Ferrocene-Appended Cyclodextrins. The Effects of Temperature, Organic Solvent, Length of Spacer, and Cavity Size on the Complexation Behavior
作者:Iwao Suzuki、Qiang Chen、Akihiko Ueno、Tetsuo Osa
DOI:10.1246/bcsj.66.1472
日期:1993.5
Inclusion phenomena of cyclodextrins (CyDs) bearing a ferrocene moiety, 1—4, which have different cavity sizes and spacer lengths, were investigated by circular dichroism (CD) spectroscopy in pure ethylene glycol (EG) and 20% EG aqueous solution. β-CyD derivatives, 1 and 3, and a γ-CyD derivative, 4, form intramolecular complexes, including the ferrocene moiety in the CyD cavity with orientation similar to that in corresponding native CyD–ferrocene complexes, while another γ-CyD derivative, 2, which has no spacer alkyl chain, takes various conformations. The host–guest binding constants of 1—4 for several guests revealed that the ferrocene moiety of 1—4 depresses the guest binding, acting as an intramolecular inhibitor in guest binding. In particular, the depression was remarkable for 3 and 4 and the spacer alkyl chain was suggested to stabilize the intramolecular complexes. The ferrocene modified CyDs exhibit similar trends in guest selectivity to those of native CyDs. The effects of EG content on the binding constants of 1 and 2 revealed that hydrophobic effect operated in the guest accommodation. Thermodynamic parameters for the binding processes of 1 and 2 for 1-adamantanol were obtained from the temperature variations in binding constants, the values being −21.9 kJ mol−1 for ΔH° and 2.76 J mol−1 K−1 for ΔS° for 1 and −25.1 kJ mol−1 for ΔH° and −36.1 J mol−1 K−1 for ΔS° for 2. These values indicated that the complexation of 1 and 2 for 1-adamantanol was governed both by hydrophobic effect and van der Waals interaction, and the latter was especially important in the case of 1 and 1-adamantanol.
在纯乙二醇(EG)和 20% EG 水溶液中,通过圆二色性光谱(CD)研究了含有二茂铁分子的环糊精(CyDs)1-4 的包合现象,这些环糊精具有不同的空腔尺寸和间隔长度。β-CyD衍生物1和3以及一种γ-CyD衍生物4形成了分子内配合物,包括CyD空腔中的二茂铁分子,其取向与相应的原生CyD-二茂铁配合物相似,而另一种没有间隔烷基链的γ-CyD衍生物2则呈现出各种构象。1-4 与几种客体的主-客体结合常数显示,1-4 的二茂铁分子抑制了客体的结合,在客体结合中起到了分子内抑制剂的作用。尤其是 3 和 4 的抑制作用更为明显,这表明间隔烷基链能稳定分子内复合物。二茂铁修饰的 CyDs 在客体选择性方面的趋势与原生 CyDs 相似。EG 含量对 1 和 2 结合常数的影响表明,疏水效应在客体容纳中起作用。根据结合常数的温度变化,得到了 1 和 2 与 1-金刚烷醇结合过程的热力学参数,其中 1 的 ΔH° 值为 -21.9 kJ mol-1,ΔS° 值为 2.76 J mol-1 K-1;2 的 ΔH° 值为 -25.1 kJ mol-1,ΔS° 值为 -36.1 J mol-1 K-1。这些数值表明,1-金刚烷醇与 1 和 2 的络合受疏水效应和范德华相互作用的影响,而后者在 1 和 1-金刚烷醇的络合中尤为重要。