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The perfluoroaryl tellurolates C6F5TeLi (1) and 4-CF3C6F4TeLi (2) were prepared. These intermediates were identified by NMR spectroscopy and may form, depending on the reaction conditions, either the corresponding ditellanes C6F5TeTeC6F5 (3) and CF3C6F4TeTeC6F4CF3 (4) by subsequent oxidation, or in the case of 1, a telluranthrene (C6F4Te)2 (5) by reaction with itself. The halogenation products of 5, ( C6F4Te)2F4 (6), (C6F4Te)2Cl4 (7), (C6F4Te)2Br4 (8), as well as the azidation product (C6F4Te)2(N3)4 (9) were synthesized. Furthermore, in pursuit of our recent work on tellurium azides, the syntheses and properties of R2Te(N3)2 (R=CF3 (10), C6F2H3 (11)) and RTe(N3)3 (R=CF3 (12) and C6F5 (13)) are reported. The crystal structures of CF3C6F4TeTeC6F4CF3 (4), (C6F4Te)2Br4 (8), and (C6F2H3)2Te(N3)2 (11) were determined.  相似文献   
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The synthesis and peptide-binding properties of a Zn(II)nitrilotriacetate complex substituted with pyrimidine hydrazine amides are reported. The metal complex provides millimolar binding affinity in aqueous buffer to peptides bearing N-terminal His. The pyrimidine heterocycles intermolecularly interact with the bound peptide and quench the emission of nearby Trp residues by energy transfer.  相似文献   
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Flowers of Jasminum rincospernum convert deuterium-labeled jasmonic acid [2H5]- 4a and methyl 1,2-didehy-drojasmonate [2H4]- 8 into labeled cis-jasmone [2H4]- 1. The labeling pattern of the resulting cis-jasmone ( 1 ) is consistent with a Grob fragmentation of the didehydrojasmonic acid 8a by decarboxylation after protonation of the keto group. The pathway is also operative in leaves of several higher plants, including mono- and dicotyledonous specimens. In Lima beans besides cis-jasmone ( 1 ) an equimolar mixture of trans- and cis-isomers of methyl jasmonate ( 4 ) and epi- 4 , is emitted after treatment with Jasmonic acid ( 4a ). The relative ratio of 1 and 4 /epi- 4 is critically dependent on the concentration of the administered jasmonic acid ( 4a ) and the ambient temperature of the plant. Unlike 4a , the 1,2-didehydrojasmonic acid ( 8a ) is not able to induce volatile biosynthesis. Therefore, the transformation of 4a via 8 a into 1 appears to have a special importance for the irreversible inactivation and disposal of the plant stress hormone jasmonic acid to the gas phase and may serve, besides other modes of inactivation, as a shunt in case of high internal of the stress hormone 4a. The conversion of the biologically active jasmonic acid ( 4a ) into the inactive and volatile cis-jasmone (1) is the first example of a disposal of an inactive metabolite of a phytohormone to the gas phase as an infinite sink.  相似文献   
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Ab initio MO calculations have been performed for neutral and cationic C2H2F2 structures. Olefinic and carbene structures are investigated for the neutral isomers, while olefinic, carbene, and fluoronium-type cations are found. Stability orders and rotational barriers are discussed in terms of orbital and Coulomb interaction. Contrary to previous studies, the higher stability of the geminal isomers is interpreted to be caused by Coulomb attraction.  相似文献   
39.
The optical absorption of anthracene vapour for photon energies from 5 to 8.5 eV was found to differ in finer structure from the spectra reported earlier for parts of this range. Above the strong 1B2u long axis polarized πlπ* transition at 5.24 eV three short axis polarized 1B1u ππ* transitions are assigned on the basis of the oriented gas model in comparison to spectra from anthracene single crystals. A tentative new assignment for most of the additionally observed sharp Rydberg bands leading to the first ionization potential at 7.47 eV is given.  相似文献   
40.
X-ray crystallography and NMR spectroscopy provide the only sources of experimental data from which protein structures can be analyzed at high or even atomic resolution. The degree to which these methods complement each other as sources of structural knowledge is a matter of debate; it is often proposed that small proteins yielding high quality, readily analyzed NMR spectra are a subset of those that readily yield strongly diffracting crystals. We have examined the correlation between NMR spectral quality and success in structure determination by X-ray crystallography for 159 prokaryotic and eukaryotic proteins, prescreened to avoid proteins providing polydisperse and/or aggregated samples. This study demonstrates that, across this protein sample set, the quality of a protein's [15N-1H]-heteronuclear correlation (HSQC) spectrum recorded under conditions generally suitable for 3D structure determination by NMR, a key predictor of the ability to determine a structure by NMR, is not correlated with successful crystallization and structure determination by X-ray crystallography. These results, together with similar results of an independent study presented in the accompanying paper (Yee, et al., J. Am. Chem. Soc., accompanying paper), demonstrate that X-ray crystallography and NMR often provide complementary sources of structural data and that both methods are required in order to optimize success for as many targets as possible in large-scale structural proteomics efforts.  相似文献   
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