Synthesis and (spectro)electrochemistry of mixedvalent diferrocenyl–dihydrothiopyran derivatives

Three novel diferrocenyl complexes were prepared and characterised. 2,2-Diferrocenyl-4,5-dimethyl- 3,6-dihydro-2H-thiopyran (1, sulphide) was accessible by the hetero-Diels–Alder reaction of diferrocenyl thioketone with 2,3-dimethyl-1,3-butadiene. Stepwise oxidation of 1 gave the respective oxides 2,2- diferrocenyl-4,5-dimethyl-3,6-dihydro-2H-thiopyran-1-oxide (2, sulfoxide) and 2,2-diferrocenyl-4,5- dimethyl-3,6-dihydro-2H-thiopyran-1,1-dioxide (3, sulfone), respectively. The molecular structures of 1 and 3 in the solid state were determined by single crystal X-ray crystallography. The oxidation of sulphide 1 to sulfone 3, plays only a minor role on the overall structure of the two compounds. Electrochemical (cyclic voltammetry (= CV), square wave voltammetry (= SWV)) and spectroelectrochemical (in situ UV-Vis/NIR spectroscopy) studies were carried out. The CV and SWV measurements showed that an increase of the sulphur atom oxidation from −2 in 1 to +2 in 3 causes an anodic shift of the ferrocenylbased oxidation potentials of about 100 mV. The electrochemical oxidation of 1–3 generates mixedvalent cations 1+–3+. These monooxidised species display low-energy electronic absorption bands between 1000 and 3000 nm assigned to IVCT (= Inter-Valence Charge Transfer) electronic transitions. Accordingly, the mixed-valent cations 1+–3+ are classified as weakly coupled class II systems according to Robin and Day.Authors (K. K. and G. M.) thank the National Science Centre (Poland) for financial support (Project Maestro-3; Dec-2012/06/ A/ST5/00219) and R. C. thanks the German Federal Ministry of Education and Research (BMBF) for support. The support from the German Academic Exchange Service (DAAD) in the framework of the exchange program “Ostpartnerschaften” is highly appreciated

Developing Time-Resolved Synchrotron Infrared Spectroscopy for Spectroelectrochemical Measurements

This thesis details my work in developing spectroelectrochemical platforms utilizing synchrotron infrared radiation (SIR) and time-resolved FTIR to study the kinetics of electrochemical reactions on second to millisecond scale with high chemical sensitivity. It will cover development of spectroelectrochemical cells and procedures compatible with the mid-IR beamline at the Canadian Light Source to study irreversible electrocatalytic processes with rapid scan FTIR in reflection mode. The thesis demonstrates application of SIR-based rapid scan FTIR to spatially map catalytic activity on heterogenous PtNi electrode and provides proof-of-principle for its capability for combinatorial screening for binary electrocatalysts. The thesis discusses the development of time-resolved step scan FTIR in attenuated total reflection - surface enhancing infrared absorption spectroscopy configuration (ATR-SEIRAS) to improve signal-to-noise of the measurement for increased detection limits and time-resolution, before demonstrating the utility of the developed step scan ATR-SEIRAS platform by investigation of the kinetics of conformational changes within self-assembled monolayers (SAM) of ferrocene alkanethiols. Overall, the work described in this thesis outlines the advancement of SIR-based spectroelectrochemical platforms within the group to a point, where they can be directly applied to investigation of dynamics processes within electrochemical reaction

Developing Time-Resolved Synchrotron Infrared Spectroscopy for Spectroelectrochemical Measurements

This thesis details my work in developing spectroelectrochemical platforms utilizing synchrotron infrared radiation (SIR) and time-resolved FTIR to study the kinetics of electrochemical reactions on second to millisecond scale with high chemical sensitivity. It will cover development of spectroelectrochemical cells and procedures compatible with the mid-IR beamline at the Canadian Light Source to study irreversible electrocatalytic processes with rapid scan FTIR in reflection mode. The thesis demonstrates application of SIR-based rapid scan FTIR to spatially map catalytic activity on heterogenous PtNi electrode and provides proof-of-principle for its capability for combinatorial screening for binary electrocatalysts. The thesis discusses the development of time-resolved step scan FTIR in attenuated total reflection - surface enhancing infrared absorption spectroscopy configuration (ATR-SEIRAS) to improve signal-to-noise of the measurement for increased detection limits and time-resolution, before demonstrating the utility of the developed step scan ATR-SEIRAS platform by investigation of the kinetics of conformational changes within self-assembled monolayers (SAM) of ferrocene alkanethiols. Overall, the work described in this thesis outlines the advancement of SIR-based spectroelectrochemical platforms within the group to a point, where they can be directly applied to investigation of dynamics processes within electrochemical reaction

Influence of RTIL Nanodomains on the Voltammetry and Spectroelectrochemistry Of Fullerene C\u3csub\u3e60\u3c/sub\u3e in Benzonitrile/Room Temperature Ionic Liquids Mixtures

The cyclic voltammetry of fullerene C60 was examined in mixed benzonitrile/RTIL solvents in order to probe the effect of nanodomains in the mixed RTIL/benzonitrile solutions and their effect upon the voltammetry. In probing the interactions of the fullerides (up to C603−) with RTILs, BMIm+ (1-butyl-3-methylimidazolium, mostly planar) and tetraalkylammonium (more spherical/flexible) salts were used. In order to investigate these shifts in more detail, the ΔE12° (=E°1–E°2) and ΔE23° (=E°2–E°3) values, which were independent of the reference potential, were used. At higher concentrations of the RTILs, greater stabilization of the more highly charged fullerides were observed. These shifts were attributed to the interaction of the fullerides with nanodomains of the RTIL. This was further confirmed by examining the shifts in the E1/2 values of non-RTIL and RTIL salts at constant ionic strength and the changes in diffusion coefficient with %RTIL. The observed shifts in the E1/2 values with increased concentration of the RTIL salts could not be explained by ion pairing equilibria alone. Changes in the visible and near infrared spectra between benzonitrile and mixed benzonitrile/RTIL spectra were most significant for C603−, where voltammetric evidence indicates the strongest interaction between the fullerides and the RTIL. Among the RTILs studied, preliminary DFT calculations showed that the more flexible tetraalkylammonium ion was able to stabilize the C60-anionic species better than the planar BMIm+ species, under similar solution conditions

Building and Optimizing a Spectroelectrochemical System for the Study of Shewanella Putrefaciens

Shewanellaceae are among the most widely studied electroactive microorganisms. This study reports on Shewanella putrefaciens under anaerobic conditions during applied potential while monitored by spectroscopy. The attachment of the microbe Shewanella putrefaciens onto an indium tin oxide electrode was found to occur after 2 hr of +0.2 V applied potential. Microbial detachment occurred with a 5 mV/s scan rate cyclic voltammogram from +0.2 V to -0.5 V to +0.2 V. This was confirmed through use of a spectroelectrochemical apparatus utilizing a standard 3 electrode setup with evanescent wave spectroscopy

Fiber Optic Spectroelectrochemical Sensing for In-Situ Determination of Metal Ions

In-situ chemical sensing techniques are increasingly utilized for a variety of applications, including industrial process control, on-site environmental assessment, and detection of explosives and chemical and biological weapons. A common category of sensors for such purposes entails the use of optical fibers for making spectral measurements of target compounds or species derived from these compounds via physical, chemical, enzymatic or immunological reactions. A less common, but potentially advantageous approach involves the electrochemical conversion of the analyte subsequent to its spectroscopic detection. These spectroelectrochemical schemes represent versatile, essentially reagent-free analyses that could provide superior alternatives to existing methods. Reported here is a summary of progress made by the authors’ group toward the development of fiber optic spectroelectrochemical sensors for in-situ measurements. The aqueous copper (II)/copper (0) couple was chosen as a model system to investigate the merit of an analytical scheme involving (i) cathodic preconcentration of Cu2+ 2 as Cu0 followed by (ii) anodic stripping of Cu0 to Cu2+, (iii) complexation of Cu2+ by an appropriate ligand, and finally (iv) absorbance determination of the copper/ligand complex or fluorescence determination of the unbound ligand. Results are encouraging and indicate the need for further refinement of the sensor’s design and the experimental protocol in order to improve the method’s sensitivity

A novel heteroditopic terpyridine-pincer ligand as building block for mono- and heterometallic Pd(II) and Ru(II) complexes

A palladium-catalyzed Stille coupling reaction was employed as a versatile method for the synthesis of a novel terpyridine-pincer (3, TPBr) bridging ligand, 4'-{4-BrC6H2(CH2NMe2)(2)-3,5}-2,2':6',2 ''-terpyridine. Mononuclear species [PdX(TP)] (X = Br, Cl), [Ru(TPBr)(tpy)](PF6)(2), and [Ru(TPBr)(2)](PF6)(2), synthesized by selective metalation of the NCNBr-pincer moiety or complexation of the terpyridine of the bifunctional ligand TPBr, were used as building blocks for the preparation of heterodi- and trimetallic complexes [Ru(TPPdCl)(tpy)](PF6)(2) (7) and [Ru(TPPdCl)(2)]-(PF6)(2) (8). The molecular structures in the solid state of [PdBr(TP)] (4a) and [Ru(TPBr)(2)](PF6)(2) (6) have been determined by single-crystal X-ray analysis. Electrochemical behavior and photophysical properties of the mono-and heterometallic complexes are described. All the above di- and trimetallic Ru complexes exhibit absorption bands attributable to (MLCT)-M-1 (Ru -> tpy) transitions. For the heteroleptic complexes, the transitions involving the unsubstituted tpy ligand are at a lower energy than the tpy moiety of the TPBr ligand. The absorption bands observed in the electronic spectra for TPBr and [PdCl(TP)] have been assigned with the aid of TD-DFT calculations. All complexes display weak emission both at room temperature and in a butyronitrile glass at 77 K. The considerable red shift of the emission maxima relative to the signal of the reference compound [Ru(tpy)(2)](2+) indicates stabilization of the luminescent (MLCT)-M-3 state. For the mono- and heterometallic complexes, electrochemical and spectroscopic studies (electronic absorption and emission spectra and luminescence lifetimes recorded at room temperature and 77 K in nitrile solvents), together with the information gained from IR spectroelectrochemical studies of the dimetallic complex [Ru(TPPdSCN)(tpy)](PF6)(2), are indicative of charge redistribution through the bridging ligand TPBr. The results are in line with a weak coupling between the {Ru(tpy)(2)} chromophoric unit and the (non)metalated NCN-pincer moiety

Bidimensional spectroelectrochemistry: application of a new device in the study of a o-vanillin-copper(II) complex

A new bidimensional spectroelectrochemistry setup for UV-Vis absorption measurements has been developed. The new device has been used to follow electrochemical reactions using two different arrangements: 1) a near-normal configuration that supplies information about the processes taking place both on the electrode surface and in the solution adjacent to it, and 2) a long-optical-pathway configuration based on a mobile slit that controls the position of a light beam passing parallel and adjacent to the electrode surface providing information only about the processes taking place in solution during the electrochemical reaction. The new setup has been validated using o-tolidine, a typical reference system for spectroelectrochemistry. The electrochemical mechanism of oxidation/reduction of Cu(o-Va)2(H2O)2 complex (o-Va = o-Vanillin = 2-hydroxy-3-methoxybenzaldehyde) has been studied using bidimensional UV-Vis absorption spectroelectrochemistry. This Cu(II) complex exhibits antimutagenic, anticarcinogenic and superoxide dismutase mimic properties.Junta de Castilla y León (BU033U16), and Ministerio de Economía y Competitividad (CTQ2014-55583-R, CTQ2014-61914-EXP, CTQ2015-71955-REDT)CONICET, UNLP, Junta de Castilla y León (BU033U16), and Ministerio de Economía y Competitividad (CTQ2014-55583-R, CTQ2014-61914-EXP, CTQ2015-71955-REDT

Development and applications of condensed phase cavity ring-down spectroscopy for studies of electrochemical and interfacial.

This dissertation reports the development of ultra-sensitive platforms based on the laser cavity ring-down spectroscopic (CRDS) technique to enable optical and spectroelectrochemical investigations in the condensed phase of matter at challenging scenarios. Firstly, an electrically-active solid/liquid interface for the evanescent-wave cavity ring-down spectroscopy (EW-CRDS) was developed to specroelectrochemically investigate redox events. By coating the interface of total internal reflection of the EW-CRDS platform with a high quality optically transparent and electrically conductive indium tin oxide thin film (ITO), we demonstrated that sufficiently long ring-down times can be achieved to allow for spectroelectrochemical investigations of redox species at solid/liquid interfaces at low surface coverages. The effects of an applied electric potential on the adsorption behavior of a redox protein onto different interfaces were investigated. For each interface, the adsorption and desorption constants, the surface equilibrium constant, the Gibbs free energy of adsorption, and the surface coverage were optically measured by our electrically-active EW-CRDS tool. Cyclic voltammetry (CV) scans under synchronous optical readout were performed to study the effects of each molecular interface in the redox process of surface-adsorbed protein species. The electro-active EW-CRDS technology is experimentally tested and demonstrated to provide a high-performance platform for studies of electrode-driven redox events of surface-confined molecular species at low submonolayer coverages and at a single diffraction-limited spot. Next, the electrically-active capability of the EW-CRDS device has been extended to develop a bio-sensing strategy based on the combination of the electro-active EW-CRDS platform with a sandwich immunoassay approach for the detection antigens of the influenza A virus (H5N1). Initially, the EW-CRDS was deployed to characterize in-situ and in real-time the formation of the assembly of the immunoassay-based biosensor. Our strategy proceeds in a stepwise manner: in the first step, the surface of the electro-active EW-CRDS device is functionalized with a capture antibody (Ab) aimed at a specific virus antigen. Next, the capture Ab-coated surface is exposed to a target antigen, which after binding to the surface it promotes the immobilization of secondary Ab that has been labeled with a redox-active probe. The redox-active probe methylene blue acts as a transduction element for monitoring molecular binding events and can be electrochemically modulated on the EW-CRDS platform to provide a unique optical interrogation signal. Based on this novel detection strategy, the experimental results have demonstrated an outstanding level of sensitivity in the pico-molar range for the detection of the influenza virus antigen. Finally, we used an electrically modulated optical signal collected with an electro-active EW-CRDS platform under CV potential modulation for fast detection and direct quantification of a target antigen. Such results demonstrate the potential of the electro-active EW-CRDS technology for high sensitive detection of surface-confined biomarkers at a single spot and at very low concentrations, which open the prospect towards an arrayed-detection technology. In addition, the highly sensitive CRDS technology in the liquid phase was applied for trace detection of nitrite ions in aqueous environment. The principle of the analytical method used for the determination of trace nitrite is based on the changing of the chromatic reagent color from purple to yellow due to its reduction reaction of nitrite ions in an acidic medium, which results in a decrease of optical absorbance. The decrease in absorbance is directly proportional to the nitrite concentration and the CRDS technique was used to measure the absorbance decrease at 532 nm. The experimental results show that nitrite ions could be detected accurately within a low detection limit, which can reach as low as 8 ng/ml. With the current CRDS setup, we have achieved an absorption sensitivity of about 1x10-6 cm-1. Finally, we have explored the ultra-sensitivity of the CRDS platform for direct measurements in changes of optical loss in ultra-thin films of a semiconductor material (ITO) during surface treatment with ultra-violet (UV) radiation. The results demonstrated the ability of the CRDS to measure minute absorption changes in the ITO ultra-thin film during UV treatment. Upon inserting a glass slide coated with an ITO film at Brewster’s angle inside the optical cavity, the cavity ring-down time of about 1.6 μs was achieved, which enables measurements of optical absorption loss as low as 3x10-6 cm-1. The ITO ultra-thin film was treated with UV radiation in two ways: after and during the deposition process at different oxygen flow rates. In order to evaluate the effect of surface treatment, the CRDS platform was employed to measure the extinction coefficient for each coated sample with and without UV exposure, while the change in electrical resistivity was monitored simultaneously. Based on the measurements of optical constants and cavity ring-down times, the UV treatment could be tuned to increase the optical efficiency of an ITO ultra-thin film. These applications are demonstrated to provide novel tools to study the interfacial phenomena with high sensitivity and specificity, which are expected to open several opportunities to investigate a wide range of molecular assemblies and sensing applications

Numerical Simulation of Electrochemical Processes at a Tubular Electrode. Application to Spectroscopy

A model of spectroelectrochemical cell design based on a tubular working electrode with optical fibers connected to a spectrometer entering it from two ends is built. Both current and absorbance responses of the cell are numerically simulated and the operation regimes are determined in terms of ranges of governing parameters for chronoamperometry and linear sweep voltammetry