Amperometric tyrosinase biosensor based on a sol-gel-derived titanium oxide-copolymer composite matrix for detection of phenolic compounds

A new type of tyrosinase biosensor was developed for the detection of phenolic compounds, based on the immobilization of tyrosinase in a sol-gel-derived composite matrix that is composed of titanium oxide sol and a grafting copolymer of poly(vinyl alcohol) with 4-vinylpyridine. Tyrosinase entrapped in the composite matrix can retain its activity to a large extent owing to the good biocompatibility of the matrix. The parameters of the fabrication process and the variables of the experimental conditions for the enzyme electrode were optimized. The resulting sensor exhibited a fast response (20 s), high sensitivity (145.5 muA mmol(-1) 1) and good storage stability. A detection limit of 0.5 muM catechol was obtained at a signal-to-noise ratio of 3.

Synthesis and characterization of metallocenes containing tert-butyl substituted cyclopentadienyl ligands and their activities in ethylene polymerization

The metallocene complexes ((BuC5H4)-Bu-t)(2)MCl2 (M=Ti (1a), Zr (1b), Hf (1c)) and (tBu2C5H3)(2)MCl2 (M=Ti (2a), Zr (2b), Hf (2c)) were synthesized by the react ions of Li (BuC5H4)-Bu-t and (LiBu2C5H3)-Bu-t with metal tetrachloride in THF solution. The complexes were characterized by their IR, H-1-NMR and EI-MS. The molecular structure of Ic was determined by X-ray single-crystal structure analysis. The complexes (1a similar to 2c) exhibited high activities for ethylene polymerizatin (up to 3.2x10(6) gPE/mol.h) in the presence of methylaluminoxane (MAO) at room temperature.

Mechanical properties of poly(beta-hydroxybutyrate)/poly(ethylene oxide) blends

Tensile properties of poly (P-hydroxybutyrate)/poly (ethylene oxide) (PHB/PEO) blends were reported in this paper. It was found that the blends of PHB with different molecular-weight PEO exhibited different mechanical properties. The mechanical properties of the blends of PHB and PEO3 (M-w=0.3x10(6)) were very poor. However, the blends of PHB and PEO5 (M-w=5x10(6)) showed compatible in mechanical properties. Excellent synergism was observed not only in tensile stress and tensile elongation but also in modulus. Moreover, the ductility of the blends could be improved further under proper heat-treatment.

Allyl containing iron post-metallocene catalyst for ethylene polymerization

Tridentate ligand[(2,6-ArN=C(Me))(2)C5H3N](Ar=4-allyl-2,6-(i-Pr)(2)C6H3)(4)which contains allyl groups on each aryl ring was ready prepared and reacted with FeCl2. 4H(2)O to give the precatalyst [(2,6-ArN=C(CH3))(2)C5H3N]. FeCl2 (5). Compounds 2-5 were characterized by H-1 NMR, EI-MS,and IR. The complex 5 which was actived by methylaluminoxane(MAO) exhibits high activity for ethylene polymerization [1.9 x 10(6) g pE.(mol Fe . h)(-1) at 0 degreesC]. It was showed that the activity was decreased with increasing temperature and the polymer product was highly linear PE with (M) over bar (eta) varying from 50000 to 260000.

Acid-stable amperometric soybean peroxidase biosensor based on a self-gelatinizable grafting copolymer of polyvinyl alcohol and 4-vinylpyridine

A peroxidase was extracted from Chinese soybean seed coat, and its thermostability and acid-stability were characterized. This peroxidase was immobilized into a self-gelatinizable grafting copolymer of polyvinyl alcohol with 4-vinylpyridine(PVA-g-PVP) to construct an acid-stable hydrogen peroxide biosensor. The effect of pH was studied for optimum analytical performances by amperometric and spectro-photometric methods, also the K-m(app) and the stability of the soybean peroxidase-based biosensor are discussed. At pH 3.0, the soybean peroxidase maintained its bioactivity and the enzyme electrode had a linear range from 0.01 to 6.2 mM with a detection limit of 1.0 x 10(-7) M. In addition, the main characteristics of different hydrogen peroxide sensors were compared.

Spectrometric investigation on the thermooxidative degradation of ethylene oxide and tetra-hydrofuran co-polyether

The thermooxidative degradtion of ethylene oxide and tetra-hydrofuran (EO-THF) co-polyether has been studied by electron spin resonance (ESR), Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopy. The initial degradation site was found to be at the a-carbon of the ether bond. Two free radicals which derived from dehydrogenation and oxygen addition were successfully detected by spin-trapping technique which used alpha -phenyl-N-tert-butyl nitrone(PBN) as spin trap. Both FT-IR and NMR have been used to follow structural changes of the copolyether during degradation. Nearly 20 product fragments including formate, carbonate, methyl, alcohol, methylene-dioxy, hydroperoxide and semiformal have been characterized by D-1 and D-2 NMR. The thermooxidtion of co-polyether preferred to occur on the THF units especially at the alternating linkage of EO and THF. Antioxidant (BHT) not only retarded the thermooxidation but also modified the degradation products with less ester and methylene-dioxy groups hut more hydroxyl and methyl groups.

A new type of polymer-supported metallocene catalyst for ethylene polymerization

A new polymer-supported metallocene catalyst has been prepared, The polymer-supported metallocene displayed considerably high activity in ethylene polymerization, the highest being 3.62x10(7) gPE/molZr.h, the molecular weight of the polyethylene produced was Mn = 1.29x10(5). about 3-4 times those of corresponding homogeneous zirconocenes. The polymer-supported metallocene keeps the characteristics of homogeneous metallocene catalysts, and offers some features, such as adaptable to gas phase and slurry processes: easy to prepare in low cost: relatively high activity and lower MAO/Zr ratio; lower inorganic residues in the polyolefins as compared to cases of SiO2, Al2O3 or MgCl2; unitary active structure, no complex surface as with SiO2; good control of morphology of the resulting polymer.

Determination of electron mobility in a blue-emitting alternating block copolymer by space-charge-limited current measurements

In this communication we analyse current versus voltage data obtained using one carrier injection at metal/polymer/metal structures, The used polymer is a soluble blue-emitting alternating block copolymer, Our experimental results demonstrate that the electron current is limited by a large amount of traps with exponential energy distribution in the copolymer. The electron ;mobility of 5.1 x 10(-10) cm(2)/V s is directly determined by space-charge-limited current measurements. The electron mobility is at least three orders of magnitude smaller than that for holes in the copolymer. (C) 1999 Elsevier Science Ltd. All rights reserved.

Miscibility and crystallization behavior of poly(beta-hydroxybutyrate)/poly(ethylene oxide) blends

The miscibility and crystallization behavior of poly(beta-hydroxybutyrate) (PHB)/poly(ethylene oxide) (PEO) blends were studied by differential scanning calorimetry(DSC) and polarizing microscopy (POM). It is found that the miscibility is related to the composition of the blends. When the PEO content is over 20 percent, the miscible blends turn into partially miscible and the phase separation can be observed with POM. The addition of the PEO influences not only the morphology of PHB crystals and the radial growth rate of spherulites, but also the cold crystallization temperature.

Stimulated emission in blue wavelength region from a copolymer

A dye laser based on the soluble conjugated polymer, Poly[1,8-octanedioxy-2,6-dimethoxy-1,4-phenylene-1,2-ethenylene-1, 4-phenylene-1,2-ethenylene-3,5-dimethoxy-1,4-phenylene], has been fabricated. The laser was pumped by light pulses from the third harmonic radiation of an Nd:YAG laser. The lasing was observed in the blue wavelength region with the peak at 450 nm. The threshold energy is about 19 mu J. The energy conversion yield of the laser is about 3.4%. The maximum peak power of the laser output pulse arrives at about 20 kW.

Luminescence enhancement by blending PVK with blue PPV copolymer

The PL and EL properties of the polymer blends of PVK and blue PPV copolymer were studied. Considerable enhancement of both the photoluminescent and the electroluminescent intensity were observed by using the polymer blends as emission layer in the LED devices. The energy transfer process and the formation of exciplex in the polymer blends were also discussed.

In-situ microscopic FTIR spectroelectrochemistry of ascorbic acid in poly(ethylene glycol)/LiClO4 electrolyte paste and in the presence of dispersed cobalt hexacyanoferrate microcrystalline powder

In-situ microscopic FTIR spectroelectrochemical technique(MFTIRs) was applied to studying the electrochemical oxidation of ascorbic acid(AA) in poly(ethylene glycol)(PEG) paste at a 100 mu m diameter Pt disk electrode. Using this technique, the catalytic ability of cobalt hexacyanoferrate(CoHCF) microcrystalline toward AA oxidation was also studied, it was found that the dispersed CoHCF powder in the PEG paste can generate well-shaped thin-layer cyclic voltammetric waves with the peak height proportional to the scan rate, corresponding to the Fe centered redox reactions. This oxidation step catalyzed the AA oxidation. Also, this pasted CoHCF powder generated well-resolved in-situ MFTIRs spectra, by which a chemical interaction between C = C bond of AA ring and CoHCF lattice was revealed. A corresponding surface docking mechanism for the catalytic reaction has been proposed.

Self-gelatinizable graft copolymer of poly(vinyl alcohol) with 4-vinylpyridine as an immobilization matrix for the construction of a tyrosinase-based amperometric biosensor

A tyrosinase-based amperometric biosensor using a self-gelatinizable graft copolymer of poly(vinyl alcohol) with 4-vinylpyridine (PVA-g-PVP) as an immobilization matrix was constructed. The 4-vinylpyridine component of PVA-g-PVP enhances the adherence to a glassy carbon electrode surface. The content of 4-vinylpyridine in this immobilization matrix plays a key role in retaining the activity of tyrosinase. A simple, milder method was adopted by simply syringing the copolymer-tyrosinase aqueous solution on to the electrode surface and allowing water to evaporate at 4 degrees C in a refrigerator. Several parameters, including copolymer composition; pH, applied potential and enzyme membrane composition, ware optimized. The enzyme membrane composition can be varied to obtain higher sensitivity or a wider linear detection range. The biosensor was used for the determination of phenol, p-cresol and catechol. The biosensor exhibited excellent reproducibility, stability and sensitive response and can be used in flow injection analysis. The biosensor showed an extended linear range in hydrophilic organic solvents and it can be used in monitoring organic reaction processes. The analytical performance demonstrated this immobilization matrix is suitable for the immobilization of tyrosinase.

Syndiotactic polystyrene/thermoplastic polyurethane blends using poly(styrene-b-4-vinylpyridine) diblock copolymer as a compatibilizer

The effect of adding diblock copolymer poly(styrene-b-4-vinylpyridine) (P(S-b-4VPy), to immiscible blends of syndiotactic polystyrene (sPS)/thermoplastic polyurethane (TPU) on the morphology, thermal transition, crystalline structure, and rheological and mechanical properties of the blends has been investigated. The diblock copolymer was synthesized by sequential anionic copolymerization and was melt-blended with sPS and TPU. Scanning electron microscopy (SEM) showed that the added block copolymer reduced the domain size of the dispersed phase in the blends. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) revealed that the extent of compatibility between sPS and TPU affected the crystallization of the sPS in the blends. Tensile strength and elongation at break increased, while the dynamic modulus and complex viscosity decreased with the amount of P(S-b-4VPy) in the blend. The compatibilizing effect of the diblock copolymer is the result of its location at the interface between the sPS and the TPU phases and penetration of the blocks into the: corresponding phases, i.e. the polystyrene block enters the noncrystalline regions of the sPS, and the poly(4-vinylpyridine) block interacts with TPU through intermolecular hydrogen bonding. (C) 1999 Elsevier Science Ltd. All rights reserved.

A study of dimethylferrocene diffusion and electrode kinetics using microelectrode voltammetry in poly(ethylene glycol) solvent

The heterogeneous electron transfer rate constant (k(s)) of dimethylferrocene (DMFc) was estimated using cyclic voltammetric peak potential separations taken typically in a mixed diffusion geometry regime in a polyelectrolyte, and the diffusion coefficient (D) of DMFc was obtained using a steady-state voltammogram. The heterogeneous electron transfer rate constant and diffusion coefficient are both smaller by about 100-fold in the polymeric solvent than in the monomeric solvent. The results are in agreement with the difference of longitudinal dielectric relaxation time (tau(L)) in the two kinds of solvents, poly(ethylene glycol) (PEG) and CH3CN, indicating that k(s) varies inversely with tau(L); k(s), is proportional to D of DMFc. Both D and k(s) of DMFc in PEG containing different supporting electrolytes and at different temperatures have been estimated. These results show that D and k(s) of DMFc increase with increasing temperature in the polyelectrolyte, whereas they vary only slightly with changing the supporting electrolyte.