A Close Cognition of Charged Poly(l-methionine) Derivatives for Antifreeze

Ice formation poses a significant challenge across various fields, from industrial processes to biological preservation. Developing antifreeze agents and recognizing the antifreeze mechanism have gained considerable attention. Herein, a series of poly(l-methionine) derivatives, poly(S-carboxymethyl-l-methionine sulfonium) (PMetA), poly(S-methyl-l-methionine sulfonium chloride) (PMetM), and poly(S-carbamidomethyl-l-methionine sulfonium chloride) (PMetAM), with carboxyl, methyl, and acetamide groups, respectively, are synthesized and investigated for antifreeze. The relationship between the polymer structure and the ice recrystallization inhibition (IRI) activity is examined, suggesting that zwitterionic PMetA shows the highest IRI activity, about 27.0 ± 3.9% at 10 mg mL^-1 relative to that of water. Results of low-field nuclear magnetic resonance and differential scanning calorimetry indicate that the IRI activity is associated with the activation energy for hydrogen bond breakage. PMetA exhibits acceptable cytocompatibility at 10.0 mg mL^-1 and a good cryoprotective efficiency. This finding provides a valuable insight into the antifreeze mechanism, contributing to the development of potent cryoprotectants.