Janice Limson

The interaction of melatonin and its precursors with aluminium, cadmium, copper, iron, lead, and zinc: An adsorptive voltammetric study

Limson J, Nyokong T, Day a S. The interaction of melatonin and its precursors with aluminium, cadmium, copper, iron, lead, and zinc: An adsorptive voltammetric study. J. Pineal Res. 1998; 24:15–21.

Antioxidant and Iron-Binding Properties of Curcumin, Capsaicin, and S-Allylcysteine Reduce Oxidative Stress in Rat Brain Homogenate

Research demonstrates that antioxidants and metal chelators may be of beneficial use in the treatment of neurodegenerative diseases, such as Alzheimers disease (AD). This study investigated the antioxidant and metal-binding properties of curcumin, capsaicin, and S-allylcysteine, which are major components found in commonly used dietary spice ingredients turmeric, chilli, and garlic, respectively. The DPPH assay demonstrates that these compounds readily scavenge free radicals. These compounds significantly curtail iron- (Fe2+) and quinolinic acid (QA)-induced lipid peroxidation and potently scavenge the superoxide anion generated by 1 mM cyanide in rat brain homogenate. The ferrozine assay was used to measure the extent of Fe2+ chelation, and electrochemistry was employed to measure the Fe3+ binding activity of curcumin, capsaicin, and S-allylcysteine. Both assays demonstrate that these compounds bind Fe2+ and Fe3+ and prevent the redox cycling of iron, suggesting that this may be an additional method through which these agents reduce Fe2+-induced lipid peroxidation. This study demonstrates the antioxidant and metal-binding properties of these spice ingredients, and it is hereby postulate that these compounds have important implications in the prevention or treatment of neurodegenerative diseases such as AD.

Melatonin protects against copper‐mediated free radical damage

Copper is an essential trace element which forms an integral component of many enzymes. While trace amounts of copper are needed to sustain life, excess copper is extremely toxic. Copper has been implicated in various neurodegenerative disorders, such as Wilsons and Alzheimers diseases. Previous studies showed that melatonin, the principle secretory product of the pineal gland, binds Cupric chloride (Cu2+) and that this may have implications in copper‐induced neurodegenerative diseases. In the present study, in vitro copper‐mediated lipid peroxidation was induced. Melatonin (5 mM) protected against copper‐mediated lipid peroxidation in liver homogenates. Electron micrographs of in vivo administered Cu2+ and melatonin show that melatonin affords some protection to rat hepatocytes in the presence of copper. Electrochemical studies performed show that melatonin, in addition to binding Cu2+, may provide protection against copper‐mediated free radical damage by binding Cu1+. The findings of these studies provide further evidence for the neuroprotective role of melatonin.

6-Hydroxymelatonin converts Fe (III) to Fe (II) and reduces iron-induced lipid peroxidation.

Disorders of iron accumulation are known to produce hepatotoxicity. Agents, which can reduce Fe(3+) to a more usable form Fe(2+) could potentially limit such damage. Since it has been previously demonstrated that the pineal secretory product, melatonin, is able to bind iron, we decided to investigate the potential protective properties of the principal melatonin metabolite and degradant, 6-hydroxymelatonin (6-OHM). Using adsorptive cathode stripping voltammetry (AdCSV) we showed that Fe(3+) in the presence of 6-OHM is converted to Fe(2+). We further demonstrated that 6-OHM reduces the Fe(2+)-induced rise in lipid peroxidation in rat liver homogenates. The results imply that 6-OHM facilitates the conversion of Fe(3+) to Fe(2+) which is a more biologically usable form of iron. While such a conversion could also potentially make more Fe(2+) available for driving the Fenton reaction and the consequent generation of the dangerous hydroxyl radical, 6-OHM is able to quench these radicals, thereby providing tissue protection.

Substituted catechols as complexing agents for the determination of bismuth, lead, copper and cadmium by adsorptive stripping voltammetry

Copper, cadmium, lead and bismuth (> 5 μg ml−1) are determined by adsorptive cathodic stripping voltammetry (AdCSV) on a mercury film glassy carbon electrode, using catechol, 4-methylcatechol, 4-t-butylcatechol and resorcinol as complexing ligands. Complexes of lead, copper and bismuth with resorcinol showed the largest increase in current with increase in metal concentration, whereas complexes of these metals with 4-t-butylcatechol showed the lowest current response. Cadmium showed a different behaviour from the other three metals in that the highest current response was observed with 4-methylcatechol. The four metals could be determined simultaneously in the presence of resorcinol, although considerable interference was observed between bismuth and copper.

Applications of polymerized metal tetra-amino phthalocyanines towards hydrogen peroxide detection

This work reports the use of metallo tetra-amino phthalocyanines (MTAPc, M = Co and Mn) polymer thin films on gold and glassy carbon electrode surfaces for the detection and monitoring of hydrogen peroxide (H2O2). The polymer-modified electrodes were characterized using electrochemical and microscopic-based methods. Atomic force microscopy (AFM) was used to study the bare and polymer-modified ITO surfaces. The electrocatalytic reduction of H2O2 with glassy carbon polymer-modified electrodes gave higher current densities compared to their gold counterparts. The electroanalytical properties of H2O2 were obtained using a real-time calibration curve of the amperometric determination in pH 7.4 aqueous solution. The limits of detection (LoD) of the polymer-modified electrodes towards electroreduction of H2O2 were of the order of 10–7 M, with high sensitivity ranging from 6.0–15.4 mA.mM-1.cm-2.

Cimetidine: antioxidant and metal‐binding properties

Cimetidine is one of the most potent H2 receptor antagonists for inhibiting excessive histamine‐induced acid secretion and is currently used worldwide to treat peptic ulcers. In this study, levels of free radicals were assessed and the ability of cimetidine to act as an antioxidant was determined using nitroblue‐tetrazolium assay and lipid peroxidation assays. Free radical generation in the brain is promoted by the presence of iron, as occurs in the Fenton reaction. The results show that cimetidine reduces the generation of superoxide anion formed in the nitroblue‐tetrazolium assay. In addition, cimetidine (1 mm) is able to reduce the iron‐induced rise in lipid peroxidation in rat brain homogenates. Electrochemistry, UV/Vis spectroscopy and HPLC experiments show metal‐ligand interactions between cimetidine and transition metals. The results imply that cimetidine provides a neuroprotective effect by binding to iron and copper, thus making them unavailable for free radical production.

Probing fundamental film parameters of immobilized enzymes--towards enhanced biosensor performance. Part I--QCM-D mass and rheological measurements.

Enzyme immobilization is an ever-growing research-area for both analytical and industrial applications. Of critical importance in this area are the effects of immobilization procedures upon the functionality of the immobilized biomolecules. Both beneficial and detrimental effects can be conferred through the selection and tuning of the immobilization procedure. Quartz-crystal microbalance with dissipation (QCM-D) has been previously used to great effect in tracking alterations to thin films of biomolecules immobilized onto quartz transducers. In this study, we investigate the ability of QCM-D to track and monitor film parameters of a monolayer of laccase immobilized on a series of self-assembled monolayers (SAMs), differing in lateral density of binding residues on the SAM and height of the SAM from the quartz surface. Both mass gains and rheological parameters for these varying surfaces were measured and trends later compared to the apparent enzyme kinetics of the immobilized laccase films, assessed electroanalytically (Paper II in this two part study). For covalent attachment of proteins, both shear and viscosity were increased relative to physically adsorbed proteins. An increase in lateral density of protein-binding surface of the SAM components was shown to increase the shear/viscosity of the resultant film while an increase in distance from the electrode (through incorporation of lysine linkers) was shown to decrease the shear/viscosity while simultaneously increasing the wet mass gain of the films. Shear and viscosity may be indicative of both enzyme denaturation and increased lateral protein packing within the film structure hence it is assumed that less distortion occurs with the inclusion of linkers which allow for more optimal protein immobilization.

Voltammetric Studies of Spinach Ferredoxin on a Glassy Carbon Electrode Modified with Cobalt(II) Tetrasulfophthalocyanine

Spinach ferredoxin has been studied electrochemically at a glassy carbon electrode (GCE) modified with cobalt(II) tetrasulfophthalocyanine ([Co(II)TSPc]4−). Anodic peak currents due to the oxidation of the cysteine component of ferredoxin were observed at 0.90 V (vs. Ag/AgCl) (pH 7.4, HEPES buffer). The magnitudes of the peak currents were dependent on pH. Catalytic oxidation of ferredoxin was also observed when the GCE was modified with cobalt(II) and oxomolybdenum(V) phthalocyanine [CoPc and OMo(OH)Pc, respectively], and with copper(II) tetrasulfophthalocyanine complexes ([Cu(II)TSPc]4−).

Developing Biosensors in Developing Countries: South Africa as a Case Study

A mini-review of the reported biosensor research occurring in South Africa evidences a strong emphasis on electrochemical sensor research, guided by the opportunities this transduction platform holds for low-cost and robust sensing of numerous targets. Many of the reported publications centre on fundamental research into the signal transduction method, using model biorecognition elements, in line with international trends. Other research in this field is spread across several areas including: the application of nanotechnology; the identification and validation of biomarkers; development and testing of biorecognition agents (antibodies and aptamers) and design of electro-catalysts, most notably metallophthalocyanine. Biosensor targets commonly featured were pesticides and metals. Areas of regional import to sub-Saharan Africa, such as HIV/AIDs and tuberculosis diagnosis, are also apparent in a review of the available literature. Irrespective of the targets, the challenge to the effective deployment of such sensors remains shaped by social and economic realities such that the requirements thereof are for low-cost and universally easy to operate devices for field settings. While it is difficult to disentangle the intertwined roles of national policy, grant funding availability and, certainly, of global trends in shaping areas of emphasis in research, most notable is the strong role that nanotechnology, and to a certain extent biotechnology, plays in research regarding biosensor construction. Stronger emphasis on collaboration between scientists in theoretical modelling, nanomaterials application and or relevant stakeholders in the specific field (e.g., food or health monitoring) and researchers in biosensor design may help evolve focused research efforts towards development and deployment of low-cost biosensors.