to form a stable G-quadruplex structure. [ 48 [[ http://en.wikipedia.org/wiki/Dna#cite_note-Burge-47 |]]] These structures are stabilized by hydrogen bonding between the edges of the bases and chelation of a metal ion in the centre of each four-base unit. [ 49 [[ http://en.wikipedia.org/wiki/Dna#cite_note-48 |]]] Other structures can also be formed, with the central