A thermodynamic study of two anionic amphiphilic penicillins in aqueous solution by ultrasound speed measurements

The critical concentrations of sodium cloxacillin and sodium dicloxacillin penicillins in aqueous solution were determined over the temperature range 288.15–313.15 K by a method based on deconvolution into Gaussians of the second derivative of the measured ultrasound velocity. The mass action model was used to calculate the thermodynamic standard quantities: free Gibbs energy, enthalpy and entropy of aggregate formation. The results are discussed in terms of the structure of the drug aggregates.