Adsorption, micellization and antimicrobial activity of formyl-containing cationic surfactant in diluted aqueous solutions

Recyclable Magnetic Iron Immobilized onto Chitosan with Bridging Cu Ion for the Enhanced Adsorption of Methyl Orange

Chitosan (CS) is a natural and low-cost adsorbent for capturing metal ions and organic compounds. However, the high solubility of CS in acidic solution would make it difficult to recycle the adsorbent from the liquid phase. In this study, the CS/Fe₃O₄ was prepared via Fe₃O₄ nanoparticles immobilized onto a CS surface, and the DCS/Fe₃O₄-Cu was further fabricated after surface modification and the adsorption of Cu ions. The meticulously tailored material displayed the sub-micron size of an agglomerated structure with numerous magnetic Fe₃O₄ nanoparticles. During the adsorption of methyl orange (MO), the DCS/Fe₃O₄-Cu delivered a superior removal efficiency of 96.4% at 40 min, which is more than twice the removal efficiency of 38.7% for pristine CS/Fe₃O₄. At an initial MO concentration of 100 mg L^-1, the DCS/Fe₃O₄-Cu exhibited the maximum adsorption capacity of 144.60 mg g^-1. The experimental data were well explained by the pseudo-second-order model and Langmuir isotherm, suggesting the dominant monolayer adsorption. The composite adsorbent still maintained a large removal rate of 93.5% after five regeneration cycles. This work develops an effective strategy to simultaneously achieve high adsorption performance and convenient recyclability for wastewater treatment.

Synthesis, Characterization and Application of Novel Cationic Surfactants as Antibacterial Agents

It is of great necessity to develop new antimicrobial agents to overcome the accelerated increment in drug-resistant bacteria. The main aim of this work is to manufacture two cationic surfactants, QHETA-9 and QHETA-14, based on quaternary hexamethylenetetramine with long alkyl chains (C-9 and C-14) by simple one-step alkylation reaction. These surfactants were characterized by analytical and statistical data, including FTIR, 1H NMR, 13C NMR and DLS. The antibacterial activities of QHETA-9 and QHETA-14 against some pathogenic bacterial strains were tested using agar disk diffusion method. The results exhibited that QHETA-14 has higher antibacterial activity than that of QHETA-9. It displayed inhibitory zone values for Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA) and Enterococcus faecalis, as Gram-positive bacteria, of 22.7, 21.5 and 25.9 mm, respectively, at 200 μg/disk. Meanwhile, it recorded inhibition zone values of 17.5, 25.2 and 23.8 mm for Escherichia coli, Agrobacterium tumefaciens and Erwinia carotovora, respectively, at 200 μg/disk. As a result, the current investigation verified that the antibacterial properties of QHETA-14 were greater than those of QHETA-9 due to the increase in the length of the alkyl chain. It is clear that QHETA-14 has the potential to be used as an antibacterial agent against bacteria that cause nosocomial infections and food poisoning diseases.

Design of Stimuli-Responsive Dynamic Covalent Delivery Systems for Volatile Compounds (Part 2): Fragrance-Releasing Cleavable Surfactants in Functional Perfumery Applications

Amphiphilic imines prepared by condensation of a hydrophobic fragrance aldehyde with a hydrophilic amine derived from a poly(propylene oxide) and poly(ethylene oxide) diblock copolymer were investigated as cleavable surfactant profragrances in applications of functional perfumery. In water, the cleavable surfactants assemble into micelles that allow solubilization of perfume molecules that are not covalently attached to the surfactant. Dynamic headspace analysis on a glass surface showed that solubilized perfume molecules evaporated in a similar manner in the presence of the cleavable surfactant as compared with a non-cleavable reference surfactant. Under application conditions, the cleavable surfactant imine hydrolysed to release the covalently linked fragrance aldehyde. The profragrances were stable during storage in aqueous media, and upon dilution showed a blooming effect for the hydrolytical fragrance release and a more balanced performance of a solubilized perfume by retaining the more volatile fragrances and boosting the evaporation of the less volatile fragrances.

Oxidation-Induced Breakage of the Imine Bond and Aggregate Transition in a Se-Containing Dynamic Covalent Surfactant

Controlling the dynamic imine bonds upon a novel trigger except for pH and temperature is still a significant challenge. Here, a Se-containing imine-based dynamic covalent surfactant (HOBAB-BSeEA) was developed for the first time by mixing two precursors in situ: an asymmetric double-chain cationic surfactant bearing a formyl group at the terminal of one hydrophobic tail and a Se-containing amine (2-(benzylselanyl)ethan-1-amine) in order to confirm the effect of redox on the imine bonds. The imine bond in HOBAB-BSeEA can be regulated not only upon changing the pH as well as other common imine-based surfactants but also by oxidation. The conversion efficiency of imine bonds is closely related with the degree of oxidation and pH. Complete oxidation can decrease the conversion efficiency from ∼87 to 48%, which is comparable to the result of changing the pH from 10.0 to 7.0. With the formation and breaking of imine bonds, the surfactant can be reversibly switched between symmetric and asymmetric structures, accompanied by a morphological transition from vesicles to spherical micelles. Although oxidation cannot demolish all imine bonds, it can completely convert vesicles to spherical micelles, which is mainly ascribed to an increase in the polarity of the micellar microenvironment stemming from the oxidation of Se. However, this transition can only be achieved by reducing the pH to 5.0 instead of 7.0. Nile red loaded in HOBAB-BSeEA vesicles can be quickly, controllably, and step-by-step released upon oxidation stimulus but not pH. Understanding the mechanism of oxidation-induced breakage of imine bonds and disruption of vesicles would be useful in designing redox-responsive imine-based carriers that can unload cargoes according to the level of the local reactive oxygen species.