Complexation characteristics of permethylated cycloinulohexaose, cycloinuloheptaose, and cycloinulooctaose with metal cations†
作者:Motohiro Shizuma、Yoshio Takai、Mishio Kawamura、Tokuji Takeda、Masami Sawada
DOI:10.1039/b102710g
日期:——
The host–guest complexation behavior of cyclic oligosaccharides, permethylated cycloinulohexaose 1, permethylated cycloinuloheptaose 2, and permethylated cycloinulooctaose 3 with metal cations has been characterized by means of UV-visible, NMR, and electrospray ionization (ESI) mass spectrometry. In the crystal state, the structures of 1·K+, 1·Rb+, and 1·Cs+ were same as that of the 1·Ba2+ complex which has a u-u-d-u-u-d (u = up, d = down) furanose ring arrangement for the plane of the crown ring moiety. The association
constants (KS) in THF and in [2H6]acetone at 298 K were evaluated. The binding ability of host 1 with metal cations was of the same degree as that of calix[6]arene derivative 4 and much higher than those of hosts 2 and 3. The thermodynamic parameters of the complexation of host 1 with metal cation in THF were determined, and it was suggested that the entropy change for the solvation of the metal cations was one of the important factors in the complexation equilibrium. It was clarified that the structure of the host 1·K+ complex in solution at low temperature (furanose ring arrangement: u-d-u-d-u-d) was different from that in the crystal state (u-u-d-u-u-d arrangement)
by the coalescence behavior in 1H-NMR. The relative peak intensity of the complex ions of host 1 or 2 with two alkali metal ions in ESI mass spectrometry (in acetone) showed a correlation in the first order approximation with the ratio of the corresponding complex ion concentrations estimated from the KS values.
环状低聚糖与金属离子的主客体络合行为,即全甲基化环状菊粉六聚糖1、全甲基化环状菊粉七聚糖2和全甲基化环状菊粉八聚糖3,已通过紫外-可见光谱、核磁共振和电喷雾电离(ESI)质谱法进行了表征。在晶体状态下,1·K+、1·Rb+和1·Cs+的结构与1·Ba2+络合物的结构相同,其中皇冠环部分平面的呋喃糖环排列为u-u-d-u-u-d(u=向上,d=向下)。在298 K下,THF和[2H6]丙酮中的结合常数(KS)得到了评估。宿主1与金属离子的结合能力与杯[6]芳烃衍生物4相当,远高于宿主2和3。确定了宿主1与金属离子在THF中的络合作用的热力学参数,并提出金属离子的溶剂化熵变是络合平衡中的重要因素之一。通过1H-NMR中的合并行为,明确了在低温溶液中宿主1·K+络合物的结构(呋喃糖环排列:u-d-u-d-u-d)与晶体状态下的结构(u-u-d-u-u-d排列)不同。在ESI质谱法(在丙酮中)中,宿主1或2与两种碱金属离子的络合离子相对峰强度与根据KS值估计的相应络合离子浓度比在第一近似中呈相关性。