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941.
Kovalchuk A Bricks JL Reck G Rurack K Schulz B Szumna A Weisshoff H 《Chemical communications (Cambridge, England)》2004,(17):1946-1947
A charge transfer-type fluorescent molecular sensor consisting of a bisamidopyridine receptor and two styryl base chromophores shows H(2)PO(4)(-) and acetate-enhanced fluorescence due to the conversion of weak intramolecular hydrogen bonds into strong ones in the host-guest ensemble. 相似文献
942.
A novel method for N-methylation of the cyclic amide in the 1,4-benzodiazepine ring system is presented. Methods traditionally used involve treatment of the 1,4-benzodiazepinone anion with an alkyl halide. It has been demonstrated that these derivatives can be methylated on the amide nitrogen atom by use of dimethyl-formamide dimethyl acetal which acts as both reagent and solvent for the reaction. 相似文献
943.
The conditions for the preparation and cyclisation of the title compounds are described. The stability of the intermediate lithio-thiacyclohexenes is shown to depend on the reaction conditions and the substituents R1-R4. The final products , and arise from via a [1.4] sigmatropic rearrangement, a [1.3]prototropic shift followed by a [2.3] sigmatropic rearrangement, or the elimination of lithium methanethiolate respectively. 相似文献
944.
The preparation and characterization by LCMS of a library of 55 fluorescence- quenched peptides is described. The peptides bear a terminal anthranilamide fluorophore and a penultimate 2,4-dinitrophenyl-L-lysine quencher, and will be used to probe the substrate binding domain of the human blood coagulation enzyme, factor Xa. 相似文献
945.
Kovnir KA Zaikina JV Reshetova LN Olenev AV Dikarev EV Shevelkov AV 《Inorganic chemistry》2004,43(10):3230-3236
A novel tin phosphide bromide, Sn(24)P(19.3(2))Br(8), and Sn(24)P(19.3(2))Br(x)()I(8)(-)(x) (x = 0-8) solid solution have been prepared and structurally characterized. All compounds crystallize with the type-I clathrate structure in the cubic space group Pmn (No. 223). The clathrate framework of the title solid solution shows a remarkable chemical compressibility: the unit cell parameter drops from 10.954(1) to 10.820(1) A on going from x = 0 to x = 8, a feature that has never been observed for normally rigid clathrate frameworks. The chemical compressibility as well as non-Vegard dependence of the unit cell parameter upon the bromine content is attributed to the nonuniform distribution of the guest halogen atoms in the polyhedral cavities of the clathrate framework. The temperature-dependent structural study performed on Sn(24)P(19.3(2))Br(8) has shown that, in contrast to the chemical compressibility, the thermal compressibility (linear contraction) of the phase is similar to that observed for the Group 14 anionic clathrates. The tin phosphide bromide does not undergo phase transition down to 90 K, and the atomic displacement parameters for all atoms decrease linearly upon lowering the temperature. These linear dependencies have been used to assess such physical constants as Debye temperature, 220 K, and the lattice part of thermal conductivity, 0.7 W/(m K). Principal differences between the title compounds and the group 14 anionic clathrates are highlighted, and the prospects of creating new thermoelectric materials based on cationic clathrates are briefly discussed. 相似文献
946.
Stefan Brode Hans Horn Michael Ehrig Diane Moldrup Julia E. Rice Reinhart Ahlrichs 《Journal of computational chemistry》1993,14(10):1142-1148
A parallel direct SCF and gradient program for workstation clusters has been implemented on the basis of the ab initio program package TURBOMOLE. Applications on large molecular systems monitor an appreciable speedup in residence time. © John Wiley & Sons, Inc. 相似文献
947.
Nadal ML Bosch J Vila JM Klein G Ricart S Moretó JM 《Journal of the American Chemical Society》2005,127(30):10476-10477
We report here on a highly efficient catalytic method to synthesize intermolecularly the cyclopentane skeleton from starting products as simple as allyl halides, alkynes, and carbon monoxide under very mild reaction conditions by means of a substoichiometric amount of iron, acetone, and a catalytic amount of Ni(II) iodide. 相似文献
948.
Fruetel JA Renzi RF Vandernoot VA Stamps J Horn BA West JA Ferko S Crocker R Bailey CG Arnold D Wiedenman B Choi WY Yee D Shokair I Hasselbrink E Paul P Rakestraw D Padgen D 《Electrophoresis》2005,26(6):1144-1154
We report the development of a hand-held instrument capable of performing two simultaneous microchip separations (gel and zone electrophoresis), and demonstrate this instrument for the detection of protein biotoxins. Two orthogonal analysis methods are chosen over a single method in order to improve the probability of positive identification of the biotoxin in an unknown mixture. Separations are performed on a single fused-silica wafer containing two separation channels. The chip is housed in a microfluidic manifold that utilizes o-ring sealed fittings to enable facile and reproducible fluidic connection to the chip. Sample is introduced by syringe injection into a septum-sealed port on the device exterior that connects to a sample loop etched onto the chip. Detection of low nanomolar concentrations of fluorescamine-labeled proteins is achieved using a miniaturized laser-induced fluorescence detection module employing two diode lasers, one per separation channel. Independently controlled miniature high-voltage power supplies enable fully programmable electrokinetic sample injection and analysis. As a demonstration of the portability of this instrument, we evaluated its performance in a laboratory field test at the Defence Science and Technology Laboratory with a series of biotoxin variants. The two separation methods cleanly distinguish between members of a biotoxin test set. Analysis of naturally occurring variants of ricin and two closely related staphylococcal enterotoxins indicates the two methods can be used to readily identify ricin in its different forms and can discriminate between two enterotoxin isoforms. 相似文献
949.
Pérez-Prieto J Boscá F Galian RE Lahoz A Domingo LR Miranda MA 《The Journal of organic chemistry》2003,68(13):5104-5113
Laser flash photolysis, density functional theory (DFT) calculations, and product studies have been performed to understand the mechanism of photoreduction of 2-benzoylthiophene (BT) in the presence of phenol or indole. Time-resolved experiments showed that BT ketyl (BTH) and phenoxy (PhO) or indolyl (In) radicals are generated with high rate constants and quantum yields close to 1. However, low conversions (specially in the case of indole) of the starting reagents are obtained upon prolonged lamp irradiation, indicating that recombination within the radical pairs must occur to a large extent, regenerating the starting materials. The solvent-dependence of the quenching rate constants, together with DFT theoretical studies, indicate fundamental differences between the mechanisms of the reaction of BT triplet with phenol and indole. Thus, data for phenol agree with the involvement of a hydrogen-bonded exciplex BT(.)HOPh, where concerted electron and proton transfer leads to the BTH(.)OPh radical pair. However, in the case of indole, electron transfer at the BT(.)HIn stage precedes proton transfer. Finally, C-C cross-coupling products have been isolated and characterized in the preparative irradiation of BT in the presence of phenol and indole. The structures of the products have been confirmed by alternative synthesis. 相似文献
950.
The Reaction Behaviour of the Polycylic Oligoalumosiloxane [Ph2SiO]8[AlO(OH)]4 towards Hexamethyldisilazane The reaction of the oligoalumosiloxane [Ph2SiO]8[AlO(OH)]4 ( 1 ) with hexamethyldisilazane leads to the triple ionic [Ph2SiO]8[AlO2]2[AlO(O‐SiMe3)]2[NH4·THF]2·2 THF ( 2 ) and in the presence of pyridine to [Ph2SiO]8[AlO1.5]4·2py·1.5 C7H8 ( 3 ). Apart from the usual characterization techniques (NMR and IR spectroscopy) the molecular structures of 2 and 3 have been determined by single‐X‐ray diffraction analyses. Both alumosiloxanes 2 and 3 present new types of molecular structures with a central four membered Al2O2‐ring, on which the further aluminium atoms are attached via oxygen atoms. This leads to an Al4‐lozenge, which is centered in subtriangles by oxygen atoms. 相似文献