Dynamic nuclear polarisation of 1H in Gd-doped In(OH)3.

[Display omitted] • Gd3+ incorporation in In(OH) 3 demonstrated by EPR and 1H PRE. • 1H DNP enhancement of 9 for Gd-doped In(OH) 3. • DNP-enhanced natural abundance 17O NMR spectrum using PRESTO-II. • Breaking of symmetry by proton disorder explored with quadrupolar 115In NMR. Dynamic nuclear polarisation (DNP) of solids doped with high-spin metal ions, such as Gd3+, is a useful strategy to enhance the nuclear magnetic resonance (NMR) sensitivity for these samples. Spin diffusion can relay polarisation throughout a sample, which is most effective for dense 1H networks, while the efficiency of DNP using Gd3+ depends on the symmetry of the metal site. Here, we investigate cubic In(OH) 3 as a high-symmetry, proton-containing material for endogenous Gd DNP. A 1H enhancement of up to 9 is demonstrated and harnessed to measure the 17O spectrum at natural abundance. The enhancement is interpreted in terms of clustering of the Gd3+ dopants and the local reduction in symmetry of the metal site induced by proton disorder, as demonstrated by quadrupolar 115In NMR. This is the first example of 1H DNP using Gd3+ dopants in an inorganic solid. [ABSTRACT FROM AUTHOR]