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This thesis is concerned with the electrochemical and spectroelectrochemical characterisation of cyano (CN) and trifluoromethyl (CF3) substituted polypyridine ligands and their metal complexes. The ligands investigated were X-CN-py (X = 3, 4 and 5, py = pyridine), X,X´-(CN)2-bpy) (X,X´ = 3,3´, 4,4´ and 5,5´ bpy = 2,2´- bipyridine) and X,X´-(CF3)2-bpy (X,X´ = 3,3´, 4,4´ and 5,5´). The Pt(II) complexes of the X-CN-py and X,X´-(CN)2-bpy ligands were studied along with the Fe(II) complexes of the X,X´-(CN)2-bpy and X,X´-(CF3)2-bpy ligands. Electrochemical studies of the X-CN-py ligands indicated that 2-CN-py and 4-CN-py have one reversible 1e- reduction and 3-CN-py has one quasi-reversible reduction. 4-CN-py is more easily reduced than 2-CN-py. EPR experiments on [2-CN-py]1- and [4-CN-py]1- combined with DFT calculations have indicated that the semi-occupied molecular orbital (SOMO) is delocalised over the entire molecule. The complex [Pt(4-CN-py)2Cl2] undergoes two reversible 1e- reductions, attributed to the sequential reduction of the two 4-CN-py ligands. [Pt(3-CN-py)2Cl2] was found to exhibit one irreversible reduction. The electrochemistry of the X,X´-(CN)2-bpy ligands indicated that 3,3´-(CN)2-bpy and 5,5´-(CN)2-bpy have two reversible 1e- reductions while 4,4´-(CN)2-bpy has only one reversible 1e- reduction. The reductions of 5,5´-(CN)2-bpy occur at significantly less negative potentials than those in 3,3´ or 4,4´ analogue. In-situ UV/Vis/NIR and EPR experiments on the X,X´-(CN)2-bpy ligands indicate that the reduction electron is delocalised over both the CN-py rings with the SOMO being spread across the entire molecule. [Pt(3,3´-(CN)2-bpy)Cl2] and [Pt(5,5´-(CN)2-bpy)Cl2] undergo two reversible 1e- reductions, attributed to the sequential reduction of the X,X´-(CN)2-bpy ligand. 4,4´-(CF3)2-bpy and 5,5´-(CF3)2-bpy, whose X-ray crystallographically determined structures are reported, both have one reversible 1e- reduction while 3,3´-(CF3)2-bpy exhibits an irreversible reduction. Again the 5,5´ analogue is the most easily reduced. Spectroelectrochemical results indicate that the reduction electron enters a SOMO that is delocalised over both the CF3-py rings. Substitution in the 5,5´ positions is determined to be electronically most significant. Complexes of the general formula [Fe(II)(X2-bpy)3][BF4] (where X = CN or CF3 in the 4,4´ or 5,5´ positions) exhibit three reversible ligand based reduction processes and a metal based oxidation. UV/Vis/NIR and EPR studies have confirmed that the reduction electron in each case enters a molecular orbital that is predominantly based on a bpy ligand. The redox potentials of 4-CN-py and 5,5´-(CN)2-bpy are solvent dependent with 1e- reduction of 4-CN-py and the two 1e- reductions of 5,5´-(CN)2-bpy moving to less negative potentials as the acceptor number (AN) of the solvent increases. A computational model has been developed for the study of the electronic properties of substituted bipyridines using DFT methods. This model has been used to aid the analysis of the EPR and UV/Vis/NIR spectra of the X2-bpys studied.

The effect on conductivity of progressively substituting foreign alkali for host alkali in a series of lithium aluminoborate glasses has been studied. The shape of the conductivity isotherm in the dilute foreign alkali region was found to be the same for both Na+ and K+ dopants. Assuming a 'regular interstitialcy model' for ionic conduction conductivity data for a variety of glasses were subjected to isothermal analysis, allowing concentrations of mobile species and mobilities to be calculated. Conductivity changes were found to be largely attributable to changes in mobility, the concentration term remaining remarkably constant. The a.c. behaviour of aluminoborate glasses has also been studied and modulus spectra fitted using the Kohlrausch-Williams-Watts function for various beta-values. Decreasing the total alkali content and substituting foreign alkali for host alkali was observed to cause some narrowing of the modulus, mixed-alkali glasses behaving much as though only 'host' cations were present. 'Microscopic' activation energies (E_a) have been calculated from beta-values (Ea=beta Ead.c.). These are found to follow the trend in experimentally observed activation energies indicating that the mixed alkali effect occurs as the result of decreases in both long- and short-range ionic mobilities. A cluster-bypass model has been proposed in an attempt to reconcile the above results. The model assumes that the mobile species are to be found in a tissue material surrounding the clusters. A brief examination of the site preferences of spectroscopic probe ions (T1+ and Pb2+) in mixed cation glasses by u.v. spectroscopy indicated a dependence of the frequency of the absorption band on the reagents used in glass preparation. This result is thought to point towards some structural effects persisting in the melt which in turn may be important with respect to cluster formation in the glass.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. / A quartz microbalance electrode (QME) was constructed for the investigation of the electrochemistry of electroless plating baths. To this end, the electronic oscillator circuitry required for the microbalance was developed from literature examples, and the techniques of forming electrodes and mounting the crystal in an appropriate holder were established. The device thus developed was compact, allowing for in situ frequency and electrochemical measurements to be made in a commercially available 100 mL Metrohm cell. The precision .and accuracy obtained with the home-built device were shown to be adequate for electrochemical research, and the sensitivity was found to be consistent with the value expected from the Sauerbrey equation.(Abbreviation abstract) / Andrew Chakane 2018

Orientador: Alexandre Luiz Souto Borges / Co-orientador: Anderson de Oliveira Lobo / Banca: Alberto Noriyuki Kojima / Banca: João Paulo Barros Machado / Resumo:A eletrofiação é um método para a síntese de fibras poliméricas. Neste sentido, a quitosana é um polímero que por meio deste processo origina biomateriais com boas propriedades biológicas. Já a hidroxiapatita é a principal de reserva de cálcio dos vertebrados. Assim, o presente estudo fabricou mantas de nanofibras a partir de solução de quitosana pura 7% (m/v)(Ch) e de solução de quitosana com adição de cristais de nanohidroxiapatita 0,5% (m/v)(ChHa), na tentativa de unir, sob diferentes parâmetros de eletrofiação (distância, tensão elétrica e fluxo da solução), as propriedades do biopolímero e do complexo de fosfato de cálcio. Ambas soluções foram eletrofiadas e, as mantas obtidas, caracterizadas de acordo com a morfologia (diâmetro médio das fibras), topografia superficial (perfilometria e AFM) e características físicas, químicas, estruturais e térmicas (EDS, FTIR, DRX, ângulo de contato, taxa de degradação, termogravimetria). As amostras Ch, quanto à análise morfológica, apresentaram maior diâmetro de fibras (690,3±102,5nm) em relação às ChHa (358,7±49,2nm) e quanto à topografia, Ch mostrou maior homogeneidade, lisura superficial do que ChHa. O EDS foi capaz de identificar presença de Cálcio nas amostras de ChHa. A partir do FTIR, verificou-se bandas caracteríscas de formação de sal de TFA, respaldando a instabilidade de todas as amostras em meio aquoso, sofrendo imediata dissolução sob os testes de molhabilidade e taxa de degradação. As análises térmicas mostraram que, tanto em Ch como em ChHa, três principais estágios de degradação, sendo a primeira, representação de uma grande perda de água / Abstract: The electrospinning is a method used to synthesize polymeric fibers. Chitosan polymer was the one used by this process that originates a biomaterial with good biological properties. The hydroxyapatite is a important calcium reserve of vertebrates. The synthesize process to create nanofibers were made using pure chitosan solution 7% (w/v) (Ch) and chitosan solution added with nanohydroxyapatite (0,5%, w/v) (ChHa), as an attempt to unite, under different electrospinning parameters (distance, electric tension and flow rate), the properties of the biopolymer and calcium phosphate complex. Both solutions were electrospun and the specimens obtained were characterized according to the superficial morphology (mean diameter) topography (profilometry and atomic force microscopy) and physico-chemical characteristics (EDS, FTIR, DRX, contact angle and thermogravimetry). The Ch samples showed from the morphology analysis, a higher mean diameter (690,3±102,5nm) in comparison to ChHa (358,7±49,2nm) and the topograpghy analysis indicated a greater homogeneity and surface smoothness. The EDS was able to identify the presence of calcium in samples of ChHa. From the FTIR, it was verified characteristic peaks of TFA salt formation, which explains the instability of all samples in aqueous solution, with immediate dissolution under the contact angle and degradation rates tests. The thermal analysis presented three main stages of degradation in Ch and ChHa nanofibers with a higher water loss / Mestre

Joseph Chung-Yin Lam. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 62-64). / Abstracts in English and Chinese. / Contents --- p.i / Acknowledgements --- p.ii / Abstract --- p.iii / Abbreviations --- p.v / Chapter Chapter I. --- Introduction / Chapter (1) --- General background of dendrimers --- p.1 / Chapter (2) --- Electrochemically active dendrimers --- p.2 / Chapter (3) --- Electrochemically active dendrimers as models for studying the redox behaviour of complex proteins --- p.11 / Chapter Chapter II --- . Synthesis and Characterization / Chapter (1) --- Structure of the electrochemically active dendrimers --- p.16 / Chapter (2) --- Retrosynthetic analysis --- p.17 / Chapter (3) --- Synthesis --- p.18 / Chapter (4) --- Structural Characterization --- p.26 / Chapter (5) --- Conclusion --- p.33 / Chapter Chapter III. --- Physical and Electrochemical Properties / Chapter (1) --- Physical appearance and solubility properties --- p.34 / Chapter (2) --- Cyclic voltammetry studies --- p.34 / Chapter Chapter IV. --- Summary --- p.40 / Chapter Chapter V. --- Experimental --- p.41 / References --- p.62 / Spectra --- p.65

Thesis (Ph.D.)--Boston University

Digitized by Kansas Correctional Industries

This thesis describes modulated methods using both voltammetric and microfluidic perturbations to study mechanisms of electrolysis reactions. The initial chapters provide an overview of applications and research development in the fields of micro-engineering and electrochemistry, including microfabrication methodology, electrochemical detection techniques and analysis methods. Some typical electrochemical reactions have been studied for different kinds of industrial applications. Also hydrodynamic modulation methods have been investigated. The result chapters begin in Chapter 3 with detailed investigation of various electrochemical reactions by using cyclic voltammetry (CV) and large amplitude Fourier transformed alternating current voltammetry (FTACV) under microfluidic conditions. Single electron transfer reactions with different kinetics were studied first by using potassium ferrocyanide and ferrocenecarboxylic acid (FCA). Dual electron transfer reactions with different pathways were investigated by using 2,5-dihydroxybenzoic acid for one step oxidation and N,N,N',N'-tetramethyl-para-phenylene-diamine (TMPD) for two consecutive one-electron step oxidation. An irreversible reaction was explored by using borohydride solution. Examples of homogeneous reaction mechanisms were studied by using the combinations of Fe(CN)64-/L-cysteine or TMPD/ascorbic acid. The current response of all the electrolysis reactions except single electron transfer reactions was first reported under microfluidic conditions with FTACV, which has shown sensitive with the change of volume flow rates and the substrate concentrations when homogeneous reactions are involved. The linear relationships between peak current and volume flow rates or substrate concentrations can be obtained in every harmonic component. In chapter 4, the modulated technique was applied to microfluidic hydrodynamic systems. A range of electrolysis mechanisms including single electron transfer reactions, dual electron transfer reactions, irreversible reaction and homogeneous reactions were studied under hydrodynamic modulated conditions. The system showed rapid response with the change of volume flow rates during one measurement. The linear relationships between peak current and flow rates, as well as substrate concentrations, can be obtained simultaneously in one scan, which reveals a promising approach to get more information in a short-time measurement. Chapter 5 demonstrated a new protocol by forcing an oscillation of the electrochemical active solution flowing. Analysis of transition time and its effect on limiting current are presented to begin exploration of this new tool for supporting researchers on understanding redox mechanisms. A short simulated study was carried out to help better understand the mechanism under different hydrodynamic conditions.