An Electron Density Source-Function Study of DNA Base Pairs in Their Neutral and Ionized Ground States^†

Area of Science:

• * Quantum Chemistry
• * Molecular Interactions
• * Computational Biology

Background:

• * The source function (SF) method analyzes electron density contributions within molecules.
• * It identifies regions influencing electron density at specific points, like bond critical points (BCPs).
• * Bader's Quantum Theory of Atoms in Molecules provides a framework for atomic resolution analysis.

Purpose of the Study:

• * To investigate the atomic contributions to hydrogen bonds in Watson-Crick DNA dimers (AT and GC).
• * To analyze these contributions in both neutral and ionized states.
• * To understand the role of the source function in characterizing hydrogen bond control.

Main Methods:

• * Application of the source function (SF) analysis at atomic resolution.
• * Examination of hydrogen bonds in adenine:thymine (AT) and guanine:cytosine (GC) DNA dimers.
• * Study of both neutral and singly ionized (radical cationic and anionic) states.

Main Results:

• * Atomic contributions to electron density at hydrogen bond BCPs are delocalized.
• * Ionization (electron gain or loss) shows similar net effects on some hydrogen bonds due to subtle atomic compensations.
• * Distant groups and rings significantly influence weaker hydrogen bonds, like the C-H def ⋅⋅⋅O bond in AT dimers.
• * Neither purine nor pyrimidine moieties consistently dominate hydrogen bond interactions.

Conclusions:

• * The source function effectively maps atomic contributions to hydrogen bonding in DNA dimers.
• * Molecular ionization introduces complex electronic effects on hydrogen bonds, involving inter-atomic compensations.
• * Delocalized electronic effects and contributions from remote molecular regions are crucial for understanding hydrogen bond strength and behavior.