Preparation and properties of thermo- and pH-responsive polypeptide bearing OEG and aldehyde pendants

OEGylated polypeptide bearing triethylene glycol monomethylether (OEG(3)) and poly(ethylene glycol) methyl ether 350 (OEG(7)) were first prepared by copper-mediated 1,3-dipolar cycloaddition. H-1 NMR, FTIR, and GPC results indicated the successful conjugation of oligo(ethylene glycol) (OEG) pendants with high grafting efficiency (>= 98%). Variable temperature UV-vis spectroscopy revealed a reversible lower critical solution temperature (LCST)-type phase transition of the resulting polypeptides. The LCST-type cloud point temperature (T-cp) in the range of 20-60 degrees C can be readily tuned by changing the OEG(3) and OEG(7) composition. Thermo- and pH-responsive polypeptide was prepared by first conjugating of OEG and 6-aldehyde hexyl pendants, then crosslinking in the presence of 1,6-hexanediamine, yielding OEGylated polypeptide bearing pH-labile imine bonds. The resulting polypeptide showed pH-responsive property and less pronounced thermoresponsive property at high pH values (i.e., >= 6.15) and noticeable thermo- and pH- dual responsive properties at low pH values (i.e., <= 5.80).