Practice question

Tryptophan fluorescence quantum yield and wavelength are exquisitely sensitive to local polarity and hydrogen bonding. Fully solvent-exposed indole in water emits near 350-355 nm because excited state dipole stabilized by reorientation of surrounding water dipoles, lowering emission energy. When buried inside hydrophobic interior of proteins such as azurin, ribonuclease or lysozyme, nonpolar surroundings restrict solvent relaxation, destabilize excited state and reduce dipole stabilization. Consequently emission blue shifts to about 308-335 nm, commonly centered near 325 nm. This shift serves as valuable intrinsic reporter for folding, ligand binding and conformational dynamics.