Slice-selective single scan protonCOSY with dynamic nuclear polarisation

Short acquisition time and single scan capability of gradient-assisted ultrafast multidimensional spectroscopy makes it possible to record 2D spectra of highly polarised spin systems in the liquid state using dynamic nuclear polarization (DNP) in conjunction with fast dissolution. We present a slice selective experiment, suitable for back-to-back acquisition of two independent single-scan 2D experiments from different sample volumes. This scheme maximizes the amount of information obtainable from a sample that is prepolarised with a non-repeatable DNP technique. It is particularly suitable for samples with the short longitudinal relaxation times common to proton NMR spectroscopy. This technique is demonstrated by applying two filtered proton 2D COSY experiments on a DNP-polarised mixture of glutamine and glutamate to selectively amplify the correlation pattern of the protons connected to the β and γ carbons of either one of the two amino acids. Particular emphasis was put on the reproducibility of the experiments, especially the polarisation enhancement. Data for the liquid-state proton enhancement from amino acids and small proteins was assembled in a map that allowed the prediction of signal levels in liquid-state NMR experiments employing dissolution DNP.