REACTION PATTERN OF AMINO-ACID CHELATES OF COBALT(III) IN ACIDIC AQUEOUS-SOLUTION

The reactions of amino acid chelates of cobalt(III) have been investigated in order to study the influence of chelate size, ring pattern and nature of bonding on the rates of reactions. The complex ion chosen is Co(BigH)2(am)2+, where BigH = biguanide and am = glycinate (Gly), alpha-alaninate (alpha-Alan), beta-alaninate (beta-Alan) and cysteinate (Cyst) ions. In the case of the first three complexes k(obs) varies linearly with [acid]. However, for the cysteinato complex, reciprocal plot (1/k(obs) versus 1/[H+]) is linear. The reactivity order of the complexes is: beta-Alan < Gly < alpha-Alan < Cyst. A plot of -log k versus pK of amino acids indicates that for the Gly, alpha-Alan and Cyst complexes, basicity of the chelate ring controls the mechanism, while for the beta-Alan complex, the mechanism is not well understood.