Proton exchange rates measured by saturation transfer using delayed randomization of the solvent magnetization

Area of Science:

• Magnetic Resonance Spectroscopy
• Nuclear Magnetic Resonance (NMR) techniques

Background:

• The spin-lock saturation transfer (SLST) experiment is a method for studying molecular interactions.
• Analysis of SLST experiments using Bloch equations reveals complexities in proton decay under rapid exchange conditions.

Purpose of the Study:

• To analyze the spin-lock saturation transfer experiment using Bloch equations.
• To investigate the influence of solvent T1rho relaxation on exchangeable proton decay.
• To propose an improved experimental approach for accurate analysis of proton exchange.

Main Methods:

• Bloch equation analysis of the spin-lock saturation transfer experiment.
• Development of an alternative NMR experiment incorporating pulsed field gradients.
• Evaluation of signal decay characteristics and excitation profiles.

Main Results:

• Solvent T1rho relaxation significantly affects exchangeable proton decay in rapid exchange regimes.
• The proposed alternative experiment demonstrates a single exponential intensity decay for protons across all exchange rates.
• The alternative method achieves efficient water suppression and an even excitation profile.

Conclusions:

• The conventional spin-lock saturation transfer experiment is limited by solvent relaxation effects.
• A modified NMR experiment using pulsed field gradients offers a more robust method for studying proton exchange.
• The enhanced method provides accurate decay analysis and improved spectral quality.