Glycopolymer-Grafted Nanoparticles: Synthesis Using RAFT Polymerization and Binding Study with Lectin

The weak binding between carbohydrates and proteins is a major constraint toward the development of carbohydrate-based therapeutics. To address this, here we report the synthesis of glycopolymer (GP)-grafted silica nanoparticles (SiNP) by using reversible addition-fragmentation chain transfer (RAFT) polymerization through the grafting from approach using a multistep process. GP chains of various lengths with controlled molecular weight and narrow polydispersities were grown on the RAFT agent anchored SiNP surface using mannosyloxyethyl methacrylate (MEMA) as a glycomonomer. Spectroscopic (FT-IR, NMR) and thermogravimetric studies confirmed the grafting of poly(MEMA) chains on the SiNP surface and also showed that the dry DMF is a better solvent as compared to water/ethanol mixture for carrying out the MEMA polymerization on SiNP surface. The mean diameter of the dry GP-grafted SiNPs (GP-g-SiNPs) obtained from microscopic studies was in the range 50-60 nm, whereas the hydrodynamic diameter as obtained using light scattering measurements varied between 90 and 165 nm depending on the chain length of poly(MEMA). Hydrolysis of silica cores using aqueous HF enabled characterization of cleaved polymer using GPC, and the obtained unimodal chromatogram and narrow PDI confirmed that the polymerization proceeded through the RAFT mechanism. GP-g-SiNPs displayed stronger binding to the mannose specific lectin, Concanavalin A, owing to the larger positive binding entropic contribution which resulted in an association constant that is 800- and 400-fold stronger than that of monomeric mannose and GP chains, respectively.