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951.
Diastereomers of 3-amino-2-hydroxy-6-methylheptanoic acid (AHMHA), a new amino acid unit in perthamides C and D, have been synthesized from commercially available 4-methylpentanol in a concise manner and 50% average overall yield. Comparison of the 1H and 13C NMR data, optical rotation data and Marfey’s analysis of the resulting isomers with the natural fragment unambiguously allowed the configurational assignment of the natural residue as (2R,3R). A structural revision of perthamides C and D is also reported. 相似文献
952.
M. Rajeswara Rao 《Tetrahedron》2010,66(9):1728-1162
3,5-Bis(trimethylsilylethynyl)-4,4-difluoro-8-(4-tolyl)-4-bora-3a,4a-diaza-s-indacene [BODIPY(CCTMS)2] has been synthesized by coupling of 3,5-dibromo-4,4-difluoro-8-(4-tolyl)-4-bora-3a,4a-diaza-s-indacene with trimethylsilylacetylene under pd(0) coupling conditions. The BODIPY(CCTMS)2 was used as a selective colourimetric and fluorescent chemodosimeter for fluoride ion, following the F− ion induced cleavage of trimethylsilyl group, the protecting group of ethyne functionality by monitoring the changes in UV-vis and fluorescence properties. The dosimeter BODIPY(CCTMS)2 display clear changes in colour, absorption and emission bands selectively for F− ion over other anions such as Cl−, Br−, I−, ClO4− and HPO42−. 相似文献
953.
Integrally skinned asymmetric poly(vinylidene fluoride) hollow fibre membranes were prepared and characterized. The effects of phase inversion methods (dry-wet or wet) and spinning conditions, such as the type of solvent (NMP, DMAc), the concentration of polymer in dope solution, temperature of the external coagulation bath and the composition of the inner coagulant on the morphology and on the formation of a dense skin layer were investigated. The structure of the membranes was analyzed by scanning electron microscopy and the gas permeation properties with six different gases (He, H2, N2, O2, CH4 and CO2) were measured at 25 °C to confirm the integrity of the selective skin layer. Under the proper conditions highly selective and permeable PVDF hollow fibre membranes were thus obtained by dry-wet spinning of a 30 wt.% PVDF solution in DMAc, using hot water (50 °C) as the external coagulant and a bore fluid of pure water as the internal coagulant. The best membrane had a selective outer skin with an effective thickness of approximately 0.2 μm. The ideal selectivity of the hollow fibres approached or even exceeded the intrinsic ideal selectivity of a dense PVDF film, for instance the selectivity for He over N2 was 86.2 for the hollow fibre, whereas it was 83.5 for a dense PVDF reference film. DSC and FT-IR/ATR analysis indicated a higher fraction of the β-crystal phase in the selective skin and a high overall crystallinity than in the melt-processed film. The latter explains the relatively high selectivity and low permeability of the membranes. Intrinsic polymer properties make the membranes also suitable for vapour transport than for gas separation. 相似文献
954.
In the framework of a recently developed scheme for a hybrid particle-field simulation techniques where self-consistent field (SCF) theory and particle models (molecular dynamics) are combined [J. Chem. Phys. 130, 214106 (2009)], we developed a general formulation for the calculation of instantaneous pressure and stress tensor. The expressions have been derived from statistical mechanical definition of the pressure starting from the expression for the free energy functional in the SCF theory. An implementation of the derived formulation suitable for hybrid particle-field molecular dynamics-self-consistent field simulations is described. A series of test simulations on model systems are reported comparing the calculated pressure with those obtained from standard molecular dynamics simulations based on pair potentials. 相似文献
955.
A calix[4]arene derivative has been anchored to carboxyl CPG and TentaGel supports by an easily cleavable ester bond and DMT groups allow a simple loading evaluation via UV-vis spectroscopy. The loading of the calixarene on TentaGel resin has also been estimated by HR-MAS NMR experiments. The potential of the polymer supported calixarenes (9 and 10) in solid phase synthesis has been tested by condensation of four thymine nucleotide units onto the upper rim of the calix[4]arene skeleton. 相似文献
956.
J.S. Yadav B.V. Subba Reddy T. Srinivasa Rao K. Bhavani A. Raju 《Tetrahedron letters》2010,51(19):2622-4577
The vinyl arenes undergo smooth hydroalkylation with 1,3-diketones in the presence of 10 mol % of iodine to afford phenethyl diketones and ketoesters in good yields in short reaction times. The use of inexpensive and readily available molecular iodine makes this method quite simple, more convenient and practical. 相似文献
957.
C.V. Yelamaggad Rashmi Prabhu D.S. Shankar Rao S. Krishna Prasad 《Tetrahedron letters》2010,51(34):4579-5311
Supramolecular liquid crystalline tris(N-salicylideneamine)s (TSANs) featuring both inter- and intra-molecular hydrogen bonding have been synthesized and characterized for the first time. These TSANs formed by condensing 3 equiv of 3,4,5-trialkoxybenzoylhydrazine with 1,3,5-triformylphloroglucinol exist as the single C3h-symmetric keto-enamine product solely, unlike the previously reported TSANs. Their self-assembly into supramolecular fluid hexagonal columnar phase over a wide thermal range is evidenced with the aid of optical microscopic, calorimetric, and powder X-ray diffraction techniques. 相似文献
958.
959.
Reaction of the benzene-linked bis(pyrazolyl)methane ligands, 1,4-bis{bis(pyrazolyl)-methyl}benzene (L1) and 1,4-bis{bis(3-methylpyrazolyl)methyl}benzene (L2), with pentamethylcyclopentadienyl rhodium and iridium complexes [(η5-C5Me5)M(μ-Cl)Cl]2 (M = Rh and Ir) in the presence of NH4PF6 results under stoichiometric control in both, mono and dinuclear complexes, [(η5-C5Me5)RhCl(L)]+ {L = L1 (1); L2 (2)}, [(η5-C5Me5)IrCl(L)]+ {L = L1 (3); L2 (4)} and [{(η5-C5Me5)RhCl}2(μ-L)]2+ {L = L1 (5); L2 (6)}, [{(η5-C5Me5)IrCl}2(μ-L)]2+ {L = L1 (7); L2 (8)}. In contrast, reaction of arene ruthenium complexes [(η6arene)Ru(μ-Cl)Cl]2 (arene = C6H6, p-iPrC6H4Me and C6Me6) with the same ligands (L1 or L2) gives only the dinuclear complexes [{(η6-C6H6)RuCl}2(μ-L)]2+ {L = L1 (9); L2 (10)}, [{(η6-p-iPrC6H4Me)RuCl}2(μ-L)]2+ {L = L1 (11); L2 (12)} and [{(η6-C6Me6)RuCl}2(μ-L)]2+ {L = L1 (13); L2 (14)}. All complexes were isolated as their hexafluorophosphate salts. The single-crystal X-ray crystal structure analyses of [7](PF6)2, [9](PF6)2 and [11](PF6)2 reveal a typical piano-stool geometry around the metal centers with six-membered metallo-cycle in which the 1,4-bis{bis(pyrazolyl)-methyl}benzene acts as a bis-bidentate chelating ligand. 相似文献
960.
Mika Mahosenaho Felice Caprio Laura Micheli Adama M. Sesay Giuseppe Palleschi Vesa Virtanen 《Mikrochimica acta》2010,170(3-4):243-249
A disposable tri-enzymatic biosensor is presented for the determination of α-amylase in human saliva. It is based on the quantity of maltose generated by hydrolysis of maltopentose in the presence of salivary α-amylase. The biosensor is fabricated by co-immobilization of the enzymes α-glucosidase, glucose oxidase, and mutarotase on screen-printed electrodes modified with Prussian Blue. The assay can be performed with a “drop” of sample, this allowing for ease and simplicity. A linear relationship is found for the range from 5 to 250 units per mL, with an LOD of 5 units per mL. The biosensor is stable for at least one month and over this time retains 80% of its original activity. The system was then evaluated for matrix effects of human saliva and compared to a spectrometric method using a commercially available kit. 相似文献