Effect of La3+ on structure and electrochemical reaction of microperoxidase-11 in imitated physiological solution

In this paper, the interaction mechanism between La3+ and microperoxidase-11 (MP-11) in the imitated physiological solution was investigated with the electrochemical and spectroscopic methods. It was found that when the molar ratio of La3+, and MP-11 is low, such as 2, La3+ can coordinate with oxygen in the propionic acid group of the heme group in the MP-11 molecule, forming the La-MP-11 complexes and leading to the increase in the non-planarity of the porphyrin cycle in the heme group and then the increase in the extent of exposure of the electrochemically active center, Fe(I I I) in the porphyrin cycle of the heme group. The increase in the extent of exposure of the electrochemically active center, Fe(III) in the porphyrin cycle of the heme group would increase the reversibility of the electrochemical reaction of the La-MP-11 complexes and its electrocatalytic activity for the reduction of H2O2. The results of the chromatographic analysis demonstrated that the average molar ratio of La3+ and MP-11 in the La-MP-11 complexes is 1.62.When the molar ratio of La3+ and MP-11 is high, such as 3, La3+ would shear some amino acid residues of the peptide of MP-11. Therefore, many La3+ ions can bind to the oxygen- and/or nitrogen-containing groups in the sheared amino acid residues except coordinating with the sheared and non-sheared MP-11 molecules.

Interaction between La3+ and MP-11 in the physiological solution

In this paper, the interaction between La3+ and microperoxidase-11 (MP-11) in the imitated physiological solution was investigated with the electrochemical method, circular dichroism (CD) and ultraviolet-visible (UV-vis) absorption spectroscopy. It was found that the interaction ways between La3+ and MP-11 are different with increasing the molar ratio of La3+ and MP-11. When the molar ratio of La3+ and MP-11 is less than 2, La3+ mainly interacts with the metacetonic acid group of the heme group in the MP-11 molecules, causing the increase in the non-planarity of the porphyrin cycle in the heme group and the decrease in the content of the random coil conformation of MP-11. These structural changes would increase the exposure extent of the electrochemical active center of MP-11 and thus, La3+ can promote the electrochemical reaction of MP-11 and its electrocatalytic activity for the reduction of H2O2 at the glassy carbon (GC) electrode. However, when the molar ratio of La3+ and MP-11 is larger than 3, except binding to the carbonyl oxygen of the metacetonic acid group in the heme group, La3+ interacts also with the oxygen-containing groups of the amides in the polypeptide chains of the MP-11 molecules, leading to the increase in the contents of the random coil conformation in the peptide of the MP-11 molecule, comparing with that for the molar ratio of less than 2.

Electrochemiluminescence detection with integrated indium tin oxide electrode on electrophoretic microchip for direct bioanalysis of lincomycin in the urine

In this article, an antibiotic, lincomycin was determined in the urine sample by microchip capillary electrophoresis (CE) with integrated indium tin oxide (ITO) working electrode based on electrochemiluminescence (ECL) detection. This microchip CE-ECL system can be used for the rapid analysis of lincomycin within 40 s. Under the optimized conditions, the linear range was obtained from 5 to 100 muM with correlation coefficient of 0.998. The limit of detection (LOD) of 3.1 muM was obtained for lincomycin in the standard solution. We also applied this method to analyzing lincomycin in the urine matrix. The limit of detection of 9.0 muM was obtained. This method can determine lincomycin in the urine sample without pretreatment, which demonstrated that it is a promising method of detection of lincomycin in clinical and pharmaceutical area.

Direct electron transfer between cytochrome c and a gold nanoparticles modified electrode

Quasi-reversible and direct electrochemistry of cytochrome c (cyt. c) has been obtained at a novel electrochemical interface constructed by self-assembling gold nanoparticles (GNPs) onto a three-dimensional silica gel network, without polishing or any modification of the surface. A cleaned gold electrode was first immersed in a hydrolyzed sol of the precursor (3-mercaptopropyl)-trimethoxysilane to assemble three-dimensional silica gel, then the GNPs were chemisorbed onto the thiol groups of the sol-gel network and modified the kinetic barrier of this self-assembled silicate film. Cyclic voltammetry and AC impendance spectroscopy were performed to evaluate electrochemical properties of the as prepared interface. These nanoparticle inhibits the adsorption of cyt. c onto bare electrode and acts as a bridge of electron transfer between protein and electrode.

A novel hydrogen peroxide sensor based on horseradish peroxidase immobilized on colloidal Au modified ITO electrode

A novel method to fabricate a hydrogen peroxide sensor was developed by immobilizing horseradish peroxidase (HRP) on colloidal An modified ITO conductive glass support. The cleaned glass support was modified with (3-aminopropyl)trimethoxysilane (APTMS) first to yield an interface for the assembly of colloidal An. Then 15 nm colloidal Au particles were chemisorbed onto the amine groups of the APTMS. Finally, HRP was adsorbed onto the surface of the colloidal An. The immobilized HRP displayed excellent electrocatalytical response to the reduction of hydrogen peroxide. The performance and factors influencing the resulted biosensor were studied in detail. The resulted biosensor exhibited fast amperometric response (within 5 s) to H2O2. The detection limit of the biosensor was 8.0 mumol l(-1), and linear range was from 20.0 mumol l(-1) to 8.0 mmol l(-1). Furthermore, the resulted biosensor exhibited high sensitivity, good reproducibility, and long-term stability.

Preparation of hybrid thin film modified carbon nanotubes on glassy carbon electrode and its electrocatalysis for oxygen reduction

A hybrid thin film containing Pt nanoparticles and [tetrakis(N-methylpyridyl)porphyrinato] cobalt (CoTMPyP) modified multi-walled carbon nanotubes (MWNTs) on a glassy carbon (GC) electrode surface was fabricated. This hybrid film electrode exhibited remarkable electrocatalytic activity for oxygen reduction and high stability with promising applications in fuel cells.

Preparation of a phosphopolyoxomolybdate P2Mo18O626- doped polypyrrole modified electrode and its catalytic properties

A phosphopolyoxomolybdate (P2Mo18) doped polypyrrole (PPy) modified electrode was prepared in aqueous solution by a one-step method. During the polymerization of PPy, P2Mo18 acted as both catalyst and dopant. The electrochemical behavior of the PPy/P2Mo18 modified electrode before and after the overoxidation of PPy was investigated. Both of these showed a catalytic effect toward bromate. The PPy/P2Mo18 composite film was characterized by chronoamperometry, cyclic voltammetry, the rotating disk electrode technique, X-ray photoelectron spectroscopy and Raman spectroscopy.

Polyaniline-coated carbon particles and their electrode behavior in organic carbonate electrolyte

In an attempt to increase the interface stability of carbon used in Li-ion batteries, a thin conducting polyaniline (PANI) film was fabricated on the surface of carbon by in situ chemical polymerization. The chemical and electrochemical properties of the composite material were characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscope, cyclic voltammetry, and electrochemical impedance spectroscopy. It was confirmed that the PANI film has an obvious effect on the morphology and the electrochemical performance of carbon. The results could be attributed to the electronic and electrochemical activity of the conducting PANI films.

Electrocatalytic oxidation of catechol at multi-walled carbon nanotubes modified electrode

In 0.05 mol/L phosphate buffer solution (pH 7.0), carbon nanotubes modified electrode exhibits rapid response, strong catalytic activity with high stability toward the electrochemical oxidation of catechol. The electrochemical behavior of catechol on both the multi-walled and single-walled carbon nanotubes modified electrode was investigated. The experimental conditions, such as pH of the solution and scan rate were optimized. The currents (measured by constant potential amperometry) increase linearly with the concentrations of catechol in the range of 2.0 x 10(-5) - 1.2 x 10(-3) mol/L. Moreover, at the multi-walled carbon nanotubes modified electrode the electrochemical responses of catechol and ascorbic acid can be separated clearly.

Electrocatalytic reduction of oxygen at multi-walled carbon nanotubes and cobalt porphyrin modified glassy carbon electrode

The multi-walled carbon nanotubes (MWNTs) modified glassy carbon electrode exhibited electrocatalytic activity to the reduction of oxygen in 0.1 M HAc-NaAc (pH 3.8) buffer solution. Further modification with cobalt porphyrin film on the MWNTs by adsorption, the resulted modified electrode showed more efficient catalytic activity to O-2 reduction. The reduction peak potential of O-2 is shifted much more positively to 0.12 V (vs. Ag/AgCl), and the peak current is increased greatly. Cyclic voltammetry (CV), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), were used to characterize the material and the modified film on electrode surface. Electrochemical experiments gave the total number of electron transfer for oxygen reduction as about 3, which indicated a co-exist process of 2 electrons and 4 electrons for reduction of oxygen at this modified electrode. Meanwhile, the catalytic activities of the multilayer film (MVVNTs/CoTMPyP)(n) prepared by layer-by-layer method were investigated, and the results showed that the peak current of O-2 reduction increased and the peak potential shifted to a positive direction with the increase of layer numbers.

pH-dependent conformational changes of ferricytochrome c induced by electrode surface microstructure

pH-dependent processes of bovine heart ferricytochrome c have been investigated by electronic absorption and circular dichroism (CD) spectra at functionalized single-wall carbon 'nanotubes (SWNTs) modified glass carbon electrode (SWNTs/ GCE) using a long optical path thin layer cell. These methods enabled the pH-dependent conformational changes arising from the heme structure change to be monitored. The spectra obtained at functionalized SWNTs/GCE reflect electrode surface microstructure-dependent changes for pH-induced protein conformation, pK(a) of alkaline transition and structural microenvironment of the ferricytochrome c heme. pH-dependent conformational distribution curves of ferricytochrome c obtained by analysis of in situ CD spectra using singular value decomposition least square (SVDLS) method show that the functionalized SWNTs can retain native conformational stability of ferricytochrome c during alkaline transition.

Synthesis and chirooptical properties of optically active poly(ester imide)s based on axially asymmetric 1,1 '-binaphthyls

A series of optically active poly(ester imide)s (PEsI's) has been synthesized by the polycondensation reactions of new axially asymmetric dianhydrides, that is, (R)-2,2'-bis(3,4-dicarboxybenzoyloxy)-1,1'-binaphthyl dianhydride and (S)-2,2'-bis(3,4-dicarboxybenzoyloxy)-1,1'-binaphthyl dianhydride, and various diamines with aromatic, semiaromatic, and aliphatic structures. The polymers have inherent viscosities of 0.45-0.70 dL/g, very good solubility in common organic solvents, glass-transition temperatures of 124-290 degreesC, and good thermal stability. Wide-angle X-ray crystallography of these polymers shows no crystal diffraction. In comparison with model compounds, an enhanced optical rotatory power has been observed for the repeat unit of optically active PEsI's based on aromatic diamines, and it has been attributed to a collaborative asymmetric perturbation of chiral 1,1'-binaphthyls along the rigid backbones.

Copolymers derived from bismaleimide oligomer with active solvent

An oligomer from 4, 4'-bis(maleimido)diphenyl methane and methylenedianiline were dissolved in active solvent N,N-dimethyl acrylamide in a solid content up to 50-70%; the solution was poured in a sheet-shaped module and irradiated b y Co-60 with the dose from 20 to 350 kGy at room temperature. The polymerized sheet was postcured at 180degreesC to obtain a transparent red-orange sheet with tensile strength above 100 MPa. The glass transition temperature before and after postcuring was around 100degreesC and 150-180degreesC, respectively. Styrene was used along with DMAA to decrease the water absorption for the copolymers.

Crystal structure and electrochemical properties of rare earth non-stoichiometric AB(5)-type alloy as negative electrode material in Ni-MH battery

The La0.85MgxNi4.5Co0.35Al0.15 (0.05less than or equal toxless than or equal to0.35) system compounds have been prepared by are melting method under Ar atmosphere. X-ray diffraction (XRD) analysis reveals that the as-prepared alloys have different lattice parameters and cell volumes. The electrochemical properties of these alloys have been studied through the charge-discharge recycle testing at different temperatures and discharge currents. It is found that the La0.85Mg0.25Ni4.5Co0.35Al0.(15) alloy electrode is capable of performing high-rate discharge. Moreover, it has very excellent electrochemical properties as negative electrode materials in Ni-MH battery at low temperature, even at -40degreesC.