By G. H. Nancollas (auth.), G. H. Nancollas (eds.)
normal and pathological mineralization in vertebrates but in addition with the attention-grabbing difficulties excited by the formation of in tracellular deposits of calcium oxalate in vegetation. right here cal cium carbonate and silica can also be interested by the mineral ization methods. Calcium carbonate is a vital part within the formation of mollusc and avian shells. The statement that either calcite and aragonite will be shaped in biogenic cal cium carbonate increases vital questions as to what components keep watch over the formation of the ultimate mineral section. there's no doubt that thermodynamically much less good stages could be kinetically stabilized for lengthy classes of time by means of different mole cules found in vivo. In general mineralization, calcium salts may possibly firstly be deposited either in the cells and extracel lularly. within the latter case, the function of matrix vesicles and the ways that the matrix elements may possibly keep watch over mineral ization have been specifically emphasised. there's truly a necessity for extra structural and useful info concerning cells, matrix elements, and their linked crystals. The enhance ment of extra innovations related to mutants, chromofluors, and fixatives for upkeep of tissue and the ions found in vivo was once steered. In facing irregular and pathological mineralization, the Workshop focused on urolithiasis, gout and pseudo-gout, and the formation of dental caries. Discussions in response to the impression of media of low pH on mineral surfaces highlighted a few of the elements of value in controlling crystal dis solution.
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Extra info for Biological Mineralization and Demineralization: Report of the Dahlem Workshop on Biological Mineralization and Demineralization Berlin 1981, October 18–23
NUCLEATION PHENOMENA The first step in a crystallization process is the attainment of a supersaturated state. The condition of supersaturation alone, however, is not sufficient for a system to begin to crystallize. Before crystals can grow, new crystallization centers must exist in the solution. This formation of one phase in another, under conditions where a free energy barrier exists, is the process of nucleation. If nuclei are formed in perfectly clean solutions in the absence of any foreign particles or surfaces, then the mechanism is one of "homogeneous" nucleation, also sometimes called spontaneous nucleation.
Also ripening, agglomeration, epitaxy, and inhibition are treated. Future progress will be assisted by measurements of well-defined parameters in simple solutions parallel with experiments in "biological media," and interpretation in terms of precise molecular models. INTRODUCTION The use of the word "mineralization" for processes where crystals are formed in a biological system indicates that the crystals are considered as nonbiological elements. This may be reasonable because inside a crystal one will not find the usual biological system with hundreds (or thousands) of different kinds of organic substrate molecules, enzymes, and coenzymes, etc.
4b). However, new kinks will appear spontaneously. If a growth unit is added at a step in a non-kink site (a on Fig. 5), the surface area of the crystal is increased by 2a 2 , where a is the length of the edge of the cube describing the geometry of the growth unit (accurately enough for our purpose), and two kinks are created. E. Nielsen and J. Christoffersen The energy e (work) needed to creat a kink (in a saturated solution) is thus a 2 o, where ° is the surface tension (assumed uniform on all sides of the growth unit in our primitive model) .