Solution and Surface Properties of Metformin Hydrochloride in Aqueous Solution and Its Interaction with Amino Acids and Anionic Surfactant, Sodium Dodecyl Sulphate

Abstract

This manuscript reports critical micelle concentration of metformin hydrochloride in aqueous solution which was determined by electrical conductivity, surface tension and refractive index measurements. From conductometric and surface tension data, different parameters were calculated which include surface excess concentration, area per molecule, dissociation constant and free energy of adsorption. Thermodynamic parameters like free energy of micellization, enthalpy of micellization and entropy of micellization were also calculated. The effect of change in pH on the CMC of drug was studied in pH range of 2–9. Three amino acids, i.e. glycine, tyrosine and tryptophane, were used to study their effect on CMC of drug. The interaction of this drug with two common surfactants, i.e. sodium dodecyl sulphate (SDS) and cetyl trimethylammonium bromide, was also studied with the help of UV–visible spectroscopy and conductivity measurements. Viscometric study was carried out to find the constants of Jones–Dole equation which are helpful to find the different types of interactions in solution. The results showed the spontaneous nature of adsorption of drug at air solution interface and spontaneous nature of micellization, becoming more spontaneous at elevated temperature. Strong interaction of drug with anionic surfactant SDS was observed. The increase in pH decreased CMC of drug, but higher CMC was found at pH of 7. The amino acids affect the CMC of the drug in different ways. Viscometric study showed the hydrophobic interaction of drugs with the solvent molecules.