Participation of electrolyte cations in albumin adsorption onto negatively charged polymer latices

The participation of electrolyte cations in the adsorption of bovine serum albumin (BSA) onto polymer latices was investigated. The latices used were hydrophobic polystyrene (PS), and hydrophilic copolymers, i.e., styrene (St)/2-hydroxyethyl methacrylate(HEMA) copolymer [P(St/HEMA)] and styrene/acrylamide (AAm) copolymer [P(St/AAm)]. Three kinds of electrolyte cations (Na⁺, Ca²⁺, Mg²⁺) were used as the chloride. The amount of BSA adsorbed in every cation medium showed a maximum near the isoelectric point (iep, pH about 5) of the protein. The amounts of BSA adsorbed onto copolymer latices (except in the acidic pH region lower than the iep) were considerably smaller than that onto PS latex because of the steric repulsion and the decrease in the hydrophobic interaction between BSA and copolymer latices. In the acidic pH region, there was little difference in the amount of BSA adsorbed in every cation medium. However, in the pH region higher than the iep, the amounts of BSA adsorbed (particularly onto PS latex) in divalent cations (Ca²⁺ and Mg²⁺) media were relatively greater compared with that in a monovalent (Na⁺) one. This result was interpreted on the basis of the differences in such effects of electrolyte cations as dehydration power, suppression of the electrostatic repulsion, and binding affinity to BSA molecule. Ion Chromatographic estimation of the amounts of electrolyte cations captured upon BSA adsorption (in pH > 5) revealed that divalent cations were incorporated into the contact interface between the latex and BSA molecule so as to prevent the accumulation of anion charge and facilitate the protein adsorption.     

Preferential adsorption of bovine serum albumin dimer onto polymer microspheres having a heterogeneous surface consisting of hydrophobic and hydrophilic parts

The adsorption behaviors of bovine serum albumin (BSA) containing both dimeric and monomeric species onto polymer microspheres were examined using various homopolymers and poly(2-hydroxyethyl methacrylate)/polystyrene composite microspheres which were produced by the emulsifier-free (seeded) emulsion polymerization technique. The preferential adsorption of the BSA dimer was clearly observed in an optimum region of the surface hydrophilicities of the polymer microspheres. The preferential adsorption of the BSA dimer onto the composite polymer microspheres having heterogeneous surfaces consisting of hydrophilic and hydrophobic parts was more marked than those onto the homopolymer and copolymer microspheres having homogeneous surfaces.     

Effect of surface charge on adsorption of bovine serum albumin as studied by ellipsometry 1. Adsorption on cationic monolayer

The adsorption of bovine serum albumin (BSA) onto a cationic monolayer (N,N-dimethyl-N,N-dialkylammonium chloride) spread at the air/water interface was studied by ellipsometry. Both thicknesses and refractive indices of the BSA layer adsorbed at the monolayer/solution interface are estimated from the observed change in phase difference and the ratio of reflection coefficients. The amount of adsorption of BSA resembles a Langmuir type isotherm. The adsorption changes with pH asymmetrically with respect to the pH of maximum adsorption, which was calculated to be 5.06 ± 0.47 mg/m². The amount of maximum adsorption implies that the BSA molecule adsorbs to the surface in a mode intermediate between side-on and end-on.     

Behavior of pure and mixed DPPC liposomes spread or adsorbed at the air-water interface

Liposomes from pure dipalmitoylphosphatidylcholine (DPPC) and mixed DPPC: distearoylphosphatidylcholine (DSPC): soybean lecithin (SL) prepared by the Bangham method with sonication were dispersed into solution or spread at the interface and the kinetics of the surface film formation was studied by measuring and recording the evolution of superficial tension, surface potential, and superficial (¹⁴C labeled) DPPC density.A simple theoretical approach can describe these kinetics by two processes: irreversible diffusion of closed vesicles into or from the bulk phase, and irrevers ible transformation of closed spherical vesicles into destroyed ones which form the surface film. Diffusion controls the phenomenon for small initial amounts of liposomes.Transformation controls the phenomenon for important initial amounts of liposomes. The kinetic constant of the transformation,K, does not depend on the technique used to form the surface film (spreading or adsorption).The equilibrium and rheological properties of surface films formed after liposome spreading are compared to those of monolayers     

An absolute differential maximum bubble pressure surface tensiometer employing displaced capillaries

A modification of the differential maximum bubble pressure method for determining surface tensions is described. In this method, surface tension is calculated from the difference between maximum bubble pressures reached at capillaries of differing internal radii, vertically displaced by an amount calculated from the theory of Cuny and Wolf (1956) Ann Physik 17:57). The density dependence of the technique is eliminated and surface tension becomes a truly linear function of the differential maximum bubble pressure, which is easily measured. The absolute measuring technique is illustrated for equilibrium and dynamic surface tensions of a series of pure liquids and aqueous solutions.For dynamic measurements on surfactant solutions some important experimental considerations and limitations are described. In particular, a previously unrecognized source of error in estimating bubble surface ages is identified. It was found that the maximum bubble pressure for a large capillary does not immediately precede the detachment of the bubble, but occurs at one-third the overall bubble period. Thus, for large capillaries, subsequent to attaining the maximum bubble pressure, there exists a significant decay time in addition to the dead time. In general, surface ages corresponding to maximum pressure at small and large capillaries bubbling with the same period are not equal. This can lead to a large error in dynamic and equilibrium surface tensions of surfactant solutions. With suitable correction the technique is capable of measuring absolute surface tension, even for quite slowly equilibrating surfactant solutions.     

Grafting onto ultrafine ferrite particles: Reaction of isocyanate-capped polypropylene glycol with hydroxyl groups on the surface

The grafting of polypropylene glycol (PPG) onto an ultrafine ferrite by the reaction of hydroxyl groups on the surface with isocyanate-capped PPG (PPG-NCO), prepared by the reaction of an equimolecular amount of PPG with tolylene 2,4-diisocyanate, was investigated. When PPG-NCO (M _n=2.5×10³) was heated with the ferrite in bulk, the percentage of grafting onto the ferrite at 120 °C was increased up to 18.5%. On the contrary, the grafting by the reaction of PPG with hydroxyl groups on the ferrite at 120°C was scarcely observed. The grafted PPG onto the ferrite was removed by hydrolysis with a dilute methanol solution of potassium hydroxide. Therefore, it was considered that PPG was grafted onto the ferrite surface with urethane bond. The grafting of PPG onto the surface was also confirmed by infrared spectra. The reaction of PPG-NCO with the ferrite was accelerated by the addition of-picoline as a catalyst. PPG-grafted ferrite was found to produce a stable colloidal dispersion in organic solvents. Furthermore, the effect of molecular weight of PPG-NCO on the grafting onto the ferrite was discussed.     

Interaction of nitrophenols with lipids at the air/water interface

The uptake of ortho and para nitrophenol to charged and neutral lipid monolayers spread at the air/solution interface was studied by reflection spectroscopy. The adsorption characteristics of the two nitrophenols have been studied by measuring the surface pressure and surface potential as a function of molecular area of the different lipid monolayers in the presence of nitrophenols in the subphase. The results have been interpreted in terms of the electrostatic interaction between the negatively charged dissociated phenolate ions and the positively charged head group of dioctadecyldimethylammonium bromide monolayers.     

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     

New protocols for preparing dipalmitoylphosphatidylcholine dispersions and controlling surface tension and competitive adsorption with albumin at the air/aqueous interface

The adsorption behavior of dipalmitoylphosphatidylcholine (DPPC), which is the major component of lung surfactant, at the air/aqueous interface and the competitive adsorption with bovine serum albumin (BSA) were studied with tensiometry, infrared reflection absorption spectroscopy (IRRAS), and ellipsometry. Dynamic surface tensions lower than 1 mN/m were observed for DPPC dispersions, with mostly vesicles, prepared with new protocols, involving extensive sonication above 50 °C. The lipid adsorbs faster and more extensively for DPPC dispersions with vesicles than with liposomes. For DPPC dispersions by a certain preparation procedure at T > T_c, when lipid particles were observed on the surface, dynamic surface tensions as low as 1 mN/m were measured. Moreover, IRRAS intensities and ellipsometric δΔ values were found to be much higher than the values for other DPPC dispersions or spread DPPC monolayers, suggesting that a larger amount of liposomes or vesicles adsorb on the surface. For DPPC/BSA mixtures, the tension behavior is controlled primarily by BSA, which prevents the formation of a dense DPPC monolayer. When BSA is injected into the subphase with a spread DPPC monolayer or into a DPPC dispersion with preadsorbed layers, little or no BSA adsorbs and the DPPC layer remains on the surface. When a DPPC monolayer is spread on a BSA solution at 0.1 wt% at 25 °C, then DPPC lipid can displace the adsorbed BSA molecules. The lack of BSA adsorption, and the expulsion of BSA by DPPC monolayer is probably due to the strong hydrophilicity of the lipid polar headgroup. When a DPPC dispersion is introduced with Trurnit's method or when dispersion drops are sprayed onto the surface of a DPPC/BSA mixture, the surface tension becomes lower and is controlled by DPPC, which can prevent the adsorption of BSA. The results may be important in understanding inhibition of lung surfactants by serum proteins and in designing efficient protocols of surfactant preparation and administration.     

Surfactant monolayers on a clean mercury surface: Apparatus and experiments

A Langmuir trough for studying monolayers on a mercury surface was constructed usingT. Smith's design. The surfactant (long-chain alkyl-trimethylammonium compounds) in aqueous solution were spread on a clean mercury surface in an atmosphere of helium, and the surface pressure re-areaA and thickness of surface filmd-areaA curves were obtained. The-A curves were characterized by the appearance of multiple inflection points and plateaus, being explained as stepwise dense surface packing of molecules, and the formation of multilayers by film compression with long axes of molecules lying flat on the mercury surface.     

Stability of modified surface CaCO3 in the non-polar medium

The adsorption isotherm of methacrylic acid (MAA) and polymethacrylic acid (PMAA) molecules on CaCO₃ were studied. The isotherm of (MAA) adsorption from cyclohexane was found formed from two steps, while that of (PMAA) from ethanol is formed from one step. The effects of surface modification of CaO₃ with (MAA) and (PMAA) in the sedimentation properties in a non-polar medium (cyclohexane) have been studied. It was found that the most stable suspension formed is concerned with monolayer surface coverage for the two adsorptives. Also, studies were made for the rheological properties of concentrated suspension of CaCO₃ modified with (MAA) and (PMAA) in a paraffin oil. The equilibrium flow curves of CaCO₃ modified with (PMAA) suspensions exhibit pseudoplastic characteristics, accompanied by some degree of complex thixotropy, while that modified with (MAA) exerts a thickening effect with rheopexy characteristics.     

Effect of polymerized silicic acid on mixed lipid-protein monolayers used as cell membrane models. I. Hemoglobin-stearoyl erythroceramide films

The effect of polysilicic acid on mixed monolayers of hemoglobin and stearoyl erythroceramide used as cell membrane models has been studied. The presence of the sphingolipid at the interface stabilizes the hemoglobin monolayer, hindering expulsion of its residues from the surface when the collapse pressure (ca. 23 mN/m) is reached. The interaction between the components of the mixed film results in non-additivity of their molecular areas to a degree depending on film composition and substrate pH. The presence of polysilicic acid in the substrate increases the miscibility of the components in the mixed monolayer as a result of ionic interaction between the silicic acid and the protein.     

Swelling of poly(methacrylic acid) gels and adsorption of L-lysine and its polymer on the gels

Poly (methacrylic acid) gels (PMAA gels) of various degrees of crosslinking were prepared and the dissociation behavior of these gels was examined; the swelling behavior was investigated as a function of the solution pH values. A reentrant phenomenon of swelling was observed and interpreted based on the Flory-Huggins equation and the Donnan equilibrium formula. Moreover, adsorption of L-lysine, oligo(L-lysine)s (Lys-n,n=3, 9, and 19) and poly(L-lysine) onto PMAA gels from aqueous solutions was investigated under different conditions of pH and concentration of adsorbate. The adsorption ratio of L-lysine onto PMAA gel is dependent on both the pH of solution and the degree of crosslinking. In a pH range between 8 and 9, the protonated form of L-lysine is strongly adsorbed on the PMAA gel by electrostatic interactions. Oligomers and polymer of L-lysine are adsorbed in a somewhat different way from the monomeric L-lysine. In addition, the desorption behavior of L-lysine from PMAA gels by a change in pH was also investigated.     

Removal of Reactive Yellow 84 from aqueous solutions by adsorption onto hydroxyapatite

The adsorption of a reactive dye, Reactive Yellow 84, from aqueous solution onto synthesized hydroxyapatite was investigated. The experiments were carried out to investigate the factors that influence the dye uptake by the adsorbent, such as the contact time under agitation, absorbent dosage, initial dye concentration, temperature and pH of dye solution. The experimental results show that the amount of dye adsorbed increases with an increase in the amount of hydroxyapatite. The maximum adsorption occurred at the pH value of 5. The equilibrium uptake was increased with an increase in the initial dye concentration in solution. The experimental isotherm data were analyzed using Langmuir isotherm equation. The maximum monolayer adsorption capacity was 50.25 mg/g. The adsorption has a low temperature dependency and was endothermic in nature with an enthalpy of adsorption of 2.17 kJ mol⁻¹.     

Nonideal mixing of 16-(9-anthroyloxy) palmitic acid and fatty acid in monolayer

The surface pressure-molecular area curve of the mixed monolayer of 16-(9-anthroyloxy) palmitic acid (16AP) and fatty acid (palmitic or stearic acids) showed various kink points which indicated the phase transitions of the monolayer. On the basis of the surface phase rule, the phase diagrams of the mixed monolayer were elucidated. The bifunctional molecule, 16AP, takes two orientations in a monolayer state, that is, horizontal and vertical ones. Horizontally oriented 16AP and vertically oriented fatty acid form a mixed monolayer but this exhibits deviation from the ideal mixing, which was interpreted in terms of the surface regular solution theory. On the other hand, the 16AP molecule in the vertical state was found to be immiscible with the fatty acid molecule in a monolayer de spite both molecules being vertical to the surface and parallel to each other. This was caused by the participation of the 9-anthroyloxy moiety of 16AP in the interaction of 16AP and fatty acid in the hydrophobic region of the monolayer.     

Distribution of local anesthetics in lipid membranes

Absorption of local anesthetics into lipid membranes and adsorption onto their surfaces were studied as a function of the pH of aqueous bulk solutions by measuring lipid vesicle electrophoretic mobility, the partition of the anesthetics between the aqueous and membrane phases by the use of fluorescence and radioactive tracer methods, and the effect of the anesthetics on interfacial tension of lipid monolayers formed at the oil/aqueous interface.

At a pH much lower than the pK_a value of the local anesthetic, the charged form of the local anesthetic was only adsorbed onto the membrane surface, as determined from vesicle electrophoretic mobility, radioisotope tracer and the monolayer surface tension studies. Surface partition coefficients of the charged form of the local anesthetics on phosphatidylcholine and phosphatidylserine membranes were obtained from the data of electrophoretic mobilities for lipid vesicles. The surface partition coefficients of various local anesthetics paralleled those of the bulk partition coefficients.

As the pH of the solutions increased, the adsorbed amount of the charged form of the anesthetic at the membrane interface decreased, while the absorption of the uncharged form of the local anesthetic into the membrane increased. The total amount of local anesthetic adsorbed per unit area of the membrane generally increased as the pH of the solution increased. This was also observed from the measurements of the fluorescence of local anesthetics adsorbed into the membranes. At lower pH than that corresponding to the pK_a value of the local anesthetic, the amount of anesthetic adsorbed depended greatly upon the membrane surface charge. At a higher pH than its pK_a, it did not depend appreciably on the surface charge density of the membrane but did depend on the bulk partition coefficients between the aqueous and oil phases.     

Adsorption of bovine serum albumin onto poly(methyl methacrylate) stereocomplex films with a molecularly regulated nanostructure

Stereoregular poly(methyl methacrylate)s (PMMAs) were stepwise assembled on a quartz crystal microbalance (QCM) substrate after the immersion of the QCM into alternating acetonitrile solutions at ambient temperature. A quantitative QCM analysis at each step showed stereocomplex formation on the substrate surface. The adsorption of bovine serum albumin (BSA) onto stereocomplex films with a molecularly regulated nanostructure was analyzed quantitatively. The adsorption constant and the maximum adsorption amount, calculated by the assumption of Langmuir‐type adsorption, showed that BSA adsorbed with a relatively weak interaction onto the stereocomplex films. The BSA adsorption onto the stereocomplex films occurred in an end‐on manner, with a smaller adsorption constant than for that onto individual spin‐coated films. The amount of BSA adsorbed was significantly affected by the molecular weight of syndiotactic PMMA. Attenuated total reflection spectra indicated that BSA adsorbed onto the films with or without denaturing. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1807–1812, 2003     

Scanning force microscopic study of protein adsorption on the surface of organosilane monolayers prepared by the Langmuir‐Blodgett method

The n‐octadecyltrichlorosilane (OTS, CH₃(CH₂)₁₇SiCl₃), 18‐nonadecenyltrichlorosilane (NTS, CH₂=CH(CH₂)₁₇SiCl₃), [2‐(perfluorooctyl)ethyl] trichlorosilane (FOETS, CF₃(CF₂)₇CH₂CH₂SiCl₃) monolayers, and their mixed monolayers were used as the model substrates for the study of protein adsorption mechanism. Surface plasmon resonance (SPR) spectroscopy was applied to analyze the protein adsorption behavior onto the surface of the monolayers. Atomic force microscope (AFM) was used to observe the monolayer surfaces after exposure of these monolayers to bovine serum albumin (BSA) and γ‐globulin(IgG) solution. AFM observation revealed that the charged protein either below or above the isoelectric point was preferentially adsorbed onto the FOETS phase of the (OTS/FOETS) mixed monolayer. SPR revealed that the amount of adsorbed protein in the charged state was lower than that in the neutral state. These results indicate that the preferential adsorption of protein onto the FOETS phase for the mixed monolayer systems at either below or above pI is due to (1) the minimization of interfacial free energy between the monolayer surface and the buffer solution, and (2) the electrostatic repulsion among protein molecules bearing charges.     

Evaluation of the adsorption affinity of proteins to calcium hydroxyapatites by desorption and pre-adsorption methods

The adsorption affinity of bovine serum albumin (BSA) and lysozyme (LSZ) to calcium hydroxyapatite (CaHAP) was evaluated by desorption and two step adsorption methods. These experiments were carried out at 15°C in a 1×10⁻⁴ mol dm⁻³ KCl solution of pH 6.0. BSA molecules were scarcely desorbed, exhibiting an irreversible adsorption of BSA, though LSZ slightly desorbed. This result supports our previous findings that LSZ adsorbs weakly onto phosphate ions exposed on ac or bc faces of CaHAP while BSA adsorbs strongly onto positively charged sites on ac or bc faces of CaHAP. The amount of adsorbed LSZ was markedly increased by the pre-adsorption of BSA, where LSZ was adsorbed onto BSA-covered CaHAP. On the other hand, the amount of adsorbed BSA was not changed by the pre-adsorption of LSZ. In both pre-adsorption systems it was confirmed by an HPLC method that no protein molecule pre-adsorbed was desorbed after the post-adsorption procedure. Therefore, it was interpreted that the enhancement of adsorption of positively charged LSZ is induced by an electrostatic attractive force through pre-adsorption of negatively charged BSA molecules with a high coverage. However, since the coverage of LSZ onto CaHAP is considerably low, no stimulation of BSA adsorption occurred on the LSZ-covered surface. The formation of double protein adsorbed layers consisting of pre- and post-adsorbed proteins was proposed.