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101.
The ligand precursors P(CH2NH-3,5-(CF3)2C6H3)3 (1a), P(CH2NHPh)3 (1b), and P(CH2NH-3,5-Me2C6H3)3 (1c), react with the reagents Ti(NMe2)4 and tBuN=Ta(NEt2)3 to generate metal complexes of the type P(CH2NAr(R))3TiNMe2 (2a-c) and P(CH2NAr(R))3Ta=NtBu (3a-c) (where Ar(R) = 3,5-(CF3)2C6H3, Ph, and 3,5-Me2C6H3). Due to ring strain, the phosphine lone pair cannot chelate and is available to bind a second metal, and this feature can be utilized to synthesize heterometallic polynuclear complexes. The 31P chemical shifts observed upon complexation of the early transition metals to the amido donors are large and in the opposite direction expected for the increased C-P-C bond angles in these complexes; these unusual shifts are due to P-Ti and P-Ta distances that are significantly shorter than the sum of van der Waals radii. The reaction of 2c with Ni(CO)4 produces at first the bimetallic complex (CO)3Ni[P(CH2N-3,5-Me2C6H3)3TiNMe2] (4c), which gradually converts to the trimetallic complex (CO)2Ni[P(CH2N-3,5-Me2C6H3)3TiNMe2]2 (5c). The effect of the complexation of Ti and Ta fragments on the donor ability of the phosphine ligand was determined by the preparation of the bis-phosphine complexes trans-L(2)Rh(CO)Cl, (where L = 1a-c, 2a-c, and 3a-c) prepared by the reaction of the appropriate phosphine with [Rh(CO)2(mu-Cl)]2, and a measurement of the resultant CO stretching frequencies. Surprisingly, the complexes with the larger C-P-C angles are significantly poorer donors. Density functional theory calculations were performed to determine what factors affect the donor ability of the phosphine and if through-space interactions might play an important role in the observed electronic properties. 相似文献
102.
In this paper the (2 + 1)-dimensional Boiti-Leon-Pempinelli (BLP) equation will be studied. The tanh-coth method will be used to obtain exact travelling wave solutions for this equation. The Exp-function method will also be applied to the BLP equation to derive a new variety of travelling wave solutions with distinct physical structures. 相似文献
103.
A protocol for the construction of poly-oxazoles with consecutive 2,4'-linkages is described, and has afforded an efficient route to a penta-oxazole which demarcates a route to telomestatin and related macrocyclic poly-oxazole systems. 相似文献
104.
Commercially available titania (TiO2) is reported as an extremely efficient catalyst for the synthesis of α-aminophosphonates. A three-component reaction of an amine, an aldehyde or a ketone and a dialkyl phosphite (Kabachnik–Fields reaction) took place in one-pot, under solvent-free conditions to afford the corresponding α-aminophosphonates in high yields and short times. The TiO2 catalyzed α-aminophosphonate synthesis in the present study perhaps represents a true three-component reaction as no intermediate formation of either an imine or α-hydroxyphosphonate was observed that indicated the simultaneous involvement of the carbonyl compound, the amine and the phosphite in the transition state. Furthermore, the catalyst can be reused for several times without any significant loss of catalytic activity. 相似文献
105.
Tian X Cecal R McLaurin J Manea M Stefanescu R Grau S Harnasch M Amir S Ehrmann M St George-Hyslop P Kohlmann M Przybylski M 《European journal of mass spectrometry (Chichester, England)》2005,11(5):547-556
Alzheimer's disease (AD) is the most common cause for human age-related dementia, characterised by formation of diffuse plaques in brain that are directly involved in AD pathogenesis. The major component of AD plaques is beta-amyloid, a 40 to 42 amino acid polypeptide derived from the amyloid precursor protein (APP) by proteolytic degradation involving the specific proteases, beta-and gamma-secretase acting at the N- and C- terminal cleavage site, respectively. In this study we have prepared polypeptides comprising the carboxy-terminal and transmembrane sequences of APP, by bacterial expression and chemical synthesis, as substrates for studying the C-terminal processing of APP and its interaction with the gamma-secretase complex. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was used as a major tool for structure analysis. Immunisation of transgenic mouse models of AD with Abeta42 has been recently shown to be effective to inhibit and disaggregate Abeta-fibrils, and to reduce AD-related neuropathology and memory impairments. However, the mechanism underlying these therapeutic effects has been as yet unclear. Using proteolytic epitope excision from immune complexes in combination with FT-ICR-MS, we identified the epitope recognised by the therapeutically active antibody as the N-terminal Abeta(4-10) sequence; this soluble, nontoxic epitope opens new lead structures for AD vaccine development. A monoclonal antibody (Jonas; JmAb) directed against the cytosolic APP domain was used in studies of APP biochemistry and metabolism. Here we report the identification of the epitope recognised by the JmAb, using the combination of epitope excision and peptide mapping by FT-ICR-MS. The epitope was determined to be located at the C-terminal APP(740-747) sequence; it was confirmed by ELISA binding assays and authentic synthetic peptides and will be an efficient tool in the development of new specific vaccines. These results demonstrate high-resolution FT-ICR-MS as a powerful method for characterising biochemical pathways and molecular recognition structures of APP. 相似文献
106.
Sanaa T. El-Sayed Etidal W. Jwanny Mona M. Rashad Abeer E. Mahmoud Nadia M. Abdallah 《Applied biochemistry and biotechnology》1995,55(3):219-230
Glycosidases namely myrosinase and β-amylase, have been isolated fromBrassicaceae. These enzymes were identified and estimated by the rate of glucose and maltose formation from sinigrin (thioglucosinolate) and amylose (polysaccharides) hydrolysis, respectively. Their activities (U/g dry tissues) varied with the different species of the plant and with the different parts of their tissues. Generally, they were higher in the germinated seeds (3.3-8.0 times) than in powdered or defatted powdered dry seeds. The best amylase and myrosinase extracting solution for radish and white mustard germinated seeds was distilled water, and for turnip germinated seeds, it was 0.1M phosphate buffer, pH 6.0. In the light, the optimum germination temperature for amylase production or activation by radish and white mustard seeds was 25°C, and for turnip seeds, it was 30°C, whereas for myrosinase production or activation by radish and turnip, 25–27°C was the optimum temperature. The highest myrosinase activities in black mustard and radish defatted dry seeds were obtained by extraction with 1% NaCl at 272/30°C and distilled water at 25–27°C, after an incubation period of 4–6 h. Comparative studies indicated that fresh radish roots were the most potent amylase and myrosinase producers compared with radish leaves or roots, stems, and leaves of turnip and cabbage. Amylase and myrosinase were partially purified from water extracts of fresh radish roots by optimum precipitation with ammonium sulfate (100%). Some physicochemical properties were studied. 相似文献
107.
Alkaline Molybdotellurates: Preparation and Crystal Structures of Rb6[TeMo6O24] · 10H2O and Rb6[TeMo6O24] · Te(OH)6 · 6H2O Single crystals of Rb6[TeMo6O24] · 10 H2O and Rb6[TeMo6O24] · Te(OH)6 · 6 H2O, respectively, were grown from aqueous solution. Rb6[TeMo6O24] · 10 H2O possesses the space group P1 . The lattice dimensions are a = 963.40(13), b = 972.56(12), c = 1 056.18(13) pm, α = 97.556(10), β = 113.445(9), γ = 102.075(10)°; Z = 1, 2 860 reflections, 215 parameters refined, Rg = 0.0257. The centrosymmetrical [TeMo6O24]6? anions are stacked parallel to [010]. Rb(2) is coordinated with one exception by water molecules only. Folded chains consisting of [TeMo6O24]6? anions and Rb(2) coordination polyhedra which are linked to pairs represent the prominent structural feature. Rb6[TeMo6O24] · Te(OH)6 · 6 H2O crystallizes monoclinically in the space group C2/c with a = 1 886.4(3), b = 1 000.9(1), c = 2 126.5(3) pm, and β = 115.90(1)°; Z = 4, 3 206 reflections, 240 parameters refined, Rg = 0.0333. It is isostructural in high extent with (NH4)6[TeMo6O24] · Te(OH)6 · 7 H2O. Hydrogen bonds between Te(OH)6 molecules and [TeMo6O24]6? anions establish infinite strands. The [TeMo6O24]6? anions gather around Te(OH)6 providing channel-like voids extending parallel to [001]. 相似文献
108.
Mona Mouallem-Bahout Sarah Bertrand Octavio Peña 《Journal of solid state chemistry》2005,178(4):1080-1086
Nanocrystalline single-phase samples of Zn1−xNixFe2O4 ferrites (0<x<1) have been obtained via a soft-chemistry method based on citrate-ethylene glycol precursors, at a relatively low temperature (650 °C). The influence of the nickel and zinc contents as well as that of heat treatments were investigated by means of X-ray powder diffraction, Brunauer-Emmett-Teller (BET) surface area, scanning electron microscopy (SEM) and Fourier Transform Infrared (FTIR) Spectroscopy. Higher Ni content increases the surface areas, the largest one (∼20 m2/g) being obtained for NiFe2O4 annealed at 650 °C for 15 h. For all compositions, the surface area decreases for prolonged annealing at 650 °C and for higher annealing temperatures. Those results were correlated to the particle size evolution; the smallest particles (∼50 nm) observed in the NiFe2O4 sample (650 °C, 15 h) steadily increase as Ni ions were replaced by Zn, reaching ∼100 nm in the ZnFe2O4 sample (650 °C, 15 h). For all the Zn1−xNixFe2O4 samples and, whatever the heat treatments was, the FTIR spectra show two fundamental absorption bands in the range 650-400 cm−1, characteristics of metal vibrations, without any superstructure stating for cation ordering. The highest ν1-tetrahedral stretching, observed at ∼615 cm−1 in NiFe2O4, shifts towards lower values with increasing Zn, whereas the ν2-octahedral vibration, observed at 408 cm−1 in NiFe2O4, moves towards higher wavenumbers, reaching 453 cm−1 in ZnFe2O4. 相似文献
109.
Ohne Zusammenfassung
An den Versuchen war auch Herr stud. Franz Jandraschitsch beteiligt. 相似文献
110.
Yvonne Syha Charlene Valmalle Jan W. Bats Michael Kock Mona Abdel-Tawab Manfred Schubert-Zsilavecz 《Monatshefte für Chemie / Chemical Monthly》2006,58(2):1357-1364
Although various thiazoles are known in literature for their biological and pharmacological properties only a few multi-step
synthesis pathways for the preparation of thiazolo[3,2-a]pyrimidinones have been reported, which are tedious and time-consuming. An alternative synthesis pathway is described, which
allows the preparation of 2,3-dihydrothiazolo[3,2-a]pyrimidin-5-ones in a one-step process based on a Michael-type tandem reaction. By heating of 2-thiobarbituric acid with ethyl 4-bromocrotonate in ethanol at 60°C for 2 h, a 2,3-dihydrothiazolo[3,2-a]pyrimidin-5-one was obtained in 73% yield, whereas carrying out the reaction at room temperature results in the formation
of an unstable unsaturated ester. The structures of both, the α,β-unsaturated ester as well as the 2,3-dihydrothiazolo[3,2-a]pyrimidin-5-one were confirmed by NMR spectroscopy. Additionally, the structure of the 2,3-dihydrothiazolo[3,2-a]pyrimidin-5-one was investigated by single-crystal X-ray analysis. The described approach offers a significant improvement
over previously reported synthesis pathways because it allows the simple preparation of 2,3-dihydrothiazolo[3,2-a]pyrimidin-5-ones with good yields in a one-step reaction. 相似文献