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731.
Roca-Sanjuán D Rubio M Merchán M Serrano-Andrés L 《The Journal of chemical physics》2006,125(8):084302
Quantum chemical high level ab initio coupled-cluster and multiconfigurational perturbation methods have been used to compute vertical and adiabatic ionization potentials of the five canonical DNA and RNA nucleobases: uracil, thymine, cytosine, adenine, and guanine. Several states of their cations have been also calculated. The present results represent a systematic compendium of these magnitudes, establishing theoretical reference values at a level not reported before, calibrating computational strategies, and guiding the assignment of the features in the experimental photoelectron spectra. 相似文献
732.
Brillouin spectra obtained in dynamic light-scattering experiments are reported for the three isomeric xylenes (ortho-, meta-, and paradimethylbenzenes) between 288 and 363 K. Limiting sound velocities and relaxation times, as obtained from the polarized spectra using the theory developed by Mountain [J. Res. Natl. Bur. Stand. 70A, 207 (1966)], reveal the existence of a relaxation process. Our results suggest that the relaxation process in liquid xylenes has a purely vibrational nature. Vibrational-translational energy exchanges in xylenes are analyzed in terms of available molecular models and compared to those previously obtained for toluene and benzene. The results presented here confirm the important role played by the molecular geometry in the vibrational relaxation process, as the relative arrangement of the methyl groups has significant effect in determining the relaxing vibrational modes. 相似文献
733.
Balbuena P Rubio EM Ortiz Mellet C García Fernández JM 《Chemical communications (Cambridge, England)》2006,(24):2610-2612
Protection of trans-1,2-diol segments as cyclic o-xylylene ethers strongly favours diequatorial over diaxial dispositions; the possibility of using this grouping for remote control of the stereochemistry in the synthesis of spiroketals is here demonstrated by the stereoselective synthesis of tricyclic spirodisaccharides (di-D-fructose dianhydrides). 相似文献
734.
The oxygen radical absorbance capacity (ORAC) method has been adapted to the instrumental laboratory and optimized for the
determination of the antioxidant capacity of a novel active packaging. As the ORAC assay requires the monitorization of a
reaction at controlled temperature by means of the fluorescence signal decrease over time, specific instrumental is usually
necessary. In this work, a common liquid chromatographic device has been adapted to perform the ORAC assay, leaving it accessible
to any laboratory. Using this adaptation, five different essential oils have been determined resulting in the following antioxidant
order: clove (2.66 g Trolox per gram of essential oil), oregano (2.25), cinnamon (1.93), rosemary (1.66), and ginger (1.47).
After incorporating the essential oils to the film, its antioxidant capacity has also been checked and related to the concentration
of essential oil as well as the thickness of the active film. The results point out that for the same amount of essential
oil incorporated measured as grams per square meter, thicker films have more antioxidant capacity than the thinner and more
concentrated ones. Furthermore, the antioxidant capacity found in the films was always higher than expected taking into account
the amount of essential oil incorporated. Some likely explanations have been proposed, leading to the improvement of the antioxidant
film under development. 相似文献