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51.
The Schmidt reaction is the acid-catalyzed analogue of the Curtius reaction and is extensively used in organic synthesis. In this work, the mechanism of this reaction has been explored using DFT calculations at the B3LYP/6-311+G(d,p) level. Protonated formyl azide may undergo rearrangement to the product, protonated isocyanic acid, with simultaneous extrusion of molecular nitrogen (concerted mechanism), or undergo rearrangement to the anti conformer, followed by removal of nitrogen to form the nitrenium ion, which then rearranges to the final product, protonated isocyanic acid (step-wise mechanism). Like the Curtius reaction, it is found that the concerted pathway is definitely preferred. The key role of acidification in decreasing the overall energy barrier is more highlighted in case of phenyl substitution, with negligible effect on the lower homologues. For methoxy and amine substituents, there is very little difference in the activation energies of the concerted and step-wise reactions, with the former being still slightly preferred. Unlike the parent compound, the rearrangement of substituted nitrenium ion in some cases involves side reactions like C-H insertion and cyclization. 相似文献
52.
A tri-armed-pyrene-linked molecular receptor, 5 has been designed, synthesised and evaluated for ionic recognition. It has been observed that the synthesised molecular receptor can recognise mercury and cyanide ions through a change in colour, UV–Vis and fluorescence intensity. The binding stoichiometry of the receptor and these ionic species has been found to be 1:1 through Job’s plots, Benesi–Hildebrand plots and isothermal titration calorimetry (ITC). 相似文献
53.
Heikkinen JJ Kivimäki L Määttä JA Mäkelä I Hakalahti L Takkinen K Kulomaa MS Hytönen VP Hormi OE 《Colloids and surfaces. B, Biointerfaces》2011,87(2):409-414
A bio-ink for covalent deposition of thermostable, high affinity biotin-binding chimeric avidin onto sol-gel substrates was developed. The bio-ink was prepared from heterobifunctional crosslinker 6-maleimidohexanoic acid N-hydroxysuccinimide which was first reacted either with 3-aminopropyltriethoxysilane or 3-aminopropyldimethylethoxysilane to form silane linkers 6-maleimide-N-(3-(triethoxysilyl)propyl)hexanamide or -(ethoxydimethylsilyl)propyl)-hexanamide. C-terminal cysteine genetically engineered to chimeric avidin was reacted with the maleimide group of silane linker in methanol/PBS solution to form a suspension, which was printed on sol-gel modified PMMA film. Different concentrations of chimeric avidin and ratios between silane linkers were tested to find the best properties for the bio-ink to enable gravure or inkjet printing. Bio-ink prepared from 3-aminopropyltriethoxysilane was found to provide the highest amount of active immobilized chimeric avidin. The developed bio-ink was shown to be valuable for automated fabrication of avidin-functionalized polymer films. 相似文献
54.
Yanfei YangGaurav Arora Fernando A. FernandezJennifer D. Crawford Kazimierz SurowiecEun Kyung Lee Richard A. Bartsch 《Tetrahedron》2011,67(7):1389-1397
Two series of di-ionizable calix[4]arene-crown-5 isomers in the cone conformation are synthesized to probe the effect of the pendant acidic group location on their metal ion extraction properties. In one series, the ionizable groups are attached to the lower rim of the calix[4]arene scaffold, which orients them near the crown ether cavity. In the second series, the ionizable groups are connected to the upper rim positioning them away from the crown ether ring, but close to the hydrophobic pocket of the calix[4]arene unit. The metal ion extraction behaviors of the two series of ligands are compared in extractions of alkaline earth metal cations, Hg2+, and Pb2+. 相似文献
55.
Fungal isolates (Aspergillus wentii 1, A. wentii 2, Penicillium citrinum, Penicillium granulatum) were selected to study their in vitro antioxidant potential by various assay procedures. Czapek–Dox’s medium was selected
for the growth of fungi as it supported the best antioxidant activity based on their EC50 values, P. citrinum was the best followed by P. granulatum, A. wentii 1, and A. wentii 2. The chromatographic analyses showed several compounds possessing antioxidant activity in the fungal extracts. Two such
compounds were partially purified from P. citrinum which demonstrated potent antioxidant activity, equally effective or better than some of the standard antioxidants. 相似文献
56.
Wallace IM Urbanus ML Luciani GM Burns AR Han MK Wang H Arora K Heisler LE Proctor M St Onge RP Roemer T Roy PJ Cummins CL Bader GD Nislow C Giaever G 《Chemistry & biology》2011,18(10):1273-1283
Preselection of compounds that are more likely to induce a phenotype can increase the efficiency and reduce the costs for model organism screening. To identify such molecules, we screened ~81,000 compounds in Saccharomyces cerevisiae and identified ~7500 that inhibit cell growth. Screening these growth-inhibitory molecules across a diverse panel of model organisms resulted in an increased phenotypic hit-rate. These data were used to build a model to predict compounds that inhibit yeast growth. Empirical and in silico application of the model enriched the discovery of bioactive compounds in diverse model organisms. To demonstrate the potential of these molecules as lead chemical probes, we used chemogenomic profiling in yeast and identified specific inhibitors of lanosterol synthase and of stearoyl-CoA 9-desaturase. As community resources, the ~7500 growth-inhibitory molecules have been made commercially available and the computational model and filter used are provided. 相似文献
57.
Synthesis of a novel class of multinucleate pyrimidine chalcogen (S/Se/Te) derivatives has been successfully attempted for the first time by the selective substitution of chlorine at the C-2 position of 2,4-dichloropyrimidine with nucleophilic dichalcogenide anion E22− (E = S, Se, Te) to afford bis[4-chloro-2-pyrimidyl] dichalcogenide. The highly electrophilic nature of 2,4-dichloropyrimidine compared to aryl chlorides has been further exploited to prepare a variety of 4-chloro-2-(arylchalcogenyl) pyrimidine compounds by substituting the chlorine exclusively at the C-2 position of 2,4-dichloropyrimidine with a variety of chalcogen bearing aryl anions ArE− (Ar = phenyl, 1-naphthyl, p-tolyl, 4,6-dimethyl-2-pyrimidyl, 2-pyridyl, 4-methyl-2-pyridyl). All the newly prepared symmetrical and unsymmetrical pyrimidyl chalcogen compounds have been thoroughly characterized with the help of various spectroscopic techniques viz., NMR (1H, 13C, 77Se), FT-IR and mass spectrometry (in representative cases). The crystal structures of 4-chloro-2-(phenylselanyl) pyrimidine and 2-(p-tolylselanyl)-4-chloropyrimidine have been determined by X-ray crystallography. 相似文献
58.
The activation of nuclear factor-kappa B1 (NFkB1) in cancer cells may confer resistance to ionizing radiation (IR). To enhance the therapeutic efficiency of IR in lung cancer, we screened for microRNAs (miRNAs) that suppress NFkB1 and observed their effects on radiosensitivity in a human lung cancer cell line. From time series data of miRNA expression in γ-irradiated H1299 human lung cancer cells, we found that the expression of miR-9 was inversely correlated with that of NFκB1. Overexpression of miR-9 down-regulated the level of NFκB1 in H1299 cells, and the surviving fraction of γ-irradiated cells was decreased. Interestingly, let-7g also suppressed the expression of NFκB1, although there was no canonical target site for let-7g in the NFκB1 3' untranslated region. From these results, we conclude that the expression of miR-9 and let-7g could enhance the efficiency of radiotherapy for lung cancer treatment through the inhibition of NFκB1. 相似文献
59.
For an integer k ≥ 2, kth‐order slant Toeplitz operator Uφ [1] with symbol φ in L∞(??), where ?? is the unit circle in the complex plane, is an operator whose representing matrixM = (αij ) is given by αij = 〈φ, zki–j〉, where 〈. , .〉 is the usual inner product in L2(??). The operator Vφ denotes the compression of Uφ to H2(??) (Hardy space). Algebraic and spectral properties of the operator Vφ are discussed. It is proved that spectral radius of Vφ equals the spectral radius of Uφ, if φ is analytic or co‐analytic, and if Tφ is invertible then the spectrum of Vφ contains a closed disc and the interior of the disc consists of eigenvalues of infinite multiplicities. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
60.
M. J. Adamovich M. M. Aggarwal Y. A. Alexandrov R. Amirikas N. P. Andreeva Z. V. Anzon R. Arora F. A. Avetyan S. K. Badyal A. M. Bakich et al. 《Zeitschrift fur Physik C Particles and Fields》1995,65(3):421-429
The mechanism for producing slow, target associated particles in high energy heavy ion collisions is investigated. It is shown that the same mechanism which was proposed for hadron induced interactions is likely to appear also for heavy-ion reactions. The results indicate however a much weaker correlation between impact parameter and yield of slow particles. 相似文献