Department of Chemistry, Shanghai University, Shanghai 200444, P. R. China.
Org Biomol Chem. 2010 Apr 7;8(7):1568-76. doi: 10.1039/b920146g.
The complexation behavior of a series of paraquats (G1.2PF(6)-G5.2PF(6)) and bis(pyridinium) derivatives (G6.2PF(6)-G14.2PF(6)) with pillar[5]arene (P5A) host has been comprehensively investigated by (1)H NMR, ESI mass and UV-vis absorption spectroscopy. It is found that P5A forms 2 : 1 external complexes with N,N'-dialkyl-4,4'-bipyridiniums (G1-G4.2PF(6)); while it forms 1 : 1 pseudorotaxane-type inclusion complexes with methylene [-(CH(2))(n)-] linked bis(pyridinium) derivatives possessing appropriate chain lengths (n = 3-6, G7-G10.2PF(6)). Host-guest association constants in dimethyl sulfoxide (DMSO) were determined, indicating G7-G10.2PF(6) axles form stable [2]pseudorotaxanes with P5A wheel in this very high polarity solvent and 1,4-bis(pyridinium)butane (G8.2PF(6)) was the most suitable axle unit. Meanwhile, the nature of the substituents attached to 1,4-bis(pyridinium)butane dramatically affects the molecular recognition behavior. The introduction of pyridyls (G13.2PF(6)) increases not only the K(a) value (4.5 x 10(2) --> 7.4 x 10(2) M(-1)), but also the charge transfer (CT) absorption (colorless --> yellow). Furthermore, the solvent effects have also been investigated, showing they significantly influence the association strength during the course of host-guest complexation. Particularly, the K(a) value of P5A-G13.2PF(6) in 1 : 1 (v:v) acetone-d(6)/DMSO-d(6) is enhanced by a factor of 7.3 compared with pure DMSO-d6 (7.4 x 10(2) --> 5.4 x 10(3) M(-1)).
一系列 1,2-二（对氟苯基）-4,4'-联吡啶（G1.2PF(6)-G5.2PF(6)）和双（吡啶鎓）衍生物（G6.2PF(6)-G14.2PF(6)）与杯[5]芳烃（P5A）主体的络合行为通过（1）H NMR、ESI 质谱和紫外可见吸收光谱得到了全面研究。结果发现，P5A 与 N,N'-二烷基-4,4'-联吡啶（G1-G4.2PF(6)）形成 2 : 1 外部配合物；而对于亚甲基[-(CH(2))(n)-]连接的双（吡啶鎓）衍生物（具有适当的链长 n = 3-6，G7-G10.2PF(6)），则形成 1 : 1 伪轮烷型包合物。在二甲亚砜（DMSO）中测定了主体-客体结合常数，表明在这种高极性溶剂中，G7-G10.2PF(6)轴与 P5A 轮形成稳定的[2]伪轮烷，而 1,4-双（吡啶鎓）丁烷（G8.2PF(6)）是最合适的轴单元。同时，连接到 1,4-双（吡啶鎓）丁烷上的取代基的性质极大地影响了分子识别行为。吡啶基的引入（G13.2PF(6)）不仅增加了 K(a) 值（4.5 x 10(2) --> 7.4 x 10(2) M(-1)），而且增加了电荷转移（CT）吸收（无色 --> 黄色）。此外，还研究了溶剂效应，表明它们在主体-客体络合过程中显著影响结合强度。特别是，在 1 : 1（v:v）丙酮-d(6)/DMSO-d(6)中，P5A-G13.2PF(6)的 K(a) 值比纯 DMSO-d6 时提高了 7.3 倍（7.4 x 10(2) --> 5.4 x 10(3) M(-1)）。
