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881.
C. K. Ghosh S. R. Popuri T. U. Mahesh K. K. Chattopadhyay 《Journal of Sol-Gel Science and Technology》2009,52(1):75-81
Nanocrystalline powders of CuAlO2 were synthesized through sol–gel method using nitrate-citrate route and also through solid state reaction method. We used
a new set of precursor materials for the synthesis of CuAlO2 through sol–gel route which were not reported in the past. A little lowering of the synthesis temperature (1,000 °C) was
observed in case of sol–gel process compared to the solid state reaction method (1,100 °C) and also at shorter time duration.
The particle size of the synthesized powders was determined through small angle X-ray scattering. It has been observed that
the particle size prepared by nitrate-citrate technique is less than the particle size prepared by the solid-state reaction
method. Chemical states of the atomic species were determined by X-ray photoelectron spectroscopy. The formation of phase
pure CuAlO2 were also confirmed by Fourier transformed infrared spectroscopy. A number of solvents were also used for finding the best
possible combinations for obtaining phase pure CuAlO2 at 1,000 °C and it was observed that only the combination of nitrate salts, citric acid and ethanol resulted phase pure CuAlO2. 相似文献
882.
Facile oxidation of aldehydes to acids and esters with Oxone 总被引:1,自引:0,他引:1
[reaction: see text] A highly efficient, mild, and simple protocol is presented for the oxidation of aldehydes to carboxylic acids utilizing Oxone as the sole oxidant. Direct conversion of aldehydes in alcoholic solvents to their corresponding ester products is also reported. These reactions may prove to be valuable alternatives to traditional metal-mediated oxidations. 相似文献
883.
Oxidative folding is the concomitant formation of the native disulfide bonds and the native tertiary structure from the reduced and unfolded polypeptide. Of interest is the inherent conformational tendency (bias) present in the reduced polypeptide to dictate the formation of the full set of native disulfide bonds. Here, by application of a novel tool, we have been able to assess this "native conformational tendency" present in reduced and unfolded bovine pancreatic ribonuclease A (RNase A). The essence of this method lies in the ability of the oxidant [Pt(en)(2)Cl(2)](2+) (where "en" is ethylenediamine) to oxidize disulfide bonds under conditions in which both reduction and disulfide reshuffling, which are essential for rearranging non-native disulfide bonds, are extremely slow. When applied to RNase A, the method revealed little or no bias toward formation of the full native set of disulfide bonds in the fully reduced protein. 相似文献
884.
K.?VenkatakrishnanEmail author P.?Stanley N.R.?Sivakumar B.?Tan L.E.N.?Lim 《Applied Physics A: Materials Science & Processing》2003,77(5):655-658
Femtosecond-pulse laser pulses have been shown to hold great potential for high-precision micromachining. Much research has been done to characterize the laser parameters for predicting the feature size, and the most important of these is the number of pulses incident at each point of ablation. Theoretical modeling, so far, has been restricted to a single point where the number of pulses incident at each point of ablation depends on the pulse-repetition rate and the dwell time of the laser beam at that machining point. However, to make the theoretical model useful, a laser scanning system with the ability to fabricate complex microfeatures is considered in this work. In this case, the scanning resolution determines the number of pulses incident at each scanning point. This has been taken into account while presenting a theoretical and experimental analysis of the effect of the scanning resolution on the threshold fluence of the material. Results of ablation on a gold thin film were subjected to theoretical analysis to predict the feature size. In addition, the effect of the energy fluctuation of the laser on the feature size has been evaluated to predict the minimum achievable feature size for a gold thin film. PACS 42.65; 61.80 相似文献
885.
Direct fabrication of surface-relief grating by interferometric technique using femtosecond laser 总被引:1,自引:0,他引:1
K.?VenkatakrishnanEmail author N.R.?Sivakumar C.W.?Hee B.?Tan W.L.?Liang G.K.?Gan 《Applied Physics A: Materials Science & Processing》2003,77(7):959-963
A surface-relief grating is a key element in optical communication and opto-electronic integrated devices. To date, many techniques for fabricating surface-relief gratings have been reported, but the present techniques still have many limitations and disadvantages. In this paper we present a new optical configuration to imprint a surface-relief grating by two-beam interferometry using a femtosecond laser. A relatively simple set-up is proposed in order to generate two parallel laser beams and then focus them by a common focusing lens to obtain an interference pattern. With the use of the common focusing lens, the two parallel beams will interfere exactly at the focal plane. This new optical set-up not only facilitates the alignment but also enhances the tunability to obtain different grating periods. Experimental results on solid copper targets are presented. The grating surface morphologies are studied by a scanning electron microscope and the grating relief profiles are characterized by an atomic force microscope. The prominent experimental results obtained have verified the feasibility of the new technique. In addition, the influence of laser fluence and pulse number on the surface morphology is presented. PACS 42.15.Eq; 42.25.Hz; 42.62.Cf 相似文献
886.
Ramasamy Ramaraj V. Mahesh Kumar C. Retna Raj V. Ganesane 《Journal of inclusion phenomena and macrocyclic chemistry》2001,40(1-2):99-104
The formation of -cyclodextrin (-CD) inclusioncomplexes of aromatic amines and nitrocompounds have been studied by absorptionand emission spectral methods. Among the different compounds studied, p-nitrobenzoic acid showed the smallest Kf value. 3,5-dinitrobenzoic acid showed the highest Kf value due to the formation of a hydrogenbond between the nitro group and the hydrogen in the hydroxyl groupof CD, and this is not possible with p-nitrobenzoic acid. The lower Kf values in the range 60–70 observed for ortho substituted compounds indicate the steric effect imposed by the ortho substitution of the compound. The para substituted compounds showed higher Kf values in the range 110–130 due to the hydrophobic effect and also due tothe absence of a steric effect. The lifetime of the Ru(II) complex is not affected by the presence of -CD. When the aromatic amines and nitrocompounds are used as quenchers for the excited state [Ru(bpy)3]2+, the quenching rate constant (kq) values are not significantly affected by the presence of -CD. This indicates that the electron donor or electronacceptor groups are not included into the cavity of -CD. 相似文献
887.
Summary -Amino acid esters, NH2CH(R)CO2R, interact withcis- [Pd(pip)2(OH2)2]2+ (pip = piperidine) in aqueous solution according to the equilibrium (1).
The kinetics of hydrolysis of the ester group in the complexes [Pd(pip)2(NH2CH(R)CO2R°)]2+ have been studied by pH-stat methods and rate constants for the kinetic processes (2) and (3) determined for methyl glycinate, ethyl glycinate, ethyl L--alaninate, methyl L--phenylalaninate, ethyl picolinate, methyl L-cysteinate and methyl L-histidinate.
For the first five esters, substantial rate enhancements are observed for base hydrolysis (factors of 2.8 × 105 fold for methyl glycinate to 4.9 × 107-fold for ethyl picolinate). The effects with methyl L-cysteinate and methyl L-histidinate are much less marked as the mixed ligand complexes do not involve alkoxycarbonyl donors. Thus with methyl cysteinate donation occursvia the primary amino group and the thiolate group. Activation parameters have been determined for reactions (2) and (3) with methyl glycinate. Possible mechanisms for these hydrolytic reactions are considered. Nucleophilic attack by water or hydroxide ion on a chelate ester species satisfactorily accounts for the experimental observations. 相似文献
888.
889.
Mahesh L Patil 《Tetrahedron》2004,60(8):1869-1873
Synthesis of 4-carboxy-2,6-dimethoxyphenyl 2′-carboxy-6′-methoxyphenyl ketone, an important precursor for balanol's benzophenone portion, has been achieved via a short and efficient route in three steps using ortho-lithiation as the key step. In another approach aromatization of 2-(2′-methoxy-6′-methylbenzoyl)-5-methyl-1,3-cyclohexanedione afforded benzophenone precursor 2,6-dimethoxy-4-methylphenyl 2′-methoxy-6′-methylphenyl ketone along with the formation of substituted xanthone. 相似文献
890.