Physicochemical characterization of lauryl glycinate-dodecyl sulfate equimolar complex: A base-triggerable catanionic liposomal system

Abstract

A catanionic liposomal system made up of lauryl glycinate hydrochloride (LG·HCl) and sodium dodecyl sulfate (SDS) has been characterized by physicochemical techniques. Results of turbidimetric and isothermal titration calorimetric studies gave strong evidence the formation of an equimolar complex by the two amphiphiles in aqueous dispersion. Differential scanning calorimetric (DSC) studies suggested the two surfactants form an equimolar complex in the solid state also. Results of transmission electron microscopic experiments indicated that equimolar mixtures of LG·HCl and SDS formed spherical unilamellar liposomes in aqueous dispersion, whereas DSC studies showed that they underwent a phase transition at 52.2 °C, with a transition enthalpy of 5.8 (±0.4) kcal/mol, which corresponds most likely to a lamellar-gel to a micellar phase transition. The catanionic liposomes are base labile and undergo disruption at high pH ( > 8.0). Powder X-ray diffraction studies on the LG-DS complex yielded a d-spacing of 36.81 (±0.29) Å, which is consistent with a lamellar bilayer packing of the complex. Overall the present studies strongly suggest that equimolar mixtures of LG·HCl and SDS form catanionic liposomes. This catanionic system can potentially be used to develop base-triggerable liposomal formulations for delivering therapeutic agents to tissues/organs that have a high local pH, e.g., colon.