Solid versus solution: Examining the electronic structure of metallic DNA with soft x-ray spectroscopy

Soft x-ray spectroscopy is used to investigate solution and powder samples of $\left(\mathrm{Ni}\right)\bullet M$-DNA. The nickel $2p$ absorption spectra are representative of the metal-DNA interaction, and they are not dominated by residual nickel structures. Both solution and solid samples of $\left(\mathrm{Ni}\right)\bullet M$-DNA contain a high spin Ni(II) configuration. Differences in the electronic structures of the solution and powder, an $8.2\mathrm{eV}$ loss process, and variations in hydrogen bonding are discussed. It is found that the drying process alters the electronic structure of the metallic DNA sample.

Figure 1

Molecular structure of the nickel containing metallic DNA nucleobase pairs used for calculations. Part (a) displays the adenine-thymine nucleobase pair (Ni-AT), while part (b) shows the cytosine-guanine nucleobase pair (Ni-GC).

Figure 2

Experimental Ni $2p$ XAS spectra of the $\left(\mathrm{Ni}\right)\bullet M$-DNA solution, $\left(\mathrm{Ni}\right)\bullet M$-DNA powder, and Ni metal are compared with theoretical spectra of NiO, NiOH, $\mathrm{Ni}{\mathrm{Cl}}_2$, Ni-AT, and Ni-GC. The experimental spectra were measured in partial fluorescence yield (PFY) mode.

Figure 3

$L_{2,3}$ RIXS spectra of the $\left(\mathrm{Ni}\right)\bullet M$-DNA solution (solid dots), $\left(\mathrm{Ni}\right)\bullet M$-DNA powder (hollow dots), and Ni metal (solid line). Part (a) shows resonant emission spectra when excited on the $L_2$ threshold, and (b) displays resonant emission spectra when excited on the $L_3$ threshold. The inset shows the $\left(\mathrm{Ni}\right)\bullet M$-DNA liquid spectrum (solid dots) from part (b) compared to a RIXS calculation of ${\mathrm{Ni}}^{2+}$ (gray line).