Competitive ligand exchange of Fe3+ catecholate complexes with novel biobased chelators: a DFT-metadynamics investigation.

Abstract

The complexation of metal ions by polyphenolic compounds is a ubiquitous phenomenon in both natural and engineered systems, encompassing a vast multidimensional landscape of metal-ligand interactions. An important challenge in a range of applications, including textile care, is the efficient removal of stains formed by polyphenolic compounds coordinated to metal ions at the molecular level. In this study, we investigate the ligand-exchange process between a catecholate ligand coordinated to an Fe3+ center - a key molecular origin of persistent colored stains - and six candidate chelating ligands using ab initio molecular dynamics (AIMD) simulations. The selected ligands were chosen for their potential derivation from bio-based feedstocks, offering promising routes toward sustainable and environmentally benign stain-removal technologies. Our results reveal that effective metal-ion sequestration is governed not only by the thermodynamic stability of the resulting metal-ligand complexes but also by the kinetics of ligand exchange. Furthermore, we elucidate how the electronic structure of the incoming ligand influences the energetics of the exchange process and demonstrate the critical role of protonation state in determining both exchange accessibility and the relative stabilities of reactant and product complexes. Collectively, these findings provide molecular-level insights into Fe3+ chelation and ligand substitution mechanisms, advancing our understanding of structure-property relationships in metal binding. The knowledge generated in this work provides molecular-level insights into ligand exchange in a model Fe3+-catecholate system and may guide the development of novel bio-based chelating agents for stain-removal applications.

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