Slow Propagation of Ice Binding Limits the Ice-Recrystallization Inhibition Efficiency of PVA and Other Flexible Polymers

Abstract

Ice recrystallization inhibitors (IRI) are of critical importance in biology, cryopreservation of cells and organs, and frozen foods. Antifreeze glycoproteins (AFGPs) are the most potent IRI. Their cost and cytotoxicity drive the design of synthetic flexible polymers that mimic their function. Poly­(vinyl alcohol) (PVA) is the most potent biomimetic found to date, although it is orders of magnitude less potent than AFGPs. A lack of molecular understanding of the factors that limit the IRI efficiency of PVA and other flexible ice-binding polymers hinders the design of more potent IRI. Here, we use molecular and numerical simulations to elucidate how the degree of polymerization (DP) and functionalization of PVA impact its IRI. Our simulations indicate that the onset of IRI activity of PVA occurs for 15 < DP < 20, in agreement with experiments. We predict that polymers with stronger binding to ice per monomer attain IRI activity at lower DP and identify this as a contributor to the higher IRI potency of AFGPs. The simulations reveal that the limiting step for binding of flexible molecules to ice is not the alignment of the molecule to the surface or the initiation of the binding but the propagation to reach its full binding potential. This distinguishes AFGPs and PVA from rigid antifreeze proteins and, we argue, is responsible for their different scaling of efficiencies with molecular size. We use the analysis of PVA to identify the factors that control the IRI activity of flexible polymers and assess the molecular characteristics that endow AFGPs with their exceptional IRI potency.

Ice recrystallisation inhibiting polymer nano-objects via saline-tolerant polymerisation-induced self-assembly

“…We used commercial PVA (B80% hydrolysis), which along with the grafted RAFT agent, breaks up the consecutive hydroxyl group sequence, which has been shown to be crucial for PVA IRI. 13,52,53 The scaling behaviour of IRI's in different salt solutions may also affect the magnitude of the results seen here. 54 To further demonstrate the IRI activity, an alternative assay was conducted in 45 wt% sucrose ('sucrose sandwich').…”

Is Ice Nucleation by Organic Crystals Nonclassical? An Assessment of the Monolayer Hypothesis of Ice Nucleation

“…We perform simulations of ice nucleation on phloroglucinol dihydrate using united atom models, which individually represent all atoms except hydrogen. These models are based on short-ranged interactions that mimic the effect of hydrogen bonding through a combination of two- and three-body potentials and are about 100 times computationally more efficient than all-atom models based on long-range interactions − and were previously developed for water and several biological and organic molecules. ,,,,,− We represent water with the mW model, which reproduces well the structures, phase behavior, and thermodynamics of water and its interfaces. ,,,,− The melting temperature of hexagonal ice in the mW model is 273 K . The mW water model has been extensively used to investigate the heterogeneous nucleation of ice. ,,,− …”

Ice-binding proteins and bioinspired synthetic mimics in non-physiological environments

“… A proven mechanism of action for synthetic IBP mimics does not yet exist, which represents a significant—if not the primary—challenge for the field. While a paucity of molecular dynamics studies have been performed ( Naullage et al., 2017 ; Naullage and Molinero, 2020 ), further molecular dynamics studies could be employed to further delve into and discover the mechanism(s) of action for synthetic molecules with regard to IRI activity, ice growth rate, and potential ice nucleation. Additionally, validation of the results from molecular dynamics simulations with experiments is still needed to elucidate a universal mechanistic theory of ice interaction.…”