Direct glycosylation with anomeric hydroxy sugars by activation with 3-fluorophthalic anhydride and trifluoromethanesulfonic anhydride

An efficient and direct one-pot glycosylation method using anomeric hydroxy sugars as glycosyl donors, employing 3-fluorophthalic anhydride and triflic anhydride as activating agents, has been developed. The present glycosylation utilizing 3-fluorophthalic anhydride resulted in few to no undesired self-condensed esters than the glycosylation using phthalic anhydride. Intermediates in the present glycosylation were identified by an NMR study.     

Sub-iteration leads to accuracy and stability enhancements of semi-implicit schemes for the Navier–Stokes equations

We present an iterative semi-implicit scheme for the incompressible Navier–Stokes equations, which is stable at CFL numbers well above the nominal limit. We have implemented this scheme in conjunction with spectral discretizations, which suffer from serious time step limitations at very high resolution. However, the approach we present is general and can be adopted with finite element and finite difference discretizations as well. Specifically, at each time level, the nonlinear convective term and the pressure boundary condition – both of which are treated explicitly in time – are updated using fixed-point iteration and Aitken relaxation. Eigenvalue analysis shows that this scheme is unconditionally stable for Stokes flows while numerical results suggest that the same is true for steady Navier–Stokes flows as well. This finding is also supported by error analysis that leads to the proper value of the relaxation parameter as a function of the flow parameters. In unsteady flows, second- and third-order temporal accuracy is obtained for the velocity field at CFL number 5–14 using analytical solutions. Systematic accuracy, stability, and cost comparisons are presented against the standard semi-implicit method and a recently proposed fully-implicit scheme that does not require Newton’s iterations. In addition to its enhanced accuracy and stability, the proposed method requires the solution of symmetric only linear systems for which very effective preconditioners exist unlike the fully-implicit schemes.     

RKKY ferromagnetism with Ising-like spin states in intercalated Fe(1/4)TaS2

We investigated the magnetic nature of Fe(1/4)TaS2 using x-ray absorption spectroscopy, photoemission spectroscopy, and first principles band calculations. The results show a large unquenched orbital magnetic moment (～1.0 μ(B)/Fe) at intercalated Fe sites, resulting in a gigantic magnetic anisotropy (H(A)?60 T). The magnetic coupling is well understood in terms of the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, suggesting a novel RKKY ferromagnet with Ising-type spin states. We also found that this indirect exchange coupling between the neighboring Fe spins is ferromagnetic and maximized at the Fe-Fe distance of 2×2 superstructure.     

Preparation of functional spherical polysilsesquioxane/gold nanoparticle composites and their applications in DNA assay

Functional spherical solid and hollow particles of polysilsesquioxanes (PSQs) containing amine, thiol, and vinyl groups were prepared by polymerizing organotrialkoxysilanes (OTASs) containing corresponding chemical groups. Fluorescent PSQ particles were prepared by physically entrapping Rhodamine 6G, Coumarin 7, and Fluoresceine sodium salts. The intensity of fluorescent light increased initially with increasing amount of entrapped fluorophores and then leveled off or decreased slightly after reaching a maximum value. PSQ particles containing gold nanoparticles (GNPs), both inside and on the surface, were prepared by the in situ reduction of gold ions by the PSQ particles. When the reduction reaction was carried out for extended periods of time, the GNP that had formed inside the poly(3-mercaptopropyl)silsesquioxane (PMPSQ) and polyvinylsilsesequioxane (PVSQ) particles underwent interesting morphological changes. PSQ particles containing amine and thiol groups fixed the GNPs on the surface, which could be utilized further in binding amine-modified oligo-DNA strands. The aggregation of PSQ/GNP particles combined with complementary oligo-DNA strands was examined to demonstrate that these particles could be applied to DNA assays and isolation. The particles were characterized by scanning electron microscopy, transmission electron microscopy, solid state nuclear magnetic resonance spectroscopy, ultraviolet/visible spectroscopy, and fluorescence microscopy.     

Interactions between tri-methylaluminum molecules and their effect on the reaction of tri-methylaluminum with an OH-terminated Si (0 0 1) surface

We studied the interaction between tri-methylaluminum (Al(CH₃)₃, TMA) molecules and their effect on TMA reactions with a fully OH-terminated Si (0 0 1) surface for initial aluminum oxide thin-film growth using density functional theory. The reaction between an adsorbed TMA and the surface produced a di-methylaluminum (-Al(CH₃)₂, DMA) group, and further reaction to a uni-methylaluminum (-AlCH₃, UMA) group with energy barriers of 0.50 and 0.21 eV, respectively. A second TMA adsorbed near the already adsorbed TMA, DMA, or UMA group showed higher energy barriers (0.68-1.01 eV) for its reaction to produce a DMA group due to the interaction between them. Therefore, the fully OH-terminated Si (0 0 1) surface would be covered by the mixture of the adsorbed TMA and UMA groups at an intermediate surface temperature.     

A new phenolic glycoside from the fruits of <Emphasis Type="Italic">Capsicum annuum</Emphasis>

A new compound, 4-O-(6'-O-p-hydroxybenzoyl-β-D-glucopyranosyl)-cis-p-coumaric acid, was isolated from the fruits of hot pepper (Capsicum annuum L.). The structure of the compound was established on the basis of NMR, FAB-MS, and IR spectroscopic data.     

Preparation and tomographic reconstruction of an arbitrary single-photon path qubit

We report methods for preparation and tomographic reconstruction of an arbitrary single-photon path qubit. The arbitrary single-photon path qubit is prepared losslessly by passing the heralded single-photon state from spontaneous parametric down-conversion through variable beam splitter. Quantum state tomography of the single-photon path qubit is implemented by introducing path-projection measurements based on the first-order single-photon quantum interference. Using the state preparation and path-projection measurements methods for the single-photon path qubit, we demonstrate preparation and complete tomographic reconstruction of the single-photon path qubit with arbitrary purity.     

Viscoelastic behavior,order-disorder transition,and phase equilibria in mixtures of a block copolymer and an endblock-associating resin

The viscoelastic behavior, order-disorder transition, and phase equilibria in mixtures of a block copolymer and an endblock-associating resin were investigated. The block copolymer was a polystyrene-block-polyisoprene-block-polystyrene (KRATON® D-1107, Shell Development Co.) copolymer. The endblock-associating resins investigated were two different grades of a commercially available random copolymer of poly(α-methyl styrene) and polystyrene, one with a weight-average molecular weight \[\bar M_{\rm w}\] of 710 (KRISTALEX® 3085, Hercules Inc.) and the other with \[\bar M_{\rm w}\] = 4100 (KRISTALEX® 5140, Hercules Inc.). Mixtures of various proportions of the block copolymer and the endblock-associating resin were prepared in toluene solvent. With the mixtures, measurements of dynamic viscoelastic properties were made, namely, dynamic storage modulus G″ and dynamic loss modulus G″ as a function of temperature from temperature scans of the samples using a Rheometrics Mechanical Spectrometer. The following observations were made. (1) The plateau modulus of the block copolymer increased with increasing amount of KRISTALEX 3085 or KRISTALEX 5140, indicating that the low-molecular-weight resin was associated with the polystyrene microdomains of the block copolymer. (2) When KRISTALEX 3085 (up to 30 wt %) was added to the block copolymer, the glass transition temperature (T_g) of the polyisoprene midblock of the SIS block copolymer was shifted toward higher temperatures, indicating that part of the KRISTALEX 3085 added had associated with the rubbery midblock of the block copolymer. Also investigated was the order-disorder transition behavior of the mixtures, using a rheological technique (log G′ versus log G″ plots) recently introduced by Han and Kim. It has been found that the order-disorder transition temperature T_r of mixtures of the SIS block copolymer and KRISTALEX 3085 decreased steadily with increasing amount of KRISTALEX 3085, whereas the addition of KRISTALEX 5140 increased the T_r of the block copolymer. It was found by light scattering and hot-stage microscopy that macrophase separation occurred in the KRATON 1107/KRISTALEX 5140 mixtures while microdomains of polystyrene were present in the block copolymer.     

Synthesis of phenylquinoxaline oligomers containing pendant electron‐donating and electron‐withdrawing groups

A series of extended 6‐substituted quinoxaline AB monomer mixtures, 2‐(4‐fluorophenyl)‐3‐[4‐(4‐hydroxyphenoxy)phenyl]‐6‐substituted quinoxaline and 3‐(4‐fluorophenyl)‐2‐[4‐(4‐hydroxyphenoxy)phenyl]‐6‐substituted quinoxaline, were prepared and polymerized to afford phenylquinoxaline oligomers. High‐molecular‐weight polymers could not be obtained because of the formation of cyclic oligomers. On the basis of matrix‐assisted laser desorption/ionization time‐of‐flight analysis and molecular modeling results, the formation of a cyclic dimer could be a favorable process resulting in low‐molecular‐weight oligomers. They were completely soluble and amorphous, with glass‐transition temperatures varying from 165 to 266 °C, and they had thermooxidative stability, with samples displaying 5% weight loss temperatures of 419–511 °C in nitrogen. The thermal properties of the monomers and resultant polymers dramatically depended on the polarity of the substituents. The monomers and resultant oligomers displayed high fluorescence in tetrahydrofuran solutions and N‐methyl‐2‐pyrrolidinone solutions, respectively. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6465–6479, 2005