Eliasquevici Rafaela, Bernardino Kalil
Laboratório de Química Computacional, Departamento de Química, Universidade Federal de São Carlos, Rod. Washington Luiz S/N, São Carlos, 13565-905, Brazil.
J Mol Model. 2024 Mar 11;30(4):101. doi: 10.1007/s00894-024-05897-1.
Choline-based surfactants are interesting both from the practical point of view to obtaining environmental-friendly surfactants as well as from the theoretical side since the interactions between the choline and surfactants can help to understand self-assembly phenomena in deep eutectic solvents. Although no significant change was noticed in the micelle size and shape due to the exchange of the sodium counter-ion by choline in our simulations, the adsorption of the choline cation over the micelle surface is stronger than the adsorption of the sodium, which leads to a reduction of the exposed surface area of the micelle and remarkable effects over the electrostatic potential. The choline neutralizes the surface charge of the surfactant better than sodium; however, this is partially compensated by a stronger water orientation around the SDS micelle. The balance between the contributions from the surfactant, the counter-ion, and water to the electrostatic potential leads to a complex pattern with alternate regions of positive and negative potential at the micelle/water interface which can be important to the incorporation of other charged species at the micelle surface as well as for the interaction between micelles in solution.
To evaluate the effects of the counter-ion substitution, micelles of sodium dodecyl sulfate (SDS) and choline dodecyl sulfate (ChDS) were studied and compared by means of molecular dynamics simulations in aqueous solution. In both cases, the simulations started from pre-assembled micelles with 60 dodecyl sulfate ions and 240-ns simulations were performed at NPT ensemble at T = 323.15 K and P = 1 bar using the Gromacs software with the OPLS-AA force field to describe dodecyl sulfate and choline, Åqvist parameters for sodium, and SPC model for water molecules.
基于胆碱的表面活性剂从实际角度来看对于获得环境友好型表面活性剂很有趣，从理论方面来看也很有趣，因为胆碱与表面活性剂之间的相互作用有助于理解深共熔溶剂中的自组装现象。尽管在我们的模拟中，由于胆碱取代了钠离子，胶束的大小和形状没有明显变化，但胆碱阳离子在胶束表面的吸附比钠离子更强，这导致胶束暴露表面积减小，并对静电势产生显著影响。胆碱比钠能更好地中和表面活性剂的表面电荷；然而，这被SDS胶束周围更强的水取向部分抵消。表面活性剂、抗衡离子和水对静电势的贡献之间的平衡导致在胶束/水界面处出现正负电位交替区域的复杂模式，这对于胶束表面其他带电物种的掺入以及溶液中胶束之间的相互作用可能很重要。
为了评估抗衡离子取代的影响，通过水溶液中的分子动力学模拟研究并比较了十二烷基硫酸钠（SDS）和十二烷基硫酸胆碱（ChDS）的胶束。在这两种情况下，模拟均从含有60个十二烷基硫酸根离子的预组装胶束开始，并使用Gromacs软件和OPLS - AA力场在NPT系综下于T = 323.15 K和P = 1 bar条件下进行240 ns的模拟，以描述十二烷基硫酸根和胆碱，使用Åqvist参数描述钠，使用SPC模型描述水分子。
