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61.
The structures of B32 and B32H2–32 with Ih symmetry have been investigated by means of ab initio calculations at STO-3G level. The relationship between molecular orbitals of them has been analyzed and their bonding properties have been discussed. Then the possibility of their existence, as well as the similarity and difference between B32 (B32H2–32) and C60 (C60H60) have been inferred. 相似文献
62.
Yu Tang 《Tetrahedron letters》2006,47(23):3823-3825
5-Endo iodocyclization of various β,γ-unsaturated amides proceeded smoothly to give the corresponding conjugated iminolactones exclusively in satisfactory yields with the use of tBuOCl and I2 as the reagents, which proved to be much advantageous over the conventional I2/NaHCO3. 相似文献
63.
Lipophilic crown ether carboxylic acids such as 2-(sym-dibenzo-16-crown-5-oxy)stearic acid with a cavity size comparable to the ionic radius of rare-earth elements are selective chelation agents for preconcentration and separation of lanthanides from natural waters for NAA. Interfering matrix elements such as sodium and bromine can be simultaneously eliminated during the extraction. The lanthanides can be back-extracted into a dilute acid solution for NAA, thus providing a large preconcentration factor. This two-step extraction method appears suitable for the determination of lanthanides in natural waters and in biological samples. 相似文献
64.
Characteristic polynomials of acyclic carbon chains (Huckel trees) are treated in a systematic way. Formulas of coefficients (ak) of the polynomial are obtained in terms of connectivities that were introduced for dealing with moments in a previous paper. Based on the meaning of ak, a graph-theoretical analysis is given such that ak can be expressed as a linear combination of binomial factors specified by a set of graphs containing ½k edges. The numerical relationship is disclosed between each binomial factor and its specified graph. This stimulates the proposal of a novel approach for evaluating ak by simply collecting the graph set of defnite edges. The approach is equally applicable for the evaluation of matching polynomials of cyclic systems and extendable to the investigation of general trees. 相似文献
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A method of quickly determining ascorbic acid and sorbic acid by capillary zone electrophoresis with ultraviolet detection was developed. The choice of background electrolyte, wavelength, injection time and applied voltage were discussed. Ascorbic acid and sorbic acid were well separated in 80 mmol L−1 boric acid-5 mmol L−1borax (pH = 8.0) in 5 min at the detecting wavelength of 270 nm. Under the optimum condition, the method has linear ranges of 2.54-352.00 mg L−1 for ascorbic acid and 1.08-336.39 mg L−1 for sorbic acid with the detection limit of 1.70 mg L−1 for ascorbic acid and 0.54 mg L−1 for sorbic acid, respectively. Other organic acids in fruit juices have no effect on the detection. This method is very feasible and simple and can be used to detect ascorbic acid and sorbic acid in fruit juices. 相似文献
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70.
Moon-Shong Tang Tzu-chien V. Wang‡ Michael H. Patrick 《Photochemistry and photobiology》1979,29(3):511-520
Abstract— Continuous DNA degradation and resynthesis, without a net change in cellular DNA content, were observed in buffer-held, non-irradiated E. coli B/r. This constant DNA turnover probably involves most of the genome and reflects random sites of DNA repair due to the polA-dependent excision-resynthesis repair pathway. Under these non-growth conditions, it appears that at any given time there is a minimum of one repair site per 6.5 × 106 daltons DNA, each of which is at least 160 nucleotides long.
While the amount of DNA degradation is not influenced by prior exposure to UV radiation, the synthetic activity decreases with increasing UV fluence. We suggest that when sites of DNA turnover occur opposite to cyclobutyl dipyrimidines in UV-irradiated cells, repair of the latter damage can be prevented. This implies that both beneficial and deleterious processes take place in irradiated buffer-held cells, and that cell survival depends on the delicate balance between DNA turnover and repair of UV-damage. Based on these findings, we propose a model to explain the limited repair observed during post-irradiation liquid-holding and to account for the large difference in cell survival between irradiation at low fluence rates (fluence-rate dependent recovery) and at high fluence rates followed by liquid-holding (liquid-holding recovery). 相似文献
While the amount of DNA degradation is not influenced by prior exposure to UV radiation, the synthetic activity decreases with increasing UV fluence. We suggest that when sites of DNA turnover occur opposite to cyclobutyl dipyrimidines in UV-irradiated cells, repair of the latter damage can be prevented. This implies that both beneficial and deleterious processes take place in irradiated buffer-held cells, and that cell survival depends on the delicate balance between DNA turnover and repair of UV-damage. Based on these findings, we propose a model to explain the limited repair observed during post-irradiation liquid-holding and to account for the large difference in cell survival between irradiation at low fluence rates (fluence-rate dependent recovery) and at high fluence rates followed by liquid-holding (liquid-holding recovery). 相似文献