Growth suppression of ice crystal basal face in the presence of a moderate ice-binding protein does not confer hyperactivity

Ice-binding proteins (IBPs) affect ice crystal growth by attaching to crystal faces. We present the effects on the growth of an ice single crystal caused by an ice-binding protein from the sea ice microalga Fragilariopsis cylindrus (fcIBP) that is characterized by the widespread domain of unknown function 3494 (DUF3494) and known to cause a moderate freezing point depression (below 1 °C). By the application of interferometry, bright-field microscopy, and fluorescence microscopy, we observed that the fcIBP attaches to the basal faces of ice crystals, thereby inhibiting their growth in the c direction and resulting in an increase in the effective supercooling with increasing fcIBP concentration. In addition, we observed that the fcIBP attaches to prism faces and inhibits their growth. In the event that the effective supercooling is small and crystals are faceted, this process causes an emergence of prism faces and suppresses crystal growth in the a direction. When the effective supercooling is large and ice crystals have developed into a dendritic shape, the suppression of prism face growth results in thinner dendrite branches, and growth in the a direction is accelerated due to enhanced latent heat dissipation. Our observations clearly indicate that the fcIBP occupies a separate position in the classification of IBPs due to the fact that it suppresses the growth of basal faces, despite its moderate freezing point depression

Step-bunching instability of growing interfaces between ice and supercooled water

金沢大学学術メディア創成センターIce-crystal growth in supercooled water is one of the most familiar examples of phase-transition dynamics, playing essential roles in various natural phenomena on Earth. Despite its fundamental importance, the microscopic view at the elementary step level remains elusive. Here, using an advanced optical microscope, we find self-organization of elementary steps during ice-crystal growth, called step-bunching instability (SBI), driven by the competition between step dynamics, interfacial stiffness, and latent heat diffusions. We also find that the SBI transiently induces screw dislocations and resulting spiral growth in the late stage of the growth process. Furthermore, quantitative observations with a two-beam interferometer allow us to obtain insights into the relative importance of the various mechanisms of the step–step interactions. Our finding offers a significant clue to understanding the general mechanism of melt growth beyond ice-crystal growth, inseparably involving several broad research fields, including cryobiological, geophysical, and material branches

Direct observation of bunching of elementary steps on protein crystals under forced flow conditions

Bunching of elementary steps by solution flow is still not yet clarified for protein crystals. Hence, in this study, we observed elementary steps on crystal surfaces of model protein hen egg-white lysozyme (HEWL) under forced flow conditions, by our advanced optical microscopy. We found that in the case of a HEWL solution of 99.99% purity, forced flow changed bunched steps into elementary ones (debunching) on tetragonal HEWL crystals. In contrast, in the case of a HEWL solution of 98.5% purity, forced flow significantly induced bunching of elementary steps. These results indicate that in the case of HEWL crystals, the mass transfer of impurities is more significantly enhanced by forced solution flow than that of solute HEWL molecules. We also showed that forced flow induced the incorporation of microcrystals into a mother crystal and the subsequent formation of screw dislocations and spiral growth hillocks

In-situ observation of crystal surfaces by optical microscopy

In this experimental course, attendees will learn how to obtain useful information about growth processes of crystals using ordinary optical microscopes, which are usually available in laboratories. We will demonstrate how thicknesses of crystals can be estimated from interference colors. We will also show in-situ observations of spiral steps and strain distributions by differential interference contrast microscopy and polarizing microscopy, respectively

Colloidal crystallization utilizing interfaces of unidirectionally growing ice crystals

We show the possibility of unidirectional freezing of colloidal random suspensions as a novel method for growing colloidal crystals. First we confirmed the rejection of polystyrene particles from unidirectionally growing ice water interfaces by observing color gradations of colloidal crystals formed in front of the interfaces. The rejection of particles from the growing interfaces increased particle concentration in the colloidal crystals. Then we succeeded in achieving colloidal crystallization in front of ice water interfaces during the unidirectional freezing of water suspensions of polystyrene particles. The colloidal crystals thus brained exhibited a columnar shape that is typically observed in the unidirectional colloidal crysrallizarion using centrifugation. (C) 2013 Elsevier B.V. All rights reserved

Quasi-liquid layers on ice crystal surfaces are made up of two different phases

Ice plays crucially important roles in various phenomena because of its abundance on Earth. However, revealing the dynamic behavior of quasi-liquid layers (QLLs), which governs the surface properties of ice crystals at temperatures near the melting point, remains an experimental challenge. Here we show that two types of QLL phases appear that exhibit different morphologies and dynamics. We directly visualized the two types of QLLs on ice crystal surfaces by advanced optical microscopy, which can visualize the individual 0.37-nm-thick elementary steps on ice crystal surfaces. We found that they had different stabilities and different interactions with ice crystal surfaces. The two immiscible QLL phases appeared heterogeneously, moved around, and coalesced dynamically on ice crystal surfaces. This picture of surface melting is quite different from the conventional picture in which one QLL phase appears uniformly on ice crystal surfaces

Two types of quasi-liquid layers on ice crystals are formed kinetically

Surfaces of ice are covered with thin liquid water layers, called quasi-liquid layers (QLLs), even below their melting point (0 °C), which govern a wide variety of phenomena in nature. We recently found that two types of QLL phases appear that exhibit different morphologies (droplets and thin layers) [Sazaki G. et al. (2012) Proc Natl Acad Sci USA 109(4):1052−1055]. However, revealing the thermodynamic stabilities of QLLs remains a longstanding elusive problem. Here we show that both types of QLLs are metastable phases that appear only if the water vapor pressure is higher than a certain critical supersaturation. We directly visualized the QLLs on ice crystal surfaces by advanced optical microscopy, which can detect 0.37-nm-thick elementary steps on ice crystal surfaces. At a certain fixed temperature, as the water vapor pressure decreased, thin-layer QLLs first disappeared, and then droplet QLLs vanished next, although elementary steps of ice crystals were still growing. These results clearly demonstrate that both types of QLLs are kinetically formed, not by the melting of ice surfaces, but by the deposition of supersaturated water vapor on ice surfaces. To our knowledge, this is the first experimental evidence that supersaturation of water vapor plays a crucially important role in the formation of QLLs

Quasi-liquid Layers in Grooves of Grain Boundaries and on Grain Surfaces of Polycrystalline Ice Thin Films

In nature, a large proportion of ice is present in a polycrystalline state. Thus, understanding the formation of quasi-liquid layers (QLLs) on/in polycrystalline ice is indispensable for understanding a wide variety of natural phenomena. In this study, we observed surfaces of polycrystalline ice thin films using our advanced optical microscope. We focused our attention on the macroscopic fluidity of objects observed on polycrystalline ice surfaces as evidence for the presence of QLLs. Systematic observations under various temperatures and water vapor pressures showed that, with increasing temperature, QLLs first appeared preferentially in grooves of grain boundaries and continued to exist at -1.9 +/- 0.4 degrees C, irrespective of the water vapor pressure (even in immediate vicinities of the vapor-ice equilibrium curve). From this result, we concluded that the QLLs were formed by melting of grain boundaries to relax lattice mismatches. With a further increase of temperature, droplet-type QLLs appeared on grain surfaces at -0.7 +/- 0.2 degrees C. However, as time elapsed, the droplet-type QLLs on the grain surfaces spontaneously disappeared within 5 +/- 3 min even though temperature and water vapor pressure were kept constant. Such appearance and subsequent disappearance of the droplet-type QLLs on the grain surfaces were observed even under relatively highly supersaturated and undersaturated conditions

First In Situ X-ray Scattering Measurements of Insect Body Surface Lipids: American Cockroach

In situ X-ray scattering measurements of insect body surface lipids were successfully attempted by using a synchrotron X-ray source. The temperature-dependent structural changes of the cuticular hydrocarbons covering the forewing of an American cockroach were able to be followed, which showed that the majority of the hydrocarbons were in a liquid state even far below the critical temperature of water transpiration through the body surface. The results clearly demonstrated that synchrotron radiation X-ray scattering has the potential to obtain the detailed information about the intact lipid structure and physical properties on insect body surfaces