Controlling the extent of spin exchange coupling in 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) biradicals via molecular recognition with cucurbit[n]uril hosts.
Controlling the extent of spin exchange coupling in 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) biradicals via molecular recognition with cucurbit[n]uril hosts.
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DOI：
10.1021/la2005198
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发表时间：
2011-04
期刊：
影响因子：
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通讯作者：
S. Yi;B. Captain;M. Ottaviani;A. Kaifer
中科院分区：
文献类型：
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作者：
S. Yi;B. Captain;M. Ottaviani;A. Kaifer
用电子吸收光谱、核磁共振和电子顺磁共振(EPR)光谱、质谱学和X-射线结晶学相结合的方法研究了两个顺磁性钴客体与主客体瓜环(CB7)和瓜环(CB8)之间的结合作用。客体1、(4-amido-2，2，6，6-tetramethylpiperidine-1-oxyl)cobaltocenium，与Cb7、Cb8形成非常稳定的包合物。然而，CB7通过包括有机金属钴镉单元与1相互作用，而CB8吞噬了Tempo残基。Cb7·1和Cb8·1的平衡缔合常数(K)分别为2.8±0.3×10(6)M(-1)和2.1±1.0×10(8)M(-1)。双自由基客体2，1，1‘-bis(4-amido-2，2，6，6-tetramethylpiperidine-1-oxyl)cobaltocenium，与两个Cb8主体形成一个非常稳定的三元络合物，其中每个2，2，6，6-四甲基哌啶-1-氧基(TEMPO)残基都被主体分子包围.用单晶X-射线单晶衍射法确定了该三元配合物的结构。TEMPO侧臂与CB8主体的结合逐渐降低了观察到的两个氮氧化物之间的自旋交换耦合水平。在最终的2：1络合物中，没有观察到自旋交换耦合，但通过在溶液中加入竞争客体金刚烷基三甲基铵(AdTMA)，自旋交换耦合的初始能级可以以可逆的方式再生。2与CB7的结合作用相似，但1：1和2：1络合物的稳定性远低于相应的CB8络合物。
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.