Lifetime of Parahydrogen in Aqueous Solutions and Human Blood

Molecular hydrogen has unique nuclear spin properties. Its nuclear spin isomer, parahydrogen (pH₂ ), 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 pH₂ 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 (T₁ ) and lifetimes of pH₂ ( $$ ) in methanol and water, with or without O₂ , NaCl, rhodium-catalyst or human blood. Furthermore, we present a relaxation model that uses T₁ and $$ for more precise theoretical predictions of the H₂ spin state in PHIP experiments. All measured T₁ values were in the range of 1.4-2 s and $$ 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.