Network formation involving polyelectrolytes in solution: the role of counterions

The network-forming ability of a small fraction of nanosized trianions of the triarylmethyl class (TAM) with poly(diallyldimethylammonium chloride) (PDADMAC) polyelectrolyte is studied by high-field/high-frequency (94 GHz) electron paramagnetic resonance spectroscopy. These tristar-shaped organic ions are expected to undergo both electrostatic and hydrophobic interactions with PDADMAC chains. The dependence of electron spin echo (ESE)-detected spectra of the TAM spin probe on PDADMAC concentration reveals a heterogeneous distribution of the spin-carrying counterions. One fraction of these ions forms densely packed clusters while another one is highly diluted. On varying the concentration ratio of TAM spin probe/PDADMAC, the mean distance between closest neighbors within clusters of approximately 1.5 nm does not change significantly, while their fraction increases with decreasing polyelectrolyte content. These findings indicate that the nanosized organic TAM trianions induce network formation in solutions of PDADMAC polyelectrolyte. The data are consistent with a zip-like cooperative binding effect of TAM ions, making this spin probe an interesting building block for electrostatic self-assembly.Dedicated to Professor E.W. Fischer on the occasion of his 75th birthday.     

Formation of a silicato complex of zinc in aqueous solution and its accelerating effect on the formation of silica scales in cooling water systems

This study elucidates the effect of zinc (Zn), which is an anticorrosive water additive, on the formation of silica scales from cooling water. In these experiments, the silica scales were analyzed by EPMA, and the results indicate that Zn is sorbed into the silica scales during formation. Measurements of the solubility of Zn(OH)(2) at various concentrations of silicic acid demonstrate that Zn is present as a silicato complex of Zn (SCZ) in cooling water. From adsorption experiments of the SCZ on silica and alumina, which are major components of the silica scales, it can be concluded that the SCZ accelerates the formation of silica scales from cooling water.     

The role of complex formation in the flocculation of negatively charged sols with anionic polyelectrolytes

Summary Flocculation of negatively charged colloids by anionic polyelectrolytes, resulting from the adsorption of polymers on the colloid surface and from bridging of polymer chains between solid particles, is only possible if an appropriate concentration of electrolyte is present in the solution. Complex formation in the immediate vicinity of the sol surface between the counter cation and the functional groups of the polyelectrolyte plays a major role in the attachment of anionic polyelectrolytes to negative hydrophobic sols.Stability constants for Cu(II) polyacrylate and for the Ca complexes of a polyacrylic acid, hydrolyzed polyacrylamide and polystyrene sulfonate have been determined, and the effect of solution variables upon flocculation of AgBr/Br^– sols by anionic polyelectrolytes have been investigated. Ca⁺² ions affect the adsorption of polystyrenesulfonate on a negatively polarized mercury surface, as reflected in measurements of the differential capacitance; the presence of complex bound functional groups apparently changes the structure and orientation ability of the adsorbed polymer.With 5 figures in 10 details and 2 tables     

2H NMR evidence for the formation of random mesh phases in nonionic surfactant-water systems

Random mesh phases share many common features with the classical lamellar phase in that they are layered phases; but crucially, they possess nonuniform interfacial curvature, since the lamellae are pierced by water-filled pores. The introduction of curvature into the lamellae has been posited as a transitional precursor for other lyotropic phases. In this paper, we show that simple 2H nuclear magnetic resonance (NMR) experiments provide strong indication for the formation of the random mesh phase and the NMR data correlate well with literature results from small-angle X-ray scattering. The thermal evolution of the recorded quadrupolar splitting (DeltanuQ) is monitored within the lamellar phase of two nonionic surfactants, C16E6 and C12E5, as the samples are cooled or heated, and a marked and reversible change in the evolution of DeltanuQ is observed. Data from heavy water and deuterium labeled surfactant show the same temperature dependence and consequently report on the same structural changes with temperature. The formation of the random mesh phase is quantified in terms of an effective order parameter that is unity in the classical lamellar phase and takes values of <1 in the random mesh phase, reaching 0.6 at lower temperatures.     

The role of the surfactant head group in the emulsification process: Single surfactant systems

To clarify the effect of the surfactant head group on the emulsification process, dilute dodecane in water emulsions were prepared in a small flow-through cell with three surfactants which had the same hydrocarbon tail length but different head groups. The different surfactants types were (a) a nonionic, hexa(ethyleneglycol) mono n-dodecyl ether (C12E6), (b) an anionic, sodium dodecyl sulfate (SDS), and (c) a cationic, n-dodecyl pyridinium chloride (DPC), and the emulsions were prepared under the same conditions. From dynamic light scattering measurements, it was shown that the mean steady state droplet size of the emulsions (obtained after 20 min dispersion) could be related to the interfacial tension at concentrations in the region of the cmc. This result was in agreement with laminar and turbulent viscous flow theory. However, the particle size versus surface tension data for the different surfactant systems did not fall on a single line. This behavior suggested that the surfactant played a secondary role in defining the droplet size (in addition to reducing the interfacial tension) possibly through diffusion and relaxation, during deformation of the interface. In addition, it was found that the values of the equilibrium "surfactant packing densities" of the different surfactants at the oil/water interface were almost equal near the cmc, but the mean droplet size and the interfacial tension at the cmc decreased following the order DPC>SDS>C12E6 .     

The role of water in lanthanide-catalyzed carbon-carbon bond formation

Luminescence-decay measurements in combination with high-performance liquid chromatography analyses were used to study the relationship between rates of catalysis and water-coordination numbers of europium-based precatalysts in the aqueous Mukaiyama aldol reaction. A correlation between reactivity and water-coordination number was observed and is reported here.     

Hydrolysis of schiff bases 2: Intramolecular catalysis of an ortho-hydroxy group in nonionic surfactant systems

The rates of hydrolysis of N-(2&4-hydroxybenzylidene)-2-aminobenzothiazoles has been studied in the pH range 4–13 in a 10% dioxane-water system and in various nonionic surfactant systems. The reaction is found to be due to water mediated intramolecular general base catalysis within the pH range 4.0 to 12.0 and due to nucleophilic catalysis beyond pH 12.0. A ten membered intermediate facilitating transannular attack of a water molecule on the methine carbon forming a naphthalene type transition state has been proposed. The reactivity difference in water and nonionic surfactants has been explained by a suitable entrapment model.     

The role of polyelectrolytes in the stabilisation and destabilisation of colloids

The aim of this study was to investigate the adsorption of polyelectrolytes on charged colloids with regard to their different modes of action in the destabilisation or stabilisation of colloidal suspensions. Polyvinyl pyridine was employed as polyelectrolyte and polystyrene latexes bearing sulfonate or carboxylate groups as colloids.Adsorption of the polyelectrolyte was followed using a radiolabelling technique which allowed determination of (i) the concentration of polymer remaining in the supernatant liquid phase and (ii) the rate of establishment of the interfacial layer at very low polymer concentrations. In fact, this situation generally led to destabilisation of the colloidal suspension. Changing the rate of polymer supply to the adsorbent enabled characterisation of the interfacial reconformation of the adsorbed polymer molecules. Slow supply rates limited the amount of polymer instantaneously adsorbed, while fast rates induced a desorption of the macromolecules in excess.Destabilisation and stabilisation processes were investigated using a particle counting method (Coulter Counter TA 11, Coultronics). This technique provides a histogram which is analysed to give the size (mass) frequency curve of the aggregates c(n,t) vs. n and the weight S(t) and number N(t) average sizes of the aggregates. The experimental data were interpreted with the aid of results from numerical and theoretical studies. Self-similarity of the aggregate and fragment size distributions throughout aggregation and fragmentation could be demonstrated, while modifications of the reduced size distribution revealed changes in the rate limiting phenomena. Dynamic scaling laws were derived to describe the temporal variations of the aggregation and fragmentation processes. According to the relative values of the dynamic exponents z and w and the exponent of the power-law cluster size distribution τ it was possible to determine the aggregation mechanism. In fragmentation however the situation appeared to be more complex. No clear correlation could be established between the dynamic exponents λ and μ of the rates of variation of S(t) and N(t) and the exponents of the reduced size distribution λ′ and ν determined at large and small values of the fragment size n. Whereas λ and μ were functions of the interfacial and solution characteristics, λ′ and ν depended on the mode of aggregate formation.     

Characterization of Mazuj galls of Quercus infectoria tree as green corrosion and scale inhibitor for effective treatment of cooling water systems

Research on Chemical Intermediates - The corrosion and scale inhibition efficiency of Mazuj gall extract in simulated cooling water has been evaluated. Potentiodynamic polarization, electrochemical...     

On the functional role of a water molecule in clade 3 catalases: a proposal for the mechanism by which NADPH prevents the formation of compound II

X-ray structures of the 13 different monofunctional heme catalases published to date were scrutinized in order to gain insight in the mechanism by which NADPH in Clade 3 catalases may protect the reactive ferryloxo intermediate Compound I (Cpd I; por (*+)Fe (IV)O) against deactivation to the catalytically inactive intermediate Compound II (Cpd II; porFe (IV)O). Striking similarities in the molecular network of the protein subunits encompassing the heme center and the surface-bound NADPH were found for all of the Clade 3 catalases. Unique features in this region are the presence of a water molecule (W1) adjacent to the 4-vinyl group of heme and a serine residue or a second water molecule hydrogen-bonded to both W1 and the carbonyl group of a threonine-proline linkage, with the proline in van der Waals contact with the dihydronicotinamide group of NADPH. A mechanism is proposed in which a hydroxyl anion released from W1 undergoes reversible nucleophilic addition to the terminal carbon of the 4-vinyl group of Cpd I, thereby producing a neutral porphyrin pi-radical ferryloxo (HO-por (*)Fe (IV)O) species of reduced reactivity. This structure is suggested to be the elusive Cpd II' intermediate proposed in previous studies. An accompanying proton-shifting process along the hydrogen-bonded network is believed to facilitate the NADPH-mediated reduction of Cpd I to ferricatalase and to serve as a funnel for electron transfer from NADPH to the heme center to restore the catalase Fe (III) resting state. The proposed reaction paths were fully supported as chemically reasonable and energetically feasible by means of density functional theory calculations at the (U)B3LYP/6-31G* level. A particularly attractive feature of the present mechanism is that the previously discussed formation of protein-derived radicals is avoided.     

Study of the mechanism action of sodium gluconate used for the protection of scale and corrosion in cooling water system

This work based on the mechanism action study of sodium gluconate (SG) for ordinary mild steel used for cooling water system treatment. In the first time, we evaluated the temperature effect on the scale inhibition of SG using statistic scale inhibition method. Result showed that the inhibition efficiency became more important with increasing temperature, at great concentration (10⁻² and 10⁻³ M). This can be explained by forming of stable complex SG–Ca²⁺. In the second time, the present work focuses on the study of operational parameters and corrosion products effect on SG performance using potentiodynamic polarization and electrochemical impedance spectroscopic method. The obtained results show that SG is a very good inhibitor for corrosion and scale and remains effective in the presence of corrosion products. For this study we were proposed a mechanism action for SG on metallic surface. In addition, the SG keeps its effectiveness in a more aggressive medium such as 3% NaCl. Finally, to complete the formulation, we added a not oxidizing biocide (CTAB) to SG. The results obtained show that SG remains its effective.     

The properties of a binary mixture of nonionic surfactants in water at the water/air interface

The behavior of mixed nonionic/nonionic surfactant solutions, that is, p-(1,1,3,3-tetramethylbutyl)phenoxy poly(ethylene glycol)s Triton X-100 (TX100) and Triton X-165 (TX165) have been studied by surface tension and density measurements. The obtained results of the surface tension measurements were compared with those calculated from the relations derived by Joos, Miller, and co-workers. From the comparison, it appeared that by using these two approaches the adsorption behavior of TX100 and TX165 mixtures at different mole fractions can be predicted. The negative deviation from the linear relationship between the surface tension and composition of TX100 and TX165 mixtures in the concentration range corresponding to that of the saturated monolayer at the interface, the values of the parameters of molecular interaction, the activity coefficients, as well as the excess Gibbs energy of mixed monolayer formation calculated on the basis of Rosen and Motomura approaches proved that there is synergism in the reduction of the surface tension of aqueous solutions of TX100 and TX165 mixture when saturation of the monolayer is achieved. The negative parameters of intermolecular interaction in the mixed micelle and calculations based on MT theory of Blankschtein indicate that there is also synergism in the micelle formation for TX100 and TX165 mixture. It was also found that the values of the standard Gibbs energy of adsorption and micellization for the mixture of these two surfactants, which confirm the synergetic effect, can be predicted on the basis of the proposed equations, which include the values of the mole fraction of surfactant and excess Gibbs energy TX100 and TX165 in the monolayer and micelle.     

The role of elastases secreted by fibroblasts in wrinkle formation: implication through selective inhibition of elastase activity

We have previously demonstrated that decreases in skin elasticity, accompanied by increases in the tortuosity of elastic fibers, are important early events in wrinkle formation. In order to study the role of elastases in the degeneration of elastic fibers during wrinkle formation we examined the effects of an inhibitor of skin fibroblast elastase, N-phenethylphosphonyl-L-leucyl-L-tryptophane (NPLT), on wrinkle formation in hairless mice skin following UV irradiation. Dorsal skins of hairless mice were exposed daily to UV light for 18 weeks at doses of 65-95 mJ/cm2 and treated topically with 100 microL of 1 mM NPLT immediately after each UV irradiation. Wrinkles on dorsal skins were evaluated from week 6 through week 18. The daily exposure of mouse skin to UV light with less than 1 minimal erythemal dose significantly enhanced the activity of elastase in the exposed skin by week 4, and the elevated levels of elastase activity were significantly reduced by the in vitro incubation with NPLT in a dose-dependent manner to a level similar to that in unexposed mice skin, indicating that NPLT can efficiently inhibit the UV-inducible elastase activity. Topical application of NPLT significantly suppressed wrinkle formation when compared with vehicle controls by week 15 of treatment (P < 0.05). Histochemistry of elastic fibers with Orcein staining demonstrated that there were no obvious decreases of the fine elastic fibers in UV-exposed NPLT-treated skin in contrast to their marked decreases in the UV-exposed vehicle-treated skin. These findings suggest that skin fibroblast elastase plays a decisive role in wrinkle formation through the degeneration of elastic fiber.     

The role of asynchronous bond formation in the diastereoselective epoxidation of cyclic enol ethers: a density functional theory study

Density functional theory (DFT) (Becke3LYP functional and the D95 basis set) was used to study the influence of substitution on the dimethyldioxirane epoxidation reaction of six- and seven-membered cyclic enol ethers. In agreement with our previously reported experimental results, the calculations predict that substitution on the cyclic enol ether influences the level of diastereoselectivity. Apparent only from the calculations is that the degree of synchronicity in the transition state is important in the diastereoselectivity.     

The role of organic solvents in the separation of nonionic compounds by capillary electrophoresis

Although nonionic compounds can be separated by micellar electrokinetic chromatography (MEKC), application of this technique is restricted by a somewhat limited elution range. Incorporation of organic solvents in the background electrolyte (BGE) greatly extends the scope of MEKC and provides a major variable in optimizing the separation of neutral analytes. This paper provides a systematic review of the principles and scope of the separation of neutral analytes by capillary electrophoresis (CE) in organic-aqueous solution. The methods surveyed include those that use tetraalkylammonium salts, dioctyl sulfosuccinate, lauryl poly(oxyethylene) sulfate. Polyaromatic hydrocarbon (PAH) compounds can be separated using sodium hexadecyl sulfate in 70% methanol (30% aqueous) to 100% methanol.     

Alcohols solubilization in a nonionic fluorinated surfactant based system: effects on the characteristics of mesoporous silica

In this study, we have used hydrogenated alcohols with different chain lengths and one fluorinated alcohol as additives to determine their effect on the characteristics of mesoporous materials prepared from fluorinated micelles.     

Conformational study of the trinucleotide CpGpCp-pentapeptide Gly5 complex: The important role of bridging water in the complex formation

Conformational changes in the RNA-protein interaction were studied by calculating the intramolecular interaction energy of a model complex with the use of potential functions. The model complex has hydrogen-bonded water molecules bridging polypeptide NH groups to 2'-hydroxyl groups and sugar ring oxygen atoms. Since the sugar ring is constrained by the bridging water, preliminary calculations with the model compounds, the sugar ring, mononucleoside diphosphates, pCp and pGp, were carried out, and the flexibility and energetics of the sugar ring were compared with the previous results of DNA. The shift of the phase angle of the sugar ring occurred in the complex formation because of the hydrogen bond through the bridging water and the flexibility of the sugar ring. The free energy difference at 298 K is about ?74.0 kcal/mol which was obtained from the intramolecular interaction energy difference of ?67.5 kcal/mol by adding the conformational entropy change of 21.9 e.u., which in turn was calculated from the evaluation of the determinant of the matrix containing variances and covariances of the internal coordinates.     

The conformational origin of the barrier to the formation of neighboring group assistance in glycosylation reactions: a dynamical density functional theory study

Static and dynamical Density Functional Theory studies of 2,6-di-O-acetyl-3,4-O-isopropylidene-D-galactopyranosyl cation have shown that this cation can exist in two conformers characterized as (2)S(O) and B(2,5), respectively. The (2)S(O) conformer has the O-2 acyl group equatorial with the carbonyl syn to H-2 and is populated by monocyclic oxocarbenium ions. These conformational features are present in the structurally related glycosyl donor ethyl 2,6-di-O-benzoyl-3,4-O-isopropylidene-beta-D-galactothiopyranoside as determined by X-ray diffraction studies. The B(2,5) conformer has O-2 axial and allows the carbonyl to rotate and close the five-membered ring to form a bicyclic dioxolenium ion. Constraints based on natural internal coordinates were implemented to study this conformational transition. In this way the barrier to interconversion has been determined to be 34 kJ mol(-)(1) with a transition state characterized as (O)S(2) and a pathway involving pseudorotation. Thus, for the first time the structures and energetics of the key ions postulated to be involved in neighboring group assisted glycosylation reactions have been determined.