Cationic gemini surfactant as a dual linker for a cholic acid-modified polysaccharide in aqueous solution: thermodynamics of interaction and phase behavior

Coagulation of Hydrophobic Ionic Associates of Cetyltrimethylammonium Bromide and Carrageenan

In aqueous solutions, cetyltrimethylammonium cations bind to carrageenan polyanions, and the resulting ionic associates form macroscopic aggregates due to hydrophobic interaction. At certain ratios of cetyltrimethylammonium to carrageenan, the resulting colloidal particles auto-flocculate. According to visual observations, the ratio ranges from 1 to 3 mmol/g; otherwise the suspensions are stable. By measuring the sedimentation rate and particle size distribution, the most extensive flocculation was found to be from 1.7 to 2.3 mmol/g. The ratio corresponding to the fastest auto-flocculation was precisely determined by titrating the reagents with small increments and recording the turbidity. The turbidimetric titration plots contain distinct break points corresponding to the most extensive flocculation. These break points occur at the same ratio of carrageenan to cetyltrimethylammonium over a wide range of reagent concentrations. The precise values of the critical ratio were found to be 1.78 and 1.53 mmol/g, respectively, during the titration of cetyltrimethylammonium with carrageenan and vice versa. The number of anionic sulfate groups in carrageenan was measured by ICP OES and found to be 1.35 mmol/g. This value is consistent with the critical ratio of the auto-flocculation.

Activation and Inhibition of Isomerization of a Cationic Azobenzene Surfactant in the Large Void Space of Polyglycerol Dendron Micelles

Owing to the unique geometric structure of dendritic amphiphiles with voluminous dendrons, their micelles can harbor a large void space, which provides a new research focus and approach for micellar functionalization. In this work, we used the void space to construct a UV responsive micelle system of the mixed dendritic amphiphile (C₁₂-(G3)₂) and cationic azobenzene surfactant (C4AzoTAB). The synthesized C₁₂-(G3)₂ that possesses double third generation polyglycerol (PG) dendrons and a single alkyl chain is expected to highlight the large void space within the inside of the micelles. Thus, the aims of this work are to achieve the isomerization of C4AzoTAB in situ and to deeply understand the intermolecular interaction in the mixed micelles. The effect of the large void room with a wall decorated with the ether oxygen atoms on the isomerization of C4AzoTAB was studied by isomerization kinetics, conductivity measurements, isothermal titration calorimetry (ITC), and ¹H NMR and 2D NOESY spectroscopies. The isomerization behavior of C4AzoTAB in C₁₂-(G3)₂ micelles was presented in terms of its kinetic constant, counterionic association, interaction enthalpy, and position and orientation of C4AzoTAB. The results of NMR and conductivity show that the quaternary ammonium group of C4AzoTAB situates on the surface of the mixed micelles with C₁₂-(G3)₂ both before and after UV-irradiation, while the position of azobenzene group in C₁₂-(G3)₂ micelles depends on its conformation. The C₁₂-(G3)₂ micelles can inhibit the UV response of the trans-isomer and activate the thermal relaxation of the cis-isomer, which has a potential application in the field of light-controlled smart nanocarriers.