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571.
Richard Asher 《BMJ (Clinical research ed.)》1958,1(5065):265-266
572.
Raman spectra are reported for crystalline nonactin, monactin, dinactin, trinactin, and tetranactin and their solutions in CCl4, CHCl3, CH3OH, and 4:1 (v/v) CH3OH:CHCl3. The macrotetrolide nactins selectively bind a wide variety of cations, and are important model compounds for the study of ion complexation. The conformations of nonactin, monactin, and dinactin in solution are similar. Their conformations are found to be sufficiently open to permit the ester carbonyl groups to form hydrogen bonds with CH3OH; this gives rise to characteristic changes in the vibration frequencies associated with the ester groups. Nonactin, which is the least soluble of the nactins in CH3OH, is also the least effective at forming hydrogen bonds with CH3OH. The greater ability of the higher nactins to form hydrogen bonds with CH3OH may be due to the increased inductive effect of ethyl over methyl side chains, which may increase the dipole moment of the ester carbonyl groups. Spectra of crystalline nonactin, monactin, and tetranactin are fairly similar, while the spectra of dinactin and trinactin comprise a second, distinct family. This is consistent with X-ray crystallographic studies, which show that nonactin and tetranactin form monoclinic crystals, while trinactin is triclinic. 相似文献
573.
Ohne Zusammenfassung 相似文献
574.
T. H. Thomas B. C. Loughman M. J. C. Asher Dr G. D. Weston 《Plant Growth Regulation》1993,12(1-2):161-164
575.
Ohne Zusammenfassung 相似文献
576.
Influence of phosphate status on phosphate uptake kinetics of maize (Zea mays) and soybean (Glycine max) 总被引:1,自引:0,他引:1
To obtain plants of different P status, maize and soybean seedlings were grown for several weeks in flowing nutrient solution culture with P concentrations ranging from 0.03–100 µmol P L-1 kept constant within treatments. P uptake kinetics of the roots were then determined with intact plants in short-term experiments by monitoring P depletion of a 3.5 L volume of nutrient solution in contact with the roots. Results show maximum influx, Imax, 5-fold higher in plants which had been raised in solution of low compared with high P concentration. Because P concentrations in the plants were increased with increase in external P concentration, Imax was negatively related to % P in shoots. Michaelis constants, Km, were also increased with increased pretreatment P concentration, only slightly with soybean, but by a factor of 3 with maize. The minimum P concentration, Cmin, where net influx equals zero, was found between 0.06 and 0.3 µmol L-1 with a tendency to increase with pretreatment P concentration. Filtration of solutions at the end of the depletion experiment showed that part of the external P was associated with solid particles.It was concluded that plants markedly adapt P uptake kinetics to their P status, essentially by the increase of Imax, when internal P concentration decreases. Changes of Km and Cmin were of minor importance. 相似文献
577.
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579.
Sodium perchlorate salt (NaClO4) is commonly used as an internal intensity standard in ultraviolet resonance Raman (UVRR) spectroscopy experiments. It is well known that NaClO4 can have profound effects on peptide stability. The impact of NaClO4 on protein stability in UVRR experiments has not yet been fully investigated. It is well known from experiment that protein stability is strongly affected by the solution composition (water, salts, osmolytes, etc.). Therefore, it is of the utmost importance to understand the physical basis on which the presence of salts and osmolytes in the solution impact protein structure and stability. The aim of this study is to investigate the effects of NaClO4, on the helical stability of an alanine peptide in water. Based upon replica-exchange molecular dynamics data, it was found that NaClO4 solution strongly stabilizes the helical state and that the number of pure helical conformations found at room temperature is greater than in pure water. A thorough investigation of the anion effects on the first and second solvation shells of the peptide, along with the Kirkwood-Buff theory for solutions, allows us to explain the physical mechanisms involved in the observed specific ion effects. A direct mechanism was found in which ClO4− ions are strongly attracted to the folded backbone. 相似文献
580.
Schistosomiasis and hydration status: Schistosoma haematobium,but not Schistosoma mansoni increases urine specific gravity among rural Tanzanian women 下载免费PDF全文