Spontaneous ¹⁵N nuclear spin hyperpolarization in metal-free activation of parahydrogen by molecular tweezers
Sorochkina, Kristina; Zhivonitko, Vladimir V.; Chernichenko, Konstantin; Telkki, Ville-Veikko; Repo, Timo; Koptyug, Igor V. (2018-02-05)
Kristina Sorochkina, Vladimir V. Zhivonitko, Konstantin Chernichenko, Ville-Veikko Telkki, Timo Repo, and Igor V. Koptyug. Spontaneous 15N Nuclear Spin Hyperpolarization in Metal-Free Activation of Parahydrogen by Molecular Tweezers. The Journal of Physical Chemistry Letters 2018 9 (4), 903-907 DOI: 10.1021/acs.jpclett.7b03433.
© 2018 American Chemical Society. ACS AuthorChoice - This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. https://pubs.acs.org/page/policy/authorchoice_termsofuse.html
The ability of frustrated Lewis pairs (FLPs) to activate H₂ is of significant interest for metal-free catalysis. The activation of H₂ is also the key element of parahydrogen-induced polarization (PHIP), one of the nuclear spin hyperpolarization techniques. It is demonstrated that o-phenylene-based ansa-aminoboranes (AABs) can produce ¹H nuclear spin hyperpolarization through a reversible interaction with parahydrogen at ambient temperatures. Heteronuclei are useful in NMR and MRI as well because they have a broad chemical shift range and long relaxation times and may act as background-free labels. We report spontaneous formation of ¹⁵N hyperpolarization of the N−H site for a family of AABs. The process is efficient at the high magnetic field of an NMR magnet (7 T), and it provides up to 350-fold ¹⁵N signal enhancements. Different hyperpolarization effects are observed with various AAB structures and in a broad temperature range. Spontaneous hyperpolarization, albeit an order of magnitude weaker than that for ¹⁵N, was also observed for ¹¹B nuclei.
- Avoin saatavuus