The chemistry of the bile pigments. Part VI. The effect of metal complex formation upon optical activity and spectral absorption of urobilins

The changes in optical activity and absorption spectra of stercobilin, (+)-urobilin IXα, and (+)-urobilin occurring during the formation of zinc and copper complexes have been measured. For all pigments there is a loss of optical activity and for stercobilin there is a change in sign of rotation. These observations are discussed in relation to the stereochemistry of the pigments.