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Information from the water stripe in TOCSY experiments on systems with exchangeable protons
T T Nakashima1, R E McClung, G Kotovych
1Department of Chemistry, University of Alberta, Edmonton, Alberta, T6G 2G2, Canada.
Summary
Water "stripes" in TOCSY maps reveal proton correlations linked to solvent-exchanging OH/NH groups. Their intensity depends on spin-lock duration and exchange rate, offering insights into molecular dynamics.
Area of Science:
- Nuclear Magnetic Resonance Spectroscopy
- Biophysical Chemistry
- Solution State Chemistry
Background:
- Total Correlation Spectroscopy (TOCSY) is a key NMR technique for elucidating molecular structures.
- Understanding proton exchange dynamics is crucial for interpreting NMR spectra of biological molecules in solution.
- Previous TOCSY analyses often overlooked or misinterpreted signals arising from chemical exchange.
Purpose of the Study:
- To investigate the origin and characteristics of water "stripes" observed in TOCSY spectra of aqueous solutions.
- To theoretically analyze the phenomenon of chemical exchange during the spin-lock period in TOCSY.
- To determine the factors influencing the intensity of these exchange-correlated signals.
Main Methods:
- Acquisition and analysis of TOCSY NMR spectra for sucrose, a 15-aminoacid peptide, and individual amino acids in aqueous solutions.
- Theoretical modeling of chemical exchange processes within the TOCSY pulse sequence, specifically during the spin-lock period.
- Quantitative assessment of the relationship between signal intensity, spin-lock time, and proton exchange rates.
Main Results:
- Observed "stripes" in TOCSY maps correspond to protons scalar-coupled to solvent-exchanging OH or NH protons.
- Theoretical analysis confirmed that chemical exchange during the spin-lock period is the source of these correlations.
- The intensity of these exchange-correlated signals was found to be dependent on both the spin-lock duration and the rate of proton exchange.
Conclusions:
- The study elucidates the origin of water "stripes" in TOCSY spectra, attributing them to solvent-exchangeable protons.
- This finding provides a deeper understanding of TOCSY spectral interpretation for molecules in aqueous environments.
- The demonstrated dependence on spin-lock time and exchange rate offers a potential method for studying proton exchange dynamics using TOCSY.
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