Electrochemical behavior of alpha-Keggin-type nanoparticles, Co(en)(3)(PMo12O40), in polyethylene glycol

The electrochemical behavior of alpha-Keggin-type nanoparticles, Co(en)(3)(PMo12O40) (abbreviated as PMo12-Co), have been studied in poly(ethylene glycol) for four different molecular weights (PEG, average MW 400, 600, 1000, and 2000 g mol(-1)) and containing LiClO4 (O/Li=100/1) supporting electrolyte. The diffusion coefficients of the PMo12-Co nanoparticles were determined using a microelectrode by chronoamperometry for PEG of different molecular weights that were used to describe the diffusion behavior of PMo12-Co nanoparticles in different phase states. Moreover, the conductivity of the composite system increases upon addition of PMo12-Co nanoparticles, which was measured by an a.c. impedance technique. FT-IR spectra and DSC were used to follow the interactions of PEG-LiClO4-PMo12-Co, and well described the reason that the PMo12-Co nanoparticles could promote the conductivity of the PEG-LiClO4-PMo12-Co system.

Lipid membrane immobilized horseradish peroxidase biosensor for amperometric determination of hydrogen peroxide

Stable films of didodecyldimethylammonium bromide (DDAB, a synthetic lipid) and horseradish peroxidase (HRP) were made by casting the mixture of the aqueous vesicle of DDAB and HRP onto the glassy carbon (GC) electrode. The direct electron transfer between electrode and HRP immobilized in lipid film has been demonstrated. The lipid films were used to supply a biological environment resembling biomembrane on the surface of the electrode. A pair of redox peaks attributed to the direct redox reaction of HRP were observed in the phosphate buffer solution (pH 5.5). The cathodic peak current increased dramatically while anodic peak decreased by addition of small amount H2O2. The pH effect on amperometric response to H2O2 was studied. The biosensor also exhibited fast response (5 s), good stability and reproducibility.

Defect formation induced by PAMAM dendrimers on Pt-supported bilayer lipid membranes investigated by electrochemistry

The interaction of polyamidoamine (PAMAM) dendrimers (generations 1-7) with supported bilayer lipid membranes was studied by cyclic votammetry and ac impedance. It is shown that the dendrimers (generations 4-6) can induce defects in the Pt-electrode-supported bilayer lipid membrane. The ability of dendrimers to induce defects was dependent on their shapes and surface charge. The results are consistent with a change in the morphology of the dendrimers from an open, branched structure for generations 1-4 to a closed, increasingly compact surface for generations 5-7.

Concentration-dependent behavior of nisin interaction with supported bilayer lipid membrane

Nisin is a positively charged antibacterial peptide that binds to the negatively charged membranes of gram-positive bacteria. The initial interaction of the peptide with the model membrane of negatively charged DPPG (dipalmitoylphosphatidylglycerol) was studied by cyclic voltammetry and a.c. impedance spectroscopy. Nisin could induce pores the supported bilayer lipid membrane, thus, it led to the marker ions Fe(CN)(6)(3-/4-) crossing the lipid membrane and giving the redox reaction on the glassy carbon electrode (GCE). Experimental results suggested that the pore formation on supported bilayer lipid membrane was dependent on the concentration of nisin and it included three main concentration stages: low, middling, high concentration.

Characterization and property of DNA incorporated bilayer lipid membranes

Calf-thymus DNA-incorporated bilayer lipid membranes supported on a glassy carbon (GC) electrode was prepared by making layers of phosphatidylcholine dimyristoyl (DMPC) on GC electrode. DNA in the BLM was characterized by cyclic voltammetry, IR and AFM, and lipid layers formed on the GC electrode were demonstrated to be a bilayer lipid membrane by electrochemical impedance experiment. In IR and AFM experiments the findings indicated that DNA was incorporated into BLM. The ion channel of bilayer lipid membranes incorporated was studied. The result showed that the ion channel was opened in the presence of the stimulus quinacrine. In the absence of quinacrine the channel was switched. The process can repeat itself many times. The impedance spectroscopy measurements demonstrate that the stimulus quinacrine opens the channel for permeation of marker ion. The mechanism of forming an ion channel was investigated.

Interaction of K7Fe3+P2W17O62H2 with supported bilayer lipid membranes on platinum electrode

The influence of K7Fe3+P2W17O62H2 on l-alpha-phosphatidylcholine/cholesterol bilayer lipid membrane on Pt electrode was studied by voltammetry and AC impedance spectroscopy. The interaction of the polyoxometalates with the BLM can promote the access of Ru(NH3)(6)(3+) and [Fe(CN)(6)](3-/4-) to the electrode surface. It was found that some kind of pores had been formed on the BLM by AFM. The phenomenon is attributed to the interaction of K7Fe3+P2W17O62H2 with phosphatidylcholine phosphate groups located in its outer leaflet. Experimental results are helpful to understand the biological activity of the polyoxometalates in vivo.

Preparation of poly(thionine) modified screen-printed carbon electrode and its application to determine NADH in flow injection analysis system

A poly(thionine) modified screen-printed carbon electrode has been prepared by an electrooxidative polymerization of thionine in neutral phosphate buffer. The modified electrodes are found to give stable and reproducible electrocatlytic responses to NADH and exhibit good stability. Several techniques, including cyclic voltammetry, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), have been employed to characterize the poly(thionine) film. Further, the modified screen-printed carbon electrode was found to be promising as an amperometric detector for the flow injection analysis (FIA) of NADH, typically with a dynamic range of 5-100 muM.

Microperoxidase-11 modified electrode and its electrocatalytic activity on the reduction of O-2 and H2O2

Microperoxidase-11 (MP-11) was immobilized on the surface of a silanized glass carbon electrode by means of the covalent bond with glutaraldehyde. The measurements of cyclic voltammetry demonstrated that the formal redox potential of immobilized MP-11 was -170 mV. which is significantly more positive than that of MP-11 in a solution or immobilized on the surface of electrodes prepared with other methods. This MP-11 modified electrode showed a good electrocatalytic activity and stability for the reduction of oxygen and hydrogen peroxide.

Promoter effect of La3+ on the electrochemical reaction of microperoxidase-11

The effect of La3+ on the electrochemical behavior and structure of heme undecapeptide-microperoxidase-11 (MP-11)-in the aqueous solution was investigated using cyclic voltammetry, circular dichroism (CD) and UV-vis absorption spectrometry. It was found for the first time that La3+ would promote the electrochemical reaction of MP-11 at the glassy carbon (GC) electrode. This is mainly due to the fact that La3+ would induce more beta-turn and alpha-helical conformations from the random coil conformation of MP-11 and increase the non-planarity of the heme.

Effect of alkyl group length on the conductivity in the 2,3,7,8,12,13,17,18-octakis(alkyl-thio)tetraazaporphyrins and redox properties of the metallooctakis(hexyl-thio)tetraazaporphyrins

A series of 2,3,7,8,12,13,17,18-octakis(alkyl-thio)tetraazaporphyrins (H(2)OATTAP) with different alkyl chain lengths have been synthesized. Cyclic voltammetry and differential pulse voltammetry have been used to investigate the effect of the controlled lengths of the eight peripheral thioether tails on the redox behavior of the molecules. The electrochemical reduction of octakis(hexyl-thio)tetraazaporphyrins, MOHTTAP (where M = Cu, Ni), was studied in 1,2-dichloroethane at a platinum electrode. The Cu derivative was oxidized in one single-electron-transfer step to yield a pi-cation radical and reduced in three single-electron-transfer steps to yield a pi-anion radical, dianion and trianion, respectively. For the Ni derivative, electron transfer reactions involving both the central metal atom and the macrocyclic ring were observed. Electron transfer pathways are proposed based upon voltammetric and in situ spectroelectrochemical results.

Conformation change of horseradish peroxidase in lipid membrane

The electrochemical behavior of horseradish peroxidase (HRP) in the dimyristoyl phosphatidylcholine (DMPC) bilayer on the glassy carbon (GC) electrode was studied by cyclic voltammetry. The direct electron transfer of HRP was observed in the DMPC bilayer. Only a small cathodic peak was observed for HRP on the bare GC electrode. The electron transfer of HRP in the DMPC membrane is facilitated by DMPC membrane. UV-Vis and circular dichroism (CD) spectroscopy were used to study the interaction between HRP and DMPC membrane. On binding to the DMPC membrane the secondary structure of HRP remains unchanged while there is a substantial change in the conformation of the heme active site. Tapping mode atomic force microscopy (AFM) was first applied for the investigation on the structure of HRP adsorbed on supported phospholipid bilayer on the mica and on the bare mica. HRP molecules adsorb and aggregate on the mica without DMPC bilayer. The aggregation indicates an attractive interaction among the adsorbed molecules. The molecules are randomly distributed in the DMPC bilayer. The adsorption of HRP in the DMPC bilayer changes drastically the domains and defects in the DMPC bilayer due to a strong interaction between HRP and DMPC films.

Fabrication of metalloporphyrin-polyoxometalyte hybrid film by layer-by-layer method and its catalysis for dioxygen reduction

Through layer-by-layer method [tetrakis(N-methylpyridyl)porphyrinato] cobalt (CoTMPyP) and polyoxometalyte were alternately deposited on 4-aminobenzoic acid (4-ABA) modified glassy carbon electrode. The resulting organic-inorganic hybrid films were characterized by cyclic voltammetry (CV), UV/visible absorption spectroscopy, and atomic force microscopy (AFM). It was proved that the multilayer films are uniform and stable. CoTMPyP-containing multilayer films exhibit remarkable electrocatalytic activity for the reduction of O-2. Rotating disk electrode (RDE) voltammetry and rotating ring-disk electrode (RRDE) voltammetry confirm that P2W18/CoTMPyP multilayer films can catalyze the four-electron almost reduction of O-2 to water in pH > 4.0 buffer solution, while SiW12/CoTMPyP multilayer films catalyze about two-electron reduction of O-2 to H2O2 in pH 1 - 6 buffer solutions. The kinetic constants for O-2 reduction were comparatively investigated at P2W18/CoTMPyP and SiW12/CoTMPyP multilayer films electrodes.

Gold nanoparticles as fine tuners of electrochemical properties of the electrode/solution interface

Recently, a novel approach for preparing SERS and SPR substrates was developed, which indicates a potential application in tailoring the interfacial structure of an electrode surface. In this study, (3-mercaptopropyl)trimethoxysilane (MPTMS) was selected as a polymeric adhesive layer, and a low concentration of colloid Au solution was used to achieve a more accurate control over interface morphology at nanoscale dimensions due to slow self-assembling kinetics of gold nanoparticle's. Subsequent seeding growth of these MPTMS-supported submonolayers of gold nanoparticles in Au3+/NH2OH aqueous solution enlarges particle size and eventually results in the generation of conductive gold films (similar to previous (3-aminopropyl)trimethoxysilane-supported gold films). Such tunable interface structure was evaluated by atomic force microscopy (AFM). Also, ac impedance spectroscopy (ACIS) and cyclic voltammograms were performed to evaluate electrochemical properties of the as-prepared interfaces by using Fe(CN)(6) (3-/4-) couples as a probe. Furthermore, relevant theories of microarray electrodes were introduced into this study to explain the highly tunable electrochemical properties of the as-prepared interfaces. As a result, it is concluded that the electrochemical properties toward Fe(CN)(6) (3-/4-) couples are highly dependent on the active nanoelectrode (nanoparticles) area fraction and nanoparticles are fine-tuners of interfacial properties because the number density. (numbers/unit area) and size of nanoparticles are highly tunable by self-assembling and seeding growth time scale control. This is in agreement with the theoretical expectations for a microarray electrode if a single nanoparticle tethered to a blocking SAM is taken as a nanoelectrode and 2-D nanoparticle assemblies are taken as nanoelectrode arrays.

Separation of heavy rare earth elements with extraction resin containing 1-hexyl-4-ethyloctyl isopropylphosphonic acid

This paper presents the results of the adsorption of heavy rare earth ions (Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III), Lu(III) and Y(III)) from hydrochloric acid solutions at 30 degreesC by the extraction resin containing 1-hexyl-4-ethyloctyl isopropylphosphonic acid (HEOPPA), which has higher steric hindrance, higher selectivities and lower extraction and stripping acidity than di(2-ethylhexyl)phosphoric acid (DERPA) or 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH/EHP). The dependence of acid concentration, flow rate and amounts of rare earth ions sorbed on the separation of Er-Tm, Tm-Yb and Er-Tm-Yb mixtures has been studied. The baseline chromatographic separation of Er-Tm-Yb mixture has been observed. Satisfactory results with purity and yield of Tm2O3>99.71% and >71.25%, Er2O3>99-81% and >94.17%, and Yb2O3>99.74% and >89.83%, respectively, have been obtained. The parameters such,as resolution, separation factors and efficiencies have been determined as a function of acidity, loading of rare earth elements and flow rates. The stoichiometry of the extraction of rare earth ions has been suggested as well.

Charge transfer across the water/nitrobenzene interface by three-electrode system

A droplet of aqueous solution containing a certain molar ratio of redox couple is first attached onto a platinum electrode surface, then the resulting drop electrode is immersed into the organic solution containing very hydrophobic electrolyte. Combined with reference and counter electrodes, a classical three-electrode system has been constructed, Ion transfer (IT) and electron transfer (ET) are investigated systematically using three-electrode voltammetry. Potassium ion transfer and electron transfer between potassium ferricyanide in the aqueous phase and ferrocene in nitrobenzene are observed with potassium ferricyanide/potassium ferrocyanide as the redox couple. Meanwhile, the transfer reactions of lithium, sodium, potassium, proton and ammonium ions are obtained with ferric sulfate/ferrous sulfate as the redox couple. The formal transfer potentials and the standard Gibbs transfer energy of these ions are evaluated and consistent with the results obtained by a four-electrode system and other methods.