Paramagnetic Organocobalt Capsule Revealing Xenon Host-Guest Chemistry.
Paramagnetic Organocobalt Capsule Revealing Xenon Host-Guest Chemistry.
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DOI：
10.1021/acs.inorgchem.9b03634
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发表时间：
2020-10-05
影响因子：
4.6
通讯作者：
Dmochowski IJ
中科院分区：
文献类型：
--
作者：
Du K;Zemerov SD;Hurtado Parra S;Kikkawa JM;Dmochowski IJ
我们研究了以前报道的顺磁性金属-有机四面体胶囊[Co4L6]4 4，4‘-bis[(2-pyridinylmethylene)amino]-[1，1’-biphenyl]-2，2‘-disulfonate.中Xe的结合，其中L2−=−核磁共振氢谱表明，在饱和Xe气体的水溶液中，Xe包合物[XeCo4L6]4−是主要物种。在[XeCo4L6]4−(4.4(5)×10~2 S−1)中测得的Xe解离速率至少是类似的[XeFe4L6]4−中的40倍，突出了金属-配体相互作用对胶囊大小和客体渗透性的调节能力。129Xe在[XeCo4L6]4−中的快速交换在298K产生了显著的超极化129Xe化学交换饱和转移核磁共振信号，在低至100 pm的[XeCo4L6]4−浓度下检测到，预饱和温度为−ppm，参照129Xe在H2O中的溶剂化。饱和偏移量与温度高度相关，斜率为−0.41(3)ppm/K，这归因于包裹的129Xe核和四个CoII中心上的电子自旋之间的超精细相互作用。因此，[XeCo4L6]4−代表了顺磁超CEST(ParHYPERCEST)传感器的第一个例子。值得注意的是，[XeCo4L6]4−(δ=−的高CEST129Xe核磁共振共振峰从抗磁类似物[XeFe4L6]4−(δ=+16ppm前移了105ppm。Xe包合物的晶体结构为(C(NH2)3)4[Xe0.7Co4L6]·75H2O(1)。(C(NH_2)_3)~+与胶囊-连接基磺酸盐基团之间的氢键稳定了胶囊-胶囊之间的固态相互作用，并有助于将Xe原子(~42ä3)捕获到1的大空腔中。磁化率测量证实，在1中存在四个不相互作用的、各向异性的高自旋CoII中心。此外，[Co4L6]4−对聚集和氧化稳定，[Co4L6]4−的CEST性能不受水中生物大分子的影响。这些结果推荐金属有机胶囊用于Xe主客体化学的基础研究以及高灵敏度的基于129Xe的传感器的应用。一个结晶学表征的顺磁笼子[Co4L6]4−可逆地结合了溶解的超极化的129Xe在H2O中，具有良好的化学交换动力学。在选择性射频饱和后，去极化的129Xe的交换提供了与块体的对比，使得PM能够在H2O中检测到[XeCo4L6]4−。顺磁位移的129Xe共振也是高度温度敏感的。因此，[Co4L6]4−是一种很有前途的129Xe磁共振生物传感器/温度计。
We investigated Xe binding in a previously reported paramagnetic metal-organic tetrahedral capsule, [Co4L6]4−, where L2− = 4,4'-bis[(2-pyridinylmethylene)amino]-[1,1'-biphenyl]-2,2'-disulfonate. The Xe-inclusion complex, [XeCo4L6]4−, was confirmed by 1H NMR spectroscopy to be the dominant species in aqueous solution saturated with Xe gas. The measured Xe dissociation rate in [XeCo4L6]4− (4.4(5) × 102 s−1) was at least forty times greater than in the analogous [XeFe4L6]4− complex, highlighting the capability of metal-ligand interactions to tune capsule size and guest permeability. The rapid exchange of 129Xe nuclei in [XeCo4L6]4− produced significant hyperpolarized 129Xe chemical exchange saturation transfer (hyper-CEST) NMR signal at 298 K, detected at a concentration of [XeCo4L6]4− as low as 100 pM, with presaturation at −89 ppm, which was referenced to solvated 129Xe in H2O. The saturation offset was highly temperature-dependent with a slope of −0.41(3) ppm/K, which is attributed to hyperfine interactions between the encapsulated 129Xe nucleus and electron spins on the four CoII centers. As such, [XeCo4L6]4− represents the first example of a paramagnetic hyper-CEST (paraHYPERCEST) sensor. Remarkably, the hyper-CEST 129Xe NMR resonance for [XeCo4L6]4− (δ = −89 ppm) was shifted 105 ppm upfield from the diamagnetic analog [XeFe4L6]4− (δ = +16 ppm). The Xe inclusion complex was further characterized in the crystal structure of (C(NH2)3)4[Xe0.7Co4L6]·75 H2O (1). Hydrogen bonding between capsule-linker sulfonate groups and exogenous guanidinium cations, (C(NH2)3)+, stabilized capsule-capsule interactions in the solid-state, and also assisted in trapping a Xe atom (~42 Å3) in the large (135 Å3) cavity of 1. Magnetic susceptibility measurements confirmed the presence of four non-interacting, magnetically anisotropic high-spin CoII centers in 1. Furthermore, [Co4L6]4− was found to be stable towards aggregation and oxidation, and the CEST performance of [XeCo4L6]4− was unaffected by biological macromolecules in H2O. These results recommend metal-organic capsules for fundamental investigations of Xe host-guest chemistry as well as applications with highly sensitive 129Xe-based sensors. A crystallographically characterized paramagnetic cage, [Co4L6]4−, reversibly binds dissolved hyperpolarized 129Xe in H2O with favorable chemical exchange kinetics. Upon selective radiofrequency saturation, the exchange of depolarized 129Xe delivers contrast to the bulk, enabling pM detection of [XeCo4L6]4− in H2O. The paramagnetically shifted 129Xe resonance is also highly temperature sensitive. Therefore, [Co4L6]4− represents a promising 129Xe MR biosensor/thermometer.
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