Second-generation total synthesis of haterumalide NA using B-alkyl Suzuki-Miyaura coupling

Second-generation total synthesis of haterumalide NA, a potent cytotoxic marine macrolide, was achieved by using B-alkyl Suzuki-Miyaura coupling and Nozaki-Hiyama-Kishi coupling as key steps (1.2% in 33 steps). Compared to our first-generation approach, the second-generation synthesis is much improved in the yield of key intermediate.     

Size-dependence of Fermi energy of gold nanoparticles loaded on titanium(iv) dioxide at photostationary state

TiO(2) particle-supported Au nanoparticles (NPs) with varying sizes and good contact (Au/TiO(2)) were prepared under a constant loading amount by the deposition-precipitation method. The Fermi energy of Au NPs loaded on TiO(2) at the photostationary state (E(F)') was determined in water by the use of S/S(2-) having specific interaction with Au as a redox probe. The E(F)' value goes up as the mean size of Au NPs (d) increases at 3.0 相似文献   

Novel chiral cyclic polysulfides with a biphenyl backbone: investigation of atropisomerism and pentathiepin ring inversion

Novel axially chiral benzopolysulfides were synthesized on biaryls by sulfurization of dithiastannoles. Pentathiepin, trithiole, and trithiole 2-oxide rings were observed as single isomer on 1,1′-biaryls. The rotational energy barrier of chiral axis was increased by incorporation of a methyl group at ortho-position. In that case, both trithiole oxide and pentathiepin rings appeared as diastereomer. ortho-Tolyl functionality was also replaced by naphthyl moiety to create more rotational hindrance. Chiral axis was incorporated at the neighborhood of polysulfide functionality by Suzuki-Miyaura cross-coupling reaction. Calculated rotational energy barriers were very much consistent with experimental observations to show atropisomerism. Energy barrier for the inversion of pentathiepin ring was experimentally determined by variable temperature ¹H NMR. The kinetic data suggested that pentathiepin ring inversion was prompt in solution. Insufficient rotational energy barriers of chiral axis and pentathiepin ring inversion make substantially impossible to separate optically pure diastereomer even by chiral chromatography [Preliminary report: Sato, R.; Ohta, H.; Yamamoto T.; Nakajo, S.; Ogawa, S.; Alam, A. Tetrahedron Lett.2007, 48, 4991-4994.].     

Shear-thickening flow of nanoparticle suspensions flocculated by polymer bridging

The steady-shear viscosity, dynamic viscoelasticity, and stress relaxation behavior were measured for suspensions of silica nanoparticles dispersed in aqueous solutions of poly(ethylene oxide) (PEO). The suspensions of silica with diameters of 8-25 nm show striking shear-thickening profiles in steady shear and highly elastic responses under large strains in oscillatory shear. Since the silica particles are much smaller than the polymer coils, one molecule can extend through several particles by intrachain bridging. Each polymer coil may remain isolated as a floc unit and the silica particles hardly connect two flocs. Therefore, the flow of suspensions is Newtonian with low viscosity at low shear rates. When the polymer coils containing several nanoparticles are subjected to high shear fields, three-dimensional network is developed over the system. The shear-thickening flow may arise from the elastic forces of extended bridges. But, the polymer chain is easily detached from particle surface by thermal energy because of large curvature of particles. As a result, the network structures are reversibly broken down in a quiescent state and the suspensions behaves as viscoelastic fluids with the zero-shear viscosity.     

Mg substitution effect on the hydrogenation behaviour, thermodynamic and structural properties of the La2Ni7-H(D)2 system

The present work is focused on studies of the influence of magnesium on the hydrogenation behaviour of the (La,Mg)₂Ni₇ alloys. Substitution of La in La₂Ni₇ by Mg to form La_1.5Mg_0.5Ni₇ preserves the initial Ce₂Ni₇ type of the hexagonal P6₃/mmc structure and leads to contraction of the unit cell. The system La_1.5Mg_0.5Ni₇-H₂ (D₂) was studied using in situ synchrotron X-ray and neutron powder diffraction in H₂/D₂ gas and pressure-composition-temperature measurements. La replacement by Mg was found to proceed in an ordered way, only within the Laves-type parts of the hybrid crystal structure, yielding formation of LaMgNi₄ slabs with statistic and equal occupation of one site by La and Mg atoms. Mg alters structural features of the hydrogenation process. Instead of a strong unilateral anisotropic expansion which takes place on hydrogenation of La₂Ni₇, the unit cell of La_1.5Mg_0.5Ni₇D_9.1 is formed by nearly equal hydrogen-induced expansions proceeding in the basal plane (Δa/a=7.37%) and along [001] (Δc/c=9.67%). In contrast with La₂Ni₇D_6.5 where only LaNi₂ layers absorb hydrogen atoms, in La_1.5Mg_0.5Ni₇D_9.1 both LaNi₅ and LaMgNi₄ layers become occupied. Nine types of sites were found to be filled by D in total, including tetrahedral (La,Mg)₂Ni₂, (La,Mg)Ni₃, Ni₄, tetragonal pyramidal La₂Ni₃ and trigonal bipyramidal (La,Mg)₃Ni₂ interstices. The hydrogen sublattice around the La/Mg site shows formation of two co-ordination spheres of D atoms: an octahedron MgD₆ and a 16-vertex polyhedron LaD₁₆ around La. The interatomic distances are in the following ranges: La-D (2.28-2.71), Mg-D (2.02-2.08), Ni-D (1.48-1.86 Å). All D-D distances exceed 1.9 Å. Thermodynamic PCT studies yielded the following values for the ΔH and ΔS of hydrogenation/decomposition; ΔH_H=−15.7±0.9 kJ (mol_H)⁻¹ and ΔS_H=−46.0±3.7 J (K mol_H)⁻¹ for H₂ absorption, and ΔH_H=16.8±0.4 kJ (mol_H)⁻¹ and ΔS_H=48.1±1.5 J (K mol_H)⁻¹ for H₂ desorption.     

A green process for coupling manganese oxides with titanium(IV) dioxide

MnO(2) nanoparticle-loaded TiO(2) prepared by a green process capable of removing harmful MnO(4)(-) ions from water exhibits catalytic activity for a test reaction, H(2)O(2) decomposition, in the dark with its activity enhanced by UV light irradiation.     

Regularity condition by mean oscillation to a weak solution of the 2-dimensional Harmonic heat flow into sphere

We show a regularity criterion to the harmonic heat flow from 2-dimensional Riemannian manifold M into a sphere. It is shown that a weak solution of the harmonic heat flow from 2-dimensional manifold into a sphere is regular under the criterion

Patterning reactive microdomains inside polydimethylsiloxane microchannels by trapping and melting functional polymer particles

This paper describes a facile technique to pattern reactive microdomains inside polydimethylsiloxane microchannels by utilizing polymer particles as the carrier of functional groups. The air/liquid interface formed in microchannels equipped with microwells exerts lateral force on the particles, trapping particles only inside the wells. We then fix the polymer matrix on the wells by melting the trapped particles to form reactive domains with flexible shapes and high resolution. We employed monodisperse poly(styrene-co-glycidyl methacrylate) microparticles having an epoxy group and patterned various types of microdomains with a resolution of several micrometers. Several tests confirmed the presence of the epoxy group and the flatness of the patterned domain. The presented scheme provides a new way of preparing highly functional microsystems by using simple operations and would be useful for various applications, including local patterning of graft polymers and the site-specific cultivation of cells in a confined space.     

A new homostilbene and two new homoisoflavones from the bulbs of Scilla scilloides

A new homostilbene, named scillabene A (2), and two new homoisoflavones, named scillavones A (3) and B (4), were isolated from the bulbs of Scilla scilloides DRUCE (Liliaceae) along with 13 known compounds comprising a homostilbene, seven homoisoflavones, a xanthone, a lignan, and three nortriterpenes. The structures of 2-4 were characterized as 3,5,4'-trihydroxy-3'-methoxy-4-methyl-trans-stilbene, (3R)-5,7,2'-trihydroxy-3',4'-dimethoxyspiro{2H-1-benzopyran-7'-bicyclo[4,2,0]octa[1,3,5]-trien}-4-one and (3S)-3-(3,4-dihydroxybenzyl)-5-hydroxy-6,7-dimethoxychroman-4-one, respectively, on the basis of spectroscopic data and X-ray crystallographic analysis.