An accurate expression for radial distribution function of the Lennard-Jones fluid

A simple and accurate expression for radial distribution function (RDF) of the Lennard-Jones fluid is presented. The expression explicitly states the RDF as a continuous function of reduced interparticle distance, temperature, and density. It satisfies the limiting conditions of zero density and infinite distance imposed by statistical thermodynamics. The distance dependence of this expression is expressed by an equation which contains 11 adjustable parameters. These parameters are fitted to 353 RDF data, obtained by molecular dynamics calculations, and then expressed as functions of reduced distance, temperature and density. This expression, having a total of 65 constants, reproduces the RDF data with an average root-mean-squared deviation of 0.0152 for the range of state variables of 0.5  T^*  5.1 and 0.35  ρ^*  1.1 (T^*=kT/ε and ρ^* = ρσ³ are reduced temperature and density, respectively). The expression predicts the pressure and the internal energy of the Lennard-Jones fluid with an uncertainty that is comparable to that obtained directly from the molecular dynamics simulations.     

Preparation and characterization of new thermally stable and optically active poly(ester‐imide)s by direct polycondensation with thionyl chloride in pyridine

4,4′‐hexafluoroisopropylidene‐2,2‐bis‐(phthalic acid anhydride) (1) was reacted with L ‐methionine (2) in acetic acid and the resulting N,N′–(4,4′‐hexafluoroisopropylidenediphthaloyl)‐bis‐L ‐methionine (4) was obtained in high yield. The direct polycondensation reaction of this diacid with several aromatic diols such as bisphenol A (5a), phenolphthalein (5b), 1,4‐dihydroxybenzene (5c), 4,4′‐dihydroxydiphenyl sulfide (5d), 4,6‐dihydroxypyrimidine (5e), 4,4′‐dihydroxydiphenyl sulfone (5f) and 2,4′‐dihydroxyacetophenone (5g) was carried out in a system of thionyl chloride and pyridine. Expecting that the reaction with thionyl chloride in pyridine might involve alternative intermediates different from an acyl chloride, the polycondensation at a higher temperature favorable for the reaction of the expected intermediate with nucleophiles was attempted, and a highly thermally stable poly(ester‐imide) was obtained by carrying out the reaction at 80°C. All of the above polymers were fully characterized by ¹H‐NMR, ¹⁹F‐NMR FT‐IR spectroscopy, elemental analysis and specific rotation. Some structural characterization and physical properties of these optically active poly(ester‐ imide)s are reported. Copyright © 2006 John Wiley & Sons, Ltd.     

Mn(II) and VO(IV) Schiff base complexes encapsulated in nanocavities of zeolite-Y: catalytic activity toward oxidation of alkenes and reduction of aldehydes

Oxovanadium(IV) and manganese(II) complexes of two Schiff base ligands, bis(2,4-dihydroxyacetophenone)-1,2-propandiimine (H₂L₁) and bis(2,4-dihydroxyacetophenone)-ethylenediimine (H₂L₂) were synthesized and characterized. The encapsulation of these complexes in the nanocavities of zeolite-Y was achieved by a flexible ligand method. The prepared heterogeneous catalysts have been characterized by FTIR, NMR and atomic absorption spectroscopy, X-ray diffraction patterns, scanning electron microscopy and BET. The catalytic activities of the encapsulated complexes were studied in the oxidation of alkenes with H₂O₂ and the reduction of aldehydes with NaBH₄. In most cases, the manganese (II) complexes (MnL₁-Y, MnL₂-Y) showed better activity than the oxovanadium (IV) complexes (VOL₁-Y, VOL₂-Y) in both oxidation of alkenes and reduction of aldehydes. The catalytic activity of the recovered catalysts was compared with the fresh ones.     

SMFs-supported Pd nanocatalysts in selective acetylene hydrogenation:Pore structure-dependent deactivation mechanism

In the present study,CNFs,ZnO and Al2O3 were deposited on the SMFs panels to investigate the deactivation mechanism of Pd-based catalysts in selective acetylene hydrogenation reaction.The examined supports were characterized by SEM,NH3-TPD and N2adsorption-desorption isotherms to indicate their intrinsic characteristics.Furthermore,in order to understand the mechanism of deactivation,the resulted green oil was characterized using FTIR and SIM DIS.FTIR results confirmed the presence of more unsaturated constituents and then,more branched hydrocarbons formed upon the reaction over alumina-supported catalyst in comparison with the ones supported on CNFs and ZnO,which in turn,could block the pores mouths.Besides the limited hydrogen transfer,N2 adsorption-desorption isotherms results supported that the lowest pore diameters of Al2O3/SMFs close to the surface led to fast deactivation,compared with the other catalysts,especially at higher temperatures.     

Electrodeposited Silver Nanoparticles on Carbon Ionic Liquid Electrode for Electrocatalytic Sensing of Hydrogen Peroxide

Silver nanoparticles (narrowly dispersed in diameter) were electrodeposited on carbon ionic liquid electrode (CILE) surface using a two‐step potentiostatic method. Potentiostatic double pulse technique was used as a suitable and simple method for controlling the size and morphologies of silver nanoparticles electrodeposited on CILE. The obtained silver nanoparticles deposited on CILE surface showed excellent electrocatalytic activity (low overpotential of ?0.35 V vs. Ag/AgCl) towards reduction of hydrogen peroxide. A linear dynamic range of 2–200 μM with an experimental detection limit of 0.7 μM (S/N=3) and reproducibility of 4.1% (n=5) make the constructed sensor suitable for peroxide determination in aqueous solutions.     

Injectable poloxamer/graphene oxide hydrogels with well‐controlled mechanical and rheological properties

Although significant progress has been made in the design and application of injectable hydrogels for biomedical applications, concurrent control of rheological and mechanical properties of injectable hydrogels has remained as an open challenge to the researchers. In this work, we introduce and put into practice a photo‐curable poloxamer (also known as Pluronic)/graphene oxide (Plu/GO) injectable hydrogel with well‐controlled rheological and mechanical properties. Acrylate group was anchored to hydrogel structure to endow photo‐crosslinking ability through decelerating degradation rate of poloxamer hydrogels after injection. It was found that the modified Plu remains stable in biological media for a long‐term period without significant weight loss. Rheological properties of hydrogels were also carried out as essential prerequisite for an ideal injectability via frequency sweep, flow curve, recovery, and yield stress before and after modification, signifying shear‐thinning behavior of Plu/GO hydrogels with high recoverability. The viscosity of shear‐thinning‐like hydrogels dropped at higher shear stress, which facilitated injection process. Moreover, mechanical behavior of Plu was optimized by manipulating the content of Plu, degree of modification with reactive precursor, curing, and particularly incorporation of GO without deteriorating effects on rheological behavior of Plu.     

Development of a Novel Electrochemical Biosensor for Detection and Discrimination of DNA Sequence and Single Base Mutation in dsDNA Samples Based on PNA‐dsDNA Hybridization – a new Platform Technology

In spite of the extensive attention paid on the development of various DNA detection strategies, very few studies have been reported regarding direct detection of DNA sequence and mutation in dsDNA. Here, we describe the feasibility of detection and discrimination of target DNA sequences and single base mutations (SBM) directly in double‐stranded oligonucleotides and PCR products without the need for denaturation of the target dsDNA samples. This goal was achieved by employing a peptide nucleic acid (PNA) chain, self‐assembled on the gold electrode as a probe, which binds to dsDNA and forms PNA‐dsDNA hybrid.     

SMFs-supported Pd nanocatalysts in selective acetylene hydrogenation: Pore structure-dependent deactivation mechanism

In the present study, CNFs, ZnO and Al₂O₃ were deposited on the SMFs panels to investigate the deactivation mechanism of Pd-based catalysts in selective acetylene hydrogenation reaction. The examined supports were characterized by SEM, NH₃-TPD and N₂ adsorption-desorption isotherms to indicate their intrinsic characteristics. Furthermore, in order to understand the mechanism of deactivation, the resulted green oil was characterized using FTIR and SIM DIS. FTIR results confirmed the presence of more unsaturated constituents and then, more branched hydrocarbons formed upon the reaction over alumina-supported catalyst in comparison with the ones supported on CNFs and ZnO, which in turn, could block the pores mouths. Besides the limited hydrogen transfer, N₂ adsorption-desorption isotherms results supported that the lowest pore diameters of Al₂O₃/SMFs close to the surface led to fast deactivation, compared with the other catalysts, especially at higher temperatures.