Letter to the Editor

This paper begins by reviewing our crystallographic studies of planar intercalators complexed to a series of self-complementary DNA and RNAlike dinucleoside monophosphates done in earlier years. The results of these studies readily explain the observation of neighbor exclusion that is why intercalation is limited to occur between every other base pair in DNA at high drug/DNA binding ratios. Neighbor-exclusion has been proposed to reflect the presence of an entirely different DNA conformational state in DNA this being called beta-DNA; a key metastable and hyperflexible liquid-like phase that acts as a transition-state intermediate in DNA-melting and in the Bto Astructural phase-transition.