This article is not about DNP. However, the authors describe how to use paramagnetic relaxation enhancers to speed up the data acquisition and with this increase the sensitivity. A similar effect happens when a paramagnetic polarization agent is used in a DNP-NMR experiment and often the only reason why it is actually possible to run 1H-DNP-NMR experiments with recycling delays of several seconds is because of the relaxation enhancing nature of the polarizing agent.
Yamamoto, K., et al., Shortening spin-lattice relaxation using a copper-chelated lipid at low-temperatures – A magic angle spinning solid-state NMR study on a membrane-bound protein. J Magn Reson, 2013. 237(0): p. 175-81.
Inherent low sensitivity of NMR spectroscopy has been a major disadvantage, especially to study biomolecules like membrane proteins. Recent studies have successfully demonstrated the advantages of performing solid-state NMR experiments at very low and ultralow temperatures to enhance the sensitivity. However, the long spin-lattice relaxation time, T1, at very low temperatures is a major limitation. To overcome this difficulty, we demonstrate the use of a copper-chelated lipid for magic angle spinning solid-state NMR measurements on cytochrome-b5 reconstituted in multilamellar vesicles. Our results on multilamellar vesicles containing as small as 0.5mol% of a copper-chelated lipid can significantly shorten T1 of protons, which can be used to considerably reduce the data collection time or to enhance the signal-to-noise ratio. We also monitored the effect of slow cooling on the resolution and sensitivity of (13)C and (15)N signals from the protein and (13)C signals from lipids.