XPS of oxygen atoms on Ag(111) and Ag(110) surfaces: Accurate study with SAC/SAC‐CI combined with dipped adcluster model

O1s core‐electron binding energies (CEBE) of the atomic oxygens on different Ag surfaces were investigated by the symmetry adapted cluster‐configuration interaction (SAC‐CI) method combined with the dipped adcluster model, in which the electron exchange between bulk metal and adsorbate is taken into account properly. Electrophilic and nucleophilic oxygens (O_elec and O_nuc) that might be important for olefin epoxidation in a low‐oxygen coverage condition were focused here. We consider the O1s CEBE as a key property to distinguish the surface oxygen states, and series of calculation was carried out by the Hartree–Fock, Density functional theory, and SAC/SAC‐CI methods. The experimental information and our SAC/SAC‐CI results indicate that O_elec is the atomic oxygen adsorbed on the fcc site of Ag(111) and that O_nuc is the one on the reconstructed added‐row site of Ag(110) and that one‐ and two‐electron transfers occur, respectively, to the O_elec and O_nuc adclusters from the silver surface. © 2013 Wiley Periodicals, Inc.     

Multiscale geometric modeling of macromolecules II: Lagrangian representation

Geometric modeling of biomolecules plays an essential role in the conceptualization of biolmolecular structure, function, dynamics, and transport. Qualitatively, geometric modeling offers a basis for molecular visualization, which is crucial for the understanding of molecular structure and interactions. Quantitatively, geometric modeling bridges the gap between molecular information, such as that from X‐ray, NMR, and cryo‐electron microscopy, and theoretical/mathematical models, such as molecular dynamics, the Poisson–Boltzmann equation, and the Nernst–Planck equation. In this work, we present a family of variational multiscale geometric models for macromolecular systems. Our models are able to combine multiresolution geometric modeling with multiscale electrostatic modeling in a unified variational framework. We discuss a suite of techniques for molecular surface generation, molecular surface meshing, molecular volumetric meshing, and the estimation of Hadwiger's functionals. Emphasis is given to the multiresolution representations of biomolecules and the associated multiscale electrostatic analyses as well as multiresolution curvature characterizations. The resulting fine resolution representations of a biomolecular system enable the detailed analysis of solvent–solute interaction, and ion channel dynamics, whereas our coarse resolution representations highlight the compatibility of protein‐ligand bindings and possibility of protein–protein interactions. © 2013 Wiley Periodicals, Inc.     

Nonrandom adsorption of polyelectrolyte chains on finite regularly charged surfaces

Adsorption phenomena are relevant in a wide variety of subjects, from biophysics to technological applications. Different aspects, such as molecular recognition, multilayer deposition, and dynamics of polymer adsorption have been addressed. The methodologies used range from analytical and numerical methods to molecular dynamics or Monte Carlo simulations. In this work, a coarse‐grained model is used to explore the adsorption of charged backbones to oppositely charged regions of a surface. These regions encompass those small enough to prevent complete adsorption, but extend to surfaces sufficiently large to promote adsorption with minimal effect on the three‐dimensional conformation in bulk. Apart from the different surface areas explored, variations on the surface charge density, polyelectrolyte chain length, and chain stiffness were also considered. The degree of compaction of the polyelectrolyte, on adsorption, is different from that found in the bulk. Also, results indicate an nonuniform adsorption pattern on regularly charged surfaces. © 2013 Wiley Periodicals, Inc.     

Grand challenges in quantum‐classical modeling of molecule–surface interactions

A detailed understanding of the adsorption of small molecules or macromolecules to a materials surface is of importance, for example, in the context of material and biomaterial research. Classical atomistic simulations in principle provide microscopic insight in the complex entropic and enthalpic interplay at the interface. However, an application of classical atomistic simulation techniques to such interface systems is a nontrivial problem, mostly because commonly used force fields cannot be straightforwardly applied, as they are usually developed to reproduce bulk properties of either solids or liquids but not the interfacial region between two phases. Therefore, a dual‐scale modeling approach has often been the method of choice in the past, in which the classical force field is parameterized such that quantum chemical information on near‐surface conformations and adsorption energies is reproduced by the classical force field. We will discuss in this review the current state‐of‐the‐art of quantum‐classical modeling of molecule–surface interactions and outline the major challenges in this field. In this context, we will, among other things, lay emphasis on discussing ways to obtain representable force fields and propose systematic and system‐independent strategies to optimize the quantum‐classical fitting procedure. © 2013 Wiley Periodicals, Inc.     

FEW: A workflow tool for free energy calculations of ligand binding

In the later stages of drug design projects, accurately predicting relative binding affinities of chemically similar compounds to a biomolecular target is of utmost importance for making decisions based on the ranking of such compounds. So far, the extensive application of binding free energy approaches has been hampered by the complex and time‐consuming setup of such calculations. We introduce the free energy workflow (FEW) tool that facilitates setup and execution of binding free energy calculations with the AMBER suite for multiple ligands. FEW allows performing free energy calculations according to the implicit solvent molecular mechanics (MM‐PB(GB)SA), the linear interaction energy, and the thermodynamic integration approaches. We describe the tool's architecture and functionality and demonstrate in a show case study on Factor Xa inhibitors that the time needed for the preparation and analysis of free energy calculations is considerably reduced with FEW compared to a fully manual procedure. © 2013 Wiley Periodicals, Inc.     

THE USE OF CARBOXYMETHYL ETHOXYLATE SURFACTANT TO DISSOLVE VITAMIN K1 AND TO OBTAIN LOW INTERFACIAL TENSION AND STABLE EMULSION SYSTEMS

Abstract

The presence of vitamin K₁ in human body is important for preventing the hemorrhagic disease. Due to its very long side chain, vitamin K₁ is highly insoluble in water. We have successfully dissolve a substantial amount of vitamin K₁ in solutions of a commercial surfactant containing carboxymethyl ethoxylates (Hüls B433) and obtained low interfacial tension (IFT) and stable emulsion systems. This paper will present the details of these experiments. The solubilization of vitamin K₁ was estimated from UV absorption. The IFT values were measured by using a spinning drop apparatus and all particle sizes were determined by using laser light scattering. By using the Hüls B433 surfactant and an optimum amount of CaCl₂, we can dissolve vitamin K₁ in water and obtain low IFT systems in the order of 10^?2 dyne/cm. The emulsions obtained in these systems are stable and contain droplet sizes below 65 nm. The dissolution of vitamin K₁ and the IFT behavior in these systems follow the rules for crude oil and prefer larger surfactant micelles.     

Experimental Design Approach to Investigate the Effects of Operating Factors on the Surface Tension,Viscosity, and Stability of Heavy Crude Oil-in-Water Emulsions

In this article, the effects of various operating factors on the surface tension, viscosity, and stability of two heavy oil types in water emulsions for pipeline transportation are studied using the Taguchi experimental design approach. The surface tension of heavy crude oil-in-water emulsion is decreased by increasing the emulsifier concentration while the stability of emulsions is increased. The viscosity and stability are increased by an increase in oil content. An increase in the salinity and mixing speed leads to an increase in the stability of emulsion.     

Interactions between apolar,basic and acidic model oils and a calcite surface

Abstract

In this study, the atomic force microscopy colloidal probe technique was employed to investigate the interaction between apolar, basic and acidic model oil probes and a calcite surface in solutions containing different concentrations of NaCl, CaCl₂ and Na₂SO₄. In the presence of SO₄^2?, hydration and structural forces were observed between apolar model oil probes and a calcite surface on approach. Relatively low adhesion forces were observed between the basic model oil probes and the calcite surface, while higher adhesion forces were observed between the acidic model oil probes and the calcite surface. Furthermore, the adhesion forces between the basic model oil probes and the calcite surface significantly increased in the presence of SO₄^2?, while the adhesion force between the acidic model oil probes and the calcite surface decreased in the presence of Ca²⁺ or SO₄^2?. The differences in the adhesion forces are related to electrostatic attraction and ion bridging forces between the model oil probes and the calcite surface.     

Polymer-Surfactant Interactions and the Effect of Tail Size Variation on Micellization Process of Cationic ATAB Surfactants in Aqueous Medium

The interactions between oppositely charged surfactant-polymer systems have been studied using surface tension and conductivity measurements and the dependence of aggregation phenomenon over the polyelectrolyte concentration and chain length of cationic ATAB surfactants, cetyltrimethyl ammonium bromide (CTAB), tetradecyltrimethyl ammonium bromide (TTAB), and dodecyltrimethyl ammonium bromide (DTAB) have been investigated. It was observed that cationic surfactants induce cooperative binding with anionic polyelectrolyte at critical aggregation concentration (cac). The cac values of ATAB surfactants in the presence of anionic polyelectrolyte, sodium carboxy methyl cellulose (NaCMC), are considerably lower than their critical micelle concentration (cmc). After the complete complexation, free micelles are formed at the apparent critical micelle concentration (acmc), which is slightly higher in polyelectrolyte aqueous solution than in pure water. Among the cationic surfactants (i.e., CTAB, TTAB, and DTAB), DTAB was found to have least interaction with NaCMC. Surfactants with longer tail size strongly favor the interaction, indicating the dependence of aggregation phenomenon on the structure, morphology, and tail length of the surfactant.      

Investigation of Combined Effects of Xanthan Gum,Sodium Dodecyl Sulphate,and Salt on Some Physicochemical Properties of Their Mixtures Using a Response Surface Method

Aqueous solutions containing sodium dodecyl sulphate, xanthan gum, and salt were characterized by ionic conductivity, viscosity, and surface tension methods. A preliminary experimental study was performed to evaluate the effect of the mixture compositions on the surface behavior of the mixed polymer/surfactant systems under different solution conditions. An experimental design using response surface method (RSM) was then applied to assess factors interactions and empirical models regarding the physicochemical responses variables (i.e., conductivity, surface tension and viscosity). The main effects of the three independent factors: SDS concentration (x₁), NaCl concentration (x₂) and xanthan concentration (x₃) were determined using in particular a D-optimal design. The results show an important effect of the factors on responses; they also indicate that the synergetic action of surfactant, electrolyte and biopolymer greatly influences these properties. Analysis of variance (ANOVA) showed high variance coefficient (R ² Avarnas , A. and Panagiotis , I. ( 2003 ) J. Colloid Int. Sci. , 258 : 102 – 109 .[Crossref], [Web of Science ®] , [Google Scholar]) values, thus, ensuring a satisfactory adjustment of the second-order regression model with the experimental data.