Langmuir最新文献

Gemini surfactants, also called Gemini, especially those with quaternary ammonium head groups, are recognized for their distinctive aggregation behavior and enhanced structure-activity relationships. The unique dual-head and dual-tail structure of Gemini grants them superior surface activity, allowing them to effectively lower surface and interfacial tension. To investigate the self-assembly behavior and surface-active properties that make them suitable as anticorrosion and antimicrobial agents, a series of cationic Gemini featuring amide bonds and varying alkyl chain lengths were synthesized. Surface activity and self-assembly characteristics of these cationic Gemini were analyzed using methods such as surface tension, electrical conductivity, fluorescence, and isothermal titration calorimetry. The findings revealed that these Gemini possess enhanced surface-active and self-assembly properties in comparison to traditional single-tail, monoheaded surfactants. Thermodynamic studies confirmed that these Gemini self-assemble spontaneously in water above a relatively low threshold concentration, with the self-assembly process becoming less favorable as the alkyl chain length decreased. The length of the chains also affected the size and shape of the aggregates formed. These Gemini have been shown to exhibit remarkable anticorrosion properties on steel surface. The performance of these compounds as corrosion inhibitors showed a clear dependence on chain length, with the shortest chain length Gemini providing the highest inhibition efficiency. These Gemini have also exhibited pronounced antibacterial activities against Escherichia coli (DH5alpha) and Staphylococcus aureus bacteria.

Two-dimensional materials and ionic liquids are widely used as lubricating materials due to their excellent tribological properties. This study designed three water-based proton-ionic liquids (PILs) and synthesized molybdenum disulfide (MoS₂) nanosheets for their combination as water-based lubricant additives. The composite lubrication system exhibits excellent tribological properties, with a friction coefficient as low as 0.024, reducing friction by 90.77% compared to water-glycol. Mechanism studies have shown that the excellent lubrication performance comes from the adsorption of ionic liquids at sliding interfaces, the interlayer slip of MoS₂, and the generation of tribofilms at wear scars. This work provides theoretical support and technical guidance for the design and preparation of new water-based lubricating additives.

Bullvalene is the archetypical "shape shifting" molecule, undergoing continuous Cope rearrangements in solution at room temperature at a rate of about 3 kHz. In the confined spaces of an scanning tunneling microscopy break junction (STMBJ) setup, isolated bisarylbullvalene molecules have recently been shown to exhibit very restricted isomerization and slower interconversion rates. The restricted number of populated bullvalene isomers displayed large variances in conductivity with the confinement to manifest high piezoresistivity. Herein, the confinement is increased by forming self-assembled monolayers (SAMs), focusing on measuring the resulting electron-transfer rates, as well as identifying viable SAM structural possibilities. First, bis-4-phenyl acetylene bullvalene was synthesized and its SAMs were produced on Au(111). Redox active ferrocene tail groups were then attached via a copper catalyzed azide-alkyne cycloaddition (CuAAC) to enable electrochemical measurements of SAM coverages and electron-transfer rates. The results are consistent with only a single isomeric form being present on the surface at any one time, with its nature varying with monolayer coverage density. Density functional theory (DFT) simulations indicate that a combination of steric interactions induced by the bisarylbullvalene substitution, combined with head group and SAM packing effects, results in this coverage-dependent isomeric selectivity. A small number of very different types of SAM structural possibilities are identified. These findings provide a pathway forward for the exploitation of bullvalene's constitutional isomerism in facilitating nano-electromechanical systems (NEMS).

Immobilization of enzymes on (nano)porous metal carriers provides the foundation for an advanced design of bioelectrodes suitable for catalysis and sensing. However, interactions upon adsorption are still poorly understood, and so the efficient coupling of the enzymes to the electrode surface remains one of the major challenges. Here, we present a comprehensive study of the immobilization behavior of Aerococcus viridans l-lactate oxidase (LOx) on nanoporous gold (npAu) in dependence of electrode modification with differently charged self-assembled monolayers (SAMs). The highest activity (up to 14 U/g) and electrocatalytic response (sensitivity of 3.9 μA mM^-1) were observed for a sulfonate-terminated SAM. This is contrary to enzyme behavior on conventional polymer carriers, and thus, the effect is specific to the metal electrodes. We propose the capture of the negatively charged LOx in a dense counterion layer in close proximity to the strongly negatively charged gold surface. Adsorption on positively charged amine-terminated SAMs resulted in a similar immobilization yield but gave much lower activity (4-fold). Importantly, the effect of the sulfonate SAM was strongly dependent on the npAu electrode pore size: the highest LOx activity (in U/cm²) was found with pores (diameter of ∼170 nm) supposedly large enough to facilitate enzyme diffusion into the porous structure during immobilization. Electrochemical sensing of H₂O₂ produced by the LOx reaction showed a 2.5-fold higher sensitivity for l-lactate on the negatively charged surface. Lixiviation studies supported the proposed layer capture and revealed a faster decline in the electrode activity with sulfonate surface modification. Collectively, the present study reveals enhanced activity of LOx on sulfonate-charged gold surfaces and a strong pore size dependence. These findings deepen the understanding of the immobilization behavior of LOx on charged nanoporous metals and have importance for the advanced design of enzyme electrodes.

Microwell plates absorb bioactive compounds and are commonly used for disease prediction, diagnosis, and monitoring. Chemical absorption is more effective than physical absorption for stabilizing these compounds. This study systematically investigates the fundamental mechanisms of air plasma-induced surface modifications in poly(methyl methacrylate) (PMMA), focusing on carboxyl group formation kinetics, morphological evolution, and optical property changes. Air plasma treatment enhances the hydrophilicity and surface roughness of the PMMA plates. Light transmission remains comparable to untreated plates for 10 min treatment durations. Treatment for 3 min significantly increases the large-molecular-weight carboxyl compounds, with minimal loss after wash buffer rinsing. Thus, a 3 min air plasma treatment optimally enhances PMMA microwell plates for effective bioactive compound absorption.