Characterization of Cationic Polyelectrolytes Adsorption to an Anionic Emulsion via Zeta-Potential and Microcalorimetry

The adsorption of cationic polyelectrolytes (PEs) onto anionic silicone emulsion droplets, suspended in a sodium chloride solution is studied via electrophoretic mobility measurements and isothermal titration calorimetry. These model systems are studied to better understand the interactions governing PE adsorption-induced emulsion flocculation, which is relevant to many industrial applications. Electrophoretic mobility measurements provide critical information for rationalizing the effect of the PE charge density on the loss of stability of silicone emulsions. The interaction strength is calculated from a Langmuir adsorption isotherm determined by a ζ-potential titration measurement. Microcalorimetry measurements independently validate the adsorption free energy. Emulsion flocculation and coacervation are observed in the visual phase behavior as well as the ζ-potential titration measurements. The effect of PE charge density shows that PE-surfactant coacervation is the driving force in these PE-emulsion systems.     

Dissipative particle dynamics simulations of polyelectrolyte self-assemblies. Methods with explicit electrostatics

This feature article is addressed to a broad community of polymer scientists, both theoreticians and experimentalists. We present several examples of our dissipative particle dynamics (DPD) simulations of selfand co-assembling polyelectrolyte systems to illustrate the power of DPD. In the first part, we briefly outline basic principles of DPD. Special emphasis is placed on the incorporation of explicit electrostatic forces into DPD, on their calibration with respect to the soft repulsion forces and on the use of DPD for studying the self-assembly of electrically charged polymer systems. At present, the method with explicit electrostatics is being used in a number of studies of the behavior of single polyelectrolyte chains, their interaction with other components of the system, etc. However, in DPD studies of self-assembly, which require high numbers of chains, only a few research groups use explicit electrostatics. Most studies of polyelectrolyte self-assembly are based on the “implicit solvent ionic strength” approach, which completely ignores the long-range character of electrostatic interactions, because their evaluation complicates and considerably slows down the DPD simulation runs. We aim at the analysis of the impact of explicit electrostatics on simulation results.     

Magnetic‐induced coil‐globule transition for polyelectrolytes

The effects of an applied magnetic field on the system composed of polyelectrolytes (PEs) and magnetic nanoparticles oppositely charged are studied by means of Monte Carlo method within the framework of “single‐site bond fluctuation model.” For a certain concentration of chains, the coil‐globule transition can be induced by the applied magnetic field. The mean‐square end‐to‐end distance and gyration radius as well as the shape factor of PE chains are used to characterize the conformational transitions. The statistical analysis of the system energy demonstrates this significant physical process. The role of entropy‐energy balance is well‐understood for different chain lengths, and a typical phase‐transition anomaly concerned with specific heat curve is observed. Under a certain magnetic field, the PE chains will regularly collapse due to the enough adsorption of magnetic particles. The magnetic particles exhibit peculiar spatial distribution at high magnetic fields: the string‐like arrangement along the magnetic field and the square lattice‐like arrangement perpendicular to the magnetic field. The applied magnetic field has a great influence on the length of string‐like structures formed by nanoparticles. This investigation may cast light on the collapse of PEs and provide a promising method for producing new nanocomposites. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

An extension of the Painter-Coleman miscibility guide to ternary polymer blends

The idea of separating the free energy of mixing into two contributions (corresponding to the “physical” or “nonspecific” and to the “specific” interactions, respectively) proposed by Painter and Coleman has been extended to ternary polymer/polymer/polymer blends. In this paper experimental phase diagrams of three ternary blends have been reproduced by estimating both contributions for the interaction energy density (B_ij) which characterizes each polymer pair. In contrast to the Painter-Coleman Miscibility Guide rules, we have found that, in some cases, “specific” contributions positive and unfavorable to the mixing, due to the self-association of one of the components, can describe more adequately the experimental trends.     

Solvent Penetration and Sterical Stabilization of Reverse Aggregates based on the DIAMEX Process Extracting Molecules: Consequences for the Third Phase Formation

Abstract

Studies on third phase formation during the extraction of nitric acid by malonamide extractants in various diluents are investigated. This “third phase transition” is studied from a fundamental point of view, combining vapor pressure osmometry, phase diagram, and scattering studies. The organization of the organic phases of the “malonamides/alkane/water/nitric acid” systems was studied at three “scales”: 1/at a molecular scale by determining the compositions of the extracted complexes; 2/at a macroscopic scale by determining the phase transition boundaries quantified by the limiting organic concentration (LOC) of solutes; and 3/at a supramolecular scale by analyzing the organization of the species in the organic phases (i.e. measuring the critical micellization concentration, the aggregation number, and the interactions between the aggregates). The instability (third phase apparition) has a supramolecular origin: it is a “long range” attraction between polar cores of the reverse micelles formed by the extracting agent. Water and nitric acid extraction are decoupled from these interactions. The alkyl chains of the extractant and the diluent play a symmetrical role in the physical stability of the organic phase: decreasing the diluent chain length or increasing the chain length of the complexing agent both promotes phase stability, i.e. they increase the LOC. We demonstrate here that this effect is the same as the effect observed and known for all other w/o “reverse” micelles: chains protruding from any aggregate stabilize polar solute in oil and shorts oil penetrate and swells the reverse micelles apolar layer.     

A Pharm-Ecological Perspective of Terrestrial and Aquatic Plant-Herbivore Interactions

We describe some recent themes in the nutritional and chemical ecology of herbivores and the importance of a broad pharmacological view of plant nutrients and chemical defenses that we integrate as “Pharm-ecology”. The central role that dose, concentration, and response to plant components (nutrients and secondary metabolites) play in herbivore foraging behavior argues for broader application of approaches derived from pharmacology to both terrestrial and aquatic plant-herbivore systems. We describe how concepts of pharmacokinetics and pharmacodynamics are used to better understand the foraging phenotype of herbivores relative to nutrient and secondary metabolites in food. Implementing these concepts into the field remains a challenge, but new modeling approaches that emphasize tradeoffs and the properties of individual animals show promise. Throughout, we highlight similarities and differences between the historic and future applications of pharm-ecological concepts in understanding the ecology and evolution of terrestrial and aquatic interactions between herbivores and plants. We offer several pharm-ecology related questions and hypotheses that could strengthen our understanding of the nutritional and chemical factors that modulate foraging behavior of herbivores across terrestrial and aquatic systems.     

Electrostatic and Entropic Interactions between Parallel Interfaces Separated by a Glassy Film

A simple classical density functional model is set up to describe the electrostatic and entropic interactions between two parallel planar charged interfaces separated by a thin film of a phase (the glass) containing a distribution of charged ions. The total charge in the system is zero. Three cases are treated: (1) the two interfaces carry a fixed surface charge; (2) the first interface carries a fixed surface charge, simulating a ceramic, while the second is held at zero potential, simulating a metal; and (3) both interfaces are held at zero potential. A discretized form of the nonlinear Poisson–Boltzmann equation is derived and solved by a Newton–Raphson method. The continuum approximation is compared with a model in which the ions are only allowed to occupy discrete planes. The effect of correlation among the ions is included within the local density approximation. Inserting parameters appropriate to the copper–alumina interface, we find that the attractive image force between the ceramic and metal dominates the entropic (DLVO) repulsive force in the 1–2 nm range.     

Polymer compatibility with and without a solvent

A qualitative review of the thermodynamics of polymer systems will be given in terms of three contributions: positional (or combinatorial) entropy, an “international” term and a free volume term. From this one finds that a simple polymer-solvent system phase separates on lowering T to an Upper Critical Solution Temperature (UCST) or raising it to Lower Critical Solution Temperature (LCST), To achieve miscibility of two polymers of high molecular weight, one requires a “specific” interaction, usually a weak charge-transfer complex or a hydrogen bond. Phase separation takes place on raising the temperature to an LCST. These various UCST and LCST are predicted semi-quantitative by the Prigogine-Flory theory. When a solvent is added to two miscible polymers, a new type of phase separation appears since there is an effect of any difference in the strengths of the two polymer-solvent interactions. Phase separation may easily occur in the ternary system where there is none in the three binary systems, and examples will be given. In the case of two highly-attractive polymers in a solvent, a quite different phase separation occurs, sometimes called complex coacervation. A simple Flory-Huggins type theory predicts these phenomena in ternary systems.     

Electrostatics at the nanoscale

Electrostatic forces are amongst the most versatile interactions to mediate the assembly of nanostructured materials. Depending on experimental conditions, these forces can be long- or short-ranged, can be either attractive or repulsive, and their directionality can be controlled by the shapes of the charged nano-objects. This Review is intended to serve as a primer for experimentalists curious about the fundamentals of nanoscale electrostatics and for theorists wishing to learn about recent experimental advances in the field. Accordingly, the first portion introduces the theoretical models of electrostatic double layers and derives electrostatic interaction potentials applicable to particles of different sizes and/or shapes and under different experimental conditions. This discussion is followed by the review of the key experimental systems in which electrostatic interactions are operative. Examples include electroactive and "switchable" nanoparticles, mixtures of charged nanoparticles, nanoparticle chains, sheets, coatings, crystals, and crystals-within-crystals. Applications of these and other structures in chemical sensing and amplification are also illustrated.     

Close-range electrostatic interactions in proteins

Two types of noncovalent bonding interactions are present in protein structures, specific and nonspecific. Nonspecific interactions are mostly hydrophobic and van der Waals. Specific interactions are largely electrostatic. While the hydrophobic effect is the major driving force in protein folding, electrostatic interactions are important in protein folding, stability, flexibility, and function. Here we review the role of close-range electrostatic interactions (salt bridges) and their networks in proteins. Salt bridges are formed by spatially proximal pairs of oppositely charged residues in native protein structures. Often salt-bridging residues are also close in the protein sequence and fall in the same secondary structural element, building block, autonomous folding unit, domain, or subunit, consistent with the hierarchical model for protein folding. Recent evidence also suggests that charged and polar residues in largely hydrophobic interfaces may act as hot spots for binding. Salt bridges are rarely found across protein parts which are joined by flexible hinges, a fact suggesting that salt bridges constrain flexibility and motion. While conventional chemical intuition expects that salt bridges contribute favorably to protein stability, recent computational and experimental evidence shows that salt bridges can be stabilizing or destabilizing. Due to systemic protein flexibility, reflected in small-scale side-chain and backbone atom motions, salt bridges and their stabilities fluctuate in proteins. At the same time, genome-wide, amino acid sequence composition, structural, and thermodynamic comparisons of thermophilic and mesophilic proteins indicate that specific interactions, such as salt bridges, may contribute significantly towards the thermophilic-mesophilic protein stability differential.     

Interaction of aluminoxane particles with weakly charged cationic polyelectrolytes

In terms of the known concepts about noncovalent bonds in polycomplexes, the unusual case of interaction between positively charged aluminoxane particles (AP) ～ 4.6 nm in size, which comprise the main portion of the dispersed phase in the sols of poly(aluminum hydroxychloride) (PAHC), and weakly charged cationic polyelectrolytes from the Praestol, Organopol, and Zetag series (WCPE) has been examined. Using viscometry, turbidimetry, and elemental analysis, it has been found that interaction between these compounds proceeds if the content of cationic groups in the polyelectrolyte is small and ions of a low‐molecular‐weight electrolyte occur in solution. Under the given conditions, the electrostatic repulsion of likely charged reagents does not manifest itself but other kinds of noncovalent interactions are realized that lead to formation of water‐soluble polymer‐colloid complexes (PCCs). Fully charged polyelectrolytes are incapable of such interactions because of a strong electrostatic repulsion of reagents. The scheme illustrating formation of PCC has advanced. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Electrophoretic,dynamic, and static light scattering on charged polymer emulsions

Light scattering studies on dispersions formed by phase separation of a polymer-solvent-non-solvent mixture show that the dispersions comprise charged droplets of the polymer-rich phase. The charge number is not large, and data on the electrophoretic-scattering and the dynamic scattering in the absence of an external electric field are both consistent with distribution of charge among the droplets. Data on the dependence of the static scattering on concentration and scattering angle show that the droplets are also disperse in radius. The data are discussed in terms of an interaction potential among the charged droplets relating the electrostatic interactions to the charge number and radius of the droplets, and the ionic strength of the solvent.     

Influence of cation-π interactions in protein-DNA complexes

Protein-DNA recognition plays a crucial role in gene expression and regulation. In this work, we have analyzed the influence of cation-π interactions to the stability of 62 protein-DNA complexes. A new criterion has been formulated to delineate the cation-π interactions based on (i) the distribution of atoms in the π system (5 and 6-member rings) of DNA bases around the positive charged atoms of Lys and Arg and (ii) the energetic contribution of contacting atoms from electrostatic and van der Waals interactions. Our method shows the presence of cation-π interactions in 92% of the complexes. The side chain of Arg is more likely than that of Lys to be in cation-π interactions. In both Lys and Arg, the cationic groups have stronger cation-π interaction energy than the atoms with effective positive charge. The aromatic chains of purines (A and G) are exhibiting more cation-π interactions than pyrimidines (C and T). The Arg-G pair has the strongest interaction energy of −4.3 kcal/mol among all the possible pairs of amino acids and bases. The interaction energy is always positive for T and we observed few favorable interactions with C. Further, we found that the cation-π interactions due to 5-member rings of A and G are stronger than that with the atoms in 6-member rings. The distribution of base atoms around the charged atoms shows that the N7 in the 5-member ring of G is making significant number of close contacts with NZ of Arg, which is important to establish dominant cation-π interactions.     

Preparation of amorphous carbon nanofilm by magneto-luminous polymerization

The method and mechanisms to convert methane in gas phase into nanofilm of amorphous carbon; a unique method described as “magneto-luminous polymerization, and characteristic features of such films, with particular emphasis on biocompatibility imparting onto conventional materials, are described. The first key issue is the dissociation of methane in a mode of electrical discharge under the influence of magnetic field to create “magneto-luminous” gas phase in which the deposition of amorphous carbon nanofilm occurs. The amorphous carbon nanofilms (10–30 nm) have unique feature that the carbon film has no chemical functional group, which could cause various forms of interfacial interactions with surrounding medium, particularly with biological systems. Such a nanofilm could provide a great potential of imparting biocompatibility to various (metallic, ceramic, and polymeric) functional implants. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Exploiting Folding and Degradation Machineries To Target Undruggable Proteins: What Can a Computational Approach Tell Us?

Advances in genomics and proteomics have unveiled an ever-growing number of key proteins and provided mechanistic insights into the genesis of pathologies. This wealth of data showed that changes in expression levels of specific proteins, mutations, and post-translational modifications can result in (often subtle) perturbations of functional protein–protein interaction networks, which ultimately determine disease phenotypes. Although many such validated pathogenic proteins have emerged as ideal drug targets, there are also several that escape traditional pharmacological regulation; these proteins have thus been labeled “undruggable”. The challenges posed by undruggable targets call for new sorts of molecular intervention. One fascinating solution is to perturb a pathogenic protein's expression levels, rather than blocking its activities. In this Concept paper, we shall discuss chemical interventions aimed at recruiting undruggable proteins to the ubiquitin proteasome system, or aimed at disrupting protein-protein interactions in the chaperone-mediated cellular folding machinery: both kinds of intervention lead to a decrease in the amount of active pathogenic protein expressed. Specifically, we shall discuss the role of computational strategies in understanding the molecular determinants characterizing the function of synthetic molecules typically designed for either type of intervention. Finally, we shall provide our perspectives and views on the current limitations and possibilities to expand the scope of rational approaches to the design of chemical regulators of protein levels.     

COSMO-RS-PDHS: A new predictive model for aqueous electrolytes solutions

This work introduces a new tool able to predict water activities and activity coefficients of electrolytes in binary {water–electrolyte} systems. In mixtures containing electrolytes, the system is characterized by the presence of both molecular and ionic species, resulting in three different types of interactions: ion–ion, molecule–molecule and ion–molecule.Ion–ion interactions are governed by electrostatic forces between ions that have a much longer range than other intermolecular forces. The long range interactions between ions are taken in account by the Pitzer term based on the Debye–Hückel theory.Molecule–molecule and ion–molecule interaction forces are known to be short-range in nature. To determine short range mean activity coefficients of salts in {water–electrolyte} binary mixtures, a chemical treatment of ions solvation is combined with the predictive power of the COSMO-RS model. The main originality of this work resides in this chemical treatment model that provides the thermodynamic relations which enable to determine the equilibrium properties of the real solution {water–salt}, knowing those of a hypothetical mixture containing water and hydrated clusters.The resulting model called “COSMO-RS-PDHS” predicts results that are in good agreement with experimental data.     

阴离子型双功能含环氧基团酶固定化载体的制备及其固定辣根过氧化酶

利用接枝聚合在微米级硅胶微粒表面的甲基丙烯酸缩水甘油酯(GMA)和对羟基苯磺酸钠(SHBS)发生环氧基团的部分开环反应,制得阴离子型双功能复合载体SHBS-PGMA/SiO2,研究了辣根过氧化酶(HRP)与载体SHBS-PGMA/SiO2间的静电相互作用在共价固定HRP过程中的作用及其机理. 结果表明,在较大的pH值范围内,复合载体SHBS-PGMA/SiO2表面携带高密度负电荷,pH=6.0时HRP分子荷正电,酶蛋白分子与载体间会产生强静电相互作用,显著促进HRP的固定化;当载体表面SHBS的键合率约为18%时,静电相互作用对固酶的促进作用最强,固定化酶的偶联率和比活力最高. 离子强度对酶的固定化也有很大影响,加入NaCl对载体与酶蛋白之间的静电相互作用力产生屏蔽作用,增大NaCl浓度可使固定化酶的偶联率和比活力降低.     

非水相体系中枯草杆菌蛋白酶-表面活性剂离子对的形成条件

枯草杆菌蛋白酶在水相pH值小于其等电点条件下带正电,能与异辛烷中带负电的阴离子表面活性剂二辛基丁二酸磺酸钠（AOT）通过静电引力结合形成离子对进入有机相。详细研究了两相接触方式、水相初始pH值、水相离子强度等因素对酶转移率的影响。采用120 r/min磁力搅拌使两相混合能得到较好的酶转移率,作用时间为6 h。水相初始pH值5.0有利于离子对的形成及酶蛋白的转移。水相中CaCl2的加入有利于消除两相混合过程中的乳化;但是过高的CaCl2浓度会减弱酶分子与AOT间的静电引力,不利于酶分子与AOT的结合。水相中酶浓度不变,随着有机相中AOT初始浓度的增加,酶的转移率呈现增长趋势。固定异辛烷中AOT浓度,随着水相中初始酶浓度的增加,转移至有机相中酶量先增加后减少。进入异辛烷的酶分子仍旧保持活性,能催化转酯化反应的进行,但随着反应时间的延长,酶的催化效率出现下降。     

Experimental Study of Electrostatic Aerosol Filtration at Moderate Filter Face Velocity

Aerosol collection efficiency was studied for electrostatically charged fibrous filters (3M Filtrete?, BMF-20F). In this study, collection efficiencies at moderate filter face velocities (0.5–2.5 m/s) representative of some high volume sampling applications was characterized. Experimental data and analytical theories of filter performance are less common in this flow regime since the viscous flow field assumption may not be representative of actual flow through the filter mat. Additionally, electrostatic fiber charge density is difficult to quantify, and measurements of aerosol collection efficiency are often used to calculate this fundamental parameter. The purpose of this study was to assess the relative influence of diffusion, inertial impaction, interception, and electrostatic filtration on overall filter performance. The effects of fiber charge density were quantified by comparing efficiency data for charged and uncharged filter media, where an isopropanol bath was used to eliminate electrostatic charge. The effects of particle charge were also quantified by test aerosols brought into the equilibrium Boltzmann charge distribution, and then using an electrostatic precipitator to separate out only those test particles with a charge of zero. Electrostatically charged filter media had collection efficiencies as high as 70–85% at 30 nm. Filter performance was reduced significantly (40–50% collection efficiency) when the electrostatic filtration component was eliminated. Experiments performed with zero charged NaCl particles showed that a significant increase in filter performance is attributable to an induction effect, where electrostatic fiber charge polarizes aerosol particles without charge. As filter face velocity increased the electrostatic filtration efficiency decreased since aerosol particles had less time to drift toward electrostatically charged fibers. Finally, experimental data at 0.5 m/s were compared to theoretical predictions and good agreement was found for both electrostatic and nonelectrostatic effects.

© 2013 American Association for Aerosol Research     

On the modeling of phase and chemical equilibria by equations of state for systems containing supercritical components and ionic species

A technique of modeling of phase and chemical equilibria by equations of state for systems containing supercritical components and ionic species is considered. Attention is focused on the structure of equation of states with inclusion of non-electrolyte and electrostatic contributions. A hole quasichemical model was applied to illustrate the technique and to show how an EOS can be modified for systems with chemical reactions and electrostatic interactions in the liquid phase. The concentration dependency of the density and dielectric permittivity was taken into account in describing the electrostatic contribution that is required for thermodynamic consistency of the results of modeling. A method of assessing the appropriate relationships for mixtures containing supercritical components is suggested, alongside with the way to estimate the “true” composition of mixtures where ionic species are formed due to chemical reactions. The raised questions are discussed with respect to the following systems: solutions of acid gases in water-alkanolamine mixtures and water-ammonia-carbon dioxide system in a broad interval of temperatures and pressures.