Inactivation of Aspergillus flavus spores by curcumin-mediated photosensitization

Minimizing fungal infection is essential to the control of mycotoxin contamination of foods and feeds but many potential control methods are not without their own safety concerns for the consumers. Photodynamic inactivation is a novel light-based approach which offers a promising alternative to conventional methods for the control of mycotoxigenic fungi. This study describes the use of curcumin to inactivate spores of Aspergillus flavus, one of the major aflatoxin producing fungi in foods and feeds. Curcumin is a natural polyphenolic compound from the spice turmeric (Curcuma longa). In this study the plant has shown to be an effective photosensitiser when combined with visible light (420 nm). The experiment was conducted in in vitro and in vivo where A. flavus spores were treated with different photosensitiser concentration and light dose both in buffer solution and on maize kernels. Comparison of fungal load from treated and untreated samples was determined, and reductions of fungal spore counts of up to 3 log CFU ml−1 in suspension and 2 log CFU g−1 in maize kernels were obtained using optimal dye concentrations and light dose combinations. The results in this study indicate that curcumin-mediated photosensitization is a potentially effective method to decontaminate A. flavus spores in foods and feeds.

An incipient 310 helix in Piv-Pro-Pro-Ala-NHMe as a model for peptide folding

The molecular mechanism of helix nucleation in peptides and proteins is not yet understood and the question of whether sharp turns in the polypeptide backbone serve as nuclei for protein folding has evoked controversy1,2. A recent study of the conformation of a tetrapeptide containing the stereochemically constrained residue alpha-aminoisobutyric acid, both in solution and the solid state, yielded a structure consisting of two consecutive beta-turns, leading to an incipient 310 helical conformation3,4. This led us to speculate that specific tri- and tetra-peptide sequences may indeed provide a helical twist to the amino-terminal segment of helical regions in proteins and provide a nucleation site for further propagation. The transformation from a 310 helical structure to an alpha-helix should be facile and requires only small changes in the phi and psi conformational angles and a rearrangement of the hydrogen bonding pattern5. If such a mechanism is involved then it should be possible to isolate an incipient 310 helical conformation in a tripeptide amide or tetrapeptide sequence, based purely on the driving force derived from short-range interactions. We have synthesised and studied the model peptide pivaloyl-Pro-Pro-Ala-NHMe (compound I) and provide here spectroscopic evidence for a 310 helical conformation in compound I.

From the {Cu(μ2-S)N}4 butterfly architecture to the {Cu(μ3-S)N}12 double wheel

Copper(I) complexes with {Cu(μ2-S)N}4 and {Cu(μ3-S)N}12 core portions of butterfly-shaped or double wheel architectures have been isolated in the reaction of Cu(I) with the Schiff base ligand C6H4(CHNC6H4S)2, aiso-abtâ, under different conditions. View the MathML source containing the tetranuclear electroneutral complex View the MathML source is formed by the reaction of CuI in acetonitrilic solution and recrystallization from DMF, whereas View the MathML source containing dodecanuclear View the MathML source wheels is accessible starting from CuBF4. Complexes 2 and 4 represent the first examples of cyclic complexes with the same overall stoichiometry but different ring sizes. The ligand induces two different coordination environments around copper(I) by switching between μ2- and μ3-sulfur bridging modes.

New insights from a fixed-point analysis of single cell IEEE 802.11 WLANs

We study a fixed-point formalization of the well-known analysis of Bianchi. We provide a significant simplification and generalization of the analysis. In this more general framework, the fixed-point solution and performance measures resulting from it are studied. Uniqueness of the fixed point is established. Simple and general throughput formulas are provided. It is shown that the throughput of any flow will be bounded by the one with the smallest transmission rate. The aggregate throughput is bounded by the reciprocal of the harmonic mean of the transmission rates. In an asymptotic regime with a large number of nodes, explicit formulas for the collision probability, the aggregate attempt rate, and the aggregate throughput are provided. The results from the analysis are compared with ns2 simulations and also with an exact Markov model of the backoff process. It is shown how the saturated network analysis can be used to obtain TCP transfer throughputs in some cases.

Strong motion compatible source geometry

Strong motion array records are analyzed in this paper to identify and map the source zone of four past earthquakes. The source is represented as a sequence of double couples evolving as ramp functions, triggering at different instants, distributed in a region yet to be mapped. The known surface level ground motion time histories are treated as responses to the unknown double couples on the fault surface. The location, orientation, magnitude, and risetime of the double couples are found by minimizing the mean square error between analytical solution and instrumental data. Numerical results are presented for Chi-Chi, Imperial Valley, San Fernando, and Uttarakashi earthquakes. Results obtained are in good agreement with field investigations and those obtained from conventional finite fault source inversions.

Interdiffusion in the Ni-Mo system

The interdiffusion coefficient in Ni(Mo) solid solution, impurity diffusion of Mo in Ni, average interdiffusion coefficient of the NiMo-sigma phase and activation energies for diffusion in solid solution and in the sigma phase of the Ni-Mo binary system are evaluated through the diffusion couple approach. These results are utilized to identify the possible diffusion mechanism. Low activation energy in the sigma phase indicates a grain-boundary-controlled diffusion process. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Metal-spinel-corundum three phase equilibria in the system Ni-Cr-Al-O at 1373 K

The tie-lines representing the inter-crystalline ion exchange equilibria between the NiCr2O4-NiAl2O4 spinet solid solution and Cr2O3-Al2O3 corundum solid solution are determined by electron microprobe andEDAX pointcountanalysis of the oxide phases equilibrated with metallic Ni at 1373 K. The component activities in the spinet solid solution are derived from the tie-lines and thermodynamic data for Cr2O3-Al2O3 solid solution available in the literature. The Gibbs energy of mixing of the spinet solid solution calculated from the experimental data is discussed in relation to the values derived from the cation distribution models which assume random mixing of cations on both tetrahedral and octahedral sites. Positive deviation from the models is observed indicating significant positive enthalpy contribution arising form the size mismatch between Al+3 and Ni+2 ions on the tetrahedral site and Al+3, Ni+2 and Cr+3 on the octahedral site. Variation of the oxygen potential for threephase equilibrium involving metallic nickel, spinet solid solution and corundum solid solution is computed as a function of composition of the solid solutions at 1373 K. The oxygen potential exhibits a minimum at aluminum cationic fraction eta(Al)/(eta(Al) + eta(Cr)) = 0.524 in the oxide solid solutions.

Chemical modification of sheep plasma glycoprotein

Glycoprotein isolated from sheep plasma was chemically modified, and the effect of chemical modification on biological activities and immunological cross reactions has been studied. The removal of sialic acid resulted in a change in the “overall conformation” of the glycoprotein as evidenced by a decrease in viscosity of the glycoprotein solution and an increased susceptibility of the glycoprotein to proteolytic enzymes. Sialic acid-free glycoprotein no longer inhibited the tryptic activity or prolonged the clotting time of plasma. However, it could react with the antiserum to sheep plasma glycoprotein. The periodate oxidation of sheep plasma glycoprotein resulted in a complete loss of inhibition of trypsin activity, prolongation of plasma clotting time, and the ability to cross-react with the rabbit antiserum. The significance of periodate oxidation in relation to the possible sequence of sugars in the carbohydrate prosthetic group in the glycoprotein is discussed. Iodination and heating in buffers of acid and alkaline pH values of sheep plasma glycoprotein resulted in complete loss of trypsin activity and ability to prolong plasma clotting time. Iodination of the glycoprotein did not affect the immunological cross-reactivity.

Studies in the polarographic behaviour of zinc-amino acid complexes

1. The polarographic behaviour of amino-acid complexes of zinc has been studied using seven amino acids as complexing agents. 2. The effect of varying the pH of the base solution and the concentration of amino-acid anion on the polarographic behaviour of zinc in these solutions have indi cated the formation of twelve amino-acid complexes. The stability constants could not be calculated due to the irreversible nature of the waves. 3. The effect of sodium hydroxide, sodium carbonate, and ammonia on the polarographic behaviour of zinc has been investigated. The results can be interpreted as due to the formation of mixed complexes in many systems. 4. Amino-acid base solutions have been found to be suitable for the polarographic estimation of zinc.

Use of Abel integral equations in water wave scattering by two surface-piercing barriers

In this paper the classical problem of water wave scattering by two partially immersed plane vertical barriers submerged in deep water up to the same depth is investigated. This problem has an exact but complicated solution and an approximate solution in the literature of linearised theory of water waves. Using the Havelock expansion for the water wave potential, the problem is reduced here to solving Abel integral equations having exact solutions. Utilising these solutions,two sets of expressions for the reflection and transmission coefficients are obtained in closed forms in terms of computable integrals in contrast to the results given in the literature which,involved six complicated integrals in terms of elliptic functions. The two different expressions for each coefficient produce almost the same numerical results although it has not been possible to prove their equivalence analytically. The reflection coefficient is depicted against the wave number in a number of figures which almost coincide with the figures available in the literature wherein the problem was solved approximately by employing complementary approximations. (C) 2009 Elsevier B.V. All rights reserved.

Adhesion of Acidithiobacillus ferrooxidans to mineral surfaces

Direct contact mechanism in bioleaching implies prior mineral adhesion of Acidithiobacillus ferrooxidans and subsequent enzymatic attack.Prior bacterial adaptation to sulfide mineral substrates influences bacterial ferrous ion oxidation rates. It is highly beneficial to understand major biooxidation mechanisms with reference to solution- and mineral-grown cells in order to optimize bioleaching reactions. For A. ferrooxidans grown in the presence of solid substrates such as sulfur, pyrite and chalcopyrite, bacterial adhesion is required for its enzymatic machinery to come into close contact for mineral dissolution.But when grown in solution substrate such as ferrous ions and thiosulfate, such an adhesion machinery is not required for substrate utilization. Proteinaceous compounds were observed on the surface of sulfur-grown cells. Such an induction of relatively hydrophobic proteins and down regulation of exposed polysaccharides leads to changes in cell surface chemistry. Sulfur-grown and pyrite- and chalcopyrite-grown bacterial cells were found to be more efficient in the bioleaching of chalcopyrite than those grown in the presence of ferrous ions and thiosulfate. (C) 2010 Elsevier B.V. All rights reserved.

The evolution of microstructure in the undercooled Zn-Sn entrained droplets

The existence of a metastable miscibility gap has been indicated from the metastable phase diagram of the Zn-Sn system calculated using regular solution and Krupkowski's models. To validate this phenomenon experimentally, the entrained droplet technique was used to achieve high undercooling and to access the metastable regions. The microstructural analysis confirms the miscibility gap and the associated monotectic reaction. Evidence is also presented for a possible massive solidification of the undercooled melt.

Interdiffusion Studies in the Co- Mo System

Study of interdiffusion in the Co-Mo system is important to understand the performance of turbine blades in jet engine applications. Mo is added to superalloys to increase the solid solution strengthening and the creep resistance. In this study, the interdiffusion coefficient in the Co(Mo) solid solution and impurity diffusion coefficient of Mo in Co are determined. Further, the activation energy and pre-exponential factors are calculated, which provide an idea about the atomic mechanism of diffusion.

Characterization of Alloy-Spinel-Corundum Equilibrium in the System Fe-Ni-Al-O

The three phase equilibrium between alloy, spinel solid solution and α-alumina in the Fe-Ni-Al-O system has been fully characterized at 1823K as a function of alloy composition using both experimental and computational methods. The oxygen potential was measured using a solid state cell incorporating yttria-doped thoria as the electrolyte and Cr+ Cr2O3 as the reference electrode. Oxygen concentration of the alloy was determined by an inert gas fusion technique. The composition of the spinel solid solution, formed at the interface between the alloy and an alumina crucible, was determined by EPMA. The variation of the oxygen concentration and potential and composition of the spinel solid solution with mole fraction of nickel in the alloy have been computed using activities in binary Fe-Ni system, free energies of formation of end member spinels FeO•(1+x)Al2O3 and NiO•(1+x)Al2O3 and free energies of solution of oxygen in liquid iron and nickel, available in the literature. Activities in the spinel solid solution were computed using a cation distribution model. The variation of the activity coefficient of oxygen with alloy composition in Fe-Ni-O system was calculated using both the quasichemical model of Jacob and Alcock and the Wagner's model, with the correlation of Chiang and Chang. The computed results for the oxygen potential and the composition of the spinel solid solution are in good agreement with the measurements. The measured oxygen concentration lies between the values computed using models of Wagner and Jacob and Alcock. The results of the study indicate that the deoxidation hyper-surface in multicomponent systems can be computed with useful accuracy using data for end member systems and thermodynamic models.

Analysis of performance of a hot gas injection thrust vector control system

The complex three-dimensional flowfield produced by secondary injection of hot gases in a rocket nozzle for thrust vector control is analyzed by solving unsteady three-dimensional Euler equations with appropriate boundary conditions. Various system performance parameters like secondary jet amplification factor and axial thrust augmentation are deduced by integrating the nozzle wall pressure distributions obtained as part of the flowfield solution and compared with measurements taken in actual static tests. The agreement is good within the practical range of secondary injectant flow rates for thrust vector control applications.