Structural Evolution of Protonated Phenylalanine Induced by Stepwise Hydration.

Area of Science:

• Physical Chemistry
• Chemical Physics
• Spectroscopy

Background:

• Protonated amino acids are crucial in biological systems.
• Understanding ion hydration is key to solvation processes.

Purpose of the Study:

• Investigate the structural evolution of protonated phenylalanine ions (H+Phe) upon stepwise hydration.
• Determine the site-specific binding of water molecules to H+Phe.

Main Methods:

• Cryogenic ion spectroscopy
• Ultraviolet photodissociation (UVPD) spectroscopy
• IR photodissociation and IR ion-dip spectroscopy
• Quantum chemical calculations

Main Results:

• The first water molecule binds to the NH bond of the protonated NH3+ group.
• Subsequent water molecules bind to NH bonds or the carboxyl terminus.
• H+Phe(H2O)4 forms a single conformer, completing the first hydration shell.
• Hydration induces conformational selection in H+Phe.

Conclusions:

• Detailed insights into site-specific hydration of protonated phenylalanine.
• Revealed progressive conformational changes due to sequential water attachment.
• Demonstrated hydration-induced conformational selection.