Search

Surfaces of ice act as sites of various chemical reactions of atmospheric acidic gases, which cause serious environmental issues, such as the catalytic ozone depletion by hydrogen chloride (HCl) ga...

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.

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.

ConspectusThe ice premelt, often called the quasi-liquid layer (QLL), is key for the lubrication of ice, gas uptake by ice, and growth of aerosols. Despite its apparent importance, in-depth understanding of the ice premelt from the microscopic to the macroscopic scale has not been gained. By reviewing data obtained using molecular dynamics (MD) simulations, sum-frequency generation (SFG) spectroscopy, and laser confocal differential interference contrast microscopy (LCM-DIM), we provide a unified view of the experimentally observed variation in quasi-liquid (QL) states. In particular, we disentangle three distinct types of QL states of disordered layers, QL-droplet, and QL-film and discuss their nature.The topmost ice layer is energetically unstable, as the topmost interfacial H2O molecules lose a hydrogen bonding partner, generating a disordered layer at the ice-air interface. This disordered layer is homogeneously distributed over the ice surface. The nature of the disordered layer changes over a wide temperature range from -90 °C to the bulk melting point. Combined MD simulations and SFG measurements reveal that the topmost ice surface starts to be disordered around -90 °C through a process that the topmost water molecules with three hydrogen bonds convert to a doubly hydrogen-bonded species. When the temperature is further increased, the second layer starts to become disordered at around -16 °C. This disordering occurs not in a gradual manner, but in a bilayer-by-bilayer manner.When the temperature reaches -2 °C, more complicated structures, QL-droplet and QL-film, emerge on the top of the ice surface. These QL-droplets and QL-films are inhomogeneously distributed, in contrast to the disordered layer. We show that these QL-droplet and QL-film emerge only under supersaturated/undersaturated vapor pressure conditions, as partial and pseudopartial wetting states, respectively. Experiments with precisely controlled pressure show that, near the water vapor pressure at the vapor-ice equilibrium condition, no QL-droplet and QL-film can be observed, implying that the QL-droplet and QL-film emerge exclusively under nonequilibrium conditions, as opposed to the disordered layers formed under equilibrium conditions.These findings are connected with many phenomena related to the ice surface. For example, we explain how the disordering of the topmost ice surface governs the slipperiness of the ice surface, allowing for ice skating. Further focus is on the gas uptake mechanism on the ice surface. Finally, we note the unresolved questions and future challenges regarding the ice premelt.

The cuticular lipid covering the integument of insects is exposed to the environment and involved in a variety of functions offered by insect body surfaces, ranging from protection against the environment, such as the control of water transpiration, the reduction of abrasive damage, and the prevention of pathogen intrusion, to the communication between insects from intraspecific to interspecific interactions. In comparison with the importance of their physiological functions, there is remarkably little information on the structure and physical property of cuticular lipids on insect body surfaces. The lipid layer on the outer exoskeleton is very thin, estimated on the order of 0.01-1 μm or less, and this has led to a lack of practical methodologies for detailed structural analyses. To fill this devoid, we have exploited the characteristics of Fourier transform infrared (FTIR) attenuated total reflection (ATR) spectroscopy, which allows us to conduct a chemical analysis on insect body surfaces and also to investigate depth-dependent structural changes. We have applied a combination of FTIR ATR microspectroscopy with IR radiation provided by a synchrotron facility to obtain in situ two-dimensional (2D) information of the cuticular lipid layer on the surface of the integument. The 2D FTIR spectra measured on the two-spotted cricket and the American cockroach show that the IR bands due to the cuticular lipid, such as CH2 symmetric and antisymmetric stretch, νa(CH2) and νs(CH2), change in intensity significantly, depending on the location of measurements. As if to keep pace with this, the bands of the amide group for the underlying cuticular layer also change in intensity significantly, although the changes are in the opposite direction; as the lipid bands increase in intensity, the amide band decreases, and vice versa. The ATR spectral analysis, which takes into account the characteristics of the evanescent wave, points out that the lipid layer would vary tens of times in the range of 0.01-1 μm significantly. The νa(CH2) and νs(CH2) bands show frequency shifts, which correlate to some extent with their intensity changes, suggesting that the drastic uneven distribution of the cuticular lipid would be related to the solid-liquid phase separation and also the coarsening of the solid phase domains. The formation of such topological features, significant heterogeneity in the lipid layer thickness, and solid-liquid phase ratios would be accompanied by the partitioning of lipid components according to molecular structures and physicochemical properties. Considering that each lipid component in insect body surface lipids is involved in various physiological roles, the segregation of lipid components during the formation of such heterogeneous structures is thought to have a significant impact on the functionality of the insect body surface.

To protect themselves, insects cover their bodies with what is called cuticular lipid. The cuticular lipid of an American cockroach has a unique lipid content; the most abundant is a cis-alkadiene, cis,cis-6,9-heptacosadiene, amounting to about 70%, which is followed by a branched alkane 3-methylpentacosane. In order to clarify the structural features of the unique lipid composition below the critical temperature, the cuticular lipid was studied by Fourier transform infrared (FTIR) spectroscopy in combination with an attenuated total reflection (ATR) sampling technique. The infrared spectra measured on an extracted lipid sample at 20 °C suggested that the lipid keeps an appreciable level of conformational and lateral packing regularity, in spite of a high cis-unsaturated lipid content, and also a highly disordered condition around the methyl terminals and cis-olefin groups. The CH2 scissoring and the CH2 rocking regions showed the characteristics of the O⊥ subcell. The same characteristics were observed a...

Surface melting of ice crystals proceeds below the melting point (0 °C) and forms thin liquid water layers, called quasi-liquid layers (QLLs), which govern a wide variety of phenomena in nature. Hence, many studies have been performed so far; however, the lowest temperature above which QLLs exist on ice crystal surfaces varied from −90 to −1 °C. To reveal the cause of such significant variations, here we show, by laser confocal microscopy combined with Michelson interferometry, the behavior of QLLs on polycrystalline ice thin films that include a large amount of grain boundaries and defects. We found that the QLLs can exist stably on the polycrystalline ice thin films even at −16.2 °C (the lowest temperature adopted in this study), although the QLLs on ice single crystals disappear at temperature lower than −2.4 ± 0.5 °C. These results emphasize the importance of grain boundaries and defects for the presence of QLLs. In addition, we also found that critical water vapor pressure above which the QLLs can gr...

Surfaces of ice have attracted considerable attention as “reaction sites” where atmospheric gases cause various chemical reactions in nature. Hence, revealing the uptake mechanism of atmospheric gases on/in ice remains an experimental challenge. Here we show the direct observation of ice crystal surfaces by advanced optical microscopy in the presence of hydrogen chloride (HCl) gas, which triggers a series of chemical reactions that cause ozone depletion. We found that the HCl gas induced the appearance of droplets of HCl solution on ice crystal surfaces. Under supersaturated water vapor pressure, the HCl droplets were quickly embedded in the ice crystals during the growth of the ice. In contrast, under undersaturated conditions, the embedded HCl droplets reappeared on the ice crystal surfaces during the evaporation of the ice. We estimated that the mole fraction of HCl incorporated into the ice as the HCl droplets (0.19% at −15 °C) was ten times larger than the solubility of HCl gas in an ice crystal (0.0...

The morphology and growth kinetics of ice single crystals in aqueous solutions of type III antifreeze protein (AFP-III) have been studied in detail over a range of AFP-III concentrations and supercoolings. In pure water, the shape of ice crystals changes from the circular disklike to planar dendritic with increasing supercooling. In AFP-III solutions, ice crystals in the form of faceted plates, irregular dendrites with polygonized tips, and needles appear with increasing supercooling and AFP-III concentration. The growth rate of ice crystals in the crystallographic a direction is 2 orders of magnitude higher than that in the c direction. AFP-III molecules cause the stoppage of the growth of the prismatic and basal faces at low supercoolings. When supercooling exceeds the critical value, AFP-III favors the acceleration of the growth in both a and c directions. The observed behavior of AFP-III is explained in terms of the Cabrera-Vermilyea pinning model and the specificity of the dissipation of latent heat ...

We measured the velocity Vstep of isolated elementary spiral steps and the distance Leq between adjacent equivalent spiral steps on ice basal faces by advanced optical microscopy. We determined the step kinetic coefficient β from Vstep measured under various supersaturations. We performed similar experiments under various temperatures T, and determined the temperature dependence of β of ice basal faces, for the first time, in the temperature range of −26.0 to −2.7 °C. When −6.2 ≤ T ≤ −2.7 °C, the value of β decreased significantly with decreasing T. In contrast, when −15.0 ≤ T ≤ −6.2 °C, the value of β increased with decreasing T, and had the maximum at T ≈ −15 °C. When −26.0 ≤ T ≤ −15.0 °C, the value of β decreased monotonically with decreasing T. Such complicated temperature dependence of β strongly implies the existence of unknown phenomena in the temperature range examined. To obtain a clue to the complicated behavior of β, we also measured dependence of Leq on surface supersaturation Δμsurf. When −13...

Ice is one of the most abundant materials on the earth's surface, and its growth governs various natural phenomena. Hence, the molecular-level understanding of ice crystal surfaces is crucially important. However, it is generally acknowledged that the molecular-level observation of ice crystal surfaces by ordinary microscopy techniques, such as atomic force microscopy and scanning electron microscopy, is very difficult at temperatures near the melting point (0 °C). To overcome such difficulties, we have developed laser confocal microscopy combined with differential interference contrast microscopy (LCM-DIM). We proved that LCM-DIM can visualize individual elementary steps (0.37 nm in thickness) on a basal face by observing two-dimensional nucleation growth. Then we found by LCM-DIM that spiral steps on a basal face exhibit a double-spiral pattern, which can be expected from ice's crystallographic structure. In addition, we revealed that temperature dependence of growth kinetics of elementary spiral steps on a basal face exhibits complicated behaviors, which show the presence of unknown phenomena in the growth kinetics. Furthermore, we proved that surface diffusion of water admolecules on a basal face plays a crucially important role in the lateral growth of elementary steps when the distance between adjacent spiral steps is smaller than 15 µm. These findings will provide a clue for unlocking growth kinetics of ice crystals. In addition, through the use of LCM-DIM much progress has been made in studies on the surface melting of ice and the interaction between ice and atmospheric gasses.

Self-organized formation of parallel-banded structures was demonstrated through the twisted growth of K2Cr2O7 in a thin layer of a viscous solution containing poly(acrylic acid) on a glass substrate. Dense branching of the twisted crystals was induced by increasing their growth rate under a controlled flow of nitrogen gas. Periodically banded structures were then obtained by the synchronization of the twist in the parallel branches. Specific structural colors originating from the parallel-banded structures as a diffraction grating were observed on the self-organized patterns of the twisted crystals.

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.

A microscopic understanding of crystal-melt interfaces, inseparably involved in the dynamics of crystallization, is a long-standing challenge in condensed matter physics. Here, using an advanced optical microscopy, we directly visualize growing interfaces between ice basal faces and quasiliquid layers (QLLs) during ice crystal growth. This system serves as a model for studying the molecular incorporation process of the crystal growth from a supercooled melt (the so-called melt growth), often hidden by inevitable latent heat diffusion and/or the extremely high crystal growth rate. We reveal that the growth of basal faces inside QLLs proceeds layer by layer via two-dimensional nucleation of monomolecular islands. We also find that the lateral growth rate of the islands is well described by the Wilson-Frenkel law, taking into account the slowing down of the dynamics of water molecules interfaced with ice. These results clearly indicate that, after averaging surface molecular fluctuations, the layer by layer stacking still survives even at the topmost layer on basal faces, which supports the kink-step-terrace picture even for the melt growth.

The spiral growth of crystals, mediated by their screw dislocations, is a general crystal-growth mechanism observed over a large variety of crystalline solids. Despite its general nature, direct observations of the spiral growth of ice have been rarely reported so far. Here, with the aid of advanced optical microscopy, we succeed in making in situ observations of the perfect spiral growth during the vapor growth of ice. We find that the spiral steps observed are well described by the classical Burton--Cabrera--Frank theory, taking into account surface diffusion of water admolecules between adjacent steps. This is distinct from the dominant growth mode that we have assigned as spiral in our recent studies, which accompanies fluctuations of the adjacent step interval. We also successfully capture the birth of a screw dislocation and the ensuing spiral growth, originating in the lattice mismatch arising from the coalescence of single ice crystals. Furthermore, we demonstrate that the nucleation of quasi-liquid layers (QLLs) takes place at the spiral center immediately after the birth of the dislocation, which suggests a link between screw dislocations and the generation of QLLs near the ice melting point.

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.

Surface melting of ice crystals forms quasi-liquid layers (QLLs) on ice surfaces, and affects a wide variety of natural phenomena. Since QLLs enhance various chemical reactions in ice clouds, the formation of QLLs by atmospheric gases has been studied intensively. However, such studies were performed using spectroscopy techniques, which have low spatial resolution. Here we show the first direct visualization of QLLs on ice basal faces in the presence of hydrogen chloride (HCl) gas (model atmospheric gas) by advanced optical microscopy, which can visualize individual 0.37 nm-thick elementary steps on ice crystal surfaces. We found that the HCl gas induced the appearances of QLLs with a droplet shape in the temperature range from −15.0 to −1.5 °C, where no QLL appears in the absence of HCl gas. This result indicates that HCl gas adsorbed on ice crystal surfaces probably changed the surface structure of ice crystals and then induced the subsequent melting of ice surfaces. We also observed the movement, shape...

Surface melting of ice significantly governs a wide variety of phenomena in nature. We recently succeeded in directly observing the surface melting on ice basal faces (Proc. Natl. Acad. Sci. U.S.A. 2012, 109, 1052–1055) by our advanced optical microscopy, which can detect 0.37-nm-thick elementary steps on basal faces. However, the direct observation of surface melting on the other prism and high-index faces remains an experimental challenge. To fully obtain a comprehensive understanding, we need to examine the surface melting on these faces. Here we show the appearance of two types of quasi-liquid layers (QLLs) on prism and high-index faces just below the melting point. We quickly raised the temperature of ice crystals and then observed prism and high-index faces during a roughening process. We found that with increasing temperature, round liquid-like droplets (α-QLLs) first appeared at temperatures higher than −1.4 to −0.5 °C, and then thin liquid-like layers (β-QLLs) also appeared at temperatures higher...

A specimen that has an even magnitude of reflectivity all over the surface is called a phase object.

The free growth of ice crystals in supercooled bulk water containing an impurity of glycoprotein, a bio-macromolecule that functions as ‘antifreeze’ in living organisms in a subzero environment, was observed under microgravity conditions on the International Space Station. We observed the acceleration and oscillation of the normal growth rates as a result of the interfacial adsorption of these protein molecules, which is a newly discovered impurity effect for crystal growth. As the convection caused by gravity may mitigate or modify this effect, secure observations of this effect were first made possible by continuous measurements of normal growth rates under long-term microgravity condition realized only in the spacecraft. Our findings will lead to a better understanding of a novel kinetic process for growth oscillation in relation to growth promotion due to the adsorption of protein molecules and will shed light on the role that crystal growth kinetics has in the onset of the mysterious antifreeze effect in living organisms, namely, how this protein may prevent fish freezing.

The surfaces of ice crystals near the melting point are covered with thin liquid water layers, called quasi-liquid layers (QLLs), which play crucial roles in various chemical reactions in nature. So far, there have been many spectroscopic studies of such chemical reactions on ice surfaces, however, revealing the effects of atmospheric gases on ice surfaces remains an experimental challenge. In this study, we chose HNO3 as a model atmospheric gas, and directly observed the ice basal faces by advanced optical microscopy under partial pressure of HNO3 (~10&minus, 4 Pa), relevant to those found in the atmosphere. We found that droplets (HNO3-QLLs) appeared on ice surfaces at temperatures ranging from &minus, 0.9 to &minus, 0.2 &deg, C with an increase in temperature, and that they disappeared at temperatures ranging from &minus, 0.6 to &minus, 1.3 &deg, C with decreasing temperature. We also found that the size of the HNO3-QLLs decreased immediately after we started reducing the temperature. From the changes in size and the liquid&ndash, solid phase diagram of the HNO3-H2O binary system, we concluded that the HNO3-QLLs did not consist of pure water, but rather aqueous HNO3 solutions, and that the temperature and HNO3 concentration of the HNO3-QLLs also coincided with those along a liquidus line.

We measured velocities Vstep of lateral displacement of individual elementary steps on an ice basal face, for the first time, by advanced optical microscopy, under various bulk water vapor pressure PH2O∞. Distances L between adjacent spiral steps exhibited considerable variation under constant PH2O∞. Hence, we analyzed Vstep as functions of L and PH2O∞. Then we found that (1) under a constant PH2O∞, Vstep decreased with decreasing distances L when L ≤ 15 μm and that Vstep remained constant when L ≥ 15 μm. We named Vstep of L ≥ 15 μm (isolated steps) Vstepint and analyzed dependencies of Vstepint on PH2O∞. Then we found that (2) the slope of the Vstepint vs PH2O∞ plot gradually decreased with increasing PH2O∞. We proposed a model that took into account both the volume diffusion of water vapor molecules and the surface diffusion of water admolecules on a terrace. Our model could explain result (1) mainly by the competition of adjacent spiral steps for water admolecules diffusing on a terrace but could not e...

During the growth of ice crystals, spiral growth is one of the important growth mechanisms that dominate their growth. However, the structure of spiral steps on ice crystal surfaces at temperatures near the melting point has not been identified. Here we show a possible model structure of spiral steps on basal and prism faces of Ih ice crystals grown from water vapor just below 0 °C. We observed in situ the coalescences of spiral steps and steps of two-dimensional (2D) islands by our advanced optical microscopy, which can visualize individual elementary steps (single-bilayer height) of 2D islands on ice basal faces. We found that both spiral steps and 2D island steps on basal and prism faces show single-bilayer heights, though Burgers’ vectors of screw dislocations on both faces need to have double-bilayer heights because of a crystallographic requirement. These results suggest that at the center of a spiral growth hillock, steps of two adjacent single bilayers coincide and then form a double-bilayer step ...

An impurity effect on ice crystal growth in supercooled water is an important subject in relation to ice crystal formation in various conditions in the Earth's cryosphere regions. In this review, we consider antifreeze glycoprotein molecules as an impurity. These molecules are well known as functional molecules for controlling ice crystal growth by their adsorption on growing ice/water interfaces. Experiments on free growth of ice crystals in supercooled water containing an antifreeze protein were conducted on the ground and in the International Space Station, and the normal growth rates for the main crystallographic faces of ice, namely, basal and prismatic faces, were precisely measured as functions of growth conditions and time. The crystal-plane-dependent functions of AFGP molecules for ice crystal growth were clearly shown. Based on the magnitude relationship for normal growth rates among basal, prismatic and pyramidal faces, we explain the formation of a dodecahedral external shape of an ice crystal in relation to the key principle governing the growth of polyhedral crystals. Finally, we emphasize that the crystal-plane dependence of the function of antifreeze proteins on ice crystal growth relates to the freezing prevention of living organisms in sub-zero temperature conditions. This article is part of the theme issue ‘The physics and chemistry of ice: scaffolding across scales, from the viability of life to the formation of planets’.

Hydrogels with tunable elasticity has been widely used as micromechanical environment models for cells. However, the imaging of physical contacts between cells and hydrogels with a nanometer resolution along the optical axis remain challenging because of low reflectivity at hydrogel-liquid interface. In this work, we have developed an advanced interferometric optical microscopy for the high contrast visualization of cell-hydrogel contact. Here, reflection interference contrast microscopy (RICM) was modified with a confocal unit, high throughput optics and coherent monochromatic light sources to enhance interferometric signals from cell-hydrogel contact zones. The advanced interferomety clearly visualized physical contacts between cells and hydrogels, and thus enabled the quantitative evaluation of the area of cell-hydrogel adhesion.

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.

Agarose has been utilized in protein crystallization to control nucleation of protein crystals. It reduces convection, prevents crystal sedimentation, and increases tolerance to environmental perturbations, resulting in high-quality protein crystals. However, crystallographers have seldom used agarose hydrogel because it requires preincubating the crystallization solution at high temperatures where a high-temperature-sensitive protein may be inactivated or aggregated. To overcome this disadvantage, we used a thermoreversible gel polymer (TGP) made from synthetic polymer. TGP turns into hydrogel upon warming and liquefies upon cooling. This novel approach enabled us to prepare the crystallization solutions at low temperature (277–283 K) and to crystallize elastase, glucose isomerase, and lysozyme with TGP. We also found that TGP clearly increased the number of elastase, glucose isomerase, and lysozyme crystals. This approach will provide a wide variety of possibilities for protein crystallization in hydrogels.

Ice crystal surfaces melt at temperatures below 0 °C, and then quasi-liquid layers (QLLs) are formed. However, revealing the dynamic behavior of QLLs, which dominates the surface properties of ice crystals at temperatures near the melting point, remains an experimental challenge. Here, we demonstrate the similarities and differences in the generation mechanisms of two types of QLL phases, which show different morphologies and dynamics. We directly visualized the appearance of round liquidlike droplets (α-QLLs) and thin liquidlike layers (β-QLLs) on ice basal faces by advanced optical microscopy, which can allow visualization of the individual elementary steps on basal faces. We found that α-QLLs always appear at outcrops of dislocations, and that β-QLLs emerge from crystal surfaces where many microdefects are embedded. These results clearly demonstrate the similar function that strain induces the appearance of both types of QLLs. We also found that β-QLLs are spontaneously formed at interfaces between bas...

Since the pioneering prediction of surface melting by Michael Faraday, it has been widely accepted that thin water layers, called quasi-liquid layers (QLLs), homogeneously and completely wet ice surfaces. Contrary to this conventional wisdom, here we both theoretically and experimentally demonstrate that QLLs have more than two wetting states and that there is a first-order wetting transition between them. Furthermore, we find that QLLs are born not only under supersaturated conditions, as recently reported, but also at undersaturation, but QLLs are absent at equilibrium. This means that QLLs are a metastable transient state formed through vapor growth and sublimation of ice, casting a serious doubt on the conventional understanding presupposing the spontaneous formation of QLLs in ice–vapor equilibrium. We propose a simple but general physical model that consistently explains these aspects of surface melting and QLLs. Our model shows that a unique interfacial potential solely controls both the wetting and thermodynamic behavior of QLLs.

We developed a spatially precise, soft microseeding method for the production of single protein crystals that are suitable for X-ray crystallographic studies. We used focused femtosecond laser pulses to produce, via multiphoton absorption processes, seed crystals from small regions (∼1 μm2) of crystals. Hen egg-white lysozyme seed crystals, produced in this manner, grew to be single crystals without any deterioration in their crystallinity. We also validated the technique using polycrystals for the membrane protein, acriflavine resistance protein B, for which single crystals are very difficult to obtain. In addition, we found that the shape of a tetragonal lysozyme crystal prepared from the seed could be controlled by altering the time interval between the initiation of crystallization and laser ablation. We also tried to comprehend the mechanism of femtosecond laser-induced microseeding. We visualized the ablated surfaces of the lysozyme crystals by atomic force microscopy and by laser confocal microscop...

The morphology and step kinetics of 2D islands and spiral hillocks of lysozyme crystals growing from purified and contaminated solutions were determined and compared. It was found that the morphology and step dynamics of spiral hillocks of lysozyme crystals are less affected by the presence of impurities in the growth solution as compared to steps generated by 2D nucleation. These observations could be satisfactorily explained considering the terrace exposure time of spiral hillocks (NLGÑsp) and 2D islands (NLGÑ2D) and the characteristic impurity adsorption time (NLGÑi). For lysozyme, overlapping time scales of terrace exposure and impurity adsorption exist and NLGÑi . NLGÑsp

To grow protein crystals of better quality, there still exists an open question whether a solution flow should be suppressed or intentionally introduced. To obtain a comprehensive understanding of the effects of a solution flow, we directly measured the velocities of individual elementary steps (on {110} faces of tetragonal lysozyme crystals) under a forced solution flow, for the first time, by laser confocal microscopy combined with differential interference contrast microscopy. When we used crystals grown by a two-dimensional (2D) nucleation growth mechanism in a solution of commercial lysozyme (98.5% purity, from Seikagaku Co.), while increasing the solution flow rate, the step velocity decreased monotonically. We confirmed that this decrease in the step velocity with flow rate was due to the enhancement of the mass transfer of impurity (mainly covalently bonded dimer), by the observation using a lysozyme further purified (dimer was removed). In contrast, when we used crystals grown by a spiral growth ...

High-throughput protein X-ray crystallography offers a significant opportunity to facilitate drug discovery. The most reliable approach is to determine the three-dimensional structure of the protein-ligand complex by soaking the ligand in apo crystals. However, protein apo crystals produced by conventional crystallization in a solution are fatally damaged by osmotic shock during soaking. To overcome this difficulty, we present a novel technique for growing protein crystals in a high-concentration hydrogel that is completely gellified and exhibits high strength. This technique allowed us essentially to increase the mechanical stability of the crystals, preventing serious damage to the crystals caused by osmotic shock. Thus, this method may accelerate structure-based drug discoveries.

We measured step velocity Vstep in the direction of two dimensional islands on the {110} faces of tetragonal lysozyme crystals under high pressure, and calculated step kinetic coefficients βstep. Vstep and βstep decreased with increasing pressure. The decrease in βstep indicates the increase in activation energy of the crystallization εkink or the mean distance between kinks on the step λ.

The adsorption/desorption behavior of mobile solute molecules at a solution-crystal interface has been explored using crystals of model protein hen egg-white lysozyme (HEWL) and fluorescent-labeled HEWL (F-HEWL) molecules. We have tracked the transient processes occurring during adsorption/desorption of identical F-HEWL molecules on a tetragonal HEWL crystal surface by single-molecule visualization using a total internal reflection fluorescent microscope and pulsed discontinuous laser illumination. We found an induction period (similar to 70 min) after which the number density of F-HEWL molecules adsorbed mainly on steps increased linearly with the adsorption time. We show direct evidence that the residence time of molecules on the crystal surface gradually increases during the transition process from a solute species to the crystal after successive multistep processes.

In this work we studied the kinetics of gypsum crystals growing from aqueous solutions as a function of temperature and supersaturation. Laser confocal differential interference contrast microscopy (LCM-DIM) and atomic force microscopy (AFM) were used to observe in situ the step advancement and the evolution of the surface morphology of the {010} face. We found that, for the experimental conditions used in this study, 2D nucleation is the main step generation mechanism, even at low supersaturations, and only a few spiral hillocks were observed. Due to the elongated morphology of2D islands along the c-axis and the frequent nucleation of multilayer 2D islands, {010} faces growing from a supersatured solution developed a "hill and valley" topography. This type of surface topography is observed at all temperatures. The step kinetic coefficient, β s1 , was determined in the temperature range 20—80 °C, and a steep increment in the kinetic coefficient is found with increasing temperature. From these data, the activation barrier for incorporation of building units in the {010} face was determined to be 70.7 ± 5.0 kJ/mol. Analysis of the kinetic data shows that at low temperatures (≤40°C) growth of the {010} face is dominated by a mixed regime and at higher temperatures (>40 °C) growth is controlled solely by diffusion.

We propose a technique for DNA crystallization using the thermal reversible process of DNA. A double-stranded DNA (dsDNA) can be converted into two single-stranded DNAs (ssDNAs) at high temperatures to improve its water solubility. Thus, this thermal conversion can be utilized for increasing the solubility of DNA crystals by changing solute species. We investigated the solubility of the crystals of a DNA hexamer d(CGCGCG) and their melting temperature, at which thermal conversion occurs from a dsDNA to ssDNAs or vice versa. A van’t Hoff plot showed two crystallization processes with a change in temperature dependency of the solubility at around 315 K. This result almost corresponded to the melting temperature (322 K) measured by UV spectroscopy. These findings suggest that the conversion from a dsDNA to ssDNAs results in an increase in solubility. Using this temperature-controlled technique, single crystals of the DNA hexamer could be obtained from a small amount of DNA samples; X-ray assessment demonstra...