Synthesis of Hetero-Telechelic α,ω Bio-Functionalized Polymers

Reversible addition−fragmentation chain transfer (RAFT) polymerization was used to synthesize poly[diethylene glycol monomethylether methacrylate] (PDEGMA) (M n = 6250 g/mol, PDI = 1.14) with a pentafluorophenyl (PFP) activated ester and a dithioester end group. The hormone thyroxin (T4) was quantitatively attached to the PFP activated ester α end group via its amino group. The ω-terminal dithioester was not harmed by this reaction and was subsequently aminolyzed in the presence of N-biotinylaminoethyl methanethiosulfonate, yielding a polymer with a thyroxin and a biotin end group with very high heterotelechelic functionality. The polymer was characterized by 1H, 13C, and 19F NMR, UV−vis, and IR spectroscopy and gel permeation chromatography. The thyroxin transport protein prealbumin with two thyroxin binding sites and streptavidin, which has four biotin binding sites, was conjugated using the biotarget labeled polymer, resulting in the formation of a protein−polymer network, confirming the heterotelechelic nature of the polymer. Polymer−protein microgel formation was observed with dynamic light scattering. To realize a directed protein assembly, prealbumin was immobilized onto a surface, exposing one of its two thyroxin binding groups and thus allowing the conjugation with the thyroxin α end group of the heterotelechelic polymer. The biotin ω end group of the attached polymer layer enabled the subsequent immobilization of streptavidin, yielding a defined multilayer system of two proteins connected with the synthetic polymer (efficiency of streptavidin immobilization 81% based on prealbumin). Without the polymer, no streptavidin immobilization occurred. The layer depositions were monitored by surface plasmon resonance. The synthetic approach of combining PFP activated esters with functional MTS reagents presents a powerful method for obtaining well-defined heterotelechelic (bio-) functionalized polymers.