Molecular dynamics of diclofenac potassium at 300.15 K temperature: Insights from broadband dielectric, thermal and MD simulation analysis

Abstract

Diclofenac potassium (DK) has been categorised as a class II drug by the biopharmaceutics classification system (BCS) based on its high permeability and low solubility. Solubility and stability of such a pharmaceutical medicine must be increased to make a good clinical candidate, which can be accomplished by understanding its molecular dynamics. In the current study, experimental and computational techniques are used to investigate the structural characteristics and the molecular interactions of DK at 300.15 K temperature. The thermal analysis of DK has been done by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Molecular dynamics of DK is investigated through broadband dielectric spectroscopy (BDS) and molecular dynamic (MD) simulation. Complex permittivity spectra of DK were obtained over two frequency ranges: i) low frequency (20 Hz ≤ f ≤ 2 MHz) and ii) high frequency (0.2 ≤ f ≤ 20 GHz). Relaxation mechanism in DK takes place in two ways; one is associated with the reorientation of whole molecule, so-called primary (α) relaxation and other is originated from the small angle reorientation or group rotation of DK, so-called secondary (β,δ,γ) relaxation. Interactions between molecules/atoms/ions form different types of bonds in the DK molecules. Among them, interaction through H-bond is discussed in detail. Orientational dynamics revealed through DRS data is further confirmed by the MD simulation study.