Department of Chemistry, Faculty of Science, University of Zagreb, Horvatovac 102a, 10000 Zagreb, Croatia.
Inorg Chem. 2012 Jun 4;51(11):6264-78. doi: 10.1021/ic300474s. Epub 2012 May 9.
The calix[4]arene secondary-amide derivative L was synthesized, and its complexation with alkali-metal cations in acetonitrile (MeCN) was studied by means of spectrophotometric, NMR, conductometric, and microcalorimetric titrations at 25 °C. The stability constants of the 1:1 (metal/ligand) complexes determined by different methods were in excellent agreement. For the complexation of M(+) (M = Li, Na, K) with L, both enthalpic and entropic contributions were favorable, with their values and mutual relations being quite strongly dependent on the cation. The enthalpic and overall stability was the largest in the case of the sodium complex. Molecular and crystal structures of free L, its methanol and MeCN solvates, the sodium complex, and its MeCN solvate were determined by single-crystal X-ray diffraction. The inclusion of a MeCN molecule in the calixarene hydrophobic cavity was observed both in solution and in the solid state. This specific interaction was found to be stronger in the case of metal complexes compared to the free ligand because of the better preorganization of the hydrophobic cone to accept the solvent molecule. Density functional theory calculations showed that the flattened cone conformation (C(2) point group) of L was generally more favorable than the square cone conformation (C(4) point group). In the complex with Na(+), L was in square cone conformation, whereas in its adduct with MeCN, the conformation was slightly distorted from the full symmetry. These conformations were in agreement with those observed in the solid state. The classical molecular dynamics simulations indicated that the MeCN molecule enters the L hydrophobic cavity of both the free ligand and its alkali-metal complexes. The inclusion of MeCN in the cone of free L was accompanied by the conformational change from C(2) to C(4) symmetry. As in solution studies, in the case of ML(+) complexes, an allosteric effect was observed: the ligand was already in the appropriate square cone conformation to bind the solvent molecule, allowing it to more easily and faster enter the calixarene cavity.
杯[4]芳烃仲酰胺衍生物 L 的合成及其与碱金属阳离子在乙腈（MeCN）中的络合作用通过 25°C 下的分光光度法、NMR、电导滴定法和微量量热滴定法进行了研究。不同方法测定的 1:1（金属/配体）配合物的稳定常数非常吻合。对于 M(+)（M = Li、Na、K）与 L 的络合，焓和熵贡献都是有利的，其值和相互关系强烈依赖于阳离子。在钠配合物的情况下，焓和整体稳定性最大。游离 L、甲醇和 MeCN 溶剂化物、钠配合物及其 MeCN 溶剂化物的分子和晶体结构通过单晶 X 射线衍射确定。在溶液和固态中都观察到 MeCN 分子进入杯芳烃疏水性空腔。这种特殊相互作用在金属配合物中比游离配体更强，因为疏水性锥体更好地预组织以接受溶剂分子。密度泛函理论计算表明，L 的扁平锥体构象（C(2)点群）通常比正方形锥体构象（C(4)点群）更有利。在与 Na(+)的配合物中，L 呈正方形锥体构象，而在与 MeCN 的加合物中，构象略微偏离完全对称。这些构象与在固态中观察到的一致。经典分子动力学模拟表明，MeCN 分子进入游离配体及其碱金属配合物的 L 疏水性空腔。MeCN 进入游离 L 的锥体伴随着从 C(2)到 C(4)对称的构象变化。与溶液研究一样，在 ML(+)配合物的情况下，观察到变构效应：配体已经处于适当的正方形锥体构象以结合溶剂分子，使其更容易和更快地进入杯芳烃空腔。
