Towards Optimising and Understanding Reversible Hyperpolarisation of Lactate Esters Relayed from Parahydrogen

The SABRE-Relay hyperpolarisation method is used to enhance the 1H and 13C NMR signals of lactate esters, which find use in a wide range of medical, pharmaceutical, and food science applications. This is achieved by the indirect relay of magnetisation from parahydrogen, a spin isomer of dihydrogen, to OH-containing lactate esters via a SABRE-hyperpolarised NH intermediary. This delivers 1H and 13C NMR signal enhancements as high as 245-fold and 985-fold, respectively, which makes the lactate esters far more detectable using NMR. DFT-calculated J-couplings and spin dynamics simulations indicate that, while polarisation can be transferred from the lactate OH to other 1H nuclei via the J-coupling network, incoherent mechanisms are needed to polarise the 13C nuclei at the 6.5 mT transfer field used. The resulting sensitivity boost is predicted to be of great benefit for the NMR detection and quantification of low concentrations (< mM) of lactate esters and could provide a useful precursor for the production of hyperpolarised lactate, a key metabolite.