Low-energy ion irradiation of DNA has been of special interest
in studying mechanisms of ion beam induced mutation in both
biotechnological [1] and biomedical [2] fields. Both direct interaction
between the irradiating ions and DNA and indirect interactions
induced by the ion irradiation can cause certain-degree
damage to DNA [3–5]. One of the factors involved in mechanisms
of the ion-beam-induced DNA damage is the electrical charge
introduced by implanting ions. Charge or static electric field has
been found to have certain effects on DNA stability and structural
deformation [6]. Introduction of charged side chains to DNA could
result in oligonucleotides with a marked increase in duplex DNA
and RNA–DNA stability but no decrease in base-pairing fidelity
[7]. The influences of cations on nucleic acid structure were multifaceted
and subtle, which could simultaneously stabilize and unstuck
DNA and cause static bends of DNA from dynamical states
[8,9]. Positively charged side chains within the DNA helix could alter
the conformation and flexibility of DNA [10]. However, reports
have not yet been found on effect from introduced ion charge on
DNA damage and subsequent mutation. Our previous studies have
found that ions with energy of keV from either ion beam or plasma
could cause DNA conformation change from natural supercoil to
relaxed and even linear shapes [11,12]. Direct nuclear interaction
of atomic collision between the ion and DNA atom could surely
cause the damage. But, how is the indirect contribution from the
introduced ion charge to the DNA conformation change and how
much is the contribution? To look for answers to the questions,
we designed and performed experiments by comparing effects of
ion beam and neutralized beam bombardments of DNA to investigate
the ion charge effect separately.We still kept the beam energy
low as the same as used in our previous experiment for a consistent
study.