Practice question

Tryptophan indole emission critically reports local polarity and hydration. In aqueous exposure, solvent dipoles reorient around the large excited-state dipole, stabilizing S1 and lowering emission energy near 350-355 nanometers, producing red shift. When buried in hydrophobic protein interior, membrane or ligand pocket, dipolar relaxation is minimal, excited state remains high energy, emission shifts to higher energy blue region around 330-335 nanometers. Bathochromic denotes red shift, hypochromic refers to intensity change. Therefore blue shift clearly signals burial, folding or membrane insertion, widely exploited for protein conformation monitoring.