Impact of hydrophobic tails of new phospho-zwitterionic surfactants on the structure, catalytic, and biological activities of AgNPs

Synthesis, Surface Activity, Emulsifiability and Bactericidal Performance of Zwitterionic Tetrameric Surfactants

In this paper, a series of tetrameric surfactants (4CnSAZs, n = 12, 14, 16) endowed with zwitterionic characteristic were synthesized by a simple and convenient method and their structures were characterized by FT-IR, 1H NMR and elemental analysis. Their physicochemical properties were studied using the Wilhelmy plate method, fluorescence spectra and dynamic light scattering technique. 4CnSAZs have higher surface activities and tend to adsorb at the air/water surface rather than self-assembling in aqueous solution. The thermodynamic parameters obtained from surface tension measurements show that both processes of adsorption and micellization of 4CnSAZs are spontaneous and that the micellization processes of 4CnSAZs are entropy-driven processes. Both adsorption and micellization of 4CnSAZs are inclined to occur with the increase of alkyl chain length or temperature. For 4C12SAZs, there are only small-size aggregates (micelles), while the large aggregates (vesicles) are observed at the alkyl length of 4CnSAZs of 14 or 16. This shows that the alkyl chain length for oligomeric surfactants has a greater sensitivity for aggregate growth. The aggregate morphologies obtained from the calculated values of critical packing parameter (p) for 4C14SAZs and 4C16SAZs can be supported by the DLS measurement results. The test results obtained by the separation-water-time method show that 4CnSAZs have good emulsification performance and that the prepared emulsions appear to exit in the form of multiple emulsions. In addition, 4CnSAZs have good antibacterial activities against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The present study reveals the unique behavior of a zwitterionic tetrameric surfactant and may give new insights into molecular design and synthesis of a high degree of surfactants with different structure characteristics for potential application in various industrial fields.

Potent biological activity of newly fabricated silver nanoparticles coated by a carbon shell synthesized by electrical arc

Highly effective AgNPs@C was efficiently synthesized by electrical arc powered by single spark unit which was sufficient to ionize the dielectric media (deionized water) through applying strong electric field between the electrodes (silver and carbon). The AgNPs@C shell was characterized in terms of stability, morphology and phase structure. All characterizations showed that the prepared silver nanoparticles were spherical with average size reached 17 nm coated with carbon shell. The antibacterial effect of the synthesized nanoparticles was tested against Pseudomonas aeruginosa in comparison to Ceftazidime (commonly used antibiotic against P. aeruginosa infections). It was revealed that AgNPs@C shell has superior activity with inhibition zone diameter reached 15 mm and minimum inhibitory concentration reached 2 µg/mL. The observed activity was further confirmed by confocal microscope which showed an increased red region, representing the dead cells, correlated with the presence of AgNPs@C. Moreover, transmission electron microscope studies implied the possible AgNPs@C antibacterial mechanism of action was the nanoparticles adherence to the bacterial membrane causing cell lysis. The molecular studies against fimH (virulence adhesion gene), rmpA (mucoid factor encoding gene), and mrkA (biofilm forming gene) proved the inhibition of their genetic expression. The cytotoxic effect of the synthesized AgNPs@C showed CC50 reached 235.5 μg/mL against normal lung cells (L929 cell line).

Homogeneous regulation of arranged polymorphic manganese dioxide nanocrystals as cathode materials for high-performance zinc-ion batteries

Rechargeable aqueous zinc-ion batteries have emerged as attractive energy storage devices by virtue of their low cost, high safety and eco-friendliness. However, zinc-ion cathodes are bottlenecked by their vulnerable crystal structures in the process of zinc embedding and significant capacity fading during long-term cycling. Herein, we report the rational and homogeneous regulation of polycrystalline manganese dioxide (MnO₂) nanocrystals as zinc cathodes via a surfactant template-assisted strategy. Benefiting from the homogeneous regulation, MnO₂ nanocrystals with an ordered crystal arrangement, including nanorod-like polyvinylpyrrolidone-manganese dioxide (PVP-MnO₂), nanowire-like sodium dodecyl benzene sulfonate-manganese dioxide and nanodot-like cetyltrimethylammonium bromide-manganese dioxide, are obtained. Among these, the nanorod-like PVP-MnO₂ nanocrystals exhibit stable long-life cycling of 210 mAh g^-1 over 180 cycles at a high rate of 0.3 A g^-1 and with a high capacity retention of 84% over 850 cycles at a high rate of 1 A g^-1. The good performance of this cathode significantly results from the facile charge and mass transfer at the interface between the electrode and electrolyte, featuring the crystal stability and uniform morphology of the arranged MnO₂ nanocrystals. This work provides crucial insights into the development of advanced MnO₂ cathodes for low-cost and high-performance rechargeable aqueous zinc-ion batteries.

Synthesis, surface activities and aggregation properties of asymmetric Gemini surfactants

A series of Gemini surfactants with an asymmetric structure (PKO 15-3(OH)-n; n = 12, 14 and 16) were synthesized through a simple two-step reaction consisting of a ring-opening reaction followed by a quaternization reaction. The surface tension measurements indicated that the surface activities of PKO 15-3(OH)-n were higher than those of traditional single-chain and symmetrical Gemini surfactants. The thermodynamic parameters obtained from electrical conductivity measurements showed that the micellization processes of PKO 15-3(OH)-n were spontaneous and entropy-driven. Transmission electron microscopy and dynamic light scattering measurements confirmed that PKO 15-3(OH)-n molecules with a higher asymmetric degree could form vesicles, in which surfactant molecules were interdigitated side-by-side in the vesicle membrane. The obtained results are not in accordance with those calculated from the critical packing theory, which can further complement the theory.