Mineral-mediated chemistry

The Role of Special Structural Entities - Active Sites - in Mineral-Mediated Chemistry... 

Both these catalytic centers and the reaction mechanism on them have been better than average well-characterized by the spectroscopic methods discussed and applied in this volume. The comparison between anticipated locations of the catalytic centers for these materials also points up the importance of methodology for determining not only the number, but the accessibility of catalytic sites. Therefore, it is thought that comparisons and contrasts between thermal and photo chemistry, as well as many aspects of the state of present comprehension of mineral spectroscopy and mineral-mediated catalysis will be well-illustrated by a reexamination of published studies of change, even though this reaction is not directly relevant to applications of spectroscopy discussed in the succeeding papers. 

Unlike laboratory chemistry, geological chemistry occurs in thermodynamically open systems. That is to say, there is flagrant exchange of materials and energy between the system and the environment Not only is the system as a whole not isolated from the environment, but the materials of interest are rarely isolated from each other. To further the complexity, interaction of mineral catalysts with those forms of energy most likely to affect surface-mediated reactions has barely been characterized in model systems. 

For the development of a sustainable chemistry based on clean technologies, the best solvent would be no solvent at all. For this reason, considerable efforts have recently been made to design reactions that proceed under solvent-free conditions, using modern techniques such as reactions on solid mineral supports (alumina, silica, clays), solid-state reactions without any solvent, support, or catalyst between neat reactants, solid-liquid phase-transfer catalysed and microwave-activated reactions, as well as gas-phase reactions [37-42]. However, not all organic reactions can be carried out in the absence of a solvent some organic reactions even proceed explosively in the solid state Therefore, solvents will still be useful in mediating and moderating chemical reactions and this book on solvent effects will certainly not become superfluous in the foreseeable future. 

Mineralization is the precipitation of calcium phosphate, but biochemical mediation of this process is not fully understood. In this chapter, the chemistry underlying mineralization (Sect. 1) and the structures ofbones and teeth (Sect. 2) are described. Osteoblasts secrete osteoid matrix and matrix vesicles that transport type I collagen and calcium phosphate, respectively, to the matrix where they will mineralize. Secreted matrix vesicles take up calcium and phosphate until they burst and release the calcium phosphate, which then redissolves and remineralizes around the type I collagen (Sect. 3). Glycoproteins involved in correctly modeling bone and dentin, and the role of osteocalcin in limiting excessive bone growth is then discussed (Sect. 4). There follows a detailed description of enamel (E) mineralization and of the major proteins involved (Sect. 5) followed by two summaries the difference between enamel and bone mineralization, and the vitamins required for mineralization (Sect. 6). 

The surface defines the interface between a mineral and its surroundings. In a dynamic context, reactions that occur between apatites and the environments in which they exist take place at or through their surfaces. This includes, but is not restricted to, crystal growth, dissolution, and surface-mediated reactions such as sorption, surface complexation, and catalysis (Hochella and White 1990). Because this interface is partly defined by the nature of the environment around the crystal, the properties, structure and chemistry of the crystal surface are always different than those of the bulk, and can be quite varied depending on the environment. For example, the crystal surface of apatite may have very different characteristics in contact with an aqueous solution as opposed to a polymerized silicate melt. 

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