Physicochemical Properties of Protoporphyrin IX by Metal Ions in Acetonitrile-Water Mixture Solution

The UV-vis absorption spectrum of protoporphyrin IX shows a very sharp and strong absorption maximum peak at 398 nm in acetonitrile-water mixture solution (1:1 v/v). When divalent metal ions such as Cu²⁺ , Zn²⁺ , and Ca²⁺ ion were added to protoporphyrin IX, metal protoporphyrin IX complexes were thereby produced. Cu-protoporphyrin IX complexes have the largest formation constant ( Kf ) among them. The fluorescence intensity of protoporphyrin IX was diminished by the presence of Cu²⁺ , Zn²⁺ , Ca²⁺ , Mn²⁺ , and Ni²⁺ ions as quenchers. However, Mg²⁺ , Mn²⁺ , and Ni²⁺ ions are hardly combined with protoporphyrin IX. Mg²⁺ ion does not take part in the fluorescence quenching process of protoporphyrin IX in acetonitrile-water mixture solution. According to the Stern-Volmer plots, fluorescence quenching by Cu²⁺ , Zn²⁺ , and Ca²⁺ ions involves static quenching, which is due to complex formation. On the contrary, dynamic quenching has a large influence on the overall quenching process, when Mn²⁺ and Ni²⁺ ions were added to protoporphyrin IX in acetonitrile-water mixture solution.