STRUCTURE CHARACTERIZATION OF STRONTIUM(II) BILIRUBINATE COMPLEXES

Calcium bilirubinate (CaBR) is the main component of pigment gallstone s. At present no crystal structure of CaBR is available. Extended x-ra y absorption fine structure (EXAFS) is a powerful tool for local atomi c structure determination, but it is difficult to measure the EXAFS sp ectra of calcium in compounds. Strontium bilirubinate (SrBR) was used instead of calcium, because of the similarity of IR spectra between Ca BR and SrBR complexes. In this investigation a series of SrBR was synt hesized. FTIR and EXAFS spectroscopic techniques were adapted to chara cterization. The results provide evidence of SrBR formation. It follow s that the first shell about Sr (II) of the neutral BR compound consis ts of oxygen and nitrogen atoms with Sr-O and Sr-N distances of 2.61 A ngstrom and 2.69 Angstrom, respectively. The coordination number of Sr is eight, consisting of four O atoms and four N atoms. It can lead to the unfolding of the coordination structure of CaBR. (C) 1995 John Wi ley & Sons, Inc.