Sensitivity enhancement of multidimensional NMR experiments by paramagnetic relaxation effects

One of the main goals of NMR method development is to increase the sensitivity of multidimensional NMR experiments or reduce the required acquisition time. In these experiments, more than 80% of the NMR instrument time is spent on the recycle delay, where the instrument idles to wait for the recovery of proton magnetization. In this study, we report a method of using paramagnetic relaxation effects to shorten the recycle delays required in multidimensional NMR experiments of biological macromolecules. This approach significantly reduces the NMR instrument time required. Ni²⁺ ion, complexed with the chelating molecule DO2A, is used to decrease the proton T₁ relaxation time of biological macromolecules without the significant line-broadening effects that ate associated with most paramagnetic ions. The Ni(DO2A) also significantly decreases the T₁ relaxation time of water, thus providing additional sensitivity gain by eliminating the saturation of labile amide resonances.