THE LOCATION OF ELECTROSTATIC CHARGES IN KIRKWOODS MODEL OF ORGANIC IONS
THE LOCATION OF ELECTROSTATIC CHARGES IN KIRKWOODS MODEL OF ORGANIC IONS
复制标题
DOI：
10.1021/ja01577a003
复制
发表时间：
1957-01-01
影响因子：
15
通讯作者：
TANFORD, C
中科院分区：
文献类型：
--
作者：
TANFORD, C
1934年，Kirkwood根据一个模型处理了有机离子上静电电荷之间的相互作用，该模型将有机离子形式化地表示为溶剂连续介质中的一个低介电常数的空穴。本文指出，根据该模型确定相互作用能的一个关键参数是腔内放置电荷或偶极子的深度d。为了解释实验观察到的相互作用能，如适当的有机酸的离解常数(Kirkwood-Westhimer理论)所反映的那样，对于离散电荷，d有必要被赋予接近1.0A的值，约为1.5°。对于偶极子来说。这一结果与早先在柯克伍德模型的扩展中发现的蛋白质分子上的电荷相互作用是一致的。根据这一发现，一种经验方法允许直接计算相互作用能，从而计算因存在带电取代基或偶极取代基而不同的相关酸之间的pk差。1934年Kirkwood 2提出的模型已经相当成功地处理了有机分子在溶液中的性质，这取决于它们上面的静电电荷之间的相互作用。在这个模型中，有机离子被视为一个低介电常数(或通常被放置在等于2的位置)的空腔，嵌入在溶剂中，被视为具有宏观介电常数的连续体。利用这个模型，人们可以证明，由距离R隔开的一对电荷q和q之间的相互作用的自由能可以表示为
The interaction between electrostatic charges on organic ions was treated by Kirkwood in 1934 in terms of a model which formally represents the organic ion as a cavity of low dielectric constant in a solvent continuum. This paper shows that a crucial parameter in determining interaction energies on the basis of this model is the depth, d, within the cavity, at which charges or dipoles are placed. To account for experimentally observed interaction energies, as reflected in the dissociation constants of appropriate organic acids (Kirkwood-Westheimer theory), it is necessary that d be assigned a value close to 1.0 A. for discrete charges and about 1.5 Á. for dipoles. This result is in agreement with that found earlier in an extension of the Kirkwood modelto charge interactions on protein molecules. An empirical procedure, based on this finding, permits the direct calculation of interaction energies, and, hence, of pK differences between related acids differingby the presence of charged or dipolar substituents.The properties of organic molecules in solution which depend on the interaction between electrostatic charges uponthem havebeen treated with considerable success by the model proposed by Kirkwood2 in 1934. In this model the organic ion is treated as a cavity of low dielectric constant (or-dinarily placed equal to 2), embedded in the sol-vent, which is treated as a continuum with its mac-roscopic dielectric constant. Using this model, one can show3 that the free energy of interaction between a pair of charges, qi and q-¡, separated by a distance R, can be expressed as