Formation and stabilities of free bilirubin and bilirubin complexes with transition and rare-earth elements.

We investigated complexes formed between bilirubin and transition or rare-earth elements, and their relative stabilities. Relativeratesof complex formation were analogous to metalloporphyrin and metal complex stabilities, according to the Irving-Williams series. Transition metals that formed strong, square planar complexes caused rapid bilirubin degradation. Iron(II) was oxidized to iron(IlI) in the bilirubin complex. Of the Ianthanide complexes, only samarium(llI) showed covalent bonding tendencies. Comparative molar absorptivities were calculated for several of the metalbilirubin complexes. The stability of bilirubin in several solvents and under various experimental conditions is reported. At room temperature, biIi rubin photooxidizesto biliverdin on exposure to laboratory light.