pH Changes in the Micelle–Water Interface of Surface-Active Ionic Liquids Dictate the Stability of Encapsulated Curcumin: An Insight Through a Unique Interfacial Reaction between Arenediazonium Ions and t-Butyl Hydroquinone

Abstract

The chemical kinetic (CK) method, which involves the reduction of 4-hexadecylbenzenediazonium ions (16-ArN 2 + ) by antioxidants (in the present case, TBHQ) occurring exclusively at the interface of the association colloids, was employed to establish the changes in the chemical reactivity of anionic surface-active ionic liquids (SAILs) as a function of the concentration and the composition in their mixed states. We used sodium dodecyl sulfate and different SAILs based on the dodecylsulfate surfactant containing 1-alkyl-3-methylimidazolium cations as counterions having a varying alkyl chain length of 4 (bmim), 8 (omim), and 12 (ddmim) carbon atoms. The structural transitions of aggregates of the SAILs from the micellar to vesicular form were observed as a function of concentration in single surfactant systems and as a function of composition in mixed surfactant systems. Results of the reduction kinetics of 16-ArN 2 + at the interface of such aggregates, which depends on the acid/base equilibria at the interface, gave an insight into the changes in the interfacial H + ions with the change in the hydrophobicity of the counterions of SAILs and the morphological changes from micelles to vesicles as a function of concentration or composition. These changes in the interfacial pH correlate very well with the stability of curcumin within these self-assemblies, which exclusively depends on the pH of the medium and highlights the importance of the results obtained from the CK method in selecting the appropriate medium/conditions for the stabilization of the bioactive molecules.

Urea Disrupts the AOT Reverse Micelle Structure at Low Temperatures

“…At high and low pH values, the concerted H-atom exchange mechanism prevalent near neutral pH changes to a charge-transfer mechanism, which can be orders of magnitude faster . Previous studies have hypothesized that if the pH of the aqueous phase in AOT reverse micelles diverges from neutral, then the interfacial region can be significantly more acidic or basic than the water core . If urea affects the intramicellar pH and it resides at the interface, we might expect faster exchange to occur.…”

“…46 Previous studies have hypothesized that if the pH of the aqueous phase in AOT reverse micelles diverges from neutral, then the interfacial region can be significantly more acidic or basic than the water core. 47 If urea affects the intramicellar pH and it resides at the interface, we might expect faster exchange to occur. However, when the charge-transfer mechanism is active, it also affects the NMR spectrum, pulling urea and water peaks closer to each other and eventually merging these peaks.…”

Improvement of Oxidative Stability of Fish Oil-in-Water Emulsions through Partitioning of Sesamol at the Interface

“…However, there is no method to determine the interfacial distribution of antioxidants by directly measuring the content of antioxidants in each phase. The relatively scientific approach is based on the reaction between the 4-hexadecyl diazenium ion (16-ArN 2 + (BF 4 − )) molecular probe and the antioxidant, and the kinetic equations are used to calculate the partition constants and interfacial molar values of the antioxidant between different interfaces in the emulsion [ 57 , 58 , 59 , 60 ]. In the future, we will validate the accuracy of the centrifugation method using molecular probe methods.…”

Counterion Association of Ionic Drugs with Sodium Tetradecyl Sulfate in the Aqueous Medium

“…Numerous drug–surfactant assemblies have been researched recently because of the vital significance of the pharmacological and therapeutic interactions between the drugs and the surfactant. − Combining a drug and a surfactant shows interaction and provides greater features than the drug or surfactant functioning independently. − Ionic medications have grown in importance recently as organic counterions or additions to enhance the interfacial and micellization properties of a charged surfactant and also to boost the concentration of pharmaceuticals that are only partially dissolved in the aqueous medium. , Whenever there are extra ingredients such as electrolytes, the critical micelle concentration (CMC) of the surfactants decreases. , Since they decrease their efficacy surface area per headgroup by limiting undesirable contact between each headgroup, additives, remarkably, make it simpler to induce an appearance change in surfactant micelles. The total amount of counterions that are physically associated with a micelle is compared to the amount of surfactant molecules (aggregate number) that reside in an ionic micelle to determine the counterion binding constant. − The most often used acceptable methods for estimating the counterion binding constant are the Corrin–Harkins (CH), modified CH approach, and the slope–ratio of conductance method …”