DNA-ligand circular dichroism

Deoxyribonucleic acid, DNA, is composed of nucleotides which are planar aromatic bases linked to a sugar and a phosphate. Ligands that bind to DNA are usually cationic with their binding further stabilized by adopting a binding site that ensures complementarity of DNA and ligand shapes. For example, planar aromatic molecules often intercalate between base pairs, and bulky proteins adopt the major groove. As long as the binding mode has an element of specificity about it, then one expects to see a change in the CD signal of the component DNA and ligand signals. This is particularly obvious when the ligand is achiral so has no intrinsic CD before binding to the DNA. The CD signals induced upon ligand binding to DNA (or any other chiral molecule) are characteristic of the interaction and may be interpreted to give data such as binding constants.