Fabrication of layer-by-layer deposited multilayer films containing DNA and its interaction with methyl green

Multilayer films were fabricated by layer-by-layer electrostatic deposition techniques between poly(diallyIdimethylammonium chloride) (PDDA) and calf thymus DNA (CT DNA) on glassy carbon and quartz substrates. Electrochemical impedance spectroscopy (EIS), Fourier transform infrared (FTIR) spectroscopy and UV-vis spectroscopy demonstrated the uniform assembly of PDDA/DNA multilayer films, and X-ray photoelectron spectroscopy confirmed the elemental composition of the films. Moreover, the interaction of DNA in PDDA/DNA films with methyl green was investigated by UV-vis spectroscopy and circular dichroism (CD). (C) 2001 Elsevier Science B.V. All rights reserved.

Studies on the room temperature conductivity of PEO-LiClO4-Al2O3 composite polymer electrolyte

A composite polymer electrolyte of Polyethylene oxide (PEO)-LiClO4 containing fine Al2O3 particles was studied by using differential scanning calorimetry, infrared spectroscopy and electrochemical impedance spectroscopy. Compared with the polymer electrolyte without Al2O3 particles, the glass transition temperature and the degree of crystallinity were decreased, and the room temperature conductivity of PEO-LiClO4-Al2O3 composite polymer electrolyte was considerably enhanced. Moreover, the equivalent circuits and the effect of dc potential on impedance spectroscopy were discussed.

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.

Formation and characterization of heteropolyacid/polycation multilayer films on gold electrode

Ultrathin multilayer films of a polybasic lanthanide heteropoly tungstate-molybdate complex and a cationic polymer of quaternized poly(4-vinylpyridine) partially complexed with osmium bis(2,2'-bipyridine) have been fabricated on a gold electrode precoated with a cysteamine self-assembled monolayer. The multilayer films have been characterized by optical spectroscopy, small-angle X-ray diffraction, and electrochemical methods (cyclic voltammetry and electrochemical impedance). Especially, the electrochemical impedance spectroscopy is developed to monitor the layer deposition processes. It provides important information such as double-layer capacitance and charge-transfer resistance. All obtained results reveal regular film growth with each layer adsorption. (C) 2001 The Electrochemical Society.

Formation of self-assembled monolayers on gold electrodes with inclusion complexes of cyclodextrins and viologens

A novel kind of electroactive self-assembled monolayer (SAM) has been successfully prepared through the following procedure: (1) formation of inclusion complexes (denoted as CD/C8VC10SH) between N-(n-octyl)-N'-(10-mercaptodecyl)-4,4'-bipyridinium dibromide (C8VC10SH) and alpha-, beta-cyclodextrin (CD) under a mild condition; (2) spontaneous formation of SAM of CD/C8VC10SH on gold electrodes at room temperature. High-resolution H-1-NMR spectrum was used to confirm the formation of CD/C8VC10SH. Cyclic voltammetry was used to characterize the redox behavior of the resulting monolayers and chronoamperometry and electrochemical impedance spectroscopy to characterize their electron transfer kinetics. It was found that the redox sites in SAM of CD/C8VC10SH are effectively diluted, with a larger electron transfer rate constant than that of SAM of C8VC10SH.

The transfer of chloride ion across an anion exchange membrane

The transfer of chloride ions into a low resistance anion exchange membrane (AEM) was investigated by cyclic voltammetry (CV) and electrochemical impedance spectra. In all cases, concentration polarization of Cl- ions is exterior to the membrane. It controls the flux and produces the limiting currents: either steady state or transient (peak type) current. In CV experiments, when the size of the holes in the membrane was much smaller than the distance between membrane holes, the Cl- anion transfer showed steady state voltammetric behavior. Each hole in the membrane can be regarded as a microelectrode and the membrane was equivalent to a microelectrode array in this condition. When the hole in the membrane was large or the distance between membrane holes was small, the CV curve of the Cl- anion transfer across the membrane showed a peak shape, which was attributed to linear diffusion. In AC impedance measurement, the impedance spectrum of the membrane system was composed of two semicircles at low DC bias, corresponding to the bulk characteristics of the membrane and the kinetic process of ion transfer, respectively. The bulk membrane resistance increases with increasing DC bias and only one semicircle was observed at higher DC bias. The parameters related to kinetic and membrane properties were discussed.

STUDIES OF SPINEL LICRXMN2-XO4 FOR SECONDARY LITHIUM BATTERY

X-ray and electrochemical studies of spinel-related manganese chromium oxides, LiCrxMn2-xO4 (0 less-than-or-equal-to x less-than-or-equal-to 1) were carried out in a lithium nonaqueous cell. X-ray diffraction spectra indicated that the substitution of manganese in LiMn2O4 by trivalent transition metals (Cr3+) cause the linear decrease of lattice parameter with the x in the LiCrMn2-xO4. Some discharge-capacity loss was obtained due to the lattice contraction of LiCrMn2-xO4, but it has a better rechargeability than LiMn2O4. Cyclic voltammetry and electrochemical impedance experiments have shown that the excellent rechargeability of LiCrxMn2-xO4 may be attributed to the good reversibility of the change in its crystal structure for the insertion and extraction of lithium ions.

Monitoring microbial populations of sulfate-reducing bacteria using an impedimetric immunosensor based on agglutination assay

An impedimetric immunosensor was fabricated for rapid and non-labeled detection of sulfate-reducing bacteria, Desulforibrio caledoiensis (SRB) by immobilizing lectin-Concanavalin A using an agglutination assay. The immobilization of lectin was conducted using amine coupling on the surface of a gold (Au) electrode assembled with 11-Mercaptounclecanoic acid. Electrochemical impedance spectroscopy (EIS) was used to verify the stepwise assembly of the sensor system. The work conditions of the impedimetric immunosensor, such as pH of the buffer solutions and the incubation time of lectin, were optimized. Faradic impedance spectra for charge transfer for the redox probe Fe(CN)(6)(3-/4-) were measured to determine SRB concentrations. The diameter of the Nyquist diagram that is equal to the charge-transfer resistance (RI) increased with increasing SRB concentration. A linear relationship between R-ct and SRB concentration was obtained in SRB concentration range of 1.8 to 1.8 x 10(7) cfu/ml. The variation of the SRB population during the growth process was also monitored using the impedimetric immunosensor. This approach has great potential for simple, low-cost. and time-saving monitoring of microbial populations. (C) 2009 Elsevier B.V. All rights reserved.

Characteristics of anodic coatings oxidized to different voltage on AZ91D Mg alloy by micro-arc oxidization technique

With increasing applied voltage, three types of anodic coatings, passive film, micro-spark ceramic coating and spark ceramic coating were made by micro-arc oxidization (MAO) technique on AZ91D magnesium alloy in alkali-silicate solution. The structure, composition characteristics and the electrochemical properties of coatings were also studied with SEM, XRD and EIS (electrochemical impedance spectroscopy) technique, respectively. It is found that the electrochemical properties are closely related to the structure and composition characteristics of the anodic coatings. At the same time, the characteristics of the three types of anodic coatings differ significantly, among them, the micro-spark ceramic coating, prepared in the voltage range of 170similar to220V exhibits compact, homogeneous structure and highest corrosion-resistance.

The inhibition of mild steel corrosion in 1 M hydrochloric acid solutions by triazole derivative

The title compound 1-(4,5-dihydro-3-phenylpyridine-1-yl)-2-(1H-1,2,4-triazole-1-yl)ethyl ketone (DTE) was synthesized and its inhibiting action on the corrosion of mild steel in 1 M hydrochloric acid solutions was investigated by means of weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and scanning electronic microscope (SEM). Results obtained revealed that DIE performed excellently as a corrosion inhibitor for mild steel in 1 M hydrochloric acid media and its efficiency attains more than 90.9% at 1.0 x 10(-3) M at 298 K. Polarization curves indicated that the inhibitor behave mainly as mixed-type inhibitor. EIS showed that the charge transfer controls the corrosion process in the uninhibited and inhibited solutions. Adsorption of the inhibitor on the mild steel surface followed Langmuir adsorption isotherm. And the values of the free energy of adsorption Delta G(ads) indicated that the adsorption of DTE molecule was a spontaneous process and was typical of chemisorption. (c) 2008 Elsevier B.V. All rights reserved.

Corrosion of carbon steel influenced by anaerobic biofilm in natural seawater

The bacteria in the anaerobic biofilm on rusted carbon steel immersed in natural seawater were characterized by culturing and molecular biology techniques. Two types of anaerobic bacterium, sulfate-reducing bacteria (SRB) Desulfovibrio caledoniensis and iron-reducing bacteria Clostridium sp. uncultured were found. The compositions of the rust layer were also analyzed and we found that iron oxide and sulfate green rust were the major components. To investigate the corrosion mechanisms, electrochemical impedance spectra was obtained based on the isolated sulfate-reducing bacteria and mixed bacteria cultured from rust layer in laboratory culture conditions. We found that single species produced iron sulfide and accelerated corrosion, but mixed species produced sulfate green rust and inhibited corrosion. The anaerobic corrosion mechanism of steel was proposed and its environmental significance was discussed. (c) 2008 Elsevier Ltd. All rights reserved.

Experimental and theoretical investigation of the adsorption behaviour of new triazole derivatives as inhibitors for mild steel corrosion in acid media

Three triazole derivatives (4-chloro-acetophenone-O-1'-(1',3',4'-triazolyl)-metheneoxime (CATM), 4-methoxyl-acetophenone-O-1'-(1',3',4'-triazolyl)-metheneoxime (MATM) and 4-fluoro-acetophenone-O-1'-(1',3',4'-triazolyl)-metheneoxime (FATM)) have been synthesized as new inhibitors for the corrosion of mild steel in acid media. The inhibition efficiencies of these inhibitors were evaluated by means of weight loss and electrochemical techniques such as electrochemical impedance spectroscopy (EIS) and polarization curves. Then the surface morphology was studied by scanning electron microscopy (SEM). The adsorption of triazole derivatives is found to obey Langmuir adsorption isotherm, and the thermodynamic parameters were determined and discussed. The relationship between molecular structure of these compounds and their inhibition efficiency has been investigated by ab initio quantum chemical calculations. The electronic properties such as the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) energy levels, energy gap (LUMO-HOMO), dipole moment and molecular orbital densities were computed. (c) 2007 Elsevier Ltd. All rights reserved.

Some new triazole derivatives as inhibitors for mild steel corrosion in acidic medium

Two triazole derivatives, 3,4-dichloro-acetophenone-O-1'-(1',3',4'-triazolyl)-methaneoxime (4-DTM) and 2,5-dichloro-acetophenone-O-1'-(1',3',4'-triazolyl)-methaneoxime (5-DTM) were synthesized, and the inhibition effects for mild steel in 1 M HCl solutions were investigated by weight loss measurements, electrochemical tests and scanning electronic microscopy (SEM). The weight loss measurements showed that these compounds have excellent inhibiting effect at a concentration of 1.0 x 10(-3) M. The potentiodynamic polarization experiment revealed that the triazole derivatives are inhibitors of mixed-type and electrochemical impedance spectroscopy (EIS) confirmed that changes in the impedance parameters (R-ct and C-dl) are due to surface adsorption. The inhibition efficiencies obtained from weight loss measurements and electrochemical tests were in good agreement. Adsorption followed the Langmuir isotherm with negative values of the free energy of adsorption Delta G(ads)(o). The thermodynamic parameters of adsorption were determined and are discussed. Results show that both 4-DTM and 5-DTM are good inhibitors for mild steel in acid media.

Effect of nano-TiO(2)on MP-25 resin

MP-25 resin is a chlorine-containing polymer widely used in coatings. The effects of two types of nano-TiO2 (P-25 and RM301 LP) on MP-25 were studied with saline immersion, UV irradiation, and electrochemical impedance spectroscopy. UV irradiation was evaluated in terms of gloss change and X-ray photoelectron spectroscopy (XPS). The results indicate that, compared to pigment R-930 TiO2, P-25 reduced the immersion resistance and accelerated UV aging of the MP-25 coating, whereas RM301 LP showed the opposite effects. XPS analysis showed that MP-25 resin degraded under UV irradiation via dechlorination and C-C bond breakage, similarly to poly(vinyl chloride), but RM301 LP could inhibit the aging of MP-25 to a certain extent. A skin effect of oxygen and chlorine was identified in MP-25 resin by XPS. RM301 LP could improve the impedance of the MP-25 coating because of its excellent fill capacity. Hence, rutile nano-TiO2 RM301 LP represents an excellent additive for MP-25 resin. (c) 2007 Wiley Periodicals, Inc.

Effect of sulfate-reducing bacteria on corrosion behavior of mild steel in sea mud

Microbiologically influenced corrosion (MIC) is very severe corrosion for constructions buried under sea mud environment. Therefore it is of great importance to carry out the investigation of the corrosion behavior of marine steel in sea mud. In this paper, the effect of sulfate-reducing bacteria (SRB) on corrosion behavior of mild steel in sea mud was studied by weight loss, dual-compartment cell, electronic probe microanalysis (EPMA), transmission electron microscopy (TEM).combined with energy dispersive X-ray analysis (EDX) and electrochemical impedance spectroscopy (EIS). The results showed that corrosion rate and galvanic current were influenced by the metabolic activity of SRB. In the environment of sea mud containing SRB, the original corrosion products, ferric (oxyhydr) oxide, transformed to iron sulfide. With the excess of the dissolved H2S, the composition of the protective layer formed of FeS transformed to FeS2 or other non-stoichiometric polysulphide, which changed the state of the former layer and accelerated the corrosion process.