Common use of SABRE hyperpolarization Clause in Contracts

SABRE hyperpolarization. Parahydrogen (pH2), Ir-catalyst, cosubstrate (1-methyl-1,2,3-triazole, mtz), and analytes are involved in a reversible binding equilibrium. During the lifetime of the complex, the spin order of pH2 is converted to nuclear hyperpolarization in analytes.[7] Polarization transfer is conducted at low field outside the NMR magnet, after which the sample is inserted into the spectrometer for detection. An excess of mtz is needed for sub-millimolar SABRE to restore catalyst activity at low analyte concentrations.[13] nitrogenous heteroaromatics,[7,8,9a,b] examples of sulfur heter- oaromatic compounds,[10] nitriles,[11a] Schiff bases[11b] and diazirines[11c] have been reported. Several such SABRE- active moieties appear in the structures of drugs,[11d,12] odor- ants[9b] and metabolites,[9a] giving rise to an interest in devising new analytical approaches for their detection. Furthermore, [*] Xx. X. Reile, R. L. E. G. Aspers, Xx. X. X. Xxxxxxx, Prof. F. P. J. T. Xxxxxx, Xx. X. Tessari Institute for Molecules and Materials, Radboud University Xxxxxxxxxxxxxx 000, 0000XX Xxxxxxxx (Xxx Xxxxxxxxxxx) E-mail: x.xxxxxxx@xxxxxxx.xx.xx J.-M. Tyburn Bruker BioSpin GmbH Silberstreifen, Rheinstetten (Germany) Xx. X. X. Xxxxx Bruker Biospin Corp. Billerica, MA 01821 (USA) Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: xxxxx://xxx.xxx/10.1002/anie.201703577. although the original SABRE methods did not maintain the quantitative abilities of NMR spectroscopy, a general approach to analytical SABRE was recently developed and used for quantification of sub-micromolar analytes (Scheme 1).[13] Figure 1 depicts the aromatic region of a single-scan SABRE spectrum of a mixture of six dilute analytes. The molecules 1–6 and similar analogues occur as low-micromolar concentration flavor components in food extracts,[14] but spectral elucidation of their mixtures is complicated if based on 1D spectra alone. Herein, we overcome this challenge with a new method that combines SABRE with DOSY to resolve the signals of analytes 1–6 at low-micromolar concentrations. 9174 T 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2017, 56, 9174 –9177 Figure 1. Region of interest of SABRE spectrum. Concentrations of analytes are 25 mm (1), 10 mm (2–5), and 5 mm (6). Catalyst-mtz background signals are highlighted with (*). Note that SABRE enhan- ces each signal by a factor that is not directly related to analyte concentration. Full spectrum and thermal reference are available in the Supporting Information. Single-scan diffusion NMR techniques are not applicable for this purpose, since these either sacrifice resolution for measurement time,[15] have reduced sensitivity due to spatial encoding,[16] or are not compatible with the T1 relaxation rate of 1H nuclei.[17] Hence, SABRE-DOSY of low-micromolar analytes is necessarily a multi-scan experiment. Several groups have implemented specialized hardware for automatic sample transfer between low- and high-field in pH2 hyper- polarization experiments.[18] In this work, we have employed the flow system described in Refs. [18b, 19] (see Experimental Section) to control sample transfer between the hyperpola- rization chamber and the NMR probe. As previously demonstrated, this system allows repeated SABRE experi- ments with a reproducibility within 2–5 %,[19] sufficient for incorporating SABRE hyperpolarization into traditional 2D NMR pulse schemes. Nevertheless, performing DOSY under stopped-flow conditions is a challenge, as convection generated by flow displacement and by associated temperature gradients can overshadow the thermal diffusion. Managing this convection is paramount, since convective effects on gradient-encoded NMR experiments cause anomalies in signal amplitude and phase.[20] Herein, the issue was mitigated by a careful optimization of experimental parameters, such as matched temperatures of sample with that of the NMR probe and judicious insertion of 5s stabilization delays to dampen the remaining convection (see Experimental Section). Under these conditions, we were able to record well- resolved DOSY spectra of a mixture of analytes 1–6 in the concentration range of 5–25 mm in 35 min (Figure 2, left panel). SABRE provides 98- to 232-fold signal enhancements for these analytes after the 5s delay, enabling DOSY at concentrations two orders of magnitude lower than would be feasible from thermal NMR signals in a similar time frame. To achieve the same SNR by signal averaging thermal signals,