Determination of selenomethionine by high performance liquid chromatography-direct hydride generation-atomic absorption spectrometry

A simple, reliable, trace determination of selenomethionine (Semet) based on a direct hydride generation atomic absorption spectrometric method was developed using sodium tetrahydroborate (0.3% in 0.2% NaOH) and hydrochloric acid (3 M). The method excluded any chemical pretreatment prior to hydride generation (HG). The optimized HG system was successfully coupled with the HPLC system. The detection limit (3σ of blank; n=5), reproducibility (R.S.D. of three successive analyses/day, performed on three different days), and repeatability (R.S.D. of three successive analyses) of the method were 1.08 ng ml⁻¹, 9.8% for 9.04 ng ml⁻¹ and 2.1–9.5% for 30.0–1.27 ng ml⁻¹ Semet as Se (standards prepared in Milli-Q water). Calibration graph was linear up to 30 ng ml⁻¹. This HPLC-HG-AAS method is very promising and successfully determined Semet (spiked) in human urine.     

A hybrid FVM–LBM method for single and multi‐fluid compressible flow problems

The lattice Boltzmann method (LBM) has established itself as an alternative approach to solve the fluid flow equations. In this work we combine LBM with the conventional finite volume method (FVM), and propose a non‐iterative hybrid method for the simulation of compressible flows. LBM is used to calculate the inter‐cell face fluxes and FVM is used to calculate the node parameters. The hybrid method is benchmarked for several one‐dimensional and two‐dimensional test cases. The results obtained by the hybrid method show a steeper and more accurate shock profile as compared with the results obtained by the widely used Godunov scheme or by a representative flux vector splitting scheme. Additional features of the proposed scheme are that it can be implemented on a non‐uniform grid, study of multi‐fluid problems is possible, and it is easily extendable to multi‐dimensions. These features have been demonstrated in this work. The proposed method is therefore robust and can possibly be applied to a variety of compressible flow situations. Copyright © 2009 John Wiley & Sons, Ltd.     

Study of layered silicate clays as synergistic nucleating agent for polypropylene

Effect of very small quantities of organically modified layered silicate clay on the nucleation of polypropylene (PP), as an additive at ppm levels dosage was investigated, in combination with two of the most commercially exploited organic nucleating agents, one of which is a cyclic aromatic phosphinate salt and the other is bis(3,4‐dimethylbenzylidene) sorbitol, each representing a separate class of nucleating molecules by itself. Substitution of a considerable fraction of either of these organic nucleating agents with organically modified inorganic nanoclay was seen to result in a unique synergy between the two in nucleating PP. Polarized light microscopy studies of these synergistic formulations with organoclay to nucleating agent ratios of 1:1 and 1:3 totaling 0.2 weight percent in PP showed significant reduction in spherulite size from that of non‐nucleated PP, and compared with the samples containing exclusive organic nucleating agent at similar loading. Differential scanning calorimetric studies provided evidence and insight into such synergistic behavior. Crystallization and supercooling temperatures for the synergistic formulations were comparable for those formulations containing only organic nucleating agents, indicating comparable nucleation efficiency, whereas organoclay alone, although showing some extent of nucleation, was clearly poorer in efficiency. Wide and small angle X‐ray scattering studies further explained these observations. An increase in the gamma polytype fraction was seen in samples that contained both organoclay and nucleating agent, pointing to the role of organoclay as a gamma nucleator. Organoclay was found to be completely exfoliated in these synergistic formulations and was seen as well‐dispersed, single platelets in the PP matrix. A hybrid network consisting of exfoliated organoclay platelets and organic nucleating agent molecules was proposed, which is more stable and stiffer than the network formed by nucleating agent alone. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1786–1794, 2010     

A numerical bifurcation study of friction effects in a slip-controlled torque converter clutch

Friction plays a key role in the efficiency and stability of the slip-controlled torque converter clutches. The effects of friction on the dynamics and stability of a slip-controlled torque converter clutch system using a bifurcation-analysis-based approach is presented in this paper. A three degree-of-freedom nonlinear driveline model with integral feedback action to control the clutch slip speed has been utilized for this study. The clutch interface friction is dependent on the slip speed and is a function of the static friction constant, μ ₀, the low velocity friction constant μ ₁, and the low velocity exponential rate, γ. Using one-parameter numerical continuation, local Hopf bifurcations of the subcritical type are observed as the friction parameters μ ₁ and γ were varied at low slip speeds. The continuation results are verified using simulations of the full nonlinear model. Stick-slip and undesirable oscillations of the model inertia elements are observed for certain parameter values. As the slip speed is increased, the bifurcation instability occurs at an increasingly higher value of μ ₁ signifying an improved tolerance of negative friction gradient at higher slip speeds. Smaller exponential rates γ are tolerated at higher slip speeds before the bifurcation instability occurs. For the range of parameter values considered, no bifurcations occur for a slip speeds higher than 3.4 and 4.5 rad/s with μ ₁ and γ as the continuation parameters, respectively. These values of slip speeds are much lower than the system’s first mode of torsional vibration of 16 Hz (≈100 rad/s).     

Specific detection of Campylobacter jejuni using the bacteriophage NCTC 12673 receptor binding protein as a probe

Campylobacter jejuni is found in the intestines of poultry, cattle, swine, wild birds and pet animals and is the major cause of foodborne gastroenteritis in developed countries. We report the use of the receptor binding protein (RBP) of Campylobacter bacteriophage NCTC 12673 for the specific capture of Campylobacter jejuni bacteria using RBP-derivatized capturing surfaces. The Gp48 RBP was expressed as a glutathione S-transferase-Gp48 (GST-Gp48) fusion protein and immobilized onto surface plasmon resonance (SPR) surfaces using glutathione self-assembled monolayers (GSH SAM). Bovine serum albumin (BSA) was used to block any non-specific binding. Glutathione SAM leads to an oriented attachment of the protein, resulting in a two- to three-fold improvement of bacterial capture when compared to dithiobis(succinimidyl propionate) (DTSP) SAM-based unoriented attachment. The specificity of recognition was confirmed using Salmonella enterica subsp. enterica serovar Typhimurium as a negative control, which indeed showed negligible binding. The detection limit of the RBP-derivatized SPR surfaces was found to be 10(2) cfu/ml. Finally, GST-Gp48 was also immobilized onto magnetic beads that were successfully used to capture and pre-concentrate the host pathogen from suspension.     

Unsymmetrical diimine complexes of iron(II) and manganese(II): synthesis, structure and photoluminescence of an isomer

Two bis(unsymmetrical diimine) complexes of (L(NO(2))(?1))(L(NO(2))(?2))M(II)Cl(2) family with M = Fe and Mn, are reported (L(NO(2))(?) = (E)-3-nitro-N-(pyridine-2-ylmethylene)aniline; ? = dihedral angle between the diimine unit including pyridine ring and the phenyl ring planes). Pure tcc-(L(NO2)(33.6))(L(NO2)(79.3))Fe(II)Cl(2)·0.5H(2)O (1) and tcc-(L(NO2)(32.0))(L(NO2)(79.4))Mn(II)Cl(2)·0.5H(2)O (2) isomers have been successfully isolated in high yields and characterized by elemental analyses, variable temperature magnetic susceptibility measurements, IR, mass, UV-vis and M?ssbauer spectra including the single-crystal X-ray structure determinations that identified strong intermolecular non-bonding interactions in lattice (tcc refers to trans-cis-cis positions with respect to pyridine N-imine N-Cl donors). Geometries optimizations of all possible tcc, ttt, ctc, ccc and cct isomers of iron at the B3LYP/DFT level in gas-phase have shown that the tcc-isomer incorporating two non-equivalent ligands as in (L(NO(2))(42))(L(NO(2))(61))Fe(II)Cl(2), 1 (g), is stabilized by 6-20 kJ mol(-1) compared to other isomers where two ligands are equivalent. The frozen methanol glasses of 1 and 2 are luminescent at 77 K (1: λ(ext) = 370, λ(em) = 521 nm, χ(2) = 1.3, τ(avg) = 0.57 ns; 2: λ(ext) = 368, λ(em) = 524 nm, χ(2) = 1.1, τ(avg) = 0.90 ns). The DFT calculations have identified four closely spaced localized π(*) orbitals comprising of two non-equivalent ligands as UPMOs. The features contrast the tcc-isomer of (L(?))(2)Fe(II)Cl(2) (3), congener of 1 without -NO(2) substitution and non-emissive (bpy)(2)Fe(II)Cl(2) (4) where two ligands are equivalent. TD-DFT calculations have assigned intra-ligand (IL) and ligand to ligand charge transfer (LLCT) dominated excited states as the origin of luminescence of 1 and 2.     

Vanadium complexes immobilized on solid supports and their use as catalysts for oxidation and functionalization of alkanes and alkenes

This review mainly discusses the immobilization strategies that have been used for vanadium complexes, typically mesoporous material, zeolites and polymers, the characterization procedures for the obtained materials, and their catalytic applications. The retention of the active metal compound within the catalyst may be based on (i) adsorption, (ii) the formation of covalent bonds between metal ligand and support, (iii) ion exchange, (iv) encapsulation, or (v) entrapment. The heterogenized complexes are used as catalysts for oxidations and functionalization of alkanes, alkenes and other substrates, and an account of the various applications reported is given.     

Automatic locking of a parametrically resonating,base-excited,nonlinear beam

Nonlinear Dynamics - Described is a closed-loop control scheme capable of stabilizing a parametrically excited nonlinear structure in several vibration modes. By setting the relative phase between...     

Construction and studies of a new class of reciprocal trees: interknitting of the Pascal's triangle

A method of construction of a new class of trees with reciprocal pairs of eigenvalues (λ, 1/λ) has been developed. They are derived from star graphs and can be symbolized as K _{1, n ?1} + n(p) + mK ₂ (1 ≤ m ≤ n ? 1 except for n = 1). The trees are minimally Kekulenoid and hence contain reciprocal pairs of eigenvalues in their eigenspectra. The characteristic polynomial coefficients of these trees with given values of n and m are shown to be obtainable by appropriate use of the Pascal's triangle. A general formula for this purpose has been developed. An analytical formula for the Wiener indices of such trees in terms of m and n has been derived and some consequences of this formula are presented. The relevance of these trees to real molecular structures is discussed. The trees have been shown to be useful in observing the subspectrallity of two series of IPR fullerenes of formulae C_{50+10 n} and C_{60+12 n} (n is a positive integer).