Electronic structure and charge carriers in metallic DNA investigated by soft x-ray spectroscopy

Abstract

Resonant inelastic x-ray scattering (RIXS) measurements of dried metallic DNA with metal ions incorporated inside the helix [(X)∙M-DNA, $\mathrm{X}=\mathrm{Co},\mathrm{Ni}$], dried DNA with metal ions attached to the outside of the helix [(X)∙B-DNA, $\mathrm{X}=\mathrm{Co},\mathrm{Ni}$], and dried double-strand DNA (B-DNA) are presented. The metal $L$ edge RIXS spectra show that the $I({L}_{2})∕I({L}_{3})$ intensity ratio can be used as a probe of metallicity in $3d$ metal-containing systems because of the influence of nonradiative Coster-Kronig transitions. Using this technique it is found that (X)∙B-DNA has fewer mobile charge carriers than (X)∙M-DNA. X-ray absorption measurements at the $L$ edge of the $3d$ metals are compared to density functional calculations to confirm that spectral features are not simply results of residual metal impurities. Nitrogen RIXS measurements reveal that the occupied electronic states are more localized in B-DNA than in (X)∙M-DNA systems.