title: Polymorphic transformation of anhydrous caffeine upon grinding and hydrostatic pressurizing analyzed by low-frequency raman spectroscopy.
abstract: Low-frequency Raman investigations were carried out upon pressurizing and grinding both crystalline forms of anhydrous caffeine at room temperature. These investigations have led to the detection of metastable states under stress. Upon moderated hydrostatic compression, only form I transform into a metastable state characterized by a Raman band-shape resembling that of form II. Above 2 GPa, both pressurized forms convert into an identical disordered state, suggesting a pressure-induced amorphization. In contrast to hydrostatic compression, grinding induces transformation of each phase into the other, leading to an intermediate state only stabilized under long enough grinding. The origin of these metastable states induced by stress was related to the disordered nature of both crystalline forms of caffeine and the stability conditions at room temperature of form I.
authors.affiliation: Univ Lille Nord de France, France USTL, UMET UMR 8207, F-59650 Villeneuve d';Ascq, France. alain.hedoux@univ-lille1.fr
authors.forename: Alain
authors.initials: A
authors.lastname: Hédoux
authors.forename: Yannick
authors.initials: Y
authors.lastname: Guinet
authors.forename: Laurent
authors.initials: L
authors.lastname: Paccou
authors.forename: Florence
authors.initials: F
authors.lastname: Danède
authors.forename: Patrick
authors.initials: P
authors.lastname: Derollez
mesh_terms: D002110:Caffeine / Q000737:chemistry*; D003460:Crystallization; D018360:Crystallography, X-Ray; D004355:Drug Stability; D006874:Hydrostatic Pressure; D044367:Phase Transition; D011208:Powders; D013059:Spectrum Analysis, Raman; D013678:Technology, Pharmaceutical / Q000379:methods*; D013696:Temperature; D013997:Time Factors
chemical_list: D011208:Powders; D002110:Caffeine