Multidentate Polysarcosine-Based Ligands for Water-Soluble Quantum Dots

Abstract

We describe the synthesis of heterotelechelic polysarcosine polymers and their use as multidentate ligands in the preparation of stable water-soluble quantum dots (QDs). Orthogonally functionalized polysarcosine with amine and dibenzocyclooctyl (DBCO) end groups is obtained by ring opening polymerization of N-methylglycine N-carboxyanhydride with DBCO amine as initiator. In a first postpolymerization modification step, the future biological activity of the polymeric ligands is adjusted by modification of the amine terminus. Then, in a second postpolymerization modification step, azide functionalized di- and tridentate anchor compounds are introduced to the DBCO terminus of the polysarcosine via strain-promoted azide-alkyne cycloaddition (SPAAC). Through the separate synthesis of the anchor compounds, it is possible to ensure reproducible introduction of a well-defined number of multiple anchor groups to all polymers studied. Finally, the obtained multidentate polymeric ligands are successfully used in the ligand exchange procedures to yield stable, water-soluble QDs. As polysarcosine-based ligands can provide biocompatibility, prevent nonspecific interactions, and simultaneously enable specific targeting, the systems presented here are promising candidates to provide QDs well suitable for ex vivo analytics or bioimaging.