Modification and Analytical Characterization of Polyol Based Polymers for Ice Recrystallization Inhibition and Thermal Hysteresis Activity

Ice formation is a global issue that poses serious challenges for many applications. Certain species in colder regions of the world have adapted to that climate by producing antifreeze (glycol)proteins (AF(G)P) which exhibit ice recrystallization inhibition (IRI). Although several synthetic approaches for the exploitation of these proteins have been investigated, challenges remain in the synthetic design of biomimics. Poly(vinyl alcohol) (PVA) is by contrast a quite simple macromolecular structure and happens to be IRI active, yet many fundamental relationships between structure and performance remain. Here, we were inspired by anti-freeze proteins (AFP), such as the ice-facing right-handed parallel beta-helix in the AFP present in the desert beetle Anatolica polita (ApAFP752) presenting threonines in an ordered array. Drawing comparison between the distance between hydrogen bonding sites in that array, we describe our approach to position small organic molecules with known anti-freeze properties (such as ethylene glycol) pendent to a host polymer chain with consideration of their conformational freedom. We have built systematic variations into both the backbone and side-chain structures and have observed tremendous impact on IRI behavior for several of our polymer scaffolds. FT-IR and NMR were used for confirmation of the functionalized polymer structures, where differential scanning calorimetry (DSC), XRD, and microscopy assays were used to observe the ice IRI behavior. Thermal hysteresis activity (THA), a depression of the freezing point without impact on the melting point (of water, here) is also characterized and corroborated with the IRI trends. The findings in this study will help pave the path for rational design of synthetic AF polymers, useful for applications such as anti-icing coatings through to cryo-preservation methods for organ transport.

Learning Objectives:

1. Define and show application of a variety of analytical performance assays for anti-freeze related behavior for proteins, peptides, and polymers

2. Contrast the performance, via these analytical techniques, of small molecule versus macromolecular performance of similar functionality

3. Understand key structure/property relationships for macromolecule-ice interaction