O presente trabalho estudou comparativamente, do ponto de vista fundamental, a reação de eletro-oxidação de monóxido de carbono (CO) em meio ácido, sobre Pt75Sn25/C, Pt65Ru35/C e Pt/C através da Espectroscopia de Impedância Eletroquímica. Os materiais foram preparados por redução com ácido fórmico e caracterizados fisicamente por EDX e DRX de alta intensidade e eletroquimicamente por voltametria. Previamente aos estudos de Impedância, foram realizados estudos potenciodinâmicos da reação de eletro-oxidação de CO adsorvido (?Stripping de CO?) e a oxidação de CO em uma solução saturada de CO. Para os materiais Pt65Ru35/C e Pt/C, estes estudos mostraram que há um deslocamento de potencial do inicio da oxidação para valores mais positivos quando CO está presente em solução se comparado a oxidação (stripping) de CO, devido a competição de sítios de adsorção entre moléculas de CO e H2O, responsáveis pela reação. Por outro lado, no material bimetálico Pt75Sn25/C a presença de CO em solução não influenciou de maneira significativa o potencial de inicio da oxidação, confirmando a ausência de adsorção competitiva neste material. A curva de polarização em estado estacionário revelou que, dentre os 3 materiais estudados, o material bimetálico Pt75Sn25/C apresentou a maior atividade eletrocatalítica, isto é, maiores densidades de correntes em menores sobrepotenciais. Este comportamento foi, em grande parte, esclarecido através dos experimentos de Espectroscopia de Impedância Eletroquímica. Com a Espectroscopia de Impedância Eletroquímica foi verificada a formação de espécies oxigenadas em Pt/C e em Pt65Ru35/C no intervalo de freqüências estudado, enquanto que em Pt75Sn25/C os diagramas de impedância revelaram um comportamento predominantemente capacitivo, indicando a ausência de reações de transferência de carga devido à oxidação da H2O para formar hidróxidos/óxidos na superfície do material. Também foi demonstrado que os processos relacionados a reação entre COads e espécies oxigenadas superficiais são mais rápidos em Pt75Sn25/C do que em Pt/C e Pt65Ru35/C, como ficou evidente no diagrama de Bode do ângulo de fase em função da freqüência. Mais especificamente, a menor resistência de transferência de carga para a reação em Pt75Sn25/C aparece em freqüências mais altas provavelmente devido à reação ocorrer com espécies oxigenadas já presentes na fase SnO2 presente no material. Por outro lado, os processos de adsorção são mais rápidos devido a menor energia de adsorção de CO sobre Pt, de acordo com os resultados encontrados por cálculos teóricos de DFT. / In this work, kinetic aspects of CO electro-oxidation on Pt/C, Pt75Sn25/C and Pt65Ru35/C prepared by chemical reduction with formic acid were studied by Electrochemical Impedance Spectroscopy (EIS). The bulk composition of the asprepared PtSn/C and PtRu/C bimetallic materials, analyzed by EDX, was 77:23 and 64:36, respectively. Using high intensity XDR measurements the bulk structure and phase determinations could be established. The analysis of the XRD profiles of Pt75Sn25/C revealed partial alloy formation and the presence of a SnO2 phase. For Pt65Ru35/C, no alloy formation was verified. Potentiodynamic oxidation of CO in a CO-saturated solution compared with CO stripping voltammetry pointed out the presence of competitive adsorption between CO and oxygen containing species on the surface of Pt/C and Pt65Ru35/C while for Pt75Sn25/C no competition for surface sites was verified. Impedance measurements were conducted in two different conditions: i) in the absence of CO in solution and ii) in a CO saturated solution. Provided by an equivalent circuit the charge transfer resistance (Rct), was obtained for the studied materials. The mean double layer capacitance (Cdl) was also estimated from circuit parameters and revealed its dependence on the carbon monoxide surface coverage (_CO). Furthermore, the relation between the _CO and the charge transfer resistance for the reaction is discussed. Using EIS it was demonstrated that the Rct for the carbon monoxide electro-oxidation reaction on Pt75Sn25/C is much lower than on Pt/C and Pt65Ru35/C, which was related to the presence of oxygen-containing species already present in the SnO2 phase as well as to the faster adsorption processes on this material compared to Pt/C and Pt65Ru35/C.

The introduction of prostate-specific antigen (PSA) testing about 3 decades ago led to the possibility of early detection of prostate cancer (PCa). Although PSA testing reduced the mortality rate, it is also associated with high risk of over diagnosis in patients with and without PCa. Despite the current drawbacks, it would be a challenge to replace PSA testing entirely. Instead, there is a need to develop parallel testing of other potential biomarkers that can complement the results from PSA tests. To address alternative biomarker sensing, this thesis highlights on the development of oligonucleotide-based biosensors for the detection of different biomarkers of PCa. Using PSA as a gold standard, the first study of this dissertation investigates the use of DNA aptamers to detect PSA using electrochemical impedance spectroscopy (EIS). The study compares 6-mercapto 1-hexanol chemistry with sulfo-betaine chemistry for the development of PSA aptasensor in terms of performance and selectivity. The second study focuses on glycoprofiling in order to complement PSA quantification as an additional information for reliable PCa diagnosis. This strategy was developed in a microfluidic channel with an optical read out using chemiluminescence. This study addresses one of the major problems of cross-reactivity with lectins in glycoprofiling, which can be solved using DNA aptamers. A third study concentrates on the development of an aptasensor for Alpha-Methylacyl-CoA Racemase (AMACR). AMACR has been reported for its high specificity and sensitivity to PCa. For the fabrication of the biosensor, a new strategy using polyethylene glycol was developed by electrochemical grafting it to a polypyrrole film. Since PCa diagnosis can be improved by looking at different biomarkers, an electrochemical platform for miRNA/DNA detection using a gold nanoparticle amplification strategy was also investigated. The sensor was fabricated using peptide nucleic acids (PNA) probes on gold electrodes. The study presents non-Faradaic EIS and amperometric techniques in order to exploit the inherent charges of nucleic acids. In conclusion, this thesis wants to serve as a potential orientation for overcoming the shortcomings of the current PCa testing and contribute towards the development of oligonucleotide-based biosensors for PCa biomarker detection and hopefully enhance the diagnosis and prognosis of PCa.

O objetivo deste trabalho foi caracterizar por meio de técnicas eletroquímicas e físicoquímicas o comportamento das camadas de silano aplicadas diretamente sobre as chapas de aço-carbono ABNT 1008 pela técnica de imersão, como uma proteção contra a corrosão. O estudo compreendeu a avaliação do comportamento das monocamadas de BTSE [Bis-1,2-(trietoxisilil)etano], VS (Viniltrietoxisilano) e BTSPA [Bis-(y-trimetoxisililpropil)amina], variando as condições de cura (tempo e temperatura) e também da dupla camada de silano. A dupla camada consistiu na combinação de BTSE como primeira camada e uma segunda camada de VS ou BTSPA. A espectroscopia de impedância eletroquímica (EIS) em solução de NaCl 0,1 M possibilitou detectarem a resistência à corrosão das camadas de silano, revelando que a sua eficiência aumenta com o aumento da temperatura e do tempo de cura e também que uma dupla camada apresenta um efeito protetor mais eficiente que o das monocamadas. Assim, a dupla camada de BTSE + BTSPA forneceu o melhor resultado, comprovando que confere melhor proteção ao aço-carbono. Com a medida ângulo de contato foi possível caracterizar a hidrofobicidade da superfície metálica revestida com o filme de silano, constatando-se que as camadas de BTSE, VS e BTSPA, e as duplas camadas curadas em altas temperaturas são mais hidrofóbicas que o aço-carbono. As curvas de polarização confirmaram os resultados obtidos por EIS, mostrando que a densidade de corrente de corrosão (icorr) diminui com o tempo e a temperatura de cura. A espectroscopia no infravermelho (IR) permitiu acompanhar a extensão da reação de polimerização dos silanos. A microscopia eletrônica de varredura (SEM) e as análises por espectroscopia de energia dispersiva de Raios-X (EDX) evidenciaram o efeito da cura na morfologia e topografia da superfície. Logo, conclui-se que os filmes à base de silanos como pré-tratamentos de aço são eficientes contra a corrosão. / The aim of this work is to characterize by means of electrochemical and physicochemical techniques the behavior of the silane layers applied directly on steel plates as a protection against corrosion. The silane film was obtained by the dip coat technique. This study present the evaluation of the behavior of monolayers of BTSE [Bis-1,2- (triethoxysilyl)ethane, BTSPA [Bis-(y-trimethoxysilylpropyl)amino] and VS (Vinyltriethoxysilane), varying the curing conditions (time and temperature) and also with a double silane layer, consisting of a combination of BTSE as first layer and a VS or BTSPA second layer. The electrochemical impedance spectroscopy (EIS) in a NaCl 0.1 M solution allowed the corrosion resistance assessment of the silane layers, showing that their protection efficiency increase for higher curing temperatures and curing times. Double layers were always more protective than monolayers. The contact angle measurements allowed to characterize the hydrophobicity of the metallic surface coated with the silane film, showing that the layers of BTSE, VS and BTSPA cured at higher temperatures are more hydrophobic and, therefore, more protective. The polarization curves confirmed the results obtained by EIS, showing that the corrosion current densities (icorr) decreased when the curing time and temperature were increased. The infrared spectroscopy (IR) showed the extension of the polymerization reaction of the silane layers. The SEM images and the EDX analyses evidenced the effect of the cure on the morphology and topography of the surface. Thus, the results lead to conclude that silane based films are good alternatives as pre-treatments for steel against corrosion.

Atualmente a maior parte da energia consumida no mundo provém de fontes como carvão, petróleo e gás natural. Nas últimas décadas, o aumento na demanda por petróleo e gás natural teve como resultado um grande aumento no uso de tubos de aço para transportar estes produtos por longas distâncias. Os aços de alta resistência e baixa liga (ARBL) produzidos de acordo com a norma API 5L são atrativos para estas aplicações por apresentarem boas propriedades mecânicas e soldabilidade aliadas a baixos custos. Entretanto, nestas aplicações os materiais são expostos a meios corrosivos com altos teores de H2S, tornando-os susceptíveis aos danos provocados pelo hidrogênio. Dentre estes um dos mais importantes é o trincamento induzido pelo hidrogênio (hydrogen induced cracking - HIC). Neste trabalho a resistência à corrosão e ao HIC de dois aços API 5L X65, cujas composições diferem principalmente com relação aos teores de Mn e de Nb, e de um aço API 5L X80 comercial foi investigada na solução A da norma NACE TM0284-2011. A avaliação da resistência à corrosão foi realizada em solução naturalmente aerada ou desaerada sem e com saturação com H2S por meio de ensaios de potencial de circuito aberto, curvas de polarização potenciodinâmica e espectroscopia de impedância eletroquímica. Análises microestruturais por microscopia óptica (MO) e eletrônica de varredura (MEV) foram realizadas para correlacionar a microestrutura com os dois parâmetros investigados. As análises por MO e MEV mostraram que os dois aços API 5L X65 possuem inclusões uniformemente distribuídas em uma matriz ferrítica com ilhas de perlita degenerada e microconstituintes M/A (martensita/ austenita) nos contornos de grão da ferrita. Por sua vez, o aço API 5L X80 apresentou matriz ferrítica com microconstituintes M/A, e inclusões de formas arredondadas e irregulares em maior número e distribuídas de forma irregular. Os resultados dos ensaios eletroquímicos mostraram que, para os três aços, a resistência à corrosão diminui sensivelmente na presença de H2S. Por outro lado, os ensaios de impedância evidenciaram aumento da resistência à corrosão com o tempo de imersão em todos os meios, provavelmente associado à formação de produtos de corrosão insolúveis e que precipitam sobre a superfície dos aços. Todos os ensaios mostraram que os dois aços API 5L X65 são mais resistentes à corrosão que o aço API 5L X80. Os ensaios de HIC mostraram que os dois aços API 5L X65 não são suscetíveis a este tipo de falha, contrariamente ao aço API 5L X80. Neste último houve formação de trincas da parte central e inferior (interna) da amostra fornecida em forma de tubo. A análise do caminho de propagação da trinca mostrou a presença de inclusões ricas em Mn e S, indicando que elas têm um papel relevante no mecanismo de trincamento. Os resultados de todos os ensaios de corrosão mostraram que o aço experimental API 5L X65 produzido pela CBMM com baixos teores de Mn e altos teores de Nb apresentou resistência à corrosão ligeiramente superior ao aço API 5L X65 comercial, indicando ser esta composição promissora para aplicações em meios sour. / Currently most of the energy consumed in the world comes from sources such as coal, oil and natural gas. In recent decades the increase in demand for oil and natural gas has resulted in a large increase in the use of steel tubes to transport these products over long distances. High strength low alloy (HSLA) steels produced according to the API 5L standard are attractive for these applications because they have good mechanical properties and weldability combined with low costs. However, in these applications the materials are exposed to corrosive media with high levels of H2S, making them susceptible to damage caused by hydrogen. Among them, one of the most important is hydrogen-induced cracking (HIC). In this work the resistance to corrosion and HIC of two API 5L X65 steels, whose compositions differ mainly with respect to their Mn and Nb contents, and a commercial API 5L X80 steel were investigated in solution A of the NACE standard TM0284-2011. The evaluation of the corrosion resistance was carried out in naturally aerated or in deaerated solution without and with saturation with H2S by means of open circuit potential tests, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). Microstructural analysis by optical microscopy (OM) and scanning electron microscopy (SEM) were performed to correlate the microstructure with the two investigated parameters. OM and SEM analyzes showed that the two API 5L X65 steels have inclusions evenly distributed in a ferritic matrix with degenerated perlite islands and M/A (martensite/austenite) microconstituents at the perlite grain boundaries. In turn, the API 5L X80 steel presented a ferritic matrix with M/A microconstituents and round-shaped and irregular-shaped inclusions in greater number and irregularly distributed. The results of the electrochemical tests showed that, for all three steels, the corrosion resistance decreases significantly in the presence of H2S. On the other hand, the EIS tests showed an increase in corrosion resistance with immersion time in all media, which is probably due to the formation of insoluble corrosion products that precipitate on the steels surfaces. All assays showed that the two API 5L X65 steels are more resistant to corrosion than the API 5L X80 steel. The HIC assays showed that the two API 5L X65 steels are not susceptible to this type of failure, unlike the API 5L X80 steel. In the latter there was cracks formation in the central and lower (inner) part of the sample supplied as a tube. The analysis of the crack propagation path showed the presence of Mn and S-rich inclusions, indicating that they play a key role in the cracking mechanism. The results of all corrosion tests showed that the experimental steel API 5L X65 produced by CBMM with low Mn contents and high levels of Nb exhibited slightly higher corrosion resistance than the API 5L X65 commercial steel, indicating that this composition is promising for sour media applications.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Os molibdatos tÃm sido introduzido como possÃvel substituinte dos cromatos, como pigmento anticorrosivo, devido a suas propriedades de inibiÃÃo, sua baixa toxicidade e a possibilidade de formaÃÃo de um filme de conversÃo em superfÃcies metÃlicas semelhante à camada de conversÃo formada pelos cromatos. Neste trabalho, foram formuladas tintas com os seguintes pigmentos: Cromato de zinco, fosfato de zinco, fosfato Molibdato de zinco e fosfato Molibdato de zinco-cÃlcio. Foi formulado ainda, uma tinta sem pigmentos (verniz) e outra somente com a carga. O trabalho consiste em um estudo comparativo do desempenho anticorrosivo das pinturas formuladas, por testes cÃclicos em laboratÃrio (cÃmara de nÃvoa salina) e imersÃo total. As principais tÃcnicas empregadas foram: monitoramento do potencial de circuito aberto, curvas de polarizaÃÃo e impedÃncia eletroquÃmica. De um modo geral, o cromato de zinco apresentou melhores resultados. PorÃm, em certas condiÃÃes de trabalho, os pigmentos nÃo tÃxicos apresentaram resultados satisfatÃrios. / Os molibdatos tÃm sido introduzido como possÃvel substituinte dos cromatos, como pigmento anticorrosivo, devido a suas propriedades de inibiÃÃo, sua baixa toxicidade e a possibilidade de formaÃÃo de um filme de conversÃo em superfÃcies metÃlicas semelhante à camada de conversÃo formada pelos cromatos. Neste trabalho, foram formuladas tintas com os seguintes pigmentos: Cromato de zinco, fosfato de zinco, fosfato Molibdato de zinco e fosfato Molibdato de zinco-cÃlcio. Foi formulado ainda, uma tinta sem pigmentos (verniz) e outra somente com a carga. O trabalho consiste em um estudo comparativo do desempenho anticorrosivo das pinturas formuladas, por testes cÃclicos em laboratÃrio (cÃmara de nÃvoa salina) e imersÃo total. As principais tÃcnicas empregadas foram: monitoramento do potencial de circuito aberto, curvas de polarizaÃÃo e impedÃncia eletroquÃmica. De um modo geral, o cromato de zinco apresentou melhores resultados. PorÃm, em certas condiÃÃes de trabalho, os pigmentos nÃo tÃxicos apresentaram resultados satisfatÃrios.

<p>The focus of this study is to synthesize a novel hinged polymer actuator. The linking molecule (hinge) is phenazine with interconnected dipyrrole units.</p>

<p class=MsoNormal style='text-align:justify;text-indent:.5in;line-height:150%'><span style='mso-bidi-font-weight:bold'>M-DNA is a novel complex formed between DNA and transition metal ions under alkaline conditions.<span style='mso-spacerun:yes'>  </span>The unique properties of M-DNA were manipulated in order to rationally place metal ions at specific regions within a double-stranded DNA helix.<span style='mso-spacerun:yes'>   </span>Investigations using thermal denaturation profiles and the ethidium fluorescence assay illustrate that the pH at which M-DNA formation occurs is influenced heavily by the DNA sequence and base composition.<span style='mso-spacerun:yes'>  </span>For instance, DNA with a sequence consisting of poly[d(TG)d(CA)] is completely converted to M-DNA at pH 7.9 while DNA consisting entirely of poly[d(AT)] remains in the B-DNA conformation until a pH of 8.6 is reached.<span style='mso-spacerun:yes'>  </span>The pH at which M-DNA formation occurs is further decreased by the incorporation of 4-thiothymine (s⁴T).<span style='mso-spacerun:yes'>  </span>DNA oligomers with a mixed sequence composed of </span>half d(AT) and the other half d(TG)d(CA)<span style='mso-bidi-font-weight: bold'> showed that only 50% of the DNA is able to incorporate Zn²⁺ ions at pH 7.9.<span style='mso-spacerun:yes'>  </span>This suggests that only regions corresponding to the tracts of <span class=GramE>d(</span>TG)d(CA) are being transformed.<span style='mso-spacerun:yes'>   </span><o:p></o:p></span></p> <p class=MsoNormal style='text-align:justify;text-indent:.5in;line-height:150%'><span style='mso-fareast-language:ZH-CN'>Duplex DNA monolayers were self-assembled on gold through <span class=GramE>a</span> Au-S linkage and both B- and M-DNA conformations were studied using X-ray photoelectron spectroscopy (XPS) in order to better elucidate the location of the metal ions.<span style='mso-spacerun:yes'>  </span>The film thickness, density, elemental composition and ratios for samples were analyzed and compared.<span style='mso-spacerun:yes'>  </span>The DNA surface coverage, calculated from both XPS and electrochemical measurements, was <span class=GramE>approximately 1.2 x 10¹³molecules/cm²</span>for B-DNA.<span style='mso-spacerun:yes'>  </span>All samples showed distinct peaks for C 1s, O 1s, N 1s, P 2p and S 2p as expected for a thiol-linked DNA.<span style='mso-spacerun:yes'>  </span></span><span style='mso-bidi-font-weight: bold'>On addition of Zn²⁺ to form M-DNA the C 1s, P 2p and S 2p showed only small changes </span><span style='mso-fareast-language:ZH-CN'>while both the N 1s and O 1s spectra changed considerably.<span style='mso-spacerun:yes'>  </span>This result is consistent with Zn²⁺ interacting with oxygen on the phosphate backbone as well as replacing the imino protons of thymine (T) and guanine (G) in M-DNA.<span style='mso-spacerun:yes'>   </span>Analysis of the Zn 2p spectra also demonstrated that the concentration of Zn²⁺ present under M-DNA conditions is consistent with Zn²⁺ binding to both the phosphate backbone as well as replacing the imino protons of T or G in each base pair.<span style='mso-spacerun:yes'>  </span>After the M-DNA monolayer is washed with a buffer containing only Na⁺ the Zn²⁺ bound to the phosphate backbone is removed while the Zn²⁺ bound internally still remains. </span><span style='mso-bidi-font-weight:bold'>Variable angle x-ray photoelectron spectroscopy (VAXPS) was also used to examine monolayers consisting of mixed sequence oligomers.<span style='mso-spacerun:yes'>  </span>Preliminary results suggest that under M-DNA conditions, the zinc to phosphate ratio changes relative to the position of the <span class=GramE>d(</span>TG)d(CA) tract being at the top or bottom of the monolayer.<span style='mso-spacerun:yes'>  </span><span style='mso-spacerun:yes'> </span><o:p></o:p></span></p> <p class=MsoNormal style='text-align:justify;text-indent:.5in;line-height:150%'><span style='mso-bidi-font-weight:bold'>Electrochemistry was also used to investigate the properties of M-DNA monolayers on gold and examine how the localization of metal ions affects the resistance through the DNA monolayer.<span style='mso-spacerun:yes'>  </span>T</span>he effectiveness of using the IrCl₆^2-/3-redox couple to investigate DNA monolayers and the potential advantages of this system over the standard Fe(CN)₆^3-/4- redox couple are demonstrated.<span style='mso-spacerun:yes'>  </span>B-DNA monolayers were converted to M-DNA by incubation in buffer containing 0.4 mM Zn²⁺ at pH 8.6 and studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) with IrCl₆^2-/3-.<span style='mso-spacerun:yes'>  </span>^{<span style='mso-spacerun:yes'> </span>}Compared to B-DNA, M-DNA showed significant changes in CV, EIS and CA spectra.<span style='mso-spacerun:yes'>  </span>However, only small changes were observed when the monolayers were incubated in Mg²⁺at pH 8.6 or in Zn²⁺ at pH 6.0.<span style='mso-spacerun:yes'>  </span>The heterogeneous electron-transfer rate (<i style='mso-bidi-font-style:normal'>k</i>_ET) between the redox probe and the surface of a bare gold electrode was determined to be 5.7 x 10^-3 cm/s.<span style='mso-spacerun:yes'>  </span>For a B-DNA modified electrode, the <i style='mso-bidi-font-style:normal'>k</i>_ET through the monolayer was too slow to be measured.<span style='mso-spacerun:yes'>  </span>However, under M-DNA conditions, a <i style='mso-bidi-font-style:normal'>k</i>_ET of 1.5 x 10^-3 cm/s was reached.<span style='mso-spacerun:yes'>  </span>As well, the percent change in resistance to charge transfer (R_CT), measured by EIS, <span class=GramE>was</span> used to illustrate the dependence of M-DNA formation on pH.<span style='mso-spacerun:yes'>  </span>This result is consistent with Zn²⁺ ions replacing the imino protons on thymine and guanine residues.<span style='mso-spacerun:yes'>  </span>Also, at low pH values, the percent change in R_CT seems to be greater for <span class=GramE><span style='mso-bidi-font-weight:bold'>d(</span></span><span style='mso-bidi-font-weight: bold'>TG)₁₅d(CA)₁₅ compared to oligomers with mixed d(AT) and d(TG)d(CA) tracts.<span style='mso-spacerun:yes'>  </span></span>The IrCl₆^2-/3-redox couple was also effective in differentiating between single-stranded and double-stranded DNA during dehybridization and rehybridization experiments.<span style='mso-spacerun:yes'>  </span><span style='mso-bidi-font-weight:bold'><o:p></o:p></span></p>

<p class=MsoNormal style='text-align:justify;text-indent:.5in;line-height:150%'><span style='mso-bidi-font-weight:bold'>M-DNA is a novel complex formed between DNA and transition metal ions under alkaline conditions.<span style='mso-spacerun:yes'>  </span>The unique properties of M-DNA were manipulated in order to rationally place metal ions at specific regions within a double-stranded DNA helix.<span style='mso-spacerun:yes'>   </span>Investigations using thermal denaturation profiles and the ethidium fluorescence assay illustrate that the pH at which M-DNA formation occurs is influenced heavily by the DNA sequence and base composition.<span style='mso-spacerun:yes'>  </span>For instance, DNA with a sequence consisting of poly[d(TG)d(CA)] is completely converted to M-DNA at pH 7.9 while DNA consisting entirely of poly[d(AT)] remains in the B-DNA conformation until a pH of 8.6 is reached.<span style='mso-spacerun:yes'>  </span>The pH at which M-DNA formation occurs is further decreased by the incorporation of 4-thiothymine (s⁴T).<span style='mso-spacerun:yes'>  </span>DNA oligomers with a mixed sequence composed of </span>half d(AT) and the other half d(TG)d(CA)<span style='mso-bidi-font-weight: bold'> showed that only 50% of the DNA is able to incorporate Zn²⁺ ions at pH 7.9.<span style='mso-spacerun:yes'>  </span>This suggests that only regions corresponding to the tracts of <span class=GramE>d(</span>TG)d(CA) are being transformed.<span style='mso-spacerun:yes'>   </span><o:p></o:p></span></p> <p class=MsoNormal style='text-align:justify;text-indent:.5in;line-height:150%'><span style='mso-fareast-language:ZH-CN'>Duplex DNA monolayers were self-assembled on gold through <span class=GramE>a</span> Au-S linkage and both B- and M-DNA conformations were studied using X-ray photoelectron spectroscopy (XPS) in order to better elucidate the location of the metal ions.<span style='mso-spacerun:yes'>  </span>The film thickness, density, elemental composition and ratios for samples were analyzed and compared.<span style='mso-spacerun:yes'>  </span>The DNA surface coverage, calculated from both XPS and electrochemical measurements, was <span class=GramE>approximately 1.2 x 10¹³molecules/cm²</span>for B-DNA.<span style='mso-spacerun:yes'>  </span>All samples showed distinct peaks for C 1s, O 1s, N 1s, P 2p and S 2p as expected for a thiol-linked DNA.<span style='mso-spacerun:yes'>  </span></span><span style='mso-bidi-font-weight: bold'>On addition of Zn²⁺ to form M-DNA the C 1s, P 2p and S 2p showed only small changes </span><span style='mso-fareast-language:ZH-CN'>while both the N 1s and O 1s spectra changed considerably.<span style='mso-spacerun:yes'>  </span>This result is consistent with Zn²⁺ interacting with oxygen on the phosphate backbone as well as replacing the imino protons of thymine (T) and guanine (G) in M-DNA.<span style='mso-spacerun:yes'>   </span>Analysis of the Zn 2p spectra also demonstrated that the concentration of Zn²⁺ present under M-DNA conditions is consistent with Zn²⁺ binding to both the phosphate backbone as well as replacing the imino protons of T or G in each base pair.<span style='mso-spacerun:yes'>  </span>After the M-DNA monolayer is washed with a buffer containing only Na⁺ the Zn²⁺ bound to the phosphate backbone is removed while the Zn²⁺ bound internally still remains. </span><span style='mso-bidi-font-weight:bold'>Variable angle x-ray photoelectron spectroscopy (VAXPS) was also used to examine monolayers consisting of mixed sequence oligomers.<span style='mso-spacerun:yes'>  </span>Preliminary results suggest that under M-DNA conditions, the zinc to phosphate ratio changes relative to the position of the <span class=GramE>d(</span>TG)d(CA) tract being at the top or bottom of the monolayer.<span style='mso-spacerun:yes'>  </span><span style='mso-spacerun:yes'> </span><o:p></o:p></span></p> <p class=MsoNormal style='text-align:justify;text-indent:.5in;line-height:150%'><span style='mso-bidi-font-weight:bold'>Electrochemistry was also used to investigate the properties of M-DNA monolayers on gold and examine how the localization of metal ions affects the resistance through the DNA monolayer.<span style='mso-spacerun:yes'>  </span>T</span>he effectiveness of using the IrCl₆^2-/3-redox couple to investigate DNA monolayers and the potential advantages of this system over the standard Fe(CN)₆^3-/4- redox couple are demonstrated.<span style='mso-spacerun:yes'>  </span>B-DNA monolayers were converted to M-DNA by incubation in buffer containing 0.4 mM Zn²⁺ at pH 8.6 and studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA) with IrCl₆^2-/3-.<span style='mso-spacerun:yes'>  </span>^{<span style='mso-spacerun:yes'> </span>}Compared to B-DNA, M-DNA showed significant changes in CV, EIS and CA spectra.<span style='mso-spacerun:yes'>  </span>However, only small changes were observed when the monolayers were incubated in Mg²⁺at pH 8.6 or in Zn²⁺ at pH 6.0.<span style='mso-spacerun:yes'>  </span>The heterogeneous electron-transfer rate (<i style='mso-bidi-font-style:normal'>k</i>_ET) between the redox probe and the surface of a bare gold electrode was determined to be 5.7 x 10^-3 cm/s.<span style='mso-spacerun:yes'>  </span>For a B-DNA modified electrode, the <i style='mso-bidi-font-style:normal'>k</i>_ET through the monolayer was too slow to be measured.<span style='mso-spacerun:yes'>  </span>However, under M-DNA conditions, a <i style='mso-bidi-font-style:normal'>k</i>_ET of 1.5 x 10^-3 cm/s was reached.<span style='mso-spacerun:yes'>  </span>As well, the percent change in resistance to charge transfer (R_CT), measured by EIS, <span class=GramE>was</span> used to illustrate the dependence of M-DNA formation on pH.<span style='mso-spacerun:yes'>  </span>This result is consistent with Zn²⁺ ions replacing the imino protons on thymine and guanine residues.<span style='mso-spacerun:yes'>  </span>Also, at low pH values, the percent change in R_CT seems to be greater for <span class=GramE><span style='mso-bidi-font-weight:bold'>d(</span></span><span style='mso-bidi-font-weight: bold'>TG)₁₅d(CA)₁₅ compared to oligomers with mixed d(AT) and d(TG)d(CA) tracts.<span style='mso-spacerun:yes'>  </span></span>The IrCl₆^2-/3-redox couple was also effective in differentiating between single-stranded and double-stranded DNA during dehybridization and rehybridization experiments.<span style='mso-spacerun:yes'>  </span><span style='mso-bidi-font-weight:bold'><o:p></o:p></span></p>

Hard turning is a machining process where a single point cutting tool removes material harder than 45 HRC from a rotating workpiece. Due to the advent of polycrystalline cubic boron nitride (PCBN) cutting tools and improved machine tool designs, hard turning is an attractive alternative to grinding for steel parts within the range of 58-68 HRC, such as bearings. There is reluctance in industry to adopt hard turning because of a defect called white layer. White layer is a hard, 1-5 쭠deep layer on the surface of the specimen that resists etching and therefore appears white on a micrograph. When aggressive cutting parameters are used, even using a new tool, white layer is expected. If more conservative parameters are selected, one does not expect white layer. There is some debate if white layer actually decreases the strength or fatigue life of a part, but nevertheless it is not well understood and therefore is avoided. This research examines the use of two different non-destructive evaluation (NDE) sensors to detect white layer in hard turned components. The first, called a Barkhausen sensor, is an NDE instrument that works by applying a magnetic field to a ferromagnetic metal and observing the induced electrical field. The amplitude of the signal produced by the induced electrical field is affected by the hardness of the material and surface residual stresses. This work also examines the electrochemical properties of white layer defects using electrochemical impedance spectroscopy. This idea is verified by measuring the electrochemical potential of surfaces with white layer and comparing to surfaces without any. Further corrosion tests using the electrochemical impedance spectroscopy method indicate that parts with white layer have a higher corrosion rate. The goal of this study is to determine if it is possible to infer white layer thickness reliably using either the Barkhausen sensor or electrochemical impedance spectroscopy (EIS). Measurements from both sensors are compared with direct observation of the microstructure in order to determine if either sensor can reliably detect the presence of white layer.

Severe corrosion damage and even complete failure was recently discovered in external post-tensioned (PT) tendons of three Florida's pre-cast, segmental bridges over seawater. A key deterioration factor was the formation of large bleed water grout voids at or near the anchorages. Steel corrosion may occur at the grout-void interface or in the air space of the void itself. Since the tendons are critical to the structural integrity of the bridges, reliable and non-intrusive damage detection methods are desirable to manage or prevent future occurrences. In recent years several indirect non-destructive methods have been developed or improved to evaluate the conditions of the tendons. One of those methods is vibration-based tension measurements, consisting of detecting tendon tension loss by analyzing the tendon's natural frequencies. Until recently, vibration-based tension measurements were costly and laborious since they required several operators to conduct the tests and complicated analysis through different programs. The first objective of this research is to provide a practical, simplified, user-friendly testing and analysis method for screening tendons by vibration measurements. Electrochemical Impedance Spectroscopy, Linear Polarization, and Electrical Resistance are alternative methods that could nondestructively detect or monitor corrosion before strand failures occur. The reliability and sensitivity of these conventional monitoring methods in solid or liquid media are well proven. However, few investigations exist on applying these methods to air-space corrosion as it may occur in tendon anchors. The second objective of this research is to establish the feasibility of using the above conventional monitoring methods for detecting air-space corrosion. In this investigation, two different types of Electrical Resistance probes were designed and evaluated. Also, electrochemical probes were constructed simulating strands conditions in the grout-void interface. Electrochemical Impedance Spectroscopy and Linear Polarization measurements were conducted in the electrochemical probes to calculate their instantaneous corrosion rates. Electrical Resistance and Electrochemical probes results indicate that both methods provide sufficient sensibility to determine the ongoing damage.