Botta Bruno, D'Acquarica Ilaria, Delle Monache Giuliano, Nevola Laura, Tullo Danila, Ugozzoli Franco, Pierini Marco
Dipartimento di Studi di Chimica e Tecnologia delle Sostanze Biologicamente Attive, Università La Sapienza, P.le A. Moro 5, 00185 Roma, Italy.
J Am Chem Soc. 2007 Sep 12;129(36):11202-12. doi: 10.1021/ja072855i. Epub 2007 Aug 17.
Resorc[4]arene octamethyl ethers 1-3, when treated with NOBF4 salt in chloroform, form very stable 1:1 nitrosonium (NO+) complexes, which are deeply colored. The complexation process is reversible, and the complexes dissociate and bleach upon addition of methanol or water, to give the starting macrocycles. Resorc[4]arenes 1 and 2 are in the same cone conformation, but with different side-chains, whereas 3 possesses a different conformation (chair), while bearing the same side-chain as 2. Kinetic and spectral UV-visible analysis revealed that NO+ interacts with resorc[4]arenes 1 and 2 both outside and inside their basket, leading to complexes with two absorption patterns growing at different rates, one featuring high-energy bands (HEB) within the near-UV zone, and the other one low-energy bands (LEB), attributed to charge-transfer interactions, within the visible range. The presence of ester carbonyl groups in 2 strongly drives the NO+ cation outside the resorcarene. Resorc[4]arene 3 showed a spectral pattern pointing out a clear involvement of the ester moieties in the NO+ entrapping, beside the formation of significant charge-transfer interactions. 1H NMR spectroscopy and molecular modeling clearly supported these findings.
间苯二酚[4]芳烃八甲基醚1 - 3在氯仿中用NOBF₄盐处理时，会形成非常稳定的1:1亚硝基鎓（NO⁺）配合物，这些配合物颜色很深。络合过程是可逆的，加入甲醇或水后，配合物会解离并褪色，得到起始大环化合物。间苯二酚[4]芳烃1和2具有相同的锥形构象，但侧链不同，而3具有不同的构象（椅式），同时带有与2相同的侧链。动力学和光谱紫外可见分析表明，NO⁺在间苯二酚[4]芳烃1和2的笼状结构内外均有相互作用，导致形成两种以不同速率增长的吸收模式的配合物，一种在近紫外区具有高能带（HEB），另一种在可见光范围内具有低能带（LEB），这归因于电荷转移相互作用。2中酯羰基的存在强烈地将NO⁺阳离子驱赶到间苯二酚芳烃之外。间苯二酚[4]芳烃3显示出一种光谱模式，表明除了形成显著的电荷转移相互作用外，酯基部分在捕获NO⁺中也有明显参与。¹H NMR光谱和分子模拟清楚地支持了这些发现。
