Structure of Intermolecular Drug-Polymer Interactions: Ascorbic Acid−PVP K30 Complex

Abstract

Ascorbic acid (AA) is widely used in pharmaceuticals and food industries, predominantly exists in a crystalline form due to its strong intramolecular hydrogen bonding and high lattice energy. This research explores the structural and intermolecular interactions of AA in a co-amorphous system with polyvinylpyrrolidone K30 (PVP K30), prepared by melt-quenching. The findings reveal that various hydrogen bonding between the hydroxyl groups of AA and the carbonyl groups of PVP K30 plays a key role in forming the amorphous phase. The broadening and shifting of vibrational peaks in FTIR spectra suggest intermolecular interactions, supported by DFT calculations that show reduced HOMO-LUMO energy gaps and enhanced dipole moments in the complex system. FTIR suggests molecular-level interactions promoting amorphization consistent X-ray diffraction (XRD) analysis that confirm the presence of some degree of amorphicity based on peak broadening. This highlights the complex interplay between local molecular interactions and long-range structural organization. Despite the limitations, the results indicate that PVP K30 has the potential to reduce the crystallinity of ascorbic acid and stabilize the amorphous phase, yet not completely. These findings provide insight into the challenges of achieving full amorphization and suggest further optimization in polymer selection and preparation techniques for improved stability.