Dual Effect of Secondary Solutes on Binding Equilibria: Contributions from Solute-Reactant Interactions and Solute-Water Interactions.
Dual Effect of Secondary Solutes on Binding Equilibria: Contributions from Solute-Reactant Interactions and Solute-Water Interactions.
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DOI：
10.1021/acsomega.3c09329
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发表时间：
2024-01-16
期刊：
影响因子：
4.1
通讯作者：
Castellano, Bria M.
中科院分区：
文献类型：
--
作者：
Eggers, Daryl K.;Le, Jennifer M.;Nham, Nhi T.;Pham, Duc N.;Castellano, Bria M.
本研究探讨了水在结合平衡中的作用，特别关注影响平衡但不是最终产品成分的二级溶质（cosolutes）。使用一个热力学框架，其中包括一个明确的条款，为水分子的释放结合，这项研究揭示了溶质如何可能改变平衡，通过改变反应物的活性，反映在ΔG°（obs），并通过改变溶剂的化学势，反映在ΔGS。该框架适用于四个实验结合系统，不同程度的静电贡献。模型体系包括EDTA对Ca ~（2+）的螯合作用和对磺酸基杯[4]芳烃与四甲基铵离子、葫芦[7]脲与N-乙酰基苯丙氨酸酰胺、β-环糊精与金刚烷羧酸盐的三种主客体反应。在25 °C下，在常见的渗透剂蔗糖和常见的离液剂尿素的存在下，通过等温滴定量热法检查每个反应对。海藻糖和磷酸盐的摩尔溶液也与选定的模型进行了测试。一般来说，增强结合的共溶质倾向于减少溶剂化自由能罚分，而减弱结合的共溶质倾向于增加溶剂化自由能罚分。值得注意的是，金刚烷羧酸盐和β-环糊精之间的非极性-非极性相互作用的特征在于接近零的ΔGS值。特别是β-环糊精的结果，促使进一步讨论海藻糖的疏水作用和生物相容性。鼓励其他研究人员测试和改进这里采取的方法，以进一步了解溶剂对分子识别的影响。
This study examines the role of water in binding equilibria with a special focus on secondary solutes (cosolutes) that influence the equilibrium but are not constituents of the final product. Using a thermodynamic framework that includes an explicit term for the release of water molecules upon binding, this investigation reveals how solutes may alter equilibria by changing the activity of the reactants, reflected in ΔG°(obs), and by changing the chemical potential of the solvent, reflected in ΔGS. The framework is applied to four experimental binding systems that differ in the degree of electrostatic contributions. The model systems include the chelation of Ca2+ by EDTA and three host–guest reactions; the pairings of p-sulfonatocalix[4]arene with tetramethylammonium ion, cucurbit[7]uril with N-acetyl-phenylalanine-amide, and β-cyclodextrin with adamantane carboxylate are tested. Each reaction pair is examined by isothermal titration calorimetry at 25 °C in the presence of a common osmolyte, sucrose, and a common chaotrope, urea. Molar solutions of trehalose and phosphate were also tested with selected models. In general, cosolutes that enhance binding tend to reduce the solvation free energy penalty and cosolutes that weaken binding tend to increase the solvation free energy penalty. Notably, the nonpolar–nonpolar interaction between adamantane carboxylate and β-cyclodextrin is characterized by a ΔGS value near zero. The results with β-cyclodextrin, in particular, prompt further discussions of the hydrophobic effect and the biocompatible properties of trehalose. Other investigators are encouraged to test and refine the approach taken here to further our understanding of solvent effects on molecular recognition.
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