Calcium water structure former

Carbopol is widely used in cosmetic and pharmaceutical practice as a gel-former. Carbopol resins are hydrophilic polymers which swell in water solutions and transform into the gel form at neutralization. At the elaboration of special cosmetic preparations in which carbopol is used, the problem of raw materials compatibility appears. For example, some extracts of aromatic pectin containing materials destroy the gel structure of carbopol. High contents of bivalent metal ions, in particular calcium ions, destructively influence onto the gel-making ability of the system too. 

Both calcium oxalate monohydrate and dihydrate - whewellite and weddelite - contain eight-coordinated Ca2+ in distorted square-antiprismatic geometry, but there is one coordinated water in the former, two in the latter. Whewellite has a layer structure through the sharing of three edges of each coordination square-antiprism with three adjacent polyhedra weddelite has a chain structure (128). The trihydrate also contains eight-coordinated Ca2+ (129). 

Based on biochemical data (Aharoni et al, 2004 Josse et al, 1999a, b, c, 2001) but mainly on their 2.2 A-resolution crystal stmcture of a recombinant PONl variant (Hard et al, 2004), Tawfik and co-workers recently offered a model for the architecture and fimction of the lactonase active site(s) of the PON enzymes (Khersonsky and Tawfik, 2006 Rosenblat et al, 2006). According to the crystal stracture (Hard et al, 2004), PON is a six-bladed P-propeller, with two calcium ions located in the central tunnel - the structural Ca is buried while the catalytic Ca was solvent exposed. Two His residues, the so-called His -His " dyad, mediate the lactonase (and esterase) activity of PON enzymes the former acts as general base to activate a water molecule attacking the carbonyl oxygen of... 

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