On the Binding of Calcium by Micelles Composed of Carboxy-Modified Pluronics Measured by Means of Differential Potentiometric Titration and Modeled with a Self-Consistent-Field Theory

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• 作者：Y. Lauw ; F. A. M. Leermakers ; M. A. Cohen Stuart ; J. P. Pinheiro ; J. P. A. Custers ; L. J. P. van den Broeke ; J. T. F. Keurentjes
• 刊名：Langmuir
• 出版年：2006
• 出版时间：December 19, 2006
• 年：2006
• 卷：22
• 期：26
• 页码：10932 - 10941
• 全文大小：152K
• 年卷期：v.22,no.26(December 19, 2006)
• ISSN：1520-5827

文摘

We perform differential potentiometric titration measurements for the binding of Ca²⁺ ions to micelles composedof the carboxylic acid end-standing Pluronic P85 block copolymer (i.e., CAE-85 (COOH-(EO)₂₆-(PO)₃₉-(EO)₂₆-COOH)). Two different ion-selective electrodes (ISEs) are used to detect the free calcium concentration; the first ISEis an indicator electrode, and the second is a reference electrode. The titration is done by adding the block copolymersto a known solution of Ca²⁺ at neutral pH and high enough temperature (above the critical micellization temperatureCMT) and various amount of added monovalent salt. By measuring the difference in the electromotive force betweenthe two ISEs, the amount of Ca²⁺ that is bound by the micelles is calculated. This is then used to determine the bindingconstant of Ca²⁺ with the micelles, which is a missing parameter needed to perform molecular realistic self-consistent-field (SCF) calculations. It turns out that the micelles from block copolymer CAE-85 bind Ca²⁺ ions both electrostaticallyand specifically. The specific binding between Ca²⁺ and carboxylic groups in the corona of the micelles is modeledthrough the reaction equilibrium -COOCa⁺ -COO^- + Ca²⁺ with pK_Ca = 1.7 ± 0.06.