  Strong influence of water molecules on the transport and magnetic properties
of DNA, observed in this study, opens up real opportunities for application of
DNA in molecular electronics. Interaction of the nucleobases with water
molecules leads to breaking of some of the $\pi$ bonds and appearance of
unbound pi electrons. These unbound electrons contribute significantly to the
charge transfer at room temperature by up to 1000 times, but at low temperature
the efficiency of charge transfer is determined by the spin interaction of the
two unbound electrons located on the intrastrand nucleobases. The charge
exchange between the nucleobases is allowed only when the spins of unbound
electrons are antiparallel. Therefore, the conductance of the DNA molecule can
be controlled by a magnetic field. That effect has potential applications for
developing a nanoscale spintronic device based on the DNA molecule, where
efficiency of spin interaction will be determined by the DNA sequence.
