A relative study on the micellization behavior of 12–2–12 Gemini surfactant with lactose and maltodextrin in aqueous medium: Spectroscopic and conductometric analysis

Light and pH responsive catanionic vesicles based on a chalcone/flavylium photoswitch for smart drug delivery: From molecular design to the controlled release of doxorubicin

Spatially and temporally localized delivery is a promising strategy to circumvent adverse effects of traditional drug therapy such as drug toxicity and prolonged treatments. Stimuli-responsive colloidal nanocarriers can be crucial to attain such goals. Here, we develop a delivery system based on dual light and pH responsive vesicles having a cationic bis-quat gemini surfactant, 12-2-12, and a negatively charged amphiphilic chalcone, C4SCh. The premise is to exploit the chalcone/flavylium interconversion to elicit a morphological change of the vesicles leading to the controlled release of an encapsulated drug. First, the phase behavior of the catanionic system is studied and the desirable composition yielding stable unilamellar vesicles identified and selected for further studies. The solutions containing vesicles (Dh ≈ 200 nm, ζ-potential ≈ 80 mV) are in-depth characterized by light microscopy, cryo-transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS) and surface tension measurements. Upon subjecting the vesicles to UV irradiation (λ = 365 nm) at near neutral pH (≈ 6.0), no morphological effects are observed, yet when irradiation is coupled with pH = 3.0, the majority of the vesicles are disrupted into bilayer fragments. The anticancer drug doxorubicin (DOX) is successfully entrapped in the non-irradiated vesicles, yielding an encapsulation efficiency of ≈ 25% and a loading capacity of ≈ 3%. The release profile of the drug-loaded vesicles is then studied in vitro in four conditions: i) no stimuli (pH = 6.0); ii) irradiation, pH = 6.0; iii) no irradiation and adjusted pH = 3.0; iv) irradiation and adjusted pH = 3.0 Crucially, irradiation at pH = 3.0 leads to a sustained release of DOX to ca. 80% (within 4 h), whereas cases i) and ii) lead to only ≈ 25 % release and case iii) to 50% release but precipitation of the vesicles. Thus, our initial hypothesis is confirmed: we present a proof of concept delivery system where light and pH act as inputs of an AND logic gate mechanism for the controlled release of a relevant biomedical drug (output). This may prove useful if the irradiated nanocarriers meet acidified physiological environments such as tumors sites, endosomes or lysosomes.

Study of interactions of the cationic 12–2–12 Gemini surfactant with saccharides in aqueous solution: volumetric, compressibility and viscometric analysis

In the present study, the interaction behaviour of 12–2–12 Gemini surfactant in aqueous saccharide solutions (lactose and maltodextrin solutions) is investigated using density, sound velocity and viscosity measurements. The density and sound velocity data were used to determine the volume and compressibility parameters. The effects of temperature and concentration/strength of the solutions on the interaction behaviour were analysed by conductivity studies over a wide temperature (293.15–313.15) K and concentration range of the saccharides as well as of the surfactant. It was found that predominantly hydrophobic interactions together with ionic/hydrophilic interactions between 12–2–12 Gemini surfactant and the saccharides maltodextrin and lactose play a role. In addition, the structural changes in the 12–2–12 Gemini solutions induced by lactose and maltodextrin were investigated by viscosity measurements. The results confirm the observations from the volume and compressibility studies. The study of the different hydrophobic/hydrophilic interactions in the Gemini surfactant-sacharide-water mixtures are very helpful to understand the structural behaviour of Gemini surfactants in the view of their biological significance.

Experimental and Molecular Dynamics Simulation Study on the Effects of the Carbon Chain Length of Gemini Surfactants on the Inhibition of the Acid-Rock Reaction Rate

A series of gemini surfactants were synthesized to examine their adsorption properties. The properties of gemini surfactants, including critical micelle concentration, electrostatic potential distributions, charge, occupied volume, lowest unoccupied molecular orbital (LUMO), and highest occupied molecular orbital (HOMO), were evaluated using conductivity and density functional theory (DFT) calculations. The calculation results indicated that the electrostatic potential distributions were similar among the four gemini surfactants. Moreover, surfactants with longer carbon chains are more likely to be oblique on the rock surface according to the energy gap between the HOMO of the surfactants and the LUMO of the calcite surface. Experimental tests and molecular dynamics (MD) simulations were conducted to analyze the calcite-surfactant interactions. Combined with the free energy (ΔG) based on the contact angle and adsorption energy (E) based on MD simulation, the adsorption ability increases as the carbon chain length decreases. MD simulation is used to understand the form of surfactant molecules on the calcite at an atomic scale at different times. An obvious aggregation of gemini surfactants was found with an increase in the carbon chain length, which reduces the adsorption density and covered area of the surfactant. The adsorption behavior of the gemini surfactant is beneficial for isolating H⁺ transfer and retarding the acid reaction with the rock. The retarding ability and etching morphology were studied by acid etching. The acid-rock reaction rate showed that 12-4-12 had the best inhibition performance. Meanwhile, the uneven surface pattern following 12-4-12 etching is beneficial for maintaining the acid fracturing conductivity.

Surface adsorption and thermodynamic properties of mixed system of ionic liquid surfactants with cetyltrimethyl ammonium bromide

The effects of temperature and concentration of CTAB added to imidazolium-based ionic liquids (CnmimBr, n = 10, 12, 16) were investigated, and surface active parameters and aggregation of these surfactants were explored by surface tension and conductivity measurements.