Thermodynamic insights into molecular interactions of sodium lauryl sulfate (SLS) with caffeine and theophylline in aqueous media at different temperatures

Abstract

Molecular interactions of the caffeine and theophylline with anionic surfactant sodium lauryl sulfate (SLS), in aqueous media, has been explored by thermodynamic parameters of micellization obtained by the conductometric method. The standard relations associated with micellization were used for the correlation and interpretation of molecular interactions by utilizing the experimental data. The various micellization parameters such as standard free energy ΔGmico, enthalpy ΔHmico and entropy ΔSmico of micellization were calculated. The increase of micellization for SLS in theophylline with an elevated temperature is attributed to the prevailing hydrophobic-hydrophobic increased interactions. The resonance and the dispersal charge on the electron-rich N atoms in caffeine tend to form an ion-dipolar interaction in the vicinity of the polar opposite charge. The thermodynamic parameters indicate that the micellization process in caffeine and theophylline with SLS are spontaneous, enthalpy and entropy controlled.