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Owing to their biocompatibility, optical, and catalytic properties, Au nanoparticles (NPs) have been the subject of much research. Since smaller NPs have enhanced catalytic properties and NP morphology greatly impacts their effectiveness, controlled and reproducible methods of generating Au NPs are still being sought. Herein, Au NPs were electrochemically generated at a water|ionic liquid (w|IL) immiscible micro-interface, 25 µm in diameter, using a redox active IL and compared to results at a water|oil (w|o) one. The liquid|liquid interface is advantageous as it is pristine and highly reproducible, as well as an excellent means of species and charge separation. In this system, KAuCl4 dissolved in the aqueous phase reacts under external potential control at the water|P8888TB (tetraoctylphosphonium tetrakis(pentafluorophenyl)borate) with trioctyl(ferrocenylhexanoyl)phosphonium tetrakis(pentafluorophenyl)borate (FcIL), an electron donor and redox active IL. FcIL was prepared with a common anion to P8888TB, which greatly enhances its solubility in the bulk IL. Simple ion transfer of AuCl4− and AuCl(4−γ)(OH)γ− at the w|P8888TB micro-interface were characterized voltammetrically as well as their heterogeneous electron transfer reaction with FcIL. This interfacial reaction generates Au NPs whose size can be thermodynamically controlled by modifying the pH of the aqueous phase. Critically, at low pH, nanoclusters, <1.7 nm in diameter, were generated owing to inhibited thermodynamics in combination with the supramolecular fluidic nature of the IL microenvironment that was observed surrounding the as-prepared NPs. [ABSTRACT FROM AUTHOR]

Nanoparticles (NPs) are of considerable interest, owing to their enhanced catalytic activity and optical properties. Ionic liquids (ILs) are employed as a medium to prepare small (<20 nm in diameter) and relatively low dispersity (typically, ±1–2 nm) NPs. While ensemble techniques (e. g., UV/Vis) can provide a great deal of information, increasingly, single‐entity electrochemistry (SEE) has been used to provide physical insight into individual NP catalysis and dynamics. Herein, Pt NP impact current spikes for particles prepared in the IL phase and based on electrocatalytic amplification (ECA) of the borohydride oxidation reaction (BOR) were recorded during i‐t measurements. Additionally, direct oxidative LiBH4 nanocrystal (NC) impact signals were observed herein for the first time. By quantifying the charge transferred during the stochastic collision events, the radius of the NCs (rNC) was calculated (∼5.5 nm) and compares favorably with TEM images. Critically, small additions (1 % v/v) of a molecular, polar organic solvent (tetrahydrofuran, THF) disrupt the ILs supramolecular fluidic nature, which enhances NC impact frequency and the aggregation of Pt NPs. [ABSTRACT FROM AUTHOR]

Phytoplankton growth in the open ocean is critical to carbon fixation and often limited by low iron concentrations. Owing to its low solubility, phytoplankton employ ligands for iron uptake; therefore, ligand binding characterization is important. Herein, a micro immiscible liquid/liquid interface was employed with four ligands through an electrochemically induced facilitated ion-transfer process. Ligands 1,10-phenathroline (phen), 1-nitroso-2-naphthol (N2N), 2-(2-thiazolylazo)-p-cresol (TAC), and salicylaldoxime (SAL), where tested using established facilitated ion-transfer thermodynamics combined with differential pulse voltammetry. Three metal ion/ligand binding stoichiometries were observed for Fe2+:phen, whereas only one was observed with Fe2+ with SAL, N2N, and TAC. Overall binding constants were calculated such that binding strengths can be ranked highest to lowest as phen>N2N>TAC>SAL. Additionally, the formal ion transfer for Fe2+ (0.66 V) for an aqueous/1,2-dichloroethane interface was also determined. [ABSTRACT FROM AUTHOR]

Miniaturization of electrochemical detection methods for point-of-care-devices is ideal for their integration and use within healthcare environments. Simultaneously, the prolific pathogenic bacteria Pseudomonas aeruginosa poses a serious health risk to patients with compromised immune systems. Recognizing these two factors, a proof-of-concept electrochemical method employing a micro-interface between water and oil (w/o) held at the tip of a pulled borosilicate glass capillary is presented. This method targets small molecules produced by P. aeruginosa colonies as signalling factors that control colony growth in a pseudo-multicellular process known as quorum sensing (QS). The QS molecules of interest are 4-hydroxy-2-heptylquinoline (HHQ) and 2-heptyl-3,4-dihydroxyquinoline (PQS, Pseudomonas quinolone signal). Hydrophobic HHQ and PQS molecules, dissolved in the oil phase, were observed electrochemically to facilitate proton transfer across the w/o interface. This interfacial complexation can be exploited as a facile electrochemical detection method for P. aeruginosa and is advantageous as it does not depend on the redox activity of HHQ/PQS. Interestingly, the limit-of-linearity is reached as [H+] ≈ [ligand]. Density functional theory calculations were performed to determine the proton affinities and gas-phase basicities of HHQ/PQS, as well as elucidate the likely site of stepwise protonation within each molecule. [ABSTRACT FROM AUTHOR]

Front Cover: Single-Entity Electrochemical Detection of As-Prepared Metallic and Dielectric Nanoparticle Stochastic Impacts in a Phosphonium Ionic Liquid (ChemElectroChem 13/2022) Keywords: ionic liquids; single-entity detection; electrocatalysis; borohydride oxidation; nanoparticles EN ionic liquids single-entity detection electrocatalysis borohydride oxidation nanoparticles 1 1 1 07/18/22 20220714 NES 220714 B The Front Cover b shows a platinum nanoparticle stochastic impact at a carbon fiber ultramicroelectrode along with the associated, recorded signal in an ionic liquid medium. Ionic liquids, single-entity detection, electrocatalysis, borohydride oxidation, nanoparticles. [Extracted from the article]

Metal nanoparticle (NP) incorporated conductive polymer films are attractive for their mechanical stability for biomedical applications and as heterogeneous electrocatalysis materials. Novel approaches to generate these materials with tunable properties are still being sought. Herein, the interface between two immiscible electrolyte solutions (ITIES) has been employed as a molecularly sharp and reproducible platform for simultaneous Au NP and poly(9-vinylcarbazole) generation. Three interfaces have been compared, including between water|1,2-dichloroethane (w|DCE), water|α,α,α-trifluorotoluene (w|TFT), and water|ionic liquid (w|IL). In this case the IL was P 8888 TB (tetraoctylphosphonium tetrakis(pentafluorophenyl)borate). 9-Vinylcarbazole (VC) can polymerize via two routes, either propagating through the vinyl substituent or the aryl rings. The former gives rise to a white semiconducting polymer with a wide bandgap, while the latter produces a green, conducting polymer. External potential control through voltammetric cycling was found to generate the film more rapidly favoring heterogeneous electron transfer with formation of the green poly(VC) variant at the ITIES. This was a free-standing film that could be easily removed from the interface. In the absence of external control, white polymer crystals formed within the oil phase spontaneously likely via AuCl 4 - w → o transfer followed by a homogeneous electron transfer reaction mechanism. Scanning electrochemical microscopy probe approach curve experiments were used to quantify the electroactivity of the film and are complemented by direct conductivity measurements.