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Low-Frequency Raman Spectroscopy: An Exceptional Tool for Exploring Metastability Driven States Induced by
Yannick Guinet1, Laurent Paccou1, Alain Hédoux1
1UMR 8207-UMET-Unité Matériaux et Transformations, Univ. Lille, CNRS, INRAE, Centrale Lille, F-59000 Lille, France.
Pharmaceutics
|July 29, 2023
Summary
Low-frequency Raman spectroscopy (LFRS) analyzes molecular material phase transformations. Different relative humidity levels dictate distinct dehydration mechanisms for theophylline and caffeine hydrates.
Area of Science:
- Solid-state chemistry
- Materials science
- Spectroscopy
Background:
- Low-frequency Raman spectroscopy (LFRS) offers valuable insights into molecular materials.
- Pharmaceutical applications increasingly utilize LFRS for analyzing phase transformations.
- Specific spectral processing is crucial for extracting information from the LFRS region.
Purpose of the Study:
- To detail spectra processing for LFRS analysis of molecular materials.
- To investigate phase transformations, specifically dehydration mechanisms, of xanthine family hydrates (theophylline and caffeine) using LFRS.
- To explore the influence of relative humidity (RH) and temperature on solid-state transformations.
Main Methods:
- Utilized low-frequency Raman spectroscopy (LFRS) with spectral processing techniques.
- Investigated the devitrification of ibuprofen as a model system.
- Analyzed the dehydration mechanisms of theophylline hydrate and caffeine hydrate under varying RH conditions.
Main Results:
- Identified two distinct solid-state transformation mechanisms for theophylline hydrate based on RH: diffusion-driven at 1% RH and nucleation/growth at >30% RH.
- Observed various metastability-driven crystalline forms of theophylline at increasing RH, representing intermediate states.
- Found that caffeine hydrate dehydration kinetics follow a single master curve indicative of a nucleation mechanism across different RH levels.
- Achieved and described metastability-driven states of caffeine as intermediate forms between anhydrous caffeine I and II.
Conclusions:
- LFRS is a powerful tool for elucidating complex solid-state transformation mechanisms in pharmaceutical hydrates.
- Relative humidity significantly influences the dehydration pathways and resulting crystalline forms of xanthine derivatives.
- Theophylline and caffeine exhibit different dehydration behaviors, with theophylline showing RH-dependent mechanisms and caffeine following a unified nucleation-driven pathway.
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