Fluorescence of tryptophan in aqueous solution

Area of Science:

• Photochemistry
• Biophysical Chemistry
• Computational Chemistry

Background:

• Tryptophan (Trp) is an essential amino acid with unique photophysical properties.
• Understanding Trp's behavior in aqueous solutions is crucial for biological and chemical applications.
• Previous studies have indicated environmental sensitivity of Trp fluorescence.

Purpose of the Study:

• To investigate the absorption and emission spectra of Tryptophan in aqueous solution.
• To elucidate the role of hydrogen bonding in Trp's fluorescence.
• To model and computationally analyze the excited-state properties of Trp in water.

Main Methods:

• Experimental measurement of absorption and emission spectra.
• Computational modeling using Density Functional Theory (DFT).
• Time-Dependent Density Functional Theory (TD-DFT) for excited-state calculations.
• Investigation of a hydrogen-bonded zwitterionic Trp(H2O)9 model.

Main Results:

• Spectroscopic data were successfully explained by a proposed Trp(H2O)9 model.
• Hydrogen bond strengthening in the excited state was identified as a key factor.
• Electron density delocalization between the indole moiety and water molecules was observed.
• A significant red-shift in Trp fluorescence was correlated with these findings.

Conclusions:

• The study confirms the significant influence of hydrogen bonding on Tryptophan's fluorescence.
• Strengthened hydrogen bonds in the excited state facilitate electron delocalization, causing fluorescence red-shift.
• Computational methods accurately predict the observed spectroscopic behavior of Trp in aqueous solution.