XANES investigation of the Co oxidation state in solution and in cancer cells treated with Co(III) complexes

XANES spectroscopy has been used to investigate whether it is possible to determine the oxidation state and coordination environment of Co complexes following treatment of cancer cells with Co(III) or Co(II) complexes. Our results show that the variation of the XANES with coordination geometry make it impossible to do this in a completely reliable way which is in contrast to the situation for platinum and chromium. It was established that the XANES spectrum obtained from cells treated with [Co(diNOsar)]Br3 remained unchanged with respect to its XANES spectrum obtained in solution, demonstrating that the [Co(diNOsar)]Br3 complex remained intact after 24 h in cellular media (diNOsar = 1,8-dinitro-3,6,10,13,16,19-hexaazabicyclo[6.6.6]eicosane). In contrast, the XANES spectra obtained from cells treated with Na[Co(acac)3] and [Co(acac)3] differed from the XANES spectra of the respective complexes obtained in solution, indicating a change in co-ordination environment for both complexes upon uptake in cells. The similarity of these spectra suggests that appearance of this XANES can be used as an indication of loss of the carrier ligands, a useful indicator in the study of hypoxia selective complexes. The results obtained for Na[Co(acac)3] and [Co(acac)3] are consistent with the intracellular coordination of cobalt(III) to sulfur ligands upon cellular uptake.