Comparison of the Ice-Regulating Properties of Side-Zwitterionic Poly(vinyl alcohol)-Poly(l-methionine) and Poly(ethylene glycol)-Poly(l-methionine).

For controlling ice nucleation and growth, bioinspired polypeptides were developed to mimic the functions of natural antifreeze (glyco)proteins, such as functionalized poly(l-methionine) (PMet) with different side groups showing moderate ice recrystallization inhibition (IRI) activity. In order to strengthen the ice-binding ability, in this work, poly(vinyl alcohol)-poly(l-methionine) is synthesized in comparison with poly(ethylene glycol)-poly(l-methionine) using macromolecular initiators, and the ice-control activities of their side-modified polypeptides, PVA-PMet-COOH and PEG-PMet-COOH in zwitterionic forms, are systematically examined. Results show that PVA-PMet-COOH exhibits potent IRI activity (mean largest grain size 28.2 ± 3.7% relative to PBS) at 0.3 mg/mL, similar to PVA via strong interaction with water molecules observed by the sucrose "sandwich" ice shaping assay, whereas PEG-PMet-COOH displays enhanced IRI activity at 50 mg/mL. Both PVA-PMet-COOH and PEG-PMet-COOH can increase the ice nucleation temperature at 5 mg/mL or higher concentrations owing to their zwitterionic structures. Analyses using differential scanning calorimetry and low-field nuclear magnetic resonance are performed to elucidate the difference in the underlying ice-control mechanism. This study provides an attempt to prepare zwitterionic polypeptides with potent IRI activity and nucleation-regulating capacity.