Synthesis of core‐shell structured carboxylated microparticles with a straightforward procedure and their evaluation as a polymer support

Poly(trimethylolpropane trimethacrylate) microspheres with a narrow size distribution were obtained by precipitation polymerization. They were subsequently modified by surface grafting with acrylic acid in a polar ethanol–water reaction medium, without stabilizer, yielding core‐shell particles with diameters in the micrometer range. The resulting polymeric material was characterized by SEM and potentiometric titration, FTIR spectroscopy, and thermal analysis. It was shown that the particle characteristics (size, size distribution, and functionality) obtained by this straightforward procedure can be controlled by modifying the synthesis parameters (monomer concentration, agitation rate, and temperature). The high functionality, the chemical and physico‐mechanical stability, as well as the possibility to control the performances of the resulting polymeric materials by synthesis allow its applications in various areas. Envisaging separation and catalysis domains, Cu(II), Cd(II), and Cr(III) uptake capacity from aqueous solutions was investigated under noncompetitive conditions as a function of synthesized particle functionality, time, and pH range. It was also found that the addition of the carboxylated microparticles to polyethylene stabilized with α‐tocopherol improved the thermo‐oxidative behaviour of the polymeric material. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5889–5898, 2005     

Visualization of red-ox proteins on the gold surface using enzymatic polypyrrole formation

We describe a new method for the visualization of the activity of red-ox proteins on a gold interface. Glucose oxidase was selected as a model system. Surfaces were modified by adhesion of glucose oxidase on (a) electrochemically cleaned gold; (b) gold films modified with gold nanoparticles, (c) a gold surface modified with self-assembled monolayer, and (d) covalent immobilization of protein on the gold surface modified with a self-assembled monolayer. The simple optical method for the visualization of enzyme on the surfaces is based on the enzymatic formation of polypyrrole. The activity of the enzyme was quantified via enzymatic formation of polypyrrole, which was detected and investigated by quartz microbalance and amperometric techniques. The experimental data suggest that the enzymatic formation of the polymer may serve as a method to indicate the adhesion of active redox enzyme on such surfaces.

Discretely weak P-sets

A discretely weak P-set is a nowhere dense closed set which is disjoint from the closure of any countable discrete subset of its complement. We show that the Stone-?ech remainder N^∗ of the discrete space N of natural numbers cannot be covered by discretely weak P-sets when the continuum hypothesis is assumed.     

Template polymerization of methacrylic acid along poly(N-acetyliminoethylene) in water. Influence of template architecture

The kinetic study of the photochemical polymerization of methacrylic acid (MAA) in aqueous dilute solution in the presence of poly(N-acetyliminoethylene) (PNAI) oligomers evidenced template features. The process proceeded in two stages, depending on [PNAI]/[MAA]₀ ratio and polymerization duration, two different complexes being formed, both by a “zip” chain-growth mechanism. Computing and transmission electron microscopy data revealed that this aspect is due to the replacing of the initial PNAI template by the newly formed poly(methacrylic acid) daughter polymer, as a result of the structural peculiarities of the latter as a component of the primary complex. Its specific mode of packing in a complex aggregate was considered to be the main reason for the reported behavior. © 1996 John Wiley & Sons, Inc.     

Antibiofilm and Anti-Quorum Sensing Potential of Cycloartane-Type Triterpene Acids from Cameroonian Grassland Propolis: Phenolic Profile and Antioxidant Activity of Crude Extract

Propolis is very popular for its beneficial health properties, such as antimicrobial activity and antioxidant effects. It is one of the most long-serving traditional medicines to mankind due to its interesting chemical diversity and therapeutic properties. The detailed chemical information of propolis samples is very necessary to guarantee its safety and for it to be accepted into health care systems. The phenolic profile of the hydroethanolic extract was determined using HPLC-DAD, and the antioxidant was evaluated using five complementary methods. Triterpenoids were isolated using column chromatography and characterized using ¹H NMR and ¹³C NMR. The effects of the extract and the isolated compounds on quorum sensing mediated processes and biofilm formation in bacteria were evaluated. Protocatechic acid (40.76 ± 0.82 µg/g), 4-hydroxybenzoic acid (24.04 ± 0.21 µg/g), vanillic acid (29.90 ± 1.05 µg/g), quercetin (43.53 ± 1.10 µg/g), and luteolin (4.44 ± 0.48 µg/g) were identified and quantified. The extract showed good antioxidant activity in the DPPH^•, ABTS^•+, CUPRAC, and metal chelating assays, and this antioxidant effect was confirmed by cyclic voltammetry. 27-Hydroxymangiferonic acid (1), Ambolic acid (2), and Mangiferonic acid (3) were isolated from anti-quorum sensing activity at MIC, and it was indicated that the most active sample was the extract with inhibition diameter zone of 18.0 ± 1.0 mm, while compounds 1, 2, and 3 had inhibition zones of 12.0 ± 0.5 mm, 9.0 ± 1.0 mm, and 12.3 ± 1.0 mm, respectively. The samples inhibited the P. aeruginosa PA01 swarming motility at the three tested concentrations (50, 75, and 100 μg/mL) in a dose-dependent manner. The propolis extract was able to inhibit biofilm formation by S. aureus, E. coli, P. aeruginosa, C. albicans, and C. tropicalis at MIC concentration. Compound 1 proved biofilm inhibition on S. aureus, L. monocytogenes, E. faecalis, E. coli, and C. tropicalis at MIC and MIC/2; compound 2 inhibited the formation of biofilm at MIC on S. aureus, E. faecalis, E. coli, S. typhi, C. albicans, and C. tropicalis; and compound 3 inhibited biofilm formation on E. faecalis, E. coli, C. albicans, and C. tropicalis and further biofilm inhibition on E. coli at MIC/4 and MIC/8. The studied propolis sample showed important amounts of cycloartane-type triterpene acids, and this indicates that there can be significant intra-regional variation probably due to specific flora within the vicinity. The results indicate that propolis and its compounds can reduce virulence factors of pathogenic bacteria.     

Copolymerization of Schiff Bases with Tetracyanoethylene

The copolymerization of four Schiff bases (substituted benzylidine anilines) with tetracyanoethylene has been investigated. The reaction takes place in the absence of an initiator through a zwitterionic mechanism, leading to copolymers with an almost alternating structure. When dimethylformamide was used as solvent, a concurrent radical homopolymerization of tetracyanoethylene with the formation of an azoporphyrin structure occurs.     

Poly(N-isopropylacrylamide)/poly[(N-acetylimino)ethylene] thermosensitive block and graft copolymers

Block and graft copolymers with poly(N-isopropylacrylamide) and poly[(N-acetylimino)ethylene] (PNAI) sequences were synthesized via PNAI derivatives (macroinitiators or macromers). The polymerization yields for block copolymers synthesized in ethanol, using the PNAI macroinitiator, were low (<10%), except where photochemical polymerization was applied. By contrast, for the copolymerizations of N-isopropylacrylamide with the PNAI macromers, performed in alcoholic solution, quite high polymerization yields, around 80-90%, were reached. ¹H-NMR and IR spectral and differential scanning calorimeter thermal data confirmed the copolymer formation. Thermosensitivity of the copolymers was investigated by means of turbidimetric technique as a function of their nature, average molecular weight and composition. It was found that the length of the chain of the PNAI macromer and the content in hydrophilic PNAI units of the resulted copolymer affected this behavior.     

Dielectric Characterization of Biopolymer/Poly(ϵ-Caprolactone) Hydrogels

The dielectric properties of a series of pure atelocollagen samples and of atelocollagen-based hydrogels long-range cross-linked with bifunctional poly(?-caprolactone) derivative, or further short-range cross-linked by UV irradiation, were discussed in relation to the cross-linking method, composition, and hierarchical assembly. Three main factors with significant influence on the electrical behavior, frequency, temperature, and moisture content, are analyzed in detail.     

Effect of nano-Al2O3 particles and of the Co concentration on the corrosion behavior of electrodeposited Ni–Co alloys

Incorporation of nano-Al₂O₃ particles into a Ni–Co alloy by electrodeposition influences the corrosion properties, morphology, and structure of the layers. The resistance against corrosion of Ni–Co/Al₂O₃ composite films deposited on stainless steel was investigated in a 0.1-M NaCl solution by potentiodynamic polarization. The presence of nanoparticles improves the corrosion resistance of Ni–Co/nano-Al₂O₃ deposits when compared to pure Ni–Co alloy. Moreover, by increasing the pH of the electrodeposition bath and the content of Co in the alloy, the resistance against corrosion is furthermore improved. The morphology of the deposits before and after their corrosion was analyzed by scanning electron microscopy. The presence of the embedded alumina particles in the Ni–Co alloys was one of the key factors that limited further propagation of corrosion on the metallic surface. Preferential corrosion attack, in the form of a pitting corrosion, was located mainly at the grain boundaries.