Low- and High-Frequency Raman Investigations on Caffeine: Polymorphism, Disorder and Phase Transformation
| Autor: | Patrick Derollez, Marc Descamps, Anne-Amandine Decroix, Laurent Paccou, Yannick Guinet, Alain Hédoux |
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| Přispěvatelé: | LDSMM (UMR CNRS 8024) and ERT 1066 |
| Jazyk: | angličtina |
| Rok vydání: | 2011 |
| Předmět: |
02 engineering and technology
Spectrum Analysis Raman 010402 general chemistry 01 natural sciences Phase Transition chemistry.chemical_compound symbols.namesake Theophylline Caffeine Materials Chemistry Physical and Theoretical Chemistry [PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] [PHYS]Physics [physics] Temperature 021001 nanoscience & nanotechnology 0104 chemical sciences Surfaces Coatings and Films Kinetics Crystallography chemistry Polymorphism (materials science) Isothermal transformation diagram symbols Crystallization 0210 nano-technology Raman spectroscopy |
| Zdroj: | Journal of Physical Chemistry B Journal of Physical Chemistry B, American Chemical Society, 2011, 115 (19), pp.5746-5753. ⟨10.1021/jp112074w⟩ |
| ISSN: | 1520-6106 1520-5207 |
| DOI: | 10.1021/jp112074w⟩ |
| Popis: | International audience; Raman investigations are carried out both in crystalline forms of caffeine and during the isothermal transformation of the orientationally disordered form I into the stable form II at 363 K. The time dependence of the Raman spectrum exhibits no significant change in the intramolecular regime (above 100 cm–1), resembling the spectrum of the liquid state. By contrast, significant changes are observed below 100 cm–1, and the low-frequency spectra of forms I and II are observed to be different from that of the liquid. The temperature dependence of the 5–600 cm–1 spectrum gives information on the static disorder through the analysis of collective motions, while information on dynamic disorder are obtained from the study of the 555 cm–1 band corresponding to internal vibrations in the pyrimidine ring. This analysis indubitably reveals that form II is also orientationally disordered with a local molecular arrangement that mimics that in form I and the liquid state. The comparison of the low-frequency spectra recorded in theophylline and form II of caffeine allows one to describe the stable form of caffeine from the packing arrangement of anhydrous theophylline with the consideration of reorientational molecular disorder. |
| Databáze: | OpenAIRE |
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