Batch-Mode Clinical-Scale Optical Hyperpolarization of Xenon-129 Using an Aluminum Jacket with Rapid Temperature Ramping

We present spin-exchange optical pumping (SEOP) using a third-generation (GEN-3) automated batch-mode clinical-scale 129Xe hyperpolarizer utilizing continuous high-power (∼170 W) pump laser irradiation and a novel aluminum jacket design for rapid temperature ramping of xenon-rich gas mixtures (up to 2 atm partial pressure). The aluminum jacket design is capable of heating SEOP cells from ambient temperature (typically 25 °C) to 70 °C (temperature of the SEOP process) in 4 min, and perform cooling of the cell to the temperature at which the hyperpolarized gas mixture can be released from the hyperpolarizer (with negligible amounts of Rb metal leaving the cell) in approximately 4 min, substantially faster (by a factor of 6) than previous hyperpolarizer designs relying on air heat exchange. These reductions in temperature cycling time will likely be highly advantageous for the overall increase of production rates of batch-mode (i.e., stopped-flow) 129Xe hyperpolarizers, which is particularly beneficial for clinical applications. The additional advantage of the presented design is significantly improved thermal management of the SEOP cell. Accompanying the heating jacket design and performance, we also evaluate the repeatability of SEOP experiments conducted using this new architecture, and present typically achievable hyperpolarization levels exceeding 40% at exponential build-up rates on the order of 0.1 min–1

Hyperpolarizing DNA Nucleobases via NMR Signal Amplification by Reversible Exchange

The present work investigates the potential for enhancing the NMR signals of DNA nucleobases by parahydrogen-based hyperpolarization. Signal amplification by reversible exchange (SABRE) and SABRE in Shield Enables Alignment Transfer to Heteronuclei (SABRE-SHEATH) of selected DNA nucleobases is demonstrated with the enhancement (ε) of 1H, 15N, and/or 13C spins in 3-methyladenine, cytosine, and 6-O-guanine. Solutions of the standard SABRE homogenous catalyst Ir(1,5-cyclooctadeine)(1,3-bis(2,4,6-trimethylphenyl)imidazolium)Cl (“IrIMes”) and a given nucleobase in deuterated ethanol/water solutions yielded low 1H ε values (≤10), likely reflecting weak catalyst binding. However, we achieved natural-abundance enhancement of 15N signals for 3-methyladenine of ~3300 and ~1900 for the imidazole ring nitrogen atoms. 1H and 15N 3-methyladenine studies revealed that methylation of adenine affords preferential binding of the imidazole ring over the pyrimidine ring. Interestingly, signal enhancements (ε~240) of both 15N atoms for doubly labelled cytosine reveal the preferential binding of specific tautomer(s), thus giving insight into the matching of polarization-transfer and tautomerization time scales. 13C enhancements of up to nearly 50-fold were also obtained for this cytosine isotopomer. These efforts may enable the future investigation of processes underlying cellular function and/or dysfunction, including how DNA nucleobase tautomerization influences mismatching in base-pairing

Aqueous, Heterogeneous <i>para</i>-Hydrogen-Induced ¹⁵N Polarization

The successful transfer of <i>para</i>-hydrogen-induced polarization to ¹⁵N spins using heterogeneous catalysts in aqueous solutions was demonstrated. Hydrogenation of a synthesized unsaturated ¹⁵N-labeled precursor (neurine) with <i>para</i>hydrogen (<i>p</i>-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 ¹⁵<i>N</i>-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 <i>T</i>₁ of ∼6 min for the product molecules, and the <i>T</i>₁ 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