When does a hydrogen bond become a van der Waals interaction? a topological answer.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Biophysical Chemistry

Background:

• Hydrogen bonds (H-bonds) are crucial noncovalent interactions (NCIs) in bioorganic systems.
• Distinguishing H-bonds from van der Waals (vdW) interactions is subjective due to the lack of a defined energy threshold.
• Accurate classification of NCIs is vital for understanding their physical and chemical significance.

Purpose of the Study:

• To establish a quantitative energy border between H-bonding and vdW interactions.
• To provide a more objective method for classifying noncovalent interactions.
• To refine the understanding of interaction transitions and long-range effects.

Main Methods:

• Utilized the Quantum Theory of Atoms in Molecules (QTAIM).
• Employed the source function to analyze electronic structure.
• Investigated water dimers and various classical/nonclassical H-bonding systems.

Main Results:

• Successfully identified a distinct energy border separating H-bonding from vdW interactions.
• Demonstrated this border by varying interatomic distances and contact angles.
• Redefined the 'critic angle' concept and identified the limit of long-range interactions via atomic basin volume analysis.

Conclusions:

• The study provides a robust method for objectively differentiating H-bonds and vdW interactions.
• This energy border enhances the interpretation of noncovalent interactions in chemical and biological contexts.
• The findings contribute to a more precise understanding of molecular interactions and their boundaries.