The strengths of intermolecular contacts (macrobonds) in four lysozyme crystals were estimated based on the strengths of individual intermolecular interatomic interaction pairs. The periodic bond chain (PBC) of these macrobonds accounts for the morphology of protein crystals. The surface area of contact, polar coordinate representation of contact site, Coulombic contribution on the macrobond strength, and the surface energy of the crystal were also evaluated. Making use of the contact strengths and taking into account bond hydration, we estimated also crystal-water interfacial energies for different crystal faces. Comparing location of intermolecular contacts in different polymorphic crystal modifications we show that these contacts form a wide variety of patches on the molecular surface. The patches are located practically everywhere on the molecular surface except for the concave active site. It was also shown that the contacts, frequently involving water molecules, are formed with specific intermolecular hydrogen-bonds on the background of non-specific attractive electrostatic interactions. Macrobond strength is compared to those of associations in other protein complex systems.
The initial stage of crystallization, often called nucleation, is critically important for the eventual size, property and perfection of crystals. For protein crystals used in structure determination by X-ray crystallography, the understanding and control of nucleation are particularly required. Based on the large ratio of the molecular size of proteins and the distance over which the attractive interaction is extended, liquid-liquid metastable coexistence curve can be situated near the solution-crystalline solubility curve. By use of the liquid-liquid phase separation, nucleation can be promoted or controlled. Three papers (ten Wolde and Frenkel, Costa et al., and Drenth and Haas) are introduced and explained. Experimental works of the author's group using transmission electron microscopy and dynamic light scattering are then explained. The former detected formation of spherical structures (15 nm in diameter) in solutions of 10, 15, and 30 mg/ml hen egg-white lysozyme at 10, 4 and 2 h after supersaturation, respectively, at 20℃, 5% (w/v) NaCl and pH 4.6. The latter showed the advantages of using polyethylene glycol as a crystallizing agent in controlling the position of the liquid-liquid coexistence curve in relation to the solution-crystalline solubility curve.
Polar fishes living underneath the sea ice can survive under the supercooled condition of their serum, because a special kind of protein, i.e., antifreeze glycoprotein (AFGP), is included in their serum. AFGP molecules adsorb at the interfaces between ice and water and prohibit the ice crystal growth. In this review, basic effects of AFGP for the ice crystal growth are firstly summarized. Results of ice crystal growth experiments by one-directional growth method are introduced in the second part of this review. Interfacial kinetic supercooling was successfully measured as a function of growth velocity. Furthermore, the self oscillation of growth rate was observed for the crystal growth of ice (1010) plane. A model for these growth modes is proposed on the basis of the non-linearity and the in-reversibility in the relationship between the driving force and growth velocity.
The crystallization behavior of trilaurin (LLL) without and with application of ultrasonic power is investigated in-situ using synchrotron radiation time resolved small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS) simultaneous measurement. Without ultrasound application, both polymorhic forms β' and β crystallised in the melt. With ultrasound treatment of the melt, the following effects were observed: (i) a marked decrease of induction times for crystallisation of LLL, (ii) an increased nucleation rate, and (iii) a crystallisation of only β forms for LLL under conditions of initial crystallisation temperature of 30℃, and applied ultrasound of 2s. In addition to this, a crystallisation of LLL under lower initial crystallisation temperature of 25℃ and with the same ultra-sonication time of 2s, revealed the presence of both β' and β polymorphs. This suggests that crystallisation of only β form does not only depend on ultrasound treatment, but on the initial temperature of crystallization, as well. Based on the dynamic nucleation of LLL crystals induced by collapsing caviatation bubbles, we argue that a pronounced decline in induction times and increase of nucleation rate, result from the melting points shift due to high pressure pulses associated with collapsing bubbles. Insufficiency of this approach to account for the nucleation of only β polymorph or both β' and β polymorphs was also considered.
The effect of a magnetic field on the orientation of diamagnetic, non-aromatic L-alanine crystals was investigated. L-alanine was crystallized from a supersaturated aqueous solution in a magnetic field of 5 T. Short prismatic crystals were oriented so that their crystallographic c-axes were aligned parallel to the direction of the magnetic field. A newly designed microscope-interferometer was used for in situ observation of crystallization processes under the magnetic field. According to the observation, the c-axes of small nucleated crystals were forced to align parallel to the magnetic field direction even when the crystals were migrating in the solution due to thermal convection. Characteristic features of the orientation were explained by the small magnetic anisotropy of the L-alanine crystal, which should be derived from the CO_2 groups.
CsLiB_6O_<10> (CLBO) is a suitable nonlinear-optical crystal for ultraviolet (UV) light generation. To fabricate high-power UV light source, high-quality crystals are required. The CLBO crystals are usually grown by the Top-Seeded Solution Growth method from self-flux solution. In general, there exists hetero-phase components and compositional nonuniformity when the solution of large volume is prepared. These factors are understood to have adverse effect on the quality of grown crystals. Recently, we succeeded in obtaining high-quality singlephase sintered powder by pre-treating the starting materials. The crystal grown from this material had 1.6-fold higher bulk laser-induced damage threshold than that of conventional crystals and the value was fairly homogeneous throughout the crystal. It was found that the concentration of OH groups in the crystal was almost the same as that of conventional crystals.