竞争包结法研究β-环糊精及其两种衍生物对一些手性脂肪族客体分子的识别作用

以酚酞作为光谱探针 ,采用紫外 可见光谱滴定法测定了 β 环糊精 (β CD)、单 (6 氧 α 麦芽糖 ) β 环糊精 (6 G2 β CD )和单 2 氧 (2 羟丙基 ) ] β 环糊精 (2 HP β CD )在 2 5℃时 ,pH =10 5缓冲液中(0 0 2 5mol/L)与几种脂肪族手性客体分子所形成超分子配合物的稳定常数 .结果表明 ,多种弱相互作用力协同作用于环糊精的配位过程 ,主 客体间的尺寸匹配决定所形成配合物的稳定性 .环糊精衍生物的取代基影响主体的配位能力 ,对于尺寸较小的客体分子配位能力的大小一般为 2 HP β CD >β CD >6 G2 β CD .另一方面 ,3种环糊精主体化合物对一些脂肪族客体分子也表现出一定的手性识别能力 ,对 (+ ) 异构体给出相对较强的键合能力 ,其中 ,2 HP β CD对 (+ ) /(- ) 樟脑的配位选择性为 1 2 5 .

Molecular Recognition Study of β-Cyclodextrin and Its Two Derivatives with Some Aliphatic Guests by Competitive Inclusion Method

Spectrophotometric titrations were performed in aqueous buffer solution(pH=10.5, c=0.025 mol/L) at 25 ℃ to determine the binding constants of β-cyclodextrin(β-CD), mono(6-O-α-maltosyl)-β-cyclodextrin(6-G2-β-CD) and mono［2-O-(2-hydroxypropyl)］-β-cyclodextrin(2-HP-β-CD) with several aliphatic chiral guest molecules using phenolphthalein as a spectral probe. The results obtained indicate that several weak interactions cooperatively contribute to the inclusion complexation of the β-cyclodextrin hosts and the complex stability is dominated by the size/shape-matching between host and guest. The substituent on the cyclodextrin derivatives changes its original binding ability. For the relatively small guest molecules, i.e., borneol, camphor and menthol, the molecular binding ability is 2-HP-β-CD＞β-CD＞6-G2-β-CD. Furthermore, the three β-cyclodextrin hosts can also serve as chiral discrimination reagents and afford stronger binding ability toward (+)-isomers. Among them, 2-HP-β-CD gives a moderate enantiometric selectivity of 1.25 for (+)/(-)-camphor.