Wiskur Sheryl L, Lavigne John J, Metzger Axel, Tobey Suzanne L, Lynch Vincent, Anslyn Eric V
Department of Chemistry and Biochemistry, 1 University Station A5300, The University of Texas at Austin, Austin, TX 78712, USA.
Chemistry. 2004 Aug 6;10(15):3792-804. doi: 10.1002/chem.200305737.
The thermodynamics of guanidinium and boronic acid interactions with carboxylates, alpha-hydroxycarboxylates, and diols were studied by determination of the binding constants of a variety of different guests to four different hosts (7-10). Each host contains a different combination of guanidinium groups and boronic acids. The guests included molecules with carboxylate and/or diol moieties, such as citrate, tartrate, and fructose, among others. The Gibbs free energies of binding were determined by UV/Vis absorption spectroscopy, by use of indicator displacement assays. The receptor based on three guanidinium groups (7) was selective for the tricarboxylate guest. The receptors that incorporated boronic acids (8-10) had higher affinities for guests that included alpha-hydroxycarboxylate and catechol moieties over guests containing only carboxylates or alkanediols. Isothermal titration calorimetry revealed the enthalpic and entropic contributions to the Gibbs free energies of binding. The binding of citrate and tartrate was investigated with hosts 7-10, for which all the binding events were exothermic, with positive entropy. Because of the selectivity of hosts 8-10, a simple boronic acid (14) was also investigated and determined to be selective for alpha-hydroxycarboxylates and catechols over amino acids and alkanediols. Further, the cooperativity of 8 and 9 in binding tartrate was also investigated, revealing little or no cooperativity with 8, but negative cooperativity with 9. A linear entropy/enthalpy compensation relationship for all the hosts 7-10, 14, and the carboxylate-/diol-containing guests was also obtained. This relationship indicates that increasing enthalpy of binding is offset by similar losses in entropy for molecular recognition involving guanidinium and boronic acid groups.
通过测定多种不同客体与四种不同主体（7 - 10）的结合常数，研究了胍盐和硼酸与羧酸盐、α - 羟基羧酸盐及二醇之间的热力学性质。每个主体包含不同组合的胍基团和硼酸。客体包括含有羧酸盐和/或二醇部分的分子，如柠檬酸盐、酒石酸盐和果糖等。结合的吉布斯自由能通过紫外/可见吸收光谱法，利用指示剂置换测定法来确定。基于三个胍基团的受体（7）对三羧酸盐客体具有选择性。含有硼酸的受体（8 - 10）对包含α - 羟基羧酸盐和儿茶酚部分的客体的亲和力高于仅含羧酸盐或链烷二醇的客体。等温滴定量热法揭示了结合吉布斯自由能的焓和熵贡献。用主体7 - 10研究了柠檬酸盐和酒石酸盐的结合，所有结合事件均为放热反应，且熵为正值。由于主体8 - 10具有选择性，还研究了一种简单的硼酸（14），并确定其对α - 羟基羧酸盐和儿茶酚的选择性高于氨基酸和链烷二醇。此外，还研究了8和9结合酒石酸盐时的协同性，结果表明8几乎没有协同性，而9具有负协同性。还获得了所有主体7 - 10、14以及含羧酸盐/二醇的客体之间的线性熵/焓补偿关系。这种关系表明，对于涉及胍基团和硼酸基团的分子识别，结合焓的增加被熵的类似损失所抵消。
