Water diffusion in hydrated crystalline and amorphous sugars monitored using H/D exchange.

Area of Science:

• Pharmaceutical Science
• Solid-State Chemistry
• Spectroscopy

Background:

• Water plays a crucial role in the structure and properties of pharmaceutical materials.
• Understanding the precise interactions of water within crystalline and amorphous forms is vital for drug formulation and stability.
• Deuterium labeling offers a potential method to probe these interactions.

Purpose of the Study:

• To investigate the utility of deuterium oxide (D(2)O) exchange experiments for elucidating the structure of hydrated pharmaceutical materials.
• To compare the D(2)O exchange behavior of crystalline hydrates with their amorphous counterparts.
• To gain insights into water accessibility and diffusion within different solid-state forms.

Main Methods:

• Raman spectroscopy was employed to monitor the exchange of water of hydration and hydroxyl groups.
• Model compounds, including raffinose pentahydrate, trehalose dihydrate, and sucrose, were exposed to D(2)O vapor.
• Amorphous forms of these compounds were studied alongside their crystalline hydrates.

Main Results:

• Complete exchange of all sugar hydroxyl groups was observed in amorphous materials upon D(2)O exposure, suggesting unrestricted water access.
• In crystalline raffinose pentahydrate and trehalose dihydrate, exchange of both hydrate water and hydroxyl groups was incomplete.
• Incomplete exchange in crystalline forms suggests the presence of specific diffusion pathways within the crystal lattice.

Conclusions:

• D(2)O exchange experiments serve as a valuable tool for probing the structural characteristics of pharmaceutical hydrates.
• The differential exchange behavior between amorphous and crystalline forms highlights differences in water mobility and site accessibility.
• Results are consistent with known crystal structures, validating the D(2)O exchange methodology for solid-state characterization.