Oxidation of NADH by dopamine incorporated in lipid film cast onto a glassy carbon electrode

Stable lipid film was made by casting lipid in chloroform onto a glassy carbon electrode. This model of a biological membrane was used to investigate the oxidation of dihydronicotinamide adenine dinucleotide (NADH) by dopamine. After this electrode had been immersed in dopamine solution for 10 h, it was found that some dopamine had been incorporated in the film. The cyclic voltammogram was obtained for the oxidation of 2.0 X 10(-3) mol 1(-1) NADH with dopamine incorporated in the films. All electrochemical experiments were performed in 0.005 mol 1(-1) phosphate buffer (pH 7.0) containing 0.1 mol 1(-1) NaCl without oxygen. The oxidation current increased gradually with successive sweeps and reached steady state. It was a different phenomenon from previous results. The anodic overpotential was reduced by about 130 mV compared with that obtained at a bare glassy carbon electrode. The diffusion coefficient for 2.0 X 10(-3) mol 1(-1) NADH was 6.7 X 10(-6) cm(2) s(-1). (C) 1999 Elsevier Science S.A. All rights reserved.

Synthesis and characterization of soluble polyimides from 2,2-bis(4-aminophenyl)cycloalkane derivatives

New aromatic diamines [(1) and (2)] containing polycycloalkane structures between two benzene rings were synthesized by HCl-catalyzed condensation reaction of aniline hydrochloride and corresponding polycycloalkanone derivatives. The structures of diamines were identified by H-1-NMR, C-13-NMR, FTIR spectroscopy, and elemental analysis. The polyimides were synthesized from the obtained diamines with various aromatic dianhydrides by one-step polymerization in m-cresol. The inherent viscosities of the resulting polyimides were in the range of 0.34-1.02 dL/g. The polyimides showed good thermal stabilities and solubility. All the polymers were readily soluble in N-methyl-2-pyrrolidone, m-cresol, tetrachloroethane, etc. Some of them were soluble even in chloroform at room temperature. The glass transition temperatures were observed in the range of 323-363 degrees C, and all of the polymers were stable up to 400 degrees C under nitrogen atmosphere. (C) 1999 John Wiley & Sons, Inc.

Processible nanostructured materials with electrical conductivity and magnetic susceptibility: Preparation and properties of maghemite polyaniline nanocomposite films

We here present a versatile process for the preparation of maghemite/polyaniline (gamma-Fe2O3/ PAn) nanocomposite films with macroscopic processibility, electrical conductivity, and magnetic susceptibility. The gamma-Fe2O3 nanoparticles are coated and the PAn chains are doped by anionic surfactants of omega-methoxypoly(ethylene glycol) phosphate (PEOPA), 4-dodecylbenzenesulfonic acid (DBSA), and 10-camphorsulfonic acid (CSA). Both the coated gamma-Fe2O3 and the doped PAn are soluble in common organic solvents, and casting of the homogeneous solutions gives free-standing nanocomposite films with gamma-Fe2O3 contents up to similar to 50 wt %. The morphology of the gamma-Fe2O3 nanoparticles are characterized by transmission electron microscopy, UV-vis spectroscopy, and X-ray diffractometry. The gamma-Fe2O3/PAn films prepared from chloroform/m-cresol solutions of DBSA-coated gamma-Fe2O3 and CSA-doped PAn are conductive (sigma = 82-237 S/cm) and superpapamagnetic, exhibiting no hysteresis at room temperature. The zero-field-cooled magnetization experiment reveals that the nanocomposite containing 20.8 wt % gamma-Fe2O3 has a blocking temperature (T-b) in the temperature region of 63-83 K.

Fluorescence and aggregation behavior of a polyimide in solutions

The UV-visible absorption and fluorescence spectra of a soluble polyimide, YS-30, in several organic solvents were measured over a wide range of concentration. The experimental results show that there exist both intramolecular and intermolecular electron donor acceptor interactions for YS-30 molecules. The fluorescence behavior of YS-30 in N,N-dimethylacetamide and in chloroform solutions is similar in general, except that its ground-state intermolecular charge transfer emission is more obvious in N,N-dimethylacetamide solution. This difference is attributed to the greater extent of disruption of the chain packing by solvent or/and the more efficient radiationless energy dissipation process from the excited state complexes to chloroform. The intensity ratio of intermolecular charge transfer emission to intramolecular charge transfer emission is used to characterize the state of aggregation of YS-30 molecules in solutions. The plot of this ratio versus concentration indicates the existence of two critical concentrations. It is also found from the same plot that the decrease of coil size is very pronounced during the initial stage of shrinkage.

Soluble and colorless polyimides from alicyclic diamines

A series of novel polyimides was synthesized from alicyclic diamines and various aromatic dianhydrides by one-step polymerization in m-cresol without a catalyst. The polymerization was conducted for 4 hours with refluxing, which was enough to obtain the polymers with high molecular weight. The inherent viscosities of the resulting polyimides were in the range of 0.30 similar to 1.29 dL/g. The prepared polyimides showed excellent thermal stabilities and good solubility. All the polymers were readily soluble in common organic solvents such as chloroform, tetrachloroethane (TCE), dimethylacetamide (DMAc), etc and the glass transition temperatures were observed at 199 to 311 degrees C. UV-visible spectra were obtained to measure the transparency of polymer films. All the polymers showed high transmission above 90% in the wavelength of 400 similar to 700 nm.

Preparation and characterization of phenoxy resin/poly(4-vinylpyridine) interpolymer complexes

The compositions and structures of interpolymer complexes formed by mixing phenoxy resin (PHEB) and poly (4-vinylpyridine) (P4VPy) in chloroform have been studied by means of elemental analysis, DSC, FTIR, UV and XPS, In the meantime, the corresponding blends prepared have been characterized and compared. The results show that compositions of the complexes were identical with the ratio of equimolar interactive units. All blends were miscible and their compositions were related to the feed ratios. Based on the experimental results, process of formation of the complex is depicted.

Chain conformation of a high-performance polyimide in organic solution

An organo-soluble polyimide based on 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride (HQDPA) and 2,2'dimethyl-4,4'-methylene dianiline (DMMDA), was synthesized via two-step polycondensation accompanied by chemical imidization. Five fractions were prepared by fractionation. The dilute solutions of the fractions were studied by LLS (Laser Light Scattering) and the intrinsic viscosities of the fractions were measured. The unperturbed dimension was determined by the intrinsic viscosity with the Stockmayer-Fox equation. The results indicate that the polyimide in this study has a flexible chain conformation in chloroform and N,N-dimethyl acetamide (DMAc). However, the degree of chain expansion differs in different solvents. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.

Synthesis and characterization of soluble polyimides from 1,1-bis(4-aminophenyl)cyclohexane derivatives

A series of novel aromatic diamines (1-3) containing kinked cyclohexylidene moieties was synthesized by a reaction of excess aniline and corresponding methyl-substituted cyclohexanone derivatives. The structures of (1-3) were identifield by H-1 NMR, C-13 NMR, and FT-IR. The polymers were synthesized from the obtained diamines and various aromatic dianhydrides by the conventional polycondensation reaction followed by chemical imidization as well as high-temperature one-step polymerization. The inherent viscosities and weight-average molecular weights of the resulting polyimides were in the ranges of 0.55-1.58 dL/g and (7.4-15.2) x 10(4) g/mol, respectively. The prepared polyimides showed excellent thermal stabilities and good solubility. All polymers were readily soluble in common organic solvents such as tetrahydrofuran, chloroform, tetrachloroethane, etc., and the glass transition temperatures were observed at 290-372 degrees C.

The synthesis of a 1,1'-bi-2-naphthol-based bis(ether anhydride) and aromatic polyimides derived therefrom

2,2'-Bis(3,4-dicarboxyphenoxy)-1,1'-binaphthyl dianhydride was used as a new monomer with various aromatic diamines to obtain polyimides by the usual two-step method. The bis(ether anhydride) was prepared by a nucleophilic substitution of I,1'-bi-2-naphthol with N-phenyl-4-chlorophthalimide, N-methyl-4-nitrophthalimide or 4-nitrophthalonitrile in aprotic polar solvent, and subsequent hydrolysis of the resulting bis(ether imide)s or bis(ether dinitrile), and then dehydration of the corresponding tetracarboxylic acid to afford the dianhydride. Most of the obtained polyimides were soluble in chloroform, pyridine, DMF, etc. The polyimide prepared from p-phenylene diamine was partial crystalline, whereas the others showed amorphous patterns in a WAXD study. These polymers have glass transition temperatures between 255-294 degrees C and 5% weight loss temperatures in the range of 502-541 degrees C in nitrogen and 473-537 degrees C in air. (C) 1997 Elsevier Science Ltd.

Single-chain single crystals of gutta-percha

Single-chain single crystals of gutta-percha have been observed by transmission electron microscopy of atomizer-sprayed particles deposited from a very dilute solution in chloroform onto a carbon film which had a filter paper wetted with ethanol in contact with its under side. Selected-area electron diffraction patterns of crystals having no definite crystal profiles showed that the crystals were of the low-melting crystalline form and that the chain segments in the single crystals were standing up from the substrate during crystallization. In cases of single crystals showing sharply defined crystal profiles, electron diffraction patterns showed that they were neither of the low-melting form nor the high-melting form. The structure of this new crystalline modification needs further studies.

Solution properties of doped polyaniline

Solution properties of polyaniline (PAn) doped by camphorsulfonic acid (CSA) were examined. PAn-CSA behaves like a polyelectrolyte to different extents depending on the solvent used. In an m-cresol/chloroform solution, PAn-CSA exhibits an expanded chain conformation because of its polyelectrolytic properties. Dilute and concentrated solution properties of PAn-CSA indicate that PAn-CSA is a semirigid polymer which has strong interchain interactions.

Amperometric biosensor for tyrosinase inhibitors in a pure organic phase

The determination of benzoic acid, thiourea and 2-mercaptoethanol in three pure organic solvents, viz., chloroform, chlorobenzene and 1,2-dichlorobenzene, by using an amperometric cryohydrogel tyrosinase biosensor is described. Measurements were carried out with phenol as the enzyme substrate. Kinetic parameters (K-i and I-50) were determined in the three solvents for various inhibitors. The sensor showed the most sensitive measurements to these inhibitors in pure chloroform. The solvent-induced deviation of the biosensor to thiourea was evaluated by means of Hill coefficients. The smallest deviation as observed in 1,2-dichlorobenzene, owing to the high hydrophobicity of this solvent. The nature of the inhibition process and its reversibility mere also examined.

Activation of a ring methyl substituent in pentamethylcyclopentadienyl rhenium(V) compounds: Synthesis and characterization of the 1,2,3,4-tetramethyl-5,6-dihydrofulvene-5,6-dithiolato complex [ReO{(S)(SCH2)C(5)Me(4)}(C(5)Me(5))]

Reaction of the half-sandwich rhenium(v) complexes [Re-Cl-4(C(5)Me(5))] or [Re(O)Cl-2(C(5)Me(5))] with H2S in chloroform in the presence of pyridine leads to the chiral dithiolato complex [ReO((S)(SCH2)C(5)Me(4))(C(5)Me(5))] 1.

Study on the UCST and LCST in PHB/PBHE-solvent system

Upper and lower critical solution temperature (UCST and LCST) behaviours have been examined for solution of PHB/PBHE blends in chloroform and chlorobenzene. Polymer-Solvent systems prepared with various solvents and concentrations were found to possess UCST and LCST characteristics. PHB/PBHE solution in chloroform displayed greater miscibility temperature region than that of the blend in chlorobenzene, but the relative tendency of both UCST and LCST were similar.

Local chain motions in a dilute solution of phenolphthalein poly(ether sulfone)

C-13 and H-1 relaxation times were measured as a function of temperature in two magnetic fields for dilute solutions of phenolphthalein poly(ether sulfone) (PES-C) in deuterated chloroform. The spin-lattice relaxation times were interpreted in terms of segmental motion characterized by the sharp cutoff model of Jones and Stockmayer (J. S. model). The phenyl group rotation is treated as a stochastic diffusion by the J. S. model. The restricted butterfly motion of the phenyl group attached to the cardo ring in PES-C is mentioned but is not discussed in detail in this work. Correlation times for the segmental motion are in the picosecond range which indicates the high flexibility of PES-C chains. The correlation time for the phenyl group internal rotation is similar to that of the segmental motion. The temperature dependence of these motions is weak. The apparent activation energy of the motions considered is less than 10 kJ/mol. The simulating results for PES are also reasonable considering the differences in structure compared with PES-C. The correlation times and the apparent activation energy obtained using the J. S. model for the main chain motion of PES-C are the same as those obtained using the damped orientational diffusion model and the conformational jump model.