@article{KappBeissenhirtzGeyeretal.2006, author = {Kapp, A. and Beissenhirtz, Moritz Karl and Geyer, F. and Scheller, F. and Viezzoli, Maria Silvia and Lisdat, Fred}, title = {Electrochemical and sensorial behavior of SOD mutants immobilized on gold electrodes in aqueous/organic solvent mixtures}, series = {Electroanalysis : an international journal devoted to fundamental and practical aspects of electroanalysis}, volume = {18}, journal = {Electroanalysis : an international journal devoted to fundamental and practical aspects of electroanalysis}, publisher = {Wiley}, address = {Weinheim}, issn = {1040-0397}, doi = {10.1002/elan.200603620}, pages = {1909 -- 1915}, year = {2006}, abstract = {A cysteine mutant of a monomeric human Cu, Zn-SOD (Glycine 61, Serine 142) has been immobilized directly on gold electrodes using the thiol groups introduced. The electrochemical behavior of the surface confined protein was studied in mixtures of aqueous buffer and DMSO up to an organic solvent content of 60\%. The formal potential was found to be rather independent of the DMSO content. However, half peak width increased and the redoxactive amount clearly decreased with raising DMSO content. In addition, the kinetics of the heterogeneous electron transfer became slower; but still a quasireversible electrochemical conversion of the mutant SOD was feasible. Thus, the electrodes were applied for sensorial superoxide detection. At a potential of +220 mV vs. Ag/AgCl advantage was taken of the partial oxidation reaction of the enzyme. A defined superoxide signal was obtained in solutions up to 40\% DMSO. The sensitivity of the mutant electrodes decreased linearly with the organic solvent content in solution but was still higher compared to conventional cyt.c based sensors. At DMSO concentrations higher than 40\% no sensor response was detected.}, language = {en} } @article{PengUteschYarmanetal.2015, author = {Peng, Lei and Utesch, Tillmann and Yarman, Aysu and Jeoung, Jae-Hun and Steinborn, Silke and Dobbek, Holger and Mroginski, Maria Andrea and Tanne, Johannes and Wollenberger, Ursula and Scheller, Frieder W.}, title = {Surface-Tuned Electron Transfer and Electrocatalysis of Hexameric Tyrosine-Coordinated Heme Protein}, series = {Chemistry - a European journal}, volume = {21}, journal = {Chemistry - a European journal}, number = {20}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0947-6539}, doi = {10.1002/chem.201405932}, pages = {7596 -- 7602}, year = {2015}, abstract = {Molecular modeling, electrochemical methods, and quartz crystal microbalance were used to characterize immobilized hexameric tyrosine-coordinated heme protein (HTHP) on bare carbon or on gold electrodes modified with positively and negatively charged self-assembled monolayers (SAMs), respectively. HTHP binds to the positively charged surface but no direct electron transfer (DET) is found due to the long distance of the active sites from the electrode surfaces. At carboxyl-terminated surfaces, the neutrally charged bottom of HTHP can bind to the SAM. For this "disc" orientation all six hemes are close to the electrode and their direct electron transfer should be efficient. HTHP on all negatively charged SAMs showed a quasi-reversible redox behavior with rate constant k(s) values between 0.93 and 2.86 s(-1) and apparent formal potentials E-app(0)' between -131.1 and -249.1 mV. On the MUA/MU-modified electrode, the maximum surface concentration corresponds to a complete monolayer of the hexameric HTHP in the disc orientation. HTHP electrostatically immobilized on negatively charged SAMs shows electrocatalysis of peroxide reduction and enzymatic oxidation of NADH.}, language = {en} } @article{NeumannKielbRustametal.2017, author = {Neumann, Bettina and Kielb, Patrycja and Rustam, Lina and Fischer, Anna and Weidinger, Inez M. and Wollenberger, Ulla}, title = {Bioelectrocatalytic Reduction of Hydrogen Peroxide by Microperoxidase-11 Immobilized on Mesoporous Antimony-Doped Tin Oxide}, series = {ChemElectrChem}, volume = {4}, journal = {ChemElectrChem}, number = {4}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {2196-0216}, doi = {10.1002/celc.201600776}, pages = {913 -- 919}, year = {2017}, abstract = {The heme-undecapeptide microperoxidase-11 (MP-11) was immobilized on mesoporous antimony-doped tin oxide (ATO) thin-film electrodes modified with the positively charged binding promotor polydiallyldimethylammonium chloride. Surface concentrations of MP-11 of 1.5 nmol cm(-2) were sufficiently high to enable spectroelectrochemical analyses. UV/Vis spectroscopy and resonance Raman spectroscopy revealed that immobilized MP-11 adopts a six-coordinated low-spin conformation, as in solution in the presence of a polycation. Cathodic reduction of hydrogen peroxide at potentials close to +500mV versus Ag/AgCl indicates that the reaction proceeds via a Compound I-type like intermediate, analogous to natural peroxidases, and confirms mesoporous ATO as a suitable host material for adsorbing the heme-peptide in its native state. A hydrogen peroxide sensor is proposed by using the bioelectrocatalytic properties of the MP-11-modified ATO.}, language = {en} } @article{BrietzkeDietzKellingetal.2017, author = {Brietzke, Thomas Martin and Dietz, Thomas and Kelling, Alexandra and Schilde, Uwe and Bois, Juliana and Kelm, Harald and Reh, Manuel and Schmitz, Markus and Koerzdoerfer, Thomas and Leimk{\"u}hler, Silke and Wollenberger, Ulla and Krueger, Hans-Joerg and Holdt, Hans-J{\"u}rgen}, title = {The 1,6,7,12-Tetraazaperylene Bridging Ligand as an Electron Reservoir and Its Disulfonato Derivative as Redox Mediator in an Enzyme-Electrode Process}, series = {Chemistry - a European journal}, volume = {23}, journal = {Chemistry - a European journal}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0947-6539}, doi = {10.1002/chem.201703639}, pages = {15583 -- 15587}, year = {2017}, abstract = {The homodinuclear ruthenium(II) complex [{Ru(l-N4Me2)}(2)(-tape)](PF6)(4) {[1](PF6)(4)} (l-N4Me2=N,N-dimethyl-2,11-diaza[3.3](2,6)-pyridinophane, tape=1,6,7,12-tetraazaperylene) can store one or two electrons in the energetically low-lying * orbital of the bridging ligand tape. The corresponding singly and doubly reduced complexes [{Ru(l-N4Me2)}(2)(-tape(.-))](PF6)(3) {[2](PF6)(3)} and [{Ru(l-N4Me2)}(2)(-tape(2-))](PF6)(2) {[3](PF6)(2)}, respectively, were electrochemically generated, successfully isolated and fully characterized by single-crystal X-ray crystallography, spectroscopic methods and magnetic susceptibility measurements. The singly reduced complex [2](PF6)(3) contains the -radical tape(.-) and the doubly reduced [3](PF6)(2) the diamagnetic dianion tape(2-) as bridging ligand, respectively. Nucleophilic aromatic substitution at the bridging tape in [1](4+) by two sulfite units gave the complex [{Ru(l-N4Me2)}(2){-tape-(SO3)(2)}](2+) ([4](2+)). Complex dication [4](2+) was exploited as a redox mediator between an anaerobic homogenous reaction solution of an enzyme system (sulfite/sulfite oxidase) and the electrode via participation of the low-energy *-orbital of the disulfonato-substituted bridging ligand tape-(SO3)(2)(2-) (E-red1=-0.1V versus Ag/AgCl/1m KCl in water).}, language = {en} } @article{KotthoffLisecSchwerdtleetal.2019, author = {Kotthoff, Lisa and Lisec, Jan and Schwerdtle, Tanja and Koch, Matthias}, title = {Prediction of transformation products of monensin by electrochemistry compared to microsomal assay and hydrolysis}, series = {Molecules}, volume = {24}, journal = {Molecules}, number = {15}, publisher = {MDPI}, address = {Basel}, issn = {1420-3049}, doi = {10.3390/molecules24152732}, pages = {12}, year = {2019}, abstract = {The knowledge of transformation pathways and identification of transformation products (TPs) of veterinary drugs is important for animal health, food, and environmental matters. The active agent Monensin (MON) belongs to the ionophore antibiotics and is widely used as a veterinary drug against coccidiosis in broiler farming. However, no electrochemically (EC) generated TPs of MON have been described so far. In this study, the online coupling of EC and mass spectrometry (MS) was used for the generation of oxidative TPs. EC-conditions were optimized with respect to working electrode material, solvent, modifier, and potential polarity. Subsequent LC/HRMS (liquid chromatography/high resolution mass spectrometry) and MS/MS experiments were performed to identify the structures of derived TPs by a suspected target analysis. The obtained EC-results were compared to TPs observed in metabolism tests with microsomes and hydrolysis experiments of MON. Five previously undescribed TPs of MON were identified in our EC/MS based study and one TP, which was already known from literature and found by a microsomal assay, could be confirmed. Two and three further TPs were found as products in microsomal tests and following hydrolysis, respectively. We found decarboxylation, O-demethylation and acid-catalyzed ring-opening reactions to be the major mechanisms of MON transformation.}, language = {en} } @article{QuanGoubardBretescheHaerketal.2019, author = {Quan, Ting and Goubard-Bretesche, Nicolas and Haerk, Eneli and Kochovski, Zdravko and Mei, Shilin and Pinna, Nicola and Ballauff, Matthias and Lu, Yan}, title = {Highly Dispersible Hexagonal Carbon-MoS2-Carbon Nanoplates with Hollow Sandwich Structures for Supercapacitors}, series = {Chemistry - a European journal}, volume = {25}, journal = {Chemistry - a European journal}, number = {18}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0947-6539}, doi = {10.1002/chem.201806060}, pages = {4757 -- 4766}, year = {2019}, abstract = {MoS2, a typical layered transition-metal dichalcogenide, is promising as an electrode material in supercapacitors. However, its low electrical conductivity could lead to limited capacitance if applied in electrochemical devices. Herein, a new nanostructure composed of hollow carbon-MoS2-carbon was successfully synthesized through an L-cysteine-assisted hydrothermal method by using gibbsite as a template and polydopamine as a carbon precursor. After calcination and etching of the gibbsite template, uniform hollow platelets, which were made of a sandwich-like assembly of partial graphitic carbon and two-dimensional layered MoS2 flakes, were obtained. The platelets showed excellent dispersibility and stability in water, and good electrical conductivity due to carbon provided by the calcination of polydopamine coatings. The hollow nanoplate morphology of the material provided a high specific surface area of 543 m(2) g(-1), a total pore volume of 0.677 cm(3) g(-1), and fairly small mesopores (approximate to 5.3 nm). The material was applied in a symmetric supercapacitor and exhibited a specific capacitance of 248 F g(-1) (0.12 F cm(-2)) at a constant current density of 0.1 Ag-1; thus suggesting that hollow carbon-MoS2 carbon nanoplates are promising candidate materials for supercapacitors.}, language = {en} } @article{KotthoffO'CallaghanLisecetal.2020, author = {Kotthoff, Lisa and O'Callaghan, Sarah-Louise and Lisec, Jan and Schwerdtle, Tanja and Koch, Matthias}, title = {Structural annotation of electro- and photochemically generated transformation products of moxidectin using high-resolution mass spectrometry}, series = {Analytical and bioanalytical chemistry : a merger of Fresenius' journal of analytical chemistry, Analusis and Quimica analitica}, volume = {412}, journal = {Analytical and bioanalytical chemistry : a merger of Fresenius' journal of analytical chemistry, Analusis and Quimica analitica}, number = {13}, publisher = {Springer}, address = {Heidelberg}, issn = {1618-2642}, doi = {10.1007/s00216-020-02572-1}, pages = {3141 -- 3152}, year = {2020}, abstract = {Moxidectin (MOX) is a widely used anthelmintic drug for the treatment of internal and external parasites in food-producing and companion animals. Transformation products (TPs) of MOX, formed through metabolic degradation or acid hydrolysis, may pose a potential environmental risk, but only few were identified so far. In this study, we therefore systematically characterized electro- and photochemically generated MOX TPs using high-resolution mass spectrometry (HRMS). Oxidative electrochemical (EC) TPs were generated in an electrochemical reactor and photochemical (PC) TPs by irradiation with UV-C light. Subsequent HRMS measurements were performed to identify accurate masses and deduce occurring modification reactions of derived TPs in a suspected target analysis. In total, 26 EC TPs and 59 PC TPs were found. The main modification reactions were hydroxylation, (de-)hydration, and derivative formation with methanol for EC experiments and isomeric changes, (de-)hydration, and changes at the methoxime moiety for PC experiments. In addition, several combinations of different modification reactions were identified. For 17 TPs, we could predict chemical structures through interpretation of acquired MS/MS data. Most modifications could be linked to two specific regions of MOX. Some previously described metabolic reactions like hydroxylation or O-demethylation were confirmed in our EC and PC experiments as reaction type, but the corresponding TPs were not identical to known metabolites or degradation products. The obtained knowledge regarding novel TPs and reactions will aid to elucidate the degradation pathway of MOX which is currently unknown.}, language = {en} } @article{BalischewskiBehrensZehbeetal.2020, author = {Balischewski, Christian and Behrens, Karsten and Zehbe, Kerstin and G{\"u}nter, Christina and Mies, Stefan and Sperlich, Eric and Kelling, Alexandra and Taubert, Andreas}, title = {Ionic liquids with more than one metal}, series = {Chemistry - a European journal}, volume = {26}, journal = {Chemistry - a European journal}, number = {72}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0947-6539}, doi = {10.1002/chem.202003097}, pages = {17504 -- 17513}, year = {2020}, abstract = {Thirteen N-butylpyridinium salts, including three monometallic [C4Py](2)[MCl4], nine bimetallic [C4Py](2)[(M1-xMxCl4)-M-a-Cl-b] and one trimetallic compound [C4Py](2)[(M1-y-zMyMz (c) Cl4)-M-a-M-b] (M=Co, Cu, Mn; x=0.25, 0.50 or 0.75 and y=z=0.33), were synthesized and their structure and thermal and electrochemical properties were studied. All compounds are ionic liquids (ILs) with melting points between 69 and 93 degrees C. X-ray diffraction proves that all ILs are isostructural. The conductivity at room temperature is between 10(-4) and 10(-8) S cm(-1). Some Cu-based ILs reach conductivities of 10(-2) S cm(-1), which is, however, probably due to IL dec. This correlates with the optical bandgap measurements indicating the formation of large bandgap semiconductors. At elevated temperatures approaching the melting points, the conductivities reach up to 1.47x10(-1) S cm(-1) at 70 degrees C. The electrochemical stability windows of the ILs are between 2.5 and 3.0 V.}, language = {en} } @article{IlicTsoukaPerovicetal.2020, author = {Ilic, Ivan K. and Tsouka, Alexandra and Perovic, Milena and Hwang, Jinyeon and Heil, Tobias and L{\"o}ffler, Felix and Oschatz, Martin and Antonietti, Markus and Liedel, Clemens}, title = {Sustainable cathodes for Lithium-ion energy storage devices based on tannic acid-toward ecofriendly energy storage}, series = {Advanced sustainable systems}, volume = {5}, journal = {Advanced sustainable systems}, number = {1}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {2366-7486}, doi = {10.1002/adsu.202000206}, pages = {8}, year = {2020}, abstract = {The use of organic materials with reversible redox activity holds enormous potential for next-generation Li-ion energy storage devices. Yet, most candidates are not truly sustainable, i.e., not derived from renewable feedstock or made in benign reactions. Here an attempt is reported to resolve this issue by synthesizing an organic cathode material from tannic acid and microporous carbon derived from biomass. All constituents, including the redox-active material and conductive carbon additive, are made from renewable resources. Using a simple, sustainable fabrication method, a hybrid material is formed. The low cost and ecofriendly material shows outstanding performance with a capacity of 108 mAh g(-1) at 0.1 A g(-1) and low capacity fading, retaining approximately 80\% of the maximum capacity after 90 cycles. With approximately 3.4 V versus Li+/Li, the cells also feature one of the highest reversible redox potentials reported for biomolecular cathodes. Finally, the quinone-catecholate redox mechanism responsible for the high capacity of tannic acid is confirmed by electrochemical characterization of a model compound similar to tannic acid but without catecholic groups.}, language = {en} } @article{OcampoEspindolaOmel'chenkoKiss2021, author = {Ocampo-Espindola, Jorge Luis and Omel'chenko, Oleh and Kiss, Istvan Z.}, title = {Non-monotonic transients to synchrony in Kuramoto networks and electrochemical oscillators}, series = {Journal of physics. Complexity}, volume = {2}, journal = {Journal of physics. Complexity}, number = {1}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {2632-072X}, doi = {10.1088/2632-072X/abe109}, pages = {15}, year = {2021}, abstract = {We performed numerical simulations with the Kuramoto model and experiments with oscillatory nickel electrodissolution to explore the dynamical features of the transients from random initial conditions to a fully synchronized (one-cluster) state. The numerical simulations revealed that certain networks (e.g., globally coupled or dense Erdos-Renyi random networks) showed relatively simple behavior with monotonic increase of the Kuramoto order parameter from the random initial condition to the fully synchronized state and that the transient times exhibited a unimodal distribution. However, some modular networks with bridge elements were identified which exhibited non-monotonic variation of the order parameter with local maximum and/or minimum. In these networks, the histogram of the transients times became bimodal and the mean transient time scaled well with inverse of the magnitude of the second largest eigenvalue of the network Laplacian matrix. The non-monotonic transients increase the relative standard deviations from about 0.3 to 0.5, i.e., the transient times became more diverse. The non-monotonic transients are related to generation of phase patterns where the modules are synchronized but approximately anti-phase to each other. The predictions of the numerical simulations were demonstrated in a population of coupled oscillatory electrochemical reactions in global, modular, and irregular tree networks. The findings clarify the role of network structure in generation of complex transients that can, for example, play a role in intermittent desynchronization of the circadian clock due to external cues or in deep brain stimulations where long transients are required after a desynchronization stimulus.}, language = {en} }