CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / O emprego das tÃcnicas de eletroquÃmica, microbalanÃa de cristal quartzo (QCM â Quartz Crystal Microbalance) e ressonÃncia de plÃsmons de superfÃcie (SPR â Surface Plasmon Resonance) mostram que as espÃcies 1,4-ditiano (1,4-dt), 4-mercaptopiridina (pyS), 5-(4-piridil)-1,3,4-oxadiazol-2-tiol (Hpyt), tionicotinamida (TNA) e isotionicotinamida (iTNA) experimentam adsorÃÃo espontÃnea formando SAMs (Self-Assembled Monolayers) como resultado da imersÃo de substratos de ouro em soluÃÃo contendo estas espÃcies. As imagens obtidas por microscopia de varredura por tunelamento (STM â Scanning Tunneling Microscopy) indicam um arranjo prÃximo do hexagonal com exceÃÃo da iTNA cujas imagens nÃo foram conclusivas. Adicionalmente, as imagens indicam a existÃncia de defeitos nas SAMs mesmo apÃs longos perÃodos de imersÃo (24 h). Os estudos termodinÃmicos e cinÃticos dos processos de adsorÃÃo foram realizados por desorÃÃo redutiva em meio alcalino e QCM. Os valores dos potenciais de desorÃÃo redutiva, Edr, foram observados em −0,9, −0,8 e −0,5 V vs. Ag/AgCl/Cl- para a desorÃÃo de iTNA, TNA e Hpyt, respectivamente. Comparativamente Ãs espÃcies 1,4-dt (−0,8 V) e pyS (−0,5 V), o valor de Edr da SAM de Hpyt indica uma interaÃÃo sigma ao passo que aqueles observados para iTNA e TNA sugerem uma contribuiÃÃo pi adicional. Os valores de quantidade de material adsorvido (gama) e da taxa de recobrimento da superfÃcie (teta), calculados por desorÃÃo redutiva e impedÃncia eletroquÃmica, respectivamente, foram consistentes com as imagens de STM. Comparativamente aos resultados de desorÃÃo, os maiores valores de gama determinados por QCM foram atribuÃdos à presenÃa de molÃculas de Ãgua co-adsorvidas visto que foi observada uma relaÃÃo linear entre o excesso de massa e o momento de dipolo das espÃcies modificadoras. As curvas de desorÃÃo obtidas para pyS indicam a decomposiÃÃo da monocamada nÃo possibilitando, portanto, a determinaÃÃo dos parÃmetros termodinÃmicos e cinÃticos de adsorÃÃo. A correlaÃÃo com os resultados obtidos apÃs imersÃo do eletrodo de ouro em soluÃÃo de Na2S sugere que este processo està associado à quebra da ligaÃÃo C─S com formaÃÃo de uma camada de enxofre atÃmico e/ou oligomÃrico. As isotermas de adsorÃÃo obtidas para os processos de formaÃÃo das SAMs de Hpyt, TNA e iTNA, adequaram-se ao modelo de Langmuir permitindo a determinaÃÃo da variaÃÃo da energia livre de adsorÃÃo, ΔGads, como −35,9, −38,5 e −34,9 kJ mol−1, respectivamente. Estes valores sÃo indicativos de interaÃÃo forte sendo caracterÃsticos de processos de quimissorÃÃo. Para o modelo de Frumkin, os dados apresentaram melhores correlaÃÃes quando o parÃmetro de interaÃÃo (g) foi fixado em −0,45, −0,30 e −0,10, respectivamente, para as SAMs de Hpyt, TNA e iTNA indicando interaÃÃes repulsivas entre as molÃculas adjacentes. Os valores de pKa das SAMs de Hpyt (4,2), TNA (5,0 e 8,5) e iTNA (4,5 e 7,9) foi determinado por voltametria utilizando-se o Ãon complexo [Fe(CN)6]3−. Neste estudo, foram sugeridas modificaÃÃes, uma vez que o mÃtodo proposto na literatura dificulta a determinaÃÃo de mais de um valor de pKa como observado para as molÃculas de TNA e iTNA. As reaÃÃes de transferÃncia de elÃtrons (TE) das metaloproteÃnas citocromo c (cyt c) e mioglobina (Mb) foram estudadas utilizando-se as SAMs de Hpyt, TNA, iTNA, pyS e 1,4-dt. Para as SAMs de TNA e iTNA, o deslocamento positivo de 0,2V no valor do potencial de meia-onda do cyt c (pH~7,0) em relaÃÃo a forma nativa, foi atribuÃdo à densidade de carga positiva resultante da protonaÃÃo do grupo NH2 (pKa ~ 8,0). Resultados de QCM e SPR indicaram que hà a formaÃÃo de uma monocamada de cyt c sobre as SAMs estudadas. Esta monocamada, embora nÃo sendo redox ativa, permite o estudo da reaÃÃo de TE das molÃculas de cyt c em soluÃÃo sugerindo que este processo pode envolver os orbitais das molÃculas modificadoras. Para a metaloproteÃna Mb, utilizou-se uma SAM formada pelo aminoÃcido L-cisteÃna (cys), uma vez que nenhuma das SAMs estudadas acessou a reaÃÃo de TE. O processo redox foi observado em 0,086 V o que sugere a forma nativa. Os dados de QCM e SPR indicaram, tambÃm, a formaÃÃo de uma monocamada sobre a SAM de cys (Au/cys/Mb). Valores de â49,67 kJ mol−1 e −0,15 para ΔGads e g, respectivamente, foram calculados para a formaÃÃo da monocamada de Mb sobre a SAM de cys. O eletrodo Au/cys/Mb apresentou atividade catalÃtica em relaÃÃo a reaÃÃo de oxidaÃÃo do Ãcido ascÃrbico com uma diminuiÃÃo de 400 mV no sobrepotencial e uma reaÃÃo cineticamente controlada com uma constante de velocidade, kf, de ~2,0 x 10^4 L mol-1 s-1. / Electrochemical techniques, quartz crystal microbalance (QCM) and surface plÃsmons resonance (SPR) were used to study the formation of self-assembled monolayers (SAMs) of 1,4-ditiano (1,4-dt), 4-mercaptopyridine (pyS), 5-(4-piridinyl)-1,3,4-oxadiazole-2-thiol (Hpyt), thionicotinamide (TNA) and thioisonicotinamide (iTNA) as a result of the immersion of gold substrates into the respective solutions. STM (Scanning Tunneling Microscopy) images indicate the sulfur atom as the adsorption site of these molecules and a hexagonal conformation on surface. For the iTNA molecule, the images were not conclusive. In addition, the images indicated the existence of defects even after longer immersion times (24 h). Thermodynamic and kinetic aspects of the adsorption process were evaluated by reductive desorption in alkaline media and QCM. The reductive desorption potentials, Edr, were observed at −0.9, −0.8, and −0.5 V vs. Ag/AgCl for the desorption of iTNA, TNA and Hpyt, respectively. In comparison to 1,4-dt (−0.8 V) and pyS (−0.5 V) species, the Edr value of Hpyt indicates a sigma interaction whereas those of iTNA and TNA indicate an additional pi contribution. The values of the concentration of adsorbed material, gama, and fractional coverage (teta ~ 0.9), determined, respectively, by reductive desorption and impedance are consistent with the STM images. In comparison to the desorption data, the higher values of gama calculated by QCM were assigned to the presence of water molecules since a linear relation was observed between the dipole moment and the mass change calculated by QCM. The desorption curves acquired for the pyS SAM indicated the decomposition of the monolayer thus not allowing the determination of the thermodynamic and kinetic parameters of adsorption. In comparison with the results obtained for the electrode modified after immersion in Na2S solution, it was suggested that this process is associated to the cleavage of the C─S bond which results in the formation of an adlayer composed of atomic and/or oligomeric sulfur species. The adsorption isotherms for Hpyt, TNA and iTNA fitted the Langmuir model of adsorption allowing the determination of the free energy of adsorption, ΔGads, as −35.9, −38.5 and −34,9 kJ/mol, respectively. These values are indicative of strong interaction being typical of chemisorption. For the Frumkin model, the best correlation was found when the interaction parameter, g, was established as −0.45, −0.20 and −0.10 for Hpyt, TNA and iTNA, respectively, indicating repulsive interactions between the adjacent molecules. Cyclic voltammetry was used to determinate the pKa of the SAMs of Hpyt (4.2), TNA (5.0 and 8.5) and iTNA (4.5 and 7.9) by using [Fe(CN)6]3− as a probe molecule. For this study, some changes were suggested since in the method proposed in the literature the existence of more than one protonation site was not considered thus not allowing the determination of more than one pKa value as was observed for TNA and iTNA molecules. Electron transfer reactions (TE) of cytochrome c (cyt c) and myoglobin (Mb) metalloproteins were studied by using the SAMs of Hpyt, TNA, iTNA, pyS and 1,4-dt. For the SAMs formed with TNA and iTNA, the positive shift of 0.2V on the half-wave potential of cyt c in relation to that of the native protein, was assigned to the positive charge density on surface in consequence of the protonation of NH2 groups (pKa~8.0) since these measurements were carried out in physiological medium. QCM and SPR data indicated the formation of a monolayer of cyt c on the studied SAMs. This monolayer, although not being electroactive, allows the study of the TE reaction of the cyt c molecules in solution suggesting that this process involves the orbitals of the modifier molecules. For the Mb metalloprotein, a SAM of L-cysteine amino acid was used since none of the studied sulfur molecules was able to access the TE reaction. The redox process was observed at 0.086 V suggesting the native form of Mb. QCM and SPR data indicated, also, the formation of a monolayer of Mb on the cys SAM (Au/cys/Mb). Values of â49.67 kJ mol−1 and −0.15 for ΔGads and g, respectively, were calculated for the formation of the monolayer of Mb on the cys SAM. The electrode Au/cys/Mb presented catalytic activity toward the oxidation reaction of ascorbic acid presenting a decrease of 400 mV in the overpotential and a kinetic controlled with a rate constant, kf, of 2.0 x 104 L mol-1 s-1.

O uso de antioxidantes sintéticos para promover a conservação de alimentos tem sido alvo de questionamentos devido a possíveis efeitos tóxicos que estes podem causar. Desse modo, a utilização de substâncias naturais com poder antioxidante mostra-se uma alternativa bastante interessante. Além de conter compostos antioxidantes, muitas plantas também apresentam atividade antimicrobiana, o que tem sido alvo de interesse nas últimas décadas. A cor da carne bovina in natura é um de seus principais atributos, pois a maioria dos consumidores associa esta característica à qualidade do produto no ato da compra. A mioglobina, pigmento responsável pela cor vermelha da carne bovina, uma vez oxidada adquire coloração amarronzada e causa a rejeição da carne. Sua oxidação está ligada também ao processo de oxidação de lipídeos, que igualmente compromete a estabilidade deste produto durante a refrigeração. Desse modo, esta tese teve como objetivo caracterizar extratos aquosos de folhas de pitanga (Eugenia uniflora L.) e alecrim (Rosmarinus officinalis) e de sementes de guaraná (Paullinia cupana Kunth), e avaliar sua aplicação na estabilidade da carne bovina moída refrigerada. Foram realizados 3 experimentos: 1) Caracterização dos materiais vegetais (composição centesimal, teor de clorofila e carotenoides totais) e extratos aquosos (cor, pH, teor de sólidos solúveis, atividade antioxidante pelos métodos do captura do radical DPPH• e o do radical ABTS•+ e capacidade redutora); 2) Estudo da estabilidade da carne bovina moída com extratos vegetais por meio de análises de cor, pH, atividade de água, oxidação lipídica (TBARS), oxidação da mioglobina e análises microbiológicas; e 3) Análise sensorial de cor e odor da carne bovina moída com extratos. Conclui-se que: os extratos vegetais de plantas nativas brasileiras, guaraná e pitanga, apresentaram melhor capacidade antioxidante; os extratos de pitanga promoveram a inibição do crescimento das bactérias testadas; o extrato de pitanga promoveu melhor estabilidade na oxidação de lipídios, além de ter apresentado ação antimicrobiana para bactérias psicrotróficas na carne; a adição de extratos aquosos de pitanga e alecrim à carne bovina moída in natura refrigerada não interferiu na preferência dos atributos de cor e odor, e ainda, que o atributo odor parece estar associado a preferências pessoais. / The use of synthetic antioxidants to promote conservation of foods has been questioned due to possible toxic effects that such substances may cause, thereby the use of natural antioxidant sources seems to be a good alternative. Besides containing antioxidant compounds, many plants also have antimicrobial activity, which has been the subject of interest in recent decades. Color is one of the main attributes of fresh beef, since most consumers associate this characteristic to the quality of the product at the moment of purchase. Myoglobin, the pigment responsible for the red color of beef, once oxidized gets brownish and cause rejection of the product. This protein oxidation is also linked to the lipid oxidation process, which also impairs the stability of the product during cold storage. Thus, this thesis aimed at characterizing aqueous extracts Pitanga (Eugenia uniflora L.) and Rosemary (Rosmarinus officinalis) leaves, and Guarana (Paullinia cupana Kunth) seeds, evaluating their use on the stability of ground refrigerated beef. The experiments were carried out in three steps, namely: 1) Characterization of plant materials (chemical composition, chlorophyll content and carotenoids) and aqueous extracts (color, pH, soluble solids content, antioxidant activity by the methods of radical DPPH• and ABTS•+ scavenging and reducing capacity); 2) Study of the stability of ground beef with plant extracts through color analysis, pH, water activity, lipid oxidation (TBARS), myoglobin oxidation and microbiological analysis; and 3) Sensory analysis of color and odor of ground beef with extracts. As conclusion, the plant extracts of Brazilian native plants, Guarana and Pitanga, showed better antioxidant capacity; Pitanga extracts promoted growth inhibition of the tested bacteria; Pitanga extract provided better stability in the oxidation of lipids, and has presented antimicrobial activity for psychotropic bacteria in the ground beef; the addition of aqueous extracts of Pitanga and Rosemary to fresh ground beef during cold storage for 6 days did not affect the preference of color and odor attributes; odor attribute of beef seems to be associated with personal preferences.

To mimic the properties of haemoglobin (Hb) and myoglobin (Mb) it has been found necessary to synthesise a five-coordinate ferrous porphyrin with a protecting structure over the sixth coordination site at iron. This thesis describes approaches to the synthesis of such a compound where the protecting structure is the "capped" moiety and where the base which occupies the fifth coordination site is held in position by two covalent linkages to the porphyrin. The preparation of the target molecule involved the synthesis of a new "capped" porphyrin and a series of difuncticnalised pyridines. These were then successfully coupled under high dilution conditions to give the "capped/strapped" porphyrin. Metallation and reduction completed the synthesis. The behaviour of the ferrous complex in the presence of dioxygen was investigated. High stability toward irreversible oxidation was found. In the presence of oxygen the ferrous complex had a half-life in excess of 40h at room temperature.

Thesis (M.S.)--University of Pittsburgh, Department of Chemistry, 2007. / Thesis advisor: Sanford A. Asher. Also available as an electronic book in PDF on the University of Pittsburgh Library Web site. Bibliography: p. 37-41.

Typescript. Includes vita and abstract. Bibliography: Includes bibliographical references (leaves 95-99). Description: xii, 99 leaves : ill. ; 29 cm. / Blood oxygen carrying capacity, myoglobin levels and LDH isozyme compositions in the heart, gastrocnemius and pectoralis muscles were determined in Common Murre adults and during maturation of the chick at sea. Oxygen stores in the chick (hemoglobin, hematocrit, muscle myoglobin) increased significantly with growth. High levels of the aerobic isozyme, LDH 1, were maintained throughout maturation in the heart. All five LDH isozymes were maintained at similar levels in the gastrocnemius muscle. The pectoralis showed an increase in LDH 1, 2, 3, and 4, yet retained relatively high levels of LDH 5 throughout maturation. Upon leaving the nesting colony, metabolic capacities in the heart and gastrocnemius of the chick are similar to those of adults. The chick pectoralis tissue, however, gains aerobic capacities with maturation which is concomitant with the needed capacity for aerial and aquatic flight upon fledging.

Cristais de mioglobina tipo A foram dopados por processo de difusão com o marcador 2, 2, 6, 6 - tetrametil-l-oxil (TEMPO). Observa-se a existência de uma espécie de marcador isotrópica e outra anisotrópica, que exibe uma simetria axial com A// = 23,4 G, A&#8869 = 20, 6 G e g = 2,0056. São estimados os tempos de correlação rotacional &#964// = 7,2.10-9s e &#964&#8869 = 4,8.10-9s. Uma análise do grau de hidrofobicidade dos resíduos, situados na parte interna da molécula, sugere como um possível sitio de localização para o TEMPO o bolso formado na região da tirosina 103 - hélice H e 151 - terminal 3HC. Este bolso tem tamanho suficiente para abrigar o radical e posição coerente com a heme, o que não acontece com outros sítios. Observa-se uma mudança conformacional da proteína, induzida pela temperatura na região 20-30&#176. Esta pode ser atribuída a um movimento da hélice H. Este resultado somado ao de outros autores indica uma mudança conformacional de grande extensão na molécula. / Type A myoglobin single crystals were doped with the 2, 2, 6, 6 -tetramethyl - 1 - oxyl (TEMPO) spin label by a diffusion process. We observed one isotropic spin label type, and another anisotropic type which shows an axial symmetry with A// = 23,4 G, A&#8869 = 20, 6 G and g = 2,0056. The rotational correlation times are estimated to be a &#964// = 7,2.10-9s and &#964&#8869 = 4,8.10-9s. A quantitative analysis on the hydrophobic nature of the residues situated inside the molecule suggests, as a possible site for the TEMPO, the pocket formed in the region of tyrosine 103-helix H and tyrpsine 151 - terminal 3HC. This pocket is of sufficient size to contain the radical and is positioned in such fashion as to be a compatible with the heme group, this not holding for other sites. A temperature induced conformational change in the protein is observed in the region 20-30&#176, which may be ascribed to a shift of the H helix. This fact, together with the finds of other authors, seems to indicate a generalized temperature induced conformational alteration in the molecule.

Of central importance to the study of heme proteins are the effects imposed by axial ligand(s) on the heme structure and, therefore, on the overall activity of the protein. In this study, we confirm and extend the spectroscopic characterization of a mutated sperm whale myoglobin in which the proximal Histidine is replaced with a Tyrosine residue (MbH93Y). The MbH93Y, as well as wild-type sperm whale myoglobin and horse erythrocyte catalase (HEC), was purified and characterized by optical absorption and x-ray absorption (XAS) spectroscopies. Optical absorption spectra of HEC and the metmyoglobin, cyanometmyoglobin, reduced, oxy, and carbon-monoxy forms of both sperm whale myoglobin (SWMb) and MbH93Y were identical to previously reported values within the respective errors:. Extended x-ray absorption fine structure (EXAFS) studies revealed that the proximal bond length in MbH93Y was 2.13 ± 0.03 A, compared to 2.14 ± 0.02 A for sperm whale metmyoglobin and 1.90 ± 0.02 A for catalase. Additionally, the sixth coordination site normally occupied in wild type sperm whale metmyoglobin and in catalase at low temperatures was vacant in MbH93Y, a result corroborated by the optical absorption spectra and cyanogen bromide modification of the distal histidine. Measurements were also made on the cyanide complexes of the three proteins as well, among which, (i) the average iron-to-pyrrole nitrogen bond distance for MbH93Y-CN was 1.96 ± 0.015 A compared to 2.00 ± 0.015 A for WT SWMb-CN and HEC-CN and (ii) the proximal bond length in MbH93Y-CN was 2.07 ± 0.02 A, while that of WT SWMb-CN was 2.10 ± 0.02 A and that of HEC-CN was found to be 2.12 ± 0.02 A. Further, upon exposure to 2-molar equivalents of hydrogen peroxide, sperm whale myoglobin formed a Compound II -like spectrum, while the Soret absorbance of MbH93Y was rapidly, significantly, and irreversibly decreased. Furthermore, the dissociation constants for CN- binding to MbH93Y were found to be, on average, approximately three orders of magnitude higher than those of wild-type sperm whale myoglobin and are consistent with the many-fold higher cyanide binding kinetics for wild type, relative to the mutant protein. Finally, the PK. of the mutant was found to be more than three orders of magnitude higher than that of the native protein. Explanations focusing on probable electronic effects of the phenolate oxygen atom in the sperm whale myoglobin pocket are discussed.

No description available.

While experiments provide valuable information about biological molecules, current technology cannot yet monitor atomic fluctuations at relevant time scales. Theoretical computational simulations are able to model the appropriate interactions at atomic resolution. Computational techniques have become widely used for identifying interactions in biological systems. Such methods have proven quite accurate in their ability to reproduce experimental data and also in screening and predicting pertinent activities. Molecular modeling employs theoretical and computational techniques to elucidate biologically relevant information from macromolecular structures. Three biological systems, the nucleosome core particle, myoglobin and glycosyl hydrolase family 1 beta-glucosidases will be examined with molecular modeling methods. Results of our analyses provide information about DNA flexibility and packaging, internal migration of ligands in a small protein, and substrate specificity of an enzyme system. / Ph. D.

Sequence analysis of the entire 3.5 kb <i>Hind</i>III genomic DNA fragment previously isolated from <i>Nostoc commune</i> UTEX 584 (Defrancesco and Potts 1988), determined the exact locations of the <i>nifU, nifH</i>, and <i>nifD</i> genes and identified two potential stem loop structures, a direct repeat, and an ORF that codes for a protein with a predicted amino acid sequence similar to that of myoglobin from <i>Paramecium caudatum</i>. The <i>N. commune</i> UTEX 584 myoglobin-like protein has a predicted length of 118 amino acids and molecular mass of 12,906 Da. A PCR copy of the gene (<i>glbN</i>) was cloned for overexpression of the protein. The recombinant protein was purified and used for spectral analysis and for the production of polyclonal antisera. Treatment of the recombinant protein with dithionite and CO resulted in spectral shifts characteristic of hemoproteins that bind oxygen. While some of the spectral characteristics are unique to the protein, in general the spectra were more like those of globins than cytochromes. Based on these characteristics and the sequence similarity to the P. caudatum mnyoglobin, we proposed the name cyanoglobin, with the gene designation glbN and the protein designation GlbN. Western analysis of GlbN expression was performed on N. commune UTEX 584 and two species of Anabaena (Anabaena sp. PCC 7120 and Anabaena variabilis). In N. commune UTEX 584 a protein with a molecular mass similar to that predicted for GlbN was detected. This protein was produced in increased amounts under the same growth conditions that resulted in increased production of nitrogenase reductase (the nifH gene product). No proteins of similar size to GlbN were detected in Anabaena sp. PCC 7120 or A. variabilis. A possible function of GlbN may be for oxygen storage, transport, or protection of the nitrogenase system. These functions as well as those of the direct repeat and the potential stem loop structures and their relationship to nitrogen fixation or other physiological processes in N. commune UTEX 584 require further analysis. / Ph. D.