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751.
Azobenzenes have attracted great interest in recent years because of their ability to change conformation upon irradiation. This property has been featured in several applications not only in organic chemistry but also in biology. Even though monoazobenzenes have been extensively studied and documented in the literature, only a few methods are available for the synthesis of oligo-ortho-azobenzenes. Also, their photochemical properties have not been reported so far. This study shows an efficient strategy for the preparation of oligo-ortho-azobenzenes and the investigation of their photochemical properties. It is demonstrated that the absorption spectra are highly influenced by the substituents. Interestingly, none of the ortho-bis-, tris-, or tetra-azobenzenes showed any E → Z isomerization. Only the ortho-nitrogen-substituted monoazobenzenes' photochromic behavior upon UV irradiation was observed. 相似文献
752.
Goddard-Borger ED Carapito R Jeltsch JM Phalip V Stick RV Varrot A 《Chemical communications (Cambridge, England)》2011,47(34):9684-9686
As part of continued efforts to understand the mechanisms of 1,5-α-l-arabinanases better, some arabinan-like iminosugar oligosaccharides were synthesized. An iminosugar analogue of arabinobiose was found to be a good inhibitor of the arabinanase Arb93A from Fusarium graminearum. Structures were determined for complexes of this inhibitor with wild-type Arb93A and a catalytically inactive mutant. 相似文献
753.
The possibility to modulate molecules reversibly by light has been fascinating chemists early on. One of the most powerful photochromic classes of compounds are azobenzenes, which have been incorporated in multiple molecular systems to alter their functionality. Recently, the incorporation of azobenzenes into macrocyclic scaffolds, azobenzenophanes, revealed a novel aspect of this interesting photoswitch. Especially, the build-in of more than one azobenzene moiety into the structure creates photochromic compounds with multiple accessible states. The cyclic arrangement also leads to a change in the photochemical properties, which offer new opportunities for functional molecular devices. In this article the synthesis as well as the photochemistry including applications of macrocyclic azobenzenes, containing more than one azobenzene unit, oligoazobenzenophanes, are reviewed. 相似文献
754.
Deschler F Da Como E Limmer T Tautz R Godde T Bayer M von Hauff E Yilmaz S Allard S Scherf U Feldmann J 《Physical review letters》2011,107(12):127402
We investigate the effect of molecular doping on the recombination of electrons and holes localized at conjugated-polymer-fullerene interfaces. We demonstrate that a low concentration of p-type dopant molecules (<4% weight) reduces the interfacial recombination via charge transfer excitons and results in a favored formation of separated carriers. This is observed by the ultrafast quenching of photoluminescence from charge transfer excitons and the increase in photoinduced polaron density by ~70%. The results are consistent with a reduced formation of emissive charge transfer excitons, induced by state filling of tail states. 相似文献
755.
Metabolic engineering seeks to redirect metabolic pathways through the modification of specific biochemical reactions or the introduction of new ones with the use of recombinant technology. Many of the chemicals synthesized via introduction of product-specific enzymes or the reconstruction of entire metabolic pathways into engineered hosts that can sustain production and can synthesize high yields of the desired product as yields of natural product-derived compounds are frequently low, and chemical processes can be both energy and material expensive; current endeavors have focused on using biologically derived processes as alternatives to chemical synthesis. Such economically favorable manufacturing processes pursue goals related to sustainable development and “green chemistry”. Metabolic engineering is a multidisciplinary approach, involving chemical engineering, molecular biology, biochemistry, and analytical chemistry. Recent advances in molecular biology, genome-scale models, theoretical understanding, and kinetic modeling has increased interest in using metabolic engineering to redirect metabolic fluxes for industrial and therapeutic purposes. The use of metabolic engineering has increased the productivity of industrially pertinent small molecules, alcohol-based biofuels, and biodiesel. Here, we highlight developments in the practical and theoretical strategies and technologies available for the metabolic engineering of simple systems and address current limitations. 相似文献
756.
Rodica Elena Chiriac Raphael Lornage Ludovic Fine Jean Carre Jean Louis Gass Thomas Lagier 《International journal of environmental analytical chemistry》2013,93(1):43-55
The development and use of a pre-concentrator-thermo-desorber/micro-gas chromatograph/mass spectrometer (μTD/μGC/MSD) coupling for the on-site analysis of VOCs in landfill gases are presented. The coupling has the advantage of analysing compounds with two detectors operated in series: the TCD (of the μGC) initially analyses the gas without destroying it, and then the MSD identifies the compounds. Due to the TCD response, the results were quantified with reference to toluene. The reliability of the analytical chain for quantitative analysis was validated by sampling two gaseous standards, including the EPA TO14 mixture, containing 39 compounds. With the OV1?μGC column, 24 compounds were identified and 16 correctly quantified. The repeatability of the measures estimated by their standard deviation was in the order of 1–2%. The detection limit was evaluated at 0.1?ppbv, for a 40?min pre-concentration on the Tenax of the μTD. The results of VOC analyses in the air of a landfill site obtained with the μTD/μGC/MSD coupling show its potential for on-site analyses: immediate results, high sensitivity, no storage for the samples, and measurements of pollution peaks. 相似文献
757.
Abstract Direct polycondensations of β-benzyl-l-aspartate (Asp.Bz) and β-benzyl-l-glutamate (Glu.Bz) were carried out in the presence of diphenyl phosphoryl azide (DPPA) as a condensation agent and triethyl amine (TEA). Poly(amino acid)s were obtained by this convenient approach whose structure was confirmed by IR and 1H-NMR spectroscopy. The effects of the monomer concentration, the polymerization time and temperature, the ratios [DPPA]/[monomer] and [TEA]/[monomer], and the solvent used on the molecular weight distribution of the polymer were studied. When the monomer concentrations were higher than 0.2 g/mL, poly(Asp.Bz) with a bimodal molecular weight distribution was obtained (Mw of 37,000 and Mw/Mn of 1.68). The polycondensations carried out in THF or in bulk provided the highest molecular weight (Mw ? 40,000). Several other amino acids were also polymerized by DPPA. 相似文献
758.
Impact of strain induced by polymer curing in benzocyclobutene embedded semiconductor nanostructures
Genziana Bussone Emmanouil Dimakis Raphael Grifone Andreas Biermanns Abbes Tahraoui Dina Carbone Lutz Geelhaar Tobias U. Schülli Ullrich Pietsch 《固体物理学:研究快报》2014,8(12):1007-1010
Polymers such as benzocyclobutene are commonly used as embedding materials for semiconductor nanostructures. During the curing process of the polymer up to 250 °C, a significant impact of strain can be induced on the embedded semiconductor material due to different thermal expansion coefficients. This strain has been revealed by X‐ray diffraction in free‐standing GaAs nanowires grown on a silicon substrate, embedded in a polymer matrix. It will be shown that this strain is released during the X‐ray irradiation if additionally an external static electric field is applied.
759.
We present a hybrid framework which aims at the modelling and simulation of Internal Traverse Grinding of hardened 100Cr6/AISI 52100 by using electro plated cBN grinding wheels. We focus on the thermo-mechanical loading conditions on the workpiece that results from the interaction of workpiece and tool. The modelling framework basically consists of three components, namely representative plane strain adaptive finite element simulations on a meso-scale, capturing the proximity of a single cBN grain when cutting through the workpiece bulk. Secondly, we incorporate a kinematic simulation on the process level to gain detailed simulation-based information on the transient grain-bulk-interaction. The third component of the framework consists of a macro-scale process model that uses the superposed results of the former two components as thermo-mechanical boundary conditions. Using this framework, we target the prediction of metallurgical effects, such as white layers, on the workpiece on the macro scale in the near future. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
760.
Raphael A. Seidel Björn Schowtka Maurice Klopfleisch Toni Kühl Andreas Weiland Alexander Koch Helmar Görls Diana Imhof Georg Pohnert Matthias Westerhausen 《Tetrahedron letters》2014
Bilirubin oxidation end products (BOXes) show significant physiological effects and are connected to severe diseases such as subarachnoid hemorrhage induced cerebral vasospasm. BOX B (2-(4-ethenyl-3-methyl-5-oxo-1,5-dihydro-2H-pyrrol-2-ylidene)ethanamide) was prepared via a five-step synthesis starting from methyl (4-bromo-3-methyl-5-oxofuran-2(5H)-ylidene)ethanoate that was vinylated and then reacted with NH4OAc, LiOH, (COCl)2, and finally with ammonia yielding Z-BOX B. Derivatives of Z-BOX A and Z-BOX B with [15N]labeled lactam rings were synthesized accordingly. 相似文献