Graduate Student , University of Utah
Size and aggregation of ice binding proteins controls their ice nucleation efficiency.
We use molecular dynamic simulations to demonstrate that the size of ice binding surface in the ice nucleating proteins determines their roles as ice nucleating proteins or antifreeze proteins. We find that increasing the length of ice nucleating protein monomer increases their nucleating ability. The critical ice nucleus on ice nucleating proteins can adapt to the surface and elongate along the ice-binding surface. Ice nucleating protein monomers dimerize with an optimized gap distance of 1.1 ~ 1.2 nm, stabilizing the stacking disordered surface of ice. We predict that the domain of ice nucleating aggregates that nucleate ice at -2 °C contain 25 monomers. We elucidate how the size, shape and dimerization influence the ice nucleating ability of ice-binding proteins. These analyses provide us a strategy to assemble small ice-binding materials to construct super effective ice nucleating agent.
Abstract: Lipid flip-flop and its associated transient pore formation are key thermodynamic properties of living cell membranes. However, there is a lack of understanding of whether ionic imbalance that exists ubiquitously across cell membranes affects lipid flip-flop and its associated functions. Potential of mean force calculations show that the free-energy barrier of lipid flip-flop on the extracellular leaflet reduces with the presence of ionic imbalance, whereas the barrier on the intracellular leaflet is generally not affected. The linear decrease of the activation energy of lipid flip-flop on the extracellular leaflet is consistent with the experimentally measured conductance-voltage relationship of zwitterionic lipid bilayers. This suggests: 1) lipid flip-flop has a directionality under physiological conditions and phospholipids accumulate at a rate on the order of 105 µm(-2) h(-1) on the cytoplasmic side of cell membranes; 2) ion permeation across a lipid membrane is moderated by lipid flip-flop; 3) the energy barrier of pore formation is aligned with the weaker leaflet that has a lower energy of lipid flip-flop. The asymmetry of lipid flip-flop and pore nucleation may have substantial implications for protein translocation, signaling, enzymatic activities, vesicle fusion, and transportation of biomolecules on cell membranes.
Pub.: 21 Apr '17, Pinned: 27 Jun '17
Abstract: Unravelling dynamical processes of liquid droplets at liquid/solid interfaces and the interfacial ordering is critical to understanding solidification, liquid-phase epitaxial growth, wetting, liquid-phase joining, crystal growth, and lubrication process, all of which are linked to different important applications in material science. In this work, we observe direct in-situ atomic-scale behaviour of Bi droplets segregated on SrBi2Ta2O9 by using aberration corrected transmission electron microscopy and demonstrate ordered interface and surface structures for the droplets on the oxide at the atomic-scale and unravel a nucleation mechanism involving droplet coalescence at the liquid/solid interface. We identify a critical diameter of the formed nanocrystal in stabilizing the crystalline phase and reveal lattice induced fast crystallization of the droplet at the initial stage of the coalescence of nanocrystal with droplet. Further sequential observations show the stepped coalescence and growth mechanism of the nanocrystals at the atomic-scale. These results offer insights into the dynamic process at liquid/solid interfaces, which may have implications for many functionalities of materials and their applications.
Pub.: 26 May '17, Pinned: 27 Jun '17
Abstract: Nanophase segregation of a bi-component thiol self-assembled monolayer is predicted using atomistic molecular dynamics simulations and experimentally confirmed. The simulations suggest the formation of domains rich in acid-terminated chains, on one hand, and of domains rich in amide-functionalized ethylene glycol oligomers, on the other hand. In particular, within the amide-ethylene glycol oligomers region, a key role is played by the formation of inter-chain hydrogen bonds. The predicted phase segregation is experimentally confirmed by the synthesis of 35 and 15 nm gold nanoparticles functionalized with several binary mixtures of ligands. An extensive study by transmission electron microscopy and electron tomography, using silica selective heterogeneous nucleation on acid-rich domains to provide electron contrast, supports simulations and highlights patchy nanoparticles with a trend towards Janus nano-objects depending on the nature of the ligands and the particle size. These results validate our computational platform as an effective tool to predict nanophase separation in organic mixtures on a surface and drive further exploration of advanced nanoparticle functionalization.
Pub.: 15 Jun '17, Pinned: 27 Jun '17