(665f) Competitive Adsorption Of Sodium Dodecyl Sulfate and Hydroxypropyl Methylcellulose On Drug MICRO-Particles
In this work we report experimental and theoretical study of the adsorption of sodium dodecyl sulfate (SDS) and hydroxypropyl methylcellulose (HPMC) on griseofulvin particles, a critical step in many pharmaceutical processes. As the concentration of SDS increased, ζ potential of griseofulvin particles decreased, indicating strong adsorption of SDS. We show that SDS adsorption occurs via a single monolayer mechanism well-described in terms of Langmuir and Dubinin-Radushkevish isotherms. Adsorption of HPMC on griseofulvin is determined by two processes that occur simultaneously: self-association of the polymer and polymer-drug adsorption. One of the processes will dominate, depending on polymer concentration. Presence of the adsorbed surfactant adds more complexity to the phenomenon due to complex formation between the surfactant and polymer. We linked observed changes in the adsorption behavior to the phase behavior of polymeric solution, using de Gennes-Teraoka scaling theory Adsorption energy was evaluated theoretically by means of atomistic level force field models, where single point energy calculations were done on the individual molecules and energy-minimized conformations of their complexes The results from molecular calculations are in good qualitative agreement with our experimental findings. The obtained data help to understand the adsorption mechanisms of surfactant and polymer on hydrophobic solid particles, allowing to optimize the formulation of aqueous suspensions of these particles to ensure their stability.