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The successful utilization of carbon nanomaterials in future electron spin-based technologies is highly dependent upon the ability to control their assembly at the nanoscale to form tailored solid-state architectures. Spin active metallofullerenes (MFs), Sc@C₈₂ and La@C<sub>82,/sub>, can be self assembled in 3D fullerene crystals or inside a carbon nanotube to form peapod structures. Single walled carbon nanotubes (SWCNTs) are an architect material to potentially allow the formation of 1-D spin chains. SWCNTs should be optimised to allow formation of spin chains and free of magnetic catalyst and carbon impurities, which have previously limited investigations of SWCNT spin properties. To address this, SWCNTs produced by laser ablation with a non-magnetic PtRhRe catalyst were purified through a multiple step centrifugation process in order to remove amorphous carbon and catalyst impurities. Centrifugation of SWCNT solutions resulted in sedimentation of carbon nanotube bundles containing clusters of catalyst particles, while isolated nanotubes with reduced catalyst particle content remained in the supernatant. Electron paramagnetic resonance (EPR) signals were detected only for samples which contained catalyst particles, with the ultracentrifuged SWCNTs showing no EPR signal at X-band (9.4 GHz) and fields ≤0.4 T. Integration of MFs into future devices requires a clear understanding of the nature of the spin and spin-spin interactions. Evaluating the spin properties of MFs, in both 3D (crystals) and 1D (peapods), will identify the spin-spin interactions and the affect of the surrounding SWCNT. Diluting spin active Sc@C₈₂ and La@C₈₂ MFs in a diamagnetic C₆₀ matrix, between 0.4% and 100%, permitted the tuning of the mean fullerene separation and thus interfullerene spin interactions. In dilute concentrations of MFs the hyper ne structure was resolved in EPR and with increasing concentration exchange narrowing was observed as a single narrow EPR peak. Encapsulation of Sc@C₈₂ MFs, of varying dilutions, into purified SWCNTs allowed formation of highly ordered 1-D array of metallofullerenes. Changing the spin environment from 3D crystal to 1D peapod resulted in the loss of the observed hyperfine structure in EPR. A single narrow peak was observed for Sc@C₈₂:C₆₀ peapods, indicating significant affect of the surrounding SWCNT structure upon the spin interactions of 1D metallofullerenes. Peapods of Ce@C₈₂ showed a similar EPR signal, suggesting that the observed narrow peak arises from charge transfer between the MF cage and the surrounding SWCNT.

O presente trabalho tem como objetivo geral a consolidação dos esforços iniciados anteriormente em nosso grupo para a utilização de marcação de spin sítio dirigida aliada à técnica de ressonância magnética eletrônica pulsada, em particular, ressonância dupla elétron-elétron (DEER), para medidas de distâncias entre sondas inseridas em moléculas biológicas. Como objetivo específico, interessa-nos a obtenção de informações estruturais de dois peptídeos pertencentes ao domínio de fusão da glicoproteína Spike do coronavírus causador da Síndrome Respiratória Aguda Grave (SARS) quando de sua ligação em modelos de membranas biológicas. Valemos-nos de uma abordagem conjunta envolvendo técnicas espectroscópicas, calorimétricas e computacionais para monitorarmos mudanças conformacionais nos peptídeos, suas conformações mais representativas e seus efeitos sobre a estrutura das membranas modelo. Os experimentos de calorimetria mostraram que os peptídeos perturbam fortemente o comportamento termotrópico de vesículas constituídas por fosfolipídios zwiteriônicos e negativamente carregados, sendo o efeito mais significativo na presença de lipídios negativos. Não somente a carga, mas também a estrutura da cabeça polar dos lipídios parece ter contribuição importante para a energética da interação. Os experimentos de dicroísmo circular mostraram que os peptídeos possuem alta flexibilidade conformacional, adotando diferentes estruturas secundárias em ambientes diversos. Uma mistura de conformações do SARSFP coexiste em solução aquosa e nos modelos de membranas, sugerindo alta plasticidade estrutural. Este peptídeo possui, ainda, alta capacidade de auto-associação e forma estruturas &beta; e/ou agregados &beta; regulares. Já o peptídeo SARSIFP adquire estrutura predominantemente &alpha;-helicoidal em micelas, estruturas &beta; em lipossomos e conformações irregulares em água. Em particular, este peptídeo parece se ligar às membranas na forma de &alpha;-hélices, mas adquirir estruturas &beta; em alta concentração. A flexibilidade conformacional dos peptídeos também foi estudada por dinâmica molecular (DM). Hélices, estruturas &beta;, voltas, dobras e estruturas irregulares são visitadas durante as trajetórias dos dois peptídeos, mas o SARSIFP apresenta menor flexibilidade estrutural. O perfil de energia livre apresentado consiste de uma superfície plana, larga e rasa, sem grandes barreiras energéticas separando os diferentes estados conformacionais. A energia térmica à 300 K é suficiente para visitar boa parte do espaço conformacional acessível aos peptídeos ao longo dos parâmetros de ordem escolhidos. Por fim, obtivemos informações estruturais de análogos paramagnéticos dos peptídeos duplamente marcados com radicais nitróxidos quando em diferentes solventes e miméticos de membranas, além de estudarmos a oligomerização de derivados unicamente marcados. As distribuições de distâncias recuperadas dos sinais de DEER mostram que o SARSIFP adota primariamente &alpha;-hélices na presença dos miméticos, com provável formação de estruturas &beta; na presença de micelas negativas. Para o SARSFP, uma larga distribuição de distâncias foi encontrada em todos os miméticos de membranas, refletindo a coexistência de conformações provavelmente bem compactas. Análogos unicamente marcados dos peptídeos ainda revelaram alta capacidade de formação de oligômeros em SDS-d25. Os resultados obtidos com esse conjunto de técnicas permitiram avanços consideráveis sobre as conformações adotadas pelos peptídeos nas diversas situações, o que pode revelar informações importantes acerca dos passos iniciais do mecanismo de fusão com membranas da glicoproteína Spike do coronavírus causador da SARS. / This thesis has the general goal of consolidating in our group the use of site directed spin labeling along with pulsed electron spin resonance, in particular double electron-electron resonance (DEER), for distance measurements in biological molecules. Our specific goal is to obtain structural information on two peptides belonging to the fusion domain of the spike glycoprotein from the SARS coronavirus when in the presence of membrane model systems. We used a joint approach involving spectroscopic, calorimetric, and computational techniques to monitor conformational changes in the peptides, their most representative conformations and their effects on the structure of model membranes. Calorimetric results showed that the peptides strongly perturb the thermotropic behavior of zwitterionic and negatively-charged lipid vesicles, with the largest effects seen with the later. Not only the charge, but also the lipid headgroup structure seems to be relevant for the energetics of the interaction. Circular dichroism experiments showed that the peptides present high conformational flexibility, assuming different secondary structures in diverse environments. A mixture of conformation of SARSFP coexists in aqueous solutions and in the membrane models, suggesting large structural plasticity. This peptide also showed high auto-association tendency forming &beta; structures and/or regular &beta; aggregates. On the other hand, the SARSIFP peptide is predominantly an &alpha;-helix when in micelles, &beta; structures in lipossomes, and assumes irregular conformations in water. In particular, this peptide seems to bind to membranes as an &alpha;-helix, transitioning to &beta; structures in high concentrations. The conformational flexibility of the peptides was also studied by molecular dynamics (MD). Helices, &beta; structures, turns, hairpins and irregular structures are visited during the trajectories of both peptides, but SARSIFP presents less structural flexibility. The free energy profile is consistent with that of a plane, broad and shallow surface, without large energetic barriers separating the different conformational states. The thermal energy at 300 K is sufficient to make the peptides visit most of the conformational space accessible for a certain choice of order parameters. Lastly, we obtained structural information from paramagnetic analogs of the peptides, which were doubly-labeled with nitroxide radicals, in different solvents and membrane mimetics. We also studied the oligomerization process of singly-labeled analogs. The distance distributions determined from the DEER traces showed that SARSIFP adopts a primarily &alpha;-helix conformation in the presence of the mimetics, with the formation of &beta; structures in the presence of negative micelles. DEER results for SARSFP showed a broad distribution of distances in all membrane mimetics, thus reflecting the coexistence of compact conformations. Singly-labeled analogs revealed the high tendency of formation of oligomers in SDS-d25. Our results allowed us to make considerable progress in understanding the conformations of the peptides in the conditions under investigation, which contributed with relevant information on the early steps of the membrane fusion mechanism carried out by the spike glycoprotein from the SARS coronavirus.

Cristais naturais de pumpelita Ca8Al8(Mg,Fe,Mn,Al)[(SiO4)4/(Si2O7)4/(OH)8(H2O, OH)4]), provenientes da mina de Brejui, município de Currais Novos, Rio Grande do Norte, foram investigados através das técnicas de termoluminescência (TL), absorção óptica (AO) e ressonância paramagnética eletrônica (EPR) com o intuito de entender os efeitos da radiação ionizante e de recozimento em altas temperaturas sobre estes cristais. As curvas TL obtidas apresentaram cinco picos, 90, 145, 220, 315 e 390 oC, após terem sido irradiadas para uma taxa de quecimento de 4 °C/s. A decomposição espectral da luz TL foi obtida para todos os picos e presentou uma emissão centrada em 575 nm e largura à meia altura de 75 nm e outras duas emissões menores em 470 nm e 660 nm indicando que o processo TL pode possuir mais de um centro de recombinação, independentemente das temperaturas dos picos. Em um segundo momento, foi investigado o efeito de diferentes tratamentos térmicos pré-irradiação (500, 600, 700, 800 e 900 °C) nas propriedades TL dos cristais. Somente a intensidade das emissões mostrou ser dependente da temperatura destes tratamentos térmicos, a posição dos quatro picos não foi alterada. Os picos em 220 e 390 °C apresentaram grande sensibilidade ao tratamento térmico. Uma análise termogravimétrica mostrou que entre 650 e 800 °C houve grande perda de massa envolvida num processo endotérmico, sugerindo uma provável mudança de estado. O espectro de ressonância paramagnética eletrônica mostra um sinal muito intenso que se estende de 1000 a 6000 Gauss e seis linhas típicas hiperfinas de Mn2+ entre 3000 e 4000 Gauss. O sinal EPR gigante é devido à interação dipolo (magnético) dipolo magnético) de Fe3+. Os espectros de AO de amostras recozidas em 600 °C, 700 °C e 900 °C mostram num resultado muito interessante, a banda em torno de 1060 nm, que, é devida a Fe2+ muda pouco com o tratamento térmico até 800 °C, mas, entre 800 °C e 900 °C a banda decresce. Nessa região de temperatura, ocorre a reação: Fe2+ temperaturae + Fe3+ Fe2+ perde um elétron e se torna Fe3+. Este processo é, também, responsável pelo aumento muito grande da intensidade EPR na região de g = 2,0, em amostras que sofreram recozimentos em temperaturas acima de 850 °C, Nestas temperaturas, a coloração da pumpelita é também afetada. Todos os picos TL sofrem fotoesvaziamento (bleaching), quando a amostra irradiada é exposta a luz UV. / Natural mineral of pumpellyite, one of the members of epidote group has been investigated. With chemical formula (Ca8Al8(Mg,Fe,Mn,Al)[(SiO4)4/(Si2O7)4/(OH)8(H2O, OH)4]), the sample here studied was collected from Brejui Mine, Currais Novos County, state of Rio Grande do Norte. The work was aimed to investigate its thermoluminescence (TL), color centers and electron paramagnetic properties. Annealing at high temperatures, heavy irradiation and UV irradiation techniques have been used. The physical properties of interest are due to the elements composing crystal structure such as Si, Al, Mg, Fe and Mn, however among about twenty elements that can be considered impurities; only Na, K and Cr participate. The TL glow curve obtained from 600 °C for one hour pre-annealed and then - irradiated sample has shown 90, 145, 220, 275 and 390 °C peaks. A heating rate of 4 °C has been used for TL read out. The lowest 90 °C peak is very unstable, however, it is by far the most sensitive one to the irradiation; at 50 Gy -dose its peak height is almost 100 times larger. Among others, the 315 °C peak grows faster. Heat treatments before irradiation increase the sensitivity of TL peaks slowly from 500 to 800 °C, but such increase becomes very large above 800 °C. For example the 390 °C peak sensitivity increases by a factor 100 on going from 500 C to 900 °C annealing. The spectral analysis of the emitted TL light has shown that there are 470, 575 and 600 nm bands indicating that there are at least three recombination centers. The 575 nm is by far the dominating one. The UV light bleaching has shown that all the TL peaks decay fast up to 10 minutes exposure and a residual TL is left after long time exposure. The optical absorption spectrum is characterized by four absorption bands in the visible region, one strong and broad band around 1060 nm and several in near IR region. The 1060 nm band is due to Fe2+ which around 850 900 °C annealing decreases indicating that Fe2+ liberates electrons leaving Fe3+. The EPR spectrum is dominated by Fe3+ spin spin interaction. Mn2+ six hyperfine lines superpose Fe line around g = 2,0. Under 850 900 °C heating, that broad Fe3+ lines becomes stronger and broader due to Fe2+ changing to Fe3+. The EPR intensity of 800 °C annealed sample and then irradiated to 1 kGy - dose increases with microwave power, but start saturation around 30 to 40 mW power.

Neoplasias ginecológicas são os tumores de maior incidência no público feminino. Como alternativa para o tratamento destes tumores existe a radioterapia, em que a sua eficácia depende prioritariamente da correta administração da dose prescrita ao tumor, com acurácia de ±5%, conforme estabelecido pela American Association of Physicists in Medicine (AAPM). Para verificar a administração de doses existem diversas técnicas dosimétricas, entre elas a ressonância de spin eletrônico (RSE) com L-alanina, material tecido-equivalente, que relaciona dose com a quantidade de radicais livres formados pela radiação. Portanto, o objetivo deste estudo é a verificação da dose administrada na região tumoral de pacientes diagnosticadas com câncer ginecológico submetidas à teleterapia, utilizando L-alanina e a RSE. Para comparação entre as modalidades de radioterapia, foi realizada braquiterapia ginecológica com objeto simulador, verificando a dose no reto durante o tratamento, que deve ser inferior a 65% da dose prescrita ao tumor, conforme a International Commission on Radiation Units (ICRU). Para a análise de teleterapia foi construído um aparato, para a inserção vaginal do material radio-sensível, que foi utilizado durante 5 das 25 sessões de tratamento. As doses foram determinadas com o sistema de planejamento do tratamento mediante as imagens da tomografia computadorizada, em conjunto com softwares de planejamento, e a existência de marcadores radiopacos no aparato permitiu a confirmação das doses, conforme referência óssea através de imagens de portal feitas no momento anterior ao tratamento. Após a irradiação foi feita a leitura das amostras com o espectrômetro de RSE, em que a amplitude pico a pico da linha principal do sinal, normalizado pela massa, determinou a dose entregue nas regiões de interesse. Previamente ao estudo in vivo foi efetuada a teleterapia com objeto simulador, nas mesmas condições de tratamentos in vivo, apresentando desvio médio em relação ao planejamento de (0,2 ± 3,5)%, viabilizando o estudo com pacientes. Para a primeira paciente o desvio médio obtido foi de (0,5 ± 3,7)% e para a segunda de (-0,7 ± 2,8)%. Na simulação da braquiterapia o desvio médio observado foi de (-1,3 ± 9,2)%. Por causa do pequeno número amostral de pacientes, esta pesquisa é classificada como um estudo de viabilidade, em que a utilização de L-alanina com a RSE se mostrou eficiente para o objetivo proposto, fazendo com que os resultados da teleterapia estivessem de acordo com o estipulado pela AAPM e na braquiterapia a dose administrada no reto obedecesse ao relatório 38 da ICRU. / Gynecological malignancies are the most incident female tumors. As an alternative treatment for these tumors exist the radiotherapy, which their effectiveness mainly depends on the right administration of the prescribed dose to the tumor, with an accuracy of ±5%, as established by the American Association of Physicists in Medicine (AAPM). There are a lot of dosimetric techniques for dose verification, including electron spin resonance (ESR) with L-alanine, a tissue-equivalent material, which relates dose with the amount of free radicals formed by radiation. Therefore, the aim of this study is to verify the dose administered in the tumor of patients diagnosed with gynecological cancer subjected to external beam radiation therapy using L-alanine and ESR. For comparison between the radiotherapy modalities was performed gynecological brachytherapy in phantom, verifying the dose to the rectum during treatment, which must be less than 65% of the prescribed dose to the tumor, according to the International Commission on Radiation Units (ICRU). For teletherapy analysis was constructed an apparatus for vaginal insertion of the radio-sensitive material, which was used in 5 of the 25 treatment fractions. The doses were determined with the treatment planning system with the computed tomography images, together with the planning software, and the existence of radiopaque markers in the apparatus allowed the dose confirmation, according to the bone reference through portal images made before treatment. After the irradiation the samples was read with the ESR spectrometer, wherein the peak to peak amplitude of the signal main line, normalized by weight, determined the dose delivered into the regions of interest. Prior to the in vivo study was performed the teletherapy with phantom, under the same conditions of in vivo treatments, presenting mean deviation to the planning dose of (0.2 ± 3.5)%, enabling the study with patients. For the first patient, the mean deviation obtained was of (0.5 ± 3.7)% and for the second one of (-0.7 ± 2.8)%. In the brachytherapy simulation the mean deviation observed was of (-1.3 ± 9.2)%. Due to the small sample of patients, this research is classified as a feasibility study, which the use of L-alanine with the ESR was efficient for the objective proposed, making the teletherapy results consistent with the stipulated by the AAPM, and in the brachytherapy the dose to the rectum obey the ICRU report 38.

O presente trabalho tem como objetivo geral a consolidação dos esforços iniciados anteriormente em nosso grupo para a utilização de marcação de spin sítio dirigida aliada à técnica de ressonância magnética eletrônica pulsada, em particular, ressonância dupla elétron-elétron (DEER), para medidas de distâncias entre sondas inseridas em moléculas biológicas. Como objetivo específico, interessa-nos a obtenção de informações estruturais de dois peptídeos pertencentes ao domínio de fusão da glicoproteína Spike do coronavírus causador da Síndrome Respiratória Aguda Grave (SARS) quando de sua ligação em modelos de membranas biológicas. Valemos-nos de uma abordagem conjunta envolvendo técnicas espectroscópicas, calorimétricas e computacionais para monitorarmos mudanças conformacionais nos peptídeos, suas conformações mais representativas e seus efeitos sobre a estrutura das membranas modelo. Os experimentos de calorimetria mostraram que os peptídeos perturbam fortemente o comportamento termotrópico de vesículas constituídas por fosfolipídios zwiteriônicos e negativamente carregados, sendo o efeito mais significativo na presença de lipídios negativos. Não somente a carga, mas também a estrutura da cabeça polar dos lipídios parece ter contribuição importante para a energética da interação. Os experimentos de dicroísmo circular mostraram que os peptídeos possuem alta flexibilidade conformacional, adotando diferentes estruturas secundárias em ambientes diversos. Uma mistura de conformações do SARSFP coexiste em solução aquosa e nos modelos de membranas, sugerindo alta plasticidade estrutural. Este peptídeo possui, ainda, alta capacidade de auto-associação e forma estruturas &beta; e/ou agregados &beta; regulares. Já o peptídeo SARSIFP adquire estrutura predominantemente &alpha;-helicoidal em micelas, estruturas &beta; em lipossomos e conformações irregulares em água. Em particular, este peptídeo parece se ligar às membranas na forma de &alpha;-hélices, mas adquirir estruturas &beta; em alta concentração. A flexibilidade conformacional dos peptídeos também foi estudada por dinâmica molecular (DM). Hélices, estruturas &beta;, voltas, dobras e estruturas irregulares são visitadas durante as trajetórias dos dois peptídeos, mas o SARSIFP apresenta menor flexibilidade estrutural. O perfil de energia livre apresentado consiste de uma superfície plana, larga e rasa, sem grandes barreiras energéticas separando os diferentes estados conformacionais. A energia térmica à 300 K é suficiente para visitar boa parte do espaço conformacional acessível aos peptídeos ao longo dos parâmetros de ordem escolhidos. Por fim, obtivemos informações estruturais de análogos paramagnéticos dos peptídeos duplamente marcados com radicais nitróxidos quando em diferentes solventes e miméticos de membranas, além de estudarmos a oligomerização de derivados unicamente marcados. As distribuições de distâncias recuperadas dos sinais de DEER mostram que o SARSIFP adota primariamente &alpha;-hélices na presença dos miméticos, com provável formação de estruturas &beta; na presença de micelas negativas. Para o SARSFP, uma larga distribuição de distâncias foi encontrada em todos os miméticos de membranas, refletindo a coexistência de conformações provavelmente bem compactas. Análogos unicamente marcados dos peptídeos ainda revelaram alta capacidade de formação de oligômeros em SDS-d25. Os resultados obtidos com esse conjunto de técnicas permitiram avanços consideráveis sobre as conformações adotadas pelos peptídeos nas diversas situações, o que pode revelar informações importantes acerca dos passos iniciais do mecanismo de fusão com membranas da glicoproteína Spike do coronavírus causador da SARS. / This thesis has the general goal of consolidating in our group the use of site directed spin labeling along with pulsed electron spin resonance, in particular double electron-electron resonance (DEER), for distance measurements in biological molecules. Our specific goal is to obtain structural information on two peptides belonging to the fusion domain of the spike glycoprotein from the SARS coronavirus when in the presence of membrane model systems. We used a joint approach involving spectroscopic, calorimetric, and computational techniques to monitor conformational changes in the peptides, their most representative conformations and their effects on the structure of model membranes. Calorimetric results showed that the peptides strongly perturb the thermotropic behavior of zwitterionic and negatively-charged lipid vesicles, with the largest effects seen with the later. Not only the charge, but also the lipid headgroup structure seems to be relevant for the energetics of the interaction. Circular dichroism experiments showed that the peptides present high conformational flexibility, assuming different secondary structures in diverse environments. A mixture of conformation of SARSFP coexists in aqueous solutions and in the membrane models, suggesting large structural plasticity. This peptide also showed high auto-association tendency forming &beta; structures and/or regular &beta; aggregates. On the other hand, the SARSIFP peptide is predominantly an &alpha;-helix when in micelles, &beta; structures in lipossomes, and assumes irregular conformations in water. In particular, this peptide seems to bind to membranes as an &alpha;-helix, transitioning to &beta; structures in high concentrations. The conformational flexibility of the peptides was also studied by molecular dynamics (MD). Helices, &beta; structures, turns, hairpins and irregular structures are visited during the trajectories of both peptides, but SARSIFP presents less structural flexibility. The free energy profile is consistent with that of a plane, broad and shallow surface, without large energetic barriers separating the different conformational states. The thermal energy at 300 K is sufficient to make the peptides visit most of the conformational space accessible for a certain choice of order parameters. Lastly, we obtained structural information from paramagnetic analogs of the peptides, which were doubly-labeled with nitroxide radicals, in different solvents and membrane mimetics. We also studied the oligomerization process of singly-labeled analogs. The distance distributions determined from the DEER traces showed that SARSIFP adopts a primarily &alpha;-helix conformation in the presence of the mimetics, with the formation of &beta; structures in the presence of negative micelles. DEER results for SARSFP showed a broad distribution of distances in all membrane mimetics, thus reflecting the coexistence of compact conformations. Singly-labeled analogs revealed the high tendency of formation of oligomers in SDS-d25. Our results allowed us to make considerable progress in understanding the conformations of the peptides in the conditions under investigation, which contributed with relevant information on the early steps of the membrane fusion mechanism carried out by the spike glycoprotein from the SARS coronavirus.

NV centers in a diamond are proving themselves to be good building blocks for quantum information, electron spin resonance (ESR) imaging, and sensor applications. The key feature of the NV is that it has an electron spin that can be polarized and read out at room temperature. The readout is optical, thus the magnetic field imaging can also be done easily. Magnetic field variation with feature sizes below 0.3 microns cannot be directly resolved, and so in this region magnetic resonance imaging must be employed. To realize the full sensitivity of NV diamond, the spin transition linewidth must be as narrow as possible. Additionally, in the case of NV ensembles for micron-sized magnetometers, there must be a high concentration of NV. To this end three techniques are explored: (1) Electron paramagnetic resonance (EPR) imaging with microwave field gradients, (2) Magic angle rotation of magnetic field, and (3) TEM irradiation to optimize the yield of NV in a diamond. For the EPR imaging demonstration a resonant microwave field gradient is used in place of the usual DC magnetic gradient to obtain enough spatial resolution to resolve two very close "double NV" centers in a type Ib bulk diamond. Microfabrication technology enabled the micron-size wire structure to sit directly on the surface of millimeter-scale diamond plate. In contrast to conventional magnetic resonance imaging pulsed ESR was used to measure the Rabi oscillations. From the beating of Rabi oscillations from a "double NV," the pair was resolved using the one-dimension EPR imaging (EPRI) and the spatial distance was obtained. To achieve high sensitivity in nitrogen-doped diamond, the dipole-dipole coupling between the electron spin of the NV center and the substitutional nitrogen (14N) electron must be suppressed because it causes linewidth broadening. Magic angle spinning is an accepted technique to push T2 and T2 * down toward the T1 limit. An experiment was performed using the HPHT diamond with a high concentration of nitrogen, and a rotating field was applied with a microfabricated wire structure to reduce line broadening. In this experiment, ~50% suppression of the linewidth was observed and the effective time constant T2* improved from 114 ns to 227 ns. To achieve the highest possible sensitivity for micro-scale magnetic sensors the concentration of NV should be large. Since the unconverted N are magnetic impurities they shorten T2 and T2*, giving a tradeoff between NV (and therefore N) concentration and sensitivity. To construct a damage monitor, a type Ib HPHT sample was irradiated with electrons from a transmission electron microscope (TEM) and the effects on the ESR transition were seen well before physical damage appeared on the diamond and thus this proved to be a sensitive metric for irradiation damage.

Mixed-valence compounds are of interest as model systems for the study of electron transfer reactions. The intramolecular electron transfer processes and patterns of charge delocalization in such compounds depend on the interplay between the electronic (V) and the vibronic (L) coupling. One can obtain both parameters from a Hush analysis of the intervalence band that arises upon optical intramolecular electron transfer if the band is intense and well-separated from other bands. This is quite often the case for mixed-valence triarylamines. As such, both Hush analysis and simulation of the intervalence band are widely used to classify these compounds as charge localized (class-II) or delocalized (class-III). Yet one must estimate the diabatic electron transfer distance (R) to calculate V in the Hush formalism. For mixed-valence triarylamines, R is commonly taken as the N-N distance; we show this to be a poor approximation in many cases. The activation barrier to thermal intramolecular electron transfer in a class-II mixed-valence compound is also related to the parameters V and L. Thus, if one can capture the rate of thermal electron transfer at multiple temperatures, then two experimental methods exist by which to extract the microscopic parameters. One technique that is widely used for organic mixed-valence compounds is variable-temperature electron spin resonance (ESR) spectroscopy. But this method is only rarely used to determine thermal electron transfer rates in mixed-valence triarylamines, as the electron transfer in most of the class-II compounds with distinct intervalence bands is too fast to observe on the ESR timescale. We show, for the first time, that one can use ESR spectroscopy to measure thermal electron transfer rates in such compounds. Simulation of ESR spectra based on density functional theory calculation and comparison with optical data also uncover the nature (i.e., adiabatic or nonadiabatic) of the electron transfer process.

Thesis (Ph. D.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains xi, 148 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.

Thesis (Ph. D.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains x, 210 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 154-185).