abstract: Natural photosynthesis dedicates specific proteins to achieve the modular division of the essential roles of solar energy harvesting, charge separation and carrier transport within natural photosynthesis. The modern understanding of the fundamental photochemistry by which natural photosynthesis operates is well advanced and solution state mimics of the key photochemical processes have been reported previously. All of the early events in natural photosynthesis responsible for the conversion of solar energy to electric potential energy occur within proteins and phospholipid membranes that act as scaffolds for arranging the active chromophores. Accordingly, for creating artificial photovoltaic (PV) systems, scaffolds are required to imbue structure to the systems. An approach to incorporating modular design into solid-state organic mimics of the natural system is presented together with how conductive scaffolds can be utilized in organic PV systems. To support the chromophore arrays present within this design and to extract separated charges from within the structure, linear pyrazine-containing molecular ribbons were chosen as candidates for forming conductive linear scaffolds that could be functionalized orthogonally to the linear axis. A series of donor-wire-acceptor (D-W-A) compounds employing porphyrins as the donors and a C60 fullerene adduct as the acceptors have been synthesized for studying the ability of the pyrazine-containing hetero-aromatic wires to mediate photoinduced electron transfer between the porphyrin donor and fullerene acceptor. Appropriate substitutions were made and the necessary model compounds useful for dissecting the complex photochemistry that the series is expected to display were also synthesized. A dye was synthesized using a pyrazine-containing heteroaromatic spacer that features two porphyrin chromophores. The dye dramatically outperforms the control dye featuring the same porphyrin and a simple benzoic acid linker. A novel, highly soluble 6+kDa extended phthalocyanine was also synthesized and exhibits absorption out to 900nm. The extensive functionalization of the extended phthalocyanine core with dodecyl groups enabled purification and characterization of an otherwise insoluble entity. Finally, in the interest of incorporating modular design into plastic solar cells, a series of porphyrin-containing monomers have been synthesized that are intended to form dyadic and triadic molecular-heterojunction polymers with dedicated hole and electron transport pathways during electrochemical polymerization. / Dissertation/Thesis / Ph.D. Chemistry 2013

A transferência de elétrons tem sido objeto de um estudo intenso nos últimos anos, por causa da importância deste tipo de reação em processos naturais como a fotossíntese. Com isto, um progresso considerável foi conseguido na proposição de modelos para o centro de reação fotossintético, em particular utilizando o sistema-modelo porfirina-quinona. Nosso intuito e estudar o processo de transferência de elétrons da porfirina para a quinona, aleatoriamente distribuídas em uma matriz polimérica, utilizando a técnica de espectroscopia fotoacústica. A utilização de um filme de polímero como meio tem duas vantagens. A primeira e aproximar nosso sistema-modelo do processo fotossintético natural, no qual os doadores e os aceitadores de elétrons estão envoltos nas proteínas do centro de reação e, portanto, em um meio polimérico. A segunda e possibilitar a utilização desses filmes como possíveis componentes eletrônicos moleculares. Identificamos os estados eletrônicos da porfirina e da quinona e tentamos determinar o estado de cargas separadas, P+ e Q-. A partir dos espectros obtidos, determinamos a eficiência quântica de fluorescência da porfirina utilizada nos filmes. Estudamos, também, a degradação da porfirina nos filmes preparados. Por fim, verificamos o efeito da concentração crescente da quinona nos filmes preparados com a porfirina / The electron transfer phenomenon has been the subject of intense study for the last years, due to the importance of this kind of reaction in natural processes as photosynthesis. A great improvement has been achieved in the proposition of models for the photosynthetic reaction center, in particular using the porphyrin-quinone model system. Our intention is to study the electron transfer process of the porphyrin to the quinone randomly distributed in a polymeric matrix, using the photo acoustic spectroscopy. The utilization of a polymeric film as an environment has two advantages. The first is to approximate our model system to the natural photosynthetic process, in which the electron donors and acceptors are surrounded by, the proteins of the reaction center, and thus in a polymeric environment. The second is to allow the utilization of these films as possible molecular electronic components. We identified the electronic states of the porphyrin and the quinone, and we attempted to determine the charge separated electronic state. We determined the fluorescence quantum efficiency of the porphyrin films, by their photo acoustic and absorption spectra. Also, we studied the degradation of the porphyrin in the prepared films. Finally, we checked the effect of the increasing concentration of the quinone in the films prepared with the porphyrin

Este trabalho teve como objetivo estudar a transferência de elétrons em um meio rígido através de técnicas espectroscópicas convencionais, tais como a fluorescência e a fotoacústica, e verificar a possibilidade de se determinar a taxa de transferência através destas técnicas. Foram utilizados como doador de elétrons a tetrafenilporfirina (TPP), como aceitador de elétrons a duroquinona (DQ), e como meio rígido o polimetilmetacrilato (PMMA) e o poliestireno (PS). As amostras foram estudadas na forma de filmes, com uma distribuição aleatória de doadores e aceitadores de elétrons. Com a espectroscopia de fotoacústica não foi possível se detectar a ocorrência da transferência de elétrons. Com a fluorescência, usando o modelo de Perrin, foi possível determinar o raio crítico de transferência, 72k para o par TPP/DQ em poliestireno. No entanto, verificou-se a impossibilidade de se determinar univocamente a taxa de transferência de elétrons. Nos filmes preparados com polimetilmetacrilato foi observada uma fotodegradação irreversível, o que inviabilizou seus estudos / The objective of this work was to study the electron transfer process in a rigid medium using conventional spectroscopic techniques, such as fluorescence and photoacoustic, and verify the possibility of determining the electron transfer rate through these techniques. The molecules used were: tetraphenylporphyrin (TPP) as electron donor, duroquinone (DQ) as the electron acceptor, and polystyrene (PS) and polymethylmetacrilate (PMMA) as the rigid medium. The samples were studied in the form of films, with a random distribution of electron donor and acceptor molecules. With the photoacoustic spectroscopy it was not possible to detect the occurrence of the electron transfer process. With the fluorescence technique, using Perrin model, it was possible to determine the criticai radius for electron transfer, 7 À, for the par TPP/DQ in polystyrene. However, it was verified the impossibility of determining univocally the electron transfer rate. In the films made with polymethylmetacrilate, an irreversible photodegradation was observed, what made the study of these films non viable

A espectroscopia fotoacústica e de fluorescência foram empregadas no estudo de reação da transferência de elétrons entre um doador (Octaetil-porfirina) dois tipos de aceitadores [Diclorodiciano-benzoquinona (DDQ) e Duroquinona (DQ)] em um meio rígido [poli (metil-metacrilato)] . Foram preparados filmes nos quais a concentração de doador foi mantida constante e a de aceitador foi variada. Observou-se um aumento exponencial da amplitude do sinal fotoacústico do doador em 620 nm, com o aumento da concentração de aceitadores nos filmes. O modelo de Perrin para a supressão de fluorescência foi aplicado aos dados de fotoacústica e o raio da esfera de ação, que representa a distância crítica para a ocorrência da transferência de elétrons, foi determinado. Os resultados obtidos foram: para DDQ37 angstron e para aDQ 32 a 34angstron. Era esperado um raio maior para a DDQ devido a sua maior elétron afinidade. Também foi aplicado a estes dados o modelo de Kaneko, desenvolvido para a supressão de fluorescência. Dele se obtém a distribuição de moléculas aceitadoras incorporadas na esfera de ação. Para uma mesma concentração de aceitadores (2,8mmoldm-3) , a probabilidade de encontrar uma molécula de DDQ na esfera de ação foi 27%, enquanto que a probabilidade de encontrar uma molécula de DQ na esferade ação foi de 20%. Este resultado é, na verdade, equivalente ao encontrado no modelo de Perrin pois a probabilidade maior encontrada para a DDQ vem do fato do raio da sua esfera de ação ser maior. O valor encontrado para o raio crítico com os dados de fluorescência foi de 34 A para a DQ. Isto demonstra que as duas técnicas são complementares e que a espectroscopia fotoacústica pode ser usada para monitorar o processo de transferência de elétrons / Steady-state photoacoustic and fluorescence spectroscopy were employed to study the electron-transfer reaction from donor molecules (Octaethyl-porphirin) to two types of acceptor molecules [Dichloro-dicyano-benzoquinone (DDQ) and Duroquinone (DQ)I in a rigid medium [poly (methyl -metacrylate)] . Films were prepared with a fixed donor concentration and severa1 acceptor concentrations. It was observed an exponential growth in the donor photoacoustic signal amplitude at 620 nm, with the increase in the acceptor concentration. Perrin model, used in fluorescence quenching, was applied to the photoacoustic data and the radius o£ an action sphere, which represents a critica1 distance for the electron transfer process, was determined. The results obtained were: for DDQ 37 angstron and for DQ from 32 to 34 angstron. It was expected a larger radius for DDQ than for DQ due to its stronger electron affinity. Kaneko\'s model, was also applied to these data. It provides the distribution o£ incorporated acceptor molecules in the action sphere. For the same acceptor concentration (2.8 mmol , the probability of finding one DDQ molecule in the action sphere was 27%, while for the DQ molecule this value was 20%. Actually, this result is equivalent to that found using Perrin model, because the larger probability obtained for DDQ comes frm the fact that its critical radius is bigger . The value obtained for the critica1 radius from the fluorescence data was 34 angstron for DQ. This shows that these two techniques are complementary and that photoacoustic spectroscopy can be used to monitor the electron transfer process

Sem resumo / Sem abstract

Foi sintetizada e caracterizada a spiro-ciclopentil-1,2-dioxetanona, um derivado de 1,2-dioxetanona inédito, de forma a se contribuir com informações acerca da quimiluminescência de peróxidos orgânicos. Estudos mecanísticos da decomposição quimiluminescente de 1,2-dioxetanonas são escassos, principalmente quando comparados à enorme quantidade de resultados existentes sobre a formação de estados excitados na decomposição de 1,2-dioxetanos. A spiro-ciclopentil-1,2-dioxetanona foi preparada pela ciclização do 1-carbóxi-1- hidroperóxiciclopentano com N,N-diciclohexilcarbodiimida, com rendimento de 1,2%, e caracterizada por RMN de 1H e 13C a baixa temperatura e pelo comportamento cromatográfico da solução peroxídica. Evidências para a ocorrência do mecanismo de Luminescência Iniciada Quimicamente por Troca de Elétron (CIEEL) na formação de estados excitados, na sua variante intermolecular, foram obtidas por estudos cinéticos da decomposição quimiluminescente dessa 1,2-dioxetanona por diferentes ativadores (ACTs). Entretanto, a decomposição desse peróxido ocorre com rendimentos de formação de estados excitados singlete baixos (ΦS≈ 10-4 E mol-1), indicando que essa 1,2-dioxetanona também possui baixa eficiência de formação de estados excitados, conforme constatado recentemente para outros derivados. Foram encontradas evidências para a ocorrência de uma transferência de elétron na etapa limitante de velocidade, onde o ACT é formado no estado excitado, com um coeficiente de transferência de elétron de α = 0,19. Ainda, foi observada uma correlação entre a energia livre liberada para a formação de estados excitados e os rendimentos quânticos, nos moldes do mecanismo CIEEL. De acordo com os resultados obtidos nesse trabalho e em trabalhos anteriores, postula-se que o tamanho do substituinte alquílico no anel da 1,2-dioxetanona causa um efeito drástico na eficiência da decomposição catalisada do peróxido na seqüência CIEEL, diminuindo o valor da constante de equilíbrio para a formação inicial do complexo de transferência de carga Em uma segunda parte do trabalho, foi averiguado o mecanismo da reação peróxi-oxalato em meios aquosos, uma vez que a maioria dos trabalhos sobre esta transformação nestes meios possui ênfase na aplicação analítica. Foi observado que as reações dos oxalatos de bis(2,4,6-triclorofenila) (TCPO), moderadamente reativo, e bis(2,4-dinitrofenila) (DNPO), altamente reativo, com H2O2 e catálise por imidazol, ocorrem pelo mesmo mecanismo, em 1,2-dimetoxietano e em misturas aquosas desse solvente. Para TCPO, observou-se que há a formação de um intermediário de catálise nucleofílica, previamente ao ataque nucleofílico do H2O2. Para DNPO, há uma adição nucleofílica direta do H2O2 ao éster, com e sem catálise básica por imidazol. Em meios aquosos, a hidrólise do éster oxálico ocorre paralelamente à peridrólise, que leva à emissão de luz. Entretanto, as constantes de velocidade para a peridrólise do éster são significativamente maiores do que as para a sua hidrólise. Observou-se que a reação de TCPO com H2O2 em meios orgânico e aquoso, catalisada por 2,6-lutidina (2,6-dimetilpiridina), ocorre com essa base agindo como um catalisador não-nucleofílico. Por último, estudou-se a reação de TCPO com H2O2 em tampão carbonato de potássio, um meio essencialmente aquoso, onde a espécie reativa é a base conjugada do H2O2; entretanto, a constante de velocidade da peridrólise se mostrou similar à de hidrólise do éster oxálico. Nessa última parte do trabalho, foi demonstrado que a reação peróxi-oxalato também pode ser conduzida em meios aquosos. / Spiro-cyclopentyl-1,2-dioxetanone, a new 1,2-dioxetanone derivate, was synthesized and characterized, in order to contribute to the present mechanistic knowledge on organic peroxide chemiluminescence. Mechanistic studies on the chemiluminescent 1,2-dioxetanone decomposition are highly limited, especially when compared to the huge amount of data available for 1,2-dioxetanes. The spiro-cyclopentyl-1,2-dioxetanone was prepared by 1-carboxy-1-hydroperoxycyclopentane cyclization with N,N-dicyclohexylcarbodiimide, in a 1.2% yield and characterized by low temperature 1H and 13C NMR and the chromatographic behavior of the peroxide solution. Evidence for the occurrence of the Chemically Initiated Electron Exchange Luminescence (CIEEL) mechanism for excited states formation, in its intermolecular version, was obtained from kinetic studies of the chemiluminescent decomposition of this 1,2-dioxetanone with different activators (ACTs). However, the decomposition of this peroxide occurs with low yields of singlet excited state formation (ΦS≈ 10-4 E mol-1), showing that also this 1,2-dioxetanone possesses low excitation efficiency, as recently found for other derivatives. Evidence was found for the occurrence of an electron transfer in the rate limiting step, where the ACT is formed in its electronically excited state, with an electron transfer coefficient α= 0.19. Moreover, a correlation between the free energy released upon excited states formation and the quantum yields is observed, in agreement with the CIEEL mechanism. The results obtained in the present work together with previous data, allow to postulate that the size of the alkyl substituent on the 1,2-dioxetanone ring plays a crucial role for the efficiency of the catalyzed peroxide decomposition in the CIEEL sequence, by lowering the equilibrium constant for initial charge transfer complex formation. In a second part of this work, the mechanism of the peroxyoxalate reaction in aqueous media was studied, due to the fact that most of recent work on this system is mainly concerned only to analytical application aspects. The reaction of the moderately reactive bis(2,4,6-trichlorophenyl) (TCPO) and the highly reactive bis(2,4- dinitrophenyl) oxalate (DNPO) with H2O2 and imidazol catalysis, showed to occur by the same mechanism, in 1,2-dimethoxyethane as well as in its aqueous mixtures. For TCPO, the formation of an intermediate due to nucleophilic catalysis by imidazole was observed, preceding the H2O2 nucleophilic attack. For DNPO, direct nucleophilic addition of H2O2 to the ester occurs, with and without imidazole catalysis. In aqueous media, oxalic ester hydrolysis also occurs concomitantly to its perhydrolysis, which leads to light emission. However, the rate constants for perhydrolysis are significantly higher than the hydrolysis rate constants. For the reaction of TCPO with H2O2 in organic and aqueous medium, catalyzed by 2,6-lutidine (2,6-dimethylpyridine), it was shown that this base acts as a nonnucleophilic catalyst. Finally, the reaction of TCPO with H2O2 in potassium carbonate buffer, an essentially aqueous media, was studied, where the reactive species is the H2O2 conjugate base; however, the oxalic ester perhydrolysis rate constant proofed to be similar to its hydrolysis rate constant. In this last part it is also shown that the peroxyoxalate reaction can be carried out in aqueous media.

O óxido nítrico (NO) é um versátil agente biológico, atuando em diversas partes do organismo, tais como cérebro, artérias, sistema imunológico, fígado e pulmões. Alterações nos níveis basais de NO são relacionadas a causas de diversas doenças como hipertenção, câncer, doença de Raymond´s e agregação plaquetária. Visando suprir tal deficiência, mostrou-se de grande valia a obtenção de fármacos capazes de liberar quantidades significativas de NO e de maneira controlada. Uma das possibilidades é o uso de compostos de coordenação, com centro metálico rutênio coordenado ao ligante nitrosil, os quais possuem como característica liberação de NO por estímulo externo. Neste trabalho foram estudados as propriedades químicas, fotoquímicas, farmacológicas e tumoricidas do complexo trans-[RuC(MAC)NO]2+, onde MAC é 1,4,8,11-tetraazaciclotetradecano (cyclam) ou 1,4,8,12-tetraazaciclopentadecano ([15]aneN4), na presença do fotossensibilizador [Ru(NH3)5pz]2+. Os estudos fotoquímicos mostraram que o fotossensibilizador utilizado, [Ru(NH3)5pz]2+, possui tempo de vida no estado excitado de 113 ps, e apresenta processos de transferências eletrônicas e de energia fotoinduzida com o oxigênio molecular, gerando espécies reativas de oxigênio (EROS) como oxigênio singlete e ânion superóxido. Na presença do complexo macrocíclico trans-[RuC(MAC)NO]2+ a irradiação luminosa de [Ru(NH3)5pz]2+ na região do visível proporciona trasferência eletrônica fotoinduzida entre o fotosenssibilizador e o complexo nitrosilo com concomitante formação de NO. O rendimento quântico de NO (NO) é dependente do meio e é de cerca de 10-4 Einstein.mol.cm-1 em meio aquoso sob argônio e 10-2 Einstein.mol.cm-1 em meio oxigenado. Os estudos farmacológicos mostraram que a mistura proposta, em tampão fosfato pH 7,4, promoveu 75% de dilatação em musculatura de aorta pré-contraída com KC enquanto que, quando incorporados em sistemas carreadores de fármacos como emulsão óleo-em-água, HEG gel e membrana sol-gel, promoveram 40%, 35% e 35% de dilatação, respectivamente. A via vasodilatadora foi detectada como sendo pela ativação da GMPc (guanosina monofosfato cíclica), através da quantificação da concentração de cálcio citosólico. Os estudos das atividades anti-tumorais com os complexos doadores de NO foram realizados com linhagens celulares do tipo B16F10, Melan A, HL-60 WMs e Jurkat. Estes experimentos mostraram redução da viabilidade celular dos melanomas entre 50% e 75%, não apresentou ação em células normais (MelanA), mostrando-se seletivos ás células neoplasicas; e 95% de redução da viabilidade celular das células leucêmica (HL-60). Os resultados obtidos e descritos neste trabalho permitem vislumbrar que o uso de espécies doadoras de NO e oxigênio singlete possam ser utilizados no futuro em terapia clínica. / Nitric oxide (NO) is a multipurpose biological agent that shows important role in brain, arteries, immunological system, liver and lungs. The NO basal level alterations have correlation with several diseases as hypertension, cancer, Raymonds disease and platelet aggregation. Aiming supply this deficient NO level, it was necessary propose new compounds that can release NO at controlled manner. One of the possibilities is utilize nitrosyl ruthenium complexes that have ability to release NO under external stimulus. In this work we have studied, the chemical, photochemical, pharmacological and anti-tumoral properties of the trans-[RuC(MAC)NO]2+ complex, were MAC is 1,4,8,11-tetraazacyclotetradecane (cyclam) or 1,4,8,12-tetraazacyclopentadecane ([15]aneN4), in the presence of the sensitizer [Ru(NH3)5pz]2+. The photochemical studies of [Ru(NH3)5pz]2+ complex showed excited state lifetime of 113 ps and presented photoinduced electron and energy transfer with oxygen resulting in reactive oxygen species (ROS) generation as singlet oxygen and superoxide anion. In the presence of trans-[RuC(MAC)NO]2+ complex, the visible light irradiation of [Ru(NH3)5pz]2+ causes photoinduced electron transfer between the photosensitizer and the nitrosyl ruthenium complex resulting NO generation. The quantum yield (NO) is milieu dependent and showed 10-4 Einstein.mol.cm-1 in inert atmosphere and 10-2 Einstein.mol.cm-1 in aerated aqueous solution. The pharmacological studies showed that the proposed mixture in phosphate buffer, under visible irradiation, induce 75% of relaxation in aorta pre-contracted with KC while this system incorporated into drug delivery system as water-in-oil emulsion, HEG gel and sol-gel membrane, the nitric oxide generated induced 40%, 35% and 35% of relaxation, respectively. The quantification of cytosolic calcium concentration, using confocal image, showed that vasodilatation pathway observed was via cGMP (cyclic guanosine monophosphate) activation. The anti-tumoral studies using NO donors were carried out for B16F10, Melan A, HL-60, WMs and Jurkat cells. Those experiments showed decrease from 50% to 75% of cell viability of tumor cells and no toxicity in melanoma cells and 95% of reduction of leukemic cells (HL-60). The obtained results described in this work permit to glimpse that the use of NO donor species and singlet oxygen maybe is a useful tool in the future in clinical therapy.

Master of Science / Department of Geology / Matthew Kirk / A growing body of evidence demonstrates that methanogenesis and Fe(III) reduction can occur simultaneously. However, environmental controls on interactions between each are poorly understood. In this study we considered pH as a control on interactions between Fe(III) reduction and methanogenesis in anoxic sediment bioreactors. The reactors consisted of 100mL of synthetic aqueous media, and 1 g of marsh sediment amended with goethite (1mmol). One set of reactors received acidic media (pH 6), and the other alkaline media (pH 7.5). Each set received media containing acetate (0.25 mM) to serve as an electron donor. Control reactors, deficient in acetate, were also included. We maintained a fluid residence time of 35 days by sampling and feeding the reactors every seven days. For pH 6.0 and pH 7.5 reactors, the measured pH of effluent samples averaged 6.33 and 7.37, respectively. The extent of Fe(III) reduction and methanogenesis varied considerably between each set of reactors. More Fe(III) was reduced in the pH 6 reactors (646.39 μmoles on avg.) than the pH 7.5 reactors (31.32 μmoles on avg.). Conversely, more methane formed in pH 7.5 reactors (127.5 μmoles on avg.) than the pH 6 reactors (78.9 μmoles on avg.). Alkalinity concentrations during the middle and end of the experiment averaged 9.6 meq/L and 5.2 meq/L in pH 6 and pH7.5 reactors, respectively Although much less Fe(III) reduction occurred in pH 7.5 reactors, the relative abundance of Fe(III) reducers in them decreased little from levels observed in the pH 6 reactors. Sequences classified within Geobacter, a genus of bacteria known primarily as dissimilatory metal reducers, accounted for 22% and 13.45% of the sequences in the pH 6 and pH 7.5 reactors and only 0.8% of the sequences in the marsh sediment inoculum. In contrast, sequences classified within orders of methanogens were low in abundance, making up only 0.47% and 1.04% of the sequences in the pH 6 and pH 7.5 reactors, respectively. Mass balance calculations demonstrate that the amount of electron donor consumed by each group varied considerably between the sets of reactors. Expressed as a quantity of acetate, the reactions consumed about 160μM of electron donor each in pH 6 reactors. In contrast, methanogenesis consumed over 30 times more electron donor than Fe(III) reduction in the pH 7.5 reactors. Thus, the results of our experiment indicate that the decrease in electron donor consumption by Fe(III) reduction at basic pH was nearly matched by the increase in electron donor consumption by methanogens. Results of geochemical modeling calculations indicate that more energy was available for Fe(III) reduction in the pH 6.0 reactors than the pH 7.5 reactors, matching variation in Fe(III) reduction rates, and that the density of sorbed ferrous iron was higher in pH 6 reactors than pH 7.5 reactors. Thus, the calculation results are consistent with bioenergetics, but not variation in ferrous iron sorption, as a potential mechanism driving variation in the balance between each reaction with pH.

This thesis deals with the impact of hydrogen bonding on the properties of phenols. The possibility for tyrosine to form hydrogen bonds to other amino acids has been found to be important for its function as an electron transfer mediator in a number of important redox enzymes. This study has focused on modeling the function of tyrosine in Photosystem II, a crucial enzyme in the photosynthetic pathway of green plants. Hydrogen bonds between phenol and amines in both inter- and intramolecular systems have been studied with quantum chemical calculations and also in some solid-state structures involving phenol and imidazole. Different phenols linked to amines have been synthesized and their possibilities of forming intra- and intermolecular hydrogen bonds have been studied as well as the thermodynamics and kinetics of the generation of phenoxyl radicals via oxidation reactions. Since carboxylates may in principle act as hydrogen bond acceptors in a manner similar to imidazole, proton coupled electron transfer has also been studied for a few phenols intramolecularly hydrogen bonded to carboxylates with the aim to elucidate the mechanism for oxidation. Electron transfer in a new linked phenol—ruthenium(II)trisbipyridine complex was studied as well. The knowledge is important for the ultimate goal of the project, which is to transform solar energy into a fuel by an artificial mimic of the natural photosynthetic apparatus

No description available.