How does the intensity of tryptophan fluorescence relate to its environment?

Tryptophan fluorescence is an important parameter when analyzing proteins and its environment, due to the unique properties of the tryptophan side chain. When tryptophan is more buried within a protein or surrounded by a hydrophobic environment, the fluorescence intensity actually increases. This is primarily because the surrounding water molecules and polar environments tend to quench the fluorescence.

In a more hydrophobic or buried environment, the ability of the surrounding medium to interact with the tryptophan residue is reduced. Consequently, the tryptophan becomes less likely to experience non-radiative decay processes that would otherwise dissipate the energy and reduce fluorescence. Essentially, a more hydrophobic and buried environment enhances the quantum yield of tryptophan fluorescence, leading to increased intensity.

Thus, the assertion that the intensity increases as tryptophan is more buried aligns with the fundamental principles of molecular fluorescence, specifically how environmental factors influence light emission of tryptophan residues in proteins.