The neutral host cucurbit[7]uril forms very stable complexes with a series of cationic cholines (R3NCH2CH2ORâ²+) and their phosphonium analogues (R3PCH2CH2ORâ²+) (R3 = Me3, Et3, or Me2Bz, or R3N = quinuclidinium, and Râ² = H, COCH3, CO(CH2)2CH3, or PO3H), and (±)-carnitine, in aqueous solution. The complexation behaviour has been investigated using 1H and 31P NMR spectroscopies, and ESI mass spectrometry. The complexation-induced chemical shift changes of the guests clearly indicate the effects of replacing the N(CH3)3+ end group by P(CH3)3+, and changing the nature of R on the position of the guest with respect to the CB[7] cavity and its polar portal-lining carbonyl groups. This study demonstrates that molecular recognition of cholines in aqueous solution is achievable with a neutral host without the need for aromatic walls for cationâÏ interactions.
中性主体瓜环[7]与一系列阳离子
胆碱(R3N OR' +)及其膦鎓类似物(R3PCH2 OR' +)(R3 = Me3、Et3、Me2Bz,或R3N =
奎宁环鎓,R' = H、CO 、CO(
CH2)2 、或PO3H)以及(±)-肉碱在
水溶液中形成非常稳定的复合物。利用1H和31P核磁共振波谱学以及ESI质谱法研究了复合行为。客体分子的复合诱导
化学位移变化清楚地表明了通过P(
CH3)3+取代N( )3+末端基团以及改变R的性质对客体相对于CB[7]腔体及其极性门户面羰基位置的影响。这一研究表明,无需利用芳香壁进行阳离子-π相互作用,即可实现
水溶液中对
胆碱的分子识别。