Complex Formation Between Ca(II), Mg(II), Al(III) Ions and Salicylglycine

For modelling the interactions of proteins/peptides with hard metal ions the complex formation of salicylglycine (SalGly) with Ca(II), Mg(ll) and AI(III) ions was studied in aqueous solution using pHpotentiometric and UV-vis spectroscopic techniques. Al(lll) ion was found to form more stable complexes with SalGiy than Ca(ll) or Mg(ll) ions. While AI(III) ion forms various 1:1 complexes of different protonation states in the pH range 2-7, Ca(ll), Mg(ll) ions seem to interact with SalGly only in the basic pH range and form mixed hydroxo species MLH(-1) at pH ~ 8. According to the UV-vis spectroscopic measurements in the species MLH(-1) the carboxylate-O(-) atom and the phenolate-O(-) coordinate to the metal ions. SaIGiy is able to keep Al(lll) in solution through inner and outer sphere coordination to metastable amorphous AI(OH)(3) particles. Deprotonation of the peptide amide Nil does not occur in these systems.