Circular dichroism

circular dichroism, or CD, is defined as the differential absorption of left and right hand circularly polarized light:

CD = (C_L - C_R).

In general, this kind of phenomenon will be exhibited by any optically active molecule. As a consequence, circular dichroism is exhibited by biological molecules, because of the dextrorotary (sugars) and levulorotary (amino acids) molecules they contain. Noteworthy as well is that secondary structure will also impart a distinct CD absorption to their respective molecules. Therefore, the alpha helix of proteins and the double helix of nucleic acids will have a CD signature representative of their structure.

The ultraviolet CD of proteins can predict their secondary structure.

At the quantum mechanical level, the information content of circular dichroism and optical rotation are identical.

See also:

• optical rotation
• optical activity
• optical isomerism
• magnetic_circular_dichroism
• dichroic