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The electrochemical behavior of three differently charged drug molecules (zwitter-ionic acetylcarnitine, bi-cationic succinylcholine and tri-cationic gallamine) was studied at the interface between two immiscible electrolyte solutions. Tetramethylammonium was used as a model mono cationic molecule and internal reference. The charge and molecular structure were found to play an important role in the drug lipophilicity. The studied drugs gave a linear correlation between the water – octanol (log P octanol ) partition coefficients and the electrochemically measured water – 1,2-dichloroethane (log P DCE ) partition coefficients. Comparison with tetraalkylammonium cations indicating that the correlation between log P octanol and log P DCE is molecular structure dependent. The highest measured sensitivity and lowest limit of detection were found to be 0.543 mA·dm 3 ·mol − 1 and 6.25 μM, respectively, for the tri-cationic gallamine. The sensitivity for all studied ions was found to be a linear function of molecular charge. The dissociation constant of the carboxylic group of zwiter-ionic acetylcarnitine was calculated based on voltammetric parameters and was found to be 4.3. This study demonstrates that electrochemistry at the liquid – liquid interface is powerful technique when it comes to electroanalytical or pharmacokinetic drug assessment. [ABSTRACT FROM AUTHOR]

In this paper, the electrochemical behavior of four fluoroquinolone antibiotics (FAs) [Ciprofloxacin (Cip), Enrofloxacin (Enr), Marbofloxacin (Mar) and Ofloxacin (Ofl)] at a polarized interface between two immiscible electrolyte solutions (ITIES) has been studied using ion–transfer voltammetry (ITV). The measurements were conducted in the traditional macroscopic (macro-ITIES) and a recently developed miniaturized (micro-ITIES) platform. The latter was obtained from fused silica micro-capillaries having an internal diameter of 25 μm. We used macroITIES to obtain a number of analytical parameters such as: standard Galvani potential of ion transfer (ΔΦ0), diffusion coefficients (D), free Gibbs energy of ion transfer (Δ G 0) and partition coefficients (logP DCE). The latter were compared with the available literature values of logP octanol. The effect of concentration of the studied antibiotics on the electrochemical response was investigated with the microITIES platform, setting statistical parameters such as: linear dynamic ranges (LDRs – studied from 1 μM up to 50 μM), lower limit of detections (LODs – around 1 μM) and sensitivity (found in the range from 2.6·10−2 to 6.8·10−2 nA·μM−). MicroITIES were further used to study the effect of pH on the analytical signal and the results are plotted in a form of ion partition diagrams. Working with microITIES supported with the fused silica capillaries significantly reduced the volumes of consumed chemicals and expedite all analytical experiments. The provided results can be successfully applied in pharmacology and electroanalysis for testing and determination of the chosen fluoroquinolone antibiotics. Image 1 • Studied fluoroquinolone antibiotics are active at the liquid – liquid interface. • Liquid – liquid interface miniaturized with fused silica micro-capillaries. • Fluoroquinolone antibiotics give signal at concentration as small as 1 μM. • Antibiotics logP DCE values correlate with calculated logP octanol values. • Ion partition diagrams for all antibiotics are plotted. [ABSTRACT FROM AUTHOR]

The behaviour of acid phosphatase at an electrified liquid–liquid interface was studied in this work. It was found that only the protonated form of the protein can undergo interfacial adsorption which is affected by the pH of the aqueous phase. With ion transfer voltammetry we could detect acid phosphatase in concentrations as low as 0.1 μM. We were able to co-deposit the protein and silica at the electrified liquid–liquid interface via controlled proton transfer to the organic phase where it catalyzed tetraethoxysilane hydrolysis, followed by polycondensation to silica. [ABSTRACT FROM AUTHOR]

• The behavior of three polyelectrolytes (PEI, PSS and PHMG) is studied at the ITIES. • Fiber glass membrane is modified with polyelectrolyte multilayer using LbL assembly. • Unmodified fiber glass membrane is used as a support of the ITIES. • Polyelectrolyte modified fiber glass membrane affect the ionic transport. In this work, the electrified liquid–liquid interface (LLI) was supported with the bare and polyelectrolyte modified fiberglass membranes. The permeability of these supports was then investigated with ion transfer voltammetry (ITV). This work descends from three mutually interconnected experimental tasks. (i) The study of an interfacial behavior of three polyelectrolytes, poly(ethyleneimine) (PEI), polystyrene sulfonate (PSS), and polyhexamethylene guanidine (PHMG) at the polarized LLI. (ii) Electrochemical characterization of the LLI supported by the unmodified fiberglass membrane. (iii) Polyelectrolyte multilayer placement, using layer-by-layer processing, at the surface of the fiberglass membrane and its further utilization as the support for the electrified LLI. Bare and modified membranes were characterized using ITV in the presence of a family of quaternary ammonium cations: tetramethylammonium (TMA+), tetraethylammonium (TEA+), tetrapropylammonium (TPrA+) and tetrabutylammonium (TBA+) initially dissolved in the aqueous phase as the chloride salts. The ionic currents related to their transmembrane transfer were affected already after the first polyelectrolyte layer placement. In addition to electrochemistry, the modification process was followed using several complementary techniques, including optical microscopy (OM), atomic force microscopy (AFM), infra-red (IR) spectroscopy, and scanning electron microscopy (SEM). The proposed methodology offers very simple, fast, and versatile (having in mind the available selection of functional polyelectrolytes) protocol for a membrane preparation having size sieving properties. In turn, the electrochemistry at the LLI can be used as an insightful tool to study the ionic transmembrane currents. Image, graphical abstract [ABSTRACT FROM AUTHOR]