A Straightforward Method for the Generation of Hyperpolarized Orthohydrogen with a Partially Negative Line.

The hydrogen molecule, which exists in two spin isomers (ortho- and parahydrogen), is a highly studied system due to its fundamental properties and practical applications. Parahydrogen is used for Nuclear Magnetic Resonance signal enhancement, which is hyperpolarization of other molecules, including biorelevant ones. Hyperpolarization can be achieved by using Signal Amplification by Reversible Exchange (SABRE). SABRE can also convert parahydrogen into orthohydrogen, and surprisingly, in some cases, it has been discovered that orthohydrogen's resonance has the Partially Negative Line (PNL) pattern. Here, an approach for obtaining orthohydrogen with a PNL signal is presented for two catalysts: Ir-IMes, and Ir-IMesBn. The type of solvent in which SABRE is conducted is crucial for the observation of PNL. Specifically, a PNL signal can be easily generated in benzene using both catalysts, but it is more intense for Ir-IMesBn. In acetone, PNL is observed only for Ir-IMesBn. In methanol, no PNL is detected. The PNL effect is only detectable during the initial steps of pre-catalyst activation, and disappears as the activation process progresses. We have proposed a working hypothesis that explains our results. The presented data may facilitate the further investigation of PNL and its applications in material science and catalysis.

Deactivation of catalysts in simultaneous reversible and irreversible parahydrogen NMR signal enhancement, and the role of co-ligands in the stabilization of the reversible method.

Signal Amplification by Reversible Exchange (SABRE) and hydrogeneable Parahydrogen Induced Polarization (hPHIP) can enhance weak NMR signals, and thus increase the range of NMR applications. Here, using an N-heterocyclic carbene Ir-based catalyst, simultaneous SABRE and hPHIP was achieved for the compound with an N-donor site and an acetylene triple bond. It was demonstrated that the interplay between SABRE and hPHIP can be manipulated. Specifically, it was found that the hPHIP effect could be almost completely suppressed, while stable SABRE was observed in subsequent consecutive experiments. The presented results have the potential to increase the numbers of parahydrogen hyperpolarizable molecules.

NMR studies of inclusion complexes: naphthalene and natural cyclodextrins.

Inclusion complexes of naphthalene (NP) with cyclodextrins (CD) have been investigated so far using non-NMR techniques resulting in inconsistent data. Here, the first application of high-field NMR spectroscopy in combination with a precise analysis of the results has allowed us to determine accurately the stoichiometry of complexes and their association constants. Titration measurements have been performed by 1H NMR spectroscopy in D2O at a magnetic field B0 of 18.8 T. NP and αCD form a 1 : 2 complex in which a single NP molecule is closed in a capsule made up of two αCD macrocycles. NP and ßCD build coexisting 2 : 1 and 2 : 2 complexes with large binding constants. Larger γCD host molecules form essentially similar complexes with NP as the ßCD but corresponding binding constants are smaller.