Principal component analysis of the absorption and resonance Raman spectra of the metallochromic indicator antipyrylazo III

Metallochromic indicators, whose spectral properties are changed in the presence of metal cations, are used mainly in biological studies to monitor Ca²⁺ and Mg²⁺ ions. Antipyrylazo III is such indicator, employed for mid-range Ca²⁺ concentrations (10-1000 μM). The stoichiometry of the interactions of antipyrylazo III with Ca²⁺, Mg²⁺, Ba²⁺, Sr²⁺ and Zn²⁺ ions and the relevant binding constants were studied by principal component analysis (PCA) of the absorption spectral changes. The resonance Raman spectra of the above systems were measured as well, and the resolved Raman spectra of the various species were calculated and assigned. The vibrational spectra are more featured, more characteristic of the binding ions and exhibit stronger relative spectral changes upon binding the cations. The basis sets of Raman spectra could thus be used as an analytical tool for these divalent metallic cations.