The use of surfactants in polymerization reactions is particularly important, mainly in emulsion polymerizations. Further, micelles from biocompatible surfactants find use in pharmaceutical dosage forms. This paper reviews recent developments in the synthesis of novel gemini and bicephalous surfactants, micelle formation, and their applications in polymer and nanoparticle synthesis, oil recovery, catalysis, corrosion, protein binding, and biomedical area, particularly in drug delivery.

Nowadays, the increase in bacteria resistant to multiple antibiotics has become a real threat to the human health, forcing researchers to develop new strategies. Silver nanoparticles (AgNPs) may be a viable solution to this problem. The green synthesis of AgNPs is considered a green, ecological and low-priced process that provides small and biocompatible nanostructures with antimicrobial activity with a potential application in medicine. In this work, pecan nut shell extracts were analyzed in order to determine their viability for the production of AgNPs. These NPs were synthesized using an extract rich in bioactive molecules, varying the reaction time and silver nitrate (AgNO₃) concentration. AgNPs production was confirmed by FT-IR, UV-Vis and EDX spectroscopy, while their morphology and size were determined by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The antibacterial activity of AgNPs was evaluated by the agar diffusion method against Salmonella typhi, Staphylococcus aureus and Proteus mirabilis. The results showed that it is possible to obtain nanoparticles from an extract rich in antioxidant molecules with a size between 39.9 and 98.3 nm with a semi-spherical morphology. In addition, it was shown that the reaction time and the concentration of the precursor influence the final nanoparticles size. Antimicrobial tests showed that there is greater antimicrobial inhibition against Gram-negative than Gram-positive microorganisms, obtaining inhibition zone from 0.67 to 5.67 mm.

Oil-in-water microemulsions (o/w MEs) were coated with chitosan to obtain new curcumin delivery systems. First, ternary phase diagrams were constructed using mixtures of Tween 20, Tween 80, ethanol, and monopropyleneglycol (MPG) to determine the macroscopic phase region of MEs and their capacity to incorporate clove oil. Particularly, MEs with size less than 20 nm could be formed using low amount of the surfactant Tween 20. The prepared MEs were subjected to diverse stability tests and characterized by dynamic light scattering (DLS), zeta potential (Z potential), conductivity, pH, and transmission electron microscopy (TEM). Stable, spherical uncoated and polymer-coated MEs were obtained with low droplet size (Dp), <50 nm, for the water/Tween 20/clove oil/ and water/Tween80/MPG/clove oil systems using a chitosan solution of 1 mg/mL. For all polymer-coated MEs, an increase of Z potential (17–54 mV) was observed due to the presence of chitosan. The loading with curcumin did not affect the Dp of MEs (e.g., for ME with Tween 20, Dp unloaded 12.35 ± 1.86 nm and Dp loaded 11.13 ± 0.32 nm) but Z potential and conductivity values were increased (typically for coated ME prepared with Tween 20 17.00 ± 0.36 mV ≤Z potential ≤41.5 mV, 162.20 ± 8.95 μS/cm ≤ conductivity ≤183.8 ± 0.56 μS/cm). Drug delivery studies for the chitosan-coated MEs were carried out at different pH (7.4, 6.5, and 5.8). The release of curcumin from the chitosan-coated MEs, formed with Tween 20, showed a dependence of the pH with a maximum release at the acidic pH of 5.8 (58%). The release of curcumin from all MEs was best described by the Korsmeyer- Peppas model with a Fickian transport mechanism. Graphical Abstract