Formation of the Metal Complexes between Protoporphyrin IX and Divalent Metal Cations in the Environment

Abstract

Protoporphyrin IX is very slightly soluble in water whereas it is soluble in acidic as well as in basic aqueous solution. The UV-vis absorption spectrum of the protoporphyrin IX shows a very sharp and strong maximum absorption peak at 400 nm in acetonitrile-water mixture solution (1∶1v/v). The maximum absorption peaks reacted with divalent transition metal ions such as Cu²⁺, Zn²⁺, Fe²⁺ were shifted to a longer wavelength and the absorbance of the maximum peak decreased as the contents of metal ions increased. However, the absorbance of the maximum absorption peak combined with representative divalent metal ion, Mg²⁺ has nearly same value and the peak did not shifted. The formation constant (K_f) of the metal protoporphyrin IX complexes reacted with Cu²⁺, Zn²⁺, Fe²⁺ in acetonitrile-water mixture solution (1∶1v/v) were found to be 370, 418 and 24, respectively.

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