2D Mapping of NMR Signal Enhancement and Relaxation for Heterogeneously Hyperpolarized Propane Gas

Abstract

Hyperpolarized (HP) propane is a promising contrast agent for magnetic resonance imaging (MRI) of lungs and for studying porous media. The parahydrogen-induced polarization (PHIP) technique is a convenient approach to produce pure propane gas with enhanced proton polarization, when hydrogenation of propylene with parahydrogen is performed over heterogeneous catalysts. Here, we present a new approach of multidimensional mapping of the efficiency of pairwise parahydrogen addition using PHIP-echo pulse sequence. We use this approach to study the performance of three model heterogeneous Rh/TiO 2 catalysts in the production of HP propane gas. The three catalysts with 1.0, 13.7, and 23.2 wt % of supported rhodium nanoparticles have been characterized by X-ray photoelectron spectroscopy (XPS) and high resolution transition electron microscopy (HRTEM). By varying the fractions of parahydrogen and propylene in the reactant mixture as well as the gas mixture pressure, 2D maps of PHIP-echo NMR signal and 2D maps of HP propane NMR signal enhancement were obtained. These maps clearly indicate that lower metal coverage results in more efficient pairwise hydrogen addition, producing greater levels of proton polarization of propane gas. The presented method can be extended to multidimensional characterization of the influence of other key parameters of PHIP reaction process including temperature or addition of an inert carrier gas. A 2D T 1 relaxation map of propane at 9.4 T is also reported as a function of propane fraction (in the mixture with hydrogen) and gas mixture pressure.

Ultrafast Single‐Scan 2D NMR Spectroscopic Detection of a PHIP‐Hyperpolarized Protease Inhibitor

“…To that end, it was necessary to convert the antiphase lines of the multiplet polarization into a net polarization.A ss hown previously,t his can be achieved either by an adiabatic-passage spin order conversion (APSOC), [24] by spin-lock inducedc rossing (SLIC) [13,25] or by applying as o-called "out-of-phase echo". [23,26] However,i nt he case of the five-spin system, formedb yt he allyl-tyrosine fragment, the latter methodw as found to be more efficient (Figures S2 and S10, Supporting Information). The resulting 1D spectrum( Figure 1D)c learly shows the efficient conversion of the antiphase lines of the PHIP signals (H 2 and H 3 )t oe nhanced in-phases ignals using the out-of-phase echo method.…”

Heterogeneous Parahydrogen Pairwise Addition to Cyclopropane

“…It should also be noted that significant % P H fraction in our experiments is lost due to relaxation effects. Optimization of experimental setup may allow to reach significantly higher HP propane polarization and improved chemical conversion . The formation of magnetically equivalent HP methyl protons in a pseudo singlet state likely formed via routes #2–3 is intriguing, because the produced HP states may have ultra‐long life time – subject of our ongoing studies.…”

Hyperpolarized NMR Spectroscopy: d‐DNP, PHIP, and SABRE Techniques

“…Another promising approach for increasing the lifetime of hyperpolarized propane is the use of higher pressures. For example, at 7.6 atm, the relaxation time of hyperpolarized propane is about 4.5 s at 9.4 T and about 13 s at 0.05 T …”

“…Another promising approach for increasing the lifetime of hyperpolarized propanei st he use of higher pressures. For example, at7 .6 atm, the relaxation time of hyperpolarized propanei s about 4.5 sa t9 .4 T [172] and about 13 sa t0 .05 T. [173] One interesting approachi st he production of hyperpolarized propene from propyne, which would require the use of a selectivec atalyst. One such suitable catalyst is the PdÀIn/Al 2 O 3 single-site catalyst.…”

“…Another promising approach for increasing hyperpolarized propane lifetime is the use of higher pressures. For example, at 7.6 atm hyperpolarized propane relaxation time is ~4.5 s at 9.4 T [172] and ~13 s at 0.05 T. [173]…”