Specificity in the interaction between poly( L ‐glutamate) and iron (III) complex ions in aqueous solution

The binding process between sodium poly(L‐glutamate) and trans‐2,2′,2″,2‴‐tetrapyridyl‐Fe(III) complex ions in aqueous solution at pH around 7 has been studied by means of equilibrium dialysis and optical measurements. The binding isotherm indicates the occurrence of a cooperative process, whereby bound molecules facilitate the association of additional molecules. According to circular dichroism (CD) data, this effect is coupled with that which sees a conformational change in the charged polypeptide upon progessive binding of complex counterions. All these features are discussed in the light of the structural characteristics of the interacting species. A stereochemical model of the association “complex” is proposed.