The presence of 14N nucleus in the scalar coupling network results in a 3-fold decrease of 15N T1 and polarization values for all 15N sites in 15N2-metronidazole versus15N3-metronidazole in SABRE hyperpolarization in microtesla fields.

Nimorazole belongs to the imidazole‐based family of antibiotics to fight against anaerobic bacteria. Moreover, nimorazole is now in Phase 3 clinical trial in Europe for potential use as a hypoxia radiosensitizer for treatment of head and neck cancers. We envision the use of [15N3]nimorazole as a theragnostic hypoxia contrast agent that can be potentially deployed in the next‐generation MRI‐LINAC systems. Herein, we report the first steps to create long‐lasting (for tens of minutes) hyperpolarized state on three 15N sites of [15N3]nimorazole with T1 of up to ca. 6 minutes. The nuclear spin polarization was boosted by ca. 67000‐fold at 1.4 T (corresponding to P15N of 3.2 %) by 15N−15N spin‐relayed SABRE‐SHEATH hyperpolarization technique, relying on simultaneous exchange of [15N3]nimorazole and parahydrogen on polarization transfer Ir‐IMes catalyst. The presented results pave the way to efficient spin‐relayed SABRE‐SHEATH hyperpolarization of a wide range of imidazole‐based antibiotics and chemotherapeutics.

Features of the near-infrared phosphorescence of singlet oxygen 1 O 2 photosensitized by TiO 2 in solutions have been investigated. The short-lived phosphorescence of 1 O 2 with spectral maximum at approximately 1300 nm is observed to follow excitation by pulsed laser radiation at 355 nm of TiO 2 suspended in CCl 4 and water H 2 O. The shorter lifetime and spectral shift of this phosphorescence, as compared with phosphorescence of 1 O 2 sensitized by phenalenone in these solvents, are attributed to the adsorbed state of emitting singlet oxygen. The observed laser pulse energy dependence indicates the two-photon and three-photon nature of this phosphorescence initiation in CCl 4 and H 2 O, respectively. The formation of 1 O 2 in CCl 4 is assumed to be provided by the sequence of one-photon excitation of TiO 2 , giving rise to superoxide anion O 2 − and one-photon photodetachment of electron from O 2 − . The photodetachment of electron from O 2 − in water H 2 O is a two-photon process because of higher solvation energy of superoxide anion in water. The processes that govern the rise and decay of singlet oxygen phosphorescence sensitized by TiO 2 are discussed. The factors affecting the yield of singlet oxygen provided by electron photodetachment are also considered.