In:
Applied Spectroscopy, SAGE Publications, Vol. 50, No. 7 ( 1996-07), p. 922-927
Abstract:
Copper is known to form complexes with bilirubin (H 2 BR). Such complexes have received increased attention because of their clinical significance as free-radical scavengers. The purpose of this study was to examine a series of Cu 2+ BR complexes to ascertain the nature of the binding between Cu 2+ and BR. Several physical measurements of the salts were made, such as Fourier transform infrared (FT-IR) and electron paramagnetic resonance (EPR). The complexes were prepared by dissolving protonated BR in NaOH and adding different ratios of aqueous CuCl 2 . At ratios of Cu 2+ /H 2 BR of 1:1 and 2:1, soluble complexes were formed. In solution, EPR spectra demonstrated nine hyperfine peaks, which, from the splitting, is indicative of Cu 2+ coordinated to four nitrogen atoms coming from two molecules of BR. The solid obtained from the solutions demonstrated predominant infrared absorptions at 1574 and 1403 cm −1 (previously assigned as COO − vibrations, asymmetric and symmetric), whereas the 1710-cm −1 vibration appears only as a shoulder (previously assigned as the free COOH vibration), indicative that most of the COO − groups have reacted with sodium, thus accounting for the aqueous solubility. The NH stretching vibration in the pyrrole group of H 2 BR has disappeared and is replaced with the OH stretching vibration in H 2 O. At higher ratios of 3:1 and 5:1 (Cu 2+ /H 2 BR), black precipitates are formed, which produce no EPR signals. Furthermore, the NH vibration disappears as in the soluble solution complexes. It can be concluded that the insoluble salts (higher Cu 2+ /H 2 BR ratios) are mixed complexes containing the Cu–nitrogen chelate and Cu salts involving the COOH groups.
Type of Medium:
Online Resource
ISSN:
0003-7028
,
1943-3530
DOI:
10.1366/0003702963905466
Language:
English
Publisher:
SAGE Publications
Publication Date:
1996
detail.hit.zdb_id:
1474251-2
SSG:
11
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