Which IR spectrum absorption range is indicative of alpha helices in proteins?

The correct absorption range for identifying alpha helices in proteins is 1650-1660 cm^-1. This range corresponds to the characteristic amide I band, which arises from the C=O stretching vibration of the peptide bonds in proteins. The specific positioning of the peaks within this range can indicate different types of secondary structures.

Alpha helices are stabilized by hydrogen bonds between the carbonyl oxygen of one amino acid and the amide hydrogen of another, which contributes to the specific wavelength of the absorption. Therefore, the amide I band is a vital tool in spectroscopic methods like infrared (IR) spectroscopy for assessing protein structures.

Understanding this concept allows researchers to delineate between various secondary structures like alpha helices and beta sheets based on their distinct spectral signatures. In contrast, the other ranges correlate with different structural features and are not characteristic of alpha helices.