Bioelectrochemistry (v.108, #C)

Bilirubin oxidase based enzymatic air-breathing cathode: Operation under pristine and contaminated conditions by Carlo Santoro; Sofia Babanova; Benjamin Erable; Andrew Schuler; Plamen Atanassov (1-7).
The performance of bilirubin oxidase (BOx) based air breathing cathode was constantly monitored over 45 days. The effect of electrolyte composition on the cathode oxygen reduction reaction (ORR) output was investigated. Particularly, deactivation of the electrocatalytic activity of the enzyme in phosphate buffer saline (PBS) solution and in activated sludge (AS) was evaluated. The greatest drop in current density was observed during the first 3 days of constant operation with a decrease of ~ 60 μAcm− 2  day− 1. The rate of decrease slowed to ~ 10 μAcm− 2  day− 1 (day 3 to 9) and then to ~ 1.5 μAcm− 2  day− 1 thereafter (day 9 to 45). Despite the constant decrease in output, the BOx cathode generated residual current after 45 days operations with an open circuit potential (OCP) of 475 mV vs. Ag/AgCl. Enzyme deactivation was also studied in AS to simulate an environment close to the real waste operation with pollutants, solid particles and bacteria. The presence of low-molecular weight soluble contaminants was identified as the main reason for an immediate enzymatic deactivation within few hours of cathode operation. The presence of solid particles and bacteria does not affect the natural degradation of the enzyme.
Keywords: Bilirubin oxidase; Oxygen reduction reaction; Enzymes durability; PBS conditions; Pollutants;

An osmium redox polymer, PAA–PVI–[Os(4,4′-dimethyl-2,2′-bipyridine)2Cl]+/2 + that has been used in enzymatic fuel cells and microbial sensors, was applied for the first time to the anode of single-chamber microbial fuel cells with the mixed culture inoculum aiming at enhancing performance. Functioning as a molecular wire connecting the biofilm to the anode, power density increased from 1479 mW m− 2 without modification to 2355 mW m− 2 after modification of the anode. Evidence from cyclic voltammetry showed that the catalytic activity of an anodic biofilm was greatly enhanced in the presence of an osmium redox polymer, indicating that electrons were more efficiently transferred to the anode via co-immobilized osmium complex tethered to wiring polymer chains at the potential range of − 0.3 V–+0.1 V (vs. SCE). The optimum amount of the redox polymer was determined to be 0.163 mg cm− 2.
Keywords: Microbial fuel cell; Redox polymer; Anode modification; Electron transfer; Power density;

An electrically controlled drug delivery system based on conducting poly(3,4-ethylenedioxypyrrole) matrix by Katarzyna Krukiewicz; Patrycja Zawisza; Artur P. Herman; Roman Turczyn; Slawomir Boncel; Jerzy K. Zak (13-20).
As numerous therapeutic agents are not well tolerated when administrated systemically, localized and controlled delivery can help to decrease their toxicity by applying an optimized drug concentration at extended exposure time. Among different types of drug delivery systems, conjugated polymers are considered as promising materials due to their biocompatibility, electrical conductivity and ability to undergo controllable redox reactions. In this work poly(3,4-ethylenedioxypyrrole), PEDOP, matrix is described for the first time as a reservoir of a model drug, ibuprofen (IBU). Drug immobilization process is performed in situ, during the electrochemical polymerization of 10 mM EDOP in the presence of 5–50 mM IBU. The loading efficiency of polymer matrix is dependent on IBU concentration and reaches 25.0 ± 1.3 μg/cm2. The analysis of PEDOP-IBU chemical structure based on Raman spectroscopy, energy dispersive spectroscopy and surface morphology data provided by scanning electron microscopy shows that IBU is accumulated in the structure of matrix and evidently influences its morphology. IBU is then released in a controlled way under the influence of applied potential (− 0.7 V vs. Ag/AgCl). It is demonstrated that the judicious choice of the synthesis conditions leads to a tailored loading efficiency of PEDOP matrix and to a tunable drug release.
Keywords: Drug delivery; Conducting polymer; Poly(3,4-ethylenedioxypyrrole); Ibuprofen; Biomedical engineering;

Light reactions of photosynthesis that take place in thylakoid membranes found in plants or cyanobacteria are among the most effective ways of utilizing light. Unlike most researches that use photosystem I or photosystem II as conversion units for converting light to electricity, we have developed a simple method in which the thylakoid monolayer was covalently immobilized on the glassy carbon electrode surface. The activity of isolated thylakoid membrane was confirmed by measuring evolving oxygen under illumination. Glassy carbon surfaces were first modified with partial or full monolayers of carboxyphenyl groups by reductive C–C coupling using 4-aminobenzoic acid and aniline and then thylakoid membrane was bioconjugated through the peptide bond between amine residues of thylakoid and carboxyl groups on the surface. Surface properties of modified surfaces were characterized by cyclic voltammetry, contact angle measurements, and electrochemical impedance spectroscopy. Photocurrent of 230 nA cm− 2 was observed when the thylakoid monolayer was formed on the mixed monolayer of 4-carboxylpheny and benzene at applied potential of 0.4 V vs. Ag/AgCl. A small photocurrent resulted when the 4-carboxyphenyl full monolayer was used. This work shows the possibility of solar energy conversion by directly employing the whole thylakoid membrane through simple surface modification.Display Omitted
Keywords: Solar energy conversion; Thylakoid membrane; Photocurrent; Photosynthesis; Surface modification;

Channel-forming activity of syringopeptin 25A in mercury-supported lipid bilayers with a phosphatidylcholine distal leaflet by Lucia Becucci; Marta Rossi; Alberto Fiore; Andrea Scaloni; Rolando Guidelli (28-35).
The channel-forming activity of the lipodepsipeptide syringopeptin 25A (SP25A) was investigated at a tethered bilayer lipid membrane (tBLM) with a dioleoylphosphatidylcholine distal leaflet, anchored to a mercury electrode through a hydrophilic tetraethyleneoxy spacer. SP25A was incorporated in the tBLM from different aqueous solutions by recording a series of impedance spectra over a potential range encompassing non-physiological transmembrane potential (Δϕ) values. Once incorporated, SP25A forms stable ion channels over the narrower range of physiological Δϕ values. Ion flow into and out of the spacer, through the lipid bilayer moiety of the tBLM, was monitored by potential step chronocoulometry and cyclic voltammetry at pH 3, 5.4 and 6.8. Potassium ion flow into the hydrophilic spacer along the SP25A channels, during the negative potential scan, proceeds in two stages, except at the higher pH and lower SP25A concentration adopted, where it proceeds in a single stage. In light of the behavior of SP25A single channel currents reported in the literature, the first stage is ascribed to large channels resulting from the aggregation of small ones, while the second more negative stage is associated with the small channels resulting from the disaggregation of the large ones.Display Omitted
Keywords: Lipodepsipeptides; Tethered bilayer lipid membranes; Potential step chronocoulometry; Cyclic voltammetry;

Fabrication of electrospun silk fibroin scaffolds coated with graphene oxide and reduced graphene for applications in biomedicine by Salvador Aznar-Cervantes; Jose G. Martínez; Antonia Bernabeu-Esclapez; A. Abel Lozano-Pérez; Luis Meseguer-Olmo; Toribio F. Otero; Jose L. Cenis (36-45).
Silk fibroin and graphene are both promising biomaterials described in the bibliography. Hybrid scaffolds combining their properties could be attractive for tissue engineering applications. In this work, a new methodology to produce electrospun fibroin scaffolds coated with graphene materials is provided. The mechanical, electrical and electrochemical properties of the materials attained were characterised. The fibre diameters were measured (from 3.9 to 5.2 μm). The samples coated with reduced graphene were electronic conductors and electroactive in liquid electrolytes, showing maximum oxidation and reduction (around − 0.4 V peak). The chronoamperometric responses showed a reduction shoulder, pointing to the entrance of balancing cations from the solution by nucleation–relaxation: the reaction induced structural changes in the graphene. In order to check the biocompatibility of the materials, they were seeded with L929 fibroblasts. The excellent biocompatibility of silk fibroin meshes was maintained after coating with graphene, being the proliferation results equal in all the treatments 7 days after the seeding (Tukey, p > 0.05).The conductive and electroactive properties of meshes coated with reduced graphene allow the potential application of local electric fields or local ionic currents to cell cultures, biological interfaces or animal models without host response.Display Omitted
Keywords: Fibroin; Electrospinning; Graphene; Electroactivity; Biomaterials;

Modeling of laccase inhibition by formetanate pesticide using theoretical approaches by Ana C.V. Martins; Francisco W.P. Ribeiro; Geancarlo Zanatta; Valder N. Freire; Simone Morais; Pedro de Lima-Neto; Adriana N. Correia (46-53).
The inhibition of laccase enzymatic catalytic activity by formetanate hydrochloride (FMT) was investigated by cyclic voltammetry and by quantum chemical calculations based on density functional theory with a protein fragmentation approach. The cyclic voltammograms were obtained using a biosensor prepared by enzyme immobilization on gold electrodes modified with gold nanoparticles and 4-aminophenol as the target molecule. The decrease in the peak current in the presence of FMT was used to characterize the inhibition process. The calculations identified Asp206 as the most relevant moiety in the interaction of FMT with the laccase enzymatic ligand binding domain. The amino acid residue Cys453 was important, because the Cys453–FMT interaction energy was not affected by the dielectric constant, although it was not a very close residue. This study provides an overview of how FMT inhibits laccase catalytic activity.Display Omitted
Keywords: Enzymatic catalysis; Inhibition; Amino acid residues; Quantum chemical calculations; Density functional theory; Molecular docking;