Perhaps the best characterized template nucleation systems are the alcohol monolayer assemblies at the air−water interface. These monolayers, consisting of aliphatic alcohols [C n H2 n +1OH, n = 16−31) have been the subject of hexagonal ice (Ih) induction experiments over a range of temperatures. To learn more about the molecular basis of alcohol monolayer template−induced ice nucleation phenomena, we performed canonical molecular dynamics (MD) simulations (1 ns) of pure C29, C30, and C31 alcohol monolayer−water droplet systems, using the reversible reference system propagation algorithm (r-RESPA). We find that the MD-determined monolayer physical parameters (at 278.15 K) exhibit reasonable agreement with experimentally determined values for crystalline C30 and C31 monolayers at 278.15 K. More importantly, as the simulation temperatures approach monolayer-specific freezing points, the water layer immediately below the monolayer surfaces adopted “ice-like” lattice parameters and hexagonal or c-centered rectangular geometries that are characteristic of the (Ih) {001} plane. The analysis of monolayer −OH headgroup orientations and surface topologies reveal that odd-carbon monolayers, and C31 in particular, are more effective nucleation templates, due to the following factors:  (1) ab-plane alcohol −OH headgroup geometries which provide a closer ab-plane lattice match to the {001} Ih interface and (2) the presence of smoother monolayer headgroup topologies (i.e., azimuthal positioning), which permit a larger percentage of water molecules to form hydrogen bonds with the monolayer alcohol headgroups.

We present an energy-based algorithm, POINTER, which can determine the permissible alignments of a polypeptide ͑or other macromolecule͒ with respect to the lattice vectors of an interfacial surface ͑this alignment is defined by the angle ͒. The algorithm represents both the interface and the macromolecule in three dimensions. For each value of , incremental moves of the macromolecule occur in the x, y, z direction along the orientation, as well as rotation ͑, ␥, ͒ of either the macromolecular chain or the interfacial slab. We utilized a simple forcefield that consists of a dipole-dipole, dipole-charge, or charge-charge electrostatic interaction term and a Lennard-Jones attraction-repulsion term to describe the nonbonding interactions between macromolecular atoms and interfacial atoms. We benchmarked our method by modeling ice-and mineral-interaction polypeptides on various Miller planes of hexagonal ice and inorganic solids, respectively. In addition, we searched phase space for a simpler, nonpolypeptide system: The ice-nucleating C31 alcohol monolayer ͑comprised of 61 C31 molecules͒ in contact with the ͕001͖ plane of hexagonal ice. Our results indicate that the POINTER simulation method can reproduce the macromolecule orientation observed for each benchmark system. In addition, our simulations point to a number of factors-polypeptide binding site structure, the positioning of hydrophobic residues near the interface, and interface topology-which can influence the adsorption orientation of polypeptides on hexagonal ice and inorganic solids.

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