Complexation of Phenols by Calix[4]arene Diethers in a Low-Permittivity Solvent. Self-Switched Complexation by 25,27-Dibenzyloxycalix[4]arene

详细信息    查看全文

• 作者：Sá ; ndor Kunsá ; gi-Má ; té ; Korné ; lia Szab&oacute ; Bernard Desbat ; Jean-Luc Bruneel ; Istvá ; n Bitter ; Lá ; szl&oacute ; Kollá ; r
• 刊名：Journal of Physical Chemistry B
• 出版年：2007
• 出版时间：June 28, 2007
• 年：2007
• 卷：111
• 期：25
• 页码：7218 - 7223
• 全文大小：225K
• 年卷期：v.111,no.25(June 28, 2007)
• ISSN：1520-5207

文摘

To improve the selectivity of sensing, the thermodynamics of the complex formation of some calix[4]arenehosts with neutral phenol guests was studied in carbon tetrachloride as nonpolar solvent. The molecular shapeof calixarenes was varied by the selective functionalization with tBu and O-CH₂-Ph (O-benzyl) or OPrgroups at the upper and lower rim, respectively. To vary the electron density on the guest's aromatic rings,the parent phenol was functionalized in the para position with electron-withdrawing Cl, as well as H, andelectron-releasing CH₃ and tBu groups. To study the interaction between calixarene and the guests, PL andquantum-chemical methods were applied. The results revealed an overall 1:1 complex stoichiometry exceptfor the parent dibenzyloxycalix[4]arene, where 1:2 host-guest stoichiometries were observed irrespective ofthe quality of phenol. In the latter case, the complex formation shows a self-switched character: the firstphenol molecule is included in the calixarene cavity, and only afterward, a second guest molecule is boundby the two benzyloxy aromatics. Although the enthalpy change predicts strong interaction between the hostand the guest, the Gibbs free energy change of the complex formation is small, resulting in a relatively lowcomplex stability. The solvent-relaxation measurements support that the unexpected entropy change could bethe consequence of the reorientation of solvent molecules around the calixarene building block. The reorientationis assisted by dispersive forces between solute and solvent molecules. IR and RAMAN analysis of thecomplexes exclude a considerable participation of the phenolic OH group in the stabilization of the complex.This result is in agreement with earlier findings where deterministic role of s/gifchars/pi.gif" BORDER=0 >-s/gifchars/pi.gif" BORDER=0 > interaction in the complexstability was assumed.