Calcium coordination chemistry

This chapter discusses the coordination chemistry of selected main group and transition metal complexes with dipicolinic acid, its analogues, and derivatives as ligands. Selected elements will be presented in terms of increasing atomic number. Out of all of the alkali metals, there has been a report of the crystal structure of sodium coordinated to dipicolinic acid. Calcium, magnesium, and strontium, three alkaline earth metals, are popular metal centers, which have been reported in the literature to be coordinated to dipicolinic acid or its analogues. ... 

It is now possible to indicate the role of coordination chemistry by means of a single example—the problem of determining calcium in sea water (4, 6). 

Further studies on the supramolecular coordination chemistry of copper(II) focused on the synthesis of oligonuclear complexes by self-assembly with the pentadentate ligand (L3)2 with 2,6-pyridinyl-spacer [70]. To this end, H2L3 (4) was treated with calcium hydride and copper(II) acetate to give the metallocoronate [(Cac Cu2(L3)2 )(OAc)2] (5 Scheme 2). In the crystal, 5 is present as a dinuclear copper(II) coronate in which a calcium ion is encapsulated in the center two acetates act as counterions. 

Ba (CN 6) 1.49 A, EN = 0.97) leads to chemistry dominated by electrostatic interactions. There are significant similarities between the chemistry of calcium and divalent ytterbium as well as strontium and divalent europium and samarium owing to quite similar size/charge ratios. SeeScandium, Yttrium the Lanthanides Organometallic Chemistry and Scandium, Yttrium the Lanthanides Inorganic Coordination Chemistry)... 

Coordination chemistry of RE(III) with amino acids has been attracting much interest since the early 1970s after the discovery that certain RE(III) ions could be used as probes of calcium ion binding sites in proteins and enzymes [118, 119], Since then, a large amount of work on the solution and structural chemistry of rare earth-amino acid complexes has been published. The solution studies involve all of the rare earth elements and 13 (Gly, Ala, Val, Leu, Phe, Met, Pro, Ser, Tyr, His, Lys, Trp, and Arg) of the 20 standard amino acids, and more than 100 of the RE(III)-amino acid complexes have been structurally characterized. This section will cover the synthetic, structural, and solution chemistry of these complexes. 

Fig. 6. The primary calcium ion of secretory phospholipases A .. Stereoviews showing the coordination chemistry of the primary calcium ion in (A) the absence (Scott etal, 1990a) and (B) the presence of a transition-state analog (White el ai, 1990). Water molecules are labeled W, the proposed attacking nucleophile is inscribed, and tbe primary calcium ion (Ca) is identified. P2 stimulates the tetrahedral intermediate of catalysis and P3 corresponds to the, sn-3 phosphate (copyrighted 1990 by the American Association for the Advancement of Science).

T.P. Hanusa (2000) Coordination Chemistry Reviews, vol. 210, p. 329 - Non-cyclopentadienyl organometallic compounds of calcium, strontium and barium . 

Several calcium-binding motifs have been characterized for proteins especially those with regulatory roles. The structural chemistry of EF hands and the coordination chemistry of calcium and other spherical metal ions, and related models, have been reviewed by Falke. " ... 

This solvent is employed widely in analytical and coordination chemistry. At its boiling point it undergoes partial decomposition to yield dimethylamine and carbon monoxide. The decomposition is catalyzed by various substances, particularly those with acidic or basic properties this must be taken into consideration in the selection of the material used for drying. Under no circumstances may this solvent be refluxed with, for example, potassium hydroxide, sodium hydroxide or calcium hydride. Dimethylformamide can be dehydrated most advantageously with a molecular sieve of pore size 0.4 nm however, calcium sulphate, magnesium sulphate or silica gel may also be employed. After dehydration, the solvent may be purified by vacuum distillation. 

Gadolinium ions are highly toxic in their hydrated form [Gd(H20)g] +. In vivo, Gd + ions compete with calcium ions and block the reticuloendothelial system. To avoid this toxicity, gadolinium is complexed with an organic thermodynamically stable matrix, (see Lanthanide Complexes with Multidentate Ligands, Organometallic Chemistry Fundamental Properties, Lanthanides Coordination Chemistry) In addition, ligands that allow coordination sites for one (or more) water molecule(s) ate preferred since they increase... 

The chemistry of aluminium combines features in common with two other groups of elements, namely (i) divalent magnesium and calcium, and (ii) trivalent chromium and iron (Williams, 1999). It is likely that the toxic effects of aluminium are related to its interference with calcium directed processes, whereas its access to tissues is probably a function of its similarity to ferric iron (Ward and Crichton, 2001). The effective ionic radius of Al3+ in sixfold coordination (54 pm) is most like that of Fe3+ (65 pm), as is its hydrolysis behaviour in aqueous solution ... 

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