Magnetic study of the electronic states ofB-DNA andM-DNA doped with metal ions

The magnetic properties of the pristine and metal ion doped deoxyribonucleic acid (DNA) of salmon are investigated with electron paramagnetic resonance (EPR), superconducting quantum interference device and energy dispersive x-ray flourescence spectroscopy. Purified salmon DNA gives intrinsically no EPR signal, which is consistent with DNA being a semiconductor, but not with DNA having metallic or superconducting properties as reported previously. Several kinds of divalent ions (Zn, Mn, Ca, …) are used as dopants, resulting in no substantial EPR signal except in the case of Mn. This leads to the conclusion that a metal ion counterbalances two phosphate anions instead of Na counterions in $B$-DNA, which contradicts the metallic behavior reported previously [A. Rakitin et al., Phys. Rev. Lett. 86, 3670 (2001)].