Calcium ion, complexes

The eight-sided geometric solid corresponding to a hexa-coordinate metal-ligand complex, as observed with fer-ricyanide [Fe(III)CN6] or calcium ion complex with EGTA. 

Cotton, F. A., Hazen, E. E., Jr., and Legg, M. J. (1979). Staphylococcal nuclease Proposed mechanism of action based on structure of enzyme-thymidine 3, 5 -bisphosphate-calcium ion complex at 1.5-A resolution. Proc. Natl. Acad. Sci. U.S.A. 76, 2551-2555. 

Urry, D. W., Cummingham, W. D., Onishi, T. A neutral polypeptide calcium ion complex. Biochim. Biophys. Acta 292, 853 (1973)... 

Dalgliesh, I), G. and Parker, T. G. 1980. Binding of calcium ions to bovine asi-casein and precipitability of protein-calcium ion complexes. J. Dairy Res. 47, 113-122. 

Sposito, G., K. M. Holtzclaw, and C. S. LeVesque-Madore. 1978. Calcium ion complexation by fulvic acid extracted from sewage sludge-soil mixtures. Soil Sci. Soc. Am. J. 42 600. 

RA. Cotton, E.E. Elazen, M.J. Legg, Staphylococcal Nuclease - Proposed Mechanism of Action Based on Structure of Enzyme-Thymidine 3, 5 -Bisphophate-Calcium ion Complex at 1.5 A Resolution , Proc. Natl. Acad. Sci. USA, 76, 2551 (1979)... 

To observe the effect of complex formation with an attendant change in the geometry of the ligand molecule, the calcium ion complex of another model compound, the 1,5-anhydrorlbltol, was investigated. It was hypothesized that the 1,5-anhydroribltol would change conformation to the alternate chair form to enhance formation of the calcium ion complex because the alternate conformation has the axial-equatorial-axial sequence preferred for complex formation. 

The three systems just discussed span the range from a relatively strong complex to a very weak complex. For the weak complexes the inositol vibrational spectra remain essentially unchanged upon complex formation. For the strong complex, the epi-inositol calcium ion complex, changes observed in the inositol spectrum were of a minor nature involving changes in the relative... 

Figure 6. Representation of the 1,5-anhydroribitol chair inversion to form the 1,5-anhydroribitol-calcium ion complex...

Equation (2) is valid for 1 1 calcium-ligand complexes and can be used in the case of polyanions where the binding sites are assumed to be mutually independent. For nonpolymeric compounds where 6 does not equal 1, higher or lower calcium-ligand complexes are indicated. A 9 value less than one indicates the presence of complexes with more than one calcium ion complexed per molecule of complexing agent, L". In such instances an additional equilibrium expression must be considered as given by equation (6). ... 

Extrinsic Pathway. Coagulation is initiated when tissue extracts with Hpid—protein properties are released from the membranes of endothehal cells following injury or insult. These substances, collectively designated tissue thromboplastin, complex with circulating Factor VII and in the presence of calcium ions subsequentiy activate Factor X (Fig. 1). In vitro evidence suggests that Factor X can be activated less rapidly through the interaction of kaUikrein [9001-01-8] with Factor VII. 

Calcium is the trigger behind the muscle contraction process (24,25). Neural stimulation activates the release of stored Ca(Il) resulting in a dramatic increase in free calcium ion levels. The subsequent binding of Ca(Il) resulting in a dramatic increase in free calcium ion levels. The subsequent binding of Ca(Il) to the muscle protein troponin C provides the impetus for a conformational change in the troponin complex and sets off successive events resulting in muscle contraction. 

Phosphates, which react with calcium to reduce the calcium ion activity, assist in stabilizing calcium-sensitive proteins, eg caseinate and soy proteinate, during processing. Phosphates also react with milk proteins. The extent of the reaction depends upon chain length. Casein precipitates upon addition of pyrophosphates, whereas whey proteins do not. Longer-chain polyphosphates cause the precipitation of both casein and whey proteins. These reactions are complex and not fully understood. Functions of phosphates in different types of dairy substitutes are summarized in Table 9 (see also Food additives). 

An interesting application is the titration of calcium. In the direct titration of calcium ions, solochrome black gives a poor end point if magnesium is present, it is displaced from its EDTA complex by calcium and an improved end point results (compare Section 10.51). 

Discussion. When calcium ions are titrated with EDTA a relatively stable calcium complex is formed ... 

With calcium ions alone, no sharp end point can be obtained with solochrome black indicator and the transition from red to pure blue is not observed. With magnesium ions, a somewhat less stable complex is formed ... 

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