Synchrotron-based Nickel Mössbauer Spectroscopy

We used a novel experimental setup to conduct the first synchrotron-based ⁶¹Ni Mössbauer 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. ⁶¹NiCr₂O₄ 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 Mössbauer approach with a radioactive source. A linear Ni amido complex, ⁶¹Ni{N(SiMe₃)Dipp}₂, where Dipp = C₆H₃-2,6-ⁱPr₂, was chosen as a sample with an "extreme" geometry and large quadrupole splitting. Finally, to demonstrate the feasibility of metalloprotein studies using synchrotron-based ⁶¹Ni Mössbauer spectroscopy, we examined the spectra of ⁶¹Ni-substituted rubredoxin in reduced and oxidized forms, along with [Et₄N]₂[⁶¹Ni(SPh)₄] as a model compound. For each of the above samples, a reasonable spectrum could be obtained in ∼1 d. Given that there is still room for considerable improvement in experimental sensitivity, synchrotron-based ⁶¹Ni Mössbauer spectroscopy appears to be a promising alternative to measurements with radioactive sources.