Zundel-type H-bonding in biomolecular ions

Area of Science:

• Chemical Physics
• Computational Chemistry
• Spectroscopy

Background:

• Peptide fragment ions are crucial for understanding protein structure and fragmentation.
• Characterizing the structure of small peptide fragments provides insights into non-covalent interactions.

Purpose of the Study:

• To determine the structure of the all-alanine (b6) fragment ion.
• To investigate the nature of proton binding in this fragment ion.

Main Methods:

• Quantum chemical calculations were employed to model potential structures.
• Infrared multiphoton dissociation (IRMPD) spectroscopy was used to probe vibrational modes.

Main Results:

• The all-alanine (b6) fragment ion exhibits a macrocyclic structure with C(2) symmetry.
• The proton is equally shared between two amide oxygen atoms, forming a symmetric Zundel-type hydrogen bond.

Conclusions:

• The macrocyclic structure is the dominant conformer for the all-alanine (b6) fragment ion.
• Symmetric hydrogen bonding plays a significant role in stabilizing peptide fragment ions.