Supramolecular host-guest interaction of trityl-nitroxide biradicals with cyclodextrins: modulation of spin-spin interaction and redox sensitivity.
Supramolecular host-guest interaction of trityl-nitroxide biradicals with cyclodextrins: modulation of spin-spin interaction and redox sensitivity.
复制标题
三苯甲基氮氧双自由基与环糊精的超分子主客体相互作用：自旋-自旋相互作用和氧化还原敏感性的调节。
DOI：
10.1039/c5ob02450a
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发表时间：
2016-02-07
影响因子：
3.2
通讯作者：
Liu Y
中科院分区：
文献类型：
--
作者：
Tan X;Song Y;Liu H;Zhong Q;Rockenbauer A;Villamena FA;Zweier JL;Liu Y
通过电子顺磁共振（EPR）光谱研究了三苯甲基 - 氮氧自由基（TN）双自由基CT02 - VT、CT02 - AT和CT02 - GT与甲基 - β - 环糊精（M - β - CD）、羟丙基 - β - 环糊精（H - β - CD）和γ - 环糊精（γ - CD）的超分子主 - 客体相互作用。在环糊精（即γ - CD、M - β - CD和H - β - CD）存在的情况下，形成了CT02 - VT的主 - 客体复合物，其中氮氧自由基和连接部分可能与环糊精的空腔相互作用。与环糊精的络合导致CT02 - VT中分子内的空间贯穿自旋 - 自旋交换耦合受到抑制，从而能够确定通过键的自旋 - 自旋交换耦合，通过EPR模拟计算其值为1.6高斯。不同类型的环糊精与CT02 - VT具有不同的结合亲和力，γ - CD（95 M⁻¹）> M - β - CD（70 M⁻¹）> H - β - CD（32 M⁻¹）。此外，还研究了TN双自由基中连接体对主 - 客体相互作用的影响。在所研究的三种TN双自由基中，CT02 - VT与一种指定的环糊精衍生物具有最高的缔合常数。另一方面，由于CT02 - GT和CT02 - AT的连接体比CT02 - VT短，它们与环糊精形成的复合物的通过键的自旋 - 自旋交换耦合（CT02 - GT约为22高斯，CT02 - AT为7.7 - 9.0高斯）比CT02 - VT（1.6高斯）高得多。此外，与环糊精络合后，TN双自由基对抗坏血酸的稳定性显著提高，所有双自由基的二级速率常数几乎降低了2倍。因此，与环糊精的超分子主 - 客体相互作用将是一种调节TN双自由基的自旋 - 自旋相互作用大小和氧化还原敏感性的替代方法，并且所得复合物有望作为高效的动态核极化（DNP）极化剂以及电子顺磁共振（EPR）氧化还原探针。
Supramolecular host-guest interactions of trityl-nitroxide (TN) biradicals CT02-VT, CT02-AT and CT02-GT with methyl-β-cyclodextrin (M-β-CD), hydroxypropyl-β-cyclodextrin (H-β-CD) and γ-cyclodextrin (γ-CD) were investigated by EPR spectroscopy. In the presence of cyclodextrins (i.e., γ-CD, M-β-CD and H-β-CD), host-guest complexes of CT02-VT are formed where the nitroxide and linker parts possibly interact with the cyclodextrins’ cavities. Complexation with cyclodextrins leads to suppression of the intramolecular through-space spin-spin exchange coupling in CT02-VT, thus allowing determination of the through-bond spin-spin exchange coupling which was calculated to be 1.6 G using EPR simulations. Different types of cyclodextrins have variable binding affinity with CT02-VT with γ-CD (95 M−1) > M-β-CD (70 M−1) > H-β-CD (32 M−1). In addition, the effect of the linkers in TN biradicals on the host-guest interactions was also investigated. Among three TN biradicals studied, CT02-VT has the highest association constant with one designated cyclodextrin derivative. On the other hand, the complexes of CT02-GT (~ 22 G) and CT02-AT (7.7–9.0 G) with cyclodextrins have much higher through-bond spin-spin exchange couplings than that of CT02-VT (1.6 G) due to the shorter linkers than that of CT02-VT. Furthermore, the stability of TN biradicals towards ascorbate was significantly enhanced after the complexation with CDs, with an almost 2-time attenuation of the second-order rate constants for all the biradicals. Therefore, the supramolecular host-guest interactions with cyclodextrins will be an alternative method to modulate the magnitude of the spin-spin interactions and redox sensitivity of TN biradicals and the resulting complexes are promising as highly efficient DNP polarizing agents as well as EPR redox probes.