Morphologies of single crystals (ployhedral, hopper, dendritic) and cryatal aggregates (spherulitic) are determined by the interface roughness and its anisotropy, driving force for crystal growth (supersaturation, super-cooling), and environmental conditions. Morphologies of crystals will be different between the cases where free growth is allowed and where growth is constrained by the environmental factors. Based on this, morphological characteristics of crystals and crystal aggregates of natural minerals and those formed by biocrystallization are compared. It is noticed that crystals formed by abnormal growth (such as gall stones, urea stones) take morphological characteristics of freely grown crystals (e. g. spherulitic), whereas those formed by normal growth (such as apatite in bone and tooth, aragonite and calcite in shells) do not show such morphologies. As possible constraining factors, 1) co-operative growth of organic and inorganic matters, and 2) growth in small enclosed environment, are mentioned.
Both stagnation and infection of bile, especially with Escherichia coli, together with dietary deficiencies, seem to induce formation of calcium bilirubinate stones. As to the mechanism by which calcium bilirubinate is separated out of bile, the activity of β-glucuronidase of bacterial origin is presumed to play an essential role; the enzyme hydrolyzes bilirubin glucuronide into free bilirubin and glucuronic acid, and calcium in bile combines at the carboxyl radical of free bilirubin to form calcium bilirubinate. On the other hand, bile usually has an inhibitory effect on β-glucuronidase activity. This is mainly due to glucaro-1, 4-lactone (glucaric acid) which is present in bile and known to be the most powerful inhibitor of β-glucuronidase.
The analysis of crystallization processes of human gallstones was made from a view point of crystal growth from the solution. It was noted that there were at least two stages in the formation of gallstones; (1) nucleation and growth of fine crystals and (2) aggregation of fine crystals. Therefore one can prevent gallstone formation by depressing either "nucleation and growth" of crystals (of cholesterol monohydrate or calcium bilirubinate) or aggregation of fine crystals. Gallstone surfaces and the internal structures were observed with polarizing light, phase microscopy, darkfield illumination and SEM. Analysis of elements was made by an energy dispersive solid state detector (SSD). Growth and dehydration processes of cholesterol monohydrate crystals were studied. Tentative model of aggregation of cholesterol crystals was proposed.
About the static organ and statolith of various animals, the existence and its place, the morphology, the crystal structure and the function to the static mechanism were reviewed. In our experiment, in situ observation of the statolith of goldfish was made through living body by the optical microscope. The shape is round in the period of vivipar and fry. As the fish grows, the shape changed irregular one similar to the receptor. The statolith is the polycrystal of CaCO_3 and its structure was mainly aragonite type. The growth rate is the order of 0.1 Å/s, and decreases as the statolith grows. The degree of supersaturation of lymph was estimated to be 12.9. In spite of the very high supersaturation, the growth rate is very small, owing to the small equillibrium concentration and the inhibition for growth. Probably, the heterogeneous nucleation must occur frequently at random orientation on many tangled fibers. From this, the surface of statolith becomes rough and isotropic for the surface energy, and the shape will be round when the size is small.
In this report, the in vivo mineralization in bivalve shells is reviewed based on the electron microscopic observations of the morphology and surface microtopographs of crystals. The nucleation and growth of crystals in initial mineralization sites where mineral crystals are absent is induced only in the specific organic granule elaborated by the mantle epithelial cells, and then needle crystals grow radially from the center of organic granules to form spherule. However, in additional mineralization during the subsequent growth of a mineralized structure, new crystals appear to bud from the imperfection, non-singular surface, step and faults, present on the host crystal surface. The new crystals grow usually in bivalve nacre by the spiral mechanism under stable secretion activity, but by the dendritic growth under unstable secretion activity. Consequently, the morphology and surface microtopographs of crystals are changed in each individual animal.
Recent advances in the knowledge about the mechanism of biological calcification was reviwed with special reference to the regulator proteins for this mechanism. Four important factors involved in this process were pointed out. These are; (1) the cells that form calcified tissues, (2) the organic matrices, (3) calcium and phosphate minerals and (4) the regulators for calcification. Generalized concept of calcification process was described in terms of these four factors. There has been an inconsistency between the facts that physiolosical extracellular fluids are, supersaturated in calcium and phosphate with respect to hydroxyapatite but it also are undersaturated with respect to the formation calcium phosphate de novo. Various theories including the booster, nucleation and inhibitor theories that have been proposed to explain this inconsistency, were criticized. It was emphasized that the systematic function of the regulator proteins for calcification may be a key to resolve the contradiction and to understand this complicated biological phenomenon.
The effects of enamel proteins, dentine phosphoproteins, and bone collagen on the seeded crystal growth of enamel apatite crystals and on the formation of amorphous calcium phosphate were studied in stable supersaturated and unstable supersaturated solutions, respectively, at pH 7.4 and 37℃. Of the two major protein classes in the enamel matrix, enamelins were much potent than amelogenins in retarding seeded growth. However, the amelogenin species that showed significant inhibitory activity are those known to be lost first from the enamel matrix during the rapid mineralization stage of enamel maturation. When compared to the enamel proteins, dentine phosphoproteins and egg yolk phosvitin were found to be up to 8 times more effective in reatrding crystal growth kinetics, whereas bone collagen showed no effect on this seeded growth kinetics at μM concentrations. None of the proteins tested accelerated the formation of amorphous calcium phosphate in unstable supersaturated solutions. This finding may suggest that they play no positive role in the initiation of mineralization in hard tissues.
In the first stage of tooth development, enamel crystals are thin, ribbon-like in shape and highly orient in their c-axis direction. Based on a hypothesis with respect to a role of Tomes' process that the cell membrane control not only the concentration of ions necessary to precipitate initial phase but also their diffusing direction to regulate the orientation of growing crystals, a new technique using ion selective membrane has been proposed. In this system nucleation and growth of calcium phosphates were initiated and controlled by allowing calcium (phosphate) ions to diffuse into phosphate (calcium) solution through synthetic ion-selective membranes. Hydroxyapatite thus obtained by hydrolysis of octacalcium phosphate, which has been proposed as a possible precursor involved in the first stage of tooth development, nucleated on and grown perpendicular to the membrane is found to be comparable to mature human enamel in degree of orientation. In this report, the dependence of morphology and orientation on such physiological factors as pH, initial concentrations of calcium, phosphate, and fluoride is studied In order to clarify the raction that might be taking place in the diffusion layer on the ion selective membrane, some reactions were carried out in nonmembrane systems in which precipitation was initiated by adding calcium (phosphate) solution dropwise to phosphate (calcium) solution.
Some orthophosphates have been known to have the polymorphism similar to SiO_2. The low temperature form (Berlinite) has been especially attracted by its superior electrical character to α-quartz. The single crystal of the Berlinite has been synthesized hydrothermally from the higher concentration of phosphoric acid solution, but the highly qualified single crystal has hardly grown. In the present paper, the features of orthophosphate crystals are reviewed and the results for the new processing to prepare the pure AIPO_4 crystal are mentioned. The low temperatrure form of Ga PO_4 could be successfully synthesized by this hydrothermal method, whereas it was found that the stabilization of Fe^8+ as FePO_4 was impossible in the hydrothermal phosphoric acid solution up to 650℃ at 1000 kg/cm^2.
The formation of large single crystals of protein is essential for the crystallographic structure analysis. The techniques of crystallization have been developed especially when only small amount of protein is available. The conditions suitable for growing good crystals can be obtained by trial and error, but at the same time it is necessary to seek good conditions from the general empirical rules. The author, an X-ray crystallographer, wanted to introduce the general techniques of protein crystallization to those in the field of crystal growth for discussions. Here the nature of protein is briefly shown and the techniques of crystallization are presented. An example of crystallization of immunological proteins is also shown in some detail.
The structure of hydrated ions has been discussed on the basis of X-ray and neutron diffraction data for electrolyte solutions. Microscopic structures of hydrated alkali metal and halide ions studied by molecular dynamics simulations have been compared with time-averaged and space-averaged structures of the ions determined by the diffraction methods. The dissolution process of a sodium chloride crystal has been simulated by using the molecular dynamies simulation with a high speed computer. The simulation shows that chloride ions at corners of the sodium chloride crystal first remove from the crystal. The driving force of the dissolution process and the role of hydration energies of ions to the dissolution phenomenon are discussed.
The effects of viscosities and sol-gel transition on the conductivity of alkali metal chlorides (MCl) and the electro-deposition and -dissolution of thallium were studied in poly (ethylene oxide)-H_2O and agarose (II) -H_2O media. Deviations from extended Walden's rule were generally observed for the molar conductivities of MCI in the poly (ethylene oxide) solutions. The deviation is considered to be related with the difference in the entropic terms for the ionic migration and viscous flow, which may be due to the loose network structure of poly (ethylene oxide) molecules in the solution. No significant effects of the sol-gel transition appeared on the electrode processes of thallium in agarose (II)- H_2O media. The anodic dissolution peak current of thallium at a rotating gold electrode was found to be practically independent of rotation speed in solutions containing poly (ethylene oxide) of very high molecular weights.
The optimum form and size of 2D nucleus and its formation energy on a singular surface in the case of AB asymmetric bond crystal are formulated. It is concluded that the nucleation characteristics of the system depend not only on the total activity but also on the respective activities of the components in the environment. As a preliminary, a critical comparison is made between the thermodynamical description of the so-called Wulff's theorem and the kinematical description of the Bulgarian school, and the equivalence of the two descriptions is demonstrated in the case of one-component symmetric bond crystal.
The concept of spacial frequency is introduced to characterize suface structures on growing crystals. Growth processes of a salol crystal were studied by the special frequencies which were obtained from in intereference fringe patterns by cross-polarized laser beams. Power spectra of the patterns were obtained from the special frequency spectra which were got by computational Foureir transformation and optical one as well. On the spacial spectrum space, the periodicities of the fringe pattern are indicated by spots and their sequences, and its irreguralities are by diffuseness of the spots. The directions of spot arrays indicate that of the periodicities which are present on the surface. The spacial frequencies of the structure on surfaces will be suitable to characterize growing and as-grown crystal surfaces, etched surfaces and biological matters such as renal stones and pearls. Forthermore a phenomenological theory will be introduced from microscopic ones on the growth by using the concept of the spacial frequeney.