Ermoluminescência (TL), Ressonância Paramagnética Eletrônica (EPR) e absorção Óptica (AO) de duas amostras de zirconita ou zircão (de cor marrom), de Minas Gerais, de origem exata e desconhecida. As duas curvas de emissão TL mostraram a presença de 4 picos TL visíveis em 140, 215, 270 e 350 ºC, bastante superpostos. Por deconvolução, outros picos foram revelados. A intensidade dos picos TL em 140, 215 ºC em função da dose apresenta um comportamento linear seguido de sublinear. O espectro de emissão TL é composto de duas bandas em 480 e 580 nm, que são devidas à presença do Dy na nossa amostra. Além de Dy muitos outros elementos são encontrados na amostra, porém, não têm influência na emissão TL. Os espectros de EPR da amostra em pó irradiada mostraram a presença de um sinal central em g=2,000, devido ao centro SiO45- que é isotrópico, o que é facilmente observado na amostra policristalina (em pó). Na amostra monocristalina pode-se observar que existem outros centros EPR não isotrópicos, produzidos durante a irradiação da amostra, e que são devidos à perda ou ganho de um elétron por parte do grupo SiO44-. Os estudos de decaimento isócrono do sinal SiO45 e dos picos TL mostraram que existe correlação entre o centro EPR e os centros TL, o que nos levou a um possível mecanismo TL, segundo o qual o Dy3+ perde um elétron passando para Dy4+ durante a irradiação. O elétron liberado é capturado por SiO44- formando o centro EPR, SiO45-. Quando se aquece a amostra para a leitura TL o processo inverso acontece, deixando Dy3+ em estados excitados, e na transição ao estado fundamental duas emissões de luz, uma em 480nm e outra em 580nm são observados. As bandas de AO são devido ao Urânio (1100), H2O (1900nm) e o radical OH (1400nm). Estas bandas não são afetadas pela irradiação gama utilizada neste trabalho. / In the present work the investigation of some properties of Thermoluminescence (TL), Electronic Paramagnetic Resonance (EPR) and Optical Absorption (OA) of two samples of zircon (of brown color) from Minas Gerais, but the unknown exact origin, were carried out. The glow curves of thermoluminescence emission have shown the presence of 4 TL peaks at 140, 215, 270 and 350 ºC although strongly overlaped. By deconvolution more peaks were revealed. The intensity of the TL peaks at 140 and 215 ºC as function of the radiation dose presents linear and sublinear behavior. The TL emission spectrum has shown two bands at 480 and 580 nm, which are due to the Dy content in our sample. Appart from Dy many other elements are found in the sample, however, they do not participate in the TL emission. The EPR spectra of the irradiated powder sample showed a central signal whith g=2,000 that is due to the SiO45- center. This signal is isotropic and easily observed in the polycrystalline sample (in powder). In the monocrystalline sample non-isotropic signals can be observed due to EPR centers produced by irradiation. They are due to the loss or gain of one electron from the SiO44- group. The isocronal decay curves of the SiO45- signal and that of TL peaks are similar indicating a correlation between the EPR and TL centers suggesting us a possible TL mechanism: the Dy3+ looses one electron and converts into Dy4+ during irradiation. The electron liberated is then captured by SiO44- forming the SiO45- EPR center. When the sample is heated in order to read out TL the inverse process takesplace leaving the Dy3+ in excited states. In the transition to the ground state two light emissions are observed, one in 480nm and other in 580nm. In the OA spectrum measuremment two bands due to the Uranium (1100 and 1503nm), one to H2O(1900nm) and one due to the radical OH (1400nm) are observed. These bands are not afected by the irradiation used in this work.

Ermoluminescência (TL), Ressonância Paramagnética Eletrônica (EPR) e absorção Óptica (AO) de duas amostras de zirconita ou zircão (de cor marrom), de Minas Gerais, de origem exata e desconhecida. As duas curvas de emissão TL mostraram a presença de 4 picos TL visíveis em 140, 215, 270 e 350 ºC, bastante superpostos. Por deconvolução, outros picos foram revelados. A intensidade dos picos TL em 140, 215 ºC em função da dose apresenta um comportamento linear seguido de sublinear. O espectro de emissão TL é composto de duas bandas em 480 e 580 nm, que são devidas à presença do Dy na nossa amostra. Além de Dy muitos outros elementos são encontrados na amostra, porém, não têm influência na emissão TL. Os espectros de EPR da amostra em pó irradiada mostraram a presença de um sinal central em g=2,000, devido ao centro SiO45- que é isotrópico, o que é facilmente observado na amostra policristalina (em pó). Na amostra monocristalina pode-se observar que existem outros centros EPR não isotrópicos, produzidos durante a irradiação da amostra, e que são devidos à perda ou ganho de um elétron por parte do grupo SiO44-. Os estudos de decaimento isócrono do sinal SiO45 e dos picos TL mostraram que existe correlação entre o centro EPR e os centros TL, o que nos levou a um possível mecanismo TL, segundo o qual o Dy3+ perde um elétron passando para Dy4+ durante a irradiação. O elétron liberado é capturado por SiO44- formando o centro EPR, SiO45-. Quando se aquece a amostra para a leitura TL o processo inverso acontece, deixando Dy3+ em estados excitados, e na transição ao estado fundamental duas emissões de luz, uma em 480nm e outra em 580nm são observados. As bandas de AO são devido ao Urânio (1100), H2O (1900nm) e o radical OH (1400nm). Estas bandas não são afetadas pela irradiação gama utilizada neste trabalho. / In the present work the investigation of some properties of Thermoluminescence (TL), Electronic Paramagnetic Resonance (EPR) and Optical Absorption (OA) of two samples of zircon (of brown color) from Minas Gerais, but the unknown exact origin, were carried out. The glow curves of thermoluminescence emission have shown the presence of 4 TL peaks at 140, 215, 270 and 350 ºC although strongly overlaped. By deconvolution more peaks were revealed. The intensity of the TL peaks at 140 and 215 ºC as function of the radiation dose presents linear and sublinear behavior. The TL emission spectrum has shown two bands at 480 and 580 nm, which are due to the Dy content in our sample. Appart from Dy many other elements are found in the sample, however, they do not participate in the TL emission. The EPR spectra of the irradiated powder sample showed a central signal whith g=2,000 that is due to the SiO45- center. This signal is isotropic and easily observed in the polycrystalline sample (in powder). In the monocrystalline sample non-isotropic signals can be observed due to EPR centers produced by irradiation. They are due to the loss or gain of one electron from the SiO44- group. The isocronal decay curves of the SiO45- signal and that of TL peaks are similar indicating a correlation between the EPR and TL centers suggesting us a possible TL mechanism: the Dy3+ looses one electron and converts into Dy4+ during irradiation. The electron liberated is then captured by SiO44- forming the SiO45- EPR center. When the sample is heated in order to read out TL the inverse process takesplace leaving the Dy3+ in excited states. In the transition to the ground state two light emissions are observed, one in 480nm and other in 580nm. In the OA spectrum measuremment two bands due to the Uranium (1100 and 1503nm), one to H2O(1900nm) and one due to the radical OH (1400nm) are observed. These bands are not afected by the irradiation used in this work.

O Relatório Mundial do Câncer, a Agência Internacional Para Pesquisa no Câncer e a Organização Mundial da Saúde estimam que, a cada ano há 12,4 milhões de novos casos de câncer no mundo, havendo 7,6 milhões de mortes causadas pela doença, onde para os homens o mais recorrente é o câncer de próstata. Por isso, o tratamento de câncer de próstata, neste caso, por radioterapia deve apresentar elevada precisão. Um complicador para tal precisão pode ser a presença de próteses metálicas no fêmur e na pélvis, podendo ser unilateral ou bilateral. O objetivo deste trabalho foi analisar e comparar o tratamento radioterápico de próstata para três situações diferentes, com duas próteses, com uma prótese e sem nenhuma prótese através da dosimetria por Ressonância Paramagnética (EPR) utilizando o aminoácido alanina com dosímetro, que se baseia na determinação de radicais livres produzidos pela interação entre a radiação e a alanina através do registro do espectro da alanina irradiada. Para tal análise foi construído um simulador físico (phantom), com as medidas reais de um ser humano, feito de acrílico e água, simulando o tecido mole, e ossos humanos. Na região da próstata foi feita uma abertura cilíndrica onde foram inseridos os dosímetros de alanina compostos 95% de DL-alanina e 5% de Polivinil Álcool (PVA) com 3mm de diâmetro, 4 mm de comprimento e massa de 0,05 g. O phantom foi irradiado para cada situação, nas condições de tratamento em um acelerador linear Oncor Plus da Siemens com feixe de raios X de 6MV para quatro campos 10x10cm2 e uma dose de 2 Gy, onde as mesmas condições foram utilizadas para a calibração dos dosímetros. Os dosímetros foram analisados em um espectrômetro de banda X JEOL JES-FA200 (9.5 GHz). Através da curva de calibração e a amplitude da linha central do espectro foi possível calcular a dose obtida em cada dosímetro de DL-alanina obtendo uma variação de até 6,15% para as medidas da dose prescrita de 2 Gy. Os resultados mostraram-se semelhantes para as três situações estudadas, assim como calculado no sistema de planejamento. / The World Cancer Report, the International Agency for Research on Cancer and the World Health Organization estimates that each year there are 12.4 million new cases of cancer worldwide, with 7.6 million deaths from the disease, for which men is the most recurrent prostate cancer. Therefore, the treatment of prostate cancer, in this case by radiotherapy should have a high accuracy. A complicating factor for such precision may be the presence of metallic prosthesis in the femur and pelvis and may be unilateral or bilateral. The objective of this study was to analyze and compare the radiotherapy of prostate for three different situations, with two prostheses, with one prosthesis and without a prosthesis through dosimetry Paramagnetic Resonance (EPR) using the amino acid alanine with dosimeter, which is based on determining free radicals produced by the interaction between radiation and alanine by recording the spectrum of irradiated alanine. For this analysis we built a physical simulator (phantom), with the real measurements of a human being, made of acrylic and water, simulating soft tissue, and human bones. In the region of the prostate was made a cylindrical opening in which the dosimeters were inserted alanine compounds 95% DL-alanine and 5% Polyvinyl Alcohol (PVA) with 3mm diameter, 4 mm in length and mass of 0.05 g. The phantom was irradiated for each situation, the conditions of treatment in a linear accelerator Oncor Plus Siemens X-ray beam with 6mV for four fields of 10x10cm2 and a dose of 2 Gy, where the same conditions were used for calibration of the dosimeter. The dosimeters were analyzed in a JEOL X-band spectrometer JES-FA200 (9.5 GHz). Through the calibration curve and the amplitude of the centerline of the spectrum was possible to calculate the dose obtained in each of DL-alanine dosimeter obtaining a variation of up to 6.15% for the measurements of the prescribed dose of 2 Gy. The results were similar for the three cases studied, as calculated in the planning system.

O Relatório Mundial do Câncer, a Agência Internacional Para Pesquisa no Câncer e a Organização Mundial da Saúde estimam que, a cada ano há 12,4 milhões de novos casos de câncer no mundo, havendo 7,6 milhões de mortes causadas pela doença, onde para os homens o mais recorrente é o câncer de próstata. Por isso, o tratamento de câncer de próstata, neste caso, por radioterapia deve apresentar elevada precisão. Um complicador para tal precisão pode ser a presença de próteses metálicas no fêmur e na pélvis, podendo ser unilateral ou bilateral. O objetivo deste trabalho foi analisar e comparar o tratamento radioterápico de próstata para três situações diferentes, com duas próteses, com uma prótese e sem nenhuma prótese através da dosimetria por Ressonância Paramagnética (EPR) utilizando o aminoácido alanina com dosímetro, que se baseia na determinação de radicais livres produzidos pela interação entre a radiação e a alanina através do registro do espectro da alanina irradiada. Para tal análise foi construído um simulador físico (phantom), com as medidas reais de um ser humano, feito de acrílico e água, simulando o tecido mole, e ossos humanos. Na região da próstata foi feita uma abertura cilíndrica onde foram inseridos os dosímetros de alanina compostos 95% de DL-alanina e 5% de Polivinil Álcool (PVA) com 3mm de diâmetro, 4 mm de comprimento e massa de 0,05 g. O phantom foi irradiado para cada situação, nas condições de tratamento em um acelerador linear Oncor Plus da Siemens com feixe de raios X de 6MV para quatro campos 10x10cm2 e uma dose de 2 Gy, onde as mesmas condições foram utilizadas para a calibração dos dosímetros. Os dosímetros foram analisados em um espectrômetro de banda X JEOL JES-FA200 (9.5 GHz). Através da curva de calibração e a amplitude da linha central do espectro foi possível calcular a dose obtida em cada dosímetro de DL-alanina obtendo uma variação de até 6,15% para as medidas da dose prescrita de 2 Gy. Os resultados mostraram-se semelhantes para as três situações estudadas, assim como calculado no sistema de planejamento. / The World Cancer Report, the International Agency for Research on Cancer and the World Health Organization estimates that each year there are 12.4 million new cases of cancer worldwide, with 7.6 million deaths from the disease, for which men is the most recurrent prostate cancer. Therefore, the treatment of prostate cancer, in this case by radiotherapy should have a high accuracy. A complicating factor for such precision may be the presence of metallic prosthesis in the femur and pelvis and may be unilateral or bilateral. The objective of this study was to analyze and compare the radiotherapy of prostate for three different situations, with two prostheses, with one prosthesis and without a prosthesis through dosimetry Paramagnetic Resonance (EPR) using the amino acid alanine with dosimeter, which is based on determining free radicals produced by the interaction between radiation and alanine by recording the spectrum of irradiated alanine. For this analysis we built a physical simulator (phantom), with the real measurements of a human being, made of acrylic and water, simulating soft tissue, and human bones. In the region of the prostate was made a cylindrical opening in which the dosimeters were inserted alanine compounds 95% DL-alanine and 5% Polyvinyl Alcohol (PVA) with 3mm diameter, 4 mm in length and mass of 0.05 g. The phantom was irradiated for each situation, the conditions of treatment in a linear accelerator Oncor Plus Siemens X-ray beam with 6mV for four fields of 10x10cm2 and a dose of 2 Gy, where the same conditions were used for calibration of the dosimeter. The dosimeters were analyzed in a JEOL X-band spectrometer JES-FA200 (9.5 GHz). Through the calibration curve and the amplitude of the centerline of the spectrum was possible to calculate the dose obtained in each of DL-alanine dosimeter obtaining a variation of up to 6.15% for the measurements of the prescribed dose of 2 Gy. The results were similar for the three cases studied, as calculated in the planning system.

Diabetic nephropathy is one of the most common causes of end stage renal disease and develops in approximately one third of all diabetes patients. Disease progression is characterized by deteriorating glomerular filtration rate and escalating urinary albumin/protein excretion; both are used as clinical markers for disease progression. Recently, it has been proposed that intrarenal hypoxia is a unifying mechanism for chronic kidney disease, including diabetic nephropathy. Several mechanistic pathways have been linked to the development of intrarenal hypoxia and diabetic nephropathy including increased angiotensin II signaling, oxidative stress and hyperglycemia per se. Furthermore, pathological endothelin signaling has recently immerged as a possible contributing factor for chronic kidney disease and diabetic nephropathy. The overall aims of this thesis were therefore to determine the temporal relationship between development of intrarenal hypoxia and kidney disease as well as elucidate the potential link between endothelin signaling, intrarenal hypoxia and kidney disease in experimental insulinopenic diabetes. It is well established that different mouse strains have different susceptibility for kidney and cardiovascular disease. The first step was therefore to compare four commonly used mouse strains with regards to development of kidney disease after onset of insulinopenic diabetes. From the results of this study, we concluded that the NMRI mouse strain has a disease progression closest to the human disease and this strain was chosen in the subsequent studies in mice. The next step was to adapt and optimize a suitable method for repetitive measurements of intrarenal oxygen tension during the course of disease development. Electron paramagnetic resonance (EPR) oximetry had previously been used in tumor biology and was now adapted and optimized for measurements of kidney oxygenation in our diabetic mouse model. EPR oximetry in normoglycemic control mice recorded cortical oxygen tension values similar to previous reports using invasive techniques. Surprisingly, intrarenal hypoxia developed already within the first 72h after induction of hyperglycemia and persisted throughout the two-week study period. Importantly, this was well before albuminuria developed. The final part of this thesis was to investigate the role of endothelin signaling for the intrarenal hypoxia in a diabetic rat model. Endothelin 1 signals via two distinctly different receptor-mediated pathways. In normal physiology, endothelin 1 binding to endothelin receptor type A (ETA) induces vasoconstriction, which can be blocked by the specific ETA antagonist BQ123, whereas endothelin 1 binding to endothelin receptor type B (ETB) induces nitric oxide-dependent vasodilation. ETB receptors can be selectively activated by Sarafotoxin 6c. The results from blocking ETA and activating ETB receptors demonstrated that endothelin 1 signaling via ETA receptors contributes to intrarenal hypoxia in the rat diabetic kidney, and that ETB stimulation significantly reduces the diabetes-induced intrarenal hypoxia. The beneficial effects on kidney oxygen availability in diabetes by ETA blockade or ETB stimulation were mainly linked to hemodynamic improvements rather than direct effects on kidney oxygen consumption or oxidative stress status. In conclusion, by applying EPR oximetry in a mouse model of insulinopenic diabetes mimicking the human disease, we demonstrated intrarenal hypoxia already within the first couple of days after the onset of hyperglycemia, which is well before detectable signs of kidney disease development. Furthermore, blockade of ETA or activation of ETB receptors significantly reduced intrarenal hypoxia in the diabetic kidney. These results demonstrate involvement of ETA receptor signaling in diabetes-induced intrarenal hypoxia and ETA blockade or ETB activation might provide new therapeutical targets to reduce kidney hypoxia and disease progression in diabetes.

No description available.

This thesis is concerned with the electrochemical and spectroelectrochemical characterisation of cyano (CN) and trifluoromethyl (CF3) substituted polypyridine ligands and their metal complexes. The ligands investigated were X-CN-py (X = 3, 4 and 5, py = pyridine), X,X´-(CN)2-bpy) (X,X´ = 3,3´, 4,4´ and 5,5´ bpy = 2,2´- bipyridine) and X,X´-(CF3)2-bpy (X,X´ = 3,3´, 4,4´ and 5,5´). The Pt(II) complexes of the X-CN-py and X,X´-(CN)2-bpy ligands were studied along with the Fe(II) complexes of the X,X´-(CN)2-bpy and X,X´-(CF3)2-bpy ligands. Electrochemical studies of the X-CN-py ligands indicated that 2-CN-py and 4-CN-py have one reversible 1e- reduction and 3-CN-py has one quasi-reversible reduction. 4-CN-py is more easily reduced than 2-CN-py. EPR experiments on [2-CN-py]1- and [4-CN-py]1- combined with DFT calculations have indicated that the semi-occupied molecular orbital (SOMO) is delocalised over the entire molecule. The complex [Pt(4-CN-py)2Cl2] undergoes two reversible 1e- reductions, attributed to the sequential reduction of the two 4-CN-py ligands. [Pt(3-CN-py)2Cl2] was found to exhibit one irreversible reduction. The electrochemistry of the X,X´-(CN)2-bpy ligands indicated that 3,3´-(CN)2-bpy and 5,5´-(CN)2-bpy have two reversible 1e- reductions while 4,4´-(CN)2-bpy has only one reversible 1e- reduction. The reductions of 5,5´-(CN)2-bpy occur at significantly less negative potentials than those in 3,3´ or 4,4´ analogue. In-situ UV/Vis/NIR and EPR experiments on the X,X´-(CN)2-bpy ligands indicate that the reduction electron is delocalised over both the CN-py rings with the SOMO being spread across the entire molecule. [Pt(3,3´-(CN)2-bpy)Cl2] and [Pt(5,5´-(CN)2-bpy)Cl2] undergo two reversible 1e- reductions, attributed to the sequential reduction of the X,X´-(CN)2-bpy ligand. 4,4´-(CF3)2-bpy and 5,5´-(CF3)2-bpy, whose X-ray crystallographically determined structures are reported, both have one reversible 1e- reduction while 3,3´-(CF3)2-bpy exhibits an irreversible reduction. Again the 5,5´ analogue is the most easily reduced. Spectroelectrochemical results indicate that the reduction electron enters a SOMO that is delocalised over both the CF3-py rings. Substitution in the 5,5´ positions is determined to be electronically most significant. Complexes of the general formula [Fe(II)(X2-bpy)3][BF4] (where X = CN or CF3 in the 4,4´ or 5,5´ positions) exhibit three reversible ligand based reduction processes and a metal based oxidation. UV/Vis/NIR and EPR studies have confirmed that the reduction electron in each case enters a molecular orbital that is predominantly based on a bpy ligand. The redox potentials of 4-CN-py and 5,5´-(CN)2-bpy are solvent dependent with 1e- reduction of 4-CN-py and the two 1e- reductions of 5,5´-(CN)2-bpy moving to less negative potentials as the acceptor number (AN) of the solvent increases. A computational model has been developed for the study of the electronic properties of substituted bipyridines using DFT methods. This model has been used to aid the analysis of the EPR and UV/Vis/NIR spectra of the X2-bpys studied.

This dissertation investigates the synthesis, characterization and electrochemical properties of viologen-containing dendrimers. Additionally, the self-assembled system of resorcinarenes was investigated with paramagnetic guests using EPR and 1H NMR techniques. Chapter one is a brief introduction to the dendrimers and describes its evolution, structural features, synthetic methods and emerging applications to various fields of research such as catalysis, material science, drug delivery and medicine. Chapter two describes the synthesis, characterization and electrochemical properties of a new series of dendrimers. These dendrimers have a viologen unit at the core surrounded by Newkome and Fr¨¦chet dendrons. The potentials of two consecutive one-electron reductions of the viologen core were determined by cyclic voltammetry. The electrochemistry of viologen unit showed a distinct and obvious trend. Newkome and Frechet dendrons having different functional groups as repeating units has opposite effect on the half-wave potentials. The overall effect of these two dendrons is reflected by the corresponding reduction potentials. The redox site encapsulation by the Frechet and Newkome dendrons is indicated by the attenuation in heterogeneous electron transfer rate constants. Chapter three describes the probing of self-assembled capsule of resorcinarenes with 4-amino tempo and 4-trimethyl-ammonium tempo derivative. EPR spectroscopy and 1H NMR spectroscopy were used to investigate the nature of complexations involved in these systems. We observed a subsequent change in their spectroscopic parameters. Careful investigation of rotational correlation times and NMR line-widths at half height revealed that 4-trimethyl-ammonium tempo has stronger binding affinity with these capsules compared to 4-amino tempo due to favorable cation -pi interactions.

The function of biomolecules is very sensitive to structure. Folding in proteins and nucleic acids is a hierarchical process progressing from primary to secondary, then tertiary, and finally, quaternary structures. RNA in its folded form performs a variety of biological activities. Obtaining intramolecular distance measurements makes it possible to generate structural models along the folding pathway that may be related to the overall function of the molecule. Distances can be measured by Site-Directed Spin-Labeling (SDSL), in which nitroxyl spin-label probes are attached and observed by EPR spectroscopy. Spin-labels can provide information concerning structure and conformational changes because they are particularly sensitive to molecular motion and interspin distances. Continuous-wave EPR spectroscopy has been commonly applied to detect and monitor nitroxide spin-label probes within biological systems. A previous published SDSL study from this laboratory investigated a 10-mer RNA duplex model system with spin-label probe succinimdyl-2,2,5,5-tetramethyl-3-pyrroline-1-oxyl-carboxylate; however, an increased spin-labeling efficiency was observed with an isocyanate derivative of tetramethylpiperidyl-N-oxy (TEMPO). In this thesis, a 4-isocyano TEMPO spin-label probe replaced the previously used succinimdyl-2,2,5,5-tetramethyl-3-pyrroline-1-oxyl-carboxylate in 10-mer SDSL studies. The influence of labeling with the 4-iscocyano TEMPO spin-label in a 10-mer RNA model system was investigated with thermal denaturation, Matrix Assisted Laser Desorption Time of Flight Mass Spectrometry (MALDI-TOF-MS), Electron Paramagnetic Resonance (EPR) spectroscopy, and reverse phase high performance liquid chromatography (RP-HPLC). In the 10-mer RNA duplex model system a 4-isocyano TEMPO spin-label is individually attached to one strand and two strands are annealed to measure distances. This methodology is limited to systems in which two oligonucleotides are annealed together. To circumvent this limitation and also to explore single-strand dynamics a new methodology was implemented, double spin-labeling. Double spin-labeled single-stranded RNA was investigated as a single-strand and within a duplex via MALDI-TOF-MS, EPR spectroscopy and RP-HPLC. A double spin-labeling strategy in this work will be applicable to large complex RNAs like Group I intron of Tetrahymena thermophilia.

The function of biomolecules is very sensitive to structure. Folding in proteins and nucleic acids is a hierarchical process progressing from primary to secondary, then tertiary, and finally, quaternary structures. RNA in its folded form performs a variety of biological activities. Obtaining intramolecular distance measurements makes it possible to generate structural models along the folding pathway that may be related to the overall function of the molecule. Distances can be measured by Site-Directed Spin-Labeling (SDSL), in which nitroxyl spin-label probes are attached and observed by EPR spectroscopy. Spin-labels can provide information concerning structure and conformational changes because they are particularly sensitive to molecular motion and interspin distances. Continuous-wave EPR spectroscopy has been commonly applied to detect and monitor nitroxide spin-label probes within biological systems. A previous published SDSL study from this laboratory investigated a 10-mer RNA duplex model system with spin-label probe succinimdyl-2,2,5,5-tetramethyl-3-pyrroline-1-oxyl-carboxylate; however, an increased spin-labeling efficiency was observed with an isocyanate derivative of tetramethylpiperidyl-N-oxy (TEMPO). In this thesis, a 4-isocyano TEMPO spin-label probe replaced the previously used succinimdyl-2,2,5,5-tetramethyl-3-pyrroline-1-oxyl-carboxylate in 10-mer SDSL studies. The influence of labeling with the 4-iscocyano TEMPO spin-label in a 10-mer RNA model system was investigated with thermal denaturation, Matrix Assisted Laser Desorption Time of Flight Mass Spectrometry (MALDI-TOF-MS), Electron Paramagnetic Resonance (EPR) spectroscopy, and reverse phase high performance liquid chromatography (RP-HPLC). In the 10-mer RNA duplex model system a 4-isocyano TEMPO spin-label is individually attached to one strand and two strands are annealed to measure distances. This methodology is limited to systems in which two oligonucleotides are annealed together. To circumvent this limitation and also to explore single-strand dynamics a new methodology was implemented, double spin-labeling. Double spin-labeled single-stranded RNA was investigated as a single-strand and within a duplex via MALDI-TOF-MS, EPR spectroscopy and RP-HPLC. A double spin-labeling strategy in this work will be applicable to large complex RNAs like Group I intron of Tetrahymena thermophilia.