A resonance Raman study of native stellacyanin and its Ni(II) derivative. On the origin of the 450-nm electronic absorption.

The resonance Raman spectra of native stellacyanin and its Ni(II) derivative has been investigated. Raman intensity as a function of the exciting frequency shows minima at about 440--460 nm. Moreover, the resonance Raman spectra of the Ni(II) derivative indicate similar symmetry and nature of ligands, namely, one cysteine and at least one histidine.Optical electronegativity of the ligand involved in the intense visible absorption band of native stellacyanin and the corresponding transition of the Ni(lI) derivative confirm this assumption. The origin of the 450 nm band is also discussed.