Abstract
Reversible transition from micelles to vesicles by regulating pH were realized by gemini amino-acid surfactants N,N⿿-dialkyl-N,N⿿-diacetate ethylenediamine. Measurement results of ζ-potential at different pH and DLS at varying solvents revealed that the protonation between H+ and double NCH2COO⿿ groups (generating NH+CH2COO⿿), expressed as pKa1 and pKa2, is the key driving force to control the aggregation behaviors of gemini surfactant molecule. Effect of pH on the bilayer structure was studied in detail by using steady-state fluorescence spectroscopy of hydrophobic pyrene and Coumarin 153 (C153) respectively and fluorescence resonance energy transfer (FRET) from C153 to Rhodamine 6G (R6G). Various pH-regulated and pH-reversible self-assemblies were obtained in one surfactant system. Vitamin D3 was encapsulated in vesicle bilayers to form nano-VD3-capsules as VD3 supplement agent for health care products. By using the electrostatic attraction between Ca2+ and double ⿿COO⿿ groups, nano-VD3-capsules with Ca2+ coated outermost layers were prepared as a formulation for VD3 and calcium co-supplement agent. DLS and TEM were performed to check stability and morphology of the nano-capsules. It is concluded that the pH-regulated gemini amino-acid surfactants can be used to construct colloidal systems for delivering hydrophobic drugs or nutritions without lipids at human physiological pH level.
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