Salicylic acid/gamma-cyclodextrin 2:1 and 4:1 complex formation by sealed-heating method.

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Pharmaceutical Science

Background:

• Salicylic acid (SA) is a widely used pharmaceutical agent.
• Gamma-cyclodextrin (gamma-CD) is a cyclic oligosaccharide known for its ability to form inclusion complexes.
• Controlling the stoichiometry and structure of SA/gamma-CD complexes is crucial for optimizing drug delivery.

Purpose of the Study:

• To investigate the formation of salicylic acid (SA) and gamma-cyclodextrin (gamma-CD) complexes using a sealed-heating method.
• To determine the influence of gamma-CD water content on the complex stoichiometry and molecular structure.
• To characterize the molecular arrangements and SA inclusion within the formed complexes.

Main Methods:

• Sealed-heating method for complex formation.
• Quantitative determination of SA content.
• Powder X-ray diffraction (PXRD) for molecular arrangement analysis.
• Infrared (IR) spectroscopy and (13)C solid-state Nuclear Magnetic Resonance (NMR) for molecular characterization.

Main Results:

• Low water content (0.8-5.4%) yielded a 2:1 SA/gamma-CD complex with monoclinic-columnar gamma-CD arrangement.
• High water content (8.5-11.5%) yielded a 4:1 SA/gamma-CD complex with tetragonal-columnar gamma-CD arrangement.
• The 4:1 complex contained two types of SA molecules, with two included in intermolecular spaces and two within the gamma-CD cavity, while the 2:1 complex had one type of SA molecule in intermolecular spaces.

Conclusions:

• The water content of gamma-CD significantly influences the stoichiometry and molecular structure of SA/gamma-CD complexes formed by sealed-heating.
• Distinct molecular arrangements of gamma-CD and varying SA inclusion modes were observed for the 2:1 and 4:1 complexes.
• This study provides insights into the controlled synthesis of SA/gamma-CD complexes with potential applications in drug formulation.