Electrochemical Characterisation And Application of Solid Electrodes Chemically Modified With C60- Fullerene, Tetrathiafulvalene and Silicon Polyoxotungstate

The modified glassy carbon electrodes by adhered microcrystals of fullerene (C60), tetrathiafulvalene (TTF) and a-Keggin silicon polyoxotungstate, has been studied extensively in characterization and application of these modified electrode in mediating some selected compounds such as cysteine, methionine and nitrite ions in the presence of aqueous electrolytes. The use of a glassy carbon electrode modified by adhered microcrystals of fullerene (C60), mediates the oxidation of cysteine in the presence of aqueous potassium containing electrolytes. Under conditions of cyclic voltarnmetry, the potential for the oxidation of cysteine was lowered by approximately 100 mV and current was enhanced significantly relative to the situation prevailing when a bare glassy carbon electrode was used. Additional mediation occurs when the potential range covered includes that of C60/C60n-r edox couples. The sensitivity under condition of cyclic voltarnrnetry was significantly dependent on pH, temperature and C60 dosage. Excellent analytical and recovery data were obtained with vitamin pill, cassamino acid (hydrolyzed casein) and for a range of beverages. The usefulness of a C60-fullerene modified gold (Au) electrode was extended in mediating the oxidation of methionine in the presence of potassium ions electrolyte. During cyclic voltarnrnetry, an oxidation peak of methionine appearing at +I000 mV vs. AgIAgC1 was observed. The oxidation current of methionine was enhanced by about 2 times using a modified gold electrode. The current enhancement was significantly dependent on pH, temperature and C60 dosage. The variation of scan rate study shows that the system undergoes diffusion-controlled process. Then, diffusion coefficient and rate constant of methionine were determined using hydrodynamic method (rotating disk electrode) with values of 1.1 1 x 10.' cm2 i' and 0.0026 cm s-I respectively for unmodified electrode while the values of diffusion coefficient and rate constant of methionine using C60 modified Au electrode were 5.67 x cm2 i1 and 0.0021 cm s-I respectively. Excellent analytical and recovery data were obtained with root beer beverage.Tetrathiafulvalene modified glassy carbon electrode has been characterized and been applied in the determination of L-cysteine at the potential of +800 mV vs. Ag/AgCl. It has shown to catalyze the oxidation peak of cysteine in the alkaline buffer solution under cyclic voltammetry conditions. The sensitivity of tetrathiafulvalene modified electrode was found to be dependent on pH and dosages of varying concentration of TTF in acetonitrile. Excellent analytical and recovery rates also has been obtained using vitamin pills and root beer syrup either with known amount of cysteine or added deliberately into the samples. The voltammetric reduction of a form of Keggin silicon polyoxotungstate anions, a - [ ~ i ~ ~ h~as0 b~ee~n ]ca~rri-ed out under acidic conditions. The cyclic voltammograms obtained from the solution voltammetry of the Keggin polyoxotungstate anions, a-[~i~12040]s~ho-w ed cyclic voltammogram of a two reversible, one-electron process and a reversible two-electron process in the potential range of +200 mV to -1000 mV (vs. Ag/AgCl). However, only the first reduction process was undertaken in this study. The use of Keggin silicon polyoxotungstate anion, a - [ ~ i ~ ~ ~ 0w4as ~ ] ~ - successfully applied to the synthesis of ruthenium bipyridine silicon polyoxotungstate, [R~(bipy)~]~[a-SivWia~ ~reOd~uc~t]io n of a-[TBA]4[SiW1~040] solvent cast onto the glassy electrode in sulphuric acid. The reduction of nitrite has shown to be catalyzed by [R~(bipy)3]2[a-SiW~~Om~o~di]f ied electrode at lower pH of aqueous sulphuric acid media. Bulk electrolysis technique was employed toreduce a - [ ~ i ~ ~ ~to 0fo4rm~ a] b~lue- s olution of a-[~i~12040T]~he- .r eduction of a - [ ~ i ~ l 2 0 ~to~ a] "- [ ~ i ~ 1 ~w0as ~m~ea]su~red- spectrophotometrically and there was no stable complex formation between a-[~i~12040an]d~ -re duction product of NO< species in the acidic solution. Therefore, the mechanism involving the catalytic effect on a-[siw1204014- in the presence of nitrite suggested that nitrous acid, HN02 has been reduced to a product that possibly containing NO. Beta, P form of Keggin [siw1204014- was found to be less active as compared to the a- [iw1204

Voltammetric detection of potassium ferricyanide mediated by multi walled carbon nanotube titanium dioxide composite modified glassy carbon electrode.

The MWCNT/TiO2 composite was homogeneously coated on the surface of GCE and applied in the electrochemical determination of 0.1 mM potassium ferricyanide in 0.1 M Na2HPO4 (pH 8.5). The redox couple of potassium ferricyanide with current enhancements of 3.0-3.1 folds was obtained using the MWCNT/TiO2/GCE when compared with unmodified GCE. A linear calibration plot showed a correlation coefficient of 0.999, with detection limits of 48.6 μM (100 mV/s scan rate) and 1.1 μM (5 mV/s scan rate) in the concentration ranges of 0.01-0.2 mM of potassium ferricyanide. High sensitivity responses of 77.6 µA/mM for the anodic and of 68.9 µA/mM for the cathodic peak currents were also obtained with an excellent correlation coefficient of 0.999. Based on plot of peak current against peak potential, the zero-current potentials were obtained as =209 mV and =189 mV. Diffusion coefficient was found as 1.52x10-5cm 2/s from chronocoulometry study. The effect of temperature study was carried at 10 oC – 80oC and activation energy obtained was 5.8-6 kJ/mol. The morphology of composite surface was examined by scanning electron microscopy

Electrocatalytic oxidation of ascorbic acid mediated by ZnO microcrystalline modified glassy carbon electrode.

Modification of a glassy carbon (GC) electrode surface by adhered microparticles of zinc oxide (ZnO) using electrochemical performance of microparticles of ZnO/GC electrode shows excellent electrocatalytic activity towards the oxidation of ascorbic acid in 0.1 M KH2PO4 electrolyte solution by cyclic voltammetry (CV). This paper seeks to critically examine the modification of GC electrode with Zinc oxide microparticles and the effect on oxidation of ascorbic acid using cyclic voltammetry technique. ZnO/GC electrode exhibited obvious enhancing and electrocatalyzing effect as it causes the oxidation current of ascorbic acid to increase by 1.5 times as compared to bare GC electrode. The sensitivity under conditions of cyclic voltammetry is significantly dependent on pH and ZnO dosage. The variation of scan rate study shows that the system undergoes diffusion-controlled process. Diffusion coefficient and rate constant of ascorbic acid were determined using hydrodynamic method (rotation disk electrode)with values of 5.4 x 10-6cm2s-1 and 2.5x 10-3cms-1 respectively for unmodified electrode, while the values of diffusion coefficient and rate constant of ascorbic acid using ZnO/GC electrode were 5.7 x10-6cm2s-1 and 2.1x10-3cms-1 respectively

Electrochemical detection of paracetamol at multi wall carbon nanotubes/titanium dioxide composite modified electrode.

Electrochemical behaviour of paracetamol at the multi wall carbon nanotubes/titanium dioxide (MWCNT/TiO2) composite film modified glassy carbon electrode (GCE) via solvent casting method was studied. It is shown that the MWCNT/TiO2/GCE exhibits remarkable improvement in analytical response as compared to other electrodes. Comparing the responses of the MWCNT/ TiO2/GCE with that obtained at the unmodified glassy carbon electrode, the peak currents were enhanced significantly by 8.5 folds (oxidation peak) and 11.0 folds (reduction peak), which showed stable response with enhanced selectivity and sensitivity. A linear calibration plot having a correlation coefficient of 0.991 was obtained in the concentration range of 0.01-0.12 mM paracetamol. The detection limit for the detection of paracetamol was calculated as 11.77 μM based on 3 σ/m. The method was applied in the determination of paracetamol in commercial tablets. The recoveries of the composite modified electrode obtained were 95.2 and 96.2 % for five determinations

Assessment of phytochemical content, polyphenolic composition, antioxidant and antibacterial activities of Leguminosae medicinal plants in Peninsular Malaysia

Background: Many medicinal plants from Leguminosae family can be found easily in Malaysia. These plants have been used as traditional medicines by local ethnic groups, where they are prepared as decoction, pastes for wound infections, and some have been eaten as salad. This paper focused on the assessment of antioxidant potential, antibacterial activity and classes of phytochemicals of nine plants from the Leguminosae family. Methods: Acacia auriculiformis, Bauhinia kockiana, Bauhinia purpurea, Caesalpinia pulcherrima, Calliandra tergemina, Cassia surattensis, Leucaena leucocephala, Peltophorum pterocarpum, and Samanea saman were extracted with aqueous methanol and dichloromethane:methanol mixture to test for antioxidant and antibacterial activities. The Folin-Ciocalteu assay was conducted to quantify the total phenolic content and 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay was used to determine the free radical quenching capacity. Antibacterial activity was assessed using disc diffusion (Kirby-Bauer) assay. Screening for major classes of phytochemical was done using standard chemical tests. Results: B. kockiana flowers and C. pulcherrima leaves contained high total phenolic content (TPC) and strong DPPH radical scavenging ability with TPC of 8280 ± 498 mg GAE/100 g, IC50 of 27.0 ± 5.0 μg/mL and TPC of 5030 ± 602 mg GAE/100 g, IC50 of 50.0 ± 5.0 μg/mL respectively. Positive correlation was observed between TPC and free radical scavenging ability. Most extracts showed antibacterial activity against Gram positive bacteria at 1 mg, while none showed activity against Gram negative bacteria at the same dose. All extracts (except Samanea saman flower) showed antibacterial activity against two strains of methicillin resistant Staphylococcus aureus (MRSA) with MID values ranging between 100 μg/disc and 500 μg/disc. Conclusion: The potential source of antioxidant and antibacterial agents, especially for MRSA infection treatments were found in B. kockiana, C. pulcherrima, C. tergemina and P. pterocarpum. These preliminary results would be a guide in the selection of potential candidates for further pharmacological study and in search of new drug candidate in treating MRSA infections

Electrocatalytic oxidation of ascorbic acid mediated by lithium doped microparticles Bi2O3/MWCNT modified glassy carbon electrode

Use of a lithium doped Bismuth oxide and MWCNT modified glassy carbon electrode (Bi2O3/Li+/CNT/GC) enhance the oxidation current of ascorbic acid during cyclic voltammetry compared to bare GC and (Bi2O3 /Li+/ CNT) modified electrode. Peak potential was observed to shift slightly to less positive value by about 220 mV and current was significantly enhanced by about two folds. The sensitivity under conditions of cyclic voltammetry is significantly dependent on pH, temperature, electrolyte and scan rate. The result of scanning electron micrograph shows that the size increased slightly by < 1 μm after electrolysis using Bi2O3 /Li+/ CNT modified electrode. The detection limit of this modified electrode was found to be 50μM. The oxidation current of ascorbic acid decreased slightly after the first cycle and became stable with minor decreases after second cycle. It is therefore evident that the Bi2O3/CNT modified GC electrode possesses some degree of stability. Potential use of Bi2O3/CNT as a useful electrode material is therefore clearly evident

Electrocatalytic oxidation of paracetamol mediated by lithium doped microparticles Bi2O3/MWCNT modified electrode.

Use of a lithium doped bismuth oxide and multi-walled carbon nanotubes modified glassy carbon electrode (Bi2O3/Li+ /CNT/GC) enhancethe oxidation current of paracetamol during cyclic voltammetry compared to bare glassy carbon electrode and (Bi2O3 /Li+ /CNT) modifiedelectrode. Peak potential was observed to shift slightly to less positive value by about 220 mV and current was significantly enhanced byabout 3.2 folds. The sensitivity under conditions of cyclic voltammetry is significantly dependent on pH, temperature and scanrate.Calibrationplot reveals linearity from the range 5.0 × 10-7-2 × 10-3M with a correlation coefficient of 0.998. The detection limit was estimated to be7.4 × 10 -7M. Practically; Bi2O3 /CNT modified electrode could be used for the determination of parecetamol in tablet samples

Electrochemical oxidation of ascorbic acid mediated by carbon nanotubes /Li+/ carbon paste modified solid electrode.

Multi-walled carbon nanotube (MWCNT) was used to modify BPPG electrode because of its unique structure and extraordinary properties. MWCNT modified electrode exhibited obvious enhancing and electrocatalyzing effects to the oxidation of ascorbic acid using cyclic voltammetry technique. MWCNT was bonded on BPPG electrode surface using carbon paste with ratio of 30% (w/w) carbon paste (binder): 70% (w/w) MWCNT. This method of modification has lowered the capacitance background current and enabled lower detection limit of ascorbic acid concentration. The electrical conductivity property of MWCNT modified electrode was further improved with the intercalation with lithium ion and resulted in current enhancement of 2 times on the oxidation current of ascorbic acid.Parameters of pH and temperature showed significant relation to the sensitivity of MWCNT modified electrode. Under the optimized parameters, the calibration curve constructed was linear up from 50 µM to 5 mM with sensitivity of 34.5 mA M-1. The practical application of MWCNT modified electrode was demonstrated with Vitamin C pill and orange juice. Good reproducibility and recovery of ascorbic acid concentration showed the feasibility of MWCNT modified electrode to be used in the detection of ascorbic acid in aqueous solution. This also proposed MWCNT modified BPPG electrode possessed advantages such as low detection limit, high stability, low cost and simplicity in fabrication

Optimization of metabolite extraction protocols for untargeted metabolite profiling of mycoparasitic Scytalidium parasiticum using LC-TOF-MS

Basal stem rot disease of oil palm caused by Ganoderma boninense is one of the most devastating diseases in oil palm plantation resulting in low yield, loss of palm stands and shorter replanting cycle. To-date, there is no effective treatment for Ganoderma infected palms. Control measures, either chemical or cultural approaches, show varying degrees of effectiveness. The application of biological control agents which is environmental-friendly could be an attractive solution to overcome the problem. Earlier, we had isolated a mycoparasite, Scytalidium parasiticum, from the basidiomata of Ganoderma boninense. In vitro assay and nursery experiment showed that this fungus could suppress Ganoderma infection and reduce disease severity. However, metabolites which might contribute to the antagonistic or mycoparasitic effect remain unknown. In the current study, optimization of fungal sample processing, extraction, and analytical procedures were conducted to obtain metabolites from the maize substrate colonized by mycoparasitic ascomycetous Scytalidium parasiticum. This technique capable of producing sexual spores in sac-like organs. Untargeted metabolomics profiling was carried out by using Liquid Chromatography Time of Flight Mass Spectrometry (LC-ToF-MS). We found that S. parasiticum in both liquid- and solid-state cultivation gave higher metabolite when extracted with 60% methanol with 1% formic acid in combination with homogenisation methods such as ultrasonication and grinding. The findings from this study are useful for optimisation of metabolite extraction from other fungi-Ganoderma-plant interactions

Electrochemical oxidation of L-cysteine mediated by a fullerene-C60-modified carbon electrode

Use of a glassy carbon electrode modified by adhered microcrystals of fullerene-C60 mediates the oxidation of cysteine in the presence of aqueous potassium-containing electrolytes. Under conditions of cyclic voltammetry, the potential for the oxidation of cysteine is lowered by approximately 100 mV and current is enhanced significantly relative to the situation prevailing when a bare glassy carbon electrode is used. Additional mediation occurs when the potential range covered includes that of C60/C60n− redox couples. The sensitivity under condition of cyclic voltammetry is significantly dependent on pH, temperature and C60 dosage. Excellent analytical and/or recovery data are obtained with vitamin pill, cassamino acid (hydrolyzed casein) and for a range of beverages