용액상과 기체상에서의 아미노산들과 쿠커비투릴[7]간 주인-손님 상호작용에 대한 연구

Abstract

Cucurbit[7]uril (CB[7]) is a macrocyclic molecule composed of partially negative charged portals and a hydrophobic cavity. CB[7] has received great attention in the supramolecular chemistry society due to its exceptional recognition properties in aqueous solution. However, the binding events of different guests to CB[7] are still unclear at the molecular level. In this study, diverse recognition properties of CB[7] with different guests in diverse phases will be discussed. It deals with the binding properties of six amino acids with CB[7] both in solution and the gas phase to elucidate various guest binding events to CB[7]. We have investigated host-guest interactions between CB[7] and six amino acids (AAs) including three aromatic amino acids (Phe, Tyr, and Trp) and three basic amino acids (Lys, Arg, and His) both in solution and the gas phase to elucidate the origin of the high selectivity of CB[7] toward AA residues in proteins. Generally, the aromatic AAs show higher binding affinities than the basic AAs in solution regardless of pH values. On the contrary, the gas-phase stabilities of the basic AA complex ions are higher than those of the aromatic AA complex ions. These observations suggest that the direct ion?dipole interactions of the charged side chains of the basic AAs with CB[7] predominate in the absence of water. The ion?dipole interactions are less significant in water, since the original interactions of the guests with water are lost upon complex formation. In contrast, the encapsulation of the hydrophobic groups into the CB[7] cavity suffers less from the desolvation penalty, resulting in higher binding affinities in water. Therefore, initial guest solvation is another key factor which should be considered when understanding high-affinity binding events between CB[7] and guest molecules.