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991.
Olivares SP Risso S Gutiérrez MI 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,71(2):336-339
A study was made on the spectroscopic properties of 4-hexylresorcinol (4HR) in several solvents at room temperature. Absorption and emission spectra were slightly affected by solvent polarity. Stokes' shifts were small (approximately 3000 cm(-1)) and the fluorescence quantum yields varied between 0.05 and 0.68, depending on the solvent. The spectral shifts were correlated with different solvent scales. Multiple regression analysis indicates that both non-specific solute-solvent interactions as well as specific solute-solvent interactions (such as hydrogen bonding) play an important role in the position of the Stokes' shift and on the fluorescence quantum yield in the solvents under study. 相似文献
992.
The temperature-independent part of the magnetic circular dichroism spectrum is conventionally divided into the Faraday A and B terms, where the A term is nonzero only for systems with degenerate states. We propose that this separation is abandoned in favor of a unified temperature-independent term. This proposal is based on complex polarization propagator calculations on three structurally similar porphyrins. These calculations also suggest that the Soret band of Zn-porphyrin is determined by an isolated degenerate 2E u state. 相似文献
993.
994.
We report the performance of a flashlamp-pumped Cr:LiSrAlF(6) (Cr:LiSAF) laser developed and built by us. The pumping cavity incorporates filters that select the flashlamps' emission spectrum to match the absorption bands of the gain medium, allowing control of the amount of nonradiactive decay heat contribution of the optical cycle, minimizing thermal effects on the laser operation. The laser generated 2 J pulses at 15 Hz, resulting in 30 W of average power, the highest power extracted from a Cr:LiSAF rod laser to our knowledge. We were able to conclude that the laser efficiency is affected by resonator configuration changes due to thermal lens effects, and not to thermal quenching of the Cr:LiSAF luminescence. 相似文献
995.
The first catalytic enantioselective alpha-aminoxylation of aldehydes and ketones using an insoluble, polymer-supported organocatalyst (1) derived from trans-4-hydroxyproline is reported (ee: 96-99%). Reaction rates in the aminoxylation of cyclic ketones with 1 are higher than those reported with l-proline. The insoluble nature of 1 simplifies workup conditions and allows catalyst recycling without an apparent decrease in enantioselectivity or yield. 相似文献
996.
Nanocomposites films have been processed from a filler and a matrix having the same nature, i.e. waxy maize starch. The filler consists of nanoplatelet-like starch particles obtained as an aqueous suspension by acid hydrolysis of starch granules and the matrix was prepared by plasticization and disruption of starch granules with water and sorbitol. Nanocomposite films were obtained by casting and evaporating the mixture of the aqueous suspension of starch nanocrystals with the gelatinized starch. The resulting films were conditioned before testing and the effect of accelerated ageing in moist atmosphere was investigated. The thermal properties of the nanocomposite films were determined from DSC measurements and the mechanical characterization was performed in both the linear and nonlinear range. 相似文献
997.
Selenium methylselenocysteine protects human hepatoma HepG2 cells against oxidative stress induced by tert-butyl hydroperoxide 总被引:1,自引:0,他引:1
Cuello S Ramos S Mateos R Martín MA Madrid Y Cámara C Bravo L Goya L 《Analytical and bioanalytical chemistry》2007,389(7-8):2167-2178
Selenium methylselenocysteine (Se-MeSeCys) is a common selenocompound in the diet with a tested chemopreventive effect. This
study investigated the potential protective effect of Se-MeSeCys against a chemical oxidative stress induced by tert-butyl hydroperoxide (t-BOOH) on human hepatoma HepG2 cells. Speciation of selenium derivatives by liquid chromatography–inductively
coupled plasma mass spectrometry depicts Se-MeSeCys as the only selenocompound in the cell culture. Cell viability (lactate
dehydrogenase) and markers of oxidative status—concentration of reduced glutathione (GSH) and malondialdehyde (MDA), generation
of reactive oxygen species (ROS) and activity of the antioxidant enzymes glutathione peroxidase (GPx) and glutathione reductase
(GR)—were evaluated. Pretreatment of cells with Se-MeSeCys for 20 h completely prevented the enhanced cell damage, MDA concentration
and GR and GPx activity and the decreased GSH induced by t-BOOH but did not prevent increased ROS generation. The results
show that treatment of HepG2 cells with concentrations of Se-MeSeCys in the nanomolar to micromolar range confers a significant
protection against an oxidative insult. 相似文献
998.
Arunprasad Veeranan Siva Karthik P. Thulasi Selvam Arul G. P. Shkir Mohd. Rajamanickam A. T. Sumathi T. Fredrick Sonia R. 《Journal of Cluster Science》2022,33(6):2651-2659
Journal of Cluster Science - A facile one step synthetic hydrothermal route was used to fabricate the Pt free Ni3S4/CoS2 heterostructure counter electrode and study the photovoltaic characteristics... 相似文献
999.
The potential of a crude peroxidase (POD) from onion solid waste as a biocatalyst for the synthesis of a naturally occurring aurone is described. The crude enzyme preparation effectively promotes the cyclization of 2′,3,4,4′,6′-pentahydroxy-chalcone (which is not a natural substrate of onion POD) into aureusidin. 相似文献