title: Crystal structure determination of thymoquinone by high-resolution X-ray powder diffraction.
abstract: 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) A, b = 6.91560(8) A, c = 10.4988(2) A, alpha = 88.864(2) degrees, beta = 82.449(1) degrees, gamma = 77.0299(9) degrees; cell volume = 472.52(1) A3, Z = 2, and space group P1. 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 degrees C and ending at 213 degrees C was noted when TGA was used. DSC allowed for the determination of onset at 43.55 degrees C and a melting enthalpy value of DeltaH(m) = 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.
authors.affiliation: Departamento de Fisicoquímica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, 5000, Córdoba, Argentina.
authors.forename: S
authors.initials: S
authors.lastname: Pagola
authors.forename: A
authors.initials: A
authors.lastname: Benavente
authors.forename: A
authors.initials: A
authors.lastname: Raschi
authors.forename: E
authors.initials: E
authors.lastname: Romano
authors.forename: M A A
authors.initials: MA
authors.lastname: Molina
authors.forename: P W
authors.initials: PW
authors.lastname: Stephens
mesh_terms: D016227:Benzoquinones / Q000737:chemistry*; D003460:Crystallization; D018360:Crystallography, X-Ray / Q000379:methods; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D016227:Benzoquinones; C003466:thymoquinone