Calcium complexes structure stabilizers

Calcium-binding proteins, 6, 564, 572, 596 intestinal, 6, 576 structure, 6, 573 Calcium carbonate calcium deposition as, 6, 597 Calcium complexes acetylacetone, 2, 372 amides, 2,164 amino acids, 3, 33 arsine oxides, 3, 9 biology, 6, 549 bipyridyl, 3, 13 crown ethers, 3, 39 dimethylphthalate, 3, 16 enzyme stabilization, 6, 549 hydrates, 3, 7 ionophores, 3, 66 malonic acid, 2, 444 peptides, 3, 33 phosphines, 3, 9 phthalocyanines, 2,863 porphyrins, 2, 820 proteins, 2, 770 pyridine oxide, 3,9 Schiff bases, 3, 29 urea, 3, 9... 

The use of alkali and alkaline earth group metal ions, especially those of sodium, potassium, magnesium, and calcium, for maintenance of electrolyte balance and for signaling and promotion of enzyme activity and protein function are not discussed in this text. Many of these ions, used for signaling purposes in the exciting area of neuroscience, are of great interest. In ribozymes, RNAs with catalytic activity, solvated magnesium ions stabilize complex secondary and tertiary molecular structure. Telomeres, sequences of DNA at the ends of chromosomes that are implicated in cell death or immortalization, require potassium ions for structural stabilization. 

Most of this section will be devoted to summarizing information relating to the stability constants reported for complexes of this group of Ca2+-binding ligands. However, we shall precede this main part with a short mention of a few relevant structures. Other properties of calcium phosphates and phosphonates will be mentioned in Sections VIII.B.4 and VIII.D below. An overall view of complexes of nucleosides, nucleotides, and nucleic acids is available (670). 

As seen in Table 2.10, the stability constants of the tartarate and citrate complexes of lead and calcium ions are much smaller than those of EDTA and DTPA complexes. The calculations show that the dominant species of cations are Pb2+ and Ca2+ at pH < 4, and so the same ion exchange can be expected as would happen without complex-forming agents. At pH > 4, the effect of citric acid is significantly higher than expected from stability constants. The structure of citrate... 

In the studies of mechanochemical synthesis of hydroxylapatite from the mixtures of calcium orthophosphates and oxides, Chaikina demonstrated that the synthesis rate is changed depending on the type of phosphate complex the more protons in the complex, the higher the reaction rate. It was demonstrated that water molecules, being one of the structural components of the intermediate phase, stabilize it, that makes the rate of the formation of this phase dependent on the amount of bound water in the mixture [39 ]. 

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