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141.
A heterocyclic peptide nanotube 总被引:3,自引:0,他引:3
An open-ended hollow tubular structure is designed based on hydrogen-bond-directed self-assembly of a chimeric cyclic peptide subunit comprised of alternating alpha- and epsilon-amino acids. The design features a novel 1,4-disubstituted-1,2,3-triazole epsilon-amino acid and its utility as a peptide backbone substitute. The N-Fmoc-protected epsilon-amino acid was synthesized in high yield and optical purity in three steps from readily available starting materials and was employed in solid-phase peptide synthesis to afford the desired cyclic peptide structure. The cyclic peptide self-assembly has been studied in solution by (1)H NMR and mass spectrometry and the resulting tubular ensemble characterized in the solid state by X-ray crystallography. 相似文献
142.
Submicrogram amounts of vanadium in rat liver tissue have been analyzed by rapid activation analysis. A 5-min radiochemical separation coupled with γ-ray spectrometry permitted utilization of the 3.8-min vanadium-52 radioisotope. With this procedure the lower limit of detection at a thermal neutron flux of 1012 n/cm2/sec was about 3·10-9 g of vanadium. 相似文献
143.
Ze'ev V. I. Zaretskii Albert Avraham Ben-Bassat David Lavie 《Journal of heterocyclic chemistry》1975,12(5):837-840
The mass spectra of α-, β- and γ-pyridine aldoximes and the respective O-methyl ethers were studied. The mass spectral behaviour of α-pyridine aldoxime is characterized by the elimination of NO, while the molecular ion of the γ-isomer expels H2 CN. In the case of the β-isomer the formation of the m/e 67 ion (C4H5N) in a concerted process is the main feature. In the α-pyridine aldoxime methyl ether, in sharp contrast to the hydroxy analog, the M-30 peak was found to be due to the elimination of CH2O, the expulsion of NO being absent. The mechanism of the fragmentation reactions is discussed, the conclusion drawn being based on the high resolution measurements as well as on the spectra of the respective deuterioanalogs and on the metastable transitions. 相似文献
144.
A computational strategy to model the amorphous phase of comblike polymers is presented. The strategy, denoted SuSi/CB (CB-configurational bias), combines the strength of an algorithm recently developed to generate reliable microstructures of dense amorphous polymers, which is based on a random search of energy minima, and configurational bias Monte Carlo method. The influence of different parameters used to define the characteristics of SuSi/CB on both the reliability of the generated structures and the computational effort has been examined in detail. Finally, we have modeled and characterized the supramolecular organization of poly(octadecyl acrylate) in the amorphous state. 相似文献
145.
Birney DM 《Organic letters》2004,6(5):851-854
Two possible pathways for the nitrosation of formamide and N-methyl formamide by nitrosonium ion (NO(+)) have been investigated at the B3LYP/6-31G(d,p) level. The key steps are pseudopericyclic 1,3-sigmatropic rearrangements to give the observed N-nitrosamides. The transition structures (8a and 8b) are close to planar on the amide moiety and have remarkably low barriers of only 6.6 and 4.8 kcal/mol from the lowest energy conformations of 6a and 6b, respectively. [reaction: see text] 相似文献
146.
Methods for the incorporation of non-natural amino acids into proteins have advanced significantly over recent years and in this tutorial review we aim to give a general overview of the area. These techniques offer the possibility of modulating the structures and functions of proteins and thus permit the generation of novel designed systems for both biocatalytic and mechanistic studies. Four complementary approaches are discussed in detail along with examples of their application. The advantages and disadvantages of each technique are also discussed. 相似文献
147.
(E)-beta-Trialkylstannyl-alpha,beta-unsaturated ketones are readily available from secondary propargylic alcohols via a two-step sequence involving highly regio- and stereoselective Pd(0)-catalyzed hydrostannation followed by mild oxidation (TPAP). The methodology has been applied to the synthesis of enantiomerically pure enone 12 which is a key intermediate for the total synthesis of zoanthamine, a structurally complex marine natural product. 相似文献
148.
Reaction of the beta-styryl radical with O2 in benzene results in a low yield of benzene oxide, which is shown by isotopic labeling to arise from the solvent. Ab initio and DFT calculations elucidate the mechanism of this reaction, and identify the properties of other radicals that should be more effective promoters of the reaction. The CN radical is found to be one candidate. 相似文献
149.
Fluorescence polarization immunoassay methods for the detection of pesticides and their metabolites or degradation products are reviewed. Advantages and limitations for application to pesticide detection in environmental and food samples are discussed. The influence of the structure of fluorescent-labeled tracers and the affinity and specificity of antibodies on analytical performance is examined. The methods are simple, readily automated, and rapid (total time for assay of a water sample is about 1 min) with sensitivity of 1 - 10 ng/ml pesticide in 0.01 - 0.1 ml sample. 相似文献
150.
An etiobilirubin‐IIβ analog with the central C(10) CH2 group replaced by a diacetylene unit ( 1 ) was synthesized by base‐catalyzed condensation of bis‐[3‐methyl‐4‐ethyl‐5‐formylpyrrol‐2‐yl]‐diacetylene ( 3 ) with 3‐methyl‐4‐ethyl‐5‐p‐toluenesulfonyl‐2‐pyrrolinone ( 10 ). Diacetylenic rubin 1 is a dark red solid, giving orange solutions with uv‐visible absorption maxima near 460 nm. 相似文献