Controllable functionalization of hydroxyl-terminated self-assembled monolayers via catalytic oxa-Michael reaction.

Traditional strategies for the functionalization of materials displaying hydroxyl groups either require active esterification reagents or involve the nucleophilic attack of the hydroxyl group toward electrophilic groups. The former tends to hydrolyze in aqueous solutions while the latter occurs under harsh conditions. Herein, the authors reported a new method for the functionalization of hydroxyl groups on the surface via catalytic oxa-Michael addition with vinyl sulfones. Using hydroxyl group terminated self-assembled monolayers as a model surface, a series of organocatalysts were screened and triphenylphosphine stood out for the best catalytic activity. The catalytic reaction on the surface was characterized by x-ray photoelectron spectroscopy. The information of reaction kinetics was obtained using static water contact angle measurements. Once conjugated with ligands onto the functionalized surfaces, the multivalence binding of proteins was investigated by quartz crystal microbalance experiments. By varying the reaction conditions, e.g., catalyst types and reaction times, ligands can be anchored with a controllable density, which would be helpful to establish the relationships between ligand density and bioactivity.