Biosynthesis and Characterization of Extracellular Silver Nanoparticles from Streptomyces aizuneusis: Antimicrobial,Anti Larval,and Anticancer Activities

The ability of microorganisms to reduce inorganic metals has launched an exciting eco-friendly approach towards developing green nanotechnology. Thus, the synthesis of metal nanoparticles through a biological approach is an important aspect of current nanotechnology. In this study, Streptomyces aizuneusis ATCC 14921 gave the small particle of silver nanoparticles (AgNPs) a size of 38.45 nm, with 1.342 optical density. AgNPs produced by Streptomyces aizuneusis were characterized by means of UV-VIS spectroscopy and transmission electron microscopy (TEM). The UV-Vis spectrum of the aqueous solution containing silver ion showed a peak between 410 to 430. Moreover, the majority of nanoparticles were found to be a spherical shape with variables between 11 to 42 nm, as seen under TEM. The purity of extracted AgNPs was investigated by energy dispersive X-ray analysis (EDXA), and the identification of the possible biomolecules responsible for the reduction of Ag⁺ ions by the cell filtrate was carried out by Fourier Transform Infrared spectrum (FTIR). High antimicrobial activities were observed by AgNPs at a low concentration of 0.01 ppm, however, no deleterious effect of AgNPs was observed on the development and occurrence of Drosophila melanogaster phenotype. The highest reduction in the viability of the human lung carcinoma and normal cells was attained at 0.2 AgNPs ppm.     

Performance improvement of plasmonic sensors using a combination of AC electrokinetic effects for (bio)target capture

Analytes concentration techniques are being developed with the appealing expectation to boost the performance of biosensors. One promising method lies in the use of electrokinetic forces. We present hereafter a new design for a microstructured plasmonic sensor which is obtained by conventional microfabrication techniques, and which can easily be adapted on a classical surface plasmon resonance imaging (SPRI) system without further significant modification. Dielectrophoretic trapping and electro‐osmotic displacement of the targets in the scanned fluid are performed through interdigitated 200 μm wide gold electrodes that also act as the SPR‐sensing substrate. We demonstrate the efficiency of our device's collection capabilities for objects of different sizes (200 nm and 1 μm PS beads, as well as 5–10 μm yeast cells). SPRI is relevant for the spatial analysis of the mass accumulation at the electrode surface. We demonstrate that our device overcomes the diffusion limit encountered in classical SPR sensors thanks to rapid collection capabilities (<1 min) and we show a consequent improvement of the detection limit, by a factor >300. This study of an original device combining SPRI and electrokinetic forces paves the way to the development of fully integrated active plasmonic sensors with direct applications in life sciences, electrochemistry, environmental monitoring and agri‐food industry.     

Palladium nanoparticles supported on mesoporous natural phosphate: An efficient recyclable catalyst for nitroarene reduction

We report the preparation of palladium nanoparticles supported on mesoporous natural phosphate (Pd@NP) using a wetness impregnation method. The prepared catalyst was characterized using various techniques. Furthermore, the reduction and preparation of the palladium nanoparticles was followed using UV–visible spectra. Based on the Scherrer equation, the crystallite size of the as‐synthesized palladium nanoparticles was 10.88 nm. The performance of the synthesized catalyst was investigated in the reduction of 4‐nitrophenol as a model substrate to 4‐aminophenol using NaBH₄ as a hydrogen source. Moreover, catalytic reduction of various nitroarenes was studied and monitored using UV–visible spectroscopy and gas chromatography. The Pd@NP catalyst showed a high activity for the selected reaction and could be recycled.     

Investigation on the effect of cellulosic nanoparticles’ morphology on the properties of natural rubber based nanocomposites

Cellulose whiskers and microfibrillated cellulose (MFC) were extracted from the rachis of date palm tree and characterized. These cellulosic nanoparticles were used as reinforcing phase to prepare nanocomposite films using latex of natural rubber as matrix. These films were obtained by the casting/evaporation method. The properties of the ensuing nanocomposite films were investigated using differential scanning calorimetry, toluene and water uptake experiments, dynamic mechanical analysis and tensile tests. The stiffness of the natural rubber was significantly increased above its glass-rubber transition temperature upon nanoparticles addition. The reinforcing effect was shown to be higher for nanocomposites with MFC compared to whiskers. It was ascribed to the higher aspect ratio and possibility of entanglements of the former. The presence of residual lignin, extractive substances and fatty acids at the surface of MFC was also suggested to promote higher adhesion level with the polymeric matrix.     

Adjustment of the moments of the project completion times when activity times are exponentially distributed

The problem of determining the moment of the project completion time (MPCT) with stochastic activity durations is addressed. In the direct approach the MPCT is obtained after analyzing all possible network paths which is NP-hard problem. A recursive method for determining MPCT by proceeding iteratively over the nodes is the computationally least demanding and therefore the most efficient approach. Unfortunately, the moment methods which are available in literature ignore some aspects. In this paper, an adjustment of the moment completion time is discussed. Two illustrative examples are presented.     

Generation of well‐defined clickable glycopolymers from aqueous RAFT polymerization of isomaltulose‐derived acrylamides

Original carbohydrate‐based acrylamides bearing one azide group in C‐2 or C‐6 position namely, 2‐[(2‐deoxy‐2‐azido‐α‐D ‐mannopyranosyloxy)ethanamido]‐ethyl acrylamide (II) and 2‐[(6‐deoxy‐6‐azido‐α‐D ‐glucopyranosyloxy)ethanamido]‐ethyl acrylamide (III), and their azide‐free analogue, 2‐[(α‐D ‐glucopyranosyloxy)ethanamido]‐ethyl acrylamide (I), have been designed. Whereas the reversible addition fragmentation chain transfer (RAFT) process ensured the preparation of well‐defined glycopolymers from I, the polymerization of monomers II and III proved to be challenging at temperatures compatible with a thermally initiated radical process, due to the presumed concomitant 1,3‐cycloaddition reactions between the azide and the acrylamide moieties. In contrast to III, for which no polymer could be obtained under any conditions, performing the RAFT polymerization of II at 30 °C clearly favored the radical polymerization and conferred a controlled character to the process, affording well‐defined azide‐functionalized glycopolymers and block copolymers. The presence of numerous azide moieties was finally exploited to introduce carbohydrates onto the glycopolymer backbone through copper catalyzed azide‐alkyne cycloaddition. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Cyano‐Functionalized Triarylamines on Coinage Metal Surfaces: Interplay of Intermolecular and Molecule–Substrate Interactions

The self‐assembly of cyano‐functionalized triarylamine derivatives on Cu(111), Ag(111) and Au(111) was studied by means of scanning tunnelling microscopy, low‐energy electron diffraction, X‐ray photoelectron spectroscopy and density functional theory calculations. Different bonding motifs, such as antiparallel dipolar coupling, hydrogen bonding and metal coordination, were observed. Whereas on Ag(111) only one hexagonally close‐packed pattern stabilized by hydrogen bonding is observed, on Au(111) two different partially porous phases are present at submonolayer coverage, stabilized by dipolar coupling, hydrogen bonding and metal coordination. In contrast to the self‐assembly on Ag(111) and Au(111), for which large islands are formed, on Cu(111), only small patches of hexagonally close‐packed networks stabilized by metal coordination and areas of disordered molecules are found. The significant variety in the molecular self‐assembly of the cyano‐functionalized triarylamine derivatives on these coinage metal surfaces is explained by differences in molecular mobility and the subtle interplay between intermolecular and molecule–substrate interactions.     

Biopolymer-layered polysilicate micro/nanocomposite based on chitosan intercalated in magadiite

On the basis of their high adsorption and cation exchange capacity, swelling potential and low toxicity, layered sodium silicate magadiite (Na–magadiite) is an attractive solid for intercalation of polymers. This study envisages the intercalation of cationic biopolymer chitosan (Chit) in Na–magadiite to prepare a Chit/magadiite micro/nanocomposite. Characterisation of starting-magadiite, pure chitosan and Chit/magadiite were investigated using powder X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy and thermal analysis. XRD confirmed that the chitosan had been intercalated into the interlayer space of magadiite by increasing the basal spacing, d₀₀₁ from 15.6 Å to 21.45 Å. The presence of characteristic bands of biopolymer and layered silicate in Chit/magadiite were confirmed by FTIR analysis. The thermal stability of micro/nanocomposite was evaluated by thermogravimetry analysis. The results suggested the formation of electrostatic interactions by protonated amine groups with the negatively charged magadiite surface as well as intercalation in the form of a predominant monolayer arrangement of chitosan chains in layered silicate magadiite.     

Convection mixte en fluide binaire avec effet Soret : étude analytique de la transition vers les rouleaux transversaux 2D

This Note deals with mixed convection in binary fluid with Soret effect in a rectangular duct heated from below. In particular, we study the transition towards transverse 2D rolls appearing at low Reynolds and Rayleigh numbers. The linear stability analysis of Poiseuille flow, with linearly stratified temperature and concentration fields, shows the influence of the separation ratio on the critical Rayleigh number at the transition towards the transversal 2D convective patterns. It highlights the presence, at low Reynolds numbers, of propagating transverse rolls in the downwards as well as in the upwards direction. Finally, we point out that, under these conditions, the propagating frequency of the rolls is the sum of two well defined frequencies: the first related to the Reynolds, the second to the separation ratio. To cite this article: E. Piquer et al., C. R. Mecanique 333 (2005).     

Some purely radial motions with drag

Summary Some academic results in the field of nonlinear mechanics are here presented. Specifically, exact solutions of the equations of motion for a body moving purely radially in nonlinear central fields of force are given, when the drag of the (homogeneous) medium is taken into account. The drag is assumed to be proportional to the velocity, and several types of forces, including gravitation, are considered. Next, for a nonhomogeneous atmosphere, we assume a density function that may represent the earth's atmosphere and a drag law consisting of two terms (linear and cubic in the velocity), and obtain the solution for a particular case.