Determination of the aggregation properties of weakly self-associating systems by NMR techniques: the self-association of propranolol hydrochloride in aqueous electrolyte solution

Abstract

An analytical method for the determination of critical aggregation concentrations (cac) from the concentration dependence of chemical shifts from ¹H nuclear magnetic resonance data for weakly self-associating systems is proposed. Application to solutions of the amphiphilic drug propranolol hydrochloride in the presence of added electrolyte (0.00, 0.05, 0.10, 0.20, 0.30 and 0.50 mol kg⁻¹ NaCl) at 293.15 K has yielded cac values which are independent of the proton selected for analysis and in reasonable agreement with values derived from other experimental techniques. Aggregation numbers calculated by the application of mass action theory to the chemical shift data, and the standard Gibbs energy of aggregation calculated from the cac data, are in agreement with previously reported values.