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Abstract

The unique properties of the entangled, antisymmetric nuclear spin state of dihydrogen, parahydrogen (pH2), has intrigued physicists, chemists, and other scientists for almost a century. pH2 was used as a model system in the early days of quantum mechanics (1) and is used for fueling rockets as well as combustion-free cars today. In the 1980s, pH2 was discovered as a convenient and potent source of spin order, allowing the enhancement of the signals of magnetic resonance (MR) by several orders of magnitude. (2−4) In the advent of hyperpolarized (HP) contrast agents (CA) for biomedical MR imaging (MRI) that followed, pH2-based hyperpolarization methods played an important role in the acquisition of the first HP 13C in vivo images (Figure 1). (5,6) Ever since, pH2 has proven to be highly valuable for analytical investigations and fundamental research, e.g., in analytical and catalytic chemistry or in the physics of singlet spin states. (7−10).