Chitons

Phylum Mollusca Chitons, snails, clams, squids, octopi... 

However, ferritins isolated from the bacterium Pseudomonos aeruginosa (Mann et ah, 1986) and from the chiton Acanthopleura hirtosa (St. Pierre et ah, 1990) have iron cores of limited crystallinity, despite having P Fe ratios of around 1 40, perhaps suggesting that core crystallinity is influenced by the rate of iron deposition as well as by the composition of the medium. The way in which phosphate may influence core development is discussed below. 

Iron Oxide Fe304 FeO(OH) Magnetite Ferritin Bacteria-chitons teeth Widespread Magnetic device Iron store... 

The best known 2,5-anhydro hexose is that which was prepared in 1894 by Fischer and Tiemann4 and named by them chitose. Chitose is a liquid with ill-defined properties and is usually characterized by its oxidation derivatives, chitonic acid and isosaccharic acid. It is prepared by the deamination of the naturally occurring chitosamine (D-glu-cosamine). 

Let us now return to the pioneering work of Fischer and Tiemann.4 Chitonic acid is produced from D-glucosamine by deamination and oxidation, in that order. If the order is reversed, however, i. e., if D-glucos-amine is first oxidized to D-glucosaminic acid (2-amino-D-gIuconic acid) and the latter substance subsequently deaminated, chitonic acid is not the product. Instead an isomeric 2,5-anhydro hexonic acid (chitaric acid) is obtained. These facts may be summarized thus ... 

Walden inversion on C2 has occurred in one of these sequences if in the first, then chitose, chitonic acid and isosaccharic acid have the configuration of D-mannose if in the second, i. e., in the deamination of 2-amino-D-gluconic acid, then chitaric acid and epi-isosaccharic acid are... 

Chitons are marine molluscs with shells consisting of movable plates. 

This approach has been used to S3mthesize a variety of valuable l,3-deox3q)oly-ketide chitons, 1,3-hydroxymethyl chitons, vicinal dimethyl chitons, and aldol-like products from trisubstituted olefins (Scheme 11). High diastereomeric ratios could be obtained often in greater than 90% for most cases. 

Higher nuclearity oxo-lron centers are present in iron storage proteins like ferritin (Ft) and hemosiderin (Hs)(l) as well as in magnetotactic organisms and in the teeth of chitons(2). In the latter two cases magnetite is the predominant phase. In the case of the storage proteins (see Chapter 9), the metallic cores are structurally poorly characterized and numerous questions concerning their formation, structure and functionality remain to... 

Chitons Teeth hardening Magnetite (lepidocrocite, ferrihydrite)... 

Biogenic hpidocrodte was first discovered by Lowenstam (1967) in the radula teeth of a chiton. The crystals are lath-shaped and several tenths of xm long with terminal 101 faces (Webb et al., 1989) (see Fig. 4.14a). The lepidocrocite is often associated with magnetite and ferrihydrite suggesting an Fe" precursor (see Chap. 13). 

The nature of the additional minerals depends on whether the chiton is a warm water or a cold water species. 

Kirschvink, J.L. Lowenstam, H.A. (1979) Mineralization and magnetization of chitons teeth. Paleomagnetic, sedimentologic and biologic implications of organic magnetite. Earth and Planet. Sci. Letters 44 193-204... 

Ghiorse.W.E. (2002) Effed of oxide formation mechanisms on lead adsorption by biogenic manganese hydroxides and their mixtures. Environ. Sci. Techn. 36 421-425 Nembrini, G. Buffle, J. Haerdi, W. (1976) Vol-tametric behavior of iron(III) hydrolyzed solutions and characterization of the reducible species. J. Colloid Interface Sci. 57 327-336 Nesson, M.H. Lowenstam, H.A. (1985) Biomineralization proceses of radula teeth of chitons. In Kirschvink, J.L. Stone, D.S. (eds.) Magnetite biomineralization and magneto reception in organisms. Plenum Press, New York, 333-363... 

Chitons, soft parts Clams, soft parts... 

Hydroxyapatite vertebrates, mammals, fish Octacalcium phosphate vertebrates Amorphous SiO limpets, chitons Magnetite chitons Goethite fimpets Phosphoferrite chitons... 

Mantun, I. Further observations on scale formation in Clerysochromulina chiton. J. Cell. Sci. 2, 411 (1967)... 

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