/- 1.7) kJ mol-1, delta rHo = -(70.0 +/- 7.5) kJ mol-1, and delta rSo = -(335 +/- 26) J K-1 mol-1 for ampicillin-(aq)+ H2O(1) = ampicillinoic acid2-(aq)+H+(aq). Calorimetric enthalpies of reaction for the beta-lactamase catalyzed hydrolysis of cephalosporin C have also been measured but the reaction products have not been identified and the measured enthalpies cannot be assigned to a specific reaction. Acidity constants for ampicillin, penicillin G, ampicillinoic acid, and penicillinoic acid are also reported. A strain energy of 116 kJ mol-1 for the beta-lactam ring is obtained from thermochemical data.
authors.affiliation: Biotechnology Division, National Institute of Standards and Technology, Gaithersburg, MD 20899.
authors.forename: N
authors.initials: N
authors.lastname: Kishore
authors.forename: Y B
authors.initials: YB
authors.lastname: Tewari
authors.forename: W T
authors.initials: WT
authors.lastname: Yap
authors.forename: R N
authors.initials: RN
authors.lastname: Goldberg
mesh_terms: D000667:Ampicillin / Q000031:analogs & derivatives / Q000737:chemistry*; D002151:Calorimetry; D002851:Chromatography, High Pressure Liquid; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007525:Isoelectric Focusing; D008970:Molecular Weight; D010397:Penicillanic Acid / Q000031:analogs & derivatives / Q000737:chemistry; D010400:Penicillin G / Q000737:chemistry*; D013816:Thermodynamics; D001618:beta-Lactamases / Q000378:metabolism
chemical_list: C008782:penicilloic acid; C086821:ampicillinoic acid; D000667:Ampicillin; D010397:Penicillanic Acid; D001618:beta-Lactamases; D010400:Penicillin G