Calcium cryptates

The term [NaL ] in Eq. (33) has to be taken into consideration because Schiefer was able to show that calcium cryptate complexes were fixed at a cation exchanger resin. 

The ultrasonic technique has been used to study the binding of calcium to sorbitol the interaction is weak and the formation rate constant (40 C) could only be approximately determined as (1-2) x 10 dm mol" s . The kinetics have also been studied of the dissociation of calcium cryptates in various solvents " (see Table 9.4) and of cryp tand exchange... 

ClsHa6CS2N2S4, Caesium di-n-butyldithiocarbamate, 34B, 401 Cl8H36IKN2O6, Potassium cryptate, 39B, 518 Cl8H36lN2Na06, Sodium cryptate, 39B, 519 Cl8H36N2Na20g, Disodium[2.2.2]-cryptate, 40B, 664 Cl8H4aBraCaNaOs, Calcium cryptate, 39B, 519... 

In order to accommodate the small, highly charged calcium ion, the cryptand adopts an unsymmetrical conformation in which two of the chains are pushed apart to allow coordination of a water molecule and the N N distance is reduced to 5.44 A (42). In the corresponding barium complex, the structural unit consists of two cryptates, two water molecules, and four thiocyanate anions, two of which (9) are bound through nitrogen to the metal, (43). 

Some indication that Mg2+ may be an important ion for cellulose synthesis comes from studies by Montezinos and Brown,83 as discussed earlier (in Section IV,1). Also of interest is the observation by Quader and Robinson84 that calcium ionophores and the cryptates 211 and 212 were potent inhibitors of cellulose synthesis in Oocystis, although their mode of action is at present not understood. 

H. Kagenow, A. Jensen, Differential kinetic analysis and flow injection analysis, Part 3. The (2.2.2) cryptates of magnesium, calcium and strontium, Anal. Chim. Acta 114 (1980) 227. 

D. Espersen and A. Jensen, Differential Kinetic Analysis and Flow Injection Analysis. Part II. The (2.2.1) Cryptates of Magnesium and Calcium. AnaL Chim. Acta, 108 (1979) 241. 

Table 2 Structural parameters for cryptate complexes of calcium and barium...

C20H35CaCl2NsOi8f Calcium perchlorate - diacetamide (1 5), 42B, 575 C20H3 8BaN, 07S2, Barium cryptate, 39B, 520... 

The Crowns were found in the U.S.A. The Cryptates , a more recent French discovery, are mixed ether-amine macrocycles that not merely encircle the salts of inorganic cations, as Crowns do, but actually surround them in all directions, leading to somewhat tighter binding (Lehn, Sauvage, and Dietrich, 1970), and to very strong binding of strontium vts d vis calcium. Of the alkali metals, potassium is often preferred to sodium and lithium. 

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