Search

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 1 H, 15 N, and/or 13 C 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 1 H ε values (≤10), likely reflecting weak catalyst binding. However, we achieved natural-abundance enhancement of 15 N signals for 3-methyladenine of ~3300 and ~1900 for the imidazole ring nitrogen atoms. 1 H and 15 N 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 15 N 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. 13 C 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.

We present a second-generation open-source automated batch-mode 129 Xe hyperpolarizer (XeUS GEN-2), designed for clinical-scale hyperpolarized (HP) 129 Xe production via spin-exchange optical pumping (SEOP) in the regimes of high Xe density (0.66-2.5 atm partial pressure) and resonant photon flux (~170 W, Δλ = 0.154 nm FWHM), without the need for cryo-collection typically employed by continuous-flow hyperpolarizers. An Arduino micro-controller was used for hyperpolarizer operation. Processing open-source software was employed to program a custom graphical user interface (GUI), capable of remote automation. The Arduino Integrated Development Environment (IDE) was used to design a variety of customized automation sequences such as temperature ramping, NMR signal acquisition, and SEOP cell refilling for increased reliability. A polycarbonate 3D-printed oven equipped with a thermo-electric cooler/heater provides thermal stability for SEOP for both binary (Xe/N 2 ) and ternary ( 4 He-containing) SEOP cell gas mixtures. Quantitative studies of the 129 Xe hyperpolarization process demonstrate that near-unity polarization can be achieved in a 0.5 L SEOP cell. For example, %P Xe of 93.2 ± 2.9% is achieved at 0.66 atm Xe pressure with polarization build-up rate constant γ SEOP  = 0.040 ± 0.005 min -1 , giving a max dose equivalent ≈ 0.11 L/h 100% hyperpolarized, 100% enriched 129 Xe; %P Xe of 72.6 ± 1.4% is achieved at 1.75 atm Xe pressure with γ SEOP of 0.041 ± 0.001 min -1 , yielding a corresponding max dose equivalent of 0.27 L/h. Quality assurance studies on this device have demonstrated the potential to refill SEOP cells hundreds of times without significant losses in performance, with average %P Xe  = 71.7%, (standard deviation σ P  = 1.52%) and mean polarization lifetime T 1  = 90.5 min, (standard deviation σ T  = 10.3 min) over the first ~200 gas mixture refills, with sufficient performance maintained across a further ~700 refills. These findings highlight numerous technological developments and have significant translational relevance for efficient production of gaseous HP 129 Xe contrast agents for use in clinical imaging and bio-sensing techniques., Competing Interests: Declaration of Competing Interest Panayiotis Nikolaou, Boyd M. Goodson, and Eduard Y. Chekmenev declare a stake of ownership in XeUS Technologies, LTD., (Copyright © 2020 Elsevier Inc. All rights reserved.)

We present spin-exchange optical pumping (SEOP) using a third-generation (GEN-3) automated batch-mode clinical-scale 129 Xe 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) 129 Xe 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 .

The Signal Amplification by Reversible Exchange (SABRE) technique employs exchange with singlet-state parahydrogen to efficiently generate high levels of nuclear spin polarization. Spontaneous SABRE has been shown previously to be efficient in the milli-Tesla and micro-Tesla regimes. We have recently demonstrated that high-field SABRE is also possible, where proton sites of molecules that are able to reversibly coordinate to a metal center can be hyperpolarized directly within high-field magnets, potentially offering the convenience of in situ hyperpolarization-based spectroscopy and imaging without sample shuttling. Here, we show efficient polarization transfer from parahydrogen ( para -H 2 ) to the 15 N atoms of imidazole- 15 N 2 and nicotinamide- 15 N achieved via high-field SABRE (HF-SABRE). Spontaneous transfer of spin order from the para -H 2 protons to 15 N atoms at the high magnetic field of an MRI scanner allows one not only to record enhanced 15 N NMR spectra of in situ hyperpolarized biomolecules, but also to perform imaging using conventional MRI sequences. 2D 15 N MRI of high-field SABRE-hyperpolarized imidazole with spatial resolution of 0.3×0.3 mm 2 at 9.4 T magnetic field and a high signal-to-noise ratio (SNR) of ~99 was demonstrated. We show that 1 H MRI of in situ HF-SABRE hyperpolarized biomolecules ( e.g . imidazole- 15 N 2 ) is also feasible. Taken together, these results show that heteronuclear ( 15 N) and 1 H spectroscopic detection and imaging of high-field-SABRE-hyperpolarized molecules are promising tools for a number of emerging applications.

The successful transfer of parahydrogen-induced polarization to 15 N spins using heterogeneous catalysts in aqueous solutions was demonstrated. Hydrogenation of a synthesized unsaturated 15 N-labeled precursor (neurine) with parahydrogen (p-H 2 ) over Rh/TiO 2 heterogeneous catalysts yielded a hyperpolarized structural analog of choline. As a result, 15 N polarization enhancements of over two orders of magnitude were achieved for the 15 N-ethyl trimethyl ammonium ion product in deuterated water at elevated temperatures. Enhanced 15 N NMR spectra were successfully acquired at 9.4 T and 0.05 T. Importantly, long hyperpolarization lifetimes were observed at 9.4 T, with a 15 N T 1 of ~6 min for the product molecules, and the T 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., Competing Interests: Notes The authors declare no competing financial interests.