Practice question

Near-ultraviolet circular dichroism signals depend not on intrinsic chirality of aromatic amino acids themselves but on their fixed orientation inside asymmetric protein tertiary structure. When phenylalanine, tyrosine, tryptophan and disulfides are locked in folded core, surrounding chiral field induces differential absorption of left and right circularly polarized light, producing distinct bands. Unfolded or highly mobile side chains average to near zero. Peptide bond n to pi-star transitions dominate far-ultraviolet. Hydrogen bonding stabilizes fold indirectly, but side chain absorption directly generates near-ultraviolet CD signatures.