PAMAM dendrimers on controlled pore glass: The effect of tethered dendrimer size and tethered affinity groups NTA and terpy on metal ion and indicator dye uptake

PAMAM dendrimer monolayers were covalently immobilized onto controlled pore glass (CPG) particles as platforms to graft the metal ion affinity groups nitrilotriacetic acid (NTA) and terpyridine (terpy). Functional end group analyses, metal ion loading capacities and indicator dye complexation to metal affinity sites were measured as a function of dendrimer size. Metal ions were efficiently extracted from 5 ppm solutions flowing through a packed column of modified CPG and loading capacities increased linearly with immobilized dendrimer size at pH 7.2 as determined by atomic absorption spectroscopy. The dendrimer tethered terpy affinity group was surprisingly effective in aqueous solution for extraction of Zn, Cu and Pb ions, but not as effective for Ni ions when compared to tethered NTA. Metal ion indicator dyes bind to the immobilized metal affinity sites showing a generational dependence. Subsequent addition of pyrophosphate releases dye back into solution as a demonstration of an immobilized indicator displacement assay.