Kinetics, Thermodynamics, and Modeling of Complex Formation between Calix[4]biscrowns and Cesium

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• 作者：Alexandre Korovitch ; Jean-Baptiste Mulon ; Vincent Souchon ; Claude Lion ; Bernard Valeur ; Isabelle Leray ; Nguyt-Thanh Ha-Duong ; Jean-Michel El Hage Chahine
• 刊名：Journal of Physical Chemistry B
• 出版年：2009
• 出版时间：October 29, 2009
• 年：2009
• 卷：113
• 期：43
• 页码：14247-14256
• 全文大小：359K
• 年卷期：v.113,no.43(October 29, 2009)
• ISSN：1520-5207

文摘

Complex formations between calix[4]arene-bis(crown-6-ether) calix-COU2 (A1) and the tetrasulfonated species calix-COUSULF (A2) with Cs⁺ are investigated in water and ethanol, and in 9:1 (M1) and 1:9 (M2) H₂O/EtOH v:v mixtures, by chemical relaxation and molecular modeling. In ethanol and M2, two Cs⁺ are included in A1 in two kinetic steps, whereas complex formation in M1 becomes controlled by a slow first-order kinetic process, which is accompanied by very fast Cs⁺ inclusions, second-order rate constant: k′₁ = (3.4 ± 0.8) × 10⁷ M⁻¹ s⁻¹. In water and M1, A2 forms 1:1 and 1:2 cesium complexes in a single kinetic step, whereas in M2, two Cs⁺ are included in two kinetic steps. The rate and thermodynamic constants involved are reported. They show that the second-order rate constants increase with the ethanol-to-water ratio, e.g., A2, second-order rate constant for the first Cs⁺ in water: k_1A2water = (9.7 ± 0.3) × 10⁴ M⁻¹ s⁻¹ and in M2: k_1A2M2 = (6.3 ± 0.4) × 10⁹ M⁻¹ s⁻¹. The affinities of both A1 and A2 for Cs⁺ also increase with the ethanol-to-water ratio, e.g., first inclusion of A1 in M1: K_1A1M1 = (5 ± 1.3) × 10³ and in ethanol: K_1A1EtOH = (7 ± 3) × 10⁶. The deviation from the expected mechanism of complex formation with alkali is attributed to the comparatively more difficult access of Cs⁺ to the inclusion cavity of the capped calixarene. An analysis of calix-COU2 and calix-COUSULF and their Cs⁺ complexes with only one rim capped by the crown ether confirms the thermodynamic and kinetic results, by showing that the inclusion cavity of calix-COUSULF is more adapted to Cs⁺ than that of calix-COU2. This added to the presence of the shielding effect of the negative sulfonates can explain that the affinity of calix-COUSULF for Cs⁺ is higher than that of calix-COU2. These results can be of interest in the search of an efficient Cs⁺ decontaminant.