Electrochemical Characterization of Fe(II) Complexation Reactions at an Electrified Micro Liquid-Liquid Interface.

Phytoplankton growth in the open ocean is critical to carbon fixation and often limited by low iron concentrations. Owing to its low solubility, phytoplankton employ ligands for iron uptake; therefore, ligand binding characterization is important. Herein, a micro immiscible liquid/liquid interface was employed with four ligands through an electrochemically induced facilitated ion-transfer process. Ligands 1,10-phenathroline (phen), 1-nitroso-2-naphthol (N2N), 2-(2-thiazolylazo)-p-cresol (TAC), and salicylaldoxime (SAL), where tested using established facilitated ion-transfer thermodynamics combined with differential pulse voltammetry. Three metal ion/ligand binding stoichiometries were observed for Fe²⁺:phen, whereas only one was observed with Fe²⁺ with SAL, N2N, and TAC. Overall binding constants were calculated such that binding strengths can be ranked highest to lowest as phen>N2N>TAC>SAL. Additionally, the formal ion transfer for Fe²⁺ (0.66 V) for an aqueous/1,2-dichloroethane interface was also determined. [ABSTRACT FROM AUTHOR]