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91.
92.
Let c be a positive constant and H a constant satisfying |H| > c. Our primary object of this paper is to give representation formulas for branched CMC H (constant mean curvature H) surfaces in the hyperbolic 3-space 3(-c2) of constant curvature c2, and for spacelike CMC H surfaces in the de Sitter 3-space S 3
1(c2) of constant curvature c2. These formulas imply, for example, that every CMC H surface in 3(-c2) can be represented locally by a harmonic map to the unit 2-sphere S2. 相似文献
93.
Glycotentacles: synthesis of cyclic glycopeptides, toward a tailored blocker of influenza virus hemagglutinin 总被引:1,自引:0,他引:1
94.
Yamayoshi A Iwase R Yamaoka T Murakami A 《Chemical communications (Cambridge, England)》2003,(12):1370-1371
Hairpin type psoralen-cojugated oligonucleotides cross-linked with RNA when they hybridized with a perfectly complementary RNA. 相似文献
95.
Masayoshi Okubo Toyoko Suzuki Reiko Shinohara Nobuko Fukami 《Colloid and polymer science》2002,280(11):1053-1056
The adsorption behavior of poly(oxyethylene) nonyl phenyl ether nonionic emulsifier molecules onto polystyrene (PS) and styrene-methacrylic acid copolymer [P(S-MAA)] particles dispersed in D2O was evaluated by in situ 1H NMR measurements at room temperature. The resonance due to the protons of the emulsifier molecules was only observed. Normalized NMR integrals of the resonance due to the protons of hydrophobic groups (nonyl and phenyl groups) and the hydrophilic group, poly(oxyethylene) chain, at a certain concentration of the emulsifier decreased with an increase in the total surface area of the PS particles dispersed in the system. The decrease for the hydrophobic groups was much larger than that for the hydrophilic groups. In the dispersion system of P(S-MAA) particles, ionized carboxyl groups at the particle surface decreased the amount of the emulsifier adsorbed. 相似文献
96.
The synthesis and characterization of the bis(bidentate) Schiff-base ligand [(R)-2] formed by the condensation reaction of (R)-1,1'-binaphthyl-2,2'-diamine [(R)-BINAM] with pyridine-2-carboxaldehyde is presented. The coordination chemistry of (R)-2 with Ni(ClO(4))(2).6H(2)O, Co(ClO(4))(2).6H(2)O, CuCl(2), and CuSO(4) has been investigated. Reaction of (R)-2 with the first two metal salts leads to complexes of the type [M((R)-4)(2)](ClO(4))(2) (M = Ni(II), Co(II)), where (R)-4 is a tridentate ligand resulting from the hydrolytic cleavage of one of the pyridyl groups from (R)-2. Both complexes were characterized by X-ray crystallography, which showed that the Lambda absolute configuration of the metal center is favored in both cases. (1)H NMR spectroscopy suggests that the high diastereoselectivity of Lambda-[Co((R)-4)(2)](ClO(4))(2) is maintained in solution. The reaction of (R)-2 with CuCl(2) leads to the dinuclear complex [Cu(2)((R)-2)Cl(4)], which has a [Cu(2)(mu(2)-Cl(2))] core. The reaction of CuSO(4) with (R)-2 gives a dimeric complex, [Cu((R)-4)SO(4)](2), which features a [Cu(2)(mu(2)-(SO(4))(2))] core. This complex can be prepared directly by the reaction of (R)-BINAM with pyridine-2-carboxaldehyde and CuSO(4). The use of rac-BINAM in this synthetic procedure leads to the heterochiral dimer [Cu(2)((R)-4)((S)-4)(SO(4))(2)]; that is, the ligands undergo a self-sorting (self/nonself discrimination) process based on chirality. The reaction of rac-BINAM, pyridine-2-carboxaldehyde, and Co(ClO(4))(2).6H(2)O proceeds via a homochiral self-sorting pathway to produce a racemic mixture of [Co((R)-4)(2)](2+) and [Co((S)-4)(2)](2+). The variable-temperature magnetic susceptibilities of the bimetallic complexes [Cu(2)((R)-2)Cl(4)], [Cu((R)-4)(mu(2)-SO(4))](2), and [Cu(2)((R)-4)((S)-4)(mu(2)-SO(4))(2)] all show weak antiferromagnetic coupling with J = -1.0, -0.40, and -0.67 cm(-)(1), respectively. 相似文献
97.
From chiral counterions to twisted membranes 总被引:1,自引:0,他引:1
Berthier D Buffeteau T Léger JM Oda R Huc I 《Journal of the American Chemical Society》2002,124(45):13486-13494
In membranes, the chirality of the amphiphile constituents is sometimes expressed at a supramolecular scale of nanometers or micrometers. We have recently reported that membranes of nonchiral dicationic n-2-n amphiphiles can also be chirally twisted upon interacting with chiral tartrate counterions. Here, we demonstrate that the mechanism of the chiral induction by counterions involves specific anion-cation recognition and the induction of conformationally labile chirality in the cations. Single-crystal X-ray diffraction shows that the amphiphilic cations exist as a mixture of chiral conformers. (1)H NMR data establish a specific recognition between tartrate and n-2-n cations and show that chiral conformers also exist in solution. Circular dichroism (CD) in the UV-vis shows a sharp conformational change of tartrate ions from anti to gauche when bound to the chiral cationic membranes. This is confirmed by CD in the infrared region which also shows concomitant induced CD bands in the vibrations of the n-2-n amphiphiles. These results represent the first example of the so-called Pfeiffer effect in a membrane. They provide a general framework for designing new tunable membrane systems. Our work also includes the first application of vibrational circular dichroism in the study of chiral conformations of amphiphiles in membranes and demonstrates the very high potential of this technique. 相似文献
98.
Yoshitane Imai Kakuhiro Kawaguchi Reiko Kuroda Yoshio Matsubara 《Tetrahedron letters》2006,47(45):7885-7888
A tunable chiral host system was developed by the self-assembly of a chiral 21-column structure formed from (1R,2R)-1,2-diphenylethylenediamine and dicarboxylic acid. This host system can include guest molecules by changing the packing of a chiral 21-column enantioselectively. 相似文献
99.
The use of a novel InBr3-Et3N reagent system to promote the alkynylation of not only a variety of aromatic/heterocyclic or bulky aliphatic aldehydes but also N,O- or N,S-acetals is described. The use of N-silyl-N,O-acetals and 1-alkynes could lead to the direct production of primary propargylic amines in good yields. 相似文献
100.
Feng F Okuyama K Niikura K Ohta T Sadamoto R Monde K Noguchi T Nishimura S 《Organic & biomolecular chemistry》2004,2(11):1617-1623
Two non-natural fluorinated 2-N-acetamidosugar nucleotides, uridine 5'-diphosphate (UDP) 2-acetamido-2,4-dideoxy-4-fluoro-alpha-D-glucopyranose (UDP-4-FGlcNAc) 1 and its galacto isomer (UDP-4-FGalNAc) 2, were enzymatically constructed by treating chemically synthesized fluorinated 2-N-acetamidosugar 1-phosphates as the donor with UDP 2-acetamido-2-deoxy-alpha-D-glucopyranose pyrophosphorylase in the presence of uridine 5'-triphosphate (UTP). 相似文献