Thermodynamic study of ionic strength effect on Deprotontion constant of gabapentin at T=308.2 K

Most drugs have acidic or basic functionalities. Acid dissociation constants are importantphysicochemical parameters, which can provide critical information about properties such assolubility, lipophilicity, acidity, transport behavior, bonding to receptors, and permeability.Acid dissociation constants are also important parameters for development of analyticalmethods and provide information about the stereochemical and conformational structures ofactive centers of enzymes. Formulation procedures for optimizing drug delivery also benefitfrom the determination of the pKa [1,2]. Because acid-base properties of a drug are dependenton experimental conditions (e.g., temperature, ionic strength, ionic media), it is necessary toprovide reliable model for the description of its acid-base behavior as a function of thesedifferent conditions. Gabapentin (1-(aminomethyl) cyclohexylacetic acid) (GBP) is ananticonvulsant medication indicated in the treatment of epilepsy and neuropathic pain [3]. Inthe present study, deprotonation constant of gabapentin was investigated in NaNO3(aq)solutions at T=308.2 K at different ionic strength (0 ≤ I (mol.kg-1) ≤ 3.36).