Chemically defined sialoside scaffolds for investigation of multivalent interactions with sialic acid binding proteins

Four glycodendrons and a glycocluster were synthesized from carbohydrate building blocks to form paucivalent (di- to tetravalent) structures of controlled scaffold architectures. Enzymatic sialylation of the functionalized cluster and dendrons, terminated in lactose residues, generated a library of paucivalent synthetic sialosides displaying sialic acids with different dispositions. These newly constructed bioactive sialic acid-based structures were differentially recognized by sialoadhesin, a mammalian macrophage sialic acid binding protein. The binding of the sialosides to sialoadhesin was evaluated by an enzyme-linked immunosorbant assay to investigate the complementarity of scaffold structure and binding to sialoadhesin. Modulating the interaction between sialoadhesin and its sialic acid ligands has important implications in immunobiology.     

Circularly polarized unidirectional emission via a coupled plasmonic spiral antenna

In this Letter, we study the emission properties of an electric dipole emitter coupled to a plasmonic spiral structure. The plasmonic spiral structure functions as an optical antenna, coupling the electric dipole emission into circularly polarized unidirectional emission in the far field. Increasing number of turns of the spiral leads to narrower angular width of the emission pattern in the far field. For a spiral antenna with six turns, antenna directivity of 23.5 dB with a directional emission into a narrow angular cone of 4.3° can be achieved. The emitted photons carry spin that is essentially determined by the handedness of the spiral antenna. By reversing the spiral, one can switch the polarization of the emission field between left-hand and right-hand circular polarizations. The spiral antenna may be used as a nanoscale circular polarization source in single molecule sensing, single-photo sources, and integrated photonic circuits.     

Spectrally dependent radiative transfer in a heat conducting medium

Coupled thermal radiation and heat conduction has been examined in a medium with a spectrally dependent mass absorption coefficient. This contrasts with prior studies in which semi-empirical total absorption correlations, having no connection with spectral characteristics, have been employed. Two spectral distribution functions were considered; the exponential and the uniform or gray. The former is a realistic model for molecular gases having both theoretical and empirical justification, while the latter is frequently employed despite its artificiality. The formulation is obtained in terms of exact expressions for the one-dimensional radiative transmission and absorption functions; other formulations of similar problems have approximated the angular integrations by the substitute kernel method. Results have been obtained for a wide range of parameters, considerably extending available results. Exponential and gray band results differ considerably in both a qualitative and a quantitative sense.     

Bis(3,5-dimethylpyrazol-1-yl)acetate bound to titania and complexed to molybdenum dioxido as a bidentate N,N′-ligand. Direct comparison with a bipyridyl analog in a photocatalytic arylalkane oxidation by O2

Bis(3,5-dimethylpyrazol-1-yl)acetate, well known as a tridentate N,N,O ligand, was bound to MoO₂Cl₂ in a bidentate N,N manner by anchoring covalently, at first, the ligand onto a titanium oxide surface, followed by its complexation with the molybdenum dioxo entity. It was fully characterized by ¹³CPMAS NMR and FT-IR spectroscopy. The tethered complex was directly compared with an analogous bipyridyl species in the catalytic ethylbenzene oxidation by O₂ at room temperature, atmospheric pressure, and under visible light. The bis(pyrazol-1-yl) catalyst exhibited a significant initial higher oxygen atom transfer (OAT) capability, well in accord with its electron donating property. It was, unfortunately, hampered by a premature leaching phenomenon, totally absent in the comparable bipyridyl system.     

Substituted 5-(D,L-erythro-1′,2′-dihydroxypropyl)pyrazines. Potential precursors for the synthesis of biopterin derivatives

A convenient synthesis of substituted 5-( D,L )-erythro-1′,2′-dihydroxypropyl)pyrazines from crotonic acid 4 is described. The anomalous behavior during decarboxylation of functionalized 2-oximino-3-oxoesters 8a,b is noted. The structures of prepared compounds were determined by spectroscopic methods.     

Anomalous ions in the chemical ionization mass spectra of aromatic nitro and nitroso compounds

The appearance of [MH-30]⁺ ions in the chemical ionization mass spectra of aromatic nitro compounds may be due to their initial reduction to the corresponding amines within the ion source. Aromatic nitroso compounds may be similarly reduced to yield [MH-14]⁺ ions. The hydroxy derivatives of the nitroso compounds yield further anomalous ions at [MH-16]⁺ probably due to the reduction of the hydroxy groups.     

Modifying Glassy Carbon (GC) Electrodes to Confer Selectivity for the Voltammetric Detection of L‐Cysteine in the Presence of dl‐Homocysteine and Glutathione

In this communication we report a proof of concept study of the use of cyclic voltammetry with a polyeugenol‐modified glassy carbon (GC) electrode to selectively detect L ‐cysteine in the presence of both dl ‐homocysteine and glutathione in perchloric acid. The formation of a polyeugenol‐modified gold electrode is also reported for the first time.     

The electronic structure of 1,2-PCB10H11 molecular films: a precursor to a novel semiconductor

The band gaps and electronic structure of undoped films of molecular icosahedra of closo-1-phospha-2-carbadodecaborane (1,2-PCB₁₀H₁₁) are reported. 1,2-PCB₁₀H₁₁ adsorbs on Au and Ag substrates to generate molecular thin films with the Fermi level (chemical potential) placed closer to the lowest unoccupied molecular orbital than has been observed with closo-1,2-dicarbadodecaborane (1,2-C₂B₁₀H₁₂, orthocarborane) adsorbed on Co, Cu or Ag. Both 1,2-PCB₁₀H₁₁ and 1,2-C₂B₁₀H₁₂ molecular films exhibit an unoccupied molecular defect state above the Fermi level. The vibrational modes, observed in infra-red absorption, are close to the values expected for the isolated 1,2-PCB₁₀H₁₁ molecule. Consistent with the placement of the Fermi level in the molecular films, fabrication of heterojunction diodes from partially dehydrogenated 1,2-PCB₁₀H₁₁ indicates that the resultant PCB₁₀H_x semiconductor film is more n-type than the corresponding boron carbide semiconductor formed from 1,2-C₂B₁₀H₁₂, orthocarborane. PACS 68.43.-h; 73.20.Hb; 31.15.Ct; 79.60.-i     

The evaluation of non-reflecting boundary conditions for duct acoustic computation

A simple method is used to quantify the performance of non-reflecting boundary conditions for duct acoustic applications. The method uses a two-dimensional wavesplitting technique to decompose the linearized Euler equations into its constitutive modes, allowing the magnitude of reflected waves from outflow boundaries to be accurately determined. Realistic conditions are simulated by conducting the boundary condition analysis using acoustic waves with characteristics often found in duct and turbomachinery problems. For this paper, the method is used to investigate the performance of three different buffer zone implementations and the Perfectly Matched Layer as non-reflecting boundary conditions. The effect of the damping properties of these boundary conditions and the incident acoustic wave characteristics on performance are considered. Results indicate that the buffer zone boundary condition using explicit damping of the solution vector after each timestep produces the best non-reflecting performance. A deterioration in performance was observed for incident waves at high angles relative to the boundary normal for all implementations.