2 research outputs found
Utilization of SABRE-Derived Hyperpolarization To Detect Low-Concentration Analytes via 1D and 2D NMR Methods
The characterization of materials by the inherently insensitive
method of NMR spectroscopy plays a vital role in chemistry. Increasingly,
hyperpolarization is being used to address the sensitivity limitation.
Here, by reference to quinoline, we illustrate that the SABRE hyperpolarization
technique, which uses <i>para</i>-hydrogen as the source
of polarization, enables the rapid completion of a range of NMR measurements.
These include the collection of <sup>13</sup>C, <sup>13</sup>CÂ{<sup>1</sup>H}, and NOE data in addition to more complex 2D COSY, ultrafast
2D COSY and 2D HMBC spectra. The observations are made possible by
the use of a flow probe and external sample preparation cell to re-hyperpolarize
the substrate between transients, allowing repeat measurements to
be made within seconds. The potential benefit of the combination of
SABRE and 2D NMR methods for rapid characterization of low-concentration
analytes is therefore established
Hyperpolarisation through reversible interactions with parahydrogen
We describe here how the complexes Ir(COD)(NHC)Cl [NHC = IMes, SIMes, IPr, SIPr, ICy, IMe and ImMe2NPri2] provide significant insight into the catalytic process that underpins the hyperpolarization method signal amplification by reversible exchange (SABRE). These complexes react with pyridine and H2 to produce [Ir(H)2(NHC)(py)3]Cl which undergo ligand exchange on a timescale commensurate with good catalytic activity for the signal amplification by reversible exchange effect. This activity results from hydride ligand magnetic inequivalence and is highly dependent on the NHC. Variable temperature and kinetic studies demonstrate that rates of ligand loss which lie between 0.1 and 0.5 s−1 are ideal for catalysis. A role for the solvent complex [Ir(H)2(MeOH)(NHC)(py)2]Cl, which contains chemically inequivalent hydride ligands is revealed in the ligand exchange pathway. By optimisation of the conditions and NHC, a 5500-fold total pyridine signal enhancement is revealed when the NHC is IMes. Both T1-reduction effects and HD exchange with the solvent are probed and shown to link to catalyst efficiency. The resulting signal enhancements suggest future in vivo MRI measurements under physiological conditions using this catalytic effect will be possible