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 (K-f) 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+ 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.