Micro-thermal analysis, FTIR- and Raman-microscopy of (R,S)-proxyphylline crystal forms

Three modifications of (R,S)-proxyphylline have been characterized by hot s tage microscopy, FTIR- and FT-Raman microspectroscopy as well as differenti al scanning calorimety, X-ray powder diffractometry and helium pycnometry. Mod. I(m.p. 136 degreesC) is thermodynamically stable in the entire tempera ture range and the only form which crystallizes from organic solvents or wa ter. The metastable mod. II (m.p. 113-116 degreesC) was prepared in gram qu antities from the supercooled melt and shows considerable kinetic stability under dry atmospheric conditions. Mod. III (m.p. 82-85 degreesC) is a new, kinetically very unstable form, which can only be produced in microscopic amounts along with mod. II. The metastable forms are monotropically related to mod. I. FTIR- and FT-Raman micro-spectroscopy, in combination with ther mal analysis, are demonstrated to be powerful tools for the characterizatio n of microphases and unstable modifications of polymorphic systems, providi ng information beyond the commonly phenomenological reports on such forms. (C) 2000 Elsevier Science B.V. All rights reserved.