CONTRIBUTION OF MINOR SPECIES TO PARAMAGNETIC LINE BROADENING OF H-1 NUCLEAR MAGNETIC-RESONANCE SPECTRA IN PEPTIDE-COPPER(II) SYSTEM

pH dependence of the paramagnetic line broadening of 1H NMR spectra has been observed for histidine (Gly•Gly•His) and glycine (Gly, Gly•Gly, Gly•Gly•Gly, and Gly•Gly•Gly•Gly) peptide-copper(II) systems. The effective line width at half-height, (πT2p)-1, of the 1H NMR signals showed a bell-shaped curve was maximum for each system. The cause of the bell-shaped curve was examined in the Gly•Gly•His-copper(II) system as the most typical and dramatic case. It was found that the line broadening was caused by the small amount of incomplete complexes present in the solution and that an extreme decrease of the incomplete complexes and exclusive formation of a complete complex having a large TM result in narrowing of the line width. This finding indicates that the 1H NMR line broadening does not always reflect the dominant complex species present in solution, so care is required in the use of line-broadening data in the study of metal binding sites. © 1979, American Chemical Society. All rights reserved.