Infrared Spectra of Proteins

The following tables summarize the frequencies and, for ordered solids, the polarization characteristics of conformation-sensitive infrared absorption bands of polypeptides and proteins. In the commonly used rock salt region of the spectra, there are two such bands, one at 1650 ± 40 cm⁻¹ and a second one at 1530 ± 30 cm⁻¹. The precise frequency and polarization (for ordered solids) of these bands depends on the secondary structure (conformation) of the sample. Table 1 lists the calculated frequencies for unordered solids and for five different ordered conformations in the solid state. Note that each conformation gives rise to more than one component of each band, but some of these predicted components are very weak. The polarization is parallel (‖) or perpendicular (⊥) with respect to the direction of chain propagation.