Intermolecular magnetic interactions in stacked DNA base pairs

Area of Science:

• Computational Chemistry
• Molecular Biophysics
• Spectroscopy

Background:

• Understanding the magnetic properties of DNA base pairs is crucial for molecular interactions.
• Nuclear Magnetic Resonance (NMR) spectroscopy is a powerful tool for probing magnetic interactions in molecules.
• The influence of pi-stacking on DNA base pair properties requires detailed computational analysis.

Purpose of the Study:

• To analyze the effect of pi-stacking on the magnetic properties of adenine-thymine (AT) and guanine-cytosine (GC) base pairs.
• To investigate how NMR spectroscopic parameters change due to the stacking of DNA base pairs in short sequences.
• To determine the sensitivity of different atoms and NMR parameters (shieldings, J-couplings) to pi-stacking.

Main Methods:

• Employed Density Functional Theory (DFT) with four functionals (B3LYP, BHANDLYP, KT2, KT3) and the SOPPA method.
• Utilized a locally dense basis set scheme for supramolecular systems with over 50 non-hydrogen atoms.
• Analyzed NMR spectroscopic parameters, including magnetic shieldings and J-couplings, for isolated and stacked base pairs.

Main Results:

• Pi-stacking of adjacent Watson-Crick base pairs measurably alters NMR spectroscopic parameters, independent of dispersion forces.
• Magnetic shieldings are more sensitive to stacking than J-couplings, with nitrogen atoms (hydrogen bond donors) and bonded carbons showing significant variation (2-5%).
• The stacking effect on NMR parameters is local, diminishing rapidly in sequences longer than three base pair layers.

Conclusions:

• Pi-stacking significantly influences the magnetic properties of DNA base pairs, particularly affecting nitrogen and hydrogen atoms involved in hydrogen bonds.
• NMR spectroscopic parameters, especially magnetic shieldings, serve as sensitive probes for detecting these stacking-induced changes.
• The localized nature of pi-stacking effects on NMR parameters is confirmed, with minimal impact beyond a few base pair layers.