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71.
72.
[structure: see text] This is the first report on the diastereoselective addition of carbon nucleophiles to vinyl sulfone-modified hex-2-enopyranosides and pent-2-enofuranosides. Nucleophiles add to the C-2 position from a direction opposite to that of the disposition of the anomeric methoxy group. This novel concept of anomeric configuration-directed stereocontrolled carbon-carbon bond formation in vinyl sulfone-modified carbohydrates is general in nature and has been implemented in the synthesis of new hexopyranosyl and pentofuranosyl branched-chain sugars and densely functionalized carbohydrates. 相似文献
73.
He YY Chignell CF Miller DS Andley UP Roberts JE 《Photochemistry and photobiology》2004,80(3):583-586
St. John's Wort (SJW), an over-the-counter antidepressant, contains hypericin, which absorbs light in the UV and visible ranges and is phototoxic to skin. To determine if it also could be phototoxic to the eye, we exposed human lens epithelial cells to 0.1-10 microM hypericin and irradiated them with 4 J/cm2 UV-A or 0.9 J/cm2 visible light. Neither hypericin exposure alone nor light exposure alone reduced cell viability. In contrast, cells exposed to hypericin in combination with UV-A or visible light underwent necrosis and apoptosis. The ocular antioxidants lutein and N-acetyl cysteine did not prevent damage. Thus, ingested SJW is potentially phototoxic to the eye and could contribute to early cataractogenesis. Precautions should be taken to protect the eye from intense sunlight while taking SJW. 相似文献
74.
The thermal decomposition of rare-earth trioxalatocobaltates LnCo(C2O4)3 · x H2O, where Ln La, Pr, Nd, has been studied in flowing atmospheres of air/oxygen, argon/ nitrogen, carbon dioxide and a vacuum. The compounds decompose through three major steps, viz. dehydration, decomposition of the oxalate to an intermediate carbonate, which further decomposes to yield rare-earth cobaltite as the final product. The formation of the final product is influenced by the surrounding gas atmosphere. Studies on the thermal decomposition of photodecomposed lanthanum trioxalatocobaltate and a mechanical mixture of lanthanum oxalate and cobalt oxalate in 1 : 2 molar ratio reveal that the decomposition behaviour of the two samples is different. The drawbacks of the decomposition scheme proposed earlier have been pointed out, and logical schemes based on results obtained by TG, DTA, DTG, supplemented by various physico-chemical techniques such as gas and chemical analyses, IR and mass spectroscopy, surface area and magnetic susceptibility measurements and X-ray powder diffraction methods, have been proposed for the decomposition in air of rare-earth trioxalatocobaltates as well as for the photoreduced lanthanum salt and a mechanical mixture of lanthanum and cobalt oxalates. 相似文献
75.
We report the results of Compton profile study on polycrystalline tantalum. Measurements have been made using 59.54 keV gamma-rays.
The results are compared with the APW band structure calculations of Papanicolaouet al and other available data. In contrast to the work of Changet al the overall agreement is better with the APW band structure which worsens on incorporating the electron correlation correction.
Estimates of the errors due to the contribution from bremsstrahlung, non-validity of impulse-approximation and anomalous dispersion
are also briefly discussed. 相似文献
76.
Weakly nonlinear stability analysis of a falling film with countercurrent gas–liquid flow has been investigated. A normal
mode approach and the method of multiple scales are employed to carry out the linear and nonlinear stability solutions for
the film flow system. The results show that both supercritical stability and subcritical instability are possible for a film
flow system when the gas flows in the countercurrent direction. The stability characteristics of the film flow system are
strongly influenced by the effects of interfacial shear stress when the gas flows in the countercurrent direction. The effect
of countercurrent gas flow in a falling film is to stabilize the film flow system. 相似文献
77.
The symmetric powers of a smooth curve determine effective cycles in the Jacobian of the curve. The classical Poincare formula
expresses these cycles in terms of the powers of the theta divisor of the Jacobian. Here we prove an analogue of this well-known
Poincare formula for the desingularisation of the compactified Jacobian of an irreducible nodal curve with arbitrary number
of nodes. We also prove an analogue of the Riemann singularity theorem and show that these effective cycles are normal. 相似文献
78.
Purkayastha S Madan T Shah A Krishnamurthy HG Sarma PU 《Applied biochemistry and biotechnology》2000,83(1-3):271-83; discussion 283-6, 297-313
The majority of Aspergillus-induced infections in man are caused by the pathogenic fungus A. fumigatus, which secretes biologically and immunologically active glycosylated and nonglycosylated proteins. The complexity in the antigenic structure of A. fumigatus and the varying host immune responses lead to a wide spectrum of clinical conditions such as allergic bronchopulmonary aspergillosis (ABPA), aspergilloma, and invasive aspergillosis. It is reported that 15-20% of allergic asthmatics suffer from Aspergillus-induced allergies. The incidence of opportunistic infections, including Aspergillus infections, has risen because of the increase in the incidence of HIV and tuberculosis. Allergic bronchopulmonary aspergillosis is an immunologically significant clinical form where type I and type III hypersensitivity reactions are involved in pathogenesis. High levels of specific IgE and IgG antibodies in these patients are of diagnostic value. Molecular characterization of certain immunodominant allergens and antigens of A. fumigatus revealed the presence of complex carbohydrate moieties, heat-shock proteins, enzyme activities such as elastase, protease, catalase, dismutase, and cytotoxic ribonuclease. A Con A binding allergen/antigen (45 kDa) and Con A nonbinding allergen/antigen (18 kDa, Asp fI) have a multifunctional nature. The multifunctional nature of these antigens may play an important role in the pathogenesis of the disease. Significant amounts of a major allergen/antigen of molecular weight 18 kDa is excreted in large amounts through the urine of patients with invasive aspergillosis. Studies on the structure-function relationship of the 18-kDa allergen/antigen revealed the involvement of tryptophan residues in binding with monoclonal antibodies (MAbs). Also, the histidine residues and cysteine disulfide bonds of the 18-kDa allergen are involved in its catalytic activity. The high load of multifunctional antigens in the serum of patients for prolonged periods, the presence of high levels of specific antibodies, and the absence of protective antibodies in ABPA patients have necessitated studies on the functional properties of the antibodies. The present study shows significant immunoreactivity of antibodies in patients of ABPA to fibronectin and collagen. Analysis of IgG antibodies from the patients of ABPA showed the presence of DNA-cleaving activity. These observations offer a new line of thinking in understanding the mechanism of pathogenesis of Aspergillus-induced clinical manifestations, and may lead to novel approaches to intervention in the inflammation and infection caused by fungal pathogens. 相似文献
79.
The temperature dependence of the monoclinic lattice constants in the two smectic phases, S1G and S2G, of HxBPA, has been obtained from X-ray diffraction data, in the temperature range 300 K < T < 240 K. The variation of b (unique axis) is consistent with the chain ordering in the S2G phase indicated by Raman and NMR measurements. 相似文献
80.
Richard S. Glass William N. Setzer Usha Devi G. Prabhu George S. Wilson 《Tetrahedron letters》1982,23(23):2335-2338
Highly diastereoselective oxidations of -alcohol to the corresponding sulfoxides, the relative stereochemistries of these sulfoxides and that of an intermediary alkoxysulfonium salt determined by X-ray crystallographic analysis is reported. 相似文献