Wright E M, Diamond J M
Physiol Rev. 1977 Jan;57(1):109-56. doi: 10.1152/physrev.1977.57.1.109.
As background for appreciating the still-unsolved problems of monovalent anion selectivity, we summarize the facts and intepretations that seem reasonably well established. In section II we saw that specific effects of monovalent anions on biological and physical systems define qualitative patterns, in that only certain sequences of anion effects are observed. For example, the 4 halides can be permitted on paper as 4! = 24 sequences, yet only 5 of these sequences have been observed in nature as potency sequences. In addition, there are quantitative regularities in anion potency that permit the construction of so-called empirical selectivity isotherms (Figs. 4 and 13). That is, a given potency sequence is found to be associated with only a certain modest range of selectivity ratios. The sequences and isotherms apply to effects with a nonequilibrium component (e.g., permeability and conductance sequences) as well as to purely equilibrium effects. Since students of cation selectivity have had difficulty accepting this conclusion, we discuss the reasons why it is not as paradoxical as it at first seems. In sections III and IV we develop four theoretical models to account for the observed anion potency sequences as sequences of equilibrium binding energies. Two of these models involve calculation of electrostatic binding energies between anions and monopolar or dipolar cationic sites, assuming anions as well as sites to be rigid and nonpolarizable. The other two models use thermochemically measured binding energies between anions and thealkali cations or occasionally alkaline-earth cations, which in fact approximate rigid, nonpolarizable spheres. All four models consider the anion selectivity pattern of a given cationic site to be determined by anion differences in the balance between hydration energies and ion-site binding energies. Site differences in anion selectivity pattern are attributed to site differences in radius, charge, coordination number, or dipole length. These models succeed in predicting all five observed selectivity sequences of the halides. The models predict in addition the possible existence of two further halide sequences that arise from very strong sites and that have not yet been observed in nature. For polyatomic anions the predictions agree approximately but not completely with observations. Thyroidlike systems, which greatly prefer iodide over other halides,re interpreted as having the weakest sites. Site hydration is predicted to affect the magnitude but not the sequence of potency ratios. For the thyroidlike systems, observed potency ratios are smaller than would be expected if anions were completely dehydrated at biological sites.
作为理解单价阴离子选择性方面仍未解决问题的背景知识，我们总结了一些似乎已得到合理确证的事实和解释。在第二节中我们看到，单价阴离子对生物和物理系统的特定影响定义了定性模式，因为仅观察到某些阴离子效应序列。例如，4种卤化物在理论上可以有4! = 24种排列顺序，但在自然界中作为效价序列仅观察到其中5种。此外，阴离子效价存在定量规律，这使得可以构建所谓的经验选择性等温线（图4和图13）。也就是说，发现给定的效价序列仅与一定适度范围的选择性比率相关。这些序列和等温线适用于具有非平衡成分的效应（例如，渗透率和电导率序列）以及纯平衡效应。由于阳离子选择性方面的研究者难以接受这一结论，我们讨论了为何它并不像乍看起来那样自相矛盾的原因。在第三节和第四节中，我们开发了四种理论模型，将观察到的阴离子效价序列解释为平衡结合能序列。其中两种模型涉及计算阴离子与单极或偶极阳离子位点之间的静电结合能，假设阴离子和位点都是刚性且不可极化的。另外两种模型使用热化学测量的阴离子与碱金属阳离子或偶尔与碱土金属阳离子之间的结合能，这些阳离子实际上近似于刚性、不可极化的球体。所有四种模型都认为给定阳离子位点的阴离子选择性模式由水合能与离子 - 位点结合能之间平衡的阴离子差异决定。位点在阴离子选择性模式上的差异归因于半径、电荷、配位数或偶极长度的位点差异。这些模型成功预测了卤化物所有5种观察到的选择性序列。这些模型还预测可能存在另外两种由非常强的位点产生的卤化物序列，而在自然界中尚未观察到。对于多原子阴离子，预测结果与观察结果大致相符但并不完全一致。甲状腺样系统极大地偏好碘化物而非其他卤化物，被重新解释为具有最弱的位点。预计位点水合会影响效价比的大小，但不会影响其序列。对于甲状腺样系统，观察到的效价比小于如果阴离子在生物位点完全脱水时预期的效价比。
