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71.
Recent research performed in our laboratory (using a butyrylcholinesterase + choline oxidase enzyme electrode) suggested the validity of the biosensor approach using enzyme inhibition OPEEs (i.e. enzyme electrodes working in organic phase) in the case of organophosphorus and carbamate pesticides, which are poorly soluble in aqueous solutions. Since these pesticides are generally much more soluble in chloroform than in water, the present research aimed at analysing this class of pesticides using a tyrosinase inhibition OPEE operating in water-saturated chloroform medium. The tyrosinase biosensor was assembled using an oxygen amperometric transducer coupled to the tyrosinase enzyme, immobilized in kappa-carrageenan gel. Lastly a detailed comparison between the inhibition monoenzymatic tyrosinase and inhibition bienzymatic (butyrylcholinesterase + choline oxidase) OPEEs was performed and discussed in this work. 相似文献
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73.
Eric J. Goethals Wouter Reyntjens Xiaochun Zhang Beatrice Verdonck Ton Loontjens 《Macromolecular Symposia》2000,157(1):93-100
Sequential living cationic polymerization of octadecyl vinyl ether (ODVE) and methyl vinyl ether (MVE) was used for the preparation of amphiphilic ABA‐type block copolymers. The polymerization of ODVE was initiated with the trimethyl silyl iodide/1,1,3,3‐tetramethoxy propane/ZnI2 system at 0°C in toluene. The living bifunctional polyODVE thus obtained was used as initiator for the polymerization of MVE. Below the LCST of polyMVE (37°C), the copolymers are amphiphiles. Above the LCST of polyMVE, the polyMVE‐blocks become hydrophobic and the amphiphilic nature of the block copolymer is lost. This was demonstrated by using the block copolymers as emulsifiers for water/decane mixtures. The emulsions were stable for several hours at room temperature, while the emulsion stability decreased to about 30 seconds at 40°C. PolyMVE‐α,ω‐bis‐methacrylates were obtained by end‐capping of living bifunctional polyMVE with 2‐hydroxyethyl methacrylate (HEMA). Copolymerization of these bis‐macromers with HEMA leads to segmented networks. The networks showed a reversible swelling/deswelling behavior in water as a function of temperature. This is caused by a change of the hydrophilicity of the polyMVE segments in the networks. Hexa(chloromethyl)melamine, combined with zinc chloride was found to be an efficient hexafunctional initiator for the living cationic polymerization of vinyl ethers. This simple initiating system opens new ways for the synthesis of endgroup‐functionalized star‐shaped poly(vinyl ethers). 相似文献
74.
75.
Kapil Shyam Lokare Nicolas Frank Beatrice Braun‐Cula Itziar Goikoetxea Joachim Sauer Christian Limberg 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(40):12513-12517
To gain molecular level insights into the properties of certain functions and units of extended oxides/hydroxides, suitable molecular model compounds are needed. As an attractive route to access such compounds the trapping of early intermediates during the hydrolysis of suitable precursor compounds with the aid of stabilizing ligands is conceivable, which was tested for the aluminum(III)/water system. Indeed, trisilanols proved suitable trapping reagents: their presence during the hydrolysis of AliBu2H in dependence on the amount of water used allowed for the isolation of tri‐ and octanuclear aluminum hydroxide cluster complexes [Al3(μ2‐OH)3(THF)3(PhSi(OSiPh2O)3)2] ( 1 ) and [Al8(μ3‐OH)2(μ2‐OH)10(THF)3(p‐anisylSi(OSiPh2O)3)4] ( 2 ). 1 can be regarded as the Al(OH)3 cyclic trimer, where six protons have been replaced by silyl residues. While 2 features a unique [Al8(μ3‐OH)2(μ2‐OH)10]12+ core. In contrast to most other known aggregates of this type, 1 and 2 can be readily prepared at reasonable scales, dissolve in common solvents, and retain an intact framework even in the presence of excessive amounts of water. This finding paves the way to future research addressing the reactivity of the individual functional groups. 相似文献
76.
Beatrice Malgesini Eduard Felder Nicola Mongelli Gianluca Papeo 《Molecular diversity》2009,13(1):53-56
Polyfluorinated N-α-Fmoc--Boc-l-lysine represents the best-in-class among a set of polyfluorinated amino acids (PFAs) which are useful tools for 19F NMR-Based Screening. In this communication, optimized reaction conditions that allowed for the multi-gram preparation of
this unnatural amino acid are reported. 相似文献
77.
A rapid protocol for the multicomponent microwave-assisted organocatalytic domino Knoevenagel/hetero Diels-Alder reaction (DKHDA) has been developed for the synthesis of 2,3-dihydropyran[2,3-c]pyrazoles. The reported procedure could be used for the fast generation of novel substituted 2,3-dihydropyran[2,3-c]pyrazoles with potential anti-tuberculosis activity. 相似文献
78.
Twinkling fractal theory of the glass transition: Rate dependence and time–temperature superposition
Richard P. Wool Alejandrina Campanella 《Journal of polymer science. Part A, Polymer chemistry》2009,47(24):2578-2590
The twinkling fractal theory (TFT) of the glass transition temperature Tg provides a new method of analyzing rate effects and time–temperature superposition in amorphous materials. The rate dependence of Tg was examined in the light of new experimental and theoretical evidence for the nature of the dynamic heterogeneity near Tg. As Tg is approached from above, dynamic solid fractal clusters begin to form and eventually percolate rigidity at Tg. The percolation cluster is a solid fractal and to the observer, appears to “twinkle” as solid and liquid clusters interchange in dynamic equilibrium with a vibrational density of states g(ω) ∼ ω. The solid-to-liquid twinkling frequencies ωTF are controlled by the Boltzmann population of intermolecular oscillators in excited energy levels of their anharmonic potential energy functions U(x) such that ωTF = ω exp −B(T*2 − T2)/kT in which T* ≈ 1.2Tg. An oscillator changes from a solid to a liquid when a thermal fluctuation causes it to expand beyond its inflection point in the anharmonic potential. This leads to a continuous solid fraction Ps near Tg given by PS ≈ 1−[(1 − pc) T/Tg] where pc ≈ 1/2 is the rigidity percolation threshold. Since g(ω) is continuous from very low to very high frequencies, the complex twinkling dynamics existing near Tg produces a continuous relaxation spectrum with many different length scales and times associated with the fractal clusters. The twinkling frequencies control the kinetics of Tg such that for a given observation time t when the rate γ > 1/t, only those parts of the twinkling spectrum with ω > γ can contribute to relaxation or percolation upto time t. The most important results in this article are as follows: The TFT describes the rate dependence of Tg, both for DSC thermal heating/cooling rates and DMA frequencies as the classic Tg − lnγ law as Tg(γ) = Tgo + (k/2B) ln γ/γo in which the constant B = 0.3 cal/mol K2. The constant B appears quite universal for the 17 thermoset polymers investigated in this study and 18 linear polymers investigated by others. Many other amorphous metal and ceramic glass materials exhibited the same rate law but required a new B value approximately half that for polymers. The same B = 0.3 value was also used to successfully describe the TTS shift factors using the twinkling fractal frequencies ωTF = ωexp −B(T*2 − T2)/kT, as ln aT(TFT) = exp B(TR2 − T2)/kT, which gave comparable results with the classical WLF equation, log aT = [−C1(T − TR)]/[C2 + (T − TR)]. The advantage of the TFT over the WLF is that C1 and C2 are not universal constants and must be determined for every material, whereas the TFT uses one known constant B which appears to be the same for all polymers. The TFT has also been found to describe the strong and fragile nature of the viscosity behavior of liquids and the rate and temperature dependence of the yield stress in polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2578–2590, 2009 相似文献
79.
Nienhaus GU Nienhaus K Hölzle A Ivanchenko S Renzi F Oswald F Wolff M Schmitt F Röcker C Vallone B Weidemann W Heilker R Nar H Wiedenmann J 《Photochemistry and photobiology》2006,82(2):351-358
EosFP is a fluorescent protein from the coral Lobophyllia hemprichii that changes its fluorescence emission from green to red upon irradiation with near-UV light. Here we present the spectroscopic properties of wild-type EosFP and a variety of monomeric and dimeric mutants and provide a structural interpretation of its oligomerization and photoconversion, which is based on X-ray structure analysis of the green and red species that we reported recently. Because functional expression of the monomeric EosFP variant is limited to temperatures of 30 degrees C, we have developed a tandem dimer. This construct, in which two EosFP subunits are connected by a flexible 12 amino acid linker, expresses well after fusion with the androgen and endothelin A receptors at 37 degrees C. A variety of applications in cellular imaging, developmental biology and automated high-content screening applications are presented, which demonstrate that EosFP is a powerful tool for in vivo monitoring of cellular processes. 相似文献
80.