Stability of DNA double helix conferred by base stacking
When you carefully look at the structure of DNA helix, you will notice that consecutive bases are partially layered i.e. one base is "on-top" of the other base. Stacking is a chemical phenomenon in which the cloud of the pi-electrons in an aromatic molecule interact with that of the other. This interaction is non-covalent. Since the DNA nucleobases are aromatic molecules, they also exhibit stacking which stabilizes the structure of the DNA. A study by Yakovchuk et al. (2006) suggests that base stacking has higher contribution to DNA stability than base pairing. Sponer at al. (1997) found that there is no great difference between the stacking energies of B- and Z- forms of DNA helix.