Giancarlo Palma

Peripheral nerve repair using a poly(organo)phosphazene tubular prosthesis

Nerve regeneration experiments were carried out using tubular nerve guides of poly[(ethylalanato)1.4(imidazolyl)0.6phosphazene] (PEIP). By means of in vivo tests, this polymer was found to be biodegradable and transformed into harmless products. The tubular nerve guides were prepared by deposition of the dissolved polymer on a glass capillary tube, followed by evaporation of the solvent (methylene dichloride). After transectioning, rat sciatic nerve stumps were immediately sutured into the ends of 10-mm-long polymer tubes. On removal of the prosthesis, after implantation for 45 d, a tissue cable was found bridging the nerve stumps in all cases. Histological analysis revealed that the tissue cable was essentially composed of a regenerated nerve fibre bundle. A parallel series of experiments was undertaken to compare the use of silicone tubes that are not biodegradable and are most frequently used for studies of nerve regeneration with tubulization techniques. The advantages of biodegradable PEIP tubular nerve guides used for peripheral nerve repair are discussed.

Amperometric biosensor involving covalent immobilization of choline oxidase and butyrylcholinesterase on a methacrylate-vinylene carbonate co-polymer

A two‐enzyme sensor for the determination of choline esters was prepared by the covalent co‐immobilization of choline oxidase and butyrylcholinesterase on polymer membranes, obtained by radiation‐induced co‐polymerization of 2‐hydroxyethylmethacrylate and vinylene carbonate at low temperature. The enzyme‐modified membrane was applied to a platinum electrode and the determination of substrates was based on the electrochemical detection of enzymically generated H2O2. The analytical characteristics of this sensor, including the optimization of immobilization procedures, calibration curves for different substrates, pH and temperature effects and stability, are described.

Hydrogenation of benzene to cyclohexene over polymer-supported ruthenium catalysts

Abstract Partial liquid-phase hydrogenation of benzene to cyclohexene over ruthenium catalysts supported on charcoal and anionic cross-linked polymers is described. The influence of the polarity of polymeric supports, nature of the solvent and the presence of zinc additives on the performance of the catalyst in a glass-lined reactor at 100–110°C and a pressure of 1.5 MPa have been studied. It has been found that at 42–47% conversion of benzene, the selectivity to cyclohexene, observed in water with Ru catalysts supported on a strongly hydrophilic microporous resin, is higher than that displayed by Ru supported on charcoal. The effect of water on the performance of the catalyst is probably a result of formation of a suitable environment around Ru particles and of a good accessibility of metal particles dispersed within the hydrophilic polymer support.

Microporous poly-N,N-dimethylacrylamide-p-styrylsulfonate-methylene bis(acrylamide): a promising support for metal catalysis

Abstract The synthesis of poly- N,N -dimethylacrylamide- p -styrylsulfonate (DMAA-SS) with 4 mol% of methylene bis(acrylamide) mol% of methylene bis(acrylamide) (MBAA) as crosslinker is described. Bulk polymerization of water solution of monomers (DMAA, SS sodium salt, MBAA) was carried out under gamma irradiation. Swellability in water and various organic solvents showed mainly hydrophilic character of the resin. The ion-exchange experiments with 1 M hydrochloric acid and with [Pd(NH 3 ) 4 ] 2+ showed very good accessibility of the inner space of the material. Polymer supported [Pd(NH 3 4 ] 2+ was reduced by hydrogen in methanol, sodium borohydride in water and sodium borohydride in ethanol. Under these last conditions uniform distribution of Pd throughout the resin particles was observed. The activated material turned out to be a good catalyst for the hydrogenation of p -nitrotoluene to p -toluidine in methanol under ambient conditions.

Biocompatible polyphosphazenes by radiation-induced graft copolymerization and heparinization

Investigations were carried out on the radiation-induced graft copolymerization by direct irradiation of dimethylaminoethyl methacrylate on to poly(bis(trifluoroethoxy)phosphazene) and on to poly (bis(phenoxy)phosphazene). Kinetics of grafting were followed with the polyphosphazenes immersed in monomer - methanol mixtures of various composition. The grafted film samples were quaternized with methyl iodide and, to the produced ammonium group, heparin was ionically bonded with high yield. On the grafted and heparinized-grafted film samples an evaluation of hydrophilicity, mechanical properties, biocompatibility and anticoagulating properties was carried out.

Radiation-induced polymerization for the immobilization of penicillin acylase

The immobilization ofEscherichia coli penicillin acylase (EC 3.5.1.11) was investigated by radiation-induced polymerization of 2-hydroxyethyl methacrylate at low temperature. A leak-proof composite that does not swell in water was obtained by adding the crosslinking agent trimethylolpropane trimethacrylate to the monomer-aqueous enzyme mixture. Penicillin acylase, which was immobilized with greater than 70% yield, possessed a higherKm value toward the substrate 6-nitro-3-phenylacetamidobenzoic acid than the free enzyme form (Km = 1.7 × 10−5 and 1 × 10−5M, respectively). The structural stability of immobilized penicillin acylase, as assessed by heat, guanidinium chloride, and pH denaturation profiles, was very similar to that of the free-enzyme form, thus suggesting that penicillin acylase was entrapped in its native state into aqueous free spaces of the polymer matrix.

Metal palladium supported on amphiphilic microporous synthetic organic supports. Part I. Material preparation and textural characterization

Abstract Styrene, 2-methacryloxyethylsulfonic acid and methylenebisacrylamide are copolymerized in the presence of dimethylformamide under γ -irradiation at room temperature to give potentially amphiphilic, microporous resins. The molar fraction of methylenebisacrylamide (the cross-linker) ranges from 1 to 6 mol%. The obtained resins, after grinding and sieving, are treated with solutions of Pd(AcO) 2 and the ion-exchanged polymers are then treated with NaBH 4 in ethanol. The metal content in the materials ranges from 2.1% to 2.4% (w/w). X-ray microprobe analysis shows that Pd(0) is homogeneously dispersed throughout the particles of the polymeric materials. The polymer chain concentration and its distribution in the swollen macromolecular networks are assessed by means of Inverse Steric Exclusion Chromatography (ISEC). In spite of the higher molar proportion of styrene repeating units, the Pd(0)-resin composites swell comparably in water and tetrahydrofurane. Their amphiphilic character is the result of the different swelling properties of the hydrophilic and hydrophobic domains.

PREPARATION OF ISOCYANO POLYMER SUPPORTS AND THEIR COMPLEXES WITH CATALYTICALLY RELEVANT TRANSITION-METAL CENTERS

Abstract Suspension or mass polymerization of vinyl comonomers with 3-formamidopropyl acrylate affords widely solvent compatible, medium crosslinked polymers, which can be transformed into isocyano-containing resins. These materials (0.2–1.3 meq of isocyano functionality per g resin), exhibit a strong coordinating ability towards a variety of metal centers including catalytically relevant metal complexes. The combination of IR spectroscopy and other analytical data makes it possible to reliably speculate on the actual composition and structure of the respective polymer-supported complexes. X-ray microprobe analysis shows that the metal distribution is homogeneous throughout the polymeric beads. Thermal analyses reveal that both resins and polymer-supported complexes are thermally stable up to 300 °C. Severe leaching tests (dichloroethane or toluene at 100 °C) show that the polymer-metal complexes are characterized by high formation constants. Under certain conditions, the involvement of one polymer-bound-NC group per metal atom is achieved, so that the anchoring of catalytically active species to the support produces only a slight modification of the coordination sphere of the metal centers.

Interpenetrating organometallic polymer networks in heterogeneous catalysis: Mild hydrogenation of p-nitrotoluene

A cross-linked organometallic macroporous copolymer (P1) and an interpenetrating organometallic polymer network (IOPN) material (C1), both based on the organometallic monomer cis-(PdCl 2 (CN CH 2 ) 3 OC(O)CH=CH 2 ) 2 ) (1), are catalytically active and reusable in the mild and selective hydrogenation of p-nitrotoluene to p-toluidine in methanol, under ambient conditions. The IOPN catalyst C1 is generated by the dispersion of a copolymer of I inside a macroporous poly-dimethylacrylamide-methylen-ebisacrylamide matrix to give an expectedly microporous organometallic matrix which exhibits a catalytic productivity quite similar to that displayed by P1. The productivity of both catalysts is comparable to that exhibited by commercial Pd/C under the same conditions, with P1 and C1 far superior in terms of separability and handiness

Covalently immobilized choline oxidase and cholinesterases on a methacrylate copolymer for disposable membrane biosensors

Bienzymatic sensors for the determination of esters of choline were prepared by covalent co-immobilization of cholinesterases and choline oxidase on polymer membranes, obtained by radiation-induced copolymerization of 2-hydroxyethyl methacrylate and glycidyl methacrylate at low temperature. Optimization of the covalent attachment of choline oxidase and acetyl-or butyrylcholinesterase to copolymer was explored. The enzyme-modified polymers were applied on platinum electrodes to form amperometric sensors, based on the electrochemical detection of enzymatically developed hydrogen peroxide. Acetyl-, acetylthiobutyryl-, and butyrylthiocholine contents in standard solutions were measured, and linear calibration curves were determined. Temperature and pH effects on the electrochemical response are described.