Substituent effects on axle binding in amide pseudorotaxanes: comparison of NMR titration and ITC data with DFT calculations
作者:Lena Kaufmann、Egor V. Dzyuba、Friedrich Malberg、Nora L. Löw、Matthias Groschke、Boris Brusilowskij、Juhani Huuskonen、Kari Rissanen、Barbara Kirchner、Christoph A. Schalley
DOI:10.1039/c2ob25196e
日期:——
The binding behaviour of differently substituted diamide axle molecules to Hunter/Vögtle tetralactam macrocycles was studied with a combination of NMR titration, isothermal titration calorimetry (ITC) experiments and calculations employing density functional theory (DFT), along with dispersion-corrected exchange-correlation functionals. Guests with alkyl or alkenyl chains attached to the diamide carbonyl groups have a significantly higher binding affinity to the macrocycle than guests with benzoyl amides and their substituted analogues. While the binding of the benzoyl and alkenyl substituted axles is enthalpically driven, the alkyl-substituted guest binds mainly because of a positive binding entropy. The electronic effects of para-substituents at the benzoyl moieties have an influence on the binding affinities. Electron donating substituents increase, while electron-withdrawing substituents decrease the binding energies. The binding affinities obtained from both NMR titration and ITC experiments correlate well with each other. The substituent effects observed in the experimental data are reflected in adiabatic interaction energies calculated with density functional methods. The calculated structures also agree well with pseudorotaxane crystal structures.
不同取代的二酰胺轴分子与Hunter/Vögtle四内酯大环的结合行为通过NMR滴定、等温滴定量热法(ITC)实验以及采用密度泛函理论(DFT)和修正了色散的交换-关联泛函的计算进行了研究。与苯甲酰胺及其取代类似物相比,带有烷基或烯基链连接到二酰胺羰基的客体对大环的结合亲和力显著更高。苯甲酰和烯基取代的轴的结合主要是由焓驱动,而烷基取代的客体主要是因为正的结合熵。苯甲基部分的对位取代基的电子效应会影响结合亲和力。给予电子的取代基增加结合能,而吸电子的取代基则降低结合能。通过NMR滴定和ITC实验获得的结合亲和力彼此之间有很好的相关性。实验数据中观察到的取代基效应在用密度泛函方法计算的绝热相互作用能中得到了反映。计算出的结构也与伪旋转烷晶体结构相一致。