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71.
[reaction: see text] Various alpha-C-substituted 1,4-dideoxy-1,4-imino-d-galactitols were prepared efficiently from 1-O-acetyl-2,3,5,6-tetra-O-benzyl-d-glucofuranose by a four-step sequence involving as the key step the highly syn-selective TMSOTf-catalyzed addition of silylated nucleophiles to a glycofuranosylamine. Cross-metathesis of the alpha-C-allylated iminogalactofuranose derivative with an original uridin-5'-yl vinylphosphonate led to novel UDP-galactofuranose mimics. Such compounds are of interest as potential inhibitors of the mycobacterial galactan biosynthesis pathway. 相似文献
72.
This work concerns the studies of energy transfers between Sm3+ and Eu3+ ions in some phosphates as new luminescent materials emitting in the orange-red color. The choose of ions is based on the possibility of quantum cutting process and the matrices are selected according to the 5d bands position of Sm3+ ion. The Sm3+ and Eu3+ doped YPO4, LaP5O14 and LaP3O9 are synthesized and spectroscopic studies in ultraviolet and vacuum ultraviolet ranges have been achieved. 相似文献
73.
Alain Valla Zo Andriamialisoa Michel Giraud Virginie Prat Alain Laurent Pierre Potier 《Tetrahedron letters》1999,40(52):1261-9237
A stereoselective synthesis of 13Z retinoic acids via β-methylenealdehydes is described. In methylene-de-oxo-bisubstitution reactions (Knoevenagel, Stobbe, etc.), these new synthons produce stereoselectively E olefins. Hence, a synthesis of 13Z retinoic acids is described, via a stereospecific monodecarboxylation of carboxy-14-retinoic acids. 相似文献
74.
Laurence Moine Sandrine Cammas Catherine Amiel Estelle Renard Bernard Sbille Philippe Gurin 《Macromolecular Symposia》1998,130(1):45-52
A novel hydrophobic monomer, ethyladamantyl malolactonate, has been synthesized and copolymerized with benzyl malolactonate by anionic ring-opening polymerization. The ratio of adamantyl monomer varied from 0 to 100 mol%. Deprotection of benzyl groups leads to a water soluble copolyester with carboxylic acid lateral functions which give a polyelectrolyte character to the corresponding polymers. The mixture of a copolyester containing 10% of adamantyl groups and a β-cyclodextrin/epichlorohydrin copolymer in aqueous solution leads to a new pH-dependant associating system. The solution behavior of this system was studied by viscosimetry as a function of pH, concentration and ratio of both copolymers. At the initial solution pH (pH=2), the copolyester adopts a coiled structure as a result of hydrophobic interactions between the pendant adamantyl groups. Consequently, no network formation is observed as shown by a very low viscosity. As the pH increase, the viscosity of the medium increases and reaches a maximum at pH=5. At this pH, the copolyester expands because of electrostatic repulsions between the carboxylate pendant functions. Consequently, the adamantyl groups are accessible and can be encapsulated into the β-cyclodextrin cavities resulting in a significant increase of the viscosity. 相似文献
75.
Gorteau V Bollot G Mareda J Perez-Velasco A Matile S 《Journal of the American Chemical Society》2006,128(46):14788-14789
We report the design, synthesis, and evaluation of rigid oligonaphthalenediimide (O-NDI) rods that are expected to act as transmembrane anion-pi slides. Studies in fluorogenic large unilamellar egg yolk phosphatidylcholine vesicles reveal that rigid O-NDI rods mediate anion-selective transport with a rare halide VI selectivity sequence (Cl- > F- > Br- > I-). This and decreasing activity, selectivity, and halide sequence with increasing positive charge of the rod termini support the occurrence of anion-pi interactions. A strong anomalous mole fraction effect in Cl-/I- mixtures is in agreement with the existence of multiple active sites along the anion-pi slide and multi-anion hopping as a mechanism of transport. The strong inverted NDI quadruple moment found by DFT calculations is in excellent agreement with these results. 相似文献
76.
M. Novotny J. Bulir A. Bensalah-Ledoux S. Guy P. Fitl M. Vrnata J. Lancok B. Moine 《Applied Physics A: Materials Science & Processing》2014,117(1):377-381
ZnPc thin films were prepared by pulsed laser deposition (KrF laser, λ = 248 nm, τ = 5 ns, f = 50 Hz) on suprasil substrates in vacuum. Optical properties in UV–Vis spectral region were analyzed as functions of laser fluence from 40 to 100 mJ/cm2 by spectrophotometric and spectral ellipsometry measurements. The spectral ellipsometry data were treated using a three-layer model (substrate, film, roughness). The best results of data fitting were obtained when Q band was characterized by two Lorentz oscillators, while two Gaussian oscillators were used for B and C band fitting. We derived the band gap using Tauc plot considering ZnPc a direct band gap semiconductor. The band gap values were found decreasing from 3.13 to 3.09 eV with increasing laser fluence, which might be related with formation of trapping sites at higher fluence. 相似文献
77.
Photocyclization of N-methyldiphenylamine to N-methylcarbazole is achieved within the microenvironment provided by site I of serum albumins. Quantum yield determinations, combined with transient absorption spectroscopic detection of the dihydrocarbazole intermediate, demonstrate that protein encapsulation provides a subtle control of the kinetic parameters, leading to optimized efficiencies. 相似文献
78.
Efficient Csp(3)-Csp(3) Suzuki couplings have been developed with both potassium cyclopropyl- and alkoxymethyltrifluoroborates. Moderate to good yields have been achieved in the cross-coupling of potassium cyclopropyltrifluoroborate with benzyl chlorides possessing electron-donating or electron-withdrawing substituents. Benzyl chloride was also successfully cross-coupled to potassium alkoxymethyltrifluoroborates derived from primary, secondary, and tertiary alcohols. 相似文献
79.
The Neumann realization for the Schr?dinger operator with magnetic field is considered in a bounded two-dimensional domain
with corners. This operator is associated with a small semi-classical parameter h or, equivalently, with a large magnetic field.We investigate the behavior of its eigenpairs as h tends to zero, like in a semi-classical limit. We prove, in the situation where the domain is a polygon and the magnetic
field is constant, that the lowest eigenvalues are exponentially close to those of model problems associated with the corners.
We approximate the corresponding eigenvectors by linear combinations of functions concentrated in corners at the scale
If the domain has curved sides and the magnetic field is smoothly varying, we exhibit a full asymptotics for eigenpairs in
powers of
Communicated by Christian Gérard
Submitted: October 13, 2005 Accepted: December 19, 2005 相似文献
80.
Jules K. Djoko Virginie S. Konlack Mohamed Mbehou 《Numerical Methods for Partial Differential Equations》2020,36(1):86-117
In this work, we consider the heat equation coupled with Stokes equations under threshold type boundary condition. The conditions for existence and uniqueness of the weak solution are made clear. Next we formulate the finite element problem, recall the conditions of its solvability, and study its convergence by making use of Babuska–Brezzi's conditions for mixed problems. Third we formulate an Uzawa's type iterative algorithm that separates the fluid from heat conduction, study its feasibility, and convergence. Finally the theoretical findings are validated by numerical simulations. 相似文献