Ion channel behavior of supported bilayer lipid membranes on a glassy carbon electrode

A new kind of solid substrate, a glassy carbon (GC) electrode, was selected to support lipid layer membranes. On the surface of the GC electrode, we made layers of didodecyldimethylammonium bromide (a synthetic lipid). From electrochemical impedance experiments, we demonstrated that the lipid layers on the GC electrode were bilayer lipid membranes. We studied the ion channel behavior of the supported bilayer lipid membrane. In the presence of perchlorate anions as the stimulus and ruthenium(II) complex cations as the marker ions, the lipid membrane channel was open and exhibited distinct channel current. The channel was in a closed state in the absence of perchlorate anions.

Preparation and characteristics of polyimide-TiO2 nanocomposite film

A sol-gel approach has been developed to prepare polyimide-TiO2, hybrid films fi om soluble polyimides and a modified titanium precursor. The rate of the hydrolysis reaction of titanium alkoxide can be controlled by using acetic acid as a modifier. FTIR and XPS indicated that TiO2, particles were well distributed in polyimide matrixes with particle size small per than 60 nm. Polyimide hybrid films having the TiO2, component less than or equal to 10% exhibited high thermal stability, high optical transparency and good mechanical properties and possessed higher dielectric constants than correspondingly polyimides. (C) 2000 Society of Chemical Industry.

Bilayer lipid membranes and their application in electrochemical biosensors

The preparation and characteristics of bilayer lipid membranes including conventional bilayer membrane, solid supported self-assembling bilayer lipid membrane, solid supported hybrid bilayer membrane are described in this paper, The applications of bilayer lipid membranes in electrochemical biosensors are reviewed and the future development of electrochemical biosensor based on bilayer lipid membranes is discussed.

Degradation of polyimide induced by nitrogen laser irradiation

The degradation behavior of polyimide (PMDA-ODA) induced by nitrogen laser irradiation was studied. The changes in the surface morphology and the composition of the irradiated polyimide films were examined by scanning electron microscopy, X-ray photoelectron spectroscopy and FT-IR spectroscopy. The initial reaction was achieved by photochemical degradation of polyimide in the highly electronic excited state by the absorption of a second 337 nm photon. Atmospheric oxygen sequentially reacted with the produced radicals to form a highly oxidized layer. The formation of carbonyl group was enhanced by the heat remaining on the irradiated polyimide film surfaces. (C) 2000 Elsevier Science B.V. All rights reserved.

Excimer-laser irradiated polyimide films as temperature-sensitive materials

The temperature dependence of the resistivity of KrF laser irradiated polyimide films was studied. In all cases, the resistivity decreased with increasing temperature. The irradiated polyimide film exhibited a typical semiconducting property. This result indicated that the irradiated polyimide films can be used as temperature-sensitive materials. We demonstrated that both the sensitivity and the sensitive temperature range of the irradiated polyimide films can be altered by adjusting laser irradiation parameters. The intrinsic relationship between the temperature coefficient of the resistivity and irradiation condition was interpreted in terms of the microstructural change. The result provided a new insight into the fundamental aspects of laser irradiated polyimide film structure and a method of preparing temperature-sensitive materials. (C) 2000 Elsevier Science B.V. All rights reserved.

Effect of polyvinylidene fluoride hollow fiber membranes on mass transfer of samarium

The influence of swelling and stripping acidity on the mass transfer coefficient based on water phase and the inner diameters of membranes were studied with P507-HCl-Sm as working system in the two different kinds of hollow fiber membranes. Effects of extractant concentration, H+ concentration in aqueous phase and Sm3+ concentration on extraction rate were discussed and the corresponding reaction series were obtained. According to the investigations on the interfacial kinetics, the reaction kinetics equation and reaction rate constant were obtained.

Formation of conducting layers on excimer-laser-irradiated polyimide film surfaces

Conducting layers on KrF excimer-laser-irradiated polyimide film surfaces were investigated by XPS, SEM and Fourier transform infrared (FTIR)-Raman spectroscopy, Analysis of polyimide residue after laser irradiation provided valuable insight into the nature of the formation of conducting layers. The subtle different between KrF laser irradiation and the pyrolysis of polyimide was found by comparison of the formation process of conducting layers. A physical picture was presented to describe better the formation of conducting layers. Under KrF laser irradiation, polyimide films underwent thermal decomposition assisted by photoinduced direct bond breaking. Polycrystalline graphite was subsequently formed as the product of the secondary addition reaction of carbon-enriched clusters, Such reaction was supported by the remaining energy on the irradiated polyimide film surface. This result shows that the thermal process played an important role that was not just restricted to the formation of conducting layers, Copyright (C) 2000 John Wiley & Sons, Ltd.

Tuning the aggregation of polyimide thin films by modification of their molecular interactions

Thin films of an organo-soluble polyimide based on 1,4-(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA) and 2,2'-dimethyl-4,4'-methylene dianiline (DMMDA) have been studied. A prism coupler was used to measure the refractive indices. The average refractive indices of thin films prepared by annealing at different temperatures and times were chosen to characterize the condensation states of thin films. Thin films annealed at 200 degrees C show irreversible changes in physical properties, eg solubility. FTIR spectroscopy showed that the chain structures of the above thin films remained unchanged. It is proposed that specific molecular interactions induce the irreversible changes revealed by fluorescence spectroscopy. (C) 2000 Society of Chemical Industry.

Study on a novel polyimide precursor prepared by a modified polymerization of monomeric reactants (MPMR) procedure

A novel polyimide precursor based on the dimethyl ester of 3,3',4,4'-biphenyltetracarboxylic acid, 4,4'-methylene dianiline and the monomethyl ester of 5-norbornene-2,3-dicarboxylic acid (BPDE/MDA/NE) was prepared by a modified polymerization of monomeric reactants (PMR) approach (MPMR). The composition of the precursor was quantitatively characterized by means of FTIR, HPLC and GC. The fractions of imide, amic ester and amic acid units in the precursor, typically prepared by refluxing in 1,4-dioxane for 2 h, were 33.7, 30.8 and 1.1 mol-%, respectively. The portion of free MDA was 3.34 wt.-% as determined by HPLC.

Influence of a kind of polyanion to hybrid bilayer membranes

Hybrid bilayer membrane consisting of self-assembled alkanethiol and lipid monolayer on gold electrode was fabricated by the paint - freeze method. The interaction of a kind of polyanion, K7Fe3+P2W17O62H2 with such bilayer membrane was investigated by cyclic voltammetry and ac impedance. The hybrid bilayer membrane on the gold electrode showed remarkable insulating property, however, the property was lessened to some extent after interaction with the polyanion. It was found the process was in-eversible. It is presumed that the interaction between the polyanion and lipid is an interaction of K7Fe3+P2W17O62H2 with the polar head group of PC, which lessens the interaction among PC polar head groups. The resulting molecular arrangement becomes looser, even some pores are produced.

Gas and water vapor transport through a series of novel poly(aryl ether sulfone) membranes

The permeation behavior of water vapor, H-2, CO2, O-2, N-2, and CH4 gases in a series of novel poly(aryl ether sulfone)s has been examined over a temperature range of 30-100 degreesC. These polymers include four alkyl-substituted cardo poly(aryl ether sulfone)s and four intermolecular interaction enhanced poly(aryl ether sulfone)s. Their water vapor and gas transport properties were compared to the unmodified cardo poly(aryl ether sulfone) (PES-C). It was found that the bulky alkyl substituents on the phenylene rings were advantageous for gas permeability, while the intermolecular hydrogen bonds and ionic bonds resulted in a considerable increase in gas permselectivity. The causes of the trend were interpreted according to free volume, interchain distance, and glass transition temperature, together with the respective contribution of gas solubility and diffusivity to the overall permeability. Of interest was the observation that IMPES-L, which simultaneously bears bulky isopropyl substituent and pendant carboxylic groups, displayed 377% higher O-2 permeability and 5.3% higher O-2/N-2 permselectivity than PES-C. Furthermore, sodium salt form PES-Na+ and potassium salt form PES-K+ exhibited water vapor permeability twice as high as PES-C and H2O/N-2 selectivity in 10(5) order of magnitude.

Induction effect of Ca2+ on ion-channel behavior of supported phospholipid membranes

As a kind of supported bilayer lipid membranes, hybrid bilayer membrane (HBM) was applied to the interaction between Ca2+ and lipid for the first time. By using Fe(CN)(6)(3-) as a probe, we found that Ca2+ could induce the ion channel of HBM to be in open state. STM images study proved this phenomenon.

Thermal influence on excimer-laser-induced electrical conductivity on polyimide film surfaces

The thermal influence on the electrical conductivity of polyimide film surfaces induced by KrF-laser irradiation was investigated, The formation of conducting phases was demonstrated to be highly temperature sensitive, as evidenced by strong dependence of the electrical conductivity on repetition rate and ambient temperature. XPS and Raman studies showed that the efficiency of the formation of conducting phases could be enhanced by the increase of temperature on irradiated polyimide film surfaces. After the disruption of polymeric chain, the carbon-enriched clusters remained on the irradiated polyimide film surfaces organized into polycrystalline graphite-like clusters responsible for electrical conductivity. The resulting dangling bonds from the decomposition process of polyimide acted as centers for the rearrangement of carbon-enriched clusters. It is suggested that the motion of radicals was promoted with increasing the temperature. Therefore the formation of polycrystalline graphite-like clusters benefited from high remaining temperature on the irradiated polyimide film surfaces. These results revealed that thermal influence played a dominant role on the formation of conducting phases.

A facile approach to immobilize protein for biosensor: self-assembled supported bilayer lipid membranes on glassy carbon electrode

A kind of solid substrate, glassy carbon (GC) electrode. was selected to support self-assembled lipid layer membranes. On the surface of GC electrode. we made layers of dimyristoylphosphatidylcholine (DMPG, a kind of lipid). From electrochemical impedance experiments. we demonstrated that the lipid layers on the GC electrode were bilayer lipid membranes. We immobilized horseradish peroxidase (HRP) into the supported bilayer lipid membranes (s-BLM) to develop a kind of mediator-free biosensor for H2O2. The biosensor exhibited fine electrochemical response, stability and reproducibility due to the presence of the s-BLM. As a model of biological membrane, s-BLM could supply a biological environment for enzyme and maintain its activity. So s-BLM is an ideal choice to immobilize enzyme for constructing the mediator-free biosensor based on GC electrode. (C) 2001 Elsevier Science B.V. All rights reserved.

Structural studies of excimer laser-induced percolative phase transition on polyimide thin film surfaces

The behavior of electrical conductivity for excimer laser irradiated polyimide films in the vicinity of the critical number of laser shots was described by three-dimensional percolative phase transition model. It is: found that electrical conductivity changed more rapidly than that predicted by the percolation model. Thus, the change in microstructure with increasing number of laser shots was analyzed by FT-IR Raman spectrometry and laser desorption time-of-flight mass spectrometry. It is demonstrated that not only the number but also the average size of graphite particles on the irradiated polyimide film surfaces increased with increasing number of laser shots. These results were helpful to better understand the critical change in electrical conductivity on the irradiated polyimide film surfaces. (C) 2001 Elsevier Science B.V. All rights reserved.