1. Purpose

For biological and biochemical applications ¹H NMR spectra usually have to be recorded in normal water, with the addition of only 10% D₂O to provide the necessary lock signal. Higher D₂O content would cause the signals of the exchangeable NH protons to disappear. Thus, there is a need to suppress the huge solvent signal. For this purpose a multitude of techniques have been proposed. However, all techniques require that the magnet is well shimmed and a probe-head yielding a reasonable line-shape (see Exp. 3.5) must be available. In this experiment the presaturation method is described. It provides a check on whether the spectrometer set-up is capable of effective water suppression. For other methods see Experiments 6.19, 8.9, and 11.16 to 11.18.

2. Literature

M. Guéron, P. Plateau, M. Decorps, Prog. NMR Spectrosc. 1991, 23, 135–209.
P. J. Hore, Methods Enzym. 1989, 176, 64–77.
W. S. Price, Annu. Rep. NMR Spectrosc. 1999, 38, 289–354.

3. Pulse Scheme and Phase Cycle

Water presaturation pulse sequence and phase cycle

4. Acquisition

Time requirement: 15 min

Sample: 2 mM sucrose in 90% H₂O / 10% D₂O + 0.5 mM DSS (2,2-dimethyl-2-silapentane-5-sulfonate, sodium salt) + trace of NaN₃ against bacteria growth.

The magnet is well shimmed on the water sample. A normal ¹H NMR spectrum is recorded and the offset of the transmitter adjusted on the water resonance. The