A series of macrocyclic FeIII/II and CoIII/II transition metal complexes has been selected and tested to serve as artificial mediators in redox potentiometry of proteins and also in catalytic cyclic voltammetry of redox active enzymes. The potentials of these mediators ranges approximately from +200 mV to -600 mV vs the normal hydrogen electrode (NHE) at pH 7, which spans the range of most redox active proteins. These coordination complexes are mostly stable in both the oxidized and the reduced forms and show pH-independent electrochemistry within the range 6 < pH < 9. A significant advantage of these mediators is to exhibit very weak visible absorption maxima which enable proteins with low extinction coefficients to be studied by optical potentiometry without spectral interference from the mediators. These mediators have been applied to the catalytic electrochemistry of dimethyl sulfoxide (DMSO) reductase. DMSO reductase isolated from Rhodobacter capsulatus has been studied extensively in this work. It is an 82 kDa monomeric, soluble enzyme found in the periplasmic space of the organism where it is responsible for catalyzing the reduction of DMSO to dimethyl sulfide (DMS). DMSO is a rather inert and difficult to analyse compound, which appears in foods and beverages, such as wine, coffee, and tea. Enzyme based methods offer an effective way to detect DMSO in these samples. Rhodobacter capsulatus DMSO reductase contains only a single molybdenum cofactor which cycles between MoVI and MoIV during catalysis and provides a rare example of a Mo enzyme that has no other cofactors such as hemes, Fe-S clusters and flavins. Previous studies of direct (unmediated) electrocatalysis by DMSO reductase have shown only modest activity in comparison to that of other Mo enzymes. Mediated electrochemistry of DMSO reductase from Rhodobacter capsulatus using low-potential macrocyclic complexes such as [Co(trans-diammac)]3+, [Co(cis-diammac)]3+, or [Co(AMMEsar)]3+ as a mediator has been studied. The normal transient CoIII/II voltammetric response of the complex is converted into a sigmoidal (steady state) waveform in the presence of both DMSO and DMSO reductase. A single set of enzymatic rate and equilibrium constants has been determined through digital simulation (DigiSim) of the cyclic voltammetry performed under conditions where the scan rate, DMSO concentration, DMSO reductase concentration and mediator concentration were varied systematically. This information provides new insight to the kinetics of the DMSO reductase catalytic mechanism that has never before been obtained from steady state or stopped flow kinetics studies. Of note is that lowering the thermodynamic driving force by sequentially raising the redox potential of the mediator ([Co(trans-diammac)]3+ to [Co(cis-diammac)]3+ to [Co(AMMESar)]3+) slows the enzyme-mediator electron transfer reaction in accord with Marcus theory. Finally, preparation of enantiomerically pure sulfoxides by an electrochemical enzymatic system utilizing DMSO reductase from Rhodobacter capsulatus has also been investigated. This method has been performed using the coordination complex [Co(trans-diammac)]3+ as an electron donor during bulk electrocatalysis. The results indicate that DMSO reductase from R. capsulatus prefers to catalyze the reduction of both R-MPTSO (methyl p-tolyl sulfoxide) and R-MPSO (methyl phenyl sulfoxide) over their S-enantiomers. These results have been rationalized on the basis of the published crystal structure of DMSO reductase (R. capsulatus) with DMSO bound at the active site.

Universiẗat, Diss., 2007--Frankfurt (Main). / Zsfassung in dt. und engl. Sprache.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 5 uppsatser.

Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 89-111) Also available in print.

Thesis (Ph. D.)--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references.

Universiẗat, Diss., 2008--Frankfurt (Main). / Engl. Übers. des Hauptsacht.: Studies on the structure-function relationship of the cytochrome bc1 complex from Paracoccus denitrificans.

A Leishmaniose é uma infecção causada pelo protozoário do gênero Leishmania e transmitida pela picada de insetos. Os tratamentos atuais são caros e demorados, envolvendo compostos baseados em Sb(V), anfotericina B lipídica e miltefosina. Estudos recentes sugerem que a enzima tripanotiona redutase (TR) poderia ser um alvo específico no desenvolvimento de novos fármacos, pois ela é essencial e exclusiva dos tripanossomatídeos. Desta forma, este trabalho apresenta a síntese de novos compostos derivados da iminodibenzila com estrutura similar à clomipramina, um conhecido inibidor da TR. Tais compostos são conjugados de iminodibenzila com etilenodiamina, etanolamina e dietilenotriamina através de epicloridrina (dado-en, dado-ea e dado-dien , respectivamente). Foram obtidos com rendimentos superiores a 94% e caracterizados através de LC_MS e espectroscopia no infravermelho. Também se fez a avaliação da afinidade relativa dos novos ligantes por cobre através do teste de recuperação da fluorescência da calceína, concluindo-se que o ligante dado-dien possui uma afinidade maior com Cu (II) quando comparado com os outros ligantes sintetizados. Foram formados complexos metálicos através da adição de sulfato de cobre (II), acompanhando-se através de espectroscopia ultravioleta-visível para se obter uma estimativa da relação metal: ligante, concluindo-se que os complexos formados eram [Cu(dado-ea)]2+, [Cu(dado-en)2]2+ e [Cu(dado-dien)2]2+. A lipofolicidade foi estimada através de simulação computacional, constatando-se que os complexos formados são todos muito lipofílicos, sendo que o logP descreve na seguinte: [Cu(dado-en)2]2+ > [Cu(dado-dien)2]2+ > [Cu(dado-ea)]2+. Ensaios de atividade pró-oxidante através da oxidação da sonda fluorimétrica DHR revelaram que o complexo [Cu(dado-ea)]2+ apresentou a maior taxa de atividade pró-oxidante, sendo independente da concentração de peróxido de hidrogênio no meio reacional e alcançando seu limiar quando presente em concentração aproximada de 10 µM. Por fim, os compostos sintetizados foram testados quando à suas citotoxidades frente a promastigotas L. amazonenses e com macrófagos RAW 264,7. Quando o protozoário foi exposto a concentrações variadas dos compostos deste estudo, observou-se que os ligantes ea, en e dien tiveram os menores valores de IC50 (todos < 3µM), porém eles são muito tóxicos para serem utilizados como fármacos, Dentre os ligantes sintetizados, somente o dado-en apresentou um resultado numa faixa viável (IC50 19,9 ± 2,2 µM). Contra macrófagos RAW 264,7, dado-en apresentou IC50 > 50µM, ou seja, ele é mais tóxico para o protozoário do que para os macrófagos. A complexação com cobre não representou um aumento interessante na citotoxicidade dos compostos. O conjunto de resultados apresentados neste indica um potencial uso do composto dado-en no combate à leishmaniose. / Leishmaniasis is an infection caused by protozoa of the genus Leishmania. and transmitted by insects. Current treatments are expensive and time-consuming, involving Sb(V)-based compounds, lipossomal amphotericin B and miltefosine. Recent studies suggest that inhibition of trypanothione reductase (TR) could be a specific target in the development of new drugs, because it is essential and exclusive to trypanosomes. Thus, this work presents the synthesis of new compounds derived from iminodibenzyl with structures related to clomipramine, a known inhibitor of TR. These compounds were conjugates of iminodibenzyl with ethylenediamine, ethanolamine and diethylenetriamine, linked by epichlorohydrin. They were obtained with yields higher than 94% and their structures were confirmed by LC-MS and infrared spectroscopy. The relative affinity for copper of the new chelators was assessed by the recovery of calcein fluorescence, which showed that dado-dien has the highest affinity for Cu(II) among the new ligands. Metal complexes were synthesized by addition of copper(II) sulphate and studied by ultraviolet-visible spectroscopy, showing that the stoichiometries were [Cu(dadoea)]2+, [Cu(dado-en)2]2+ and [Cu(dado-dien)2]2+. Lipophilicity was assessed by computational methods, indicating that the complexes were all very lipophilic, with logP decreasing in the following order: [Cu(dado-en)2]2+ > [Cu(dado-dien)2]2+ > [Cu(dado-ea)]2+. Pro-oxidant activity assays by oxidation of DHR fluorimetric probe showed that [Cu(dado-ea)]2+ has the highest rate of oxidation, independent of hydrogen peroxide concentration, reaching its highest value when at ~ 10 &#181;M. Finally, the compounds were tested for citotoxicity to L. amazonensis promastigotes and RAW 264,7 macrophages. When the protozoa was exposed to varying concentrations of the compounds, it was observed that chelators ea, en and dien had the lowest values of IC50 (< 3 &#181;M). but they are too citotoxic to be used as drugs. Among the synthesized chelators, only dado-en presented a result in a pharmaceutically interesting range (IC50 19.9 ± 2.2 &#181;M). Against RAW 264,7 macrophages dado-en IC50 > 50 &#181;M. Complexation to copper did not enhance the citotoxicity of the compounds. Overall, the results in this study indicate a potential use of dado-en in combating leishmaniasis.

Class of 2012 Abstract / Specific Aims: To evaluate the quality of evidence in the literature substantiating major drug-drug interactions of the HMG-CoA reductase inhibitors (statins) atorvastatin, lovastatin, and simvastatin with the azole anti-fungals fluconazole, itraconazole, and ketoconazole. Methods: In this descriptive retrospective analysis, a list of articles reporting on each drug-drug interaction was compiled from the online databases Medline and International Pharmaceutical Abstracts, and the drug compendia Micromedex and Facts & Comparisons. The studies included in this analysis were primary literature reports, written in English, and consisted of human subjects. All studies included were evaluated using a 5-point quality of evidence scale developed to assess drug-drug interactions (van Roon scale). This scale rates the study type from lowest to highest quality, from zero to four. Case reports were additionally analyzed using the Drug Interaction Probability Scale (DIPS). The DIPS tool uses 10 questions to evaluate the probability that an adverse event is caused by a drug-drug interaction. Main Results: Twenty-one studies met the selection criteria. There were three studies involving atorvastatin, four studies involving lovastatin, and fourteen studies involving simvastatin. The mean quality of evidence score on the van Roon scale was 2.0 + 0.77, where atorvastatin studies had a score of 2.3 + 1.15, lovastatin had a score of 2.25 + 0.95 and simvastatin had a score of 1.86 + 0.66. Seventy-one percent of the studies reviewed were case reports. Conclusions: The reports substantiating some drug-drug interactions may be of little and low quality evidence.

MRI is a powerful imaging method that offers several advantages including non-ionizing radiation, significant depth of penetration, and great spatial resolution. Current demand for precision medicine and the movement toward personalized medicine have encouraged researchers in the field of medical imaging to develop MRI-based techniques. Various techniques are now available for molecular imaging by MRI. MRI started by utilizing T1 relaxation properties of molecules but soon after other relaxation mechanisms such as T2 and recently Chemical Exchange Saturation Transfer (CEST) were developed. Each of those MRI techniques offers advantages and disadvantages such as differences in experimental procedures, complexity of the method, selectivity and specificity of signals, and translation into clinical applications. We have been developing MRI techniques and responsive contrast agents for CEST MRI in the Pagel laboratory (Contrast Agent and Molecular Imaging Laboratory, also called CAMEL) for the past decade. We have mainly utilized MRI techniques and responsive contrast agents to detect and measure cancer biomarkers. Detection of the activity of enzymes and measurement of pH have been our main focus, and we have developed catalyCEST MRI probes and techniques for the detection of the activity of enzymes and acidoCEST for the measurement of pH. My research started with investigation on paramagnetic agents as potential CEST MRI probes (paraCEST) and continued with an investigation on diamagnetic agents (diaCEST). I completed several projects in which I prepared and evaluated paraCEST and diaCEST contrast agents for the detection of DT-diaphorase, and alkaline phosphatase enzymes, respectively. Although CEST MRI was my main activity in CAMEL, I started a new direction in CAMEL after encountering a series of observations that were unexplainable with CEST MRI. Through my research, I introduced a new class of responsive contrast agents based on the T2-Exchange (T2-Ex) relaxation mechanism. I employed the T2-Ex mechanism to evaluate responsive contrast agents for the detection of nitric oxide biomolecule and nitroreductase enzyme. My research activities in the CAMEL group resulted in one review paper, one book chapter, two published research articles, and two submitted research manuscripts at the time of preparing my PhD dissertation. In addition to my projects, I was involved in another project that focused on nanocapsule drug delivery, which resulted in a second author publication.

>Magister Scientiae - MSc / Sugargraze is a moderately drought tolerant sweet sorghum hybrid which is ideal for grazing, winter stand over and pit silage. A major advantage that Sugargraze has over other forages is its very high sugar content which improves feed quality thus increasing palatability and results in significantly reduced feed wastage. This study explored the influence of hyperosmotic stress on plant development, ROS accumulation, antioxidant capacity and the extent of cell death. Heat shock protein (Hsp70) expression immunoblotting assays were used to demonstrate whether the various treatment conditions induced stress within natural physiological parameters for the experimental material. This was coupled with the separation, visualization and identification of abundant proteins in Sugargraze leaves in response to hyperosmotic stress using two-dimensional gel electrophoresis (2-DE) in combination with mass spectrometry (MS). The results showed that hyperosmotic stress significantly influences plant development by reducing plant biomass and increasing the levels of ROS accumulation, proline content and subsequently reducing total chlorophyll content. An over accumulation of ROS in the form of hydrogen peroxide and lipid peroxidation was observed in the stressed plants which was supported by the extent of cell death. Although an increase in antioxidant enzyme activity (in the form of total enzymatic activity or individual isoform activity) in response to hyperosmotic stress was observed, this increase was not sufficient to counter the deleterious effects caused by the stress conditions hence the decrease in plant biomass and increase in cell death. Western blotting analysis of Sugargraze leaf tissues using Hsp70 antibodies showed that hyperosmotic stress induced Hsp70 expression to levels significantly higher than observed for the control plants. A total of thirteen CBB stained spots were selected for mass spectrometric identification, owing to their good resolution and abundance levels, and of these, nine were positively identified. Identified proteins were divided into functional categories including both known and novel/putative stress responsive proteins. Molecular and physiological functions of some of the proteins of interest identified will be subjected to further investigation via bioinformatic and molecular biology approaches.