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71.
Walvoort MT Moggré GJ Lodder G Overkleeft HS Codée JD van der Marel GA 《The Journal of organic chemistry》2011,76(18):7301-7315
With the aim to find an efficient synthetic procedure for the construction of 2,3-diamino-2,3-dideoxy-β-D-mannuronic acids, we evaluated three mannosyl donors: (S)-phenyl 4,6-di-O-acetyl-2,3-diazido mannopyranoside, (S)-phenyl 2,3-diazido-4,6-O-benzylidene mannopyranoside, and (S)-phenyl 2,3-diazido mannopyranosyl methyl uronate. The first two mannosylating agents are rather unselective or slightly α-selective in their condensation with three different acceptors. The mannuronic acid donor on the other hand reliably provides the desired β-mannosidic linkage. A mechanistic rationale is put forward to account for the different behavior of the three donor types. Suitably protected 2,3-diazido mannuronic acids were employed to construct the all-cis-linked tetrasaccharide repeating unit of the capsular polysaccharide of Bacillus stearothermophilus , featuring two 2,3-diacetamido-2,3-dideoxy-β-D-mannuronic acids. 相似文献
72.
V.P. Solntsev A.P. YelisseyevT.B. Bekker A.E. KokhS. Yu. Stonoga A.V. DavydovA. Maillard 《Optics Communications》2012,285(24):5205-5209
Optical absorption and luminescence spectra of ytterbium and terbium codoped BaB2O4 (β-BBO and α-BBO) crystals grown in different conditions have been studied. Low-temperature absorption peaks were observed in all samples. Features related to rare earth ions were observed in absorption and luminescence spectra. Absorption and emission in the range 860-1000 nm are caused by 2F5/2↔2F7/2 transitions in Yb3+ ions. Emission peaks at 500, 550, 590 and 630 nm correspond to 5D4→7F6, 7F5, 7F4, and 7F3 transitions of Tb3+ ions, respectively. The probable reasons of variations in spectroscopic features related to Yb in BBO host are discussed. It has been shown that the replacement of Ва2+ by Yb3+ in the lattice of ВаВ2О4 results in the decrease in the symmetry of oxygen surrounding of Yb3+. 相似文献
73.
Rashchenko S. V. Bakakin V. V. Kozlova S. G. Bekker T. B. Fedorov P. P. 《Journal of Structural Chemistry》2015,56(1):85-91
Journal of Structural Chemistry - In the work the structures of fluoride borates demonstrating the substitution with the stoichiometry (BO3)3− ↔ 3F− are analyzed and the specific... 相似文献
74.
The activation energy parameters for the reaction of PdX (X=Cl?, Br?) in aqueous halide acid solution with thiourea (tu) and selenourea (seu) have been determined. High rates of reaction parallel low enthalpies and appreciable negative entropy of activation. The rate law in each case simplifies to kobs=k[L] where L=tu or seu, and only ligand-dependent rate constants are observed at 25°C. The ligand-dependent rate constants for the first identifiable step in the PdCl + X system is (9.1±0.1) × 103 M?1 sec?1 and (4.5±0.1) × 104 M?1 sec?1 for X=tu and seu, respectively, while for the PdBr + X system it is (2.0±0.1) × 104 M?1 sec?1 and (9.0±0.1) × 104 M?1 sec?1 for X=tu and seu, respectively. 相似文献
75.
76.
I. N. Rozhkov S. M. Igumnov G. Ya. Bekker S. I. Pletnev G. D. Rempel' L. E. Deev 《Russian Chemical Bulletin》1989,38(10):2041-2043
On the basis of half-wave potential values E1/2 it was shown that perfluoroalkyl halides have pronounced oxidative properties in comparison with unfluorinated analogs. Tertiary perfluoroalkyl iodides, having a higher oxidation potential than iodine, react with I– by a scheme including one-electron transfer.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2222–2224, October, 1989. 相似文献
77.
78.
Natasja Schouten Louis G. J. van der Ham Gert-Jan W. Euverink André B. de Haan 《Adsorption》2007,13(5-6):523-532
Low cost adsorption technology offers high potential to clean up laundry rinsing water. From an earlier selection of adsorbents
(Schouten et al. 2007), layered double hydroxide (LDH) proved to be an interesting material for the removal of anionic surfactant, linear alkyl
benzene sulfonate (LAS) which is the main contaminant in rinsing water. The main research question was to identify the effect
of process parameters of the LDH synthesis on the stability of the LDH structure and the adsorption capacity of LAS. LDH was
synthesized with the co-precipitation method of Reichle (1986); a solution of M2+(NO3)2 and M3+(NO3)3 and a second solution of NaOH and Na2CO3 were pumped in a beaker and mixed. The precipitate that was formed was allowed to age and was subsequently washed, dried
and calcined. The process parameters that were investigated are the concentration of the initial solutions, M2+/M3+ ratio and type of cations. The crystallinity can be improved by decreasing the concentration of the initial solutions; this
also decreases the leaching of M3+ from the brucite-like structure into the water. The highest adsorption capacity is obtained for Mg2+/Al3+ with a ratio 1 and 2 because of the higher charge density compared to ratio 3. Storing the LDH samples in water resulted
in a reduction of adsorption capacity and a decrease in surface area and pore volume. Therefore, LDH is not applicable in
a small device for long term use in aqueous surroundings. The adsorption capacity can be maintained during storage in a dry
N2 atmosphere. 相似文献
79.
B. M. Bekker O. A. Ivanov A. S. Merkurjev 《Vestnik St. Petersburg University: Mathematics》2016,49(1):1-4
The first Jacobi–Trudi identity expresses Schur polynomials as determinants of matrices, the entries of which are complete homogeneous polynomials. The Schur polynomials were defined by Cauchy in 1815 as the quotients of determinants constructed from certain partitions. The Schur polynomials have become very important because of their close relationship with the irreducible characters of the symmetric groups and the general linear groups, as well as due to their numerous applications in combinatorics. The Jacobi–Trudi identity was first formulated by Jacobi in 1841 and proved by Nicola Trudi in 1864. Since then, this identity and its numerous generalizations have been the focus of much attention due to the important role which they play in various areas of mathematics, including mathematical physics, representation theory, and algebraic geometry. Various proofs of the Jacobi–Trudi identity, which are based on different ideas (in particular, a natural combinatorial proof using Young tableaux), have been found. The paper contains a short simple proof of the first Jacobi–Trudi identity and discusses its relationship with other well-known polynomial identities. 相似文献
80.
Data from the last 50 years for various classes of compounds from certain plant species of the oleaster (Elaeagnaceae) family are reviewed 相似文献