3.7. Copper-Chelating Ability

The ability of the extracts to chelate copper ions was determined using the method described by Domazetovic et al. [84]. Pyrocatechol violet, the reagent used in this assay, can associate with certain cations, such as aluminum, copper, bismuth, and thorium. In the presence of chelating agents, this combination is not formed, resulting in decreased staining. This reduction thus allows for the estimation of the chelating activity of copper ions from fucoidans. The test was performed in 96-well microplates with a reaction mixture containing different concentrations of the samples (0.1–2.0 mg/mL), pyrocatechol violet (4 mM), and copper II sulfate pentahydrate (50 mg/mL). The solution in each well was mixed using a micropipette, and the absorbance was measured at 632 nm. The chelating effect was calculated using the corresponding absorbance in the formula given below, where the blank represents the absorbance in the absence of chelating agents.