Synthesis and characterization of nickel-nitrilotriacetic (Ni-NTA) functionalized dendrimers

Abstract

Immobilized metal affinity chromatography (IMAC) is a very popular protein purification technique in biochemistry. Resins are functionalized with nitrilotriacetic acid (NTA), a chelating group often charged before use with a divalent or trivalent metal, usually Ni (II). In IMAC using Ni-NTA, open coordination sites on nickel are bound by two imidazole ring side chains of a histidine tag, which has been added to the protein of interest. In this work, the Ni-NTA ligand commonly used in IMAC was tethered to a poly(amidoamine) (PAMAM) dendrimer. PAMAM dendrimers are hyperbranched macromolecules with a well-defined structure characterized by a central core, repetitive branching, and a doubling of the termini with each successive generation. Because the number of end groups can be readily altered by changing the generation of the dendrimer, dendrimers are ideal frameworks for displaying different numbers of Ni-NTA groups. For this study, NTA derivatives containing an azide were added to propargylated PAMAM dendrimers of generations 2, 3, 4, and 6 (G(2), G(3), G(4), and G(6), respectively) using Cu(I)- mediated triazole formation, or "click" chemistry. Characterization of new compounds was performed using 1 H nuclear magnetic resonance (NMR), 13 C NMR, infrared (IR) spectroscopy, and mass spectrometry (MS). The Ni-NTA functionalized dendrimers will be used to bind histidine-tagged proteins, allowing for the study of the effect of clustering a protein on its function.