Thermodynamics of the hydrolysis of penicillin G and ampicillin

Biophys Chem. 1994 Mar;49(2):163-74. doi: 10.1016/0301-4622(93)e0067-f.

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.

MeSH terms

  • Ampicillin / analogs & derivatives
  • Ampicillin / chemistry*
  • Calorimetry
  • Chromatography, High Pressure Liquid
  • Hydrogen-Ion Concentration
  • Hydrolysis
  • Isoelectric Focusing
  • Molecular Weight
  • Penicillanic Acid / analogs & derivatives
  • Penicillanic Acid / chemistry
  • Penicillin G / chemistry*
  • Thermodynamics
  • beta-Lactamases / metabolism

Substances

  • penicilloic acid
  • ampicillinoic acid
  • Ampicillin
  • Penicillanic Acid
  • beta-Lactamases
  • Penicillin G