title: Characterization of temperature-induced phase transitions in five polymorphic forms of sulfathiazole by terahertz pulsed spectroscopy and differential scanning calorimetry.
abstract: The far-infrared properties of all five known polymorphic forms of the drug sulfathiazole have been studied by terahertz pulsed spectroscopy and low-frequency Raman spectroscopy. The observed spectra of the different polymorphs are distinctly different. Terahertz pulsed spectroscopy proves to be a rapid and complementary alternative to other physical characterization techniques reported in the literature for distinguishing between the five forms. Variable-temperature measurements (293-473 K) of all polymorphic forms have been performed. The phase transitions observed have been related to thermal analysis data. Form I is the form stable at high temperature of sulfathiazole with a melting point of about 475 K. Form II melts at around 470 K and recrystallizes at higher temperatures to form I. Forms III, IV, and V all convert to form I via a solid-solid phase transition at temperatures below 450 K. The phase transitions can be monitored by terahertz pulsed spectroscopy. Polymorphic impurities of the samples can be detected in the room temperature spectra and their effect on the phase transition behavior can be studied.
authors.affiliation: School of Pharmacy, University of Otago, PO Box 56, Dunedin, New Zealand.
authors.forename: J Axel
authors.initials: JA
authors.lastname: Zeitler
authors.forename: David A
authors.initials: DA
authors.lastname: Newnham
authors.forename: Philip F
authors.initials: PF
authors.lastname: Taday
authors.forename: Terry L
authors.initials: TL
authors.lastname: Threlfall
authors.forename: Robert W
authors.initials: RW
authors.lastname: Lancaster
authors.forename: Rolf W
authors.initials: RW
authors.lastname: Berg
authors.forename: Clare J
authors.initials: CJ
authors.lastname: Strachan
authors.forename: Michael
authors.initials: M
authors.lastname: Pepper
authors.forename: Keith C
authors.initials: KC
authors.lastname: Gordon
authors.forename: Thomas
authors.initials: T
authors.lastname: Rades
mesh_terms: D002152:Calorimetry, Differential Scanning; D008859:Microscopy, Polarization; D011095:Polyethylenes; D011108:Polymers; D011138:Polytetrafluoroethylene; D013057:Spectrum Analysis; D013059:Spectrum Analysis, Raman; D000077589:Sulfathiazole; D013432:Sulfathiazoles / Q000737:chemistry*; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D011095:Polyethylenes; D011108:Polymers; D013432:Sulfathiazoles; D011138:Polytetrafluoroethylene; D000077589:Sulfathiazole