Eine Reihe 3-(p-X-phenyl)-Thiophenmonomeren (X = -H, -CH3, -OCH3, -COCH3, -COOC2H5, -NO2) wurde elektrochemisch polymerisiert, um Filme zu erhalten, die umkehrbar reduziert und oxidiert werden konnten (n-und p-dotiert wurden). Die Oxidationspotentiale der Monomere und die formalen Potentiale der n und p-Dotierprozesse der Polymere wurden mit Resonanz- und induktiven Effekten der Substituenten (Hammett konstanten) am Phenylring sowie semiempirisch errechneten Bildungswärmen der Monomereradikalkationen korreliert. Außerdem wurden die Oxidationspotentiale mit den Ionisierungspotentialen der Monomere verglichen, die über die Dichtefunktionialtheorie (DFT) errechnet wurden, die der Energie für das Erzeugen der Radikalkationen entsprechen. Um theoretische Grundlagen für die Einstufen-Bildung regioregulär -konjungierter Oligo- und Polythiophene zu erhalten, wurden die elektronischen Zustände von 3-Phenylthiophen-Derivaten anhand von Molekülorbitalberechnungen auf Grundlage der Dichtefunktionaltheorie mit Becke’s Drei-Parameter-Funktion (B3LYP), sowie mit den Basissätzen 6-31G(d) und 3-21G(d) erklärt. Die Reaktivität der Verknüpfung von mono- und oligo-3-Phenylthiophenen wurde von den berechneten ungepaarten Elektronenspindichten der entsprechenden Radikal-Anionen abgeleitet. Die Ionisierungspotentiale, die den Energien zur Erzeugung der Radikal-Anionen während der Oxidation entsprechen, wurden abgeschätzt. Die aus den 3-Phenylthiophenen entstandenen regioselektiven Hauptprodukte können gut durch die Größe der Spindichten erklärt werden. Da die Verknüpfungsreaktion an der zwei-Position des Thiophnrings (C-2) sterisch durch die Phenylgruppe und den Thiophenring gehindert ist, startet die Initiierung der 3-Phenylthiophene über die Bildung eines Kopf-Schwanz-Dimers. Folglich spielt das Kopf-Schwanz-Dimer eine wichtige Rolle bei den Wachstumsreaktionen der 3-Phenylthiophene. Die Ursache dafür liegt darin, dass das Kopf-Schwanz-Dimer in 5-Position die höchste Spin-Dichte besitzt und die Wahrscheinlichkeit einer Kopf-Kopf-Verknüpfung aufgrund der sterischen Hinderung zwischen dem Thiophenring und der Phenylgruppe gering ist. Polymerfilme von 3-Phenylthiophenderivaten, die durch elektrochemische Polymerisation synthetisiert wurden, sind in situ und ex situ durch Resonanz-Raman-Spektroskopie bei verschiedenen Anregungswellenlängen, sowie durch in situ und ex situ UV-Vis Spektroskopie analysiert wurden. Die Entwicklung der in situ UV-Vis-Spektren der Polymer von 3-Phenylthiophene nach der Dotierung wird durch ähnliche Eigenschaften gekennzeichnet, wie für viele Polythiophene mit einem hohen Grad der Konjugation beobachtet. Während der schrittweisen Oxidation der Poly-3-phenylthiophen Filme verringert sich die Intensität der Absorption wegen des Überganges bei 450-566 nm und ein neues ausgedehntes Absorptionsband, das auf (bi)polaron Zustände bezogen wird erscheint bei ungefähr 730-890 nm. Andererseits wird während der Oxidation (p-Dotierung) des Poly3-phenylthiophen Filmes eine blau/hypsochrome Verschiebung für beide Absorptionsbänder beobachtet . Es wird durch die Tatsache erklärt, dass ein Polymer eine Verteilung der Kettenlängen enthält und die längste Polymer kette (dessen Absorption bei niedriger Energie auftritt), bei niedrigeren Potentialen zu oxidieren beginnt. Die elektrochemischen Bandlücken der Derivate von 3-Phenylthiophen sind durch zyklische Voltametrie gemessen worden. Der Effekt der Substituenten auf den Oxidations-/Reduktions- potentiale wird besprochen. Bei Bandlücken, die durch zyklische Voltammetrie erhalten wurden, hat sich herausgestellt, dass sie im Allgemeinen höher liegen als optische Bandlücken. Erste Resultate der in situ Resonanz-Raman-Spektroskopie, von dem elektrochemisch erzeugten Polymerderivate von 3-Phenylthiophen Filmen auf einer Platinelektrode, in einer organischen Elektrolytlösung, werden berichtet. Beobachtete Raman Banden werden zugewiesen; gegründet auf diesen Resultaten werden die zuvor angenommenen molekularen Strukturen diskutiert. / A series of 3-(p-X-phenyl) thiophene monomers (X= –H, –CH3, –OCH3, –COCH3, –COOC2H5, –NO2) was electrochemically polymerized to furnish polymer films that could be reversibly reduced and oxidized (n- and p-doped). The oxidation potentials of the monomers and formal potentials of the n- and p-doping processes of polymers were correlated with resonance and inductive effects (Hammett constants) of the substituents on the phenyl ring as well as the semiempirically calculated heats of formation of the monomer radical cations. Moreover, the oxidation potentials of the monomers were correlated with the ionization potentials of the monomers calculated via density functional theory (DFT), which correspond to the energies for generating radical cations during oxidative processes. For obtaining a theoretical basis for the one-step formation of regioregular –conjugated oligo-and polythiophenes, the electronic states of 3-phenylthiophene derivatives were elucidated by molecular orbital calculations using density functional theory with the Becke-type three parameters functional (B3LYP), the 6-31G(d), and 3-21G(d) basis sets. The reactivity for coupling reaction of mono- and oligo-3-phenylthiophenes are inferred from the calculated unpaired electron spin densities of the respective radical cations, and the ionization potentials which correspond to the energies for generating radical cations during oxidative processes were estimated. The major regioselective products of the oligomerization of 3-phenylthiophene can be well understood in terms of the magnitude of spin densities. Since the steric hindrance between the phenyl group and thiophene ring interferes with the coupling reaction occurring between 2-postions (C–2) of thiophene rings, the initiating reaction of 3-phenylthiophene is generaton of a head-to-tail (HT) dimer. Thus, the head-to-tail (HT) dimer plays an important role in the propagation reactions of 3-phenylthiophene. This originates from the highest spin density at the 5- position of the HT dimer and low probability of the HH coupling due to the steric hindrance between thiophene ring and phenyl group. Polymer films of the 3-phenylthiophene derivatives prepared by electrochemical polymerization were analyzed, in situ and ex situ, with resonance Raman spectroscopy using several excitation wavelengths as well as in situ and ex situ UV-Vis-spectroscopy. The evolution of the in situ UV-Vis-spectra of poly 3-phenylthiophene derivatives upon doping is characterized by similar features as observed for many polythiophenes with high degree of conjugation. During stepwise oxidation of the poly-3-phenylthiophene films the intensity of the absorption due to the transition around 450–566 nm decreases and a new broad absorption band related to (bi)polaron states appears around 730-890 nm. On the other hand, during the oxidation (p-doping) of the poly-3-phenylthiophene films a blue/hypsochromic shift is observed for both absorption bands. It is explained by the fact that a polymer contains a distribution of chain lengths, and the longest polymer chains (the absorption of which occurs at lower energies) start to oxidize at lower potentials. The electrochemical bandgaps of 3-phenylthiophene derivatives have been measured by cyclic voltammetry. The effect of substituents on the oxidation / reduction potentials is discussed. Bandgaps obtained by cyclic voltammetry have been found to be in general higher than optical bandgaps. Preliminary results of in situ resonance Raman spectroscopy of electrochemically generated poly-3-phenylthiophene derivatives films on a platinum electrode exposed to an organic electrolyte solution are reported. Observed Raman bands are assigned; based on these results previously suggested molecular structures are discussed.

In the search for alternative energy technologies, low temperature fuel cells continue to feature as technologies with the most promise for mass commercialization. Among the low temperature fuel cells, alkaline and proton exchange membrane fuel cells are the most popular. Alkaline fuel cells have typically been used for water generation as well as auxiliary power for space shuttles. Their bulkiness however makes them undesirable for other applications, especially in automobiles, where there is a great demand for alternative technologies to internal combustion engines. Proton exchange membrane fuel cells on the other hand possess numerous qualities including their compact size, high efficiency and versatility. Their mass implementation has however been delayed, because of cost among other reasons. Most of this cost is owed to the Pt/C catalyst that accounts for about half of the price of the PEM Fuel Cell. This catalyst is used to drive the sluggish oxygen reduction reaction that occurs at the cathode of the PEM Fuel Cell. To overcome this obstacle, which is to make PEM Fuel Cell technology more affordable, reducing the amount Pt has traditionally been the approach. Another approach has been to find new ideal catalyst-support combinations that increase the intrinsic activity of the supported material. One more strategy has been to find lower cost alternative materials to Pt through synthetic and kinetic manipulations to rival or exceed the current oxygen reduction reaction activity benchmark. To this end, Palladium has garnered significant interest as a monometallic entity. Its manipulation through synthetic chemistry to achieve different morphologies - which favor select lattice planes - in turn promotes the oxygen reduction reaction to different degrees. In bimetallic or, in more recent times multimetallic frameworks, geometric and ligand effects can be used to form ideal compositions and morphologies that are synergistic for improved oxygen reduction reaction kinetics. In this dissertation, we have explored three different approaches to make contributions to the catalysis and electrocatalysis body of literature. In the first instance, we look at the influence of ligand effects through the active incorporation of a PVP capping agent on the stability of ~3nm Pt NPs. Washed (no capping agent) and unwashed (with capping agent) batches of NPs were evaluated via cyclic voltammogram analyses to evaluate differences there might be between them. It was found that the current density measurements for unwashed particle batches were higher. This increase in current density was attributed to the monodentate and bidentate ligand bonding from the PVP, which increased as a function of cycle number and plateaued when the PVP was completely decomposed. The complete decomposition of PVP during the CV experiment was estimated to occur around 200 cycles. The remaining portion of the dissertation explores the electrocatalytic properties of Palladium based NPs. The first instance, a monometallic study of Palladium cubes and dendrites was aimed at building on a recent publication on the enhanced ORR activity that was achieved with a PdPt bimetallic dendrite morphology. In our work, we sought to isolate the dendritic morphology properties of the monometallic Pd composition in order to understand what advantages could be achieved via this morphology. Pd cubes were used as a comparison, since they could be generated through the combination of a similar set of reagents simply by switching the order of addition. It was found that while there was no significant variation in the ORR activity as a function of morphology / shape, there was an interesting interaction between hydrogen and the palladium NPs in the hydrogen oxidation region that varied as a function of shape. This led to further sorption and ethylene hydrogenation studies, which suggested that, the interaction between hydrogen and Pd depended on the environment. Within the electrochemical environment, the ECSA measured, suggested that hydrogen was being reversibly absorbed into the sub-surface octahedral sites of Pd. The higher ECSA for Pd cubes corroborated with higher sorption for Pd cubes as well. However ethylene hydrogenation showed that the fringes of the Pd dendrites provided additional sites for reaction, which in turn translated to higher conversion. Furthermore, through a Koutecky-Levich analysis, it was found out that the Pd dendrites while exhibiting slightly lower activity, favored the 4-electron oxygen reduction process more than the Pd cubes. In the last part of this dissertation we explored the electrocatalytic properties of Pd-based bimetallic NPs under different morphologies including nanocages and sub-10nm alloys. With the inclusion of Ag, it was found out, through Koutecky-Levich analysis that the 4-electron process was better observed under alkaline conditions using a 0.1M NaOH(aq) electrolyte solution instead of a 0.1M HClO4 (aq) for acidic media testing. It was found that, for PdAg nanocage morphologies, where the Pd galvanically replaced the Ag to form cages, the four-electron process was suited to thinner Pd shells. Indeed the average electron numbers measured for Ag nanocubes coated with a 6nm shell was in agreement, within reason of literature values for bulk Ag. However, since the binding energy that both metals have for OH is so close, the potential for contributions to the ORR kinetics in alkaline media by Pd is a potential consideration.

The electrochemical investigation of nickel, copper and silver thin films interfaced with yttria stabilized zirconia (YSZ) solid electrolyte was accomplished to determine their response to polarization in dilute oxygen environments at 350 °C and assess their viability for electrochemical promotion of catalysis (EPOC). Polycrystalline YSZ (8 mol % Y2O3-ZrO2) pellets were synthesized in the lab and films deposited onto them using evaporative physical vapor deposition (PVD). The critical thickness of copper, silver and nickel thin films were foundusing in-situ resistance measurements. Following this, 50 and 100 nm copper and nickel films were studied using solid electrolyte cyclic voltammetry (SECV) to determine their response to polarization. Given that silver thin films at such thicknesses are thermally unstable, a film of 800 nm was used in this study. The materials were found to respond to polarization in different ways, forming oxides according to Wagner and Mott-Cabrera oxidation models.

SYNTHESIS, CHARACTERIZATION, AND ELECTRICAL PROPERTIES OF DIAZOPHENYLENE AND DIAZODIPHENYLENE BRIDGED Co, Ni, Cu, Ce, AND Er PHTHALOCYANINE POLYMERS Alkan, Cemil M. Sc., Department of Polymer Science and Technology Supervisor: Prof.Dr. Leyla Aras Co- Supervisor: Prof.Dr. G&uuml / ng&ouml / r G&uuml / nd&uuml / z September 2004, 112 pages In this research, diazophenylene and diazodiphenylene bridged metal-phthalocyanine polymers were produced from diazonium salt of diaminophenylene/bensidin and pre-synthesized tetraamino metal phthalocyanines. Tetraamino metal phthalocyanine complexes of Co, Ni, Cu, Ce, and Er were obtained by reducing tetranitro metal phthalocyanine complexes synthesized from 3-nitrophthalic anhydride, urea, metal salt, and ammonium molybdate catalyst. Complexes and polymers were characterized by Fourier Transform Infrared Radiation (FTIR) and UV-Visible spectroscopies. X-Ray analysis showed that there were short range orientations in the polymers. Thermal analysis of the complexes and the polymers were done by differential scanning calorimetry and thermal gravimetric analysis at a heating rate of 10&amp / #61616 / Cmin&amp / #61485 / 1 under nitrogen atmosphere. Ash analysis was performed to determine the metal content of the polymers. Viscosity and ebullioscopy measurements of the soluble part of the polymers were carried out in THF at 25&amp / #61616 / C. Scanning electron microscopy were used for morphology investigations of the polymers. Four probe conductivity measurements showed that electrical conductivity of the polymers increased according to the metallic conductivity of the metal at the center of the phthalocyanine units. When doped with iodine, the polymer samples showed 104 fold increase in their conductivities. Current-Voltage (I-V) measurements showed that the polymers were optically sensitive and semiconductors. Electrochemical analysis of the soluble part of the polymers were determined in tributylamine perchlorite+dichloromethane mixture utilizing cyclic voltammetry (CV).

In the recent years, environmental pollution becomes a health threatening issue for human beings. Technological developments introduce industrial wastes and heavy metals, and developments in agriculture introduce pesticides into the world that we live. All these toxic wastes accumulate in drinking water and food consumed by humans. Therefore, detection of toxic wastes in all kinds of environmental samples, and development of new detection techniques become an important issue. In this study, development of a protein-based biosensor for detection of heavy metals in environmental samples, by expressing genetically modified glutathione S-transferase (GST-(His)6) protein in E.Coli BL21 (DE3) expression system, was designed. Recombinant GST proteins was expressed in E.Coli BL21 (DE3) expression system and purified with Glutathione Sepharose 4B affinity column and Ni-NTA spin kit. GST activities were determined using the GST substrate 1-chloro-2,4-dinitrobenzene (CDNB). Protein expression was tested by SDS-PAGE and Western blot analysis. Product formation linearly increased up to 1 mM CDNB, 1 mM GSH, 1.7 &micro / g proteins in 0.05 M, pH 6.9 phosphate buffer in the final volume of 1.0 ml at 25&amp / #9702 / C. The Vmax and Km values for GST-(His)6 towards CDNB and GSH were calculated with Lineweaver-Burk as CDNB Vmax / 22.88 &micro / mol/min/mg, Km / 4.29 mM,and as GSH Vmax / 6.42 &micro / mol/min/mg, 24.45 &micro / mol/min/mg, Km / 3.69 mM, respectively. Biosensor working electrode was prepared by immobilizing the GST-(His)6 by 1-(3-dimethylaminopropyl)-3-ethyl-carbodiimide hydrochloride (EDC) coupling on the gold surface. Electrode preparation was confirmed by cyclic voltammetry measurements. The biosensor was inserted as the working electrode in the constructed three(four)-electrode flow cell. The conformational change resulting from the binding of the metal ions to the recombinant protein causing a capacitance change proportional to the concentration of the metal ions was determined. After the working electrode is standardized and calibrated, the heavy metal concentration in water samples was measured. The GST-(His)6 biosensor has a large operational range between 1 fM and 10 mM and a storage stability of approximately 2 weeks. The GST-(His)6 biosensor is very sensitive to, Cu+2&gt / Cd+2&gt / Zn+2&gt / Hg+2 metal ions, at low concentrations.

Orientador: Devaney Ribeiro do Carmo / Banca: Newton Luiz Dias Filho / Banca: Marcelo Firmino de Oliveira / Resumo: O presente trabalho apresenta a preparação e caracterização de uma sílica micelar template modificada com Ti(IV), e posterior reação em H3PO4. O produto formado, chamado de SMT-2, foi caracterizado por espectroscopia na região do infravermelho (FTIR), difração de Raios X (DRX), análise de área superficial e porosidade. Este material não adsorveu metais e sim compostos fenotiazínicos. Uma caracterização dos compostos fenotiazínicos nas cavidades da SMT-2 foi realizada empregando técnicas de FTIR, termogravimetria e voltametrica cíclica. O voltamograma cíclico do eletrodo de pasta de grafite modificado apresentou dois pares redox com potencial padrão (E0'), onde E0' = (Epa+Epc)/2, 0,09 V para o pico I e 0,42 V para o pico II (v=50 mV s-1; solução tampão Britton-robinson; pH 2) versus Ag/AgCl que foi atribuído ao monômero e dímero do azul de orto toluidina nas cavidades da SMT-2, estes resultados foram análogos ao azul de metileno e azure A. Em uma segunda etapa, preparou-se óxido de titânio seguindo uma nova metodologia de síntese. Por analogia a SMT-2, o material preparado foi modificado com H3PO4, que foi descrito como TiP, e contrariamente ao SMT-2, o material apresentou capacidade de adsorver íons metálicos (Co2+, Cu2+, Ni2+). Após a caracterização do TiP pelas técnicas supracitadas, efetuaram-se os estudos de adsorção de íons de Co2+, Cu2+ e Ni2+ em meio aquoso, etanol/água (42%) e etanol (99%) onde se determinou para estes metais os respectivos tempos de equilíbrio de sorção. Após a determinação do tempo de equilíbrio para a adsorção dos íons metálicos em cada sistema, determinou-se a capacidade específica de sorção (NfMax) através de isotermas de sorção. Para o Co2+, os valores de Nf foram: em meio aquoso (4,95 x 10-4 mol g-1), etanol/água 42% (6,09 x 10-4 mol g-1) e... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This work presents the preparation of a micellar template silica modified with Ti (IV), and subsequent reaction with H3PO4. The product formed, called SMT-2, was characterized by spectroscopy in infrared region (FTIR), X-ray diffraction (XRD), surface area analysis and porosity. This material did not adsorbed metals but adsorbed phenothiazine compounds. A characterization of phenothiazine compounds in the wells of SMT-2 was performed using techniques of FTIR, thermogravimetric analysis and cyclic voltammetry. The cyclic voltammogram of modified graphite paste electrode showed two redox couples with standard potential (E0'), where E0' = (Epa + Epc) / 2, 0.09 to peak I and 0.42 to peak II ( v = 50 mV s-1 BR solution, pH 2) vs. Ag / AgCl which was assigned to the monomer and dimer of ortho toluidine blue into the wells of SMT-2, these results were similar to methylene blue and azure A. In a second step, prepared titanium oxide following a new methodology for synthesis. By analogy of SMT-2, the prepared material was modified with H3PO4, which was abbreviated as TiP, contrary to the SMT-2, the material shows the ability to adsorb metal ions (Co2+, Cu2+, Ni2+). After characterizing the TiP by the techniques described above, were conducted studies of ion adsorption of Co2+, Cu2+ and Ni2+ in water, ethanol/water (42%) and ethanol (99%) which was determined for these metals their equilibrium times sorption. After determining the equilibrium time for adsorption of metal ions in each system, we determined the specific sorption capacity (NfMax) through sorption isotherms. For the Co2+, the values of Nf were in water (4.95 x 10-4 mol g-1), ethanol/water 42% (6.09 x 10-4 mol g-1) and ethanol 99% (3.00 x 10-4 mol g-1), with concentrations of Co2 + ions ranging from 9.03 to 18.63 x 10-4 mol L-1. As for the Cu2 + these values were: in water... (Summary complete electronic access click below) / Mestre

Orientador: Devaney Ribeiro do Carmo / Banca: Newton Luiz Dias Filho / Banca: Regina Massako Takeuchi / Resumo: O presente trabalho apresenta a preparação de um silsesquioxano nanoestruturado, o cloropropilsilsesquioxano (S) que foi organofuncionalizado com os seguintes agentes modificadores: 4-amino-3-hidrazinico-5-mercapto-1,2,4-triazol (Purpald®) e o 4-amino-5-4(piridil)-4H-1,2,4-triazol-3-tiol (APTT), os materiais obtidos dessa funcionalização foram descritos como SP e SA, respectivamente. Os materiais SP e SA foram caracterizados por diversas técnicas espectroscópicas: Espectroscopia na região do infravermelho (FT-IR), Ressonância magnética nuclear 29Si e 13C no estado sólido (RMN), Difração de Raios- X (DRX), Espectroscopia de Energia Dispersiva de Raios X (EDX), Termogravimetria e Análise Térmica Diferencial (TG - DTA). Após a devida caracterização, realizaram-se estudos de adsorção de íons metálicos (Cu2+, Cd2+ e Ni2+) nos sítios ativos do SA, porém, curiosamente não se observou a mesma capacidade de sorção pelo SP. Diferentes meios foram estudados no processo de adsorção dos íons metálicos supracitados: aquoso, etanólico 99% e etanólico 42%, determinando-se o tempo de equilíbrio de adsorção, que para ambos os meios e metais esse tempo máximo foi em média 35 min. Determinado o tempo de equilíbrio de adsorção dos íons metálicos em cada sistema, determinou-se a capacidade específica de sorção (Nfmax) através de isotermas de adsorção. Para o Cu2+, os valores de Nf foram: meio aquoso (3,09 × 10-4 mol g-1), etanólico 42% (1,03 × 10-4 mol g-1) e etanólico 99% (1,86 × 10-4 mol g-1), com concentrações de íons Cu2+ variando de 1,74 a 29,64 mol L-1. Os valores encontrados para o Ni2+ foram: em meio aquoso (2,11 × 10-4 mol g-1), etanólico 42% (0,97 × 10-4 mol g-1) e etanólico 99% (1,05 × 10-4 mol g-1), com concentrações de íons Ni2+ variando de 2,25 a 33,18 mol L-1. Para os íons cádmio não foram... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This work presents the preparation of a nanostructured silsesquioxane, the cloropropilsilsesquioxano (S) that was organofunctionalised with the following modifying agents: 4-amino-3-hydrazino 5 - mercapto 1,2,4 triazole (Purpald ®) and 4- amino-5-4 (pyridyl)-4H-1,2,4-triazole-3-thiol (APTT), the materials obtained of the functionalization were described as SP and SA, respectively. The materials SA and SP were characterized by various spectroscopic techniques such as spectroscopy in the region of infrared (FTIR), nuclear magnetic resonance 29Si and 13C solid-state (NMR), X-ray diffraction (XRD), Energy Dispersive Spectroscopy Rays (EDS), Thermogravimetry and Differential Thermal Analysis (TG - DTA). After proper characterization, were carried studies on adsorption of metallic ions such as Cu2+, Ni2+ and Cd2+ in the active sites of SA, but curiously did not observe the same sorption capacity of the SP. Different methods were studied in the adsorption of metal ions above: aqueous, 99% ethanolic and 42% ethanolic, determining the adsorption equilibrium time, which for both means and metals the maximum time averaged 35 min. After determining the adsorption equilibrium time of metal ions in each system, we determined the specific sorption capacity (Nfmax) through adsorption isotherms. For Cu2+, the values of Nf were: aqueous solution (3.09 × 10-4 mol g-1), 42% ethanolic (1.03 × 10-4 mol g-1) and 99% ethanolic (1.86 × 10-4 mol g-1), with Cu2 + ion concentrations ranging from 1.74 to 29.64 mol L-1. The values obtained for the Ni2+ were: aqueous solution (2.11 × 10-4 mol g-1), 42% ethanolic (0.97 × 10-4 mol g-1) and 99% ethanolic (1.05 × 10-4 mol g-1), with Ni2 + ion concentrations ranging from 2.25 to 33.18 mol L-1. For the cadmium ions were not observed saturation of adsorption sites in the concentration range studied, not getting the maximum... (Summary complete electronic access click below) / Mestre

Magister Scientiae - MSc / Various dermatological disorders, such as formation of black pigmented patches on the surface of the skin arise from the over-activity of tyrosinase enzyme's degenerative action. This enzyme is further implicated in the involvement of melanin in malignant melanoma, the most lifethreatening skin tumors. Although, synthetic products were found effective to combat this menace, nevertheless, overtime detrimental effect on human skin is a challenge. Investigation of natural tyrosinase inhibitors from methanol extracts of medicinal plants of Lamiaceae family using L-tyrosine as substrate on three different complementary assays (TLC bio-autography, spectrophotometry and cyclic voltammetry) was carried out accordingly. The result indicated Salvia chamelaeagnea, Salvia dolomitica, Plectranthus ecklonii, Plectranthus namaensis, and Plectranthus zuluensis, with significant zone of inhibition against tyrosinase on TLC bio-autography, spectrophotometry result showed that extracts of Plectranthus ecklonii (IC50 = 21.58 μg/mL), Plectranthus zuluensis (IC50 = 23.99 μg/mL), Plectranthus madagascariensis (IC50 = 23.99 μg/mL) and Salvia lanceolata (IC50 = 28.83) demonstrated good anti-tyrosinase activity when compared with kojic acid (IC50 = 3.607 μg/mL). On the other hand, cyclic voltammetry are in consonant with above results thereby supported the nomination of some of the extracts as strong anti-tyrosinase agents. Salvia chamelaeagnea showed strong activity in cyclic voltammetry and clear zone of inhibition on TLC bioautography, these reasons gave us justification for further chemical study to isolate the bioactive constituents. Phytochemical investigation of the bioactive extract of Salvia chamelaeagnea using different chromatographic methods including column chromatographic and semi preparative HPLC afforded six (6) known compounds viz carsonol (C1), carnosic acid (C2), 7- ethoxylrosmanol (C3), ursolic acid (C4), rosmanol (C5) and ladanein (C6). Their chemical structures were elucidated by analyses of spectroscopic (1H and 13C NMR) data as well as correlations with existing literature. The methanolic extract of S. chamelaeagnea (SC) showed moderate antityrosinase (IC50 = 267.4 μg/mL) activity, total antioxidant capacities measured as: Oxygen radicals absorbance capacity (ORAC; 14970 ± 5.16 μM TE/g), ferric-ion reducing antioxidant power (FRAP; 9869.43 ± 7.87 μM AAE/g) and trolox equivalent absorbance capacity (TEAC; 13706.5 ± 0.95 μM TE/g). Excellent total antioxidant capacities were demonstrated by C1 and C5 respectively as FRAP (9338.92 ± 1.72; 8622.73 ± 1.92) μM AAE/g; TEAC (16505 ± 0.86; 10641.5 ± 0.52) μM TE/g; ORAC (14550.5 ± 3.65; 14633.90 ± 3.84) μM TE/g and including the inhibition of Fe2+ -induced lipid peroxidation (IC50 = 32.5; 30.25) μg/mL. All the compounds except C4 are electro-active with well-defined oxidation-reduction peaks while C1 demonstrated the highest tyrosinase inhibitory activity by strongly decreased the inhibition current with time using cyclic voltammetry method. The isolated compounds especially C1, C2 and C5 are well known to combat with ageing problems and documented for their powerful activity against oxidative stress and alzheimer's diseases, which are ageing related symptoms. The isolation of such bioactive compounds indicated the synergetic effect of the results of the three methods used in this thesis. This is the first report on the evaluation of both anti-tyrosinase and total antioxidant capacities of the isolated compounds from S. chamelaeagnea. The findings therefore can be used as background information for exploitation of skin depigmentation and antioxidant agents from natural source.

>Magister Scientiae - MSc / Pollution of water sources, aquifers and wetland systems caused by industry, agriculture, and municipally treated wastewater is a worldwide problem that contributes to the scarcity of clean and potable water. Rivers, channels, lakes, oceans, and ground water are often contaminated by a variety of organic substances that can affect aquatic life and threaten human health. Organic compounds such as antibiotics that are not effectively removed by modern day water treatment technology are a growing threat to water quality and health. The emergence of antibiotics in the environment particularly aquatics have become a matter of concern as they may result in induction and spread of bacterial resistance which may be harmful to humans or animals. After administration, antibiotics for human use or their metabolites are excreted into the effluent and reach the sewage treatment plant (STP). Not all Antibiotics in sewage treatment plants are eliminated. Consequently they can pass through the sewage system and may end up in environmental and even potable water systems. Antibiotic residues have been reportedly found in places such as hospital wastewaters, wastewater treatment plants and surface waters all over the world with concentrations ranging from approximately 60-120000 ng/, 2-580 ng/L and 5-1300 ng/L respectively. The current methods that are used to detect antibiotics can be quite expensive and time consuming due to sample preparation (necessary for detection of very low concentrations of antibiotics in water) and technology used in the instruments. Electrochemical sensors and biosensors are simple systems, with high selectivity and sensitivity for individual measurements and cost effectiveness. The development of composites based on conductive phases dispersed in polymeric matrices has led to important advances in analytical electrochemistry. Polyamic acid and graphene oxide are both materials with well-defined electrochemistry and are easily processable in the design of various sensor formats. In this study we present a novel polyamic acid - graphene oxide (PAA/GO) electrode which was prepared for electrochemical screening of antibiotic residues in aqueous systems. Polyamic acid (PAA) and graphene oxide (GO) were successfully synthesized independently and characterized using SEM which was used to study the morphology of the PAA, FTIR spectroscopy to confirm chemical structures and functional groups as well as CV and SWV which were used to identify the unique electrochemical behavior of PAA and GO respectively. Polyamic acid-graphene oxide nanocomposite was prepared and characterized by CV, SWV, FTIR and SEM. The novel electrode (PAA/GO/SPCE) was prepared by electrochemically depositing PAA/GO (0.03 mg/mL) onto SPCE electrodes using 5 cycles between −1000 mV and 1000 mV at 50 mVs. The analytical performance of the electrochemical sensor towards detection of neomyxin and norlfoxacin was compared to standard Uv-vis spectroscopy method. The Uv-vis spectroscopy showed LOD of 1.61x10-5 M and 1.41x10-5 M for norfloxacin and neomycin respectively. The PAA/GO electrochemical sensor had a LOD of 3.37x10-7 M for norfloxacin and 1.066x10-6 M for neomycin. Sensitivity of the UV/vis method was comparable to electrochemical sensor sensitivity for neomycin and norfloxacin.

Magister Scientiae - MSc (Biotechnology) / It has been estimated that the world population will reach about 10 billion by the year 2050 and in order to accommodate the increased demand of food, the world agricultural production needs to rise by 70 % in the year 2030. However, the realisation of the goal in food production is hindered by limited arable land caused by urbanisation, salinisation, desertification and environmental degradation. Furthermore, abiotic and biotic stresses affect plant growth and development, which lead to major crop losses. The long term goal of this study is to improve food security by producing genetically engineered agricultural crops that will be tolerant to diverse stresses. This research aims at developing stress tolerant crops through the determination of important signalling molecules and second messengers, such as nitric oxide (NO), carbon monoxide (CO) and calcium ion (Ca2+), which can bind to plant proteins such as AtNOGC1 in order to induce stress tolerance in plants.