Origin of cooperativity in hydrogen bonding

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Molecular Interactions

Background:

• Hydrogen bonds (H-bonds) exhibit non-additive effects, known as H-bond cooperativity.
• Understanding the origin of this cooperativity is crucial for molecular modeling and materials science.

Purpose of the Study:

• To investigate the fundamental origin of H-bond cooperativity in linear chains.
• To determine the contributions of electrostatic and quantum effects to H-bond non-additivity.

Main Methods:

• Density Functional Theory (DFT) calculations were employed to study infinitely-long chains of hydrogen cyanide, 4-pyridone, and formamide.
• H-bond cooperativity was compared against the dipole-dipole interactions of effective point-dipoles.
• Empirical parameters accounting for polarizability were used to estimate cooperativity along H-bond dissociation paths.

Main Results:

• H-bond cooperativity in linear chains originates solely from classical electrostatics.
• Effective point-dipole magnitudes result from mutual polarization and effects beyond simple polarizable models.
• Quantum effects in H-bonding are limited to nearest-neighbor interactions and do not contribute to non-additivity in linear chains.

Conclusions:

• The non-additivity of H-bonds in linear chains is predominantly an electrostatic phenomenon.
• Quantum mechanical contributions to H-bond cooperativity are confined to adjacent interactions.
• These findings simplify the understanding of cooperative effects in extended H-bonded systems.