Inferences on the Nature of a Cr(V) or Cr(IV) Species
Formed by Reduction of Dichromate by a Bovine Liver
Homogenate: NMR and Mass-Spectrometric Studies
A low-molecular weight chromium-containing fraction of the material resulting from dichromate
reduction by bovine liver homogenate was investigated by NMR and ES-MS. The ES-MS spectrum showed a
readily detectable peak at m/z = 786.1. The same molecular weight reasonably agreed with the relatively low
diffusion coefficient measured by NMR-DOSY experiments on the main species observed in the 1H NMR
spectrum. At least two downfield shifted and broad paramagnetic signals were apparent in the 1H NMR
spectrum. Temperature dependence of chemical shift was exploited in order to estimate the diamagnetic shift
of the signals in the diamagnetic region of the spectrum. 2D TOCSY, NOESY, COSY and 1H-3C HMQC
spectra revealed the presence of aromatic protons (which were assigned as His residues), Gly and some other
short chain amino-acids. Combinations of the molecular masses of such components together with acetate
(which is present in the solution) and chromium atoms allowed a tentative proposal of a model for the
compound