Zentrum für Umweltforschung und nachhaltige Technologien (UFT)-Centre for Environmental Research and Sustainable Technology, University of Bremen, Bremen, Germany.
Chemphyschem. 2012 Feb;13(3):780-7. doi: 10.1002/cphc.201100872. Epub 2012 Jan 27.
In order to understand molecular interaction potentials of 30 cations of ionic liquids (ILs), the well-known linear free energy relationship concept (LFER) was applied. The LFER descriptors for the excess molar refractivity and the molar volume were calculated in silico and for hydrogen-bonding acidity and basicity, and the polarizability/dipolarity of IL cations were experimentally determined through high performance liquid chromatography (HPLC) measurements. For the study, three different columns (RP-select B, Cyan, and Diol) and buffered mobile phases, based on two organic solvents acetonitrile (ACN) and methanol (MeOH), were selectively combined to the HPLC separation systems RP-select B-ACN, RP-select B-MeOH, Cyan-MeOH, Diol-ACN, and Diol-MeOH. By measuring the retention factors of 45 neutral calibration compounds and calculating LFER descriptors of three cations in the HPLC systems, the system parameters, including an ionic z coefficient, were determined. Conversely, the LFER descriptors of 30 ionic liquid cations were determined, based on the parameters of five systems and their retention factors in the HPLC systems. The results showed that the type of head group, alkyl chain length and further substituents of the cation have a significant influence on the dipolarity/polarizability and the hydrogen-bonding acidity, and functionalized groups (hydroxyl, ether, and dimethylamino) lead to hydrogen-bonding basicity of the cation. The characterization of cationic LFER descriptors opens up the chance for a more quantitative understanding of molecular interaction potentials and physicochemical properties of ILs.
为了理解 30 种离子液体（ILs）阳离子的分子相互作用势能，应用了著名的线性自由能关系概念（LFER）。通过高效液相色谱（HPLC）测量，在计算中计算了超摩尔折射度和摩尔体积的 LFER 描述符，以及氢键酸度和碱性，以及 IL 阳离子的极化率/偶极矩。对于这项研究，选择了三种不同的色谱柱（RP-select B、Cyan 和 Diol）和缓冲流动相，基于两种有机溶剂乙腈（ACN）和甲醇（MeOH），分别与 HPLC 分离系统 RP-select B-ACN、RP-select B-MeOH、Cyan-MeOH、Diol-ACN 和 Diol-MeOH 相结合。通过测量 45 种中性校准化合物的保留因子并计算三种阳离子在 HPLC 系统中的 LFER 描述符，确定了系统参数，包括离子 z 系数。相反，基于五个系统的参数及其在 HPLC 系统中的保留因子，确定了 30 种离子液体阳离子的 LFER 描述符。结果表明，阳离子的头基类型、烷基链长和进一步的取代基对极性/偶极矩和氢键酸度有显著影响，官能团（羟基、醚基和二甲氨基）导致阳离子的氢键碱性。阳离子 LFER 描述符的表征为更定量地理解 ILs 的分子相互作用势能和物理化学性质提供了机会。
