Surface-Mediated Hyperpolarization of Liquid Water from Parahydrogen Evan Wenbo Zhao, Raghu Maligal-Ganesh, Yong Du, Tommy Yunpu Zhao, James Collins, Tao Ma, Lin Zhou, Tian-Wei Goh, Wenyu Huang, Clifford R. Bowers  Chem  Volume 4, Issue 6, Pages 1387-1403 (June 2018) DOI: 10.1016/j.chempr.2018.03.004 Copyright © 2018 Elsevier Inc. Terms and Conditions

Chem 2018 4, 1387-1403DOI: (10.1016/j.chempr.2018.03.004) Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 1 Catalyst Surface Structures (A) Bright-field TEM image of Pt3Sn@mSiO2 iNPs. (B) High-resolution HAADF-STEM image of a Pt3Sn iNP taken along the <111> zone axis. The brighter dots correspond to Pt atomic columns, and the darker sites correspond to Sn atomic columns, as shown in the inset (size 2 × 2 nm). (C and D) Structural models of (C) Pt(111) and (D) Pt3Sn(111) surfaces (gray atoms represent Pt). Red triangles identify three-fold Pt hollow sites. Chem 2018 4, 1387-1403DOI: (10.1016/j.chempr.2018.03.004) Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 2 Proton NMR Spectra of Hyperpolarized and Thermally Polarized Water, Methanol, and Ethanol The 9.4 T (400 MHz) liquid-state 1H NMR spectra acquired about 10 s after 7 bar p-H2 (upper spectra) or n-H2 (lower spectra) was bubbled for 20 s at a flow rate of 350 mL/min through a suspension containing 50 mg Pt3Sn@mSiO2 and (A) water-d2 (D2O) at 120°C, (B) methanol-d4 (CD3OD) at 105°C, and (C) ethanol-d6 (CD3CD2OD) at 105°C. Proton signals of the non-exchangeable methyl and methylene groups arose only from proton isotopic impurities in the per-deuterated neat liquids. In (C), the asterisk (*) indicates a methanol impurity. Chem 2018 4, 1387-1403DOI: (10.1016/j.chempr.2018.03.004) Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 3 Effect of the Amount of Bubbling of H2 through Suspensions of 50 mg Pt3Sn@mSiO2 in Methanol-d4, Initially with 99.8% Deuterium Isotopic Purity (A) Fully relaxed, thermally polarized 400 MHz 1H NMR spectra acquired after 0–5 H2 bubbling cycles. Four free induction decays were averaged with a 120 s recycle delay. (B) Proton isotopic fraction (initially 0.2%, per manufacturer's specification), deduced from the hydroxy and methyl peak integrals in (A), plotted as a function of the number of bubbling cycles. (C) 1H NMR spectra acquired at 9.4 T immediately after 1–5 p-H2 bubbling cycles. (D) 1H SWAMP signal intensity as a function of the number of p-H2 bubbling cycles. Chem 2018 4, 1387-1403DOI: (10.1016/j.chempr.2018.03.004) Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 4 Conventional, Fully Relaxed, 9.4 T Boltzmann-Polarized 1H NMR Spectra Exhibiting H-D Exchange in Suspensions Containing Pt3Sn@mSiO2 at 105°C (A) Methanol-d4 before and after a single H2 bubbling cycle shows a 30% increase in the –OH peak. (B) Ethanol-d6 spectra before (bottom) and after (top) five H2 bubbling cycles show a 415% increase in the –OH peak. H2 bubbling caused an increase in only the –OH hydrogen signal and not the non-exchangeable methyl or methylene proton in ethanol impurity peaks. The asterisk indicates a methanol impurity. Chem 2018 4, 1387-1403DOI: (10.1016/j.chempr.2018.03.004) Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 5 Mechanistic Models for Hyperpolarization of HDO from p-H2 (A) OneH, where spin polarization transfer occurs via single H/D exchange between co-adsorbed p-H2 and D2O. (B) Spin-polarized nuclear Overhauser effect (SWAMP-OE) via unequal dipolar couplings. The magnetic equivalence of p-H2 is broken by dissociation and chemisorption into strongly coupled, magnetically inequivalent adsorption sites (a and b) with dipolar coupling Dab and chemical shift difference Δab. Dam and Dbm are the dipolar couplings to the –OH proton. (C) Coherence transfer via level anti-crossing (LAC) due to the inequivalent dipolar couplings between the strongly coupled H ad-atom pair in chemically equivalent sites (a and a′) and the HDO proton (m). Here, the m protons on the HDO molecules are assumed to be initially unpolarized, as indicated by the absence of a spin vector on the H atom. Spin exchange by LAC is productive only for the m protons initially in the spin-up state, such that total spin angular momentum is conserved. Cross-correlation (CC) relaxation is an incoherent process that does not require chemically inequivalent adsorption sites for the H ad-atom pair. Chem 2018 4, 1387-1403DOI: (10.1016/j.chempr.2018.03.004) Copyright © 2018 Elsevier Inc. Terms and Conditions

Figure 6 Thermally Polarized and SWAMP Hyperpolarized MRI of a Water/Methanol Phantom 1H images of a medium-wall NMR tube (10 mm outer diameter) containing a mixture of 900 μL of D2O, 900 μL of CD3OD, and 100 mg Pt3Sn@mSiO2 iNPs recorded at 750 MHz with the SPIRAL-EPI pulse sequence. (A) Thermally polarized image. (B) SWAMP-hyperpolarized image. Orange, absorption; blue, emission (negative phase). Chem 2018 4, 1387-1403DOI: (10.1016/j.chempr.2018.03.004) Copyright © 2018 Elsevier Inc. Terms and Conditions

Scheme 1 Hypothetical Production of p-H2O by PRC and Hyperpolarized HDO via H/D Exchange (A) or Spin Exchange (B) with p-H2 Chem 2018 4, 1387-1403DOI: (10.1016/j.chempr.2018.03.004) Copyright © 2018 Elsevier Inc. Terms and Conditions