A Cu-2(II) Paramagnetic Chemical Exchange Saturation Transfer Contrast Agent Enabled by Magnetic Exchange Coupling

作者：Du Kang; Harris T David^*

来源：Journal of the American Chemical Society, 2016, 138(25): 7804-7807.

DOI：10.1021/jacs.6b03060

The ability of magnetic exchange coupling to enable observation of paramagnetic chemical exchange saturation transfer (PARACEST) in transition metal ions with long electronic relaxation times (tau(s)) is demonstrated. Metalation of the dinucleating, tetra(carboxamide) ligand HL with Cu2+ in the presence of pyrophosphate (P2O7)(4-) affords the complex [LCu2II(P2O7)](-). Solution-phase variable-temperature magnetic susceptibility data reveal weak ferromagnetic superexchange coupling between the two S = 1/2 Cu-II centers, with a coupling constant of tau(s). +2.69(5) cm(-1), to give an S = 1 ground state. This coupling results in a sharpened NMR line width relative to a GaCu analogue, indicative of a shortening of Ts. Presaturation of the amide protons in the Cu-2 complex at 37 degrees C leads to a 14% intensity decrease in the bulk water H-1 NMR signal through the CEST effect. Conversely, no CEST effect is observed in the GaCu complex. These results provide the first example of a Cu based PARACEST magnetic resonance contrast agent and demonstrate the potential to expand the metal ion toolbox for PARACEST agents through introduction of magnetic exchange coupling.

• 出版日期2016-6-29
• 单位西北大学