Crystal structure determination of thymoquinone by high-resolution X-ray powder diffraction
AUTOR(ES)
Pagola, S.
FONTE
Springer-Verlag
RESUMO
The crystal structure of 2-isopropyl-5-methyl-1,4-benzoquinone (thymoquinone) and its thermal behavior—as necessary physical and chemical properties—were determined in order to enhance the current understanding of thymoquinone chemical action by using high resolution x-ray powder diffraction, Fourier transform infrared spectroscopy (FTIR), and 3 thermo-analytical techniques thermogravimetric analysis (TGA), differential thermal analysis (DTA), and differential scanning calorimetry (DSC). The findings obtained with high-resolution x-ray powder diffraction and molecular location methods based on a simulated annealing algorithm after Rietveld refinement showed that the triclinic unit cell was a=6.73728(8) Å, b=6.91560(8) Å, c=10.4988(2) Å, α=88.864(2)o, β=82.449(1)o, γ=77.0299(9)o; cell volume=472.52(1) Å3, Z=2, and space group \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$P\bar 1$$ \end{document}. In addition, FTIR spectrum revealed absorption bands corresponding to the carbonyl and C-H stretching of aliphatic and vinylic groups characteristically observed in such p-benzoquinones. Also, a chemical decomposition process starting at 65°C and ending at 213°C was noted when TGA was used. DSC allowed for the determination of onset at 43.55°C and a melting enthalpy value of ΔHm=110.6 J/g. The low value obtained for the fusion point displayed a van der Waals pattern for molecular binding, and the thermograms performed evidence that thymoquinone can only be found in crystalline triclinic form, as determined by DRX methods.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2750463Documentos Relacionados
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