Pulsed Magnetic Resonance to Signal‐Enhance Metabolites within Seconds by utilizing para‐Hydrogen

Abstract

Diseases such as Alzheimer's and cancer have been linked to metabolic dysfunctions, and further understanding of metabolic pathways raises hope to develop cures for such diseases. To broaden the knowledge of metabolisms in vitro and in vivo, methods are desirable for direct probing of metabolic function. Here, we are introducing a pulsed nuclear magnetic resonance (NMR) approach to generate hyperpolarized metabolites within seconds, which act as metabolism probes. Hyperpolarization represents a magnetic resonance technique to enhance signals by over 10 000‐fold. We accomplished an efficient metabolite hyperpolarization by developing an isotopic labeling strategy for generating precursors containing a favorable nuclear spin system to add para‐hydrogen and convert its two‐spin longitudinal order into enhanced metabolite signals. The transfer is performed by an invented NMR experiment and 20 000‐fold signal enhancements are achieved. Our technique provides a fast way of generating hyperpolarized metabolites by using para‐hydrogen directly in a high magnetic field without the need for field cycling.

Over 50 % 1H and 13C Polarization for Generating Hyperpolarized Metabolites—A para‐Hydrogen Approach

“…The second 90 − x pulse brings the spin density operator into I 1 x I 2 z , which is then refocused into I 1 y /2 by homonuclear J evolution during the second block. For 13 C polarization experiments (right path of Figure ), once that para ‐hydrogen is added and ethyl acetate has formed, the couplings and chemical shift difference are ideal for utilizing the recently introduced ESOTHERIC (efficient spin order transfer to heteronuclei via relayed inept chains) sequence to transfer ρ 0 = I 1 z I 2 z /2 into heteronuclear in‐phase magnetization S 3 y /4, with a theoretical efficiency close to 95 % …”

“…PASADENA‐type experiments were performed, in which the para ‐enriched hydrogen gas was bubbled for 10 s to a solution of perdeuterated vinyl acetate in [D 4 ]MeOH at 320 K in the presence of a homogeneous rhodium catalyst in high field (here: B 0 =7 T). After hydrogenation in high field, a 45° pulse is typically used to detect a PASADENA spectrum (Figure a) that displays only half of the nascent 1 H polarization, as previously discussed . Here, sequence 1 was utilized to convert in full the 1 H longitudinal two‐spin order into in‐phase magnetization on the methylene proton of ethyl acetate‐d 6 , Figure b.…”

“…[1][2][3][4][5][6] Hyperpolarization techniques include dynamic nuclear polarization (DNP), [1][2][3][4][5][6][7][8][9] spin exchange optical pumping (SEOP), [10][11][12][13] and para-hydrogen-based methods such as signal amplification by reversible exchange (SABRE) [14][15][16][17][18][19][20][21][22][23] and para-hydrogen-induced polarization (PHIP). [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] Notably,t he former technique (SABRE) represents an on-hydrogenative form of PHIP.O ne emerging application of hyperpolarized NMR is the direct observation of metabolism in vitro and in vivo. [1]…”

“…The second 90 Àx pulse brings the spin density operator into I 1x I 2z ,w hich is then refocused into I 1y /2 by homonuclear J evolution duringt he second block.F or 13 Cp olarization experiments (right path of Figure 1), once that para-hydrogen is added and ethyl acetate has formed, the couplings and chemical shift difference are ideal for utilizing the recently introduced ESOTHERIC (efficient spin order transfer to heteronucleiv ia relayed inept chains) sequencetotransfer 1 0 = I 1z I 2z /2 into heteronuclear in-phase magnetization S 3y /4, with at heoretical efficiency close to 95 %. [39] Samples were prepared from [D 4 ]MeOH solutions, containing 0.9 mm of vinyl acetate, 2mm of commercially availabler hodium catalyst, [1,4-Bis(diphenylphosphino)butane](1,5-cyclooctadiene) rhodium(I) tetrafluoroborate, and 9mm toluene-13 C a enriched (> 99 %) as internal reference for determining 13 Cp olarization levels. The precursor concentration was chosen so to avoid radiation damping effects after hyperpolarization and to perform quantitative experiments.…”

“…discussed. [39] Here, sequence 1 was utilized to convert in full the 1 Hl ongitudinal two-spin order into in-phase magnetization on the methylene protono fe thyl acetate-d 6 ,F igure 2b.C omparisonw ith the thermally polarized protons pectrum of the same sample (Figure 2c)g ives an average observable polarization P( 1 H) = 54.9 AE 3.2 %. Application of the ESOTHERIC sequenced irectly after hydrogenation leads to the 13 Cs pectrum of hyperpolarized carbonyl carbon in ethyl acetate presented in Figure 2d.C onsidering that the observed 13 Cs ignal originates from natural abundant 13 C, whichi s1 .08 %o fa ll the carbon nuclei of the sample, we estimate ap olarization P( 13 C) = 59.1 AE1.4 %.…”