Reaction of a basic chromium(III)-zirconium(IV) sulphate complex with amino acids

The basic chromium(111)-zirconium(1V) sulphate complex isolated previously [Na2Zr3Cr2(S04)4- (OH)12,6H2O = compound A] has been shown to react with a series of amino acids at moderately acidic pH values to produce a good yield of either a 1 : 1 or 2 : 1 amino acid-compound A complex. These were usually relatively insoluble, electrically neutral complexes in which sulphate groups have been displaced by amino acid residues. The reaction involves coordination of the amino acid through the carboxyl group (although some evidence was obtained for nitrogen-coordination when the reaction was performed by boiling with an excess of amino acid) and is accompanied by an increase in the number of moles of bound water from 6 to 9. A 2 : 1 cationic complex was also isolated from reaction of an excess of α-alanine with compound A. Amino acid methyl esters were shown to react with compound A after demethylation to form the same 1 : 1 complex as obtained from the corresponding free amino acid.