Considerations concerning the formation of metal chelates of bilirubin: The zinc-bilirubin system

✍ Scribed by John D. Van Norman; Robert Szentirmay

• Publisher: Elsevier Science
• Year: 1974
• Weight: 412 KB
• Volume: 4
• Category: Article
• ISSN: 0006-3061
• DOI: 10.1016/s0006-3061(00)80173-8

✦ Synopsis

Three biirubin species in solutions containing zinc(II) ion have been spectrophotometrically identified; a neutral bilirubin form, a bssic bilirubin form and a bilirubin-zinc complex. It has been established that the zinc-biibin complex has maximum formation at a biirubin: zinc: tetramethylguanidine ratio of 1:2:8 and any deviation from this ratio results in loss of complex. Reasons for this behavior are discussed and general ccnsiderations for the formation of metal chelates with bilirubin are developed.

In the course of a study of the chemistry of bilirubii (BR) in N,N-dimethylformamide, DMF, we found it necessary to determine the conditions under which z&(11) would complex with hiibin.

Evidence has been offered that zinc(H)

complexes with hiilirubm in chloroform, with a suggestion that more than two complex species may be formed (1).

Other investigators have reported the existence of zi.nc(II)-bilirubin complexes (2,3). Recently Hutchinson et. al. (4) have reported on the metal complexes of bilk&m in aprotic solvents including the isolation of solid hiilirubm-zinc acetate complexes. Strong evidence has also been given to show that other ions such as samarium(III) complexes with biibin with two Sm(II1) ions attached to one biilirubm molecule (5). Indeed, stability constants for incorporating the first and the second metal ion were calculated_

Commercial bibin (Sigma Chemical Company) of a 99% purity was used directly. This form had an ~4164 of 60,000 f 600 in chloroform. DMF was of reagent quality and was distilled under reduced pressure from anhydrous cupric sulfate to remove most of the mater and all of the basic impurities arising from its own decomposition. Solutions of bilirubin in DMF mere prepared by direct weighing. Solutions of Zn(II) were prepared