Department of Chemistry and Biochemistry, Southern Illinois University, Carbondale, IL, 62901, USA.
Department of Biomedical Engineering, University of Virginia, Charlottesville, VA, USA.
Angew Chem Int Ed Engl. 2020 Jan 2;59(1):418-423. doi: 10.1002/anie.201910506. Epub 2019 Nov 14.
Herein, we demonstrate "direct" C hyperpolarization of C-acetate via signal amplification by reversible exchange (SABRE). The standard SABRE homogeneous catalyst [Ir-IMes; [IrCl(COD)(IMes)], (IMes=1,3-bis(2,4,6-trimethylphenyl), imidazole-2-ylidene; COD=cyclooctadiene)] was first activated in the presence of an auxiliary substrate (pyridine) in alcohol. Following addition of sodium 1- C-acetate, parahydrogen bubbling within a microtesla magnetic field (i.e. under conditions of SABRE in shield enables alignment transfer to heteronuclei, SABRE-SHEATH) resulted in positive enhancements of up to ≈100-fold in the C NMR signal compared to thermal equilibrium at 9.4 T. The present results are consistent with a mechanism of "direct" transfer of spin order from parahydrogen to C spins of acetate weakly bound to the catalyst, under conditions of fast exchange with respect to the C acetate resonance, but we find that relaxation dynamics at microtesla fields alter the optimal matching from the traditional SABRE-SHEATH picture. Further development of this approach could lead to new ways to rapidly, cheaply, and simply hyperpolarize a broad range of substrates (e.g. metabolites with carboxyl groups) for various applications, including biomedical NMR and MRI of cellular and in vivo metabolism.
在此，我们通过可逆交换信号放大（SABRE）演示了 C-乙酸盐的“直接” C 极化。标准的 SABRE 均相催化剂 [Ir-IMes；[IrCl(COD)(IMes)]，（IMes=1,3-双（2,4,6-三甲基苯基），咪唑-2-基）；COD=环辛二烯]）首先在辅助底物（吡啶）存在下在醇中被激活。在添加了 1- C-乙酸钠后，在微特斯拉磁场中进行氘气鼓泡（即在屏蔽的 SABRE 条件下使异核核的对准转移成为可能，SABRE-SHEATH），与在 9.4T 下的热平衡相比，导致 C NMR 信号的增强高达≈100 倍。目前的结果与自旋顺序从氘气到与催化剂弱结合的乙酸盐的 C 自旋的“直接”转移机制一致，在与乙酸盐共振快速交换的条件下，但我们发现微特斯拉场中的弛豫动力学改变了从传统的 SABRE-SHEATH 图像的最佳匹配。这种方法的进一步发展可能会为快速、廉价且简单地极化广泛的底物（例如带有羧基的代谢物）开辟新途径，用于各种应用，包括生物医学 NMR 和细胞内和体内代谢的 MRI。
