An electrochemical approach for detecting copper-chelating properties of flavonoids using disposable pencil graphite electrodes: Possible implications in copper-mediated illnesses

We have studied the electrochemistry of eight flavonoids belonging to four flavonoid sub-classes: flavone, flavonol, flavanol and anthocyanidin using pencil graphite electrodes (PGEs). We present the electrochemistry of delphinidin, cyanidin and catechin gallate for the first time. The use of electrochemical methods in connection with PGE in the study of flavonoids and their interaction with copper ions has not been previously reported. Our results compare favorably with previously reported studies, which utilised glassy carbon electrodes (GCEs) for the detection of flavonoids. We calibrated all eight flavonoids (r(2) > 0.9620), six of them at at least two peak potentials. The relative standard deviation (R.S.D.) for peak potential was < 5.0% and peak height was < 10.0%; thus, this method could be used to characterise and quantify flavonoid-containing extracts (purified). An inverse relationship between oxidation potential and metal-chelation was established. Oxidation potential was influenced by the location of OH groups relative to each other, the oxidation state of the pyranose ring, the presence of a C-4-oxo group and the total number of OH groups. Further, we showed that the steric configuration of the compound influenced the reactivity. The order of flavonoid reactivity to Cu(II) ions was myricertin = catechin gallate > quercetin > delphinidin = baicalein > cyanidin > catechin. These findings may be significant in neuroscience and metal toxicological studies, in which copper ions have been reported to play a crucial role in initiating and/or promoting the progression of diseases such as Alzheimer's and Parkinson's. (c) 2005 Elsevier B.V. All fights reserved.