The mechanism and the oxidation potential of the dissociative single electron transfer for tetra-n-butylammonium acetate has been investigated via conventional (cyclic voltammetry) and convolution voltammetry. The oxidation potential for tetra-n-butylammonium acetate was determined to be 0.60 ± 0.10 (vs. Ag/ (0.1 M) AgNO₃) in anhydrous acetonitrile. The results also indicated the mechanism of oxidation was concerted dissociative electron transfer (cDET), rather than stepwise as was previously reported. To further investigate the mechanism, a series of aliphatic and aromatic tetra-n butylammonium carboxylates were synthesized and investigated via convolution and conventional methods under anhydrous conditions (propionate, pivalate, phenyl acetate, and benzoate). The reported results showed high reproducibility and consistency with a concerted dissociative electron transfer for aliphatic carboxylates with a systematic shift in the oxidation potentials (0.60 ± 0.09 V for acetate, 0.47 ± 0.05 V for propionate, and 0.40 ± 0.05 V for pivalate) within the series which is expected trend based on radical stabilization energies of the alkyl groups on the aliphatic carboxylates. Hydrogen bonding was investigated as a possible source for the discrepancy between our results and the reported mechanism of the dissociative electron transfer. Because of the extreme hygroscopic nature of carboxylate salts, it was hypothesized that the presence of small amounts of water might alter the reaction mechanism. Deionized water and deuterium oxide additions to anhydrous acetonitrile were performed to test this hypothesis. The mechanism was noted to shift towards a stepwise mechanism as water was added. In addition, the derived oxidation potentials became more positive with increasing concentrations of water. Several explanations are presented with regards to water effects on the shift in the electron transfer mechanism. Indirect electrolysis (homogeneous redox catalysis) was also employed as an alternative and independent approach to quantify the oxidation potentials of carboxylates. A series of substituted ferrocenes were investigated as mediators for the oxidation of tetra-n-butylammonium acetate. Preliminary data showed redox catalysis was feasible for these systems. Further analyses of the electrochemical results suggested a follow-up chemical step (addition to mediator) that competes with the redox catalysis mechanism. As predicted from theoretical working curves, a plateau region in the i_p/i_pd plots (where no meaningful kinetic information could be obtained) was observed. Products mixture analyses verified the consumption of the mediator upon electrolysis, but no further information with regards to the nature of the mechanism was deduced. In a related study the effects of hydrogen bonding and ions on the reactivity of neutral free radicals were examined by laser flash photolysis. The rate of the β-scission of the cumyloxyl radical is influenced by cations (Li⁺ > Mg²⁺ ≈ Na⁺ > ⁿBu₄N⁺) due to stabilizing ion-dipole interactions in the transition state of the developing carbonyl group. Experimental findings are in a good agreement with theoretical work suggesting metal ion complexation can cause radical clocks to run fast with a more significant effect if there is an increase in dipole moment going from the reactant to the transition state. / Ph. D. / Our work focuses on employing electrochemical techniques to investigate single electron transfer processes, which lead to unstable organic species that contain an odd number of electrons called radicals and radical ions. Many essential biological and environmental pathways are found to occur via radicals, i.e. photosynthesis, atmospheric degradation, enzyme catalyzed reactions in biology, autooxidation, DNA mutations, and more. Electrochemical techniques permit us to investigate the scientific fundamentals of radical processes by generating radicals and radical ions in a controlled manner with a higher efficiency. We have combined electrochemical techniques with established physical organic theories of electron transfer to allow us to determine of the rate and mechanism of electron transfer for a selective group of chemical compounds, specifically anions derived from carboxylic acids (carboxylates). A fundamental understanding of single electron transfer processes for carboxylates allows for a prediction of chemical behavior and the future design of novel chemical compounds for alternative chemical functionality. Our findings are the first to report experimental evidence for a so-called concerted dissociative electron transfer mechanism for carboxylates, where the transfer of an electron is accompanied by the simultaneous breakage of a carbon-carbon bond yielding a radical and carbon dioxide. The mechanism has been shown to proceed in a stepwise fashion only in the presence of water. Our work highlights the environmental effects on radical stability such as water and metals ions.

This thesis addresses simulation of electrochemical experiments, with an emphasis on processes of diffusional mass transport to electrode surface. Following system has been studied: • Applying theoretical modeling and experimentation is shown that even significant surface roughness produced by deliberate polishing or scratching is not sufficient to be distinguished in cyclic voltammetry experiments conducted under the usual conditions. In stripping voltammetry experiment the shape of the voltammograms strongly depends on the model of the electron transfer but is not always sensitive to the precise model of the electrode surface; the conditions under which this is the case are identified, and generic roughness effects on stripping voltammetry are quantified. Electrode roughness can have a significant effect on the stripping of the metals from the solid electrode especially in respect of the voltammetric waveshape. • We first consider two different models of electrodes covered with electroinactive layers: the electrode is covered with a uniform layer and the layer contains pinholes. Both models are simulated and then compared to identify conditions under which they can be distinguished. Next we propose generic model to predict the influence of electroactive layer on the cyclic voltammetric. The conditions under which deviation from the behavior of a planar electrode are predicted. • We first consider one electron, one proton and next two electron, two proton reduction of surface bound species. Two mechanisms of reaction are considered: stepwise and concerted. Voltammetry studied under the three regimes of protons mass transport: infinitely fast (fully buffered solution), infinitely slow (infinitely high surface coverage of electrode) and intermediate case of finite rate of diffusional mass transport to electrode surface. Types of voltammograms observed in each case are presented and discussed. • Theory of chronoamperometry on disc and ring-recessed microelectrodes and their arrays is reported. Three and four different regimes of transient current versus time can be observed at microelectrode arrays of disc and ring electrodes, accordingly. A generic, accurate and easy to use method of experimental chronoamperometric data analysis is proposed. It is shown that the method can be applied to the simultaneous measurement of D and nC in solution. • The fabrication, characterization, and use of arrays of ring-recessed disk generator-colector microelectrodes are reported. Experiments and simulations relating to time- of-flight experiments in which material electrogenerated at a disk is diffusionally transported to the ring are reported. We further study voltammetry of electrochemically active species which undergoes first and second order chemical reactions. Current transients are found to be sensitive to the diffusion coefficient of both the reduced and oxidised species as well as to the rate of the chemical reaction and its mechanism.

The aim of presented Diploma Thesis was to study an electrochemical behavior of nitroimidazole drugs metronidazole and ornidazole and to find optimal conditions for their voltammetric determination at a mercury meniscus modified silver solid amalgam electrode using DC voltammetry (DCV) and differential pulse voltammetry (DPV). Voltammetric behavior of selected drugs was investigated in dependence on the pH of the medium used (realized using a Britton-Robinson buffer (BR buffer)) and a mechanism of the reduction of both drugs was investigated using cyclic voltammetry (CV). The optimum medium for voltammetric determination of studied nitroimidazole drugs at the m-AgSAE in a region of cathodic potentials was found to be the BR buffer of pH 8.0. Then, the concentration dependences were measured in this optimum medium in the concentration range from 2·10-7 mol/L to 1·10-4 mol/L. The limits of quantification (LQs) for both metronidazole and ornidazole were found in the concentration order of 10-7 mol/L by using DCV and DPV at the m-AgSAE. The applicability of the newly developed voltammetric methods of the determination of nitroimidazole drugs was verified on the model samples of drinking and river water, with LQ ≈ 2·10-7 mol/L for both DC voltammetry and differential pulse voltammetry at the m-AgSAE....

Presented Diploma Thesis is focused on electroanalytical determination of the herbicide Aclonifen, which belongs to a group of herbicides derived from diphenylether. These herbicides are used due to their effects - inhibition of protoporfyrinogen oxidase synthesis and also inhibition of biosynthesis of carotenoids. Due to its widespread use in agricultural, toxical effects on humans and because of its negative impacts particularly on aquatic ecosystems there is a need for methods capable of determining the presence of Aclonifen in the environment to monitor its ecological impacts. Optimal conditions for the determination of Aclonifen have been investigated in BR buffer - methanolic solution and in BR buffer. Electrochemical behavior of the substance has been studied using direct current voltammetry (DCV), differential pulse voltammetry (DPP) and adsorptive stripping voltammetry (AdSV) on the hanging mercury drop electrode (HMDE) and by using TAST polarography and differential pulse polarography (DPP) on the dropping mercury electrode (DME). UV/VIS spectrophotometric detection was used for comparison to electrochemical detection. Used wavelengths were 308 nm and 388 nm. For electrochemical determination of Aclonifen the above mentioned techniques were used and following results were obtained: DCV...

The major directions of this dissertation involve (1) the syntheses and characterization of molecular polygons incorporating sp1hybridized carbon linkers and L2Pt corners (L2 = cis-1,3-diphosphine), (2) the development of protected carbon chain complexes featuring fluorous phosphine ligands and (3) click reactions of metal terminal polyynyl complexes and further metallations of the resulting triazole rings. A brief overview is provided in Chapter I. Chapter II details the syntheses of molecular squares containing bidendate diphosphine ligands of the formula R2C(CH2PPh2)2 where R = Me, Et, n-Bu, n-Dec, Bn, and p-tolCH2 (general designation dppp*), in which the R2 groups are intended to circumvent the solubility issues encountered by others. Their syntheses involve double substitutions of the dimesylate compounds R2C(CH2OMs)2 using KPPh2. Building blocks of the formulae (dppp*)PtCl2 and (dppp*)Pt((C≡C)2H)2 are synthesized and characterized, including one crystal structure of the latter. The target complexes are accessed by reactions of (dppp*)PtCl2 with (dppp*)Pt((C≡C)2H)2 under Sonogashira type conditions. Six new squares of the formula [(R2C(CH2PPh2)2)Pt(C≡C)2]4 are characterized including two crystal structures. Further topics include approaches to higher homologues and cyclocarbon synthesis. Chapter III focuses on carbon chain complexes bearing fluorous phosphine ligands of the formula P((CH2)mRfn)3 (Rfn = (CF2)n-1CF3; m/n = 2/8, 3/8, and 3/10). Precursors of the formula trans-(C6F5)((Rfn(CH2)m)3P)2PtCl are synthesized and characterized, including one crystal structure, which reveals phase separation of the fluorous and non-fluorous domains. Reactions with butadiyne give trans-(C6F5)((Rfn(CH2)m)3P)2Pt(C≡C)2H. Oxidative homocouplings afford the target complexes trans,trans-(C6F5)((Rfn(CH2)m)3P)2Pt(C≡C)4(C6F5)(P((CH2)mRfn)3)2Pt. Cyclic voltammetry indicates irreversible oxidations of the title compounds, in contrast to partially reversible oxidations of non-fluorous analogues. Chapter IV focuses on multimetallic complexes achieved by click reactions in metal coordination spheres. The copper catalyzed click reaction between trans-(C6F5)(p-tol3P)2Pt(C≡C)2H (1) and (η5-C5H4N3)Re(CO)3 affords the bimetallic 1,2,3-triazole trans-C6F5)(p1tol3P)2PtC≡CC=CHN((η51C5H4)Re(CO)3)N=N. Further reactions with Re(CO)5OTf and Re(CO)5Br give trimetallated adducts, which represent the first species of this type. An alternative route to a trimetallic complex involves the twofold cycloaddition of the diazide (η5-C5H4N3)2Fe and 1, giving (η5-C5H4NN=N-C(trans-(C≡C)Pt(Pp-tol3)2(C6F5)=CH)2Fe. The crystal structures of the di and trimetallic complexes are compared, but attempts to achieve a fourth metallation involving the =CH groups are unsuccessful. However, when the triazolium salt [trans-(C6F5)(p-tol3P)2PtC≡CC=CHN(CH2C6H5)N=N(Me)]+ I– is treated with Ag2O and [Rh(COD)Cl]2, a =CRh adduct is obtained. The success of =CH metallation is correlated to the 1H NMR chemical shift, indicative of an electronic effect.

Optimum detergent dosage during a washing process depends on water quality, degree of pollution and quantity of laundry. Particularly, water quality is an important factor. Other parameters like carbonate- or non-carbonate hardness and calcium / magnesium (Ca / Mg) ratio in addition to total hardness of water have an impact on the amount of detergent. This work discusses the possibilities realizing a detergent sensor that measures important parameters for the washing process and assess the ideal necessary amount of detergent during the washing process. The approach is to combine impedance spectroscopy with cyclic voltammetry in order to determine both water quality and concentration of detergent in the suds which build up the basis for an optimum detergent dosage. The results of cyclic voltammetry show that it is possible to identify the Ca / Mg ratio and the carbonate hardness separately, which is necessary for the optimization of the washing process. Impedance measurements identify total hardness and detergent concentrations.

Understanding the factors influencing the ET characteristics of redox proteins confined at an electrochemical interface is of fundamental importance from both pure (fundamental science) and applied (biosensory) perspectives. This thesis reports on progress made in the emerging field of coupled electrochemical characterization and optical imaging in moving the analysis of redox-active films to molecular scales. More specifically the combination of cyclic voltammetry and wide-field Total Internal Reflection (TIRF) microscopy, here named ‘Fluorescent Cyclic Voltammetry’ (FCV), was applied to monitoring the response of surface-confined redox active proteins at submonolayer concentrations. The combined submicrometre spatial resolution and photon capture efficiency of an inverted TIRF configuration enabled the redox reactions of localized populations of proteins to be directly imaged at scales down to a few hundreds of molecules. This represents a 6-9 orders of magnitude enhancement in sensitivity with respect to classical current signals observed in bioelectrochemical analysis. Importantly, measurements of redox potentials at this scale could be achieved from both natural and artificially designed bioelectrochemical fluorescent switches and shed fundamental light on the thermodynamic and kinetic dispersion within a population of surface confined metalloproteins. The first three chapters of this thesis provide an overview of the relevant literature and a theoretical background to both the rapidly expanding fields of electroactive monolayers bioelectrochemistry and TIRF imaging. The initial design and construction of a robust electrochemically and optically addressable fluorescent switch, crucial to the applicability of FCV is reported in chapter 5. The generation of optically transparent, and chemically modifiable electrode surfaces suitable for FCV are also described. Chapter 6 describes the response of the surface confined azurin-based switch. Analysis of the spatially-resolved redox reaction of zeptomole samples in various conditions enables the mapping of thermodynamic dispersion across the sampled areas. In chapter 7 the newly developed FCV detection method was extended to investigate more complex bioelectrochemical systems containing multiple electron transferring redox centres and responding optically at different wavelengths. This approach provides a platform for spectral resolution of different electrochemical processes on the same sample. Finally in chapter 8 an electrochemical procedure is proposed for investigating the kinetic response of redox proteins using a fundamentally new methodology based on interfacial capacitance. In using variations in the surface chemistry to tune the rate of electron transfer, the approach was shown to be a robust and facile means of characterising redox active films in considerably more detail than possible through standard electrochemical methodologies. Ultimately, it can be applied to probe dispersion within protein populations and represents a powerful means of analysing molecular films more generally.

Chapter1 gives an overview of the basic principles of electrochemistry. A rigorous electrochemical study on the solution phase and solid phase cobalt phthalocyanine (CoPC) is presented in chapter2. The formof CoPC on carbon electrodes was characterized by scanning electron microscope (SEM). The use of CoPC modified edge plane pyrolytic graphite (CoPC-EPPG) for sensing nitrite (NO₂⁻) was also investigated. It was found that the claimed mediator CoPC has no influence on the process. A bare glassy carbon (GC) electrode was successfully applied for the quantitative determination of nitrite as a simple alternative to the modified electrodes reported in the literature (chapter3). Chapter4 compares the voltammetric responses of an edge plane pyrolytic graphite electrode covalently modifed with 2-anthraquinonyl groups (EPPG-AQ2) and solution phase anthraquinone monosulphonate (AQMS) in the presence of a limited concentration of protons. The solution phase and surface bound species show analogous responses resulting in split waves. Digisim™ simulation of the AQMS voltammetry have shown that the pH adjacent to the electrode may be altered by up to 5-6 pH units in low buffered solutions; this is caused by the consumption of protons during the electrochemical reaction. Chapters5 and 6 compare the electrochemical properties of 2-anthraquinonyl groups covalently attached to an edge plane pyrolytic graphite (EPPG) and to a gold electrode. In both cases simulations using newly developedMarcus-Hush-Chidsey theory for a 2e⁻ process assuming a uniform surface did not achieve a good agreement between theory and experiment. Subsequently two models of surface inhomogeneity were investigated: a distribution of formal potentials, E^Ө, and a distribution of electron tunneling distances, r₀. For both EPPG-AQ2 and Au-AQ2 modified electrodes the simulation involving E^Ө distribution turned out to be the most adequate. This is the first time that Marcus-Hush-Chidsey theory has been applied to a 2e⁻ system. Chapter7 briefly summarizes the obtained results.

The master thesis present the possibilities of processing of electrochemical data from a group of four electrodes with non-selective response (simple sensor array) for electrochemical analysis with potential application of the results achieved in the construction of the sensor field type "electronic tongue". This simple system was applied to the sample simulating the food product. Electrochemical data were processed through mathematical operations such as Gaussian approximation, deconvolution or using basic mathematical operations.

Antimony film electrode was studied for the use in a voltammetric analysis of organic compounds. The substance chosen as an analyte was trifluralin, which is used as a pesticide. The comparison of different substrate electrodes was carried out between five electrodes, which were gold, silver, copper, polished amalgam and glassy carbon electrode (GCE). Best performance was observed on antimony film glassy carbon electrode (SbFGCE). It provided higher sensitivity and lower limit of quantification in comparison with bare GCE. The antimony film was stable and it provided good reproducibility (RSD = 5.2 %). Parameters of an electrochemical preparation of SbFGCE were optimized. Conditions for determination of concentration of trifluralin were optimized on newly prepared SbFGCE. The best conditions were in a solution of methanol and 0.1 M hydrochloric acid in 1:1 ratio measured by differential pulse voltammetry. The limit of quantification was determined as 1.2·10-6 mol·l-1 . A direct voltammetric measurement on SbFGCE was carried out in a model river sample. Lower limits of quantification were achieved with solid phase extraction (SPE). Recovery values were 86 ± 8 % in deionized water with a preconcentration factor of 125. The limit of quantification was lowered to value 1.1·10-8 mol·l-1 . The extraction...