Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade do Porto, Requimte, Rua do Campo Alegre, 4169-007 Porto, Portugal.
J Mol Model. 2011 Dec;17(12):3275-88. doi: 10.1007/s00894-011-1004-9. Epub 2011 Mar 4.
The complexation behavior of nine polyether type podands with a varying number of oxygen donor atoms (4-10) towards the alkali metal cations Li(+), Na(+) and K(+) was studied by quantum chemical methods at the DFT-B3LYP level of theory using the all-electron split-valence 6-311++G(d,p) basis set. The optimized structures of the complexes show a regular increase in the mean cation-oxygen distance with the coordination number. OC-CO dihedral angles of the podand arms were also found to increase with the coordination number and with the size of the cation. Maximum values for the number of strong cation-oxygen interactions (effective coordination numbers) were found for each cation (six for Li(+), seven for Na(+) and eight for K(+)). The calculated values for thermodynamic parameters relative to the binding of free and solvated cations to the podands allowed the assessment of binding constants in vacuum, in water and in dichloromethane. The estimated cation extraction constants mimic the experimental extraction trends, but their values are much larger than experimental values. Scale factors were determined to correct the values effectively. For each podand the ratios between the calculated extraction constants of Li(+) (or Na(+)) and the corresponding ones for K(+) (seen as extraction selectivities) compare acceptably with the corresponding experimental values.
采用量子化学方法在 DFT-B3LYP 理论水平上，使用全电子分裂价 6-311++G(d,p)基组，研究了 9 种具有不同氧供体原子数（4-10）的聚醚型荚醚与碱金属阳离子 Li(+)、Na(+)和 K(+)的络合行为。复合物的优化结构表明，随着配位数的增加，阳离子-氧平均距离呈规则增加。还发现荚醚臂的 OC-CO 二面角随着配位数和阳离子的大小而增加。对于每个阳离子（Li(+)为六个，Na(+)为七个，K(+)为八个），都发现了具有最强阳离子-氧相互作用（有效配位数）的最大数目。相对于游离和溶剂化阳离子与荚醚的结合，计算得到的热力学参数值允许评估在真空中、在水中和在二氯甲烷中的结合常数。估计的阳离子萃取常数模拟了实验萃取趋势，但它们的值比实验值大得多。确定了比例因子以有效校正值。对于每个荚醚，计算得到的 Li(+)（或 Na(+)）萃取常数与相应的 K(+)萃取常数（视为萃取选择性）的比值与相应的实验值相当。
