Kunsági-Máté Sándor, Csók Zsolt, Tuzi Angela, Kollár László
Department of General and Physical Chemistry, University of Pécs, Ifjúság 6, Pécs, Hungary.
J Phys Chem B. 2008 Sep 18;112(37):11743-9. doi: 10.1021/jp803498v. Epub 2008 Aug 20.
Considering the importance of the polarizability of the rings of calixarenes in the entropy-driven interaction processes, we examined the effect of entropy compensation on the complex formation of cone and partial cone (paco) conformers of tetranitro-calix [4]arene, possessing O-ethyl substituents at the lower rim. Both calixarene conformers were fully characterized including X-ray crystallography. Various para-substituted phenols were used as guest molecules. Photoluminescence (PL) measurements and quantum-chemical (QC) investigations were used. A permittivity dependence of the molecular interactions was obtained in different alcohols as solvents. It was found that the cone conformer of the title calixarene derivative forms stable complexes with all phenols of the p-substituted series. The free enthalpy changes show very high complex stability of cone calixarene with p-nitro and p-chloro-substituted phenols. In the cases of parent phenol, p-cresol and p- tBu-phenol, the stability is significantly lower; however, it slightly increases with the increasing electron density on the aromatic ring of guest molecules. Similarly, the entropy changes are significantly different for these two separated groups: the entropy changes obtained in the former cases are nearly the same, while large differences in the formation entropy were obtained in the latter cases. Both the experimental and theoretical investigations revealed that no considerable interaction exists between phenols and the paco conformer of the title calixarene. It is probably due to the locking of the calixarene cavity by the bent O-ethyl chain.
考虑到杯芳烃环的极化率在熵驱动的相互作用过程中的重要性，我们研究了熵补偿对具有下边缘O-乙基取代基的四硝基杯[4]芳烃的锥式和部分锥式（paco）构象体形成配合物的影响。两种杯芳烃构象体均通过X射线晶体学等手段进行了全面表征。使用了各种对取代苯酚作为客体分子。采用了光致发光（PL）测量和量子化学（QC）研究方法。在不同醇类作为溶剂的情况下获得了分子相互作用的介电常数依赖性。结果发现，标题杯芳烃衍生物的锥式构象体与对取代系列的所有苯酚形成稳定的配合物。自由焓变显示杯芳烃锥式与对硝基和对氯取代苯酚的配合物稳定性非常高。对于母体苯酚、对甲酚和对叔丁基苯酚，稳定性明显较低；然而，随着客体分子芳环上电子密度的增加，稳定性略有增加。同样，这两个分开的组的熵变也有显著差异：前一种情况下获得的熵变几乎相同，而后一种情况下形成熵有很大差异。实验和理论研究均表明，苯酚与标题杯芳烃的paco构象体之间不存在显著相互作用。这可能是由于弯曲的O-乙基链锁定了杯芳烃空腔。
