Practice question

Alpha, 3-10, and pi helices differ in hydrogen bonding register i to i+3, i+4, and i+5, yielding distinct periodicity of protected amides and varying stability, yet their far-ultraviolet CD spectra appear similar with overlapping minima near 208 and 222 nm, making discrimination difficult. Near-ultraviolet CD senses aromatic tertiary packing, fluorescence reports local environment polarity, not backbone register. Hydrogen-deuterium exchange NMR distinguishes helical variants because exchange protection pattern repeats every three, four, or five residues respectively, and protection factors reflect differing bond lengths and solvation, enabling detailed helix type assignment.