Circular dichroism (CD), the differential absorption of left- and right-handed circularly polarized light, is an excellent spectroscopic method for the study of the conformations adopted by proteins and nucleic acids in solution. Although not able to provide detailed residue specific information, CD measurements have two major advantages: they can be recorded on relatively small amounts of material in a wide range of buffers and they allow to monitor any structural alterations. The CD is one of the best method:
- to estimate the protein secondary structure content,
- to detect conformational changes in protein or nucleic acid that might result from changes in pH, salt concentration, ionic strength, added solvents or mutations in native protein,
- to assess the thermal or chemical stability by following molecule unfolding,
- to analyze macromolecule-ligand interactions.