Complexes calcium

Calcium complex soap greases, obtained by the reaction of lime and a mixture of fatty acids and acetic acid. These greases offer good high temperature and anti-wear/extreme pressure properties related to the presence, in the soap, of calcium acetate that acts as solid lubricant they have good mechanical stability. 

The influx of Ca(Il) across the presynaptic membrane is essential for nerve signal transmission involving excitation by acetylcholine (26). Calcium is important in transducing regulatory signals across many membranes and is an important secondary messenger hormone. The increase in intracellular Ca(Il) levels can result from either active transport of Ca(Il) across the membrane via an import channel or by release of Ca(Il) from reticulum stores within the cell. More than 30 different proteins have been linked to regulation by the calcium complex with calmoduhn (27,28). 

Porphyrin, octaethyl-, calcium complex cyclic voltammetry, 4, 399 <73JA5140)... 

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

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... 

Figure 2. Reporting of cytosolic free calcium levels by indo-1. Increases in cytosolic calcium, due either to entry of extracellular calcium via calcium channels or to release of intracellular calcium sequestered in organelles such as smooth endoplasmic reticulum, results in formation of the indo-l-calcium complex. Fluorescence intensity at 400 nm (excitation at 340 nm) is proportional to the concentration of this complex the dissociation constant for this complex is about 250 nff (24), making this probe useful for detecting calcium activities in the range of 25 to 2500 nJ. ...

At last, barium and calcium complexes of phosphonium bifluorenylide 19 was obtained from the corresponding phosphonium iodide (Scheme 12). The anion displays weak nucleophilicity toward both cations which prefer to coordinate with neutral oxygen of THF and with iodide. Located outside the coordination sphere of the metals, it represents thus the first example of uncomplexed phosphonium diylide [59]. 

Dosages of EDTA are delivered as the calcium disodium salt, Na2[Ca(EDTA)]. The calcium complex prevents EDTA from extracting iron from the blood. Unlike iron, heavy metal ions such as preferentially... 

The variety of prebiotic organic reactions seems to be almost unlimited. Strasdeit et al. (2002) from the University of Hohenheim (Germany) reported the synthesis of zinc and calcium complexes of the amino acids valine and isovaline. They assume that these could have had a certain significance on the mineral-rich primeval Earth on heating to 593 K under nitrogen, valine was converted to the corresponding cyclic dipeptide. 

A comparison of the crystal structures, NMR and IR spectra of various Yb(ll) and calcium complexes demonstrated that they were strikingly similar, a reflection of the nearly identical radii of Ybz+ and Ca2+.25 Nevertheless, the dibenzylytterbium(ll) analog of 127 produces polystyrene of high syndiotacticity (r= 94.9%, rr= 90.0%), whereas 127 itself yields only atactic or slightly syndiotactic polymer. A difference in Yb-L and Ca-L bond strengths, despite their similar lengths, has been proposed as the source of the difference.315... 

As with (105), ligand (106, dota) also forms strong complexes with a range of both non-transition and transition metal ions (Stetter Frank, 1976 Delgado da Silva, 1982 Spirlet, Rebizant, Desreux Loncin, 1984) which are often more stable than the corresponding edta complexes. In particular, the calcium complex shows extremely high stability and very stable complexes are also formed with the trivalent lanthanides (Desreux, 1980 Spirlet, Rebizant, Desreux Loncin, 1984). 

Stability constants for calcium complexes of a selection of hydroxycarboxylate ligands are listed in Table VII (239,246,272-274). For tartrate, malate, and citrate stabilities decrease in the expected order Ca2+> Ba2+> Ra2+ (231,275). The stability constant for the complex of pyruvate (logiOifi 0.8 (273)) is similar to that for acetate calcium complexes of a-ketoglutarate and of oxaloacetate are somewhat more stable (logio-Ki = 1.3, 1.6 respectively (273)). The sequence logio-Ki = 3.0, 1.4, 1.1, 0.6 for the dicarboxylate ligands oxalate, malonate, succinate,... 

The temperature dependence of stability constants has been documented for a few calcium complexes, giving estimates for... 

Fig. 2. Overview of stability constants (logio-Ka, on the molar scale) for formation of calcium complexes in aqueous solution, at (or close to) 298 K and in ionic strengths in the region of 0.1-0.15 M.

Fractionation of Digest Calcium. The in vitro digestion procedure provides a means of producing the starting material for a more detailed study of the calcium complexes in intestinal digests. This may be desirable in a number of situations ... 

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