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.
The single crystal and anion structure of Mn[Fe(CN)sNO'2H~_O, obtained by slow interdiffusion of reactant solutions through a TMS gel, was solved by X-ray diffraction methods and refined to RI = 0.036. Spatial group: orthorhombic, Prima, a = 14.069(2), b = 7.538(1), c = 10.543(1),~,, Z = 4. The Mn(ll) ion and the water molecules are sited on mirror planes, which bisect the nitroprusside ions. One of the water molecules is coordinated to Mn(lI) and the other, strongly hydrogen (as acceptor) bonded to the first molecule. The IR spectrum confirms the bonding of the water molecules and TGA results are in accordance with the dihydrate character of the substance and its dehydration in two successive steps. DTA results and the Raman spectrum agree with other results and the comparison between IR and Raman vNO wavenumbers confirms the expected strong vibrational interaction between the closely packed antiparallel (eclipsed) NO groups. There is a topotactic relationship between the dihydrate and the trihydrate, which crystallizes in the space subgroup P2Jn.
Context: The use of many traditional medicinal plants is often hampered by the absence of a proper biochemical characterization, which is essential to identify the bioactive compounds present in it. The essential oils (EOs) of three native species from the La Rioja province were analyzed: Lippia turbinata Griseb and Lippia integrifolia (Griseb.) Hieron (Verbenaceae), and Clinopodium gilliesii (Benth.) Kuntze (Lamiaceae). Objective: The aim of this study was to evaluate their EOs antioxidant activity (AA) and their chemical composition.
Materials and methods: EOs were analyzed by gas chromatography-mass spectrometry (GC-MS).To enhance the aqueous solubilization of the EOs, EO-water emulsions were prepared (concentration range of 0.1-6 mg mL À1 ). AA was determined using ABTS, DPPH, and peroxyl radical scavenging assays, as well as by the b-carotene bleaching test. Results: Piperitenone oxide was a major constituent in L. turbinata, pulegone and piperitenone oxide in C. gilliesii, and b-caryophyllene in L. integrifolia. Lippia turbinata EO was the most active ABTS and DPPH radical scavenger (SC 50 values of 0.40 ± 0.14 and 0.74 ± 0.08 mg mL À1 , respectively). Clinopodium gilliesii EO exhibited the highest hydrogen peroxide scavenging activity (SC 25 value ¼ 1.52 ± 0.27 mg mL
À1). In the b-carotene assay, L. turbinata EO was more effective at inhibiting lipid peroxidation than the other two oils (IC 25 value ¼ 0.15 ± 0.04 mg mL À1 ). Conclusion: Our results suggest that the AA observed can be justified by the presence of oxygenated monoterpenes, mainly piperitenone oxide. Finally, L. turbinata EO might be used as a safe natural antioxidant and food preservative in the food and cosmetic industries.
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