Chemodynamics of soft nanoparticulate metal complexes in aqueous media: basic theory for spherical particles with homogeneous spatial distributions of sites and charges

A theoretical discussion is presented to describe the formation and dissociation rate constants for metal ion binding by soft nanoparticulate complexants. The well-known framework of the Eigen mechanism for metal ion complexation by simple ligands in aqueous systems is the starting point. Expressions are derived for the rate constants for the intraparticulate individual outer-sphere and inner-sphere association and dissociation steps for the limiting cases of low and high charge densities. The charge density, binding site density, and size of the nanoparticle play crucial roles. The effects of the electrostatic potential and particle radius on the overall complexation reaction are compared with those for simple ligands. The limitations of the proposed approach for nanoparticulate ligands are discussed, and key issues for future developments are identified.