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Character of Localization and Microenvironment of Solvatochromic Reichardt’s Betaine Dye in Sodium n-Dodecyl Sulfate and Cetyltrimethylammonium Bromide Micelles: Molecular Dynamics Simulation Study
Langmuir ( IF 3.7 ) Pub Date : 2017-08-14 00:00:00 , DOI: 10.1021/acs.langmuir.7b01737 Vladimir S. Farafonov 1 , Alexander V. Lebed 1 , Nikolay O. Mchedlov-Petrossyan 1
Langmuir ( IF 3.7 ) Pub Date : 2017-08-14 00:00:00 , DOI: 10.1021/acs.langmuir.7b01737 Vladimir S. Farafonov 1 , Alexander V. Lebed 1 , Nikolay O. Mchedlov-Petrossyan 1
Affiliation
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The problem of using surfactant micellar aqueous solutions as reaction media centers on estimating the polarity of the micellar pseudophase. The most popular approach is the utilization of solvatochromic dyes. Among the last, the strongest ones are the dipolar pyridinium N-phenolate dyes. The complication of such approach, however, consists in the nonuniform character of the environment of the indicator fixed in the micellar pseudophase. The aim of this study is to reveal the character of localization and orientation of the standard solvatochromic pyridinium N-phenolate dye, 4-(2,4,6-triphenylpyridinium-1-yl)-2,6-diphenylphenolate, the so-called Reichardt’s dye, within the micellar pseudophase of an anionic (sodium n-dodecyl sulfate, SDS) and cationic (cetyltrimethylammonium bromide, CTAB) surfactants using MD simulations. The locus and hydration of the dye are found to be dependent on the surfactant nature. New approaches are proposed to quantitatively describe the state of the dye within the pseudophase. The results confirm the experimental data, which indicate the higher polarity of the interfacial region in the case of the SDS micelles. Because this dye is also used as an interfacial acid–base probe, the corresponding study is simultaneously performed for its protonated, i.e., cationic form. The neutral and protonated forms of the dye are found to be localized and hydrated in a different way in both SDS and CTAB micelles. This should be taken into account when using the Reichardt’s dye as an acid–base indicator for estimating the electrical surface potential of micelles. The presented approach may be recommended to shed light upon the locus of other solvatochromic and acid–base indicators in micelles and micellar-like aggregates.
中文翻译：
正十二烷基硫酸钠和十六烷基三甲基溴化铵胶束中溶剂变色Reichardt甜菜碱染料的定位和微环境特征：分子动力学模拟研究
使用表面活性剂胶束水溶液作为反应介质的问题集中在估计胶束假相的极性上。最受欢迎的方法是利用溶剂变色染料。在最后一种中，最强的是偶极吡啶鎓N-酚盐染料。然而，这种方法的复杂性在于固定在胶束假相中的指示剂的环境的不均匀特征。这项研究的目的是揭示标准的溶剂化变色吡啶鎓N-酚盐染料4-（2,4,6-三苯基吡啶-1-基）-2,6-二苯酚盐的定位和取向特征Reichardt染料，在阴离子（钠n十二烷基硫酸盐，SDS）和阳离子（十六烷基三甲基溴化铵，CTAB）表面活性剂，采用MD模拟。发现染料的位置和水合取决于表面活性剂的性质。提出了新的方法来定量描述假相中染料的状态。结果证实了实验数据，表明在SDS胶束的情况下界面区域的极性较高。由于该染料还用作界面酸碱探针，因此同时对其质子化即阳离子形式进行了相应的研究。发现染料的中性和质子化形式在SDS和CTAB胶束中都以不同的方式定位和水合。当使用Reichardt染料作为酸碱指示剂估算胶束的表面电势时，应考虑到这一点。可以建议使用本文提出的方法来阐明胶束和胶束状聚集体中其他溶剂变色和酸碱指示剂的位置。
更新日期：2017-08-14
中文翻译：
正十二烷基硫酸钠和十六烷基三甲基溴化铵胶束中溶剂变色Reichardt甜菜碱染料的定位和微环境特征：分子动力学模拟研究
使用表面活性剂胶束水溶液作为反应介质的问题集中在估计胶束假相的极性上。最受欢迎的方法是利用溶剂变色染料。在最后一种中，最强的是偶极吡啶鎓N-酚盐染料。然而，这种方法的复杂性在于固定在胶束假相中的指示剂的环境的不均匀特征。这项研究的目的是揭示标准的溶剂化变色吡啶鎓N-酚盐染料4-（2,4,6-三苯基吡啶-1-基）-2,6-二苯酚盐的定位和取向特征Reichardt染料，在阴离子（钠n十二烷基硫酸盐，SDS）和阳离子（十六烷基三甲基溴化铵，CTAB）表面活性剂，采用MD模拟。发现染料的位置和水合取决于表面活性剂的性质。提出了新的方法来定量描述假相中染料的状态。结果证实了实验数据，表明在SDS胶束的情况下界面区域的极性较高。由于该染料还用作界面酸碱探针，因此同时对其质子化即阳离子形式进行了相应的研究。发现染料的中性和质子化形式在SDS和CTAB胶束中都以不同的方式定位和水合。当使用Reichardt染料作为酸碱指示剂估算胶束的表面电势时，应考虑到这一点。可以建议使用本文提出的方法来阐明胶束和胶束状聚集体中其他溶剂变色和酸碱指示剂的位置。
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