配备有外围 H 键功能的锌卟啉和吡啶配体家族的合成提供了获得各种密切相关的超分子复合物的途径,这些复合物具有 0 到 4 个分子内 H 键。自动紫外/可见滴定系统用于表征 120 种不同的复合物,这些数据用于构建大量不同的化学双突变循环,以量化分子内 H 键相互作用。结果探讨了在复杂分子识别界面组装中控制协同性的定量构效关系。具体来说,复合物化学结构的变化使我们能够改变超分子结构、构象灵活性、几何互补性、氢键相互作用的数量和性质,以及复合物的整体稳定性。来自单个氢键的自由能贡献是可加的,并且在形成分子内相互作用的有效摩尔浓度中,结构几乎没有变化。在几何上不可能的复合物中没有观察到分子内 H 键,但没有出现极好的几何互补性导致非常高的亲和力的情况。同样,构象灵活性的变化似乎对有效摩尔浓度 (EM) 的影响有限。使用双突变循环检查的所有 48 种分子内相互作用中发现的主要变化是,分子内羧酸酯-苯酚
Measurement of supramolecular effective molarities for intramolecular H-bonds in zinc porphyrin–imidazole complexes
作者:Michael A. Jinks、Hongmei Sun、Christopher A. Hunter
DOI:10.1039/c3ob42246a
日期:——
The association constants for formation of 1â:â1 complexes between five different imidazole ligands and eight different porphyrins have been measured by UV/vis titration experiments in two different solvents, toluene and 1,1,2,2-tetrachloroethane (TCE). Ligands equipped with H-bond acceptors (ester or amide) and porphyrins equipped with H-bond donors (phenol) can make H-bonds in addition to the zincânitrogen coordination interaction. The free energy contributions of these H-bonds to the overall stabilities of the complexes were determined using chemical double mutant cycles. Amide-phenol H-bonds contribute up to 5 kJ molâ1 to the free energy change on complexation, and ester-phenol H-bonds contribute up to 3 kJ molâ1. Porphyrinâligand combinations with poor geometric complementarity do not make detectable H-bonding interactions. Effective molarities (EM) for the formation of H-bonds in the complexes were estimated by comparing the equilibrium constants for formation of the intramolecular interaction with the corresponding intermolecular interaction: the values are between 3 mM and 200 mM, which is comparable to previous results obtained for porphyrinâpyridine complexes. The values of EM measured for flexible and rigid ligand systems are comparable. This suggests that there is a trade off between restriction of conformational mobility in the flexible ligands and geometric strain in the rigid ligands, which results in similar binding affinities.
在甲苯和1,1,2,2-四氯乙烷(TCE)两种不同溶剂中,通过紫外/可见光滴定实验测量了五种不同咪唑配体与八种不同卟啉之间形成1:1复合物的结合常数。配有氢键受体(酯或酰胺)的配体和配有氢键供体(苯酚)的卟啉除了锌氮配位相互作用外,还能产生氢键。利用化学双突变循环测定了这些氢键对复合物整体稳定性的自由能贡献。酰胺-苯酚 H 键对络合自由能变化的贡献高达 5 kJ molâ1 ,酯-苯酚 H 键对络合自由能变化的贡献高达 3 kJ molâ1 。几何互补性较差的卟啉配体组合无法产生可检测到的氢键相互作用。通过比较分子内相互作用与相应的分子间相互作用形成的平衡常数,我们估算出了在复合物中形成 H 键的有效摩尔数(EM):其值介于 3 mM 与 200 mM 之间,这与之前在卟啉-吡啶复合物中获得的结果相当。柔性配体系统和刚性配体系统测得的 EM 值相当。这表明,在柔性配体的构象流动性限制和刚性配体的几何应变之间存在权衡,从而产生了相似的结合亲和力。
Enhanced Chelate Cooperativity in Polar Solvents
作者:Stefan Henkel、Maria Cristina Misuraca、Yudi Ding、Maxime Guitet、Christopher A. Hunter
DOI:10.1021/jacs.7b01765
日期:2017.5.17
the more polarsolvent, phenol. Phenol solvates the amide groups on the ligands strongly, increasing the steric bulk and destabilizing the complexes. These adverse steric interactions are removed when intramolecular H-bonds are formed and therefore provide an increased driving force for formation of cooperative interactions. The result is that the effects of competitive interactions with polar solvents
高通量 UV-vis 滴定结合化学双突变循环 (DMC) 已被用于研究极性溶剂对分子内 H 键形成的竞争。在甲苯和苯酚的混合物中研究了 24 种不同的锌卟啉-吡啶配合物。DMC 用于确定作为溶剂组成函数的分子内酚-酰胺 H 键形成的有效摩尔浓度 (EM)。EM 的值随着极性更大的溶剂苯酚浓度的增加而增加一个数量级。苯酚强烈地溶剂化配体上的酰胺基团,增加空间体积并使配合物不稳定。当形成分子内 H 键时,这些不利的空间相互作用被消除,因此为协同相互作用的形成提供了增加的驱动力。
Influence of non-covalent preorganization on supramolecular effective molarities
作者:Hongmei Sun、Cristina Navarro、Christopher A. Hunter
DOI:10.1039/c5ob00231a
日期:——
Formation of H-bonding interactions, which restrict the conformational mobility of a flexible linker, have no effect on chelate cooperativity in a family of porphyrin-pyridine complexes.