Interactions of α-, β- and γ-cyclodextrin with bicyclo[2.2.2]octane-1,4-derivatives in aqueous solution and in the gas phase A microcalorimetric and molecular modelling study
作者:Magnus Stödeman、Ulf Berg、Anette Svensson
DOI:10.1039/a707598g
日期:——
Binding of 1,4-di-R-bicyclo[2.2.2]octanes [R = OH (bic), Me (bim)] to α-, β- and γ-cyclodextrin (α-CD, β-CD and γ-CD) in the gas phase and in aqueous solution have been studied by force-field computations and by isothermal titration microcalorimetry, respectively. For bic, a 1:1 stoichiometric model was assumed in the treatment of the microcalorimetric data. In the gas phase, for both α-CD and β-CD, bim penetrates less deeply into the cavity than bic. The shallow penetration of bim allows a second α- cyclodextrin molecule to bind, in agreement with the 1:2 complex observed in a solvent mixture by NMR measurements, as reported earlier. In aqueous solution, β-CD binds to bic with moderate Gibbs energy change, a large and negative heat capacity change and compensating temperature dependences for the enthalpy and the entropy changes. α-CD and γ-CD bind weakly to bic in solution, whilst large binding energies were obtained for both guests for the gas-phase interactions with α-CD and β-CD.
通过力场计算和等温滴定微量热法,分别研究了气相和水溶液中 1,4-二-R-双环[2.2.2]辛烷[R = OH (bic), Me (bim)]与δ-、δ-²-和δ-³-环糊精(δ-CD、δ-²-CD 和 δ-CD)的结合情况。在处理微量热测定法数据时,假定双氧水的化学计量模型为 1:1。在气相中,对于 α-CD 和 β-CD 而言,bim 比 bic 渗入空腔的深度要小。bim 的浅层渗透允许第二个 α- 环糊精分子结合,这与之前报告的核磁共振测量在混合溶剂中观察到的 1:2 复合物一致。在水溶液中,δ-CD 与 bic 结合时的吉布斯能量变化适中,热容量变化大且为负值,焓和熵的变化与温度有补偿关系。δ-CD和δ-CD在溶液中与双酸的结合力较弱,而这两种客体与δ-CD和²-CD的气相相互作用都获得了较大的结合能。