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

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

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  • 2009-02-27
Published in:
  • The journal of physical chemistry. B. - 2009
Amides
Benzene
Carbon
Hydrogen
Hydrogen Bonding
Models, Chemical
Models, Molecular
Molecular Conformation
Nitrogen
Oxygen
Pyridones
Spectrophotometry, Infrared
Spectrophotometry, Ultraviolet
English Among the weak intermolecular interactions found in proteins, the amide N--H...pi interaction has been widely observed but remains poorly characterized as an individual interaction. We have investigated the isolated supersonic-jet-cooled dimer of the cis-amide and nucleobase analogue 2-pyridone (2PY) with benzene and benzene-d6. Both MP2 and SCS-MP2 geometry optimizations yield a T-shaped structure with a N--H...pi hydrogen bond to the benzene ring and the C=O group above, but far from the C--H bonds of benzene. The CCSD(T) calculated binding energy at the optimum geometry is De = 25.2 kJ/mol (dissociation energy D0 = 21.6 kJ/mol), corresponding to the H-bond strength of the water dimer or of N--H...O hydrogen bonds. The T-shaped geometry is supported by the infrared-ultraviolet depletion spectra of 2PY x benzene: The N--H stretch vibrational frequency is lowered by 56 cm(-1), and the C=O stretch vibration is lowered by 10 cm(-1), relative to those of bare 2PY, indicating a strong N--H...pi interaction and a weak interaction of the C=O group. The benzene C--H infrared stretches exhibit very small shifts (approximately 2 cm(-1)) relative to benzene, signaling the absence of interactions with the benzene C--H groups. The infrared spectral shifts are consistent with a strong nonconventional pi hydrogen bond and a T-shaped structure for 2PY x benzene. Symmetry-adapted perturbation theory calculations show that the N--H...pi interaction is by far the dominant stabilization factor.
Language
  • English
Open access status
hybrid
Identifiers
Persistent URL
https://sonar.ch/global/documents/1144
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