Nicotinamide–Indole Binary Drug System: Thermodynamic and Interfacial Studies

Abstract

Crystal engineering, which can potentially be applied to a wide range of crystalline materials, offer an alternative and potentially fruitful method for improving pharmaceutical properties of drugs. The molecular mobility inherent to amorphous/crystalline phases can lead to molecular associations between different components, such that a single crystalline phase of multiple components is formed. The present investigation measures the solid–liquid equilibria (SLE) of nicotinamide (NA)-indole (IN) binary drug system. The solid–liquid equilibrium phase diagram of NA-IN system was determined by the thaw-melt method in the form of a temperature-composition curve. It shows the formation of a simple eutectic at a 0.953 mole fraction of indole, at 48°C. The excess thermodynamic quantities (gE, hE, and sE) have been estimated by computing heat of fusion data and activity coefficient of the component in a binary mix. These values highlight the ordering, stability, and structure of eutectic and non-eutectic alloys. The thermodynamic mixing functions provide information about the nature of mixing of the components during alloying. The negative value of the integral mixing function, ΔGM for eutectic and some non-eutectic alloys indicates spontaneous mixing. The driving force of nucleation during solidification (ΔGv) and the critical free energy of nucleation (ΔG*) obtained at different undercoolings have also been highlighted. The values of radius of critical nucleus (r*) of alloys lies within the nm scale, which suggests new dimensions of solidification processes for nano solid drug dispersions. The solid–liquid interfacial energy (σ), the grain boundary energy (σgb), and the Gibbs–Thomson coefficient (τ) of the drug alloys have been discussed. Interface morphology of the alloys follows the Jackson's surface roughness (α) theory and predicts that faceted growth (α > 2) proceeds in all cases.Supplemental data for this article can be accessed at www.tandfonline.com/gmcl