Journal
CHEMPHYSCHEM
Volume 10, Issue 14, Pages 2434-2444Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cphc.200900293
Keywords
density functional calculations; ephedrine; terahertz spectroscopy; vibrational spectroscopy; X-ray diffraction
Funding
- National Science Foundation CAREER Program [CHE-0847405]
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The terahertz (THz) spectrum of the pharmaceutical (1R,2S)H-ephedrine from 8.0 to 100.0 cm(-1) is investigated at liquid-nitrogen (78.4 K) temperature. The spectrum exhibits several distinct features in this range that are characteristic of the crystal form of the compound. A complete structural analysis and vibrational assignment of the experimental spectrum is performed using solid-state density functional theory (DFT) and cryogenic single-crystal X-ray diffraction. Theoretical modeling of the compound includes an array of density functionals and basis sets with the final assignment of the THz spectrum performed at a PW91/6-311G(d,p) level of theory, which provides excellent solid-state simulation agreement with experiment. The solid-state analysis indicates that the seven experimental spectral features observed at low temperature consist of 13 IR-active vibrational modes. Of these modes, nine are external crystal vibrations and provide approximately 57% of the predicted spectral intensity, This study demonstrates that the THz spectra of complex pharmaceuticals may be well reproduced by solid-state DFT calculations and that inclusion of the crystalline environment is necessary for realistic and accurate simulations.
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