  Protonation of DNA basepairs is a reversible phenomenon which can be
controlled by tuning the pH of the system. Under mild acidic conditions, the
hydrogen bonding pattern of the DNA basepairs undergoes a change. We study the
effect of protonation on the electronic properties of the DNA basepairs to
probe for possible molecular electronics applications. We find that, under mild
acidic pH conditions, the A:T basepair shows excellent rectification behaviour
which is, however, absent in the G:C basepair. The mechanism of rectification
has been discussed using a simple chemical potential model. We also consider
the non-canonical A:A basepair and find that it can be used as efficient pH
dependent molecular switch. The switching action in A:A basepair is explained
in the light of pi-pi interactions which lead to efficient delocalization over
the entire basepair.
