Aluminum-nickel (Al-Ni) alloys and Al/Ni bilayers were successfully electrodeposited from AlCl3-EMIM-NiCl2 electrolyte at room temperature. Dissolution of NiCl2 was shown to be favorable in Lewis basic (with molar ratio of AlCl3 < 0.5) AlCl3-EMIM solution. The use of electrochemically active Cu working electrode as opposed to inert W induced additional Cu oxidation and dissolution in the cyclic voltammetry scan. The reduction potentials of Al and Ni were found to be ~ – 0.3 and 0.15 V vs. Al/Al3+ respectively. Increasing [NiCl2] in the electrolyte leads to an increase of Ni concentration in the deposited structures. Dense and well-adherent Al-Ni alloys with Ni concentration up to 17.7 at.% were deposited by potential control. XRD analysis revealed that the deposited Al-Ni exhibit a supersaturated fcc crystalline structure. The visual appearance of the deposits ranged from bright silver, dull silver, grey, to black, where the darker shade typically indicated higher Ni content. SEM analysis revealed that the surface morphology of the deposits ranged from nodular to flake-like structures. Al-Ni alloy typically showed nodular morphology with cauliflower structure. Flake structures, which were independent of substrate roughness, were found to develop under pulsed potential deposition with 1:1 duty ratio. The concentration of Ni in electrodeposited Al-Ni alloys increases nonlinearly with the increase in molarity of NiCl2. Al and Ni contents increase with increasing the time of positive and negative cycle of the pulse respectively. Decreasing the frequency by half resulted in almost double the amount of Ni in the deposited alloy. A smoother substrate increased Ni concentration from 6 to 17.7 at.%. Al/Ni bilayer was successfully deposited in 1.5:1 AlCl3-EMIM containing 0.026 M NiCl2. Deposition of Al on Ni was achieved using constant potential and pulse potential control. The deposition of Ni on Al is complicated since the deposition potential of Ni lies in the vicinity of Al stripping potential thus inducing competition between Ni deposition and Al stripping.

tert-butyl 1-methoxycarbonyl-1-ferrocenecarbamate, Boc-NH-Fc-COOMe, (1) was synthesized according to the literature procedure and modified to 1-amino-n′-ferrocenemethylcarboxylate, 1,n′-H2N-Fc-COOCH3 (2) by removing the Boc-group with TFA/Et3N mixture in dichloromethane. Compound 2 reacted with alkylating agents like MeI, EtI, EtSCH2CH2Cl (MA) and (CN)(EtO)2P(O) (NA) to form MeNH-Fc-COOMe (3), EtNH-Fc-COOMe (4), EtSCH2CH2NH-Fc-COOMe (5), (EtO)2P(O)NH-Fc-COOMe (6), respectively. Cyclic voltammetry (CV) of these compounds showed different half-wave potential characteristics compared to aminoferrocene and was dependent on the nature of the substituents, which was rationalized by molecular orbital calculations. Electron donating groups (Me, Et and 2-chloroethyl ethylsulfide, MA) shifted the half-wave potential towards the cathodic direction while electron withdrawing group like diethyl cyanophosphonate, NA, shifted it toward anodic direction. Anodic to cathodic peak separation were found to be within 62-88 mV indicating a quasi-reversible system. <p>Hydrolysis of compound 1 resulted in the formation of tert-butyl 1-methoxycarbonyl-1-ferrocenecarboxylic acid, Boc-NH-Fc-COOH, (11) which was coupled with cystamine using the EDC/HOBt protocol to synthesize the cystamine conjugate [BocHN-Fc-CO-CSA]2 (12). This molecule is equipped with an amino group that directly linked to the redox receptor. Compound 12 was fully characterized by spectroscopic methods and by single crystal x-ray diffraction. The cystamine conjugate 12 formed films on gold substrates, which upon deprotection of the amino group, reacted with chemical warfare agents (CWAs) mimics, such as EtSCH2CH2Cl (MA), a simulant for the sulfur mustard HD, and (CN)(EtO)2P(O) (NA), a simulant for the nerve agent Tabun. Their reaction with the surface-bound ferrocene derivative results in the formation of N-substituted products. <p>CV measurements showed anodic shifts of the Fc redox potentials by 50 (±5) mV after exposure to MA, and NA. Measurements by quartz crystal microbalance (QCM) showed an increase in mass upon exposure to MA and NA. Ellipsometry measured a film thickness increase from 6 (±1) Å for the deprotected film to 10 (±4) Å for the film modified with MA and to 7 (±2) Å for the film modified with NA. The surfaces were analyzed by x-ray photoelectron spectroscopy (XPS) and clearly showed the attachment of the cystamine conjugate on the surface and its reaction with CWAs mimics.

Metal hydrides are used as anode material in nickel metal hydride batteries and are of particular interest because of the potential to be a part of energy systems completely involving renewable sources (e.g. solar power, wind power etc.). Preparation and electrochemical characterization of metal hydride electrodes have not previously been performed at the Department of Chemistry – Ångström Laboratory. Two basic techniques that are desired to be used in the characterization are cyclic voltammetry and chronopotentiometry. This thesis work is aimed at preparation and electrochemical characterization of a metal hydride electrode and, as a complement, study the electrode with X-ray diffraction. LaNi3.55Co0.75Mn0.4Al0.3, a standard material for metal hydride electrodes previously studied by Khaldi et al. was chosen, to ensure that electrochemical absorption of hydrogen was possible, and to be able to compare electrochemical results [1-3]. LaNi3.55Co0.75Mn0.4Al0.3 was synthesized with arc melting, with additional annealing at 900˚C for five days, ground in a cemented carbide ball mill and sieved to less than 56 µm. Electrodes were prepared containing 90 wt.-% of LaNi3.55Co0.75Mn0.4Al0.3 powder, 5 wt.-% of polytetrafluoroethylene and 5 wt.-% of carbon black. The hydrogen absorption and desorption capabilities of the electrode were studied electrochemically with cyclic voltammetry and chronopotentiometry, and the structural changes associated with absorption of hydrogen was studied with X-ray diffraction. The capacity increased, probably from activation of the material, during initial cycling up to the maximum capacity of 294 mAh/g, obtained after 9 cycles, followed by a small decrease, probably caused by corrosion and passivation of the material, in capacity of the remaining 11 cycles. Activation of the material causes the charge and the discharge potential to shift to a more positive and a more negative value, respectively. The final values for the charge potential and the discharge potential were -841mV and -945 mV vs. Hg/HgO, respectively, after 16 cycles. Khalid et al. [1-3]reported a maximum capacity of 300 mAh/g, a charge potential of about -960 mV and a discharge potential of about -840 mV after 16 cycles the results obtained in this study are considered to be in good agreement with those reported. X-ray diffraction of the electrodes revealed, as expected, a cell volume change of the charged electrode compared to the discharged electrode. The change in cell volume corresponds to an estimated capacity of 303 mAh/g, which is very close to the, above mentioned, electrochemically obtained maximum capacity of 294 mAh/g.

tert-butyl 1-methoxycarbonyl-1-ferrocenecarbamate, Boc-NH-Fc-COOMe, (1) was synthesized according to the literature procedure and modified to 1-amino-n′-ferrocenemethylcarboxylate, 1,n′-H2N-Fc-COOCH3 (2) by removing the Boc-group with TFA/Et3N mixture in dichloromethane. Compound 2 reacted with alkylating agents like MeI, EtI, EtSCH2CH2Cl (MA) and (CN)(EtO)2P(O) (NA) to form MeNH-Fc-COOMe (3), EtNH-Fc-COOMe (4), EtSCH2CH2NH-Fc-COOMe (5), (EtO)2P(O)NH-Fc-COOMe (6), respectively. Cyclic voltammetry (CV) of these compounds showed different half-wave potential characteristics compared to aminoferrocene and was dependent on the nature of the substituents, which was rationalized by molecular orbital calculations. Electron donating groups (Me, Et and 2-chloroethyl ethylsulfide, MA) shifted the half-wave potential towards the cathodic direction while electron withdrawing group like diethyl cyanophosphonate, NA, shifted it toward anodic direction. Anodic to cathodic peak separation were found to be within 62-88 mV indicating a quasi-reversible system. <p>Hydrolysis of compound 1 resulted in the formation of tert-butyl 1-methoxycarbonyl-1-ferrocenecarboxylic acid, Boc-NH-Fc-COOH, (11) which was coupled with cystamine using the EDC/HOBt protocol to synthesize the cystamine conjugate [BocHN-Fc-CO-CSA]2 (12). This molecule is equipped with an amino group that directly linked to the redox receptor. Compound 12 was fully characterized by spectroscopic methods and by single crystal x-ray diffraction. The cystamine conjugate 12 formed films on gold substrates, which upon deprotection of the amino group, reacted with chemical warfare agents (CWAs) mimics, such as EtSCH2CH2Cl (MA), a simulant for the sulfur mustard HD, and (CN)(EtO)2P(O) (NA), a simulant for the nerve agent Tabun. Their reaction with the surface-bound ferrocene derivative results in the formation of N-substituted products. <p>CV measurements showed anodic shifts of the Fc redox potentials by 50 (±5) mV after exposure to MA, and NA. Measurements by quartz crystal microbalance (QCM) showed an increase in mass upon exposure to MA and NA. Ellipsometry measured a film thickness increase from 6 (±1) Å for the deprotected film to 10 (±4) Å for the film modified with MA and to 7 (±2) Å for the film modified with NA. The surfaces were analyzed by x-ray photoelectron spectroscopy (XPS) and clearly showed the attachment of the cystamine conjugate on the surface and its reaction with CWAs mimics.

none

Thesis (MTech (Physical Sciences))--Peninsula Technikon, 1999. / Word processed copy. Summary in English. Includes bibliographical references (leaves 75-79). Also available online.

published_or_final_version / Chemistry / Master / Master of Philosophy

To understand how the brain functions and what disruptions underlie neurological diseases and disorders, analytical methods are needed that can succeed in the complexity of the native brain environment. To make a measurement in functioning, live tissue, these methods must be selective for specific analytes in a matrix that has over 1000 different chemical species, be able to measure chemical changes on multiple timescales (10-3 s to 104 s), have a high spatial resolution (μm), and be sensitive (pM to μM). The work described within, details the development and application of a voltammetric method, fast-scan controlled adsorption voltammetry (FSCAV) that is capable of monitoring baseline levels of serotonin and dopamine, as well as monitoring changes on multiple time scales with high sensitivity and selectivity. Because FSCAV is performed using a carbon-fiber microelectrode, the same sensor can be used for fast-scan cyclic voltammetry to monitor rapid (phasic) changes of dopamine and serotonin in the extracellular space. Thus a single-sensor strategy for measuring tonic and phasic concentrations of these important neurotransmitters is developed and used to elucidate important insight into the differences of serotonin and dopamine regulation. Additionally it is revealed that dopamine exhibits a coaction between tonic and phasic signaling where serotonin does not. Using this approach, a method for evaluating pain processing in a preclinical model is developed, which reveals an important relationship between chronic pain and dopamine signaling. Furthermore, a mathematical model to describe mass-transport limited adsorption is developed and used to determine the diffusion coefficient of both dopamine and serotonin in situ. The work described within details an important advancement in neuroanalytical methodology that will provide new insights both short-term and long-term for studying fundamental chemical mechanisms of neurotransmission.

L-glutamate is the predominant excitatory amino acid neurotransmitter inthe mammalian central nervous system. Prior aging studies have focusedprimarily on dopaminergic circuitry of the striatum, and data obtained studyingglutamate regulation in the striatum have been largely equivocal. Thesediscrepancies are due in large part to the limitations of microdialysis; while it isextremely sensitive to minute concentrations of analyte, it is lacking in terms ofthe temporal resolution necessary to study a neurotransmitter with rapid releaseand clearance kinetics such as glutamate. In order to address this matter, ourlaboratory has designed a ceramic-based multisite microelectrode with thecapability to detect and analyze fluctuations in extracellular glutamateconcentrations on a sub-second basis. These microelectrodes were utilized tostudy the phasic release and uptake dynamics of potassium-evoked glutamate inthe striatum of young (6 month), late-middle aged (18 month) and aged (24month) Fischer 344 rats. Our results showed a reduced glutamate clearancerate and an attenuated response to potassium depolarization in the corticostriatalprojections of aged animals in comparison to other age groups. In addition,average maximal glutamate release amplitudes were decreased in the striatumof aged animals. Pressure ejection of exogenous glutamate solution furtherconfirmed the decreased glutamate clearance ability of the aged striatum. Thesepotassium and exogenous glutamate data also highlighted a markeddorsoventral gradient in the striatum in terms of glutamate release and clearanceability. We further explored this phenomenon of age-related decreased glutamateuptake by coupling our in vivo technology with classical immunoblotting andbiotinylation techniques in order to investigate glutamate transporter regulation.Decreased glutamate clearance in the aged rats cannot be attributed to areduction in steady-state total transporter protein levels. Rather, our resultsindicate that reduced plasma membrane surface trafficking of GLAST in the agedstriatum may be partially responsible for this effect. Finally, we modified ourmicroelectrodes to study basal glutamate levels in the striatum of the aging,freely moving rat. This approach allowed us to study extracellular glutamateregulation free from the potential confounding variable of anesthesia. Our resultsdemonstrate that there is no significant alteration in basal glutamate levels inaging in the brain regions investigated. More importantly, this study validated theefficacy of the utilization of ceramic-based multisite microelectrodes for the studyof alterations in glutamate neurotransmission in the aging, freely moving rat, andit lays the foundation for future work correlating such changes with age associatedimpairments in motor function.

Thesis (MSc)--University of Stellenbosch, 2007. / Bibliography. Also available via the Internet.