Synchrotron-Based Nickel Mossbauer Spectroscopy

We used a novel experimental setup to conduct the first synchrotron-based Ni-61 Mossbauer spectroscopy measurements in the energy domain on Ni coordination complexes and metalloproteins. A representative set of samples was chosen to demonstrate the potential of this approach. (NiCr2O4)-Ni-61 was examined as a case with strong Zeeman splittings. Simulations of the spectra yielded an internal magnetic field of 44.6 T, consistent with previous work by the traditional 61Ni Mossbauer approach with a radioactive source. A linear Ni amido complex, (NI)-N-61{N(SiMe3)Dipp}(2), where Dipp = C6H3-2,6-Pr-i(2), was chosen as a sample with an "extreme" gerimetry and large quadrupole splitting. Finally, to demonstrate the feasibility of metalloprotein studies using synchrotron-based 61Ni Mossbauer spectroscopy, we examined the spectra of Ni-61-substituted rubredoxin in reduced and oxidized forms, along with [Et4N](2)[Ni-61(SPh)(4)] as a model compound. For each of the above samples, a reasonable spectrum could be obtained in similar to 1 d. Given that there is still room for considerable improvement in experimental sensitivity, synchrotron based Ni-61 Mossbauer spectroscopy appears to be a promising alternative to measurements with radioactive sources.