Decoration of discretely immobilized cowpea mosaic virus with luminescent quantum dots

This report describes two related methods for decorating cowpea mosaic virus (CPMV) with luminescent semiconductor nanocrystals (quantum dots, QDs). Variants of CPMV are immobilized on a substrate functionalized with NeutrAvidin using modifications of biotin-avidin binding chemistry in combination with metal affinity coordination. For example, using CPMV mutants expressing available 6-histidine sequences inserted at loops on the viral coat protein, we show that these virus particles can be specifically immobilized on NeutrAvidin functionalized substrates in a controlled fashion via metal-affinity coordination. To accomplish this, a hetero-bifunctional biotin-NTA moiety, activated with nickel, is used as the linker for surface immobilization of CPMV (bridging the CPMVs' histidines to the NeutrAvidin). Two linking chemistries are then employed to achieve CPMV decoration with hydrophilic CdSe-ZnS core-shell QDs; they target the histidine or lysine residues on the exterior virus surface and utilize biotin-avidin interactions. In the first scheme, QDs are immobilized on the surface-tethered CPMV via electrostatic attachment to avidin previously bound to the virus particle. In the second strategy, the lysine residues common to each viral surface asymmetric unit are chemically functionalized with biotin groups and the biotinylated CPMV is discretely immobilized onto the substrate via NeutrAvidin-biotin interactions. The biotin units on the upper exposed surface of the immobilized CPMV then serve as capture sites for QDs conjugated with a mixture of avidin and a second protein, maltose binding protein, which is also used for QD-protein conjugate purification. Characterization of the assembled CPMV and QD structures is presented, and the potential uses for protein-coated QDs functionalized onto this symmetrical virion nanoscaffold are discussed.     

A hybrid quantum dot-antibody fragment fluorescence resonance energy transfer-based TNT sensor

We demonstrate the use of luminescent QDs conjugated to antibody fragments to develop solution-phase nanoscale sensing assemblies, based on fluorescence resonance energy transfer (FRET) for the specific detection of the explosive 2,4,6-trinitrotoluene (TNT) in aqueous environments. The hybrid sensor consists of anti-TNT specific antibody fragments attached to a hydrophilic QD via metal-affinity coordination. A dye-labeled TNT analogue prebound in the antibody binding site quenches the QD photoluminescence via proximity-induced FRET. Analysis of the data collected at increasing dye-labeled analogue to QD ratios provided an insight into understanding how the antibody fragments self-assemble on the QD. Addition of soluble TNT displaces the dye-labeled analogue, eliminating FRET and resulting in a concentration-dependent recovery of QD photoluminescence. Sensor performance and specificity were evaluated.     

Multiscale study of cold-rolling deformation on mechanical and corrosion behaviors of AA2024-T4 aluminum alloy

This study has been conducted to investigate the effects of plastic deformation of an AA2024 aluminium alloy by cold rolling to 25%, 50% and 75% and then heat-treating and naturally ageing for 20 days to T4 on the microstructure and the electrochemical behavior. To characterize the microstructural modifications different techniques have been applied such as X-ray Diffraction (XRD) to demonstrate the intermetallic phases formed, Optical Microscopy (OM) and Scanning Electronic Microscopy (SEM) to evaluate their microstructures and grain size. Moreover, the surface topography has been measured to establish the roughness effect on the mechanical response when subjected to tensile, fatigue and micro-indentation tests. The corrosion behaviour was evaluated by Potentiodynamic Polarization Scanning, Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). The results revealed that cold-rolled samples with 50% plastic deformation show a smoother topography and exhibit the best compromise between mechanical and corrosion resistance.     

Electrochemical performance of catalyst couples M/stainless steel 430 (M: Ni,Co, and Cu) for the hydrogen production in KOH electrolyte

Journal of Solid State Electrochemistry - In this work, three catalysts (nickel, cobalt, copper) are electrochemically deposited on stainless steel substrates AISI 430 and their performances as...     

Weak solutions for the exterior Stokes problem in weighted Sobolev spaces

We extend here some existence and uniqueness results for the exterior Stokes problem in weighted Sobolev spaces. We also study the regularity of the solutions ( u ,π) and prove optimal a priori estimates for the solutions with ∇² u ,∇π∈L^p. The influence of some compatibility conditions on the behaviour at infinity of the solution is finally studied and leads to new asymptotic expansions. Copyright © 2000 John Wiley & Sons, Ltd.     

Theoretical study of the Ni growth on Pt stepped surfaces

We have investigated the growth of Ni on Pt stepped surfaces with (1 1 1) terraces by means of potentials derived from the second moment approximation in a tight-binding model. The activation energies associated to these processes are determined. The Schwoebel barriers of Ni atoms descending steps of Pt stepped surfaces are calculated for different kinds of straight steps (A and B steps) differing by the orientation of the ledge. In addition, we study the diffusion of Ni adatoms at fcc or hcp sites in the presence of small adislands on the terraces, in the vicinity of the A and B steps. We show that a good estimate of the potential wells and diffusion barriers could be given by introducing a lateral effective pair interaction model, the interactions extending up to the next nearest neighbors. Finally, we have carried out Kinetic Monte-Carlo simulations to investigate the Ni wire formation at Pt step edges and the influence of the exchange processes in the alloy formation.     

Growth of perfect and smooth Ag and Co monatomic wires on Pt vicinal surfaces: A kinetic Monte Carlo study

Growing perfect monatomic chains on surfaces is generally a hard task since it depends strongly on the experimental conditions and on the species used as templates or adsorbates. In the present study, the growth of Co and Ag monatomic wires on a Pt(9 9 7) vicinal surface is investigated over a large range of temperature. A semi-empirical potential is used to extract the main diffusion barriers responsible for the growth of Co and Ag wires on the Pt(9 9 7) vicinal surface. Kinetic Monte Carlo simulations are performed to investigate the wire formation at step-edges. We show that step decoration occurs at 150 K for Ag and at temperatures higher than 250 K for Co in agreement with growth experiments. If no interdiffusion is taken into account, Co and Ag behave similarly and perfect wires form between 150 and 500 K for Ag and between 300 and 500 K for Co. In the case of Co, an exchange mechanism leading to interlayer diffusion at step-edges is shown to strongly influence the temperature range for which the perfect wires are observed. An activation barrier of 0.65 eV for this mechanism is found to be adequate to reproduce the experimental features observed by Gambardella et al. [P. Gambardella, M. Blanc, L. Burgi, K. Kuhnke, K. Kern, Surf. Sci., 449 (2000) 93]. At higher temperatures, above 500 K, detachment from steps strongly hinders the wire formation at step feet. As a main conclusion, the exchange diffusion barrier can be extracted directly from the comparison between observation of step decoration and numerical simulations.     

High‐Efficiency Large‐Bandgap Material for Polymer Solar Cells

High‐molecular‐weight conjugated polymer HD‐PDFC‐DTBT with N‐(2‐hexyldecyl)‐3,6‐difluorocarbazole as the donor unit, 5,6‐bis(octyloxy)benzothiadiazole as the acceptor unit, and thiophene as the spacer is synthesized by Suzuki polycondensation. HD‐PDFC‐DTBT shows a large bandgap of 1.96 eV and a high hole mobility of 0.16 cm² V⁻¹ s⁻¹. HD‐PDFC‐DTBT:PC₇₁BM‐based inverted polymer solar cells (PSCs) give a power conversion efficiency (PCE) of 7.39% with a V_oc of 0.93 V, a J_sc of 14.11 mA cm⁻², and an FF of 0.56.

     

Optimization of polysaccharides extraction from quince peels: partial characterization,antioxidant and antiproliferative properties

Abstract

In this study, Box-Behnken Design was used to optimize the ultrasonic extraction of polysaccharides from quince peels (QPPs) by ascorbic acid and the effect of extraction temperature, extraction time and pH was evaluated. Under optimized conditions of temperature 90?°C, 60?min sonication time and pH?=?3.26, the extraction yield, the galacturonic acid yield and the concentration of sample required to scavenge 50% of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic) acid (ABTS) values of QPPs were respectively 10.25%, 3.86% and 1.35?mg/mL. The QPPs extracted under optimum conditions was characterized by Fourier transform infrared spectroscopy (FTIR), Nuclear magnetic resonance (^1?H NMR) and Size exclusion chromatography (SEC/MALS/VD/DRI). The monosaccharide analysis revealed that arabinose was the most abundant, followed by galactose, glucose, mannose and xylose. Moreover, QPPs showed significant antioxidant activities (2,2-diphenyl-1-picrylhydrazyl (DPPH) and Ferric- reducing antioxidant power (FRAP)) and reduced viability of human Caco-2 and murine B-16 cell lines in a dose-dependent manner. Hence QPPs could be used as antitumor agent in functional foods andpharmaceutical industries.