Lifetime of Parahydrogen in Aqueous Solutions and Human Blood

Molecular hydrogen has unique nuclear spin properties. Its nuclear spin isomer, parahydrogen (pH(2)), was instrumental in the early days of quantum mechanics and allows to boost the NMR signal by several orders of magnitude. pH(2‐)induced polarization (PHIP) is based on the survival of pH(2) spin order in solution, yet its lifetime has not been investigated in aqueous or biological media required for in vivo applications. Herein, we report longitudinal relaxation times (T (1)) and lifetimes of pH(2) ([Formula: see text] ) in methanol and water, with or without O(2), NaCl, rhodium‐catalyst or human blood. Furthermore, we present a relaxation model that uses T (1) and [Formula: see text] for more precise theoretical predictions of the H(2) spin state in PHIP experiments. All measured T (1) values were in the range of 1.4–2 s and [Formula: see text] values were of the order of 10–300 minutes. These relatively long lifetimes hold great promise for emerging in vivo implementations and applications of PHIP.