Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK.
J Chromatogr A. 2013 Jul 12;1298:44-9. doi: 10.1016/j.chroma.2013.05.007. Epub 2013 May 10.
Retention data on an immobilised artificial membrane have been taken from the work of Li et al. and from Liu et al., and have been correlated with a set of descriptors that includes descriptors for ionized species, that is anions from deprotonated acids and cations from protonated bases. Log k(IAM) values can be predicted for acids or bases that are partially ionized at the experimental pH and log k(IAM) values for acids and bases can be predicted as a function of the fraction present as the ionized species, equivalent to prediction as a function of pH. It is shown that anions reduce the value of log k(IAM) by about 1.1 log units but that cations have almost no effect by comparison to the neutral species. By comparison to non-polar solvents, carboxylate anions and protonated base cations are considerably stabilized by both water and the IAM phase to about 6-8 log units and so the rather small influence of anions (-1.1 log unit) and cations (-0.1 log unit) on log k(IAM) is due to substantial cancellation of these stabilization effects. Indeed, the effect of change of phase from water to IAM on the neutral species is at least as large as the effect of change of phase on the ionic species.
已从 Li 等人和 Liu 等人的工作中获取了固定化人工膜上的保留数据，并将其与一组描述符相关联，这些描述符包括用于离子化物质的描述符，即来自去质子酸的阴离子和来自质子化碱基的阳离子。对于在实验 pH 下部分离子化的酸或碱，可以预测其 log k（IAM）值，并且可以将酸和碱的 log k（IAM）值预测为作为离子化物质存在的分数的函数，相当于预测 pH 的函数。结果表明，与中性物质相比，阴离子使 log k（IAM）值降低约 1.1 个对数单位，但阳离子几乎没有影响。与非极性溶剂相比，羧酸阴离子和质子化碱基阳离子在水相和 IAM 相中都被显著稳定，大约为 6-8 个对数单位，因此阴离子（-1.1 个对数单位）和阳离子（-0.1 个对数单位）对 log k（IAM）的影响很小，这是由于这些稳定作用的大量抵消。实际上，从水相到 IAM 相的变化对中性物质的影响至少与相变化对离子物质的影响一样大。
