Organic phase collagen

The bone cokes are essentially calcined bone, the organic phase - collagen - forming a black to brown coke on an inorganic hydroxylapatite q.v) substrate. Toch (1916) describes a preprocessing step in which the inorganic carbonate is dissolved... 

The most commonly employed model is the early uptake (EU) model, where U is deemed to have been taken up sufficiently shortly after burial for the bone to approximate to a closed system. Justification for the validity of early uptake seems to have stemmed from Szabo s (1979) suggestion, later elaborated on by Rae and Ivanovich (1986), that Uranium is fixed in the bone in the U oxidation state, facilitated by the reduction of U by decay products of the organic phase of bone, collagen. Since the bulk of collagen is lost rapidly from the bone (on the U-series time-scale at least), it is assumed Uranium will be taken up rapidly, and then uptake will cease. 

Organic phase bone, 132-136 collagen, 132-133 fibronectin, 134-135 laminin, 133-134... 

Phosphates are found in soft organic tissues as phosphate esters, and in hard tissues, notably bones and teeth, as solid calcium orthophosphates see Biomineralization). Hard tissues are composites of Apatite and an organic matrix collagen in bone, dentin, and dental cement, and keratin in dental enamel. The Apatite phases are defective with Ca/P ratios of 1.6-1.8 and can incorporate other cations (Na+, K+, Mg +) or anions (F , d , COs ", citrate). 

Figm 13 Schematic arrangement of mineral and organic phase in a mineralized collagen fibril subjected to tensile load. Redrawn, based on Gao, H. J. Ji, B. H. Jager, I. L. etal. Proc. Natl. Acad. Sci. U.S.A. 2003, 100, 5597-5600. ... 

Crystal development in enamel takes place in three stages each with a different mechanism. The first stage involves the initiation of a small crystal seed de novo. It takes place near the surface of the ameloblasts soon after they have begun to secrete the organic phase immediately after the first dentine has been laid down. No more is known about the mechanism of the initiation in enamel than in other mineralized tissues (Chapter 31). It may occur on one of the enamel proteins, possibly the enamelin, or perhaps on the neighbouring dentine collagen. 

Beech [154] points out that, because of the anionic character of CNA polymerization, the product obtained adheres to dental surfaces. CNA polymerization can be initiated by the NH, or OH groups in proteins. Since the initiator remains bound to the monomer, the polymer remains bound to proteinic support. Thus, because of the outstanding importance of oi anic phase in dentine, this hard tissue represents an exquisite support for CNAs. NH2 and OH groups in collagen (the main component in dentine organic phase) amino acids represent active positions... 

Moreover, the comparison of human bone tissue and a type I collagen reference material showed that the bone organic phase has a lower thermal stability with respect to pure collagen, which can be explained by the fact that the proteins denaturation leads to the formation of new bonds in the collagen (i.e. amorphous polymer formation). Within the osseous tissue these bonds occur at the interface between the organic and mineral components of bone, having a critical role in their interaction [9,40],... 

Using collagen I as the organic phase in bone-biomimetic nanocomposites comes to nature the nearest. Collagen initiates and orientates HA crystal growth and is reported to be responsible for size and distribution of HA crystals in natural bone [37]. 

---