The importance of counterion association in the calculated binding constants of Ca2+-aminopolycarboxylate complexes

Abstract

There exist a number of chemical reactions and processes that have elevated concentrations of metal ions both in solution and as part of a precipitate. To reduce the undesirable effects of metal cations and improve the performance of the active materials in various chemical systems, the application of chelators is required. To this end, different types of chelators have been developed with high affinity towards various metal cations. However, many of the most effective chelators used are limited in biodegradability and could have an impact on environmental pollution. Hence, development of highly efficacious biodegradable alternatives with high affinity for metal cations is an emerging challenge. Electronic structure calculations can assist in predicting new bio-sourced and biodegradable chelators by estimating the binding affinity of metal ion-chelator systems in aqueous solution. In this work, using a set of benchmark aminopolycarboxylate ligands, we calculate binding affinities for a number of chelator-ion systems and investigate the effect of including counterion association on the calculated binding constant. It was found that the system charge neutrality significantly improves the correlation between calculated and experimental values. Furthermore, the influence of conformational flexibility of the chelator structure and pH of the aqueous solution were addressed. The discussed modification in calculation of the log K values considering the counterion association currently serves as a prediction basis and a potential design tool toward new bio-based chelators for applications in industry.