The gas-phase recognition of native amino acids and the conformational properties of three glucosylthioureidocalix[4]arenes (1-3) were studied theoretically and experimentally using ab initio calculations, ESI-FTICR,1H and 13C NMR MS. The conformational and complexation properties of the glucocalixarenes were dependent on the number of glucose units at the upper rim and the length of the alkyl chains at the lower rim of the calixarene skeleton. ESI-MS experiments showed the compounds to form 1 : 1 complexes with the amino acids, with a marked preference for amino acids containing an aromatic nucleus and an additional H-bonding group in their side chain (Trp, Tyr, Phe ≫ Ser, Leu and Asp). The experimental data were rationalized by the results of ab initio calculations. ESI-MS competitions carried out with enantiomeric-labelled (EL) amino acids showed enantiomeric selectivities ranging from 0.61 (Phe(D)/Phe(L) with ligand 3) to 2.58 (Tyr(D)/Tyr(L) with ligand 2). In gas-phase hydrogen–deuterium (H/D) exchange reactions, diglucosylcalix[4]arene 2 exhibited extremely slow exchange rates, which were attributed to the close proximity and strong hydrogen bonding between the facing glucosylthioureido groups. H/D exchange rates were much higher for the tetraglucosylcalix[4]arenes 1 and 3 and their amino acid complexes, and the more rigid tetrapropoxy derivative 3 showed more selective H/D exchange reactions than the calixarene 1. Bi- or trimodal H/D exchange distribution was observed for the tetraglucosyl derivatives indicating that these ligands exist in multiple isomeric forms in gas phase.
研究人员利用 ab initio 计算、ESI-FTICR、1H 和 13C NMR MS 对三种
葡萄糖硫代二碳六[4]烯(1-3)的气相识别原生
氨基酸和构象特性进行了理论和实验研究。糖基卡利克沙烯烃的构象和复合特性取决于卡利克沙烯烃骨架上缘
葡萄糖单元的数量和下缘烷基链的长度。ESI-MS 实验表明,这些化合物与
氨基酸形成 1 :
氨基酸形成 1 : 1 的络合物,其中含有芳香核并在其侧链中含有额外 H 键基团的
氨基酸(Trp、Tyr、Phe ≫ Ser、Leu 和 Asp)具有明显的偏好性。实验数据通过 ab initio 计算结果得到了合理的解释。用对映体标记(EL)的
氨基酸进行的 ESI-MS 比对显示,对映体选择性从 0.61(Phe(D)/Phe(L),
配体 3)到 2.58(Tyr(D)/Tyr(L),
配体 2)不等。在气相氢-
氘(H/D)交换反应中,二
葡糖基
钙钛矿[4]炔 2 的交换速率极慢,这是因为面对面的
葡糖基
硫脲基团之间的距离很近,而且氢键很强。四
葡糖基萼[4]炔 1 和 3 及其
氨基酸复合物的 H/D 交换速率要高得多,而且刚性更强的四丙氧基衍
生物 3 比萼[4]炔 1 表现出更高的选择性 H/D 交换反应。在四
葡糖基衍
生物中观察到了双峰或三峰 H/D 交换分布,表明这些
配体在气相中以多种异构体形式存在。