Ultrafine Selective Metal-Complexing Nanoparticles:  Synthesis by Microemulsion Copolymerization, Binding Capacity, and Ligand Accessibility

Abstract

Stable translucent aqueous suspensions of ligand-functionalized nanoparticles, with average diameters ranging from 12 to 20 nm and containing from 0.25 to up to 0.75 mmol of ligand/g, are readily obtained by copolymerization in oil-in-water microemulsions of a polymerizable tetraaza macrocycle, vinylbenzylcyclam (cyclam: 1,4,8,11-tetraazacyclotetradecane). These nanoparticles exhibit a very high selectivity for cupric ions with binding capacities of up to 0.65 mmol of Cu/g as well as a remarkable ligand accessibility, deduced from spectrophotometric titration, with about 75% of the cyclam residues located near the surface for nanoparticles in the 12−13 nm range. Core−shell bimetallic nanoparticles are obtained by cation exchange. The cyclam-functionalized nanoparticles are comparable to high-generation PAMAM dendrimers in their ability to complex metals.