Interacting Quantum Atoms and Multipolar Electrostatic Study of XH···π Interactions

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Biochemistry

Background:

• Van der Waals complexes containing benzene are vital in biochemical systems.
• Understanding the nature of XH···π interactions (X = C, N, O) is key to interpreting molecular recognition and biological processes.

Purpose of the Study:

• To quantitatively analyze the interaction energies of nine XH···π benzene-containing van der Waals complexes.
• To elucidate the driving forces and characteristics of these interactions at atomic and fragment levels.
• To differentiate the nature of OH···π, NH···π, and CH···π interactions.

Main Methods:

• Utilized Quantum Theory of Atoms in Molecules (QTAIM) multipolar electrostatics.
• Employed the Interacting Quantum Atoms/Fragment (IQA/IQF) energy partitioning method.
• Applied the relative energy gradient method for quantum mechanical property interpretation.

Main Results:

• OH···π and NH···π interactions are primarily driven by electrostatics, specifically the quadrupole moment of benzene carbons interacting with X and H charges.
• The X-H bond (X = O, N) exhibits an intramonomeric role where electrostatic energy favors complex formation, while covalent energy opposes it.
• CH···π interactions are governed by exchange-correlation energies, indicating a covalent character, contrary to previous classifications as noncovalent.
• Dispersion energy plays a role but is less significant than electrostatic or covalent components in complex formation.

Conclusions:

• The study provides a detailed, quantitative understanding of XH···π interactions in benzene complexes.
• Distinguishes between electrostatic (OH/NH···π) and covalent (CH···π) characteristics of these interactions.
• Highlights the importance of considering both atomic and fragment-level analyses for accurate interpretation of noncovalent interactions in biochemical contexts.