Search Results (3)

In this work, we measured the antioxidant capacity of capers (Capparis spinosa L.) and an important component, kaempferol, as scavengers of the superoxide radical anion using hydrodynamic voltammetry with a rotating ring disk electrode (RRDE). Comparing our electrochemical results to other natural products studied using this method, this work demonstrates that kaempferol is a stronger antioxidant than vitamin C, whereas caper extract has weaker antioxidant capability than olive oil. We also investigated the synergistic scavenging relationship between vitamin C and kaempferol and found it to be potent, as all the available superoxide radicals were consumed in the presence of both compounds. Such a dramatic RRDE result was observed for the first time in our laboratory. We then utilized computational Density Functional Theory (DFT) methods to establish a viable mechanism, reminiscent of that exhibited by superoxide dismutase (SOD) enzymes, for the scavenging behavior of kaempferol. In the enzymatic reaction, two molecules of the superoxide radical anion with the assistance of two protons are disproportioned into one molecule of hydrogen peroxide and one oxygen molecule. Our DFT results show kaempferol mimicking superoxide dismutase (SOD) action when one kaempferol molecule reacts with two superoxide radicals and two protons (which can be provided by ascorbic acid); i.e., kaempferol acts as a catalyst that is restored after a cycle of superoxide scavenging. This mechanism is consistent with our experimental RRDE results. Full article

In high concentrations, ionic species can be toxic in the body, catalyzing unwanted bioreactions, inhibiting enzymes, generating free radicals, in addition to having been associated with diseases like Alzheimer’s and cancer. Although ionic species are ubiquitous in the environment in trace amounts, high concentrations of these metals are often found within industrial and agricultural waste runoff. Therefore, it remains a global interest to develop technologies capable of quickly and accurately detecting trace levels of ionic species, particularly in aqueous environments that naturally contain other competing/inhibiting ions. Herein, we provide an overview of the technologies that have been developed, including the general theory, design, and benefits/challenges associated with ion-selective electrode technologies (carrier-doped membranes, carbon-based varieties, enzyme inhibition electrodes). Notable variations of these electrodes will be highlighted, and a brief overview of associated electrochemical techniques will be given. Full article

A detailed kinetic analysis of the pertinent physical processes underlying the operation of enzyme electrodes immobilized within alkane thiol self assembled monolayers is developed. These electrodes utilize a soluble mediator, which partitions into the monolayer, regenerates the active catalytic form of the enzyme and is re-oxidized at the underlying support electrode surface giving rise to a current which reflects kinetic events at the enzyme surface. Both the enzyme/substrate and enzyme mediator kinetics have been quantified fully in terms of a ping-pong mechanism for the former and Michaelis-Menten kinetics for the latter. The effect of substrate and mediator diffusion in solution have also been specifically considered and the latter processes have been shown to result in a complex expression for the reaction flux. Four limiting kinetic cases have been enumerated and simple expressions for the reaction flux in each of these rate limiting situations have been developed. Kinetic case diagrams have been presented as an aid to mechanistic diagnosis. The complicating effects of diffusive loss of reduced mediator from the enzyme layer have also been examined and the relation between the observed flux corresponding to reduced mediator oxidation at the support electrode and the substrate reaction flux in the enzyme layer have been quantified in terms of an efficiency factor. Results extracted from recently published practical realizations of immobilized monolayer enzyme systems have been discussed in the context of the proposed model analysis. Full article