Surface Functionalization of an Aluminum Alloy to Generate an Antibiofilm Coating Based on Poly(Methyl Methacrylate) and Silver Nanoparticles.

An experimental protocol was studied to improve the adhesion of a polymeric poly(methyl methacrylate) coating that was modified with silver nanoparticles to an aluminum alloy, AA2024. The nanoparticles were incorporated into the polymeric matrix to add the property of inhibiting biofilm formation to the anticorrosive characteristics of the film, thus also making the coating antibiocorrosive. The protocol consists of functionalizing the surface through a pseudotransesterification treatment using a methyl methacrylate monomer that bonds covalently to the surface and leaves a terminal double bond that promotes and directs the polymerization reaction that takes place in the process that follows immediately after. This results in more compact and thicker poly(methyl methacrylate) (PMMA) coatings than those obtained without pseudotransesterification. The poly(methyl methacrylate) matrix modified with nanoparticles was obtained by incorporating both the nanoparticles and the methyl methacrylate in the reactor. The in situ polymerization involved combining the pretreated AA2024 specimens combined with the methyl methacrylate monomer and AgNps. The antibiofilm capacity of the coating was evaluated against P. aeruginosa, with an excellent response. Not only did the presence of bacteria decrease, but the formation of the exopolymer subunits was 99.99% lower than on the uncoated aluminum alloy or the alloy coated with unmodified poly(methyl methacrylate). As well and significantly, the potentiodynamic polarization measurements indicate that the PMMA-Ag coating has a good anticorrosive property in a 0.1-M NaCl medium.

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.

Nucleotide specificity of Saccharomyces cerevisiae phosphoenolpyruvate carboxykinase Kinetics, fluorescence spectroscopy, and molecular simulation studies.

Phosphoenolpyruvate carboxykinases, depending on the enzyme origin, preferentially use adenine or guanine nucleotides as substrates. In this work, analyses of the substrate specificity of the Saccharomyces cerevisiae ATP-dependent enzyme have been carried out. Kinetics studies gave relative values of k(cat)/K(m) for the nucleoside triphosphate complexes in the order ATP>>GTP>ITP>UTP>CTP. For the nucleoside diphosphate complexes the order is ADP>>GDP>IDP congruent withUDP>CDP. This shows that the enzyme has a strong preference for ADP (or ATP) over other nucleotides, being this preference about an order of magnitude higher for the diphosphorylated than for the triphosphorylated nucleosides. The calculated binding free energies (kcalmol(-1)) at 25 degrees C are 7.39 and 6.51 for ATP and ADP, respectively. These values decrease with the nucleotide structure in the same order than the kinetic specificity. The binding energy for any triphosphorylated nucleoside is more favourable than for the corresponding diphosphorylated compound, showing the relevance of the P(gamma) for nucleotide binding. Homology models of the adenine and guanine nucleotides in complex with the enzyme show that the base adopts a similar conformation in the diphosphorylated nucleosides while in the triphosphorylated nucleosides the sugar-base torsion angle is 61 degrees for ATP and -53 degrees for GTP. Differences are also noted in the distance between P(beta) and Mn2+ at site 1. This distance is almost the same in the ATP, GTP, and UTP complexes, however in the ADP, GDP and UDP complexes it is 2.9, 5.1, and 7A, respectively. Experimental data obtained with a Thr463Ala mutant enzyme agree with molecular simulation predictions. The results here presented are discussed in terms of the proposed interactions of the nucleotides with the protein.

Association of valdecoxib, a nonsteroidal anti-inflammatory drug, with human serum albumin.

Valdecoxib addition quenches the intrinsic human serum albumin (HSA) fluorescence. This allows an evaluation of the drug-protein association. However, both the number of binding sites and their affinity for the drug depend upon the methodology employed for their evaluation and the employed protein concentration. In this work, we measured the effect of valdecoxib on HSA fluorescence yield over a wide range of experimental conditions and discuss the validity of the binding parameters derived from the different data treatments: Stern-Volmer, Scatchard, double logarithmic, quadratic equation, Benesi-Hilderand, and Encinas-Lissi. It is proposed that a combination of Encinas-Lissi and Scatchard treatments of the data renders the most reliable results. From these data, it is concluded that HSA presents three high-affinity binding sites for valdecoxib (K(as) = 4.5 × 10(4) m(-1)) and several secondary sites of smaller activity.

Preparation and characterization of hydrogels based on homopolymeric fractions of sodium alginate and PNIPAAm.

Graft copolymers were prepared by formation of an amide bond between poly-α-L-guluronic acid (MW 24,000), isolated from sodium alginate and the free amino group of PNIPAAm-NH(2). SEM micrographs revealed the formation of a macroscopic network on the surface of the grafted hydrogels with a porosity diameter of 10-20 µm. Semi-IPN hydrogels were prepared using different proportions of sodium poly-ß-D-mannuronate (MW 21,000), isolated from sodium alginate and cross-linked PNIPAAm-NH(2) polymers. SEM micrographs showed porosities of minor size (∼5 µm). Though both types of hydrogels are good water containers, the water retention capacity of graft copolymers is more than 50% higher than that of semi-IPN hydrogels. Both hydrogel types showed significant changes in swelling ratios between 20 and 45 °C: the swelling ratio decreases near the LCST of PNIPAAm. The water absorption and retention capacity of graft hydrogels increases with pH, reaching a maximum value at pH 7.0.

Solvent and media effects on the photophysics of naphthoxazole derivatives.

The photophysical properties of 2-phenyl-naphtho[1,2-d][1,3]oxazole, 2(4-N,N-dimethylaminophenyl)naphtho[1,2-d][1,3]oxazole and 2(4-N,N-diphenylaminophenyl) naphtho[1,2-d][1,3]oxazole were studied in a series of solvents. UV-Vis absorption spectra are insensitive to solvent polarity whereas the fluorescence spectra in the same solvent set show an important solvatochromic effect leading to large Stokes shifts. Linear solvation energy relationships were employed to correlate the position of fluorescence spectra maxima with microscopic empirical solvent parameters. This study indicates that important intramolecular charge transfer takes place during the excitation process. In addition, an analysis of the solvatochromic behavior of the UV-Vis absorption and fluorescence spectra in terms of the Lippert-Mataga equation shows a large increase in the excited-state dipole moment, which is also compatible with the formation of an intramolecular charge-transfer excited state. We propose both naphthoxazole derivatives as suitable fluorescent probes to determine physicochemical microproperties in several systems and as dyes in dye lasers; consequence of their high fluorescence quantum yields in most solvents, their large molar absorption coefficients, with fluorescence lifetimes in the range 1-3 ns as well as their high photostability.

A sulfated galactan with antioxidant capacity from the green variant of tetrasporic Gigartina skottsbergii (Gigartinales, Rhodophyta).

The water soluble polysaccharide produced by the green variant of tetrasporic Gigartina skottsbergii was found to be composed of D-galactose and sulfate groups in a molar ratio of 1.0:0.65. (1)H and (13)C NMR spectroscopy studies of the desulfated polysaccharide showed a major backbone structure of alternating 3-linked ß-D-galactopyranosyl and 4-linked α-D-galactopyranosyl units, and minor signals ascribed to 3-O-methyl-substitution on the latter unit. Ethylation analysis of the polysaccharide indicated that the sulfate groups are mainly located at position O-2 of 4-linked α-D-galactopyranosyl residue and partially located at positions O-6 of the same unit and at position O-2 of 3-linked ß-D-galactopyranosyl residue, and confirmed the presence of 3-O-methyl-galactose in minor amounts (4.4%). The sulfated d-galactan presents a similar structure to λ carrageenan but with much lower sulfation at position O-6 of the α-residue and at position O-2 of ß-residue. The antioxidant capacity of the sulfated d-galactan was evaluated by the peroxyl radicals (ORAC method), hydroxyl radicals, chelating activity, and ABTS(+) assays. Kinetic results obtained in these assays were compared with those obtained for the commercial λ carrageenan. The antioxidant activity toward peroxyl radicals was higher for commercial λ carrageenan, this agrees with its higher content of sulfate group. The kinetics of the reaction of both polysaccharides with hydroxyl and ABTS(+) radicals showed a complex mechanism, but the antioxidant activity was higher for the polysaccharide from the green variant of tetrasporic Gigartina skottsbergii.