Adsorption behavior of hydrophobically modified polyelectrolytes onto amino- or methyl-terminated surfaces.

The adsorption of hydrophobically modified polyelectrolytes derived from poly(maleic anhydride-alt-styrene) (P(MA-alt-St)) containing in their side chain aryl-alkyl groups onto amino- or methyl-terminated silicon wafers was investigated. The effect of the spacer group, the chemical nature of the side chain, molecular weight of polyelectrolyte, and ionic strength of solution on the polyelectrolyte adsorbed amount was studied by null ellipsometry. The adsorbed amount of polyelectrolyte increased with increasing ionic strength, in agreement with the screening-enhanced adsorption regime, indicating that hydrophobic interactions with the surface play an important role in the adsorption process. At constant ionic strength, the adsorbed amount was slightly higher for polyelectrolytes with larger alkyl side chain and decreased with the hydrophobicity of aryl group. The adsorption behavior is discussed in terms of the side chain flexibility of the polymer. Characteristics of the adsorbed layer were studied by atomic force microscopy (AFM) and contact angle measurements. AFM images show the presence of aggregates and closed globular structure of polyelectrolyte onto the amino- or methyl-terminated surface, which agrees with a 3D and 2D growth mechanism, respectively. Fluorescence measurements showed that the aggregation of polyelectrolyte containing the hydrophobic naphthyl group occurs already in the solution. However, the aggregation of polyelectrolytes containing the phenyl group in its side chain is not observed in solution but is induced by the amino-terminated surface. This difference can be explained in terms of the higher flexibility of side chain bearing the phenyl group. The polyelectrolyte films showed a high chemical heterogeneity and moderate hydrophobicity.

Protein adsorption onto polyelectrolyte layers: effects of protein hydrophobicity and charge anisotropy.

Ellipsometry was used to investigate the influence of ionic strength (I) and pH on the adsorption of bovine serum albumin (BSA) or beta-lactoglobulin (BLG) onto preabsorbed layers of two polycations: poly(diallyldimethylammonium chloride) (PDADMAC) or poly(4-vinylpyridine bromide) quaternized with linear aliphatic chains of two (QPVP-C2) or five (QPVP-C5) carbons. Comparisons among results for the three polycations reveal hydrophobic interactions, while comparisons between BSA and BLG-proteins of very similar isoelectric points (pI)-indicate the importance of protein charge anisotropy. At pH close to pI, the ionic strength dependence of the adsorbed amount of protein (Gamma) displayed maxima in the range 10 < I < 25 mM corresponding to Debye lengths close to the protein radii. Visualization of protein charge by Delphi suggested that these ionic strength conditions corresponded to suppression of long-range repulsion between polycations and protein positive domains, without diminution of short-range attraction between polycation segments and locally negative protein domains, in a manner similar to the behavior of PE-protein complexes in solution. (1-4) This description was consistent with the disappearance of the maxima at pH either above or below pI. In the former case, Gamma values decrease exponentially with I(1/2), due to screening of attractions, while in the latter case adsorption of both proteins decreased at low I due to strong repulsion. Close to or below pI both proteins adsorbed more strongly onto QPVP-C5 than onto QPVP-C2 or PDADMAC due to hydrophobic interactions with the longer alkyl group. Above pI, the adsorption was more pronounced with PDADMAC because these chains may assume more loosely bound layers due to lower linear charge density.

Surfaces based on amino acid functionalized polyelectrolyte films towards active surfaces for enzyme immobilization.

Surface based on polyelectrolytes functionalized with amino acids onto amino-terminated solid surfaces of silicon wafers was prepared, with the purpose of evaluate the chemical functionality of the polyelectrolyte films in adsorption and catalytic activity of an enzyme. In this work, the adsorption of the enzyme glucose 6-phosphate dehydrogenase from Leuconostoc mesenteroides (LmG6PD) was studied as model. The polyelectrolytes were obtained from poly (maleic anhydride-alt-vinylpyrrolidone) [poly(MA-alt-VP)] and functionalized with amino acids of different hydropathy index: glutamine (Gln), tyrosine (Tyr) and methionine (Met). The polyelectrolytes were adsorbed onto the amino-terminated silicon wafer at pH 3.5 and 4.5 and at low and high ionic strength. At low ionic strength and pH 3.5, the largest quantity of adsorbed polyelectrolyte was on the films containing glutamine moiety as the most hydrophilic amino acid in the side chain of polymer chain (5.88 mg/m2), whereas at high ionic strength and pH 4.5, the lowest quantity was in films containing tyrosine moiety in the side chain (1.88 mg/m2). The films were characterized by ellipsometry, contact angle measurements and atomic force microscopy (AFM). The polyelectrolyte films showed a moderate degree of hydrophobicity, the methionine derivative being the most hydrophobic film. With the aim of evaluate the effect of the amino acid moieties on the ability of the surface to adsorb enzymes, we study the activity of the enzyme on these surfaces. We observed that the polarity of the side chain of the amino acid in the polyelectrolyte affected the quantity of LmG6PD adsorbed, as well as its specific activity, showing that films prepared from poly(MA-alt-VP) functionalized with Met provide the best enzymatic performance. The results obtained demonstrated that the surfaces prepared from polyelectrolytes functionalized with amino acids could be an attractive and simple platform for the immobilization of enzymes, which could be of interest for biocatalysis applications.

Detection of hydrophobic microdomains in anionic polyelectrolytes with tris-(4,7-diphenyl-1,10-phenanthroline)3Cr(III).

This paper describes the changes in the luminescent properties of the tris-(4,7-diphenyl-1,10-phenanthroline)(3)Cr(III), [Cr(dip)(3)](3+) complex in an aqueous solution of three polyelectrolytes containing cyclohexyl, phenyl or 1-naphthyl groups in the side chain. When the polyelectrolytes form hydrophobic microdomains the luminescence of [Cr(dip)(3)](3+) is affected. The luminescence increases in the presence of cyclohexyl groups in the side chains, but decreases in the presence of phenyl and naphthyl groups (in that order). This fact can be explained in terms of a reductive quenching mechanism between the complex and the aromatic groups. Indeed, experiments performed with the complex and the alcohols corresponding to the functional groups, i.e., cyclohexanol, phenol, and naphthol, also show the same behavior, confirming the interaction with the functional groups and not other components of the polyelectrolyte. The luminescent properties of the [Cr(dip)(3)](3+) complex allow the detection of hydrophobic microdomains arising from the host-guest interaction. Moreover, the complex is able to distinguish between a nonaromatic hydrophobic microdomain and an aromatic one.

Inhibiting Pathogen Surface Adherence by Multilayer Polyelectrolyte Films Functionalized with Glucofuranose Derivatives.

Inhibiting pathogenic bacterial adherence on surfaces is an ongoing challenge to prevent the development of biofilms. Multilayer polyelectrolyte films are feasible antibacterial materials. Here, we have designed new films made of carbohydrate polyelectrolytes to obtain antibacterial coatings that prevent biofilm formation. The polyelectrolyte films were constructed from poly(maleic anhydride- alt-styrene) functionalized with glucofuranose derivatives and quaternized poly(4-vinylpyridine) N-alkyl. These films prevent Pseudomonas aeruginosa and Salmonella Typhimurium, two important bacterial contaminants in clinical environments, from adhering to surfaces. When the film was composed of more than 10 layers, the bacterial population was greatly reduced, while the bacteria remaining on the film were morphologically damaged, as atomic force microscopy revealed. The antibacterial capacity of the polyelectrolyte films was determined by the combination of thickness, wettability, surface energy, and most importantly, the conformation that polyelectrolytes adopt the function of nature of the carbohydrate group. This polyelectrolyte film constitutes the first green approach to preventing pathogenic bacterial surface adherence and proliferation without killing the bacterial pathogen.

Potentiometric behavior of ion-selective electrodes to large cationic species modulated by decyl alcohol.

The effect of 1-decanol on the potentiometric response of three ion-selective electrodes to large cationic species is analyzed. The electrodes were constructed with plasticized PVC membranes. The results suggest that 1-decanol alters the ionic transport through the membrane/water interface to an extent that depends on the strength of the active ion pair. The water solubility of the cation, its molecular weight, and the size of the ion pair seem to be relevant factors in this type of behavior. The potentiometric selectivity coefficients are also dependent on the presence of 1-decanol in the membrane. These results are similar to those already described in ion-selective electrodes with membranes capable of sensing anionic benzene sulfonate-type systems. Thus, the effect of the alcohol appears to be general by affecting mainly the membrane surface polarity.

Influence of decyl alcohol on the potentiometric behavior of three p-alkylbenzenesulfonate ion-selective electrodes.

The influence of decyl alcohol on the potentiometric response of three para-alkylbenzenesulfonate (p-RBS) electrodes is analyzed. The results are clearly dependent on the membrane surface polarity due to the presence of the alcohol. The ionophore was the complex trioctylmethylammonium-p-RBS, (TOMA+)-p-RBS-, with R=H, CH3, and C2H5. The nature of the complex plays a fundamental role on the potentiometric behavior of the electrode showing that the more hydrophobic the complex, the better the potentiometric responses. Moreover, the electrodes selectivities for several hydrophilic and hydrophobic interfering anions were determined. The potentiometric results with interfering anions were coherent with the Pearson's hard and soft acid-base character of these anions.

Interfacial properties of poly(maleic acid-alt-1-alkene) disodium salts at water/hydrocarbon interfaces.

The interfacial properties of poly(maleic acid-alt-1-alkene) disodium salts at hydrocarbon/water interfaces are determined. In all the studied systems, the interfacial tension decreases markedly with the polyelectrolyte concentration as the side-chain length increases. The results of the standard free energy of adsorption, DeltaG(ads)(0), are a linear function of the number of carbon atoms in the polyelectrolyte side chain. The contribution to DeltaG(ads)(0) per mol of methylene group varies from -0.64 to -0.52 kJ/mol for the n-octane/water to n-dodecane/water interfaces. DeltaG(ads)(0) data also reveal that the adsorption process is mainly determined by adsorption efficiency. Comparatively, the adsorption effectiveness seems to play a less important role. The theoretical interaction energies calculated for the insertion of one hydrocarbon molecule into the space formed by two neighboring polyelectrolyte side chains are in good agreement with the experimental results. The latter results are consistent with van der Waals-type interactions between the hydrocarbon molecules and the polyelectrolyte side chains.

Surface properties of poly(N-monoalkylmaleamic acid-alt-styrene) sodium salts: effect of the molecular weight and the side chain length.

The surface properties of poly(N-monoalkylmaleamic acid-alt-styrene) sodium salts are studied as a function of the molecular weight and the size of the linear alkyl lateral chain of the polyelectrolyte. The experimental results are well described by the Gibbs-Szyszkowski treatment. Both the surface tension behavior and the standard free energy of adsorption depend on the polyelectrolyte side chain and on the average molecular weight, M(w). An M(w)-dependent contribution to the free energy of adsorption ranging from -1.21 to -1.05 kJ for mole of methylene groups is found. The area covered by monomer units increases with M(w) and the sizes of side chains are similar to those reported in small-molecule systems. The nature of the functional group amide in the side chain has practically no effect on the surface properties as compared with the ester group in this kind of polyelectrolytes.

Lysozyme binding to poly(4-vinyl-N-alkylpyridinium bromide).

The adsorption behavior of polycations at ionic strengths (I) ranging from 0.001 to 0.1 onto silicon wafers was studied by means of ellipsometry, contact angle measurements and atomic force microscopy (AFM). Polycations chosen were bromide salts of poly(4-vinylpyridine) N-alkyl quaternized with linear aliphatic chains of 2 and 5 carbon atoms, QPVP-C2 and QPVP-C5, respectively. Under I=0.001 the reduction of screening effects led to low adsorbed amounts of QPVP-C2 or QPVP-C5 (1.0+/-0.1 mg/m(2)), arising from the adsorption of extended chains. Upon increasing I to 0.1, screening effects led to conformational changes of polyelectrolyte chains in solution and to higher adsorbed amount values (1.9+/-0.2 mg/m(2)). Advancing contact angle theta(a) measurements performed with water drops onto QPVP-C2 and QPVP-C5 adsorbed layers varied from (45+/-2) degrees to (50+/-5) degrees, evidencing the exposure of both hydrophobic alkyl groups and charged moieties. The adsorption of lysozyme (LYZ) molecules to QPVP-C5 layers was more pronounced than to QPVP-C2 films. Antimicrobial effect of LYZ bound to QPVP-C2 or QPVP-C5 layers or to Si wafers was evaluated with enzymatic assays using Micrococcus luteus as substrates. The adsorption behavior of QPVP-C2 and QPVP-C5 at the water-air interface was studied by means of surface tension measurements. Only QPVP-C5 was able to reduce water surface tension. Mixtures of LYZ and QPVP-C5 were more efficient in reducing surface tension than pure LYZ solution, evidencing co-adsorption at liquid-air interface. Moreover, antimicrobial action observed for mixtures of LYZ and QPVP-C5 was more pronounced than that measured for pure LYZ. Hydrophobic interaction between LYZ and QPVP-C5 in solution seems to drive the binding and to preserve LYZ secondary structure.