What are the characteristic negative peaks in the CD spectra of an alpha helix?

In circular dichroism (CD) spectroscopy, the characteristic negative peaks that are observed for alpha helices occur at around 222 nm and 208 nm. These peaks arise from the unique secondary structure of the alpha helix and provide valuable information about the overall conformation of proteins.

The peak at 208 nm is primarily associated with the exciton coupling of the peptide bonds in the helical structure, while the peak at 222 nm is more indicative of the overall helical conformation and is influenced by the orientation of the dipoles of the carbonyl groups in the peptide backbone. The presence of these specific negative bands in the CD spectrum provides a signature that can be used to confirm the presence of an alpha helical structure in a protein.

Understanding these spectral characteristics is essential for interpreting protein structure and stability, and they play a significant role in the analysis of proteins using CD spectroscopy.