Thermal denaturation of A-DNA

The DNA molecule can take various conformational forms. Investigations focus mainly on the so-called 'B-form', schematically drawn in the famous paper by Watson and Crick [1]. This is the usual form of DNA in a biological environment and is the only form that is stable in an aqueous environment. Other forms, however, can teach us much about DNA. They have the same nucleotide base pairs for 'building blocks' as B-DNA, but with different relative positions, and studying these forms gives insight into the interactions between elements under conditions far from equilibrium in the B-form. Studying the thermal denaturation is particularly interesting because it provides a direct probe of those interactions which control the growth of the fluctuations when the 'melting' temperature is approached. Here we report such a study on the 'A-form' using calorimetry and neutron scattering. We show that it can be carried further than a similar study on B-DNA, requiring the improvement of thermodynamic models for DNA.