Abstract
This work deals with the formation of supramolecular complexes between ascorbic acid (AA), the guest, and β-cyclodextrin (β-CD), the host, that was first potentiodynamically immobilized on the surface of a carbon paste electrode (CPE) throughout the formation of a β-CD-based conducting polymer (poly-β-CD). With the bare CPE and the β-CD-modified CPE, an electrochemical study was performed to understand the effect of such surface modification on the electrochemical response of the AA. From this study it was shown that on the modified-CPE, the AA was surface-immobilized through formation of an inclusion complex with β-CD, which provoked the adsorption of AA in such a way that this stage became the limiting step for the electrochemical oxidation of AA. Moreover, from the analysis of the experimental voltammetric plots recorded during AA oxidation on the CPE/poly-β-CD electrode surfaces, the Gibbs’ standard free energy of the inclusion complex formed by the oxidation product of AA and β-CD has been determined for the first time, ∆G0inclus = −36.4 kJ/mol.
Highlights
Ascorbic acid, ascorbic acid (AA), termed vitamin C (Figure 1a), is quite an important biocomponent widely present in living organisms [1] as anti-oxidation promoter
In the studies carried out to form supramolecular complexes [14,15,16] with CAs in the presence of the AA [2,3,4,5,6,7,17], it was important to study the supramolecular interactions that the electrode surface-modifying agents may induce in the AA, when membranes are formed
In this study [32] we found that two different structures are energetically favored for this inclusion complex namely that formed by the interaction through the functional hydroxyl groups of the lactone in AA and the primary hydroxyl groups of the β-CD or the β-CD-AA complex formation through the alcohol group of AA, as is represented in Scheme 1
Summary
AA, termed vitamin C (Figure 1a), is quite an important biocomponent widely present in living organisms [1] as anti-oxidation promoter Such a wide scale presence in diverse biological media can be seen as the origin of interference problems, when analytical research studies aim to effect quantitative determinations of other biologically relevant analytes, which happen to be present in much smaller concentrations, but that are important, such as the catecholamines (CAs). It is important to mention that some complex polymers that include β-CD in their chemical structure have been reported for the controlled release of drugs [24,25,26,27]
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