Regulation of the Cyanobacterial Circadian Clock by Electrochemically Controlled Extracellular Electron Transfer

There is growing awareness that circadian clocks are closely related to the intracellular redox state across a range of species. As the redox state is determined by the exchange of the redox species, electrochemically controlled extracellular electron transfer (EC‐EET), a process in which intracellular electrons are exchanged with extracellular electrodes, is a promising approach for the external regulation of circadian clocks. Herein, we discuss whether the circadian clock can be regulated by EC‐EET using the cyanobacterium Synechococcus elongatus PCC7942 as a model system. In vivo monitoring of chlorophyll fluorescence revealed that the redox state of the plastoquionone pool could be controlled with EC‐EET by simply changing the electrode potential. As a result, the endogenous circadian clock of S. elongatus cells was successfully entrained through periodically modulated EC‐EET by emulating the natural light/dark cycle, even under constant illumination conditions. This is the first example of regulating the biological clock by electrochemistry.     

Comparison of Multi‐walled Carbon Nanotubes and Poly(3‐octylthiophene) as Ion‐to‐Electron Transducers in All‐Solid‐State Potassium Ion‐Selective Electrodes

Multi‐walled carbon nanotubes (MWCNTs) were compared with poly(3‐octylthiophene) (POT) as ion‐to‐electron transducer in all‐solid‐state potassium ion‐selective electrodes with valinomycin‐based ion‐selective membranes. MWCNTs and POT were mixed with the other components of the potassium ion‐selective membrane cocktail (valinomycin, KTpClPB, o‐NPOE, PVC, THF) which was then applied on a glassy carbon (GC) substrate to prepare single‐piece ion‐selective electrodes (SPISEs). Results from potentiometric and impedance measurements showed that the MWCNT‐based electrodes have a more reproducuible standard potential and a lower overall impedance than the electrodes based on POT. Both types of electrodes showed similar sensitivity to potassium ions and no redox sensitivity.     

Proton Transport in the Outer‐Membrane Flavocytochrome Complex Limits the Rate of Extracellular Electron Transport

The microbial transfer of electrons to extracellularly located solid compounds, termed extracellular electron transport (EET), is critical for microbial electrode catalysis. Although the components of the EET pathway in the outer membrane (OM) have been identified, the role of electron/cation coupling in EET kinetics is poorly understood. We studied the dynamics of proton transport associated with EET in an OM flavocytochrome complex in Shewanella oneidensis MR‐1. Using a whole‐cell electrochemical assay, a significant kinetic isotope effect (KIE) was observed following the addition of deuterated water (D₂O). The removal of a flavin cofactor or key components of the OM flavocytochrome complex significantly increased the KIE in the presence of D₂O to values that were significantly larger than those reported for proton channels and ATP synthase, thus indicating that proton transport by OM flavocytochrome complexes limits the rate of EET.     

Electrocatalysis of Water Oxidation by H2O‐Capped Iridium‐Oxide Nanoparticles Electrodeposited on Spectroscopic Graphite

Electrocatalysis of water oxidation by 1.54 nm IrO_x nanoparticles (NPs) immobilized on spectroscopic graphite electrodes was demonstrated to proceed with a higher efficiency than on all other, hitherto reported, electrode supports. IrO_x NPs were electrodeposited on the graphite surface, and their electrocatalytic activity for water oxidation was correlated with the surface concentrations of different redox states of IrO_x as a function of the deposition time and potential. Under optimal conditions, the overpotential of the reaction was reduced to 0.21 V and the electrocatalytic current density was 43 mA cm^?2 at 1 V versus Ag/AgCl (3 M KCl) and pH 7. These results beneficially compete with previously reported electrocatalytic oxidations of water by IrO_x NPs electrodeposited onto glassy carbon and indium tin oxide electrodes and provide the basis for the further development of efficient IrO_x NP‐based electrocatalysts immobilized on high‐surface‐area carbon electrode materials.     

In Situ Self Assembly of Thiolated ortho‐Quinone Capped Electrocatalysts for Bioanalytical Applications

Thiolated o‐quinone‐capped electrocatalysts modeled on the naturally occurring o‐quinone cofactor pyrroloquinoline quinone (PQQ) were designed and synthesized for the development of biosensor devices. The o‐quinone‐capped electrocatalysts self assembled on gold electrodes through a thiolated phenyleneethynylene linkage to form a monolayer less than 2 nm in thickness. Cyclic voltammetric measurements demonstrated reversible electrochemical properties between the quinone and hydroquinone forms of the head group. In an amperometric sensing mode, the modified electrodes reproducibly detected ethanethiol at micromolar levels demonstrating their robust electrocatalytic activity toward thiols. Their redox cycling and electrocatalytic properties show promise for detection of biologically important thiols and other nucleophiles.     

Solid‐contact Acetate‐selective Electrode Based on a 1,3‐bis(carbazolyl)urea‐ionophore

The construction and study of solid‐contact acetate‐selective electrodes is described using a 1,3‐bis(carbazolyl)urea derivative as a neutral hydrogen‐bonding ionophore and poly(3,4‐ethylenedioxythiophene) as the solid contact. It was shown recently that this ionophore binds acetate (logK_ass=4.98) that is used as primary ion in this study. The electrodes show linearity over the activity range of 10^?4.50–10^?1.10 with a sub‐Nernstian slope of ?51.3 mV per decade and a detection limit of 10^?5.00. The anion‐selectivity pattern of these electrodes deviates markedly from the Hofmeister pattern. When adding ionophore to the membrane the logarithm of the selectivity coefficient (logK) for SCN^? decreased from 6.5 to 1.2, logK for I^? decreased from 5.7 to 0.9, logK for NO₃^? decreased from 4.3 to 0.6 and logK for Br^? decreased from 3.3 to 0.1. The selectivity coefficients of hydrophilic anions such as Cl^?, F^?, HPO₄^2?, and SO₄^2? are significantly lower than in case of the ionophore‐free membrane. It was discovered that the constructed electrodes are also relatively selective to bicarbonate. This work is an important step towards the further development of solid‐contact anion‐selective electrodes.     

A Reversible Redox Strategy for SWCNT‐Based Supercapacitors Using a High‐Performance Electrolyte

In order to achieve pesudocapacitive performance of single‐wall carbon nanotube (SWCNT) electrodes, a high‐efficient and reversible redox strategy utilizing a redox‐mediated electrolyte for SWCNT‐based supercapacitors is reported. In this novel redox‐mediated electrolyte, the single‐electrode specific capacitance of the supercapacitor is heightened four times, reaching C=162.66 F g^?1 at 1 A g^?1. The quick charge‐discharge ability of the supercapacitor is also enhanced, and the relaxation time is as low as 0.58 s. Furthermore, the supercapacitor shows an excellent cycling performance of 96.51 % retention after 4000 cycles. The remarkable results presented here illustrate that the redox strategy is a facile and straightforward approach to improve the performances of SWCNT electrodes.     

Voltammetric Studies of Cadmium‐ and Zinc‐Containing Metallothioneins at Nafion‐Coated Mercury Thin Film Electrodes

Voltammetric studies of rabbit liver metallothioneins (MTs, containing both Zn and Cd ions) and Zn₇‐MT were carried out at Nafion‐coated mercury film electrodes (NCMFEs). The accumulation of MT molecules into the NCMFEs enhances the voltammetric signals and the electrostatic interaction between the Nafion membrane and MT facilitates facile electron transfer reactions. Two well‐defined redox waves, with reduction potential (E_pc) values at ?0.740 and ?1.173 V, respectively, were observed. The peak at E_pc =?0.740 V is attributable to the reduction of the Cd‐MT complex, whereas that at E_pc=?1.173 V was assigned to the reduction of the Zn‐MT complex. Zn₇‐MT exhibits only one redox wave with E_pc=?1.198 V. The NCMFE was found to be more advantageous than thin mercury film electrode (MFE), because the pristine metal ions in MTs (e.g., Cd²⁺ and/or Zn²⁺) are not significantly replaced by Hg²⁺. The NCMFE is also complementary to Nafion‐coated bismuth film electrode in that it has a greater hydrogen overpotential, which allows the reduction of the Zn‐MT complex to be clearly observed. Moreover, intermetallic compound formation between Cd and Zn appears to be less serious at NCMFEs. Consequently, the amounts of Cd and Zn deposited into the electrode upon the reduction reactions can be quantified more accurately.     

Substituent effect on supercapacitive performances of conducting polymer‐based redox electrodes: Poly(3′,4′‐bis(alkyloxy) 2,2′:5′,2″‐terthiophene) derivatives

This work reports the synthesis of novel poly(3′,4′‐bis(alkyloxy)terthiophene) derivatives (PTTOBu, PTTOHex, and PTTOOct) and their supercapacitor applications as redox‐active electrodes. The terthiophene‐based conducting polymers have been derivatized with different alkyl pendant groups (butyl‐, hexyl‐, and octyl‐) to explore the effect of alkyl chain length on the surface morphologies and pseudocapacitive properties. The electrochemical performance tests have revealed that the length of alkyl substituent created a remarkable impact over the surface morphologies and charge storage properties of polymer electrodes. PTTOBu, PTTOHex, and PTTOOct‐based electrodes have reached up to specific capacitances of 94.3, 227.3, and 443 F g⁻¹ at 2.5 mA cm⁻² constant current density, respectively, in a three‐electrode configuration. Besides, these redox‐active electrodes have delivered satisfactory energy densities of 13.5, 29.3, and 60.7 W h kg⁻¹ and power densities of 0.98, 1, and 1.1 kW kg⁻¹ with good capacitance retentions after 10,000 charge/discharge cycles in symmetric solid‐state micro‐supercapacitor devices. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 480–495     

Lipophilic Multi‐walled Carbon Nanotube‐based Solid Contact Potassium Ion‐selective Electrodes with Reproducible Standard Potentials. A Comparative Study

The two most promising approaches for preparing solid contacts (SCs) for polymeric membrane based ion‐selective electrodes (ISEs) are based on the use of large surface areas conducting materials with high capacitance (e. g., various carbon nanotubes) and redox active materials (e. g. conducting polymers). While many of the essential requirements for the potential stability of SCISEs were addressed, the E⁰ reproducibility and its predictability, that would enable single use of such electrodes without calibration is still a challenge, i. e., the fabrication of electrodes with sufficiently close E⁰ and slope values to enable the characterization of large fabrication batches through the calibration of only a small number of electrodes. The most generic solution seems to be the adjustment of the E⁰ potential by polarization prior to the application of the ion‐selective membrane. This approach proved to be successful in case of conducting polymer‐based solid contacts, but has to be still explored for capacitive solid contact based ISEs, which is the purpose of this paper. We have chosen a well‐established highly lipophilic multi‐walled carbon nanotube (MWCNT), i. e. octadecane modified MWCNT (OD‐MWCNT), that is investigated in the comparative context of a similarly lipophilic conducting polymer solid contact (a perfluorinated alkanoate side chain functionalized poly(3,4‐ethylenedioxythiophene)). While, the OD‐MWCNT based SCISEs had inherently small standard deviation of their E⁰ values (less than 5 mV) this could be further improved by external polarization and short circuiting the SCISEs.     

Double‐Layer Correction for Electron‐Transfer Kinetics at Glassy Carbon and Mercury Electrodes in N,N‐Dimethylformamide

The double‐layer properties of the glassy carbon electrode in N,N‐dimethylformamide (DMF) containing tetrabutylammonium perchlorate (TBAP) at different concentrations have been studied by cyclic voltammetry and impedance. The results were compared with analogous results obtained for the mercury/DMF interface. For both electrodes, the double‐layer data were treated to obtain useful equations describing the dependence of the outer Helmholtz plane potential on the applied potential. The kinetics of the dissociative reduction of a sulfide in DMF/0.1 M TBAP was studied by convolution analysis on both glassy carbon and mercury and used as an example to test the double‐layer results and compare the behavior of the two electrodes.     

Sensitive and Selective Electrochemical Analysis of Methyl‐parathion (MPT) and 4‐Nitrophenol (PNP) by a New Type p‐NiTSPc/p‐PPD Coated Carbon Fiber Microelectrode (CFME)

A novel modified carbon fiber microelectrode (CFME) was obtained by combination of tetrasulfonated nickel phtalocyanine (p‐NiTSPc) electroformed film associated to para‐phenylenediamine (p‐PPD) electropolymerized outer‐coating. The modified CFMEs where denoted C/p‐NiTSPc and C/p‐NiTSPc/p‐PPD, respectively. These electrodes are dedicated to the organophosphates compounds (OPs) methyl‐parathion (MPT) and para‐nitrophenol (PNP). Our contribution shows that both OPs can be determined simultaneously on the unmodified and modified C/p‐NiTSPc CFMEs. A clear electrocatalytic activity towards both MPT and PNP redox process was observed, for the first time, in presence of p‐NiTSPc. The obtained sensitivity for the C/p‐NiTSPc CFME was 80 nA L mg^?1 in the concentration range 0.01 to 10 mg/L with a detection limit of 40 μg/L. Also the combination of p‐NiTSPc and p‐PPD electrodeposited films show, for the first time, the possibility to discriminate on the C/p‐NiTSPc/p‐PPD CFME between MPT and PNP. Stability experiments were also conducted for 3 weeks in acetate buffer showing a good reproductibility of the sensitivity to PNP vs. time in presence of MPT with a little loss of sensitivity (5%) after 3 weeks.     

A Self‐contained Two‐electrode Nanosensor for Electrochemical Analysis in Aqueous Microenvironments

We describe the development, fabrication, and characterization of a novel two‐electrode nanosensor contained within the tip of a needle‐like probe. This sensor consists of two, vertically aligned, carbon structures which function as individual electrodes. One of the carbon structures was modified by silver electrodeposition and chlorination to enable it to function as a pseudo‐reference electrode. Performance of this pseudo‐reference electrode was found to be comparable to that of commercially available Ag/AgCl reference electrodes. The unmodified carbon structure was employed as a working electrode versus the silver‐plated carbon structure to form a two‐electrode sensor capable of characterizing redox‐active analytes. The nanosensor was demonstrated to be capable of electrochemically characterizing the redox behavior of para‐aminophenol (PAP) in both bulk solutions and microenvironments. PAP was also measured in cell lysate to show that the nanosensor can detect small concentrations of analyte in heterogenous environments. As the working and reference electrodes are contained within a single nanoprobe, there was no requirement to position external electrodes within the electrochemical cell enabling analysis within very small domains. Due to the low‐cost manufacturing process, this nanoprobe has the potential to become a unique and widely accessible tool for the electrochemical characterization of microenvironments.     

Solid‐state NMR Study of the YadA Membrane‐Anchor Domain in the Bacterial Outer Membrane

MAS‐NMR was used to study the structure and dynamics at ambient temperatures of the membrane‐anchor domain of YadA (YadA‐M) in a pellet of the outer membrane of E. coli in which it was expressed. YadA is an adhesin from the pathogen Yersinia enterocolitica that is involved in interactions with the host cell, and it is a model protein for studying the autotransport process. Existing assignments were sucessfully transferred to a large part of the YadA‐M protein in the E. coli lipid environment by using ¹³C‐¹³C DARR and PDSD spectra at different mixing times. The chemical shifts in most regions of YadA‐M are unchanged relative to those in microcrystalline YadA‐M preparations from which a structure has previously been solved, including the ASSA region that is proposed to be involved in transition‐state hairpin formation for transport of the soluble domain. Comparisons of the dynamics between the microcrystalline and membrane‐embedded samples indicate greater flexibility of the ASSA region in the outer‐membrane preparation at physiological temperatures. This study will pave the way towards MAS‐NMR structure determination of membrane proteins, and a better understanding of functionally important dynamic residues in native membrane environments.     

Electrochemistry of and Redox‐Induced Metal Release from Metallothioneins at a Nafion‐Coated Bismuth Film Electrode

Nafion‐coated bismuth film electrodes (NCBiFEs) were used to investigate the redox behavior of and metal release from rabbit liver metallothioneins (MTs) in an acetate buffer. Owing to the permselective exchange between positively charged MT molecules and cations in Nafion and the absence of detectable MT adsorption at bismuth surface, a diffusion‐controlled Nernstian redox wave of MTs (E_pc=?0.869 V) was observed for the first time. The Nernstian behavior of the diffusing MTs is in contrast to the voltammetric responses of MTs at thin mercury films or Nafion‐coated mercury film electrodes, which either result in the replacement of the metals originally present in MTs by mercury or lead to a noticeable MT adsorption. By avoiding these undesirable features, the NCBiFE provides an excellent milieu for voltammetric studies of different types of MTs and related isoforms, paving the way for studying the redox‐modulated metal transfer of MTs and understanding the biological role of MTs in heavy metal detoxification and essential metal regulations.     

Electron Transfer between Genetically Modified Hansenula polymorpha Yeast Cells and Electrode Surfaces via Os‐complex modified Redox Polymers

Graphite electrodes modified with redox‐polymer‐entrapped yeast cells were investigated with respect to possible electron‐transfer pathways between cytosolic redox enzymes and the electrode surface. Either wild‐type or genetically modified Hansenula polymorpha yeast cells over‐expressing flavocytochrome b2 (FC b₂) were integrated into Os‐complex modified electrodeposition polymers. Upon increasing the L ‐lactate concentration, an increase in the current was only detected in the case of the genetically modified cells. The overexpression of FC b₂ and the related amplification of the FC b₂/L ‐lactate reaction cycle was found to be necessary to provide sufficient charge to the electron‐exchange network in order to facilitate sufficient electrochemical coupling between the cells, via the redox polymer, to the electrode. The close contact of the Os‐complex modified polymer to the cell wall appeared to be a prerequisite for electrically wiring the cytosolic FC b₂/L ‐lactate redox activity and suggests the critical involvement of a plasma membrane redox system. Insights in the functioning of whole‐cell‐based bioelectrochemical systems have to be considered for the successful design of whole‐cell biosensors or microbial biofuel cells.     

Carbon‐Nanotube‐Supported Bio‐Inspired Nickel Catalyst and Its Integration in Hybrid Hydrogen/Air Fuel Cells

A biomimetic nickel bis‐diphosphine complex incorporating the amino acid arginine in the outer coordination sphere was immobilized on modified carbon nanotubes (CNTs) through electrostatic interactions. The functionalized redox nanomaterial exhibits reversible electrocatalytic activity for the H₂/2 H⁺ interconversion from pH 0 to 9, with catalytic preference for H₂ oxidation at all pH values. The high activity of the complex over a wide pH range allows us to integrate this bio‐inspired nanomaterial either in an enzymatic fuel cell together with a multicopper oxidase at the cathode, or in a proton exchange membrane fuel cell (PEMFC) using Pt/C at the cathode. The Ni‐based PEMFC reaches 14 mW cm⁻², only six‐times‐less as compared to full‐Pt conventional PEMFC. The Pt‐free enzyme‐based fuel cell delivers ≈2 mW cm⁻², a new efficiency record for a hydrogen biofuel cell with base metal catalysts.     

Effect of Poly(amine)s on the Redox Properties of Carboxymethylcellulose and Ferrocene‐modified Poly(amine) Layer‐by‐Layer Films

Multilayer films consisting of carboxymethylcellulose (CMC) and ferrocene‐modified poly(ethyleneimine) (Fc‐PEI) or poly(allylamine hydrochloride) (Fc‐PAH) were successfully prepared on a gold electrode to examine their redox properties. The redox current of (Fc‐PEI/CMC)_n film‐coated electrodes increased with the number of layers, while the (Fc‐PAH/CMC)_n film‐coated electrodes exhibited increased response only for the first eight bilayers. The (Fc‐PEI/CMC)_n and (Fc‐PAH/CMC)_n films deposited on the surface of Fc‐free multilayer film‐coated electrodes also showed a redox response. The (PEI/CMC)₅ film‐coated electrode showed redox responses in Fc‐PEI and Fc‐PAH solutions, confirming the uptake of the Fc‐polymers in the inner film. In contrast, the uptake of the Fc‐polymers in the (PAH/CMC)₅ film was severely suppressed, suggesting that different permeability of (PEI/CMC)₅ and (PAH/CMC)₅ films.     

Spontaneous Synthesis of Silver‐Nanoparticle‐Decorated Transition‐Metal Hydroxides for Enhanced Oxygen Evolution Reaction

The fabrication of metal‐supported hybrid structures with enhanced properties typically requires external energy input, such as pyrolysis, photolysis, and electrodeposition. In this study, silver‐nanoparticle‐decorated transition‐metal hydroxide (TMH) composites were synthesized by an approach based on a spontaneous redox reaction (SRR) at room temperature. The SRR between silver ions and TMH provides a simple and facile route to establish effective and stable heterostructures that can enhance the oxygen evolution reaction (OER) activity. Ag@Co(OH)_x grown on carbon cloth exhibits outstanding OER activity and durability, even superior to IrO₂ and many previously reported OER electrocatalysts. Experimental and theoretical analysis demonstrates that the strong electronic interaction between Ag and Co(OH)₂ activates the silver clusters as catalytically OER active sites, effectively optimizing the binding energies with reacted intermediates and facilitating the OER kinetics.     

Synthesis and self‐assembly of thermoresponsive block‐graft fluoropolymer as well as its tunable wettability surface

Thermo‐responsive block‐graft fluoropolymer is synthesized and investigated the self‐assembly morphology and the tunable wettability surface on cotton fabric by dip‐coating into the micelles with different temperatures. Well‐defined block‐graft copolymer is prepared by click chemistry with poly(hexafluorobutyl methacrylate)‐block‐poly(glycidyl methacrylate) (PHFBMA‐b‐PGMA) and homopolymer poly(N‐isopropylacrylate) with alkyne on main chain (Alkynyl‐PNIPAM) to synthesize final block‐graft polymer PHFBMA‐b‐(PGMA‐g‐PNIPAM). The thermo‐responsive behaviors of block‐graft polymer prove that the diameter for fluoropolymer micelle is about 50–70 nm with uniform sphere shape at room temperature and bigger and broader at 40 °C. The surface of cotton fabric processed in micelle solution at room temperature is smooth and has good hydrophobic property, while it has the hydrophilic property dipped in high temperature micelle solution. This work may give valuable guidance for fabricating a facile strategy to establish controllable wettability surfaces on different substrates, which is a promising candidate for the coating materials and industrial fields. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 992–1002