MINIMIZATION OF SENSITIVITY LOSSES DUE TO THE USE OF GRADIENT PULSES IN TRIPLE-RESONANCE NMR OF PROTEINS

The use of pulsed field gradients in multiple-pulse NMR experiments ha s many advantages, including the possibility of obtaining excellent wa ter suppression without the need for selective presaturation. In such gradient experiments the water magnetization is dephased deliberately; exchange between the saturated protons of the solvent water and the N H protons of a protein transfers this saturation to the protein. As th e solvent is in large excess and relaxes relatively slowly, the result is a reduction in the sensitivity of the experiment due to the fact t hat the NH proton magnetization is only partially recovered. These eff ects can be avoided by ensuring that the water magnetization remains i ntact and is returned to the +z-axis at the start of data acquisition. General procedures for achieving this aim in any triple-resonance exp eriment are outlined and two specific examples are given. Experimental results confirm the sensitivity advantage of the modified sequences.