Department of Chemistry, University at Buffalo, the State University of New York, Amherst, New York 14260, United States.
Department of Biological Sciences, University at Buffalo, the State University of New York, Amherst, New York 14260, United States.
Inorg Chem. 2020 Nov 16;59(22):16531-16544. doi: 10.1021/acs.inorgchem.0c02470. Epub 2020 Nov 2.
Four high-spin macrocyclic Co(II) complexes with hydroxypropyl or amide pendants and appended coumarin or carbostyril fluorophores were prepared as CEST (chemical exchange saturation transfer) MRI probes. The complexes were studied in solution as paramagnetic CEST (paraCEST) agents and after loading into yeast cells as cell-based CEST (cellCEST) agents. The fluorophores attached to the complexes through an amide linkage imparted an unusual pH dependence to the paraCEST properties of all four complexes through of ionization of a group that was attributed to the amide NH linker. The furthest shifted CEST peak for the hydroxypropyl-based complexes changed by ∼90 ppm upon increasing the pH from 5 to 7.5. At acidic pH, the Co(II) complexes exhibited three to four CEST peaks with the most highly shifted CEST peak at 200 ppm. The complexes demonstrated substantial paramagnetic water proton shifts which is a requirement for the development of cellCEST agents. The large shift in the proton resonance was attributed to an inner-sphere water at neutral pH, as shown by variable temperature O NMR spectroscopy studies. Labeling of yeast with one of these paraCEST agents was optimized with fluorescence microscopy and validated by using ICP mass spectrometry quantitation of cobalt. A weak asymmetry in the Z-spectra was observed in the yeast labeled with a Co(II) complex, toward a cellCEST effect, although the Co(II) complexes were toxic to the cells at the concentrations necessary for observation of cellCEST.
四种具有羟丙基或酰胺侧基的高自旋大环 Co(II) 配合物，以及连接香豆素或咔唑荧光团的配合物，被制备为 CEST（化学交换饱和转移）MRI 探针。这些配合物在溶液中作为顺磁 CEST（paraCEST）试剂进行研究，并在负载到酵母细胞中后作为基于细胞的 CEST（cellCEST）试剂进行研究。通过酰胺键连接到配合物上的荧光团通过一个基团的离解赋予了所有四个配合物的 paraCEST 特性不寻常的 pH 依赖性，该基团归因于酰胺 NH 连接体。基于羟丙基的配合物的最远移位 CEST 峰在 pH 从 5 增加到 7.5 时变化了约 90 ppm。在酸性 pH 下，Co(II) 配合物表现出三个到四个 CEST 峰，其中最显著移位的 CEST 峰在 200 ppm 处。这些配合物表现出显著的顺磁质子位移，这是开发 cellCEST 试剂的要求。质子共振的大位移归因于中性 pH 下的内球水，如变温 O NMR 光谱研究所示。使用荧光显微镜优化了一种 paraCEST 试剂对酵母的标记，并通过使用 ICP 质谱定量钴对其进行了验证。在用 Co(II) 配合物标记的酵母中观察到 Z 谱的弱不对称性，朝向 cellCEST 效应，尽管 Co(II) 配合物在观察 cellCEST 所需的浓度下对细胞有毒。
