Electron spin-nuclear spin cross-correlation effects on multiplet splittings in paramagnetic proteins

Area of Science:

• Magnetic Resonance Spectroscopy
• Physical Chemistry
• Chemical Physics

Background:

• Nuclear magnetic resonance (NMR) spectroscopy is vital for molecular structure determination.
• Paramagnetic systems present unique challenges and opportunities in NMR studies.
• Understanding spin interactions is key to interpreting complex NMR spectra.

Purpose of the Study:

• To calculate the effects of cross-correlation between Curie spin-nuclear dipole and nuclear dipole-nuclear dipole interactions.
• To investigate the impact of relaxation-induced frequency shifts (dynamic frequency shift) on residual dipolar coupling measurements.
• To assess the relevance of these effects in field-oriented systems with small and intermediate molecular tumbling.

Main Methods:

• Theoretical calculation of cross-correlation effects in paramagnetic systems.
• Analysis of linewidths and resonance frequencies for AX spin systems.
• Simulations of dynamic frequency shifts and their influence on dipolar couplings.

Main Results:

• Cross-correlation significantly affects linewidths and resonance frequencies of AX multiplets.
• Dynamic frequency shifts can impede accurate measurement of residual dipolar couplings.
• These effects are particularly relevant for systems with correlation times under 5 ns.

Conclusions:

• Accurate measurement of residual dipolar couplings in paramagnetic systems requires considering cross-correlation effects.
• The dynamic frequency shift poses a challenge for precise dipolar coupling determination in small and intermediate tumbling regimes.
• Simulations highlight the importance of these interactions for advanced NMR applications.