Department of Chemistry and Center for Supramolecular Science, University of Miami, Coral Gables, Florida 33124-0431, United States.
Langmuir. 2011 May 3;27(9):5624-32. doi: 10.1021/la2005198. Epub 2011 Apr 4.
The binding interactions between two paramagnetic cobaltocenium guests and the hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) were investigated using a combination of electronic absorption, NMR, and electron paramagnetic resonance (EPR) spectroscopies, mass spectrometry, and X-ray crystallography. Guest 1, (4-amido-2,2,6,6-tetramethylpiperidine-1-oxyl)cobaltocenium, forms very stable inclusion complexes with CB7 and CB8. However, CB7 interacts with 1 by including the organometallic cobaltocenium unit, while CB8 engulfs the TEMPO residue. The corresponding equilibrium association constant (K) values are 2.8 ± 0.3 × 10(6) M(-1) for CB7•1 and 2.1 ± 1.0 × 10(8) M(-1) for CB8•1. Biradical guest 2, 1,1'-bis(4-amido-2,2,6,6-tetramethylpiperidine-1-oxyl)cobaltocenium, forms a very stable ternary complex with two CB8 hosts, in which each 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) residue is encircled by a host molecule. The structure of this ternary complex was confirmed in the solid state using single-crystal X-ray diffraction. Binding of the TEMPO side arms by the CB8 hosts gradually decreases the observed level of spin exchange coupling between the two nitroxide groups. In the final 2:1 complex, no spin exchange coupling was observed, but the initial levels of spin exchange coupling could be regenerated in a reversible fashion by adding a competing guest, adamantyltrimethylammonium (AdTMA), to the solution. The binding interactions between 2 and CB7 are similar but the stabilities of the 1:1 and 2:1 complexes are much lower than those of the corresponding CB8 complexes.
用电子吸收光谱、NMR、电子顺磁共振(EPR)光谱、质谱和 X 射线晶体学的组合研究了两个顺磁钴卟啉客体与主体葫芦[7]脲（CB7）和葫芦[8]脲（CB8）之间的结合相互作用。客体 1，（4-酰胺基-2,2,6,6-四甲基哌啶-1-氧自由基）钴卟啉，与 CB7 和 CB8 形成非常稳定的包合物。然而，CB7 通过包含有机金属钴卟啉单元与 1 相互作用，而 CB8 则吞噬 TEMPO 残基。相应的平衡结合常数（K）值分别为 2.8 ± 0.3 × 10(6) M(-1) 用于 CB7•1 和 2.1 ± 1.0 × 10(8) M(-1) 用于 CB8•1。双自由基客体 2，1,1'-双（4-酰胺基-2,2,6,6-四甲基哌啶-1-氧自由基）钴卟啉，与两个 CB8 主体形成非常稳定的三元配合物，其中每个 2,2,6,6-四甲基哌啶-1-氧（TEMPO）残基被主体分子包围。使用单晶 X 射线衍射在固态中证实了这种三元配合物的结构。CB8 主体对 TEMPO 侧臂的结合逐渐降低了两个氮氧自由基之间观察到的自旋交换偶合水平。在最终的 2:1 配合物中，没有观察到自旋交换偶合，但可以通过向溶液中添加竞争客体金刚烷三甲铵（AdTMA）以可逆的方式重新生成初始水平的自旋交换偶合。2 与 CB7 之间的结合相互作用相似，但 1:1 和 2:1 配合物的稳定性远低于相应的 CB8 配合物。
