Sensitive LC MS quantitative analysis of carbohydrates by Cs<Superscript>+</Superscript> attachment

The development of a sensitive assay for the quantitative analysis of carbohydrates from human plasma using LC/MS/MS is described in this paper. After sample preparation, carbohydrates were cationized by Cs(+) after their separation by normal phase liquid chromatography on an amino based column. Cesium is capable of forming a quasi-molecular ion [M + Cs](+) with neutral carbohydrate molecules in the positive ion mode of electrospray ionization mass spectrometry. The mass spectrometer was operated in multiple reaction monitoring mode, and transitions [M + 133] --> 133 were monitored (M, carbohydrate molecular weight). The new method is robust, highly sensitive, rapid, and does not require postcolumn addition or derivatization. It is useful in clinical research for measurement of carbohydrate molecules by isotope dilution assay.     

Complexes of mixed silicon halides with 4‐picoline

The reaction products of an addition reaction of five different silicon tetrahalides with the aromatic nitro­gen base 4‐methyl­pyridine are presented. The following five structures are isomorphous: (I) tetra­chloro­bis(4‐methyl­pyridine)­silicon, C₁₂H₁₄­Cl₄­N₂Si, (II) bromo­tri­chloro­bis(4‐methyl­pyridine)­silicon, C₁₂H₁₄­Br­Cl₃N₂Si, (III) di­bromo­di­chloro­bis(4‐methyl­pyridine)­silicon, C₁₂H₁₄­Br₂­Cl₂N₂Si, (IV) tri­bromo­chloro­bis(4‐methyl­pyridine)­silicon, C₁₂H₁₄Br₃­Cl­N₂Si, and (V) tetra­bromo­bis(4‐methyl­pyridine)­silicon, C₁₂H₁₄Br₄N₂Si. The mol­ecules of (I) and (V), with D_2h symmetry, have crystallographic C_2h symmetry, while the molecules of (II), (III) and (IV) have a lower molecular symmetry, but as a result of the disorder of the halogen ligands, they appear to be of the same crystallographic symmetry. The environment around the Si atom can be described as a slightly distorted octahedron with the methyl­pyridine ligands occupying axial positions and the four halogen ligands in the equatorial plane. In spite of the different substitution pattern of the silicon centre, there are only insignificant differences between these five structures.     

Quantitative small-angle light-scattering studies of the melting and crystallization of LLDPE/LDPE blends

Small-angle light-scattering (SALS) patterns were obtained during melting and crystallization of blends of linear low-density polyethylene (LLDPE) with conventional low-density polyethylene (LDPE). Quantitative measurements of these SALS patterns using a two-dimensional optical multichannel analyzer apparatus (OMA2) indicate that the LLDPE which is miscible with the LDPE component in the molten state crystallizes first, forming volume-filling spherulites. The LDPE then crystallizes within the preformed spherulites. These findings are supported by optical microscopy studies showing that the blend samples were volume filled with one kind of the spherulites having a radius comparable to that of the pure LLDPE. The SALS intensity curve changes with composition of the blends in a manner that may be interpreted by considering the orientation of crystals within spherulites. It has been observed that the spherulites in the blend have more diffuse boundaries as the LDPE content increases. The lattice spacing and long spacings in blends were obtained by wide-angle and small-angle x-ray scattering, respectively. The SALS technique along with differential scanning calorimetry (DSC) is shown to be useful for determining the crystallization behavior of a crystallizable polymer blend system.     

The Ternary System Nickel/Silicon/Titanium Revisited

The constitution of the ternary system Ni/Si/Ti is investigated over the entire composition range using X‐ray diffraction (XRD), energy dispersive X‐ray spectroscopy (EDS), differential thermal analysis (DTA), and metallography. The solid state phase equilibria are determined for 900 °C. Eight ternary phases are found to be stable. The crystal structures for the phases τ₁NiSiTi, τ₂Ni₄Si₇Ti₄, τ₃Ni₄₀Si₃₁Ti₁₃, τ₄Ni₁₇Si₇Ti₆, and τ₅Ni₃SiTi₂ are corroborated. For the remaining phases the compositions are determined as Ni₆Si₄₁Ti₅₃ (τ₆), Ni₁₆Si₄₂Ti₄₂(τ₇), and Ni₁₂Si₄₅Ti₄₃ (τ₈). The reaction scheme linking the solid state equilibria with the liquidus surface is amended to account for these newly observed phases. The discrepancies between previous experimental conclusions and modeling results are addressed. The liquidus surface is dominated by the primary crystallisation field of τ₁NiSiTi, the only congruently melting phase.     

Coulomb forces on DNA polymers in charged fluidic nanoslits

We investigate the repulsive electrostatic interactions between a DNA polyelectrolyte and the charged walls of a fluidic nanoslit. The scaling of the DNA coil size with the physical slit height revealed electrostatic depletion regions that reduced the effective slit height. These regions exceeded the Debye screening length of the buffer, λ(D)(buffer), and saturated at ≈ 50 nm when λ(D)(buffer) reached 10 nm. We explain these results by modeling a semiflexible charged rod near a charged wall and the electrostatic screening by the polyelectrolyte. These results demonstrate the surprisingly long range over which a nanofluidic device can exert field-effect control over confined molecules.