Interaction of opioid molecules with PS,PC and PS/PC monolayers

The interaction between opiate molecules and phosphatidylserine (PS) or phosphatidylcholine (PC) has been studied on compression isotherms and penetration kinetics. Phosphatidylcholine-opiate interactions are weak and similar in magnitude for all opiate molecules. On contrary, PS and PS/PC interact strongly and differently with opiate molecules. The differences in penetration are not directly related to the pKa or hydrophobicity of the molecules.     

Mixed monolayers composed of PC/PS/Chol. Interaction with opioid molecules

The miscibility of phosphatidylserine, phosphatidylcholine, and cholesterol in monolayers were studied. The influence of sodium and calcium ions in this system was determined. The compression isotherms of mixed monolayers of the above cited three components spread on subphases containing opiate molecules are elucidated. Moreover, the penetration kinetics of opiate molecules in these mixed monolayers was also recorded. The results show that the presence of cholesterol always lowers the penetration of opioid molecules; this effect is weaken for meperidine, the most hydrophobic of the molecules assayed.Abreviations PS phosphatidylserine - PC phosphatidylcholine - PI phosphatidylinositol - Chol cholesterol     

Adsorption of anionic surfactants on positively charged polystyrene particles II

In the case of cationic polystyrene latex, the adsorption of anionic surfactants involves a strong electrostatic interaction between both the particle and the surfactant, which may affect the conformation of the surfactant molecules adsorbed onto the latex-particle surface. The adsorption isotherms showed that adsorption takes place according to two different mechanisms. First, the initial adsorption of the anionic surfactant molecules on cationic polystyrene surface would be due to the attractive electrostatic interaction between both ionic groups, laying the alkyl-chains of surfactant molecules flat on the surface as a consequence of the hydrophobic interaction between these chains and the polystyrene particle surface, which is predominantly hydrophobic. Second, at higher surface coverage the adsorbed surfactant molecules may move into a partly vertical orientation with some head groups facing the solution. According to this second mechanism the hydrophobic interactions of hydrocarbon chains play an important role in the adsorption of surfactant molecules at high surface coverage. This would account for the very high negative mobilities obtained at surfactant concentration higher than 5×10^–7 M. Under high surface-coverage conditions, some electrophoretic mobility measurements were performed at different ionic strength. The appearance of a maximum in the mobility-ionic strength curves seems to depend upon alkyl-chain length. Also the effects of temperature and pH on mobilities of anionic surfactant-cationic latex particles have been studied. The mobility of the particles covered by alkyl-sulphonate surfactants varied with the pH in a similar manner as it does with negatively charged sulphated latex particles, which indicates that the surfactant now controls the surface charge and the hydrophobic-hydrophilic character of the surface.Dedicated to the memory of Dr. Safwan Al-Khouri IbrahimPresented at the Euchem Workshop on Adsorption of Surfactants and Macromolecules from Solution, Åbo (Turku), Finland, June 1989     

Effect of polymerized silicic acid on mixed lipid-protein monolayers used as cell-membrane models II. Pepsin-sphingomyelin films

Mixed pepsin-sphingomyelin films exhibit behavior typical of bidimensional systems whose components are miscible in all proportions. The non-polar chains of their components are believed to establish weak hydrophobic interactions. The dynamic compression-expansion II-A curves obtained in the presence of polysilicic acid differ from those recorded in its absence, which may arise from an ionic interaction whereby silicate ions accommodate themselves among the film molecules and bind strongly to the sphingomyelin molecules to form a rigid surface network in which the protein molecules are trapped.     

Patch controlled attractive electrostatic interactions between similarly charged proteins and adsorbents

A non-uniform distribution of ionic groups on the surface of a protein can lead to attractive electrostatic interactions between itself and an adsorbent, even when the net charge of the protein is of the same type as that of the adsorbent. Chromatographic retention mapping as a function of pH and ionic strength is employed to identify electrostatic repulsion or attraction. Thus, it can be determined whether the global characteristics or an oppositely charged patch controls the adsorptive behavior of a protein on a charged adsorbent.     

Miscibility of dodecyltrimethylammonium bromide and dodecyltrimethylammonium chloride in surface-adsorbed film and micelle

Surface tension of aqueous solutions of mixtures of dodecyltrimethylammonium bromide (DTAB) and dodecyltrimethylammonium chloride (DTAC) has been measured and analyzed by using thermodynamic relations. The adsorbed film has been found to contain more DTAB molecules than the solution. The shape formed by the curves of the total molality at constant surface tension against the solution and surface compositions indicates the ideal mixing of the DTAB and DTAC molecules in the adsorbed film. Micellar composition has been estimated at the critical micelle concentration (CMC). The micelles have been found to be richer in DTAB than the solution, but poorer in DTAB than the adsorbed film at the CMC. The DTAB and DTAC molecules have been shown to mix ideally in the micelles. From the comparison with the results on the system of decylammonium bromide and decylammonium chloride, it has been concluded that, on the mixing of surfactants differing only in counter ions, the adsorbed film is influenced more significantly by the ionic head group of the surfactant than the micelle.     

Solubilization properties of aqueous solutions of alkyltrimethylammonium halides toward a water-insoluble dye

The solubility of a water-insoluble dye, Sudan Red B, in aqueous sodium halide solutions of tetradecyl-, cetyl-, and stearyltrimethylammonium halides has been measured at different surfactant and salt concentrations, and the dependence of solubilization properties on alkyl chain length has been discussed with reference to the micelle size and shape. At low ionic strengths where only spherical micelles exist, the solubilization power of micellar surfactant slightly increases with increasing the ionic strength, but it sharply increases at high ionic strengths above the threshold value of sphere-rod transition. However, the solubilization power becomes independent of the ionic strength, if their rodlike micelles are sufficiently long. The solubilization capacity increases linearly with increasing the molecular weight, almost independent of counterion species, but the rod-like micelle has a higher solubilization capacity than the spherical micelle. The solubilization capacity is larger for a surfactant with longer alkyl chain, indicating that the dye is solubilized more readily in a larger hydrophobic core. The solubilized dye is situated in a rodlike micelle of alkyltrimethylammonium halides, on average, 4.5–7.5 nm apart from each other.     

The effect of pH on emulsion polymerization of styrene in the presence of an amphoteric emulsifier

An emulsion polymerization of styrene in the presence of an amphoteric emulsifier of the betaine type; N,N-dimethyl-n-laurylbetaine (LNB), has been studied at various pH values. The relationships between the physicochemical properties of LNB aqueous solutions, the emulsion polymerization process and the characteristics of the synthesized latex particles were studied under various pH conditions. The polymerization rate and the particle number concentration decreased with increasing pH of LNB aqueous solution and changed in shape at both ca. pH 4 and pH 8–10. The properties of LNB aqueous solution also changed with the pH and changed in shape at the same pH as that of the emulsion polymerization. These pH values were in good agreement with the pH at which the LNB molecule changed its ionic form. The number of synthesized latex particles was proportional to the number of LNB micelles in the solution, below pH 10. The particle size of the synthesized latex particles and the molecular weight of the latex polymers also changed with the properties of LNB aqueous solutions, accompanying the change of the ionic form of LNB molecules.     

Deformation and fracture behavior of polystyrene ionomer and ionomer blends

The deformation and fracture behavior of sulphonated polystyrene ionomers, and of blends of these with polystyrene have been investigated. The microstructure of the ionomer, which varies with ion content, appears to have a significant effect on mechanical properties. Both tensile strength and toughness increase appreciably at ion contents near 5 mol%, where clusters become dominant over ion pairs and multiplets. In blends of the ionomers and polystyrene, phase separation occurs and the ionomer component appears in the form of fine particles dispersed in the polystyrene matrix. These particles possess a greater effective entanglement density than the matrix, as a result of ionic crosslinking, and they provide reinforcement against early craze breakdown and fracture. Tensile strength and fracture energy increase rapidly as the ionomer concentration in the blend is increased and they become essentially independent of blend ratio above about 10 wt% of the ionomer. Tests carried out on thin film specimens of the blends show that the dispersed ionomer particles adhere well to the matrix and contribute to the fracture energy both by inducing matrix crazing and by internal fibrillation within the particles.Dedicated to Professor Hans-Henning Kausch on the occasion of his 60th birthday.     

Narrow size distribution polystyrene latexes prepared in the presence of amphoteric sulfobetaine surfactants

Polystyrene latexes with a narrow size distribution (Dw/Dn < 1.05) were prepared with a large range of particle sizes (from 40 to 800 nm) in the presence of various amphoteric sulfobetaine surfactants. The influence of the nature of the surfactant and of the ionic strength, the pH and solid content were studied. The results are discussed and compared with those obtained using sodium dodecyl sulfate or in the absence of surfactants.     

Stability of spherical and rod-like micelles of ionic surfactants,in relation to their counterion binding and modes of hydration

Aqueous salt solutions of ionic surfactants in both spherical and rod-like micelles have been treated on the basis of a statistical thermodynamic theory, and the double logarithmic relationship between micelle molecular weight and ionic strength is derived for each micelle. Counterion binding on both micelles are assumed to occur specifically, and their degrees of dissociation are related to the slopes of the linear double logarithmic relations. It is found from the relationship observed for typical surfactants that the effective charge of spherical micelles is 29±4. The degree of dissociation of rod-like micelles of these surfactants is primarily determined by the counterion species, yielding values 0.8 for Na⁺, 0.4–0.6 for Cl^– and 0.2–0.3 for Br^–. Hydrophilic hydration of both micelles can be evaluated from the intercepts of the linear relations. Hydrophilic hydration acts repulsively in spherical micelles, while it is attractive or much less repulsive in rod-like micelles.     

Fluorescence and viscometry study of complexation of poly(acrylic acid) with poly(acrylamide) and hydrolysed poly(acrylamide)

Interpolymer complexation of poly(acrylic acid) with poly(acrylamide) and hydrolysed poly(acrylamide) was studied by fluorescence spectroscopy and viscometry in dilute aqueous solutions. Changes in chain conformation and flexibility due to the interpolymer association are reflected in the intramolecular excimer fluorescence of pyrene groups covalently attached to the polymer chain. Both poly(acrylamide) and hydrolysed poly(acrylamide) form stable complexes with poly(acrylic acid) at low pH. The molecular weight of poly(acrylic acid) and solution properties such as pH and ionic strength were found to influence the stability and the structure of the complexes. In addition, the polymer solutions mixing time showed an effect on the mean stoichiometry of the complex. The intrinsic viscosity of the solutions of mixed polymers at low pH suggested a compact polymer structure for the complex.     

Conformational changes of polyglutamic acid adsorbed on cationic polystyrene as characterized by microelectrophoresis technique

Polypeptides (polyglutamic acid in sodium form) of three different polymerization degrees have been adsorbed on cationic polystyrene latex. The electrokinetic behavior of the complex PG/PS has been studied by microelectrophoretic mobility. The effect of ionic strength and pH on electrokinetic properties of the complex PG/PS have also been studied. It has been found that the appearance of maximum inu _e -logc curves is related to coverage degree of polystyrene surface and the polymerization degree of polypeptides chains. Likewise, the form of such curves depends markedly on pH. An attempt has been made to explain the data in terms of conformational changes of the adsorbed polypeptides chains.Presented at the NATO Advanced Study Institut on Polymer Colloid, Strasbourg (France), July 1988.     

Effect of inorganic electrolyte concentration on anionic-cationic adsorption films Part 1. Decylpyridinium chloride + sodium octylsulphonate + sodium chloride

The effect of NaCl on simultaneous adsorption of decylpyridinium chloride (R₁₀PyCl) and sodium octylsulphonate (R₈SO₃Na) on the free surface of their aqueous solutions has been examined. The surface excess of each component was determined on the basis of a suitable form of the Gibbs adsorption equation. The ionic strength effect on the adsorption of particular components of mixtures, as well as on the composition of anionic-cationic films adsorbed from equimolar solutions, is small. This is due to little difference in surface activity of surfactants investigated.     

Role of electrokinetic phenomena in the preparation of supported metal catalysts

A model accounting for the effect of electrokinetic phenomena on the prepartion of supported metal catalysts by wet impregnation is presented. The model is able to explain the dependence of catalyst distribution profile and loading on the concentration of the impregnant, on the pH and ionic strength of the impregnating solution, as well as on the presence of a co-impregnating species.     

The salt-induced sphere-rod transition of micelles of dodecylpyridinium iodide in aqueous NaI solutions

Static light scattering has been measured on aqueous NaI solutions of dodecylpyridinium iodide (DPI) over NaI concentrations from 0 to 0.05 M. Reduced intensity of scattered light increases with increasing DPI concentration above the critical micelle concentration. The Debye plot is generally a curve with an initially positive slope and with a weakly convex, upward curvature, when the NaI concentration ranges from 0 to 0.005 M. The molecular weight of the spherical micelle of DPI is 28400 in water, and it increases slightly with increasing NaI concentration. The initial slope decreases with increasing NaI concentration and changes from positive to negative across 0.007 M NaI, which is the threshold for the sphere-rod transition and where the micelle has a molecular weight of 34400. At NaI concentrations from 0.01 to 0.05 M, the Debye plot is a curve with an initially negative slope and with a convex, downward curvature. The magnitudes of slope and curvature are larger, and the rodlike micelles of DPI have larger molecular weight and stronger mutual interaction, as the NaI concentration increases. The linear double logarithmic relationship between molecular weight and ionic strength holds for spherical and rodlike micelles, respectively.     

Temperature-dependent fracture mechanisms in ultra-high strength polyethylene fibers

The influence of the temperature on the mechanical properties of gel-spun hot-drawn ultra-high molecular weight polyethylene fibers has been investigated.From these experiments two different fracture mechanisms could be distinguished. The results indicate that above 20C a stress-induced orthorhombic-hexagonal phase transition is responsible for fiber failure. In the hexagonal or rotator phase the chains can easily slip past one another and fiber fracture is initiated by creep. Below 20C the phase transition cannot be introduced because the stress needed for the phase transition would exceed the covalent-bond strength in the polyethylene chain. The strength temperature data of the low temperature region was treated with Zhurkov's kinetic concept, leading to a bond-fracture activation energy of 160 kj/mol and an activation volume of 0.01 nm³. These values, together with the data from irradiation and shrinkage experiments, indicated that in the low temperature region fiber failure might be initiated by the fracture of trapped entanglements instead of that by overstressed, taut tie molecules.     

Interactions of proteins with uniform colloidal hematite and chromium hydroxide particles. I. Adsorption

The adsorption of ovalbumin, -globulin, and lysozyme on uniform spherical hematite and chromium hydroxide particles in aqueous media has been studied as a function of the pH at a constant ionic strength. The uptake of ovalbumin and -globulin was greatest at their isoelectric points and differed little at 10^–2 and 10^–3 mol dm^–3 NaNO₃. The adsorption of lysozyme was strongly influenced by the ionic strength.The deposition of ovalbumin on hematite in the presence of Mg (NO₃)₂ was significantly greater than that with NaNO₃ under otherwise comparable conditions. Dialysis experiments with ovalbumin against magnesium nitrate solutions showed Mg²⁺ to be specifically bound to the protein.The shapes of isotherms indicated monolayer coverage for ovalbumin and multilayer coating for lysozyme for both adsorbents. The shapes of isotherms of -globulin on hematite point to a rearrangement of the protein on the particle surface, while a monolayer was found on chromium hydroxide particles.Supported by the NSF Grant CHE-9108420Part of a Ph.D. thesis     

Coagulation kinetics of amorphous colloidal silica suspensions with and without hydroxypropyl cellulose polymer

The coagulation rate constant of submicron silica has been measured as a function of solution pH, salt concentration and hydroxypropyl cellulose (HPC) polymer concentration. Results show that the colloidal stability of silica is dominated by the cation concentration in the presence of salt in the pH range 3–9.5. The stability increases as cation concentration decreases. At low salt concentration and a minimum colloid stability was found in the intermediate pH range 4–8. These results show that differences in the literature values of the critical coagulation constant by relative light-scattering experiments can be explained by the use of the coagulation rate constant analysis. When HPC polymer was present in the solution, the colloid stability of the silica increased. The adsorption of polymer stabilizes the silica suspensions, both at low pH near the isoelectric point and at high ionic strength where it coagulates without the polymer. A monolayer coverage was necessary to provide steric stabilization. At 10^–3 M KCl a smaller equilibrium concentration of HPC in solution is needed to give monolayer coverage and steric stabilization than at 1 M KCl and pH 4.2.     

Preparations and properties of polyurethane aqueous dispersion from uncatalyzed systems of H12MDI,PTAd/bisphenol A polyol,and DMPA

Aqueous dispersions of polyrethane (PU) containing ionic and nonionic hydrophilic segments were prepared in a prepolymer mixing process using substantial amount of solvent. The acid groups were neutralized with tertiary amine, and chain extension in aqueous media was carried out with triethylene tetramine. Average particle size and particle size distribution of the dispersion, and mechanical and viscoelastic properties of the emulsion cast films were determined.