Voltammetric Study of Interaction of Copper and Model Fungal Secreted Ligands

In lieu of Abstract, excerpt from Conclusion of Voltammetric Study of Interaction of Copper and Model Fungal Secreted Ligands: In summary, the cyclic voltammetry study shows evidence that the chelatormediated Fenton reaction is favored in the wood cell wall, where it may promote the degradation process. Also, reaction mechanisms between Cu(II), 2,3-DHBA and H202 have been proposed which provide at least partial explanations for the H202 cycle, and the mechanism for non-enzymatic, chelator-mediated Fenton reactions in brown rot wood decay processes. Future research in this area should explore cyclic voltarnrnetry analyses of Cu(I1) and ligands secreted by fungi, such as 2,5-DMHQ or 2,5-DMBQ in the absence or presence of H202 under a range of acidic conditions. Cyclic voltammetry experiments should also be conducted with Fe(III), oxalic acid and ligands secreted by fungi, to gain insight into the mechanism and kinetics of the relevant redox reactions in wood decay processes

Electroactive speciation studies for metal ion sensing

Chemical speciation is an important factor in understanding the role of metals in the environment. Bioavailability of trace metals is influenced by the degree of the labile fraction of the metal that is readily available for interaction with a cell surface of an organism. Voltammetric methods are capable of measuring this labile fraction, and are able to achieve limits of detection in the biologically relevant range. In this study, voltammetric methods were used to examine a set of trffluoromethyl and tolyl pyridylsulfonamide metal-ligand systems during the formation of ML„ complexes at a fixed [M]:[T] ratio and varied pH, to investigate speciation and the potential use of these ligands in surface modified sensors. Formation constants with cobalt(II), nickel(II), copper(II), zmc(II), and the varied pyndykulfonamide moieties, were fully evaluated by potentiometry. A method for simultaneous voltammetric-spectral pH titrations was developed and used to correlate formation constant findings. Voltammetric investigations at a bare glassy carbon electrode had varying electroactive response from the metal-ligand systems. The labile and electroactive systems, e.g. [CuL(^1)(_2)] and [CuL(^4)(_2) were used in formation constant mass-balance refinements derived from voltammetric pH titration data. It is believed that under optimised conditions, formation constant measurement by voltammetry at a glassy carbon electrode is feasible, and this method would be applicable for voltammetric speciation of metal ions in the environment

Speciation of Heavy Metals in Highway Drainage Systems

A trace metal speciation scheme proposed by Batley and Florence (1976) was applied to determine the physiochemical forms of zinc, cadmium, lead, and copper in two Central Florida highway drainage systems. The linearity and limitations of the ASV technique were also examined. The measurements showed that (a) more than 70% of the soluble Zn and Cd in all of the waters analyzed existed as liable ionic metal (b) lead was divided between labile and non-labile inorganic forms, but one particular form, PbCO3, predominated (c) a substantial fraction of copper is associated with organic colloids if humic substances are present. In addition a computerized chemical model for trace and major element speciation was applied to the waters in both drainage systems using measured average water quality for input parameters. A comparison between metal species measured by ASV and those predicted by the computer model are presented. There appears to be good agreement between the metal fractions measured in the water samples by ASV and those predicted by the chemical model

An electrochemical investigation of electroless deposition : the copper-DMAB system

An electrochemical study of the copper electroless deposition process, using dimethylamine borane as a reducing agent, has been performed, in order to gain further understanding of the mechanism and kinetics of electroless deposition. An in-depth study of the electro-oxidation of dimethylamine borane (DMAB) was additionally carried out, due to its increasing relevance, not only in electroless deposition, but also in fuel cell technology. DMAB oxidation was studied using different experimental techniques such as voltammetry, chronoamperometry, single-crystal electrochemistry and in-situ Fourier Transform infrared spectroscopy, which demonstrated that adsorption of the DMAB molecule, and its intermediates, plays an important role in the oxidation mechanism and kinetics. The initial dissociation process is catalysed by the presence of metallic surfaces and the applied potential. On gold surfaces, DMAB undergoes a three-electron transfer at low overpotentials, with a further oxidation process of up to six electrons occurring at high overpotentials. Chemical interactions with gold oxide produce further oxidation of the DMAB molecule. In the potential region of gold oxide formation, in highly alkaline media, the dimethylamine is also oxidised. The voltammetric behaviour of bipolar cells was studied using model reversible and quasi-reversible redox couples, in conjunction with numerical simulations of the system. DMAB oxidation and copper electrodeposition were studied separately and together using the bipolar cell, providing useful information of the 'coupling' effects between the cathodic and anodic processes of electroless deposition. The ability to quantify side reactions associated with electroless plating, namely hydrogen evolution in the copper-DMAB system, was also demonstrated. The kinetics of the copper-DMAB electroless system was studied in detail, using the electroless bath and a galvanic cell configuration. The fact that the rate of deposition decreased upon the physical separation of the two half-reactions, as well as the observed catalysis of the oxidation of DMAB by copper surfaces, lead to the conclusion that the mixed potential theory (MPT) does not apply to this system. Faradaic efficiencies never reached 100% due to the parasitic side reactions mentioned above; the latter were especially prominent in the early stages of deposition. Crystalline copper films were obtained, with a higher fraction of Cu (111) than expected for polycrystalline copper, while the roughness of the deposits was found to increase with deposition time.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

An electrochemical investigation of electroless deposition : the copper-DMAB system

An electrochemical study of the copper electroless deposition process, using dimethylamine borane as a reducing agent, has been performed, in order to gain further understanding of the mechanism and kinetics of electroless deposition. An in-depth study of the electro-oxidation of dimethylamine borane (DMAB) was additionally carried out, due to its increasing relevance, not only in electroless deposition, but also in fuel cell technology. DMAB oxidation was studied using different experimental techniques such as voltammetry, chronoamperometry, single-crystal electrochemistry and in-situ Fourier Transform infrared spectroscopy, which demonstrated that adsorption of the DMAB molecule, and its intermediates, plays an important role in the oxidation mechanism and kinetics. The initial dissociation process is catalysed by the presence of metallic surfaces and the applied potential. On gold surfaces, DMAB undergoes a three-electron transfer at low overpotentials, with a further oxidation process of up to six electrons occurring at high overpotentials. Chemical interactions with gold oxide produce further oxidation of the DMAB molecule. In the potential region of gold oxide formation, in highly alkaline media, the dimethylamine is also oxidised. The voltammetric behaviour of bipolar cells was studied using model reversible and quasi-reversible redox couples, in conjunction with numerical simulations of the system. DMAB oxidation and copper electrodeposition were studied separately and together using the bipolar cell, providing useful information of the 'coupling' effects between the cathodic and anodic processes of electroless deposition. The ability to quantify side reactions associated with electroless plating, namely hydrogen evolution in the copper-DMAB system, was also demonstrated. The kinetics of the copper-DMAB electroless system was studied in detail, using the electroless bath and a galvanic cell configuration. The fact that the rate of deposition decreased upon the physical separation of the two half-reactions, as well as the observed catalysis of the oxidation of DMAB by copper surfaces, lead to the conclusion that the mixed potential theory (MPT) does not apply to this system. Faradaic efficiencies never reached 100% due to the parasitic side reactions mentioned above; the latter were especially prominent in the early stages of deposition. Crystalline copper films were obtained, with a higher fraction of Cu (111) than expected for polycrystalline copper, while the roughness of the deposits was found to increase with deposition time.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Pyridine assisted CO₂ reduction to methanol at high pressure

Significant research efforts have been directed towards exploring electrocatalysts for the selective reduction of CO₂ to fuels such as methanol. Bocarsly et al (Princeton University) have recently reported the use of aromatic amines (e.g. pyridine (C₅H₅N)) as electrocatalysts in aqueous electrolytes for the reduction of CO₂ at low overpotentials (50-150 mV). Importantly, the CO₂-pyridine reduction process was claimed to selectively produce methanol with Faradaic efficiencies of ~100% on p-GaP electrode and 22-30% on Pt and Pd electrodes. Moreover, the initially proposed mechanism based on a radical intermediate interaction with CO₂ as a key step toward the production of methanol was subsequently disproved. In this project, methanol formation by the CO₂-pyridine (C₅H₅N) system was assessed by conducting electrolysis under various conditions at platinum electrodes. High pressure CO₂ was used with the aim of increasing the methanol yield. In the course of the present study, the bulk electrolysis confirmed the methanol production at 1 bar and at 55bar of CO₂ in the presence of pyridine. However, the methanol yield was found to be persistently limited to sub-ppm level (<1ppm) under all conditions investigated. The observed methanol yield limitation could not be overcome by the electrode reactivation techniques used. Moreover, the methanol formation seemed unaffected by the current density or the biasing mode. This was an indication of the independence of methanol production from the charge transfer on the electrode. In agreement with these observations, analysis of the voltammetric data supported by simulation revealed that the CO₂-pyridine reduction system is mainly pyridinium assisted molecular hydrogen production under all conditions investigated. In particular, protonated pyridine (C₅H₅N) ‘pyridinium’ was confirmed to behave as a weak acid on platinum. It was found that CO₂ is merely a proton source of pyridine reprotonation via the hydration reaction followed by carbonic acid dissociation. The reprotonation reaction coupled to the electrode reaction ultimately leads to the dihydrogen production. No direct contribution of CO₂ in the reduction process was observed. The production of methanol seems to occur chemically rather than directly driven by the charge transfer on the electrode. The role of pyridine (C₅H₅N) appears to be restricted to assisting in the generation of the hydrogen necessary for the alcohol production

The Application of Curve Fitting on the Voltammograms of Various Isoforms of Metallothioneins–Metal Complexes

The translation of metallothioneins (MTs) is one of the defense strategies by which organisms protect themselves from metal-induced toxicity. MTs belong to a family of proteins comprising MT-1, MT-2, MT-3, and MT-4 classes, with multiple isoforms within each class. The main aim of this study was to determine the behavior of MT in dependence on various externally modelled environments, using electrochemistry. In our study, the mass distribution of MTs was characterized using MALDI-TOF. After that, adsorptive transfer stripping technique with differential pulse voltammetry was selected for optimization of electrochemical detection of MTs with regard to accumulation time and pH effects. Our results show that utilization of 0.5 M NaCl, pH 6.4, as the supporting electrolyte provides a highly complicated fingerprint, showing a number of non-resolved voltammograms. Hence, we further resolved the voltammograms exhibiting the broad and overlapping signals using curve fitting. The separated signals were assigned to the electrochemical responses of several MT complexes with zinc(II), cadmium(II), and copper(II), respectively. Our results show that electrochemistry could serve as a great tool for metalloproteomic applications to determine the ratio of metal ion bonds within the target protein structure, however, it provides highly complicated signals, which require further resolution using a proper statistical method, such as curve fitting.The work has been supported by the Agency for the Czech Republic Health Research (AZV) project no. 15-28334A. The presented research was financed by the Czech Ministry of Education in frame of the National Sustainability Program, the grant LO1401 INWITE

A systematic approach for controlling electrodeposition based on studies of an acidic copper electrolyte

Bekannte akademische Erkenntnisse der Elektrochemie, wie die Butler–Volmer Kinetik, und deren Veränderungen ermöglichen unter anderem einen genaueren Einblick in den Mechanismus der Metallabscheidung. Aufgrund eines fehlenden Bindegliedes wurden diesen akademischen Erkenntnissen keine oder nur wenig Beachtung in der industriellen Prozessüberwachung geschenkt. Stattdessen wird die Hull–Zell–Abscheidung als indirekter Ansatz für die Analyse des Abscheidungsverhaltens benutzt. Durch die Entwicklung einer Methode, die die Randelemente–Methode als Grundlage für die Simulation verwendet, werden die kinetischen Parameter – die Austauschstromdichte j0 und der Transferkoeffizient α – aus experimentellen Hull-Zellen-Abscheidungen gewonnen (Rückwärtsbestimmung). Dieser Ansatz wird validiert, indem zyklische voltammetrische Daten eines sauren Kupferelektrolyten in die Simulation eingesetzt und die simulierten Hull-Zellkurven mit experimentellen Kurven verglichen werden. Darüber hinaus wird der Einfluss von Additiven auf das kinetische Verhalten untersucht, ohne die visuellen Informationen und die Möglichkeiten zu verlieren, die strukturellen und physikalischen Eigenschaften der Metallabscheidung zu erhalten. Dieser Ansatz kann zu einem tieferen elektrochemischen Verständnis von industriell benutzten Elektrolyten führen.Well-known academic considerations in electrochemistry, such as Butler–Volmer kinetics, and their changes provide, among other things, a more precise insight into the mechanism of metal deposition. Due to a missing link, little or no attention is paid to these academic findings in industrial process monitoring. Instead, the Hull cell deposition is used as an indirect approach for analysing the deposition behaviour. By developing a method implementing the boundary element method as a base for the simulation, the kinetic parameters – the exchange current density j0 and the transfer coefficient α – are obtained from experimental Hull cell depositions (reverse determination). This approach is validated by inserting cyclic voltametric data of an acidic copper electrolyte and comparing the simulated Hull cell curves to experimental curves. Additionally, the influence of additives on kinetic behaviour is studied without losing the visual information and the opportunity to get the structural and physical properties of the metal deposition. This approach can offer a more profound electrochemical understanding of electrolytes used in industrial processes

Distribution, speciation and fate of trace metals in the stratified Krka river estuary

The distribution, speciation, behaviour, and fate of selected trace metals (TM) (Zn Cd, Pb, Cu, Ni, and Co) were studied in the water column of the highly stratified Krka River estuary, from 2009 to 2013, covering two contrasting seasons (summer/winter). In addition, the study involved measurements of dissolved/particulate organic carbon (DOC/POC) and major physico–chemical parameters (salinity, pH, dissolved oxygen, temperature). Water samples were taken from the three characteristic layers (brackish, the freshwater–seawater interface (FSI), and seawater). Stripping voltammetry (anodic, and adsorptive cathodic) was the primary analytical technique, while the diffusion gradient in thin films (DGT) technique was used as a complementary technique for speciation measurements. The concentrations of all TM were lower in the Krka River than in the open Adriatic which allowed the identification of pathways and processes governing the horizontal and vertical redistribution of TM across the whole estuary, whether they were added into the system by human activity or by ‘‘in-situ’’ processes (e.g. scavenging). Non-conservative behaviour for most of the studied TM observed in the surface layer of the estuary was primarily caused by their input in the Šibenik Bay area. Detailed "mapping" of the bay showed that the harbour and nautical marina are the regions with the highest concentrations of TM. A significant increase of Cu and Zn in the entire estuary transect during the summer period appeared to be directly linked to intensive nautical activity i.e. caused by the release of TM from antifouling paints. The scavenging of metals into the deeper layers, along with the longer residence time of seawater, caused an upstream increase in TM concentrations in the seawater layer. A very good agreement between the vertical profiles of DGT-labile, and dissolved TM concentrations suggests that the DGT technique can be successfully used to determine potentially bioavailable TM concentrations in estuarine conditions. The fraction of DGT-labile TM, which reflects their chemical speciation (primarily, their binding to natural organic ligands), ranged from > 90% for Cd, to < 20% for Cu, but also depends on the concentration ratios of metals and organic ligands. Voltammetric speciation of Cu showed the presence of two types of organic ligands that form strong (L1, 9.6 < logK1 < 11.9) and weak (L2, 7.8 < logK2 < 9.9) Cu complexes. The concentration of weak organic ligands (L2) is correlated with the DOC concentration, and is higher in summer, most probably due to the increased biological activity. The concentration of free Cu ions (the most bioavailable form), at ambient conditions, is regulated primarily by the complexation with strong ligands (L1). For most of the samples, the calculated free Cu slightly exceeds the toxic threshold of 10 pM. However, these values are the result of applied methodology of calculation, and does not necessarily reflect real ambient conditions.Raspodjela i specijacija odabranih metala u tragovima (TM) (Zn Cd, Pb, Cu, Ni i Co), te njihovo ponašanje i sudbina istraživani su u vodenom stupcu vertikalno uslojenog estuarija rijeke Krke tijekom dva kontrastna godišnja doba (ljeto/zima) u periodu od 2009 do 2013. Istraživanja su obuhvaćala i mjerenja otopljenog/partikulatnog organskog ugljika (DOC/POC), te osnovnih fizičko–kemijskih pokazatelja (salinitet, pH, otopljeni kisik, temperatura), a uzorkovanja su provođena u tri karakteristična sloja (boćati sloj, haloklina i morski sloj). Voltammetrija s akumulacijom (anodna i adsorptivna katodna) bila je primarna analitička tehnika, dok je za specijaciju korištena i komplementarna tehnika pasivnog uzorkovanja temeljena na principu difuzijskog gradijenta u tankom filmu (DGT). Koncentracije TM niže su u rijeci Krki nego u vodi otvorenog dijela Jadrana, što je omogućilo identifikaciju puteva i procesa koji reguliraju horizontalnu i vertikalnu preraspodjelu TM u cijelom estuariju, neovisno da li su oni u sustav uneseni ljudskom aktivnošću ili „in-situ“ procesima (npr. tonjenje -„scavenging“). Nekonzervativno ponašanje u površinskom sloju estuarija uočeno za većinu TM uzrokovano je primarno unosom metala u području Šibenskog zaljeva. Detaljno „mapiranje“ zaljeva pokazalo je da su luka i nautička marina područja s najvišom koncentracijom TM. Pokazalo se da je značajan porast Cu i Zn u cijelom estuariju tijekom ljetnih mjeseci u izravnoj vezi s pojačanom nautičkom aktivnošću, odnosno vezani su za otpuštanje metala iz protuobraštajnih boja s plovila. Vertikalni transport TM u dublje slojeve („scavenging“), te dulje vrijeme zadržavanja morske vode uzrokovali su uzvodni porast koncentracije TM u morskom sloju. Vrlo dobro slaganje vertikalnih profila DGT-labilnih i otopljenih koncentracija TM ukazuju da se DGT tehnika može uspješno koristiti za određivanje potencijalno bioraspoloživih koncentracija TM u estuarijskim uvjetima. Udio DGT-labilnih TM odraz je njihove kemijske specijacije (primarno vezanja s prirodnim organskim ligandima), te varira od > 90% za Cd, do < 20% za Cu, ali ovisan je također i o omjeru koncentracije metala i organskih liganada. Voltammetrijska specijacija Cu pokazala je prisutnost dva tipa organskih liganada koji stvaraju jake (L1, 9.6 < logK1< 11.9) odnosno slabe (L2, 7.8 < logK2< 9.9) Cu komplekse. Koncentracija slabijih organskih liganada (L2) u korelaciji je s koncentracijom DOC-a, te je veća ljeti najvjerojatnije zbog povećane biološke aktivnosti. Koncentracija slobodnih iona Cu (vrsta koja je najviše bioraspoloživa) pri okolišnim uvjetima regulirana je u većoj mjeri kompleksiranjem s jakim ligandima (L1). Za većinu uzoraka izračunate vrijednosti slobodnog Cu blago prelaze graničnu toksičnu vrijednost od 10 pM. Međutim, te vrijednosti su rezultat upotrijebljenog načina izračuna i ne odražavaju nužno stvarno stanje