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首页> 外文期刊>Biophysical Chemistry: An International Journal Devoted to the Physical Chemistry of Biological Phenomena >Thermodynamics of the hydrophobic effect. I. Coupling of aggregation and pK(a) shifts in solutions of aliphatic amines.
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Thermodynamics of the hydrophobic effect. I. Coupling of aggregation and pK(a) shifts in solutions of aliphatic amines.

机译：疏水作用的热力学。 I.脂肪胺溶液中聚集和pK（a）位移的耦合。

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摘要

Long aliphatic hydrocarbon chains aggregate in aqueous solution due to the hydrophobic effect, forming structures such as micelles and membranes, while amino groups titrate at basic pH. These two biologically important behaviors are linked in alkylamines, in which the pK(a) of the amino group is shifted downward by aggregation. In this paper we study the thermodynamics of these coupled processes, following aggregation by observing alkylamine pH titration behavior. The magnitude of the shift depended on the aliphatic chain length and on the concentration of alkylamine: longer chains and higher concentrations lowered the pK(a) to a greater extent. Gibbs free energies of protonation and aggregation were calculated from the pK(a) shifts. Enthalpies, entropies, and heat capacities were estimated by van't Hoff analysis from the pK(a) shift dependencies on temperature. However, the results were less precise than the calorimetrically measured values, as described in the following article. A model to calculate titration curves, pK(a) shifts, and aggregation of uncharged alkylamines as a function of aliphatic chain length, concentration, and temperature is presented.
机译：较长的脂族烃链由于疏水作用而在水溶液中聚集，形成胶束和膜等结构，而氨基在碱性pH下滴定。这两个生物学上重要的行为是在烷基胺中相连的，其中氨基的pK（a）通过聚集向下移动。在本文中，我们通过观察烷基胺的pH滴定行为，研究了这些偶联过程的热力学，然后进行了聚集。位移的大小取决于脂肪族链的长度和烷基胺的浓度：较长的链和较高的浓度会在更大程度上降低pK（a）。质子化和聚集的吉布斯自由能由pK（a）位移计算得出。焓，熵和热容量通过van't Hoff分析从pK（a）随温度变化的依赖性进行估算。但是，结果不如量热测量值精确，如下文所述。提出了一个计算滴定曲线，pK（a）位移和不带电荷的烷基胺的聚集量的模型，该模型是脂肪族链长，浓度和温度的函数。

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