Chemical Sciences

Circular Dichroism

Circular dichroism (CD) spectroscopy is a spectroscopic technique where the CD of molecules is measured over a range of wavelengths. CD spectroscopy is used extensively to study chiral molecules of all types and sizes, but it is in the study of large biological molecules where it finds its most important applications. A primary use is in analyzing the secondary structure or conformation of macromolecules, particularly proteins, and because secondary structure is sensitive to its environment, e.g. temperature or pH, circular dichroism can be used to observe how secondary structure changes with environmental conditions or on interaction with other molecules. Structural, kinetic and thermodynamic information about macromolecules can be derived from circular dichroism spectroscopy.


Circular dichroism spectroscopy is particularly useful for:

  • Determining whether a protein is folded, and if so characterizing its secondary structure, tertiary structure, and the structural family to which it belongs
  • Comparing the structures of a protein obtained from different sources (e.g. species or expression systems) or comparing structures for different mutants of the same protein
  • Demonstrating comparability of solution conformation and/or thermal stability after changes in manufacturing processes or formulation
  • Studying the conformational stability of a protein under stress -- thermal stability, pH stability, and stability to denaturants and how this stability is altered by buffer composition or addition of stabilizers and excipients
  • CD is excellent for finding solvent conditions that increase the melting temperature and/or the reversibility of thermal unfolding, conditions which generally enhance shelf life
  • Determining whether protein-protein or protein-ligand interactions alter the conformation of protein
  • If there are any conformational changes, this will result in a spectrum which will differ from the sum of the individual components. Small conformational changes have been seen, for example, upon formation of several different receptor/ligand complexes