Cobalt(II) as an NMR probe for the investigation of the coordination sites of conalbumin

Abstract

The bis and mono Co(II) derivatives of [chicken egg] conalbumin in the presence of bicarbonate were prepared. The 1H NMR spectra were recorded at 60 MHz. Well-shaped isotropically shifted signals in the range -100 to +100 ppm were observed for both the mono and bis Co(II) derivatives: besides the intensity, all the isotropically shifted signals for the 2 derivatives are superimposable, indicating that the 2 sites are so similar as to be indistinguishable within the resolution of the technique. With the aid of T1 measurements, the signals were assigned to the protons of 2 histidine and 2 tyrosinate ligands. The spectra are consistent with 6-coordinated, high-spin Co(II) chromophores with 2 trans tyrosinate moieties at each site.