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Electrochemical properties of 5-O- caffeoylquinic acid investigated by square-wave voltammetry and differential pulse voltammetry

Chlorogenic acids (CGAs) are one of the groups of polyphenolic compounds widely distributed in different plant materials. Chemically, CGAs are family of different esters formed between (-)- quinic acid and certain trans-cinnamic acids, most commonly caffeic, ferulic and p-coumaric acids. In this study the electrochemical properties one of the most abundant CGAs in plants, namely 5-O-caffeoylquinic acid (5-CQA) was studied by square-wave voltammetry (SWV) and differential pulse voltammetry (DPV). The electrochemical properties of 5-CQA were compared with the electrochemical properties of caffeic acid (CFA), main structural moiety of 5-CQA. The study reveals that electrochemical properties of 5-CQA strongly depends on its chemical structure and electronic properties, particularly on electron-donating effect of −OH and −CH=CH− groups, and a strong electron- withdrawing effect of ester (−COOR) group in the chemical structure of 5-CQA molecule. SWV and DPV measurements show that electrochemical oxidation/reduction of 5-CQA at a glassy carbon electrode (GCE) is reversible, pH-dependent, two electron-two proton process. The oxidation/reduction processes occurred on the catechol moiety (ortho-dihydroxyl groups) in the structure of 5-CQA molecule. The oxidation product(s) relatively strongly adsorb on the GCE surface, especially at higher concentration of 5-CQA. It was observed that the anodic peak current of 5-CQA show maximum in solution of pH 7, due to the maximum concentration of 5-CQA- anion at this pH value. The electrode reaction proceeded in the solution of 5-CQA is diffusion controlled process. The anodic peak current of 5-CQA show linear relationship with the concentration in the concentration range 5-50 µmol L-1, with low limit of detection (LOD) of 7.7·10-7 mol L-1 for SWV and 1.2·10-6 mol L-1 for DPV measurements. SWV and DPV of coffee samples have shown that electrochemical properties of water coffee extracts were very similar to that of investigated 5-CQA. Therefore, SWV and DPV can be used as very sensitive and selective methods for determination of CQAs content (and CGAs content) in different coffee samples.

chlorogenic acids, differential pulse voltammetry, square-wave voltammetry, coffee

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