What Controls the Limit of Supercooling and Superheating of Pinned Ice Surfaces?

Abstract

Cold-adapted organisms produce antifreeze proteins and glycoproteins to control the growth, melting and recrystallization of ice. It has been proposed that these molecules pin the crystal surface, creating a curvature that arrests the growth and melting of the crystal. Here we use thermodynamic modeling and molecular simulations to demonstrate that the curvature of the superheated or supercooled surface depends on the temperature and distances between ice-binding molecules, but not the details of their interactions with ice. We perform simulations of ice pinned with the antifreeze protein TmAFP, polyvinyl alcohol with different degrees of polymerization, and model ice-binding molecules to determine the thermal hystereses on melting and freezing, i.e. the maximum curvature that can be attained before, respectively, ice melts or grows irreversibly over the ice-binding molecules. We find that the thermal hysteresis is controlled by the bulkiness of the ice-binding molecules and their footprint at the ice surface. We elucidate the origin of the asymmetry between freezing and melting hysteresis found in experiments and propose guidelines to design synthetic antifreeze molecules with potent thermal hysteresis activity.

Combined molecular dynamics and neural network method for predicting protein antifreeze activity

“…Here, αp is a geometric constant (two for cylindrical ice cap, four for spherical), γ sl is the ice-liquid surface tension, Tm is the bulk freezing point, ν is the molar volume of ice, ∆Hm is the molar latent heat of fusion, θ is the ice cap contact angle, and d is distance between adsorbed AFPs. This theory has recently been supported via molecular simulation work by Naullage et al (9), who accurately calculated ∆T from θ and d for a model system. Additionally, Kuiper et al (10) confirmed that the binding of an AFP to the ice front is nearly irreversible in microsecond-long simulations, agreeing with earlier experimental evidence (11).…”

“…Work by Naullage et al (9) suggests that bulkier AFPs should display increased ∆T . We, therefore, also tested the inclusion of the following variables: protein height, H ; distance across the binding plane, D; molecular mass of the protein, Mp; and radius of gyration, Rg .…”

“…The ice surface is then forced to adopt an increased curvature as a cap grows between the bound AFPs. This increased surface curvature then depresses the freezing point through the Gibbs-Thomson (Kelvin) effect (8,9):…”

Mimicking the Ice Recrystallization Activity of Biological Antifreezes. When is a New Polymer “Active”?

“…The actual IRI seen, however, was rather weak requiring 5 mg mL −1 to inhibit 50% of ice growth. AFPs and AFGPs also show facial amphiphilicity and simulations suggest this facial amphiphilicity is crucial for AFGPs but not necessarily for AFPs . These experiments provided crucial data that a second structural feature, after ice binding, can be used to introduce IRI into a synthetic material; spatially segregated hydrophobic/hydrophilic domains, but without micellization.…”

“…AFPs and AFGPs also show facial amphiphilicity [66,68] and simulations suggest this facial amphiphilicity is crucial for AFGPs [33] but not necessarily for AFPs. [58,69] These experiments provided crucial data that a second structural feature, after ice binding, can be used to introduce IRI into a synthetic material; spatially segregated hydrophobic/ hydrophilic domains, but without micellization. Mitchell et al further used self-assembling metallohelices to probe this concept.…”