Strong N-H...pi hydrogen bonding in amide-benzene interactions

Area of Science:

• Biophysics
• Chemical Physics
• Molecular Interactions

Background:

• Amide N--H...pi interactions are common in proteins but poorly understood.
• Characterizing these weak interactions is crucial for understanding protein structure and function.

Purpose of the Study:

• To investigate the isolated amide N--H...pi interaction using 2-pyridone (2PY) and benzene.
• To determine the structure, binding energy, and dominant stabilizing forces of the 2PY-benzene dimer.

Main Methods:

• Supersonic-jet-cooled dimer formation of 2-pyridone with benzene.
• Computational methods: MP2, SCS-MP2, CCSD(T), and symmetry-adapted perturbation theory.
• Spectroscopic analysis: Infrared-ultraviolet depletion spectroscopy.

Main Results:

• A T-shaped structure was optimized, featuring a N--H...pi hydrogen bond.
• Calculated binding energy (De) is 25.2 kJ/mol, comparable to water dimer.
• Infrared spectra show significant N--H and C=O vibrational shifts, confirming a strong N--H...pi interaction.

Conclusions:

• The N--H...pi interaction is the dominant stabilizing factor in the 2PY-benzene dimer.
• Experimental and computational data support a strong, non-conventional pi hydrogen bond.
• This provides a clearer characterization of the amide N--H...pi interaction in isolation.