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1.
The isotropic Raman band shape corresponding to C=O stretching vibration of some molecules has been studied in neat liquids and as a function of solvent concentration using both polar and non-polar solvents. The Raman band shape was analyzed on the basis of correlation with the Lorentzian line shape by employinga simple method of linear curve fitting. In neat liquids and in low solvent concentration region, the band shape was found to be non-Lorentzian. With the gradual increase in solvent concentration the band shape approaches a Lorentzian function. The plot of the correlation coefficient for a Lorentzian shape shows a discontinuity in the intermediate range of solvent concentration. The influence of the structural characteristics of the solute and the solvent systems on the reference mode and various multipolar interactions together with the time varying spatial distribution of solvent molecules with respect to the reference molecule are expected to govern the microenvironmental fluctuations. This may be responsible for the discontinuity in the intermediate solvent concentration region.  相似文献   
2.
Diol capped γ-Fe2O3 nanoparticles are prepared from ferric nitrate by refluxing in 1,4-butanediol (9.5 nm) and 1,5-pentanediol (15 nm) and uncapped particles are prepared by refluxing in 1,2-propanediol followed by sintering the alkoxide formed. X-ray diffraction (XRD) shows that all the samples have the spinel phase. Raman spectroscopy shows that the samples prepared in 1,4-butanediol and 1,5-pentanediol and 1,2-propanediol (sintered at 573 and 673 K) are γ-Fe2O3 and the 773 K-sintered sample is Fe3O4. Raman laser studies carried out at various laser powers show that all the samples undergo laser-induced degradation to α-Fe2O3 at higher laser power. The capped samples are however, found more stable to degradation than the uncapped samples. The stability of γ-Fe2O3 sample with large particle size (15.4 nm) is more than the sample with small particle size (10.2 nm). Fe3O4 having a particle size of 48 nm is however less stable than the smaller γ-Fe2O3 nanoparticles.  相似文献   
3.
Efficient sunlight-responsive BiOBr–CoWO4 heterostructured nanocomposite photocatalysts were prepared via a chemical precipitation route at 100°C in 4 hours. The prepared BiOBr–CoWO4 heterostructures were characterized for phase identification, chemical composition, surface morphology, optical properties and surface area using various techniques. The X-ray diffraction pattern of the BiOBr–CoWO4 nanocomposite was composed of diffraction peaks equivalent to both the tetragonal phase of BiOBr and the monoclinic phase of CoWO4 nanoparticles. X-ray photoelectron spectral study of the BiOBr–CoWO4 nanocomposite revealed orbitals of both BiOBr and CoWO4 compounds. Transmission electron microscopy images revealed that spherical particles of CoWO4 (20–25 nm) were dispersed on the surface of BiOBr. UV–visible–near-infrared spectral study of the BiOBr–CoWO4 nanocomposite showed good visible-light absorption. Among the manufactured materials, BiOBr–CoWO4-2 nanocomposite showed better charge carrier separation efficiency, as demonstrated by photoluminescence and time-resolved fluorescence. To study the practical utility of the prepared materials, their photocatalytic capability was examined for the degradation of rhodamine B (RhB) aqueous solution under sunlight irradiation. The photodegradation results showed that BiOBr–CoWO4-2 nanocomposite degraded 98.69% RhB solution and the degradation constant was 0.067 min−1, which was 5.6 and 22.5 times larger than that of pure BiOBr and CoWO4 nanoparticles, respectively, after 60 minutes of sunlight irradiation. The superior photoactivity was facilitated by electron–hole pair separation and transfer driven by the heterostructure interface between BiOBr particles and CoWO4 nanoparticles. The removal of RhB was initiated by photogenerated h+, O2• − and OH reactive species based on the scavenger effect.  相似文献   
4.
Methylphophorbide a (MPa) has been isolated from the ethanol extract of the wheat grass plant. Its antioxidative efficacy is evaluated by hydroxyl radical scavenging activities and reducing capacity which are significantly up regulated in comparison with aqueous extract of the plant. The compound shows iron-binding capacity where the Fe2+ binds with MPa by two types of binding patterns with dissociation constants 157.17 and 27.89. It has antioxidative and cytotoxic effects on HeLa and Hep G2 cells. The cancerous cell survivability decreases with increasing concentration of MPa. These findings have provided evidence for the traditional use of the wheat grass plant in the treatment of cancers, oxidative stress and iron overloaded disorders.  相似文献   
5.
The cleavage of α-hydroxy tert-butyldimethylsilyl ether to diol takes place efficiently with LAH. It has been proposed that the reaction proceeds via intramolecular hydride transfer from the alkoxy aluminium hydride. In order to substantiate this, reduction of TBDMS ether with LAH in a variety of substrates was studied.  相似文献   
6.
Marine feed ingredients derived from cephalopods (e.g., squid) and crustaceans (e.g., krill) are commercially used to improve the palatability of shrimp diets. Increase in global demand for shrimps has resulted in overfishing of these marine organisms and is a matter of concern. Insect protein hydrolysate could be a sustainable alternative for the possible replacement of these marine feed ingredients. During this study, four formulations: diet A (control: not containing any palatability enhancer), diet B (containing squid meal and krill oil), diet C (containing 1% insect protein hydrolysate), and diet D (containing 2% insect protein hydrolysate) were tested for (1) time required by first subject to begin feeding (time to strike) and (2) palatability in Litopenaeus vannamei. Additionally, the chemical composition of all four diet formulations was also analyzed. Results indicate that all diets had similar crude composition. The major essential amino acids in all diets were leucine and lysine, whereas eicosapentaenoic acid was the major omega-3 fatty acid in all diets. There were no significant differences between the mean time to strike for all the tested formulations. Palatability of tested formulations was found in the following order: diet D > diet C > diet B = diet A (p < 0.05), indicating that addition of squid meal and krill oil has no effect on palatability in comparison to control, whereas inclusion of insect protein hydrolysates significantly improves the palatability of formulations. Palatability enhancement potential of insect protein hydrolysate could be attributed to the high free amino acid content and water solubility in comparison to squid meal.  相似文献   
7.
This paper investigates switching of one beam by another in a Kerr type nonlinear Mach–Zehnder interferometer (NMZI) with two input ports and one output port. The present investigation has been carried out using the beam propagation method (BPM). The paper presents a detailed account on the procedures used to choose the parameters of the NMZI to make it behave like a NOT gate (inverter), an AND gate, an amplifier and a wavelength converter. The paper also gives details on the manipulation of the operating inputs of the NMZI to desired values. It is shown that the operating values of both the inputs of the NMZI can simultaneously be increased/decreased by decreasing/increasing the nonlinearity coefficient of nonlinear arm of the NMZI. Variation of NMZI length varies the operating value of only the first input, keeping the second unchanged, while variation of NMZI offset varies the operating value of only the second, keeping the first unchanged. The paper also gives a detailed account on amplification of the NMZI amplifier/wavelength converter. The present investigation is useful from the scientific as well as engineering point of view.  相似文献   
8.
The characteristics of poly(ethylene glycol) (PEG)–acrylate hydrogel networks were investigated as a function of the ethanol–water solvent composition during free‐radical crosslinking copolymerization. Macromonomer (88% ω‐methoxy‐PEG–acrylate and 10% ω‐phenoxy‐PEG–acrylate) and crosslinker (2% PEG–diacrylate) concentrations were kept constant. As the copolymerization progressed, the polymer solution in 100% ethanol became increasingly turbid, indicating the development of a heterogeneous network structure. In 100% water, however, the initially turbid polymer solution became increasingly transparent as the crosslinking copolymerization progressed. All the gels were optically clear upon equilibration in water. Kinetic studies, with attenuated total reflectance‐infrared, showed a long induction period, along with a lowered reaction rate, in 100% ethanol, and a decrease in conversion with an increase in ethanol content. These results agree with the UV analysis of the sol fractions, which indicated an increase in the amounts of unreacted PEG–acrylates with an increase in the ethanol content. The gels which were formed with a high ethanol concentration exhibited lower Young's modulus and higher swelling ability, suggesting that the network structure was significantly affected by the solvent composition during free‐radical crosslinking copolymerization. From the stress–strain and swelling experiments, the Flory–Huggins interaction parameter was evaluated. The creep characteristics of the hydrogels were modeled with two Kelvin elements. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2677–2684, 2002  相似文献   
9.
10.
Density functional theory calculations, together with quantum theory of atoms in molecules (QTAIM) analyses, have been performed to investigate 18-azacrown-6 complexes of the high-spin late first transition series divalent metal ions in the gas phase and, in some cases, in aqueous solution simulated by a polarizable continuum model. Six intramolecular H-H bonding interactions in the meso-complexes are found to arise from folding of the ligand upon its electrostatic interaction with the metal ions, which are largely absent in the lowest-energy C(2h) conformer of the free ligand. The ligand-to-metal charge transfer obtained from QTAIM analysis, among other things, is found to be an important factor that controls the stability of these complexes. The inter-relationship between the ligand preorganization energy, the zero-point corrected formation energy of the metal complexes, and the H-H bonding pair distances, as well as the dependence of the electron density and the total energy density at the H-H bond critical points on the H-H bonding pair distances, provides a physical basis for understanding and explaining the stabilizing nature of these closed-shell interactions, which are often viewed as steric clashes that lead to complex destabilization.  相似文献   
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