Sarkar Yeasmin, Das Sanju, Ray Ambarish, Jewrajka Suresh K, Hirota Shun, Parui Partha Pratim
Department of Chemistry, Jadavpur University, Kolkata 700032, India.
Department of Chemistry, Maulana Azad College, Kolkata 700013, India.
Analyst. 2016 Mar 21;141(6):2030-9. doi: 10.1039/c5an02128f.
A simple pH-sensing method for cationic micelle and vesicle interfaces is introduced, utilizing a Schiff-base molecule, 2-((4H-1,2,4-triazol-4-ylimino)methyl)-6-(hydroxymethyl)-4-methylphenol (AH). AH containing a phenolic moiety was obtained by the reaction between 4-amino-4H-1,2,4-triazole containing polar O- and N-centres with opposite polarity to the cationic interface and 2-hydroxy-3-(hydroxymethyl)-5-methylbenzaldehyde. The acid/base equilibrium of AH was investigated at the interfaces of cetrimonium bromide (CTAB) micelles, tri-block-copolymeric micelles (TBPs) and large unilamellar vesicles (LUVs) of different lipid compositions using steady state UV-Vis absorption spectroscopy. AH interacted strongly with the micelle and vesicle interfaces, according to the binding studies with LUV. A larger amount of AH proton dissociation was observed when localized at the interface of micelles and vesicles compared to that in the bulk phase, indicating that the pH values at the cationic interfaces are higher than in the bulk phase. The pH values were about 2.2 and 1.6 units higher at the CTAB and TBP micelle interfaces, respectively, than the bulk pH. The pH variation decreased from 2.4 to 1.5 units by increasing the neutral 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipid content from 0 to 50% in the cationic dimethyldioctadecylammonium (DDAB) LUV, indicating that the interfacial positive charges are responsible for the higher interfacial pH. Detailed structural and absorption characteristics of neutral AH and its anionic A(-) forms were investigated by fluorescence spectroscopic measurements and DFT based theoretical calculations. The present simple pH detection method may be applied to various biological micelle and vesicle interfaces.
介绍了一种用于阳离子胶束和囊泡界面的简单pH传感方法，该方法利用了一种席夫碱分子，即2-((4H-1,2,4-三唑-4-基亚氨基)甲基)-6-(羟甲基)-4-甲基苯酚(AH)。含有酚基部分的AH是通过含极性O和N中心且与阳离子界面极性相反的4-氨基-4H-1,2,4-三唑与2-羟基-3-(羟甲基)-5-甲基苯甲醛之间的反应得到的。使用稳态紫外-可见吸收光谱法，在不同脂质组成的十六烷基三甲基溴化铵(CTAB)胶束、三嵌段共聚物胶束(TBPs)和大单层囊泡(LUVs)的界面上研究了AH的酸碱平衡。根据与LUV的结合研究，AH与胶束和囊泡界面强烈相互作用。与本体相相比，当AH位于胶束和囊泡界面时，观察到更多的质子解离，这表明阳离子界面处的pH值高于本体相。CTAB和TBP胶束界面处的pH值分别比本体pH值高约2.2和1.6个单位。通过将阳离子二甲基二十八烷基铵(DDAB)LUV中中性的1,2-二油酰基-sn-甘油-3-磷酸胆碱(DOPC)脂质含量从0%增加到50%，pH变化从2.4个单位降至1.5个单位，这表明界面正电荷是导致界面pH值较高的原因。通过荧光光谱测量和基于密度泛函理论(DFT)的理论计算，研究了中性AH及其阴离子A(-)形式的详细结构和吸收特性。目前这种简单的pH检测方法可应用于各种生物胶束和囊泡界面。
