Conditional reversible work method for molecular coarse graining applications

Systematically coarse grained models for complex fluids usually lack chemical and thermodynamic transferability. Efforts to improve transferability require the development of effective potentials with unequivocal physical significance. In this paper, we introduce conditional reversible work (CRW) potentials that describe nonbonded interactions in coarse grained models at the pair level. The method used to obtain these potentials is straightforward to implement, can be readily extended to compute hydration contributions in implicit-solvent potentials, and is easy to automize. As a first illustration of the method, we present CRW potentials for 3-site models of hexane and toluene. The temperature-transferability of the liquid phase density obtained with these potentials has been investigated, and a comparison has been made with effective potentials obtained by the iterative Boltzmann inversion method.     

Nanocatalysts for Suzuki cross-coupling reactions

This critical review deals with the applications of nanocatalysts in Suzuki coupling reactions, a field that has attracted immense interest in the chemical, materials and industrial communities. We intend to present a broad overview of nanocatalysts for Suzuki coupling reactions with an emphasis on their performance, stability and reusability. We begin the review with a discussion on the importance of Suzuki cross-coupling reactions, and we then discuss fundamental aspects of nanocatalysis, such as the effects of catalyst size and shape. Next, we turn to the core focus of this review: the synthesis, advantages and disadvantages of nanocatalysts for Suzuki coupling reactions. We begin with various nanocatalysts that are based on conventional supports, such as high surface silica, carbon nanotubes, polymers, metal oxides and double hydroxides. Thereafter, we reviewed nanocatalysts based on non-conventional supports, such as dendrimers, cyclodextrin and magnetic nanomaterials. Finally, we discuss nanocatalyst systems that are based on non-conventional media, i.e., fluorous media and ionic liquids, for use in Suzuki reactions. At the end of this review, we summarise the significance of nanocatalysts, their impacts on conventional catalysis and perspectives for further developments of Suzuki cross-coupling reactions (131 references).     

Cosolvent gel-like materials from partially hydrolyzed poly(vinyl acetate)s and borax

A gel-like, high-viscosity polymeric dispersion (HVPD) based on cross-linked borate, partially hydrolyzed poly(vinyl acetate) (xPVAc, where x is the percent hydrolysis) is described. Unlike hydro-HVPDs prepared from poly(vinyl alcohol) (PVA) and borate, the liquid portion of these materials can be composed of up to 75% of an organic cosolvent because of the influence of residual acetate groups on the polymer backbone. The effects of the degree of hydrolysis, molecular weight, polymer and cross-linker concentrations, and type and amount of organic cosolvent on the rheological and structural properties of the materials are investigated. The stability of the systems is explored through rheological and melting-range studies. (11)B NMR and small-angle neutron scattering (SANS) are used to probe the structure of the dispersions. The addition of an organic liquid to the xPVAc-borate HVPDs results in a drastic increase in the number of cross-linked borate species as well as the agglomeration of the polymer into bundles. These effects result in an increase in the relaxation time and thermal stability of the networks. The ability to make xPVAc-borate HVPDs with very large amounts of and rather different organic liquids, with very different rheological properties that can be controlled easily, opens new possibilities for applications of PVAc-based dispersions.     

Solvodynamic Properties of Sodium Polystyrenesulfo-nate in Methanol-Water Mixed Solvent Media in Absence and in the Presence of a Salt Using Viscometric Method

Linear extrapolation of the reduced viscosity values of uncharged polymer solutions as the concentration approaches zero constitutes the basis for the traditional method for the determination of the intrinsic viscosities of polymer solutions. While this method works well for uncharged polymer solutions, it fails completely for polyelectrolyte solutions especially in absence and also in presence of small amount of an added electrolyte. A very convenient method has recently been proposed by Wolf (Wolf, Macromol. Rapid Commun. 2007, 28, 164) to determine the intrinsic viscosities of polyelectrolyte solutions on the basis of the laws of phenomenological thermodynamics applied to the viscosity of polymer solutions. In spite of the success and the convenience of this method, this has so far been applied to a limited number of polyelectrolyte systems by the Wolf group alone (Wolf, Macromol. Rapid Commun. 2007, 28, 164; Eckelt et al., Macromolecules 2008, 41, 912; Badiger et al., Macromol. Chem. Phys. 2008 , 209, 2087; Ghimici et al., J. Phys. Chem.B. 2009, 113, 8020). In order to improve the situation, we have measured the viscosities of an anionic polyelectrolyte, sodium polystyrenesulfonate, in methanol-water mixed solvent media both in absence and in the presence of an electrolyte, sodium chloride. The results show that the experimental data fit well with the Wolf model and thus allow the calculation of intrinsic viscosities, which provide important insight about the dependence of the polyion conformation on solvent composition as well as on the concentration of the added electrolyte. This new evaluation method, thus, proves to be very useful to a better understanding of the rheological behaviour of the polyelectrolyte system investigated.     

A new force field for the adsorption of H2, O2, N2, CO,H2O,and H2S gases on alkali doped carbon nanotubes

The main goal of this work is the generation of a new force field data set to the interaction of several gases such as H₂, O₂, N₂, CO, H₂O, and H₂S with alkali cation-doped carbon nanotubes (CNTs) using ab initio calculations at the MP2(full)/6-311++G(d,p) level of theory. Different alkali cations including Li⁺, Na⁺_, K⁺ and Cs⁺ were used to dope in the CNT. The calculated potential energy curve for the interaction of each gas molecule with each alkali cation-doped CNTs was fitted to an analytical potential function to obtain the parameters of the potential function. A modified Morse potential function was selected for the fitting in which the electrostatic interactions has been accounted by adding the β/r term to the Morse potential. The accuracy of the calculated force field was checked via Grand Canonical Monte Carlo (GCMC) simulation of the H₂ adsorption on Li-doped graphite and Li-doped CNT. The results of these simulations were compared with the experimental measurements and the closeness of the simulation results with the experimental data indicated the accuracy of the proposed force field. The main merit of this work is the derivation of a specific force field for interaction of each of six gases with four alkali cation-doped CNT, which can be used in molecular simulation of these 24 of systems. The simulation results showed the increase of the H₂ adsorption capacity of nanotube and graphite up to 50% and 10%, respectively, due to the insertion of Li ions.     

Electric-field gradients at Ta impurities in Sc2O3 semiconductor

In this work we present an ab initio study of Ta-doped Sc₂O₃ semiconductor. Calculations were performed at dilute Ta impurities located at both cationic sites of the host structure, using the Augmented Plane Wave plus Local Orbitals (APW+lo) method. The structural atomic relaxations and the electric-field gradients (EFG) were studied for different charge states of the cell in order to simulate different ionization states of the double-donor Ta impurity. From the results for the EFG tensor at Ta impurity sites and the comparison with experimental results obtained using the Time-Differential γ–γ Perturbed-Angular-Correlations technique we could determined the structural distortions induced by the Ta impurity and the electronic structure of the doped-semiconductor.     

Synthesis of nano ZnO thin film on Al foil by rf glow discharge plasma and its effect on E. coli and P. aeruginosa

Nano ZnO thin films were deposited on thin Al foils by a rf glow discharge plasma method in which sublimed zinc acetate vapor (precursor) reacted with oxygen plasma inside a low-pressure reactor. The films were microstructurally characterized using XRD, TEM, FESEM, optical reflectance and micro-Raman spectroscopy methods. In view of the good scope of ZnO coating in food packaging, the antibacterial activity in the ZnO thin films was studied by exposing the films to E. coli and P. aeruginosa for up to 8 h. Bacterial cell inhibition of up to 98–99 % was observed in the thin films.     

Similarity solution of boundary layer stagnation-point flow towards a heated porous stretching sheet saturated with a nanofluid with heat absorption/generation and suction/blowing: A Lie group analysis

In this paper, heat and mass transfer analysis for boundary layer stagnation-point flow over a stretching sheet in a porous medium saturated by a nanofluid with internal heat generation/absorption and suction/blowing is investigated. The governing partial differential equation and auxiliary conditions are converted to ordinary differential equations with the corresponding auxiliary conditions via Lie group analysis. The boundary layer temperature, concentration and nanoparticle volume fraction profiles are then determined numerically. The influences of various relevant parameters, namely, thermophoresis parameter Nt, Brownian motion parameter Nb, Lewis number Le, suction/injection parameter S, permeability parameter k₁, source/sink parameter λ and Prandtl parameter Pr on temperature and concentration as well as wall heat flux and wall mass flux are discussed. Comparison with published results is presented.     

Modulation of Intramolecular Charge Transfer Emission Inside Micelles: A Fluorescence Probe for Studying Microenvironment of Micellar Assemblies

Modulation of intramolecular charge transfer reaction of ethyl ester of N,N-Dimethylaminonaphthyl-(acrylic)-acid (EDMANA) in anionic sodium dodecyl sulfate (SDS), cationic cetyltrimethylammonium bromide (CTAB) and non-ionic p-tert-octylphenoxy polyoxyethanol (Triton-X 100, TX-100) micelles has been addressed using steady state and time resolved spectroscopy. The interaction of the CT probe EDMANA with micelles and its location inside the micelles have been investigated by the study of fluorescence spectral band position of EDMANA in micelle, the effective polarity of micelle-water interface and cetyl pyridinium chloride induced fluorescence quenching measurement. The effects of urea on the properties of the micelles such as Critical Micelle Concentration and the interaction between EDMANA and micelles have been explored using EDMANA as emission probe.