ELECTROCATALYTIC OXIDATION AND ION-CHROMATOGRAPHIC DETECTION OF BR-, I-, SO32-, S2O32- AND SCN- AT A PLATINUM PARTICLE-BASED GLASSY-CARBON MODIFIED ELECTRODE

A modified method for dispersing platinum particles on a glassy carbon (GC) electrode was investigated. The ultramicro Pt particle-modified electrode obtained exhibited high catalytic stability and activity towards the oxidation of some halide ions (Br-, I-) and inorganic sulfur species (S2O32-, SO32- and SCN-). These anions were separated and detected by using ion chromatography and electrochemical detection via this novel dispersed Pt particles-GC working electrode. The detection limits were 20 ng/ml for Br-, 1.0 ng/ml for I-, 10 ng/ml for SO32- and 4.0 ng/ml for SCN-. This method was employed for the analysis of industrial and environmental waste waters.

THE PREPARATION OF ELECTRODES MODIFIED WITH ISOPOLYMOLYBDIC ACID PLUS POLYANILINE FILM AND ITS CATALYTIC EFFECTS ON CHLORATE IONS

Electrodes modified with isopolymolybdic acid+polyaniline film, which exhibit high stability and activity in aqueous acidic solution, have been prepared successfully using two methods: one-step synthesis by electrochemical polymerization at a constant applied potential of +0.80 V/SCE or by cycling the potential at 100 mV/s between -0.12 and +0.85 V in 0.5 M H2SO4 containing 5.0x10(-2) M aniline and 5.0x10(-3) M H4Mo8O26, or two-step synthesis by doping the polyaniline film electrode with isopoly acid (IPA) under a cycling potential between -0.20 and +0.40 V in 0.5 M H2SO4 containing the H4Mo8O26 dopant. The thickness of the film and the amount of dopant in the polyaniline film can be controlled by experimental parameters such as the charge, time and the ratio of aniline to IPA in the solution. The experimental results show that electrodes modified with isopolymolybdic acid+polyaniline film using both methods have a strong catalytic effect on the reduction of chlorate anions. Comparison of the two methods of modification shows that the catalytic effect at the modified electrode prepared by the two-step method is greater than that at the electrode prepared by the one-step method.

FLOW-INJECTION ANALYSIS OF GLUCOSE AT AN AMPEROMETRIC GLUCOSE SENSOR-BASED ON ELECTROCHEMICAL CODEPOSITION OF PALLADIUM AND GLUCOSE-OXIDASE ON A GLASSY-CARBON ELECTRODE

A glassy carbon electrode (GCE) modified with palladium provides excellent electrocatalytic oxidation of hydrogen peroxide. When the electrolyte contains palladium chloride and glucose oxidase, the GCE can be modified by electrochemical codeposition at a given potential. The resulting modified surface was coated with a thin film of Nation to form a glucose sensor. Such a glucose sensor was successfully used in the flow-injection analysis of glucose with high stability and anti-poisoning ability. It gave a detection limit of 1 X 10(-7) M injected glucose, with a linear concentration range of 0.001-8 mM. There is no obvious interference from substances such as ascorbate and saccharides.

ELECTROCHEMICAL STUDY OF ISOPOLY-OXOMETALLATES AND HETEROPOLY-OXOMETALLATES FILM MODIFIED MICROELECTRODES .3. FURTHER STUDY OF ELECTRODE PROCESS OF ISOPOLYMOLYBDIC ANION DOPED IN POLYANILINE FILM

The isopolymolybdic anion-polyaniline film modified carbon fiber (CF) microelectrode with high stability and electroactivity in aqueous acid solution has been successfully prepared by cycling the potential between -0.15 V and +0.85 V vs. sce at 100 mV s-1 or applying constant potential (+0.85 V) for electropolymerization in a 0.5 M H2SO4 solution containing 5.0 x 10(-2) M aniline and 5.0 x 10(-3) M H4Mo8O26. The electrochemical behaviour of the isopolymolybdic anion entrapped in the polyaniline film is strongly influenced by the sweep-potential range besides the acidity of electrolyte solution. In some acidic electrolyte solution (eg 0.5 M H2SO4), the change of the sweep-potential range causes the structure alternation of the isopolymolybdic anion and resulting in a new electrode process. The cyclic voltammogram of Mo8O264- in 0.5 M H2SO4 solution exhibits three two-electron reversible waves between +0.70 and -0.20 V. However, when the potential sweeps to the lower-limit of -0.3 V, where the fourth four-electron cathodic wave appears, the redoxidation process of the reduction product of Mo8O264- becomes relatively complicated. The 10-electron reduction product seems to change into other isopolyanion (this unknown structure isopolyanions are simply called [Mo-O]), which can be reoxidized to Mo8O264- by five successive two-electron oxidation steps from -0.30 to +0.70 V. However, when the lower-limit of the cycling potential is maintained at -0.30 V and the upper-limit reduces to +0.40 V from +0.70 V, the [Mo-O] in the film exhibits four two-electron reversible waves. We have presented a novel explanation about its electrode reaction mechanism on the basis of our experimental results.

ELECTROCHEMICAL STUDY OF ISOPOLY AND HETEROPOLY OXOMETALLATE FILM MODIFIED MICROELECTRODES .5. PREPARATION AND ELECTROCHEMICAL-BEHAVIOR OF A 2/18-MOLYBDODIPHOSPHATE ANION MONOLAYER MODIFIED ELECTRODE

In this paper a carbon fibre (CF) microelectrode modified with the 2:18-molybdodiphosphate anion by simple adsorption is described and its electrochemical behaviour is reported. The 2:18-molybdodiphosphate anion (alpha-P2Mo18O626-), which is a Dawson structure, undergoes five successive multielectron reductions in acidic solution. The first three redox waves correspond to the two-electron process, and the last two waves are four-electron and six-electron processes respectively. On the basis of the experimental results it is shown that the electrode process of alpha-P2Mo18O626- on the CF electrode in acidic solution is simultaneously controlled by the diffusion and adsorption of alpha-P2Mo18O626- anions. When the concentration of the alpha-P2Mo18O626- in the solution is reduced, the electrode process mainly exhibits non-diffusion-controlled behaviour, and the diffusion-limited process takes over as the concentration of alpha-P2Mo18O626- becomes higher. The CF electrode modified with a thin film of alpha-P2Mo18O626- exhibits very good stability and redox behaviour in aqueous acidic solution. The alpha-P2Mo18O626- is reduced to heteropoly blue, with an accompanying protonation process. The addition of more than six electrons to the alpha-P2Mo18O626- anion in an aqueous solution does not result in its decomposition. The result obtained is not the same as that reported previously.

ELECTROCHEMICAL STUDY OF ISOPOLY-OXOMETALLATE AND HETEROPOLY-OXOMETALLATE FILM MODIFIED MICROELECTRODES .2. ELECTROCHEMICAL-BEHAVIOR OF ISOPOLYMOLYBDIC ACID MONOLAYER MODIFIED CARBON-FIBER MICROELECTRODES

In this paper the electrochemical properties of isopolymolybdic anion thin film modified carbon fibre (CF) microelectrode prepared by simple dip coating have been described. The modified electrode shows three couples of surface redox waves between + 0.70 and - 0.1 V vs. sce in 2 M H2SO4 solution with good stability and reversibility. The pH of solution has a marked effect on the electrochemical behaviour and stability of the film, the stronger the acidity of electrolyte solution is, the better the stability and reversibility of isopolymolybdic anion film CF microelectrode will be. The scanning potential range strongly influences on the electrochemical behaviour of the film. The isopolymolybdic anion film prepared by the dip coating resulting a monolayer with estimated surface concentration (F) 2.8 x 10(-11) mol cm-2. From the half-peak widths and peak areas of the surface redox waves of the film electrode, the first three surface waves are corresponding to two-electron processes. The electron energy spectra show the products by six electrons reduction are a mixture of Mo(VI) and Mo(V) species. The electrochemical reaction of the isopolymolybdic anion monolayer can be expressed as Mo8O264- + mH+ + 2ne half arrow right over half arrow left [HmMo8-2n(VI)Mo2n(V)O26](4,2n-m)-n = 1, 2, 3; m = 2, 5, 7.

THERMAL ANALYSIS AND INFRARED SPECTRA OF DIALKYLAMMONIUM TETRAC HLOROCUPRATE

The thermal stability and the solid solid phase transitions in Ills compounds with n = 7-12 have been studied by DSC and TG methods. Comparision with CnZn compounds want made. The nature of three phases of CnCu has been discussed in terms of infrared spectroscopy and the assignment of the phase transitions has been given. The thermal stability of CnCu is lower than that of CnZn and presents an obvious odd even effect. All of these compounds exhibit two solid solid phase transitions in the temperature range of 248-337 K. The peak tempe nature of phase transitions changes regularly. The peak temperature or the main phase transition increases with the chain length. The total transition enthalpies and entropies increase with increasing chain length. When n <= 9, the high temperature phase exists in a partial disorder state. When n >= 10, the high temperature phase exists in a conformational disorder state. The main phase transition and the phase transition at 307.7 K of CnCu may mainly are from the change of the packing structure and the change of the partial conformational order-disorder of alkyl chain, respectively.

LIQUID-CHROMATOGRAPHY WITH ELECTROCATALYTIC DETECTION OF CYSTEINE, N-ACETYLCYSTEINE AND GLUTATHIONE BY A PRUSSIAN BLUE FILM-MODIFIED ELECTRODE

Chemically modified electrodes prepared by adsorbing prussian blue on a glassy carbon electrode are shown to catalyse the electro-oxidation of cysteine, N-acetylcysteine and glutathione in acidic media. The catalytic response is evaluated with respect to the potential scan rate, the solution pH, the concentration dependence, and other variables. Covering the electrode with Nafion(R) film improved the stability and reproducibility in liquid chromatography with electrochemical detection to the extent that repetitive sample injections produced relative standard deviations of less than 5% over several hours of operation. The limit of detection was 4 pmol for cysteine, 33 pmol for glutathione and 61 pmol for N-acetylcysteine.

THERMAL-ANALYSIS OF POLYARYLENE ETHER SULFONES AND POLYIMIDES

Some results on the thermal analysis of polyimides and polyaryl ether sulfones, some reactions and the purity determination of the monomers, and the thermal stability and kinetic analysis of the thermo-oxidative degradation of these polymers are described.

A GLASSY-CARBON ELECTRODE MODIFIED BY DISPERSED ALPHA-ALUMINA AS AN ENHANCED ELECTROCHEMICAL DETECTOR IN LIQUID-CHROMATOGRAPHY FOR CYSTEINE AND GLUTATHIONE

The dispersion of alumina particles on a glassy-carbon surface serving as a modified electrode significantly enhances the amperometric detection of cysteine and glutathione following liquid chromatography. With an applied potential of 0.8 V vs. SCE, the detection limits were 1.2 ng for cysteine and 8 ng for glutathione and the electrode response was linear up to 600 ng for cysteine and 1.8-mu-g for glutathione. The modified electrode displayed high sensitivity and stability and was easy and inexpensive to prepare.

Interaction between Thymidylate Synthase and Its Cognate mRNA in Zebrafish Embryos

Thymidylate synthase (TS), which catalyzes the de novo synthesis of dUMP, is an important target for cancer therapy. In this report, the effects of 5-fluorouracil (5-FU) and ZD1694 on the regulation of TS gene expression were evaluated in zebrafish embryos. Our results revealed that the expression of TS was increased by about six-fold when embryos were treated with 1.0 mu M 5-FU and there was a greater than 10-fold increase in the TS protein level after treatment with 0.4 mu M ZD1694. Northern blot analysis confirmed that expression of TS mRNA was identical in treated or untreated embryos. Gel shift and immunoprecipitation assays revealed that zebrafish TS was specifically bound with its cognate mRNA in vitro and in vivo. We identified a 20 nt RNA sequence, TS:N20, localized to the 5'-UTR of TS mRNA, which corresponded to nt 13-32; TS:N20 bound to the TS protein with an affinity similar to that of the full-length TS mRNA. The MFold program predicted that TS:N20 formed a stable stem-loop structure similar to that of the cis-acting element found in human TS mRNA. Variant RNAs with either a deletion or mutation in the core motif of TS:N20 were unable to bind to the TS protein. In vitro translation experiments, using the rabbit lysate system, confirmed that zebrafish TS mRNA translation was significantly repressed when an excess amount of TS protein was included in the system. Additionally, a TS stability experiment confirmed that treatment of zebrafish embryos with 5-FU could increase the TS stability significantly, and the half life of TS protein was about 2.7 times longer than in untreated embryos. Our study revealed a structural requirement for the interaction of TS RNA with TS protein. These findings also demonstrated that the increase in TS protein induced by 5-FU occurs at the post-transcriptional level and that increased stability and translation efficiency both contributed to the increase in TS protein levels induced by TS inhibitors.

Interaction between Thymidylate Synthase and Its Cognate mRNA in Zebrafish Embryos

Thymidylate synthase (TS), which catalyzes the de novo synthesis of dUMP, is an important target for cancer therapy. In this report, the effects of 5-fluorouracil (5-FU) and ZD1694 on the regulation of TS gene expression were evaluated in zebrafish embryos. Our results revealed that the expression of TS was increased by about six-fold when embryos were treated with 1.0 mu M 5-FU and there was a greater than 10-fold increase in the TS protein level after treatment with 0.4 mu M ZD1694. Northern blot analysis confirmed that expression of TS mRNA was identical in treated or untreated embryos. Gel shift and immunoprecipitation assays revealed that zebrafish TS was specifically bound with its cognate mRNA in vitro and in vivo. We identified a 20 nt RNA sequence, TS:N20, localized to the 5'-UTR of TS mRNA, which corresponded to nt 13-32; TS:N20 bound to the TS protein with an affinity similar to that of the full-length TS mRNA. The MFold program predicted that TS:N20 formed a stable stem-loop structure similar to that of the cis-acting element found in human TS mRNA. Variant RNAs with either a deletion or mutation in the core motif of TS:N20 were unable to bind to the TS protein. In vitro translation experiments, using the rabbit lysate system, confirmed that zebrafish TS mRNA translation was significantly repressed when an excess amount of TS protein was included in the system. Additionally, a TS stability experiment confirmed that treatment of zebrafish embryos with 5-FU could increase the TS stability significantly, and the half life of TS protein was about 2.7 times longer than in untreated embryos. Our study revealed a structural requirement for the interaction of TS RNA with TS protein. These findings also demonstrated that the increase in TS protein induced by 5-FU occurs at the post-transcriptional level and that increased stability and translation efficiency both contributed to the increase in TS protein levels induced by TS inhibitors.

A review of advances in research on marine molluscan antimicrobial peptides and their potential application in aquaculture

Antimicrobial peptides (AMPs) are important components of the host innate immune response against microbial invasion. They are usually characterized by their small-size, heat-stability and broad range of antimicrobial activity. This review covers research advances on marine mollusc AMPs, specifically those isolated from mussels, scallops, oysters, venerid clams and abalone, which mainly include MGD, mytilin, myticin, mytimycin, big defensin, and RPD-1. Their structural characteristics, antibacterial activity, and expression pattern as well as peptide distribution and their release following microbial challenge are also discussed. In addition, the prospect of the application of AMPs as food additives or their use in immunostimulation to prevent diseases of aquatic animals, as well as their potential hazards, are also discussed.

The lysosome and lysozyme response in Chinese shrimp Fenneropenaeus chinensis to Vibrio anguillarum and laminarin stimulation

The effect of laminarin and Vibrio anguillarum on neutral red retention (NRR) time of lysosome and lysozyme activity in blood cells was investigated in Chinese shrimp, Fenneropenaeus chinensis. In addition the variation, of total haemocyte counts (THC) and differential haemocyte counts (DHC) were dtermined simultaneously The. results showed that the lysosome membrane stability was significantly elongated with the longest NRR time for 180 min at 3 h after lamianrin injection, (p<0.05). The lysozyme activity of haemocytes showed a moderate increase simultaneously. THC also increased and with a highest percentage of semi-granular cell counts at 3 h after laminarin injection. However, the NRR time sharply decreased with the shortest NRR time for 13 min at 1.5 h after V. anguillarum injection. Compared to the control group, the lysozyme activity obviously increased after injection, which was demonstrated at 1.5 h though the THC decreased. The percentage of hyaline cells increased obviously after V. anguillarum injection (p<0.05). The results suggested that the shrimp immune status could be evaluated by using lysosome membrane stability and lysozyme activity. (C) 2008 Elsevier B.V. All rights reserved.

2-(2-Phenyl-1H-phenanthro-[9,10-d]imidazole-1-yl)-acetic acid (PPIA) and its application for determination of amines by high performance liquid chromatography with fluorescence detection and identification with mass spectroscopy/atmospheric pressure chemical ionization

A simple, sensitive, and mild method for the determination of amino compounds based on a condensation reaction with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC-HCI) as the dehydrant with fluorescence detection has been developed. Amines were derivatized to their acidamides with labeling reagent 2-(2-phenyl-1H-phenanthro-[9,10-d]imidazole-1-yl)-acetic acid (PPIA). Studies on derivatization conditions indicated that the coupling reaction proceeded rapidly and smoothly in the presence of a base catalyst in acetonitrile to give the corresponding sensitively fluorescent derivatives with an excitation maximum at lambda(ex) 260nm and an emission maximum at lambda(em) 380nm. The labeled derivatives exhibited high stability and were enough to be efficiently analyzed by high-performance liquid chromatography. Identification of derivatives was carried out by online post-column mass spectrometry (LC/APCI-MS/MS) and showed an intense protonated molecular ion corresponding m/z [MH](+) under APCI in positive-ion mode. At the same time, the fluorescence properties of derivatives in various solvents or at different temperature were investigated. The method, in conjunction with a gradient elution, offered a baseline resolution of the common amine derivatives on a reversed-phase Eclipse XDB-C-8 column. LC separation for the derivatized amines showed good reproducibility with acetonitrile-water as mobile phase. Detection limits calculated from 0.78 pmol injection, at a signal-to-noise ratio of 3, were 3.1-18.2 fmol. The mean intra- and inter-assay precision for all amine levels were < 3.85% and 2.11%, respectively. Excellent linear responses were observed with coefficients of > 0.9996. The established method for the determination of aliphatic amines from real wastewater and biological samples was satisfactory. (c) 2006 Elsevier B.V. All rights reserved.