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961.
[reaction: see text] Here we report a novel modification of our previously reported "Staudinger ligation" that generates an amide bond from an azide and a specifically functionalized phosphine. This method for the selective formation of an amide bond, which does not require the orthogonal protection of distal functional groups, should find general utility in synthetic and biological chemistry.  相似文献   
962.
The circular dichroism of keto derivatives with trichothecane skeleton and some of their rearrangement products has been measured. The sign (and sometimes even the magnitude) of all COTTON effects can be explained by applying the respective rules for the cyclohexanone, cyclopentanone, enone and ene-ester chromophores. Thus conformations could also be determined in those cases which did not follow unambiguously from conformational analysis. The conformation of the muconic acid moiety of the macrocyclic ring of verrucarin A is the same in dioxane solution as in the crystalline state.  相似文献   
963.
The electrochemical behaviour of kinetin (6-furfurylaminopurine) on a carbon paste modified with OV-17 silicone electrode, is studied. The determination of kinetin is possible working in square wave voltammetric techniques, reaching limits of determination of 38.7 ng ml−1. The proposed method was successfully applied to determine the cytokinin in extracts of apples (previously spiked with kinetin) and the obtained results were in accordance with the results obtained with HPLC-UV.  相似文献   
964.
Polypropylene ionomers have been prepared by sulfonation of copolymers of propene and 7 methyl, 1-6 octadiene, followed by neutralization to cesium salts. Both WAXS and SAXS were used to study the morphology of the samples, while their thermal properties were studied by DSC and their mechanical properties by DMTA. The sulfonation process is shown to cause a further drop in crystallinity in addition to the effect of comonomer incorporation. Ion clustering is observed when the extent of sulfonation is high enough, the limit being dependent on the copolymer composition. The ion pairs which are not incorporated into the cluster cause a small-angle upturn in the WAXS pattern. The mechanical properties are strongly affected by the drop in crystallinity, but may be partly recovered due to ion clustering. No disruption of the ion clusters is observed before thermal decomposition of the polymer.  相似文献   
965.
966.
The structure of an antimicrobial peptide discodermin A isolated from the marine sponge Discodermia kiiensis has been elucidated as CHO-d-Ala-l-Phe-d-Pro-d-t-Leu-l-t-Leu-d-Trp-l-Arg-d-Cys(O3H)-l-Thr-l-MeGln-d-Leu-l-Asn-l-Thr-Sar.  相似文献   
967.
The synthesis of cis- and trans-2,4-diphenylazetidines as well as that of their N-nitroso derivatives is described. The “abnormal” reduction of the N-nitrosamines gives a cis-trans mixture of the expected 1,2-diphenylcyclopropanes. However, no stereochemical correlations could be made owing to the base-induced isomerization of the starting N-nitrosamines during the course of the reaction.  相似文献   
968.
Chang RC  Fritz JS 《Talanta》1978,25(11-12):659-663
Organic pollutants in water are isolated on a mini-sampler tube containing a macroporous resin. The sorbed pollutants are next thermally transferred to a second sorption tube and then to an analytical column where they are separated and determined by temperature-programmed gas chromatography. Excellent recoveries were obtained for tests in which model organic compounds of various classes were added to water. The water sample is much smaller than that required with previous analytical methods.  相似文献   
969.
General analytic formulas for derivatives of real Slater orbitals with respect to the Cartesian coordinates x and y have been derived. The application of this result to molecular geometry optimization or to the construction of a force constant matrix is briefly discussed.  相似文献   
970.
Abstract— The triplet state of tryptophan in the solid environments of a polyvinyl alcohol) (PVA) film and the protein wool keratin has been studied by emission and absorption spectroscopy at room temperature. The decay kinetics of the triplet state vary depending on the conditions under which the study is made. The observation of second order kinetics suggests triplet-triplet interactions play a major role in the deactivation of the tryptophan triplet state in PVA films plasticised by the presence of water vapour. For wool keratin in the presence of air the major mechanism appears to be a first order reaction between tryptophan residues and oxygen. The actual effects of moisture and oxygen on the tryptophan triplet state are discussed.  相似文献   
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