The growth of inorganic crystals under the effect of biological macromolecules added as an impurity is of special importance in relation to the biocrystallization. We present the results of the free growth experiments of ice in supercooled water containing an impurity of glycoprotein, which is a bio-macromolecule that functions as ‘antifreeze’ in living organisms in a subzero environment. The interface direction dependence for the effects of antifreeze protein among the basal, prismatic and pyramidal faces were clearly shown on the basis of growth experiments carried out in both the laboratory and the International Space Station. The growth rates for prismatic and pyramidal faces were suppressed by the impurity effect of antifreeze glycoprotein, in contrast acceleration and oscillation of the normal growth rates were newly discovered as an antifreeze protein effect for the basal face. This interface direction dependence for the effect of antifreeze glycoprotein leads to a better understanding of the onset of the mysterious antifreeze effect in living organisms, namely, how this protein may prevent fish freezing.
We consider a vicinal face, where atoms and impurities impinge and evaporate to a vapor phase, to study how the surface diffusion and evaporation of impurities affect step bunching induced by impurities. When the lifetime of impurities on the vicinal face Ƭimp is long and the surface diffusion of impurities is neglected, the step bunches induced by impurities are tight. When Ƭimp decreases, the size of the step bunches, which means the number of steps in the bunches, decreases but the separation of single steps from bunches does not occur. When we take into account fast surface diffusion of impurities, the separation and collision between single steps and step bunches occur repeatedly.
We extended the Burton-Cabrera-Frank (BCF) theory for crystal growth to include incorporation of impurities into a crystal growing from aqueous solution. We considered the surface processes of impurity molecules such as adsorption from solution to crystal surface, desorption from the surface, incorporation to step edge, and release from the step edge; as well as the host molecules that compose the crystal. Our theory enables us to calculate the partition (distribution) coefficient of impurities having various physical quantities relating to the surface processes. We demonstrated some interesting results on the impurity incorporation as examples; purification by slow surface diffusion and the dependence of the partition coefficient on supersaturation. Our theory provides a theoretical framework for identifying which factors significantly affect the incorporation of impurities into the crystal.
The colloidal particles dispersed in liquid self-assemble into “crystal” structure, where the particles arrange regularly, under appropriate condition. The crystallization of colloids has been studied as a model to study phase transition in atomic/molecular systems. We can observe both melt growth like process and solution growth like process in colloidal systems depending on the interaction between colloidal particles. For attractive interaction, the crystallization is solution growth like. The particle densities in liquid and crystal phases are significantly different from each other. Here, I describe solution growth of colloidal systems and exclusion of impurity particle on the growth process from the viewpoint of the difference of the interparticle interaction between main component and impurity particles. The attractive interaction is caused by depletion attraction by depletant molecules, which are added into the colloidal dispersion as the secondary component. I also report some examples of impurity exclusion.
This paper details the results of the previous research on the fabrication of octacalcium phosphate (OCP)-based bone substitute materials, along with its new findings. OCP has received considerable attention as a new bone substitute material because it exhibits excellent biocompatibility. However, its poor formability seriously restricts its implementation in biomedical applications, especially as a bone substitute. OCP has been fabricated in aqueous solution via aqueous mediated reactions. Furthermore, the crystal growth process of OCP as a bone substitute material has also been investigated. Although previous studies have indicated that OCP is preferentially formed under weak acidic solutions, we also introduced Na+ and PO43− as key factors for OCP formation because they strongly enhance the OCP crystal structure. Based on these new findings about OCP formation, we introduced fabrication protocols for an OCP block as a bone substitute. In vivo studies have indicated that the fabricated OCP block exhibits excellent biocompatibility.