Calibration of ring-current effects in proteins and nucleic acids

Area of Science:

• Computational chemistry
• Biophysical chemistry
• Chemical physics

Background:

• Nuclear magnetic resonance (NMR) spectroscopy is crucial for determining the structure and dynamics of biomolecules.
• Accurate interpretation of NMR chemical shifts requires understanding intermolecular shielding effects.
• Aromatic systems in proteins and nucleic acids exhibit significant magnetic anisotropy ('ring-current' effects).

Purpose of the Study:

• To investigate intermolecular shielding effects on methane molecules near aromatic systems using density functional theory (DFT).
• To compare DFT results with empirical formulas based on magnetic anisotropy and electrostatic polarization.
• To reassess ring-current intensity factors and evaluate the contribution of electrostatic interactions to chemical shift dispersion.

Main Methods:

• Density functional theory (DFT) calculations of chemical shielding for methane.
• Placement of methane in various positions relative to model aromatic systems.
• Comparison of computed shielding with empirical models incorporating magnetic anisotropy and C-H bond polarization.

Main Results:

• Good agreement was observed between DFT calculations and empirical formulas.
• Electrostatic interactions were found to significantly contribute to the overall chemical shift dispersion.
• Refined ring-current intensity factors for aromatic amino acids and nucleic acid bases were obtained.

Conclusions:

• DFT calculations validate and refine existing empirical models for intermolecular shielding.
• Electrostatic effects play a substantial role in chemical shift variations near aromatic systems.
• The findings provide valuable insights for the analysis of NMR chemical shifts in proteins and nucleic acids.