A review of organic π-electron donor molecules is given. The focus is on tetrathiafulvalene (TTF) systems with particular emphasis on dimeric and oligomeric systems incorporating more than one TTF subunit. Such systems are reviewed based on the number and mode of linkage of the TTF subunits. A short discussion is given of the basic chemistry of the TTF system with emphasis on those areas which are utilised in the synthetic work undertaken. Various iodine substituted TTF systems have been synthesised, in some cases requiring the synthesis of previously unknown TTF precursors. The properties of these compounds as π-electron donors have been investigated and complexation studies yielded several salts. The structure of an insulating salt with tetracyano-p-quinodimethane (TCNQ) was elucidated by X-ray analysis. Homocoupling of these iodine substituted TTFs via an Ullman-type methodology yielded new bis(tetrathiafulvalenyl) derivatives, two of which have been studied by X-ray diffraction. Salts of these derivatives have been prepared and the structure of a perchlorate salt has been studied by X-ray diffraction. The possible effects of the conformation of these systems on their physical properties is also discussed. New bisTTF cyclophanes posessing a rare "Edge to Face" double linkage of the two TTF units have been prepared. The potential for isomerism is discussed and the X-ray structures of an isomerically pure cyclophane and a model compound have been obtained. Insulating and semiconducting salts were obtained of these systems with the structures of a perchlorate and poly iodide salt being elucidated by X-ray. New macrocyclic derivatives incorporating three TTF units have been synthesized with the aim of preparing molecular cavities capable of binding suitable guest molecules. New functionalised TTF derivatives have been synthesised as suitable precursors to these systems.

The homotetrameric enzyme dihydrodipicolinate synthase (DHDPS, E.C. 4.2.1.52) from Escherichia coli was used as a model for probing oligomeric structure in enzymes. Dimeric mutants of this enzyme have been found in previous work to be largely inactive, due to the trapping of a covalent adduct. Partial restoration of catalytic activity has been achieved by incubation in the presence of the substrate pyruvate to displace the adduct. It was hypothesized that the buttressing of dimeric units against one another in the wildtype tetrameric form of DHDPS provides stability in the dimer interface, necessary to maintain optimum catalytic performance and substrate specificity. We hypothesized that buttressing a dimeric DHDPS mutant against a surface would result in restoration of catalytic activity by mimicking the buttressing proposed to occur in the tetrameric structure. To test this hypothesis, dimeric DHDPS mutants were immobilised against an agarose support and the immobilised enzymes characterised. Three DHDPS mutants were prepared, the double mutant DHDPS-C20S/L167C was produced by mutagenesis and a crystal structure obtained in collaboration with Dr Renwick Dobson. Two other mutants, DHDPS-Ll67C and DHDPS-Ll97Y were also over expressed and purified. The quaternary structures of the three mutants were characterised in solution, DHDPS-Ll67C was determined to be tetrameric, DHDPS-C20S-Ll67C was found to equilibrate between tetramer and dimer and DHDPS-Ll97Y was confirmed as a dimer, consistent with previous findings. Modification experiments indicated that the sulfhydryl groups of DHDPS-C20S/L167C were available for immobilisation. Activation experiments indicated that both DHDPS-Ll67C and DHDPS-Ll97Y activated. These results were in accord with those of others in indicating that the displacement of an a-ketoglutarate adduct from the active site was responsible for the activation of mutant DHDPS enzymes. Wild-type DHDPS and the mutants were immobilised through amine and sulfhydryl groups. The free and immobilised enzymes were rigorously characterised, with thermal stability, pH optima, kinetic and lysine inhibition properties determined and compared to wild-type DHDPS. Following immobilisation, substrate affinity was found to decrease for wild-type and mutant enzymes, wild-type KmPyr = 0.26 mM free, 0.8-1.2 mM immobilised, Km(S)-ASA = 0.10 mM free, 1.5-2.5 mM immobilised. Lysine inhibition was determined to be largely unaffected by immobilisation. The largest change in K, was an increase to double that of the free enzyme. Restoration of some catalytic activity was found following the immobilisation of dimeric DHDPS-Ll97Y, the immobilised enzyme was 31 ± 12% more active than free DHDPS-Ll97Y. DHDPS-C20S/L167C was also found to immobilise as a dimer. Comparison ofthe immobilised DHDPS-C20S/L167C dimer with a derivatised free dimeric form ofthis enzyme indicated that an increase from 3% to 9% of wild-type activity had resulted from immobilisation. These results supported the hypothesis that buttressing of a dimeric mutant of DHDPS against a support surface would increase catalytic activity and that buttressing across the dimerdimer interface is essential for optimal catalytic activity in DHDPS enzymes.

The homotetrameric enzyme dihydrodipicolinate synthase (DHDPS, E.C. 4.2.1.52) from Escherichia coli was used as a model for probing oligomeric structure in enzymes. Dimeric mutants of this enzyme have been found in previous work to be largely inactive, due to the trapping of a covalent adduct. Partial restoration of catalytic activity has been achieved by incubation in the presence of the substrate pyruvate to displace the adduct. It was hypothesized that the buttressing of dimeric units against one another in the wildtype tetrameric form of DHDPS provides stability in the dimer interface, necessary to maintain optimum catalytic performance and substrate specificity. We hypothesized that buttressing a dimeric DHDPS mutant against a surface would result in restoration of catalytic activity by mimicking the buttressing proposed to occur in the tetrameric structure. To test this hypothesis, dimeric DHDPS mutants were immobilised against an agarose support and the immobilised enzymes characterised. Three DHDPS mutants were prepared, the double mutant DHDPS-C20S/L167C was produced by mutagenesis and a crystal structure obtained in collaboration with Dr Renwick Dobson. Two other mutants, DHDPS-Ll67C and DHDPS-Ll97Y were also over expressed and purified. The quaternary structures of the three mutants were characterised in solution, DHDPS-Ll67C was determined to be tetrameric, DHDPS-C20S-Ll67C was found to equilibrate between tetramer and dimer and DHDPS-Ll97Y was confirmed as a dimer, consistent with previous findings. Modification experiments indicated that the sulfhydryl groups of DHDPS-C20S/L167C were available for immobilisation. Activation experiments indicated that both DHDPS-Ll67C and DHDPS-Ll97Y activated. These results were in accord with those of others in indicating that the displacement of an a-ketoglutarate adduct from the active site was responsible for the activation of mutant DHDPS enzymes. Wild-type DHDPS and the mutants were immobilised through amine and sulfhydryl groups. The free and immobilised enzymes were rigorously characterised, with thermal stability, pH optima, kinetic and lysine inhibition properties determined and compared to wild-type DHDPS. Following immobilisation, substrate affinity was found to decrease for wild-type and mutant enzymes, wild-type KmPyr = 0.26 mM free, 0.8-1.2 mM immobilised, Km(S)-ASA = 0.10 mM free, 1.5-2.5 mM immobilised. Lysine inhibition was determined to be largely unaffected by immobilisation. The largest change in K, was an increase to double that of the free enzyme. Restoration of some catalytic activity was found following the immobilisation of dimeric DHDPS-Ll97Y, the immobilised enzyme was 31 ± 12% more active than free DHDPS-Ll97Y. DHDPS-C20S/L167C was also found to immobilise as a dimer. Comparison ofthe immobilised DHDPS-C20S/L167C dimer with a derivatised free dimeric form ofthis enzyme indicated that an increase from 3% to 9% of wild-type activity had resulted from immobilisation. These results supported the hypothesis that buttressing of a dimeric mutant of DHDPS against a support surface would increase catalytic activity and that buttressing across the dimerdimer interface is essential for optimal catalytic activity in DHDPS enzymes.

<p> The crystal structures of three complexes of rhenium have been determined by single crystal x-ray diffraction methods. The structure and the probable position of the hydrogen atom in the complex tetracarbonyl-rhenium(I)-μ-oxo-μ-hydroxotetracarbonylrhenate(I) are discussed.</p> <p> The structural results for the other two complexes show the presence of carboxylato-bridged dinuclear rhenium core. The very short rhenium to rhenium distances and the eclipsed rotomeric configurations are similar to those found in octachlorodirhenate(III) anion. A reaction scheme for the formation of these complexes from rhenium(III) chloride is postulated and correlated with the structural results. The nature of bonding in the carboxylato complexes of rhenium is discussed.</p> / Thesis / Doctor of Philosophy (PhD)

The scarcity of research about nitrogen containing heterocyclic discotic liquid crystal has made it an interesting subject for chemists. In this thesis, we will discuss the synthesis and properties of four kinds of new dimeric discotic liquid crystal in details. The first type of new dimeric discotic liquid crystals were synthesized based on a novel core structure, dibenzo[a,c]phenazine. All dimers linked by a hexyl-chain spacer exhibited columar phase. The range of mesomorphic temperature became wide as the chain length of spacer increased. Simultaneously, we also changed terminal chain length to investigate the influence on mesomorphic properties by attached terminal group. The second type of new dimeric discotic liquid crystals, which contained the dibenzoquinoxaline skeleton, didn¡¦t show the properties of mesomorphic phase due to the poverty of planality. The third type of molecules, which also have the dibenzoquinoxaline skeleton, were the banana-shaped discotic liquid crystals. We anticipated these dimeric molecules would demonstrate another special mesogenic phase. The last type of dimeric discotic liquid crystals were the extension of our previously research. These molecules, which comprised 5,6,11,12,17,18- hexaazatrinaphthylene skeleton, would be good candidates for using as a n-type material.

This thesis is regarded with the biomimetic total synthesis of phenolic natural products and describes two different projects. Chapter 1 introduces phenolic natural products, the most important biosynthetic pathways for their formation and some examples of relevant biomimetic syntheses. A short introduction to dimeric and pseudo-dimeric natural products can also be found in this chapter. Specific introductions can be found at the start of Chapters 2 and 3. Chapter 2 describes the total synthesis of a dimeric thymol derivative isolated from Arnica sachalinensis (which we have named “thymarnicol”). Inspired by the biosynthesis proposed by Passreiter and co-workers, we tested and confirmed the feasibility of a key hetero-Diels–Alder dimerisation step. During our investigations, we gained significant new insights into the origin and reactivity of thymarnicol. The final oxidative cyclisation has been found to occur spontaneously upon exposure to visible light in air. Chapter 3 discusses our efforts to develop a divergent biomimetic synthetic strategy towards a family of prenylated phenylpropanoid natural products isolated from Illicium genus plants. Our first biomimetic approach revealed the chemical instability of our proposed key intermediates. Therefore, a revised approach was trialled, allowing the total synthesis of a small set of natural products and related structures. We envisage that this strategy could be exploited by accessing a large number of members of this family of compounds.

Electrical doping of organic semiconductors with molecular oxidants (p-type) or reductants (n-type) can greatly improve charge injection and conductivity in devices. Simple one electron reductants that are capable of reducing most electron-transport materials will inevitably also be sensitive to reaction with oxygen. Coupling electron transfer step with bond breaking/ making processes in principle can address this problem. The rhodocene dimer and related ruthenium and iridium dimeric sandwich compounds have been discussed as example of such n-dopants, reducing a variety of organic semiconductors to the corresponding radical anions, while forming monomeric cations. This class of n-dopants can be used in both vapor- and solution-processed devices, and the dopant monomer cations are large and, therefore, fairly stable with respect to diffusion. This thesis focused on increasing the utility of these and related electrical dopants. In order to reduce various electron-transport materials with lower electron affinities, which are frequently used in OLEDs, strategies and limitations to develop stronger n-dopants is discussed. Controlling the kinetics of the dopant / semiconductor reactions to allow film processing in ambient conditions, with activation of the dopants being carried out thermally or photochemically in subsequent steps is presented. An approach to covalently tether monomeric cations with themselves, surfaces or electron-transport materials is described. Electrochemical studies that further our understanding of dopant kinetics and thermodynamics is described. The dimer dopant chemistry is also compared to the corresponding hydride-reduced complexes of the cations and manganese tricarbonyl benzene dimer. The directions for future dopant design with improved properties is discussed.

Recentemente, uma nova molécula de sinalização bacteriana, o AMP dimérico cíclico (c-di-AMP) emergiu como um regulador central dos processos fisiológicos essenciais, tais como a homeostase celular, verificação da integridade do DNA e virulência bacteriana, entre outros. O c-di-AMP é produzido a partir da condensação de duas moléculas de adenosina trifosfato (ATP) por proteínas denominadas diadenilato ciclases, que contém o domínio DisA_N, também denominado DAC. Existem 2842 sequências de proteínas que contém o domínio DAC, provenientes de 2386 organismos encontradas no banco de dados Protein Families Database (Pfam). Essas proteínas são divididas em subfamílias sendo as três subfamílias mais abundantes: DacA (69,1%), proteínas de membrana associadas a sinalização intracelular de alterações decorrentes do meio externo; DisA (24,1%), primeira diadenilato ciclase a ser amplamente estudada, é uma proteína intracelular encontrada na forma de octâmeros ativos em solução, a qual, indiretamente, controla a divisão celular através da verificação da integridade do DNA e DacB (5,5%), proteínas citoplasmáticas expressa, particularmente, durante a formação de esporos bacterianos. Uma característica interessante é que a maioria dos organismos contém uma única e essencial proteína com domínio DAC. Os organismos que contém duas ou mais proteínas-DAC, tais como Clostridium e Bacillus spp., são uma exceção. Em Staphylococcus aureus (S. aureus), um patógeno humano oportunista e responsável por inúmeras doenças infecciosas, uma única diadenilato ciclase é encontrada pendurada na porção interna da membrana celular (Sau_DacA). A atividade desta proteína é potencialmente regulada através da interação direta com uma proteína YbbR-like, que contém um domínio sensor extracelular. Sau_DacA conserva todos os elementos-chave de uma diadenilato ciclase bacteriana, e por ser a única presente em S. aureus, revela-se um excelente alvo de estudo para o desenvolvimento de novos fins terapêuticos. No entanto, até o presente momento, existem poucas informações em relação a estrutura proteica, ao mecanismo de síntese de c-di-AMP e regulação do mecanismo de síntese de nucleotídeo destas proteínas, sendo, portanto, neste aspectos que o presente trabalho pretendeu contribuir. Através de uma série de ensaios, estruturais, calorimétricos, espectroscópicos e bioquímicos, aliados a mutações sítio-dirigidas, identificou-se a relevância de uma conformação dimérica para a estabilidade conformacional e térmica para a proteína ser funcionalmente ativa, assim como a importância dos motivos conservados DGA (Aspartato-Glicina-Alanina) e RHR (Arginina-Histidina-Arginina) para a atividade da Sau_DacA. O loop L5 localizado entre o sítio ativo e a interface dimérica mostrou-se relevante, uma vez que nele é encontrado o motivo DGA - de ligação ao ATP - e o mesmo encontra-se estabilizado em uma posição favorável para ligação do ATP, apenas na conformação dimérica da proteína. Nossos resultados aliados a dados da literatura possibilitaram a proposição de um mecanismo de síntese de c-di-AMP que deve ocorrer via encontro face-a-face de dois sítios de ligação de ATP presentes em dímeros proteicos distintos, podendo a taxa de síntese de o nucleotídeo sofrer interferência via interação proteína-proteína com a proteína receptora de sinal Sau_YbbR. Desta forma, contribuímos para uma melhor compreensão da estrutura e função da Sau_DacA, possibilitando o uso desta como alvo para o desenvolvimento de novos fármacos, uma vez que é sabido que a biossíntese de c-di-AMP é essencial para a maioria dos patógenos que o sintetizam. / Recently, a new bacterial signaling molecule, the dimeric cyclic AMP (c-di-AMP) has emerged as a central regulator of essential physiological processes, such as cell wall homeostasis, DNA integrity and bacterial virulence, among others. C-di-AMP is synthesized from two molecules of adenosine triphosphate (ATP) by proteins containing DisA_N domain, also called diadenilato cyclases (DACs). A survey in the Protein Families Database database (Pfam) found 2842 protein sequences containing the DAC domain, from 2386 different organisms. These proteins are divided into subfamilies and the three most abundant are: DacA (69,1%), a membrane protein associated with intracellular signaling resulting from an external environment change; DisA (24,1%), the first and most widely studied diadenilate cyclase, an intracellular protein found as active octamers in solution which indirectly controls cell division by DNA integrity verification; and DacB (5,5%), a cytoplasmic proteins, particularly expressed during bacterial spores formation. An interesting feature is that most organisms contain just a single and essential DAC-protein. Organisms containing two or more DAC-containing proteins, such as Clostridium and Bacillus spp., are exceptions. In Staphylococcus aureus (S. aureus), an opportunistic human pathogen responsible for some life-threating diseases, there is a single membrane attached diadenilate cyclase, hanging in the inner portion of the cell membrane (Sau_DacA). The activity of this protein is potentially regulated through direct interaction with YbbR, which contains an extracellular sensor domain. Sau_DacA conserves all key elements of bacterial di-adenylate cyclase, and for being the only di-adenylate cyclase from S. aureus, proves to be an excellent study target for new therapeutic purposes. However, to date, there is a lack of information about structure, c-di-AMP synthesis mechanism and regulation of nucleotide synthesis by Sau_DacA. Therefore, in this context the present work aims to contribute. Through a series of structural, calorimetric, spectroscopic and biochemical assays combined with site-directed mutations, we solved the structure of a soluble construct of Sau_DacA and identified a dimeric interface relevance for the conformational and thermal stability to the protein. This dimer is functionally active and highlights the importance of conserved motifs DGA (Aspartate-Glycine-Alanine) and RHR (Arginine-Histidine-Arginine) for the activity of Sau_DacA. The L5 loop, located between the active site and the dimer interface where is allocated the ATP binding motif (DGA), is stabilized in a favorable position for ATP binding, just in protein dimeric conformation. Our results combined with literary allowed us infer the synthesis of c-di-AMP occurs by face-to-face encounter of two distinct ATP binding site and its rate of synthesis could be regulated through direct protein interaction with. In this way, we contribute to a better understanding of Sau_DacA structure and function, assisting in its use as a target for new drugs development since it is known the biosynthesis of c-di-AMP is essential for most pathogens that synthesize.

Produtos naturais são uma importante fonte de fármacos e muitos vegetais têm sido explorados na busca de substâncias potencialmente ativas. Dentre estas, destacam-se as espécies do gênero Hypericum, principalmente H. perforatum, utilizado há séculos com diversos fins terapêuticos, principalmente no tratamento de feridas. Mais recentemente, a planta está em evidência devido à comprovada atividade antidepressiva, sendo extensamente utilizada em várias partes do mundo no tratamento de depressões leve a moderada. Ambas as atividades citadas se devem a presença de derivados do floroglucinol. As espécies de Hypericum encontradas no sul do Brasil são fonte de floroglucinóis com diversas atividades biológicas descritas. Um dos objetivos deste estudo foi investigar a atividade proliferativa de frações enriquecidas em floroglucinóis de H. caprifoliatum, H carinatum, H. connatum, H. myrianthum e H. polyanthemum, visando indicar possível atividade cicatrizante. Outro objetivo foi ampliar o conhecimento fitoquímico acerca das frações lipofílicas de H. austrobrasiliense e H. caprifoliatum. As partes aéreas, coletadas na época de floração, foram secas, moídas e extraídas com n-hexano. Para os ensaios de proliferação celular foi utilizada uma linhagem de queratinócitos (HaCaT) cultivada in vitro. Os extratos n-hexano das espécies de Hypericum foram caracterizados por CLAE, mostrando a presença majoritária de floroglucinóis. Entre as amostras testadas, as frações de H. carinatum e H. polyanthemum foram as mais promissoras, promovendo uma proliferação 20 a 40% superior àquela obtida com o controle, indicando uma indução no processo de crescimento celular. Os processos cromatográficos realizados com os extratos n-hexano de H. austrobrasiliense levaram ao isolamento de austrobrasilol A, austrobrasilol B e isoaustrobrasilol B, derivados de floroglucinol com estruturas inéditas, do extrato n-hexano de H. caprifoliatum foram obtidos hiperbrasilol B e iso-hiperbrasilol B. Os novos derivados de floroglucinol foram submetidos ao teste da placa aquecida e rotarod, onde demonstraram serem efetivos, provocando uma redução na percepção da dor nos mesmos níveis apresentados pelo floroglucinol dimérico uliginosina B, e não provocaram prejuízo motor. Os resultados obtidos reforçam a importância de vegetais deste gênero como fontes potenciais de compostos biologicamente ativos; neste caso, induzindo a proliferação de células envolvidas na cicatrização e reduzindo a nocicepção, podendo futuramente servir como protótipos de novos agentes cicatrizantes e analgésicos. / Natural products are an important source of vegetable drugs and have been explored in the search for potentially active substances. Among these, there are the species of the genus Hypericum, especially H. perforatum, used for centuries for various therapeutic purposes, highlighting the use in the treatment of wounds. More recently, the plant has received high attention due to the antidepressant activity and is widely used all over the world to treat mild to moderate depression. Both activities could be attributed to the presence of phloroglucinol derivatives. The species of Hypericum native to southern Brazil are a source of phloroglucinols with diverse biological activities. One goal of this study was to investigate the proliferative activity of phloroglucinol enriched fractions of H. caprifoliatum, H carinatum, H. connatum, H. myrianthum and H. polyanthemum, aiming to indicate possible wound healing activity. Another objective was to expand the phytochemical knowledge of lipophilic fractions of H. austrobrasiliense and H. caprifoliatum. The aerial parts collected at flowering time were dried, ground and extracted with n-hexane. For cell proliferation assays, keratinocyte cells (HaCaT) were used, grown in vitro. The n-hexane extract of Hypericum species were characterized by HPLC, showing predominant presence of phloroglucinols. Among the tested samples, the fractions of H. carinatum and H. polyanthemum were the most promising, promoving a proliferation 20 to 40% higher than that obtained with the control, indicating the induction of cell growth. The chromatographic process carried out the n-hexane extracts of H. austrobrasiliense led to the isolation of austrobrasilol A, austrobrasilol B and isoaustrobrasilol B, new phloroglucinol derivatives, and to the n-hexane extract of H. caprifoliatum were obtained hyperbrasilol B and isohyperbrasilol B. The new phloroglucinol derivatives were tested in hot plate and rotarod tests, proving to be effective, causing a reduction in pain perception at the same levels provided by dimeric phloroglucinol uliginosin B and did not cause motor impairment. The results emphasize the importance of this kind of plants as potential sources of biologically active compounds; in this case inducing the proliferation of keratinocyte cells and reducing the nociception, and may eventually serve as prototypes of new wound healing and analgesic agents.

Five novel compounds were synthesized and characterized. Crystal structures were determined using Rigaku Mercury 375/MCCD(XtaLAB mini) diffractometer with graphite monochromated MoKα radiation. The crystal structures of [Rh2(NPhCOCH3)4•xNCC6H4R where x = 1 or 2 and R=H, 2-CH3,3-CH3 and 4-CH3 were solved to an R1 value of less than 5 (R1= Σ||Fo| - |Fc|| / Σ |Fo|). In each of the nitrile complexes, the rhodium is five or six coordinate and possesses pseudo D4h symmetry. The complexes were also characterized by NMR and IR spectroscopy. [Rh2(CO2CCH3)(PhCOCF3)3] was also synthesized. In this complex, each rhodium atom is six coordinate, thus each rhodium is in an octahedral environment. Details of each synthesized complex are discussed.