Credit: © 2009 NPG

As well as its many useful properties in genetics and, more recently, the design of functional nanomaterials, DNA can also conduct electricity. However, the conductivity of an individual strand of DNA strongly depends on the sequence of the four bases — adenine, cytosine, guanine and thymine — in the strand. Now, Kiyohiko Kawai, Tetsuro Majima and co-workers at Osaka University have shown how a small modification to one of these bases can make the conductivity independent of the sequence of bases1.

Generally, DNA conducts charge in the form of 'holes' created by the absence of an electron in the highest occupied molecular orbital of guanine bases. Unfortunately, this means that sequences with excess adenine–thymine pairs show much lower conductivity than sequences with excess guanine–cytosine pairs. To overcome this problem, Kawai, Majima and co-workers replaced one nitrogen atom in each adenine molecule with a carbon-hydrogen group to create 7-deazaadenine (see figure). This small change raises the highest occupied molecular orbital of each adenine–thymine pair to be closer to that of the guanine–cytosine pairs, without affecting the base-pairing process in the molecules.

The Osaka team tested the charge-transfer properties of several different DNA sequences, and found that all were improved by making this small change to adenine bases. The conductivity could be improved even further by modifying cytosine and thymine.