Local electronic structure of histidine in aqueous solution.

Area of Science:

• Physical Chemistry
• Biophysical Chemistry
• Spectroscopy

Background:

• Histidine is a crucial amino acid in biological systems.
• Understanding its electronic structure in aqueous solutions is vital.
• Previous methods for studying aqueous amino acids have limitations.

Purpose of the Study:

• To investigate the local electronic structure of aqueous histidine.
• To determine the protonation states of histidine across different pH levels.
• To establish aerosol X-ray photoemission spectroscopy as a viable method for studying aqueous solutions.

Main Methods:

• Aerosol generation of aqueous histidine solutions.
• X-ray photoemission spectroscopy (XPS) analysis of C1s and N1s levels.
• Density functional theory (DFT) calculations for spectral assignment and confirmation.

Main Results:

• XPS spectra successfully elucidated the electronic structure of aqueous histidine.
• Protonation states were accurately determined at pH 1 (fully protonated), pH 7 (zwitterionic), and pH 13 (carboxyl deprotonated).
• Experimental findings were corroborated by DFT calculations.

Conclusions:

• Aerosol X-ray photoemission spectroscopy provides detailed insights into histidine's electronic structure and protonation.
• This technique offers a convenient and simple approach for probing electronic structures in aqueous solutions.
• The study highlights the utility of XPS for characterizing biomolecules in different ionic states.