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151.
152.
153.
Cacciarini M Azov VA Seiler P Künzer H Diederich F 《Chemical communications (Cambridge, England)》2005,(42):5269-5271
The partially bridged resorcin[4]arene cavitand featuring a cleft-shaped recognition site formed by two anti-quinoxaline bridges and four convergent HO-groups was prepared in three steps and characterised by X-ray crystallography; cavitand was found to be a selective receptor for steroidal substrates in CDCl3, with the best binding observed for steroids with a flat A-ring and two H-bonding sites on rings A and C/D. 相似文献
154.
The range of applicability of the mean spherical approximation to a primitive-model electrolyte is extended to allow for stronger Coulomb coupling. The new terms in the approximation are extracted from the HNC formalism, which is adequate for strongly coupled Coulomb systems. The new approximation satisfies the Stillinger-Lovett conditions. The new integral equation thus obtained is presented. 相似文献
155.
Q. Beaufils A. Crubellier T. Zanon B. Laburthe-Tolra é. Maréchal L. Vernac O. Gorceix 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,56(1):99-104
We develop a theoretical model to describe the
radio-frequency (rf) induced coupling of a pair of colliding atoms
to a Feshbach molecule when a magnetic field arbitrarily far from
the Feshbach resonance is modulated in time. We use the dressed atom
picture, and show that the coupling strength in presence of rf is
equal to the Feshbach coupling strength multiplied by the square of
a Bessel function. The argument of this function is equal to the
ratio of the atomic rf Rabi frequency to the rf frequency. We
experimentally demonstrate this law by measuring the rate of
rf-association of molecules using a Feshbach resonance in d wave
collisions between ultra-cold chromium atoms. 相似文献
156.
A spacer-equipped tetrasaccharide, p-aminocyclohexylethyl alpha-l-Colp-(1-->2)-beta-d-Galp-(1-->3)-[alpha-l-Colp-(1-->4)]-beta-D-GlcpNAc, containing a 4,6-cyclic phosphate in the galactose residue, has been synthesised. The structure corresponds to a part of the repeating unit of the capsular (and lipo-) polysaccharide of the endemic bacteria Vibrio cholerae type O139 synonym Bengal. The synthetic strategy allows continuous syntheses of the complete O139 hexasaccharide repeating unit as well as of the structurally related repeating unit of serotype O22. Starting from ethyl 2-azido-4,6-O-benzylidene-2-deoxy-1-thio-beta-D-glucopyranoside, a thioglycoside tetrasaccharide donor block was constructed through two orthogonal glycosylations with glycosyl bromide donors. First, a properly protected galactose moiety was introduced using silver triflate as promoter and subsequently the two colitose residues, carrying electron-withdrawing protecting groups for stability reasons, under halide-assisted conditions. The tetrasaccharide block was then linked to the spacer in a NIS-TMSOTf-promoted coupling. Transformation of the azido group into an acetamido group using H2S followed by removal of temporary protecting acetyl groups gave a 4',6'-diol, which was next phosphorylated with methyl dichlorophosphate and deprotected to yield the 4,6-cyclic phosphate tetrasaccharide target structure. 相似文献
157.
ChemMatrix, a poly(ethylene glycol)-based support for the solid-phase synthesis of complex peptides 总被引:5,自引:0,他引:5
García-Martín F Quintanar-Audelo M García-Ramos Y Cruz LJ Gravel C Furic R Côté S Tulla-Puche J Albericio F 《Journal of combinatorial chemistry》2006,8(2):213-220
CM (ChemMatrix) resin is a new, totally poly(ethylene glycol) (PEG)-based resin, made exclusively from primary ether bonds and, therefore, highly chemically stable. It exhibits good loading and is user-friendly because of its free-flowing form upon drying. It performs excellently for the preparation of hydrophobic, highly structured, and poly-Arg peptides, as compared to polystyrene (PS) resins. In the most striking example, stepwise solid-phase assembly of the highly complex beta-amyloid (1-42) peptide resulted in a crude material of 91% purity. In contrast, literature procedures using PS or PEG-PS-based resins for this peptide required convergent approaches, additional time-consuming steps, or both. In addition to the difficulties of its synthesis, characterization of the beta-amyloid (1-42) peptide as a monomer is also a challenge, and methods for characterization by HPLC and MALDI-TOF have also been developed. 相似文献
158.
Wolpert M Hellwig P 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,64(4):987-1001
In this work, we present the absorption spectra and molar coefficients of all 20 amino acids in aqueous solutions down to 500 cm(-1). The spectral region between 1200 and 500 cm(-1) was yet disregarded for protein infrared spectroscopy, mainly due to the strong H(2)O absorption. Absorption spectra were obtained mainly for physiological relevant pH region. Intense bands for aromatic amino acids, histidine and such with OH group could clearly be identified throughout the given spectral region. For sulfur-containing amino acids cysteine and methionine some strong bands besides the weak carbon-sulfur stretching vibration was shown. Effects of aqueous solution environment, pH, protonation states were discussed, together with previously reported data from theoretical approaches. With this complete set of spectral information application to proteins in the whole mid infrared region could be described precise and the potential of the lower spectral region to study typical cofactor ligands like histidine, shown. 相似文献
159.
Standard molecular and driven molecular dynamics are used to analyze prominent spectral features in the H5O2+ infrared spectrum. In the driven method, the molecular Hamiltonian is augmented with a time-dependent term, mu x epsilon(0) sin(omegat), where mu is the dipole moment of H5O2+, epsilon0 is the electric field, and omega is the frequency. The magnitude of the electric field determines whether the driving is mild (the harmonic limit) or strong (anharmonic motion and mode coupling). We analyze the spectrum in the wavenumber range from 600 to 1900 cm(-1), where recent experimental measurements are available for H5O2+. On the basis of the simulations, we have assigned the broad feature around 1000 cm(-1) to the proton transfer coupled with the torsion motion. Intense absorption near 1780 cm(-1) is assigned to the H2O monomer bend coupled with proton transfer. 相似文献
160.
Peter Kop?anský Martina Koneracká Vlasta Závišová Katalin Fodor-Csorba Anikó Vajda Eric Beaugnon 《Journal of magnetism and magnetic materials》2010,322(22):3696-3700
The studied ferronematic is a nematic liquid crystal (ZLI1695) of low negative anisotropy of the diamagnetic susceptibility (χa<0) doped with the magnetic particles Fe3O4. Structural instabilities are interpreted within Burylov and Raikher's theory. The high magnetic fields were oriented perpendicular (Freedericksz transition) or parallel to the initial director. Using capacitance measurements the Freedericksz threshold magnetic field of the ferronematic BFN, and the critical magnetic field Bmax, at which the initial parallel orientation between the director and the magnetic moment of magnetic particles breaks down, have been determined. The values of these quantities have been used to estimate the surface density of the anchoring energy W of liquid crystal molecules on the surface of the magnetic particles. The obtained values indicate a soft anchoring of the liquid crystal on the magnetic particles with a preferred parallel orientation of the magnetic moment of magnetic particles and the director. 相似文献