Coccolithophorids are photosynthetic unicellular calcifying algae that form calcium carbonate crystals in the cell. The crystal with a fine structure, named coccolith, is synthesized in the coccolith vesicle that was derived from Golgi body, then transported onto the cell surface. The fundamental feature of coccolith growth, termed as the V/ R model, involves the assembly of a ring of single crystals with altering orientations, radial (R) and vertical (V). A living cell of a cosmopolitan species of coccolithophorid, Emilania huxleyi, seemed anomalous because only R crystals had been observed. However, relict V crystals are found in a proto-coccolith ring and the crystals were overgrown by preferential development of R units in a complete coccolith. Such composition and structure of coccolith crystals have varied during biological evolution. The calcification is mediated by organic base plate composed of acid polysaccharides. Active species of dissolved inorganic carbon utilized for intracellular calcification is a bicarbonate ion, whereas that for photosynthetic fixation is CO_2 Calcification is known as a CO_2 producing process when it proceeds chemically. However, the evolved CO_2 can immediately absorbed by photosynthesis when the activity is higher than that of intracellular calcification. Regulation of CO_2 fixation and growth of coccolithophorids is therefore very important for the balance of CO_2 between the ocean and the atmosphere . In this article the role of coccolithophorids in the global carbon cycle is also discussed.
The interfacial tension, γ, between crystals and the solution plays a key role for the rate of nucleation of crystals. Attempts have been made to measure the value by measuring the incubation time for nucleation and the 1 /σ^2 where a is the supersaturation of the solution. The discrepancy of γvalues under gravity and under microgravity was interpreted as the dominant heterogeneous nucleation under gravity, whereas under microgravity homogeneous nucleation is dominant. Theγvalue can be varied by adding some impurities to the solution, which not only changes crystallization rate but also modifies the polymorphs. Since the change ofγis the result of modification of the growing/ dissolving interface, extensive AFM works have been done on calcite surface. Some AFM works and DLS works have been reviewed, so that the importance of theγvalue could be realized.
Gas hydrate crystal is one of the clathrate compounds in which a large number of gas molecules are trapped inside well-defined cages formed by water molecules' Huge amount of gas hydrates naturally exists in the sediments of deep seas and of the permafrost, which are expected to be one of the future resources or the sources of the carbon cycle Recently gas hydrates are also expected to be applied to the engineering utilization or to the functional material agree to the environment. To estimate the effect of the gas hydrates on the global environments and on the human activities, the knowledge of the crystallographic characteristics and of the growth mechanisms are important. This paper overviews the recent activities of the hydrate study the order of the growth mechanisms.
Ice sheets and glaciers have been accumulating snow, and atmospheric gases and aerosols since they built up. It has been recognized that ice-core chemical records provide invaluable information on past climate and atmosphere. However, due to a lack of understanding of air to snow transfer and post-depositional processes of chemical substances, interpretation of ice-core chemical records could be misleading. Large amounts of chemical data have not been properly interpreted. It is essential to understand those processes to avoid the misinterpretation, and to obtain the maximum information from ice-core chemical records. Ice-core chemical records are affected by many processes: (1) large-scale transport of chemical constituents from tropical and mid-latitude (as well as high latitude) sources to polar regions; (2) cloud scavenging processes; (3) wet and dry deposition processes and their relative contributions; (4) post-depositional processes such as re-emission of chemical constituents from the snow, sublimation/ evaporation, redistribution by winds, melting and re-freezing, diffusion and chemical reactions within the snow, firn and ice . This paper reviews evidence of post-depositional changes found in polar snow, firn and ice, such as changes due to wind scouring, nitrate losses, movement of methane sulfonic acid (MSA), etc.
Biocrystallization in living organisms is qualitatively different from artificially defined crystal growth systems, because biological crystal growth occurs based on the principle of the purposefulness of living matter, which enables bio-logical systems to function and evolve. That is, biological systems select the most suitable material, and form the most efficient molecular structure and macro-forms, as though crystal growth in living organisms had been designed from the start to enable it to perform certain functions. Biocrystallization that deviate from this purposefulness causes illness. In this paper, 1) normal biocrystallization, such as the auditory apparatus, and abnormal biocrystallization related to illness, for example, asymmetric conjoined twins, oxalosis, and the hydroxyapatite of arteriosclerosis, obtained by micro-focus X-ray computed tomography (p-CT, MFXCT) have been described. 2) Crystals are characterized by sensitivity to changes in shape under the influence of crystal growth conditions, so called habit modifications, without undergoing any molecular structural changes. The central methodology of science today, however, is based on determinations of molecular structure to study the morphology and functions of objects. Applying the character of habit modifications can serve as a new methodology for obtaining useful biological information that cannot be obtained by the conventional methodology. We obtained biological information by using habit modifications of hydrated cupric chloride in the presence of blood, which is a type of general crystal growth in vitro in a complex system.
The main purpose of this article is to describe a recent improvement of Ge crystal growth on nanometer scale. It has been reported that small amount of C atoms have a key role for controlling size and structure of the Ge dot. First, the effect of the C atoms deposited on the Si(100) substrates is reviewed. The C atoms were found to form Si-C alloy layer, on which the Ge growth mode was modified. Second, we propose a multi-step procedure on the basis of AFM and TEM characterization. Our key point is that the C submonolayers were incorporated at the interface between Ge wetting layers and Ge dot. This procedureachieves to control Ge dot size, structure and density on the Si(100) substrate.