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

摘要

Three modifications of (R,S)-proxyphylline have been characterized by hot stage microscopy, FTIR- and FT-Raman microspectroscopy as well as differential scanning calorimety, X-ray powder diffractometry and helium pycnometry. Mod. I(m.p. 136 degreesC) is thermodynamically stable in the entire temperature range and the only form which crystallizes from organic solvents or water. The metastable mod. II (m.p. 113-116 degreesC) was prepared in gram quantities 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 thermal analysis, are demonstrated to be powerful tools for the characterization of microphases and unstable modifications of polymorphic systems, providing information beyond the commonly phenomenological reports on such forms. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 26]