The reaction of unsaturated substrates with hydrogen gas enriched in the para spin isomer leads to products with a high degree of nuclear singlet spin order. This leads to greatly enhanced NMR signals, with important potential applications such as magnetic resonance imaging (MRI) of metabolic processes. Although parahydrogen-induced polarization has the advantage of being cheap, compact, and mobile, especially when performed in ultralow magnetic fields, efficiency is lost when more than a few protons are involved. This strongly restricts the range of compatible substances. We show that these difficulties may be overcome by a combination of deuteration with the application of a sinusoidally modulated longitudinal field as a well as a transverse rotating magnetic field. We demonstrate a six-fold enhancement in the 13C hyperpolarization of [1-13C, 2,3-d2]-succinic acid, as compared with standard hyperpolarization methods, applied in the same ultralow field regime.
Supporting information includes explicit sketch of the experimental setup, theoretical describtion of the work, numerical simulatations and experimental optimization for procedures performed.