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Issue 20, 2013
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Achievement of high nuclear spin polarization using lanthanides as low-temperature NMR relaxation agents

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Abstract

Many approaches are now available for achieving high levels of nuclear spin polarization. One of these methods is based on the notion that as the temperature is reduced, the equilibrium nuclear polarization will increase, according to the Boltzmann distribution. The main problem with this approach is the length of time it may take to approach thermal equilibrium at low temperatures, since nuclear relaxation times (characterized by the spin-lattice relaxation time T1) can become very long. Here, we show, by means of relaxation time measurements of frozen solutions, that selected lanthanide ions, in the form of their chelates with DTPA, can act as effective relaxation agents at low temperatures. Differential effects are seen with the different lanthanides that were tested, holmium and dysprosium showing highest relaxivity, while gadolinium is ineffective at temperatures of 20 K and below. These observations are consistent with the known electron-spin relaxation time characteristics of these lanthanides. The maximum relaxivity occurs at around 10 K for Ho-DTPA and 20 K for Dy-DTPA. Moreover, these two agents show only modest relaxivity at room temperature, and can thus be regarded as relaxation switches. We conclude that these agents can speed up solid state NMR experiments by reducing the T1 values of the relevant nuclei, and hence increasing the rate at which data can be acquired. They could also be of value in the context of a simple low-cost method of achieving several-hundred-fold improvements in polarization for experiments in which samples are pre-polarized at low temperatures, then rewarmed and dissolved immediately prior to analysis.

Graphical abstract: Achievement of high nuclear spin polarization using lanthanides as low-temperature NMR relaxation agents

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Publication details

The article was received on 09 Jan 2013, accepted on 04 Apr 2013 and first published on 05 Apr 2013


Article type: Paper
DOI: 10.1039/C3CP00103B
Citation: Phys. Chem. Chem. Phys., 2013,15, 7586-7591
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    Achievement of high nuclear spin polarization using lanthanides as low-temperature NMR relaxation agents

    D. T. Peat, A. J. Horsewill, W. Köckenberger, A. J. P. Linde, D. G. Gadian and J. R. Owers-Bradley, Phys. Chem. Chem. Phys., 2013, 15, 7586
    DOI: 10.1039/C3CP00103B

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