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Aqueous, Heterogeneous para-Hydrogen-Induced 15N Polarization

Bales, Liana B., Kovtunov, Kirill V., Barskiy, Danila A., Shchepin, Roman V., Coffey, Aaron M., Kovtunova, Larisa M., Bukhtiyarov, Andrey V., Feldman, Matthew A., Bukhtiyarov, Valerii I., Chekmenev, Eduard Y., Koptyug, Igor V., Goodson, Boyd M.
The Journal of Physical Chemistry C 2017 v.121 no.28 pp. 15304-15309
aqueous solutions, catalysts, choline, hydrogenation, nitrogen, nuclear magnetic resonance spectroscopy, physical chemistry, stable isotopes, temperature
The successful transfer of para-hydrogen-induced polarization to ¹⁵N spins using heterogeneous catalysts in aqueous solutions was demonstrated. Hydrogenation of a synthesized unsaturated ¹⁵N-labeled precursor (neurine) with parahydrogen (p-H₂) over Rh/TiO₂ heterogeneous catalysts yielded a hyperpolarized structural analogue of choline. As a result, ¹⁵N polarization enhancements of over 2 orders of magnitude were achieved for the ¹⁵N-labeled ethyltrimethylammonium ion product in deuterated water at elevated temperatures. Enhanced ¹⁵N NMR spectra were successfully acquired at 9.4 and 0.05 T. Importantly, long hyperpolarization lifetimes were observed at 9.4 T, with a ¹⁵N T₁ of ∼6 min for the product molecules, and the T₁ of the deuterated form exceeded 8 min. Taken together, these results show that this approach for generating hyperpolarized species with extended lifetimes in aqueous, biologically compatible solutions is promising for various biomedical applications.