Infrared (IR) spectroscopy measures molecular vibrations due to the specific absorption of IR radiation by chemical bonds.

For more than 35 years, it has been known that the shape and frequency of the amide I band within peptide bonds are characteristic for the structure of the studied protein.

From this single band, the presence and relative percentage of secondary structure elements (α-helix and β-strand for example) in a protein can be determined and structural changes detected with high sensitivity.