Template reactions, calcium

It is surprising that rather little use has been made of template reactions in relation to calcium biochemistry, possibly since the... 

AIPO4 is isoelectronic with silica and, as such, readily forms glasses and Si02-like crystalline materials. As well, framework stmctmes similar to zeolites may be prepared by the use of amines as templates. Like zeolites, these are active in catalytic reactions such as methanol conversion to hydrocarbons (seeZeolites) As a ceramic material, AIPO4 is an infusible material that is insoluble in water but is soluble in alkali hydroxides. It is often used with calcium sulfate and sodium silicate for dental cements. AIPO4 is also used as a white pigment that also acts as a corrosion inhibitor. 

Figure 7.13 The reaction of a pyridine dialdehyde with several diamines forms a dynamic combinatorial library. From this library, several diimine macrocycles can be obtained in good yield when template ions (symbolized by polygons) of proper size are added. Magnesium ions give a ring size of 15, calcium ions one of 18, and barium ions stabilize the 21-membered rin ...

The natural-template method was developed in 1974. It can produce porous HA powders. A suitable template was found to be the calcium carbonate (CaC03) skeleton of reef-building corals, such as those found in the South Pacific. The reaction to produce HA involves a hydrothermal exchange reaction of carbonate groups with phosphate groups, which can occur via the following chemical reaction ... 

Dystrophic calcification occurs in two stages calcium deposition and the reaction of the tissue to deposited salts. Again, it is not known what precipitates calcium. It is sometimes assumed that changes in the matrix will lead to crystallization of the calcium salts because the altered matrix acts as a seed or template for hydroxyapatite crystallization. We have seen that in bone the hydroxyapatite crystal is bathed in a supersaturated solution of calcium and phosphorus and serves as a seed for further crystallization of the calcium phosphate salt. 

Two chemical ways were used to include metal nanoparticles inclusion in the microcapsule shell. It was photoreduction of silver under of UV-irradiation and chemical reduction of silver by acetaldehyde oxidation (reaction of a "silver mirror"). The polystyrene latex and calcium carbonate were used as a template for the formation of polyelectrolyte shells. 

The reaction of dap with diethylenetriamine (dien) on barium(II), strontium(ll), calcium(II) or magnesium(II) perchlorates or nitrates as template sources, in molar ratio 1 2 1 in methanol at room temperature, results in isolation of chelates [M(L678)]X2-nH20 (X - CIO4, NO3 = 0, 1) (Eq. 3-20) [57]. 

The reaction of 2,6-dfp and L794 (Eq. 3.71) in methanol yields a yellow solid which proved to be a mixture of 1 - -1 condensation products (cyclic and acyclic), as well as polymeric products. Attempts to separate the macrocyclic compound failed [165]. However, the synthesis of macrocyclic compound L795, isolated in the form of metal complexes, has been carried out in the presence of manganese(II) [149], calcium(II), strontium(II), barium(II) [165], lead(II) [170, 171] and lanthanide(III) [172]. A template method using Ln ions (Ln = La, Ce, Pr, Nd and Gd) was found to be effective in the formation of metal complexes of the macrocycle L796 [147]. 

Reaction of dff with l,5-diaminopentan-3-ol in the presence of calcium(II), strontium(II), or barium(II) perchlorates yields either the complexes of the (2 - - 2) macrocycle L810 or of the open-chain (1 +2) condensation product L811 (Eq. 3.80). In the absence of a template centre one fails to obtain macrocyclic or open-chain Schiff bases by using these ligsons [197]. 

Crystals of calcium salts have also been used for imprinting polymers of carboxyhc acid functional monomers. Instances include imprinting artificial polymers with calcite to act as a template for the growth of specific crystal phases [95]. It has been reported that the calcite-imprinted polymers induced the formation of calcite nuclei even when the reaction conditions favored the growth of its other polymorph, namely aragonite. Another example of such work is the nucleation of calcium oxalate crystals on an imprinted polymer surface [96] where 6-methacrylamidohexanoic acid/divinylben-zene copolymers imprinted with calcium oxalate monohydrate (COM) or dihydrate (COD) crystals were used to foster the nucleation of CaOx crystals. The results revealed that the polymers gave rise to the formation of crystals that were the polymorphs of the template crystals. 

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