As reduções eletroquímicas dos complexos de ferro(II) FeL32+, com ligantes diimínicos alifáticos, L=CH3-N=C(R)-C-(R\')=N-CH3, onde R,R\' = H,H; H,CH3; CH3,CH3; e ligantes diimínicos mistos, L = C5H4N-C(R\')=N-(R\"), onde R\',R\"= H,CH3; CH3,CH3 foram estudadas através de polarografia e voltametria cíclica em acetonitrila em perclorato de tetraetilamônio 0,2M a 25,0ºC. Utilizam-se eletrodo plano de platina.ou eletrodo gotejante de mercúrio como eletrodos de trabalho para a voltametria cíclica e polarografia, respectivamente. Os eletrodos auxiliar e de referência são fio de platina e Ag/AgCl , respectivamente. Os polarogramas obtidos para esses complexos no intervalo de potenciais de 0,0 a -2,4 V vs Ag/AgCl mostram duas a quatro ondas de redução. As duas primeiras etapas são controladas por difusão e os processos de eletrodo podem ser descritos como monoeletrônicos e reversíveis, com a estabilização dos baixos estados de oxidação Fe(I) e F:(0) em acetonitrila. Para o derivado R,R\' = H,CH3, observam-se três ondas reversíveis e monoeletrônicas indicando a estabilização do complexo com ferro no estado de oxidação formal (-I).Comportamento semelhante foi encontrado para complexos de ferro(II) com 2,2\'-dipiridina e 1,10 fenantrolina (. Electrochim. Acta. 13. 335 (1968) ). A estabilização dos baixos estados de oxidação deve-se ao caráter aceptor de elétrons dosoligantes diimínicos, como indicado pelo espectro de transferência de carga e,depende da presença do grupo cromofórico. Verifica-se ainda que quanto maior o valor de 10 Dq, maior a retrodoação e, maior a estabilização dos baixos estados de oxidação. Os voltamogramas cíclicos apresentam dois a três picos de redução no intervalo de potenciais de 0,0 a - 2,2V vs Ag/AgCl. A primeira etapa de redução é bem caracterizada como processo monoe1etrônico e reversível Na redução dos derivados alifáticos R,R\' = H,H; CH3.CH3; há um grande aumento da corrente de pico e os potenciais são deslocados cerca de 0,18V para regiões mais negativas. Isso é interpretado em termos de adsorção do reagente na superfície do eletrodo de platina. É interessante notar que apenas os complexos. que apresentam substituintes simétricos adsorvem na superfície do eletrodo. / The electrochemical reduction of the iron(II) complexes, FeL32+ with aliphatic diimine ligands, CH3-N=C(R)-C(R\')=N-CH3, where R,R\'= H,H; H,CH3; CH3,CH3, and mixed diimine ligands. L = C5H4N-C(R\')=N(R\"), where R\',R\" = H, CH3; CH3,CH3, was studied by means of polarography, and cyclic voltammetry in acetonitrile containing 0,2M tetraethylammonium perchlorate at 25,0ºC. A platinum disk or a dropping mercury electrode were used as working e1ectrodes for the cyclic voltammetric and polarographic experiments, respectively. A platinum wire and Ag/AgCl were employed as auxiliar and reference electrodes, respectively. The polarograms obtained for these complexes in the 0.0 to -2,4 V vs Ag/AgCl potential range exhibit two to four reduction waves. The first two reduction waves were shown to correspond to reversible one electron reductions yielding stable complexes of iron in the formal oxidation states (I) and (O). For the derivative R\',R\" = H,CH3, three reversible one electron waves were found, indicating the stability of the complex with iron in the formal oxidation state (-I). A similar be havior has been found for the 2,2\'-dipyridine and 1,10-phenan -throline complexes of iron(II) (Electrochim. Acta,.13, 335(1968)). The stabilization of the low valence states is due to the strong acceptor properties of the diimine ligands. This acceptor character is reflected in the appearence of a characteristic intense inverse charge transfer band in the visible region. in the presence of the diimine chromophore. Increased stabilization of the low oxidation states is correlated with an increase in the magnitude of the ligand-field strength (10 Dq), i.e., increased back-donation. Two or three reduction peaks were observed in the cyclic voltammograms in the region of 0.0 to -2.2 V vs Ag/AgCl. The first reduction of the aliphatic derivatives R,R =\' H,H ; CH3, CH3, there is a large increase in peak currents and a shift of 0.18 V to more negative potentials. This is interpretable in terms of the platinum electrode, It is interesting to note that only the complexes which have symmetrical ligands exhibit adsorption at the electrode surface.

>Magister Scientiae - MSc / Architecturally enhanced electrode materials for lithium ion batteries (LIB) with permeable morphologies have received broad research interests over the past years for their promising properties. However, literature based on modified porous nanoparticles of lithium manganese phosphate (LiMnPO₄) is meagre. The goal of this project is to explore lithium manganese phosphate (LiMnPO₄) nanoparticles and enhance its energy and power density through surface treatment with transition metal nanoparticles. Nanostructured materials offer advantages of a large surface to volume ratio, efficient electron conducting pathways and facile strain relaxation. The material can store lithium ions but have large structure change and volume expansion during charge/discharge processes, which can cause mechanical failure. LiMnPO₄ is a promising, low cost and high energy density (700 Wh/kg) cathode material with high theoretical capacity and high operating voltage of 4.1 V vs. Ag/AgCl which falls within the electrochemical stability window of conventional electrolyte solutions. LiMnPO₄ has safety features due to the presence of a strong P–O covalent bond. The LiMnPO₄ nanoparticles were synthesized via a sol-gel method followed by coating with gold nanoparticles to enhance conductivity. A magnesium oxide (MgO) nanowire was then coated onto the LiMnPO₄/Au, in order to form a support for gold nanoparticles which will then form a thin film on top of LiMnPO₄ nanoparticles crystals. The formed products will be LiMnPO₄/Mg-Au composite. MgO has good electrical and thermal conductivity with improved corrosion resistance. Thus the electronic and optical properties of MgO nanowires were sufficient for the increase in the lithium ion diffusion. The pristine LiMnPO₄ and LiMnPO₄/Mg-Au composite were examined using a combination of spectroscopic and microscopic techniques along with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Microscopic results revealed that the LiMnPO₄/Mg-Au composite contains well crystallized particles and regular morphological structures with narrow size distributions. The composite cathode exhibits better reversibility and kinetics than the pristine LiMnPO₄ due to the presence of the conductive additives in the LiMnPO₄/Mg-Au composite. This is demonstrated in the values of the diffusion coefficient (D) and the values of charge and discharge capacities determined through cyclic voltammetry. For the composite cathode, D= 2.0 x 10⁻⁹ cm²/s while for pristine LiMnPO₄ D = 4.81 x 10⁻¹⁰ cm2/s. The charge capacity and the discharge capacity for LiMnPO₄/Mg-Au composite were 259.9 mAh/g and 157.6 mAh/g, respectively, at 10 mV/s. The corresponding values for pristine LiMnPO₄ were 115 mAh/g and 44.75 mAh/g, respectively. A similar trend was observed in the results obtained from EIS measurements. These results indicate that LiMnPO₄/Mg-Au composite has better conductivity and will facilitate faster electron transfer and therefore better electrochemical performance than pristine LiMnPO₄. The composite cathode material (LiMnPO₄/Mg-Au) with improved electronic conductivity holds great promise for enhancing electrochemical performances, discharge capacity, cycle performance and the suppression of the reductive decomposition of the electrolyte solution on the LiMnPO₄ surface. This study proposes an easy to scale-up and cost-effective technique for producing novel high-performance nanostructured LiMnPO₄ nanopowder cathode material.

Dopamine (DA) is a key striatal neuromodulator central to normal functioning of the basal ganglia. Identifying and characterizing circuits governing striatal DA transmission is necessary for understanding DA involvement in adaptive behaviour and pathology. Properties of evoked striatal DA release can be examined using fast-scan cyclic voltammetry at carbon fibre microelectrodes, a technique enabling live monitoring of transmitter release events with sub-millisecond resolution. Experimental work presented in this thesis employed this approach to study regulation of striatal DA by acetylcholine (ACh) in health and disease in acute brain slices. Synchronous activity in a small population of striatal cholinergic interneurons (ChIs) was previously shown to directly drive striatal DA release. Here using optogenetic approach I explore physiological relevance of ChI-evoked drive of striatal DA by examining whether corticostriatal and thalamostriatal afferents to ChIs can trigger ACh-evoked DA events. Following floxed vector injections in motor cortex or caudal intralaminar thalamus of CaMK2a-Cre mice I examine the properties of evoked DA upon light activation of channelrhodopsin-2-transduced inputs to striatal ChIs. These experiments revealed that both cortical and thalamic afferents are capable of driving ACh-evoked DA release, but operate using a different complement of post-synaptic ionotropic glutamate receptors and display distinct release recovery profiles. I further explore if rebound excitation in a population of striatal ChIs could drive DA events by examining whether ACh-evoked DA release follows optical inhibition of striatal ChIs selectively expressing hyperpolarizing halorhodopsin 3.0 or archaerhodopsin 3.0 in ChAT-Cre mice. This work showed that hyperpolarizing ion pumps were not successful in triggering ChI-evoked DA release. I also investigate whether cholinergic brainstem innervation of striatum could contribute to or drive ACh-evoked striatal DA events in ChAT-Cre rat, concurrently showing that ChI-evoked DA release is not a species artefact, and is present in mouse and rat alike. Current results also suggest that cholinergic brainstem afferents do not drive or contribute to striatal ACh-evoked DA events. Close interaction between DA and ACh systems further indicates that ACh could impact dopaminergic dysfunction. To explore this I examined the state of ACh transmission in a mouse model of Parkinson’s disease overexpressing human wild type alpha–synuclein protein. These animals present with impaired striatal DA release from young age, but DA deficits could be mediated by changes in ACh tone. Here I show that impaired striatal DA release is the results of primary DA axon dysfunction, although in ventral striatum DA release deficits could be partially compensated by increased ACh tone at nicotinic receptors. I further show that the functional state of muscarinic ACh receptors in not altered following decreased DA transmission, although the data from aged animals suggest that alpha–synuclein-dependent changes in vesicle handling could contribute to impaired DA releasability. Finally, I show that vesicle handling may indeed be altered in this mouse model as impaired DA release is evident with short stimulation protocols, while with prolonged depolarization of DA axon terminals alpha–synuclein-overexpressor mice are better able to sustain evoked DA release. Overall, the main body of work presented in this thesis examined the processes regulating striatal DA transmission via ACh system. In particular, I show that ChI-evoked drive of striatal DA release can be recruited physiologically and further establish that changes in ACh transmission are not the primary drivers of impaired DA releasability in a mouse model of Parkinson’s disease overexpressing human alpha–synuclein protein.

Heme containing proteins and their reactivity play a central role in biological systems; they have a vast range of functions including electron transfer, catalysis, and respiration. Cytochromes c and heme c containing proteins have been used widely as model systems to understand how structure and dynamics lead toward function. In this thesis, a variety of biophysical methods are used to investigate two heme c containing model systems to gain insight into how redox potential and reactivity are modulated through changes in the local environment. Mitochondrial cytochrome c undergoes several pH dependent conformational rearrangements that involve different heme ligation and have associated changes in redox potential. Under basic conditions (pH greater than 8), the axial methionine (Met) residue is replaced by one of several nitrogen based ligands, usually a nearby lysine residue, and is coined the "alkaline transition". It is accompanied by a large downward shift in redox potential. The functional utility of this conformational change is not fully understood however it is strongly implicated in the signaling cascade for apoptosis. Bacterial monoheme cytochromes c exhibit similar phenomenological Met-loss behavior as a function of electrode material. In Chapter 2 we utilize Hydrogenobacter thermophilus cytochrome c552 as a model system for the assessment of redox thermodynamics and changes in redox potential associated with the Met-loss form. In Chapter 3 we extend our investigation to homologous cytochromes c. Bacterial cytochrome c peroxidases catalyze the two-electron reduction of hydrogen peroxide to water utilizing cytochrome c as an endogenous electron donor. Chapter 4 describes the first recombinant construct of the diheme Nitrosomonas europaea cytochrome c peroxidase (Ne CCP); a defining family member of constitutively active cytochrome c peroxidases. A variety of biophysical techniques were used to confirm similarity between the recombinant Ne CCP and native enzyme. Chapter 5 extends our investigation to the role of constitutively conserved glutamine and glutamic acid residues within the active site, and two conserved tryptophan residues; the first situated between hemes and the second distal to the active site. In Chapter 6, stopped flow spectroscopy is used to investigate the first intermediates of the Ne CCP catalytic mechanism.

>Magister Scientiae - MSc / This project focuses on the development of simple, highly sensitive, accurate, and low cost electrochemical sensors based on the modification of pencil graphite electrodes by the electrochemical reduction of graphene oxide-metal salts as nanocomposites (ERGO-MC-PGE; MC = Sb or Au nanocomposite). The electrochemical sensors ERGO-Sb-PGE and ERGO-Au-PGE were used in the determination of paracetamol (PC) in pharmaceutical formulations using adsorptive stripping differential pulse voltammetry. The GO was prepared from graphite via a modified Hummers’ method and characterized by FTIR and Raman spectroscopy to confirm the presence of oxygen functional groups in the conjugated carbon-based structure whilst, changes in crystalline structure was observed after XRD analysis of graphite and GO. / 2023-10-07

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Electrochemical behavior of mono- and bimetallic chromiumtricarbonyl and cationic manganesetricarbonyl of fluxional dibenzo[a,e]cyclooctatetraene (DBCOT) complexes were studied via cyclic voltammetry over a range of scan rates (20 – 2000 mV/s) and temperatures (0 °C and 25 °C). The presented work displays electrochemical reduction mechanisms associated with eight-membered ring coordinated M(CO)3 systems that undergo rapid ring inversion in solution. The electrochemical studies of these complex systems exhibit comparitively similar behaviors, which suggest relatively undifferentiated mechanisms. Slight differences between the chromium and isoelectronic cationic manganese are seen in their chemical reactions in solution and the potential at which they reduce. The significance of the electrochemical studies of these complexes are justified by their potential contribution to nanotechnology considering the possibility of generating a cylindrical nanostructure containing the tub-shaped eight-membered ring ð-coordinated M(CO)3 system. The high probability of a haptotropic shift to the eight-membered ring upon reduction could prove to be beneficial to electrocatalysis.

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No description available.

No description available.