Electrochemical evaluation of lipophilic antioxidants from Iryanthera juruensis fruits (Myristicaceae)

TLC autographic assays revealed in the hexane extract of Iryanthera juruensis (Myristicaceae) the presence of two compounds, with antioxidant properties towards beta-carotene. They were isolated and identified as 3-methyl-sargachromenol (1) and sargachromenol (2). Further investigation of the hexane extract led to isolations of 3-methyl-sargaquinoic acid (3) and sargaquinoic acid (4). The electrochemical behaviour of these compounds was studied in CH2Cl2/Bu4NBF4 at glassy carbon electrode. The phenolic group in both tocotrienols 1 and 2 are oxidized at +0.23V and +0.32V and their oxidation potentials are correlated with the observed antioxidant activities and oxidation mechanism of alpha-tocopherol. The reductive voltametric behaviour of quinone function in both plastoquinones 3 and 4 is discussed.

Electrochemical evidence of sulfinic acid derivative as an intermediate in the reduction of aromatic sulfonyl chloride in an aprotic medium

The electrochemical reduction of p-nitrobenzenesulfonyl chloride (NBSCl) in dimethylsulfoxide (DMSO) solution is used here as a model to investigate the role of sulfinic acid derivative in this compound's global reduction process. Cyclic voltammetric experiments reveal the production of sulfinic acid derivative, which is important in chemical reactions involving the original compound and other intermediates. This paper also discusses the probable mechanisms of the reduction.

Determination of carbon monoxide using a coated quartz crystal sensor

Carbon monoxide was detected and determined by a piezoelectric quartz crystal sensor coated with nickel(II)-phthalocyanine 50 % (v/v) solution in glycerine. Studies on the effect of temperature, flow rate, and some possible interferents were carried out. Calibration curves, sensor stability (lifetime) and the precision of measurements were also verified. The resulting selectivity is probably due to the coordinative binding between the electronically unsatured metal complexes and the analyte. The analytical curve is linear in the concentration range 0.10 to 1.0 % (v/v).

Ascorbic acid determination using a carbon paste electrode modified with iron(III) ions adsorbed on humic acid

An amperometric sensor was constructed, by using humic acids to immobilize Fe3+ ions on a carbon paste electrode (CPE-HA-Fe), and used for ascorbic acid (H2A) determination. The cyclic voltammogram of the electrode showed electrochemical response due to the Fe3+/Fe2+ couple at E1/2=+0.78 V vs SCE, using 0.5 mol L-1 KCl and 0.2 mol L-1 acetate/0.020 mol L-1 phosphate buffer, at pH = 5.4, as supporting electrolyte. When H2A is added to the electrolyte solution it is observed an oxidation process. The oxidation current, obtained by chronoamperommetry at +0.87 V vs SCE, is proportional to the concentration, represented by the equation I(µA) = 7.6286 [H2A] (mmol L-1) + 1.9583, r = 0.9996, for concentrations between 0.0 and 1.4 mmol L-1. The electrode showed high stability and was used for H2A determination in a natural orange juice.

Electrochemical study and dependence of 'transition state' in Co(II) and Ni(II) complexes with some antibiotics and cephalothin

Electrode kinetics and study of 'transition state' with applied potential in case of [M - antibiotics - cephalothin] system were reported at pH = 7.30 ± 0.01 at suitable supporting electrolyte at 25.0ºC. The M = Co or Ni and antibiotics were doxycycline, chlortetracycline, oxytetracycline, tetracycline, minocycline, amoxicillin and chloramphenicol used as primary ligands and cephalothin as secondary ligand. Kinetic parameters viz. transfer coefficient (a), degree of irreversibility (l), diffusion coefficient (D) and rate constant (k) were determined. The values of a and k varied from 0.41 to 0.59 and 2.60 X 10-3 cm s-1 to 9.67 X 10-3 cm s-1 in case of [Co - antibiotics - cephalothin] system. In case of [Ni - antibiotics - cephalothin], a and k varied from 0.41 to 0.58 and 2.34 X 10-3 cm s-1 to 9.19 X 10-3 cm s-1 respectively confirmed that transition state behaves between oxidant and reductant response to applied potential and it adjusts it self in such a way that the same is located midway between dropping mercury electrode and solution interface. The values of rate constant confirmed the quasireversible nature of electrode processes. The stability constants (logb) of complexes were also determined.

Energy harvesting methods for wireless sensor nodes in heavy-duty vehicles

The number of autonomous wireless sensor and control nodes has been increasing rapidly during the last decade. Until recently, these wireless nodes have been powered with batteries, which have lead to a short life cycle and high maintenance need. Due to these battery-related problems, new energy sources have been studied to power wireless nodes. One solution is energy harvesting, i.e. extracting energy from the ambient environment. Energy harvesting can provide a long-lasting power source for sensor nodes, with no need for maintenance. In this thesis, various energy harvesting technologies are studied whilst focusing on the theory of each technology and the state-of-the-art solutions of published studies and commercial solutions. In addition to energy harvesting, energy storage and energy management solutions are also studied as a subsystem of a whole energy source solution. Wireless nodes are also used in heavy-duty vehicles. Therefore a reliable, long-lasting and maintenance-free power source is also needed in this kind of environment. A forestry harvester has been used as a case study to study the feasibility of energy harvesting in a forestry harvester’s sliding boom. The energy harvester should be able to produce few milliwatts to power the target system, an independent limit switch.

Determinação de amônia no ar utilizando um sensor piezelétrico de quartzo

Neste estudo, procurou-se desenvolver e avaliar filmes para a captação e quantificação de vapores de amônia no ar, através de um sensor piezelétrico de quartzo. Muitas substâncias e suas misturas, em diferentes proporções, foram investigadas como possíveis filmes captores. Em etapas seguintes, verificaram-se alguns parâmetros importantes como o efeito da vazão do poluente, da temperatura de trabalho e da massa da película, otimizando-se as condições experimentais para a montagem do método. Concluiu-se que o filme mais promissor, sob as condições ajustadas, seria uma mistura 2:1 (v/v) de solução comercial (A) de ácido glicólico (70 % m/m) em água, adicionada a tetrakis(hidroxietil)etilenodiamina - THEED (3:4 v/v), com uma solução saturada (B) de ácido tânico em acetona. Estudos de repetibilidade, do tempo de contacto (poluente-sensor) e de alguns possíveis interferentes completaram os trabalhos. As curvas analíticas resultantes mostraram faixas lineares na região de trabalho (2,0 a 11 ppm v ou 1,4 a 7,7 mg/m³ de NH3), para quatro diferentes tempos de exposição (0,5; 1; 2 e 3 min), com coeficientes de correlação (r) variando entre 0,9994 e 0,9980, e respectivas sensibilidades de 13,5 a 42,0 Hz / ppm v.

The Cellular Oxygen Sensor PHD2 in Cancer Growth

Adequate supply of oxygen is essential for the survival of multicellular organisms. However, in several conditions the supply of oxygen can be disturbed and the tissue oxygenation is compromised. This condition is termed hypoxia. Oxygen homeostasis is maintained by the regulation of both the use and delivery of oxygen through complex, sensitive and cell-type specific transcriptional responses to hypoxia. This is mainly achieved by one master regulator, a transcription factor called hypoxiainducible factor 1 (HIF-1). The amount of HIF-1 is under tight oxygen-dependent control by a family of oxygen-dependent prolyl hydroxylase domain proteins (PHDs) that function as the cellular oxygen sensors. Three family members (PHD1-3) are known to regulate HIF of which the PHD2 isoform is thought to be the main regulator of HIF-1. The supply of oxygen can be disturbed in pathophysiological conditions, such as ischemic disorders and cancer. Cancer cells in the hypoxic parts of the tumors exploit the ability of HIF-1 to turn on the mechanisms for their survival, resistance to treatment, and escape from the oxygen- and nutrient-deprived environment. In this study, the expression and regulation of PHD2 were studied in normal and cancerous tissues, and its significance in tumor growth. The results show that the expression of PHD2 is induced in hypoxic cells. It is overexpressed in head and neck squamous cell carcinomas and colon adenocarcinomas. Although PHD2 normally resides in the cytoplasm, nuclear translocation of PHD2 was also seen in a subset of tumor cells. Together with the overexpression, the nuclear localization correlated with the aggressiveness of the tumors. The nuclear localization of PHD2 caused an increase in the anchorage-independent growth of cancer cells. This study provides information on the role of PHD2, the main regulator of HIF expression, in cancer progression. This knowledge may prove to be valuable in targeting the HIF pathway in cancer treatment.

Implementing gateway monitoring service for infrastructure sensor networks

Wireless sensor networks and its applications have been widely researched and implemented in both commercial and non commercial areas. The usage of wireless sensor network has developed its market from military usage to daily use of human livings. Wireless sensor network applications from monitoring prospect are used in home monitoring, farm fields and habitant monitoring to buildings structural monitoring. As the usage boundaries of wireless sensor networks and its applications are emerging there are definite ongoing research, such as lifetime for wireless sensor network, security of sensor nodes and expanding the applications with modern day scenarios of applications as web services. The main focus in this thesis work is to study and implement monitoring application for infrastructure based sensor network and expand its usability as web service to facilitate mobile clients. The developed application is implemented for wireless sensor nodes information collection and monitoring purpose enabling home or office environment remote monitoring for a user.

Tratamento de ruídos e caracterização de fisionomias do Cerrado utilizando séries temporais do sensor MODIS

O Cerrado é formado por um mosaico de fisionomias campestres, savânicas e florestais que possuem um típico ciclo fenológico. Nesse contexto, os dados do MODIS fornecem medidas diárias que permitem monitorar a sazonal fenologia da vegetação. O objetivo deste trabalho foi caracterizar formações savânicas, formações florestais e áreas de cerrado convertido pela ação antrópica, utilizando séries temporais de NDVI e EVI do sensor MODIS, após a suavização de ruídos. A metodologia adotada pode ser subdividida nos seguintes passos: (a) confecção do cubo temporal com NDVI e EVI, onde o perfil em z corresponde à assinatura temporal, (b) tratamento do ruído e (c) detecção das assinaturas temporais. A Transformação pela Fração Mínima de Ruído (MNF) foi aplicada para suavizar ruídos contidos nas séries temporais. Os resultados indicaram que os valores de NDVI foram maiores que os valores de EVI e existiu relação com as estações do ano. As formações florestais foram as que apresentaram maiores valores de NDVI e EVI, possuindo ainda as menores variações entre as estações. As áreas convertidas apresentaram os menores valores dos dois índices, tendo grande queda em seus valores no início da estação seca, provavelmente por se tratar do período de colheita. O estudo concluiu que as séries temporais NDVI e EVI são úteis na diferenciação dos tipos de vegetação.

Uso do produto MOD13Q1 do sensor Modis para análise temporal e mapeamento das florestas nas Serras do Sudeste e Campanha Meridional do Rio Grande do Sul

Imagens NDVI (Índice de Vegetação por Diferença Normalizada) do sensor Modis foram utilizadas para mapear as classes de uso e cobertura da terra nas Serras do Sudeste e Campanha Meridional do Rio Grande do Sul. A metodologia compreendeu a elaboração de um banco de dados espaciais e a aplicação de técnicas de processamento digital (contraste linear, classificação digital e operações aritméticas) sobre imagens dos satélites Landsat e Terra de diversas datas. Os resultados indicaram que a cobertura florestal passou de 8,6% para 11,6% e 14,3% da área total da microrregião Serras do Sudeste, entre os anos 2000, 2004 e 2008. Na Campanha Meridional, a expansão da cobertura florestal passou de 11,1% para 11,2% e 11,5% da área total no mesmo período. Conclui-se que imagens MOD13Q1, de baixa resolução espacial (250 m), podem ser usadas em grandes áreas para mapear florestas e os demais temas adequadamente.

Electrical Equivalent Circuit for Dry Bacteriorhodopsin Sensor

Bacteriorhodopsin (BR) is a photosensitive protein which functions as a light-driven proton pump. Due to its photoactivity, BR could be used in photosensing and information processing which has inspired researchers to study the photoelectric response and the appropriate measurement instrumentation for BR. In this thesis, the measurement instrumentation connected to a dry BR sensor was confirmed to affect the photovoltage response measured by using voltage amplifiers. Changing of the input impedance of the measurement instrumentation was shown to alter a part of the measured photovoltage response. The photocurrent measurements using transimpedance amplifier and the presented electrical equivalent circuit were used to show that the photocurrent measurements have no significant effect on the photoelectric response. The photocurrent was shown to be a derivate of the photovoltage response measured from the dry BR sensor when it was compared to the response measured with a voltage amplifier. This confirmed that another part of the photovoltage response was not affected by the measurement instrumentation. The time-variant behavior of the dry BR sensor was confirmed in both the photocurrent and the photovoltage measurements. This was caused by the fact that the capacitance of the dry BR sensor changes with the excitation light intensity.

Modelo para estimativa do potencial produtivo em trigo e cevada por meio do sensor GreenSeeker

Áreas com diferentes potenciais de rendimento dentro de uma lavoura necessitam ser manejadas separadamente, para fins de aplicação da adubação nitrogenada em cobertura. O equipamento baseado em sensoriamento remoto terrestre (GreenSeeker) é um dos instrumentos utilizados para separar diferentes zonas de manejo. Para fazer isso, o sensor permite a definição de classes para estimar o potencial produtivo de forma ágil, precisa e em tempo real. Com o instrumento, foi desenvolvido um modelo para estimativa do potencial produtivo em trigo e cevada, correlacionando o Índice de Vegetação por Diferença Normalizada (NDVI) com a biomassa seca acumulada na parte aérea, por ocasião da emissão da sexta folha do colmo principal. A base do modelo foi a formação de classes de potencial produtivo correspondentes a zonas específicas de manejo da lavoura. Essas classes não necessitam ser específicas para diferentes cultivares e/ou espécies, visto que não se detectaram diferenças que justificassem a formação de grupos para elas. As superfícies de fundo (resíduos de restevas de soja e milho) tiveram efeitos significativos nas leituras do sensor. O modelo continua válido mesmo se as leituras de NDVI forem feitas antes ou após o período recomendado para tal, podendo ser ajustado com sub ou superestimação. As análises de variabilidade espacial, futuramente, podem avaliar se, as zonas de potencial produtivo estimadas pelas classes de NDVI propostas pelo modelo, correspondem à flutuação espacial da biomassa, doses de N aplicadas e rendimento de grãos.

Electrochemical and spectroelectrochemical characterization of alkylated and thiolated polyanilines

Vi omges i vardagen av alla sorters plaster, som kemiskt kallas för polymerer. Vi anknyter dem oftast till vardagliga föremål såsom muggar, leksaker eller platskassar. Det finns dock en särklass av polymerer som fås elektriskt ledande genom en så kallad dopningsprocess. Dopning innebär i detta fall oxidation eller reduktion av konjugerade dubbelbindningar i polymerstrukturen. Detta har lett till utveckling av elektriska apparater där dyra, och i vissa fall även sällsynta, metall och halvledarmaterial ersätts genom av elektriskt ledande polymerer (plaster). Utöver elektronisk ledningsförmåga uppvisar dessa polymerer också jonisk ledningsförmåga. Denna kombination av unika egenskaper möjliggör skapandet av t.ex. nya sensormaterial som kan överföra kemisk information till en mätbar elektronisk signal. Detta öppnar i sin tur möjligheter att göra snabba, billiga och känsliga sensorer för bl.a. mediciniska analyser. I denna avhandling karakteriserades elektrokemiskt och spektroelektrokemiskt N- och ring-substituerade polyanilinfilmer. Polyanilin (PANI) hör till de mest studerade elektriskt ledande polymererna. Den är stabil och lätt att framställa. Substituerade polyaniliner har ändå studerats måttligt, mest p.g.a. att substituerade PANIs ledningsförmåga är lägre än PANIs och deras framställning kan vara svår. De nya grupperna i PANI-kedjan ger dock en möjlighet att binda ytterligare molekyler av intresse till PANI-kedjan, som t.ex. jonselektiva grupper. Kovalent bundna selektiva molekyler ger upphov till stabila, känsliga och selektiva sensormaterial. Karakteriseringen av de studerade polymerer är viktig för den fundamentala förståelsen av deras unika egenskaper och för utvecklingen av framtidens sensormaterial. -------------------------------------- Käytämme joka päivä monenlaisia muoveja, joita kutsutaan kemiassa myös polymeereiksi. Olemme tottuneet yhdistämään muovit arkisiin esineisiin kuten mukeihin, leluihin tai muovikasseihin. On kuitenkin olemassa erityisiä polymeerejä, jotka voidaan saada sähköä johtaviksi hapetus- ja pelkistysreaktioiden avulla. Tästä johtuen on kehitteillä sähköisiä laitteita, joissa kalliit ja jossain tapauksissa myös harvinaisia metalleja sisältävät osat ja puolijohteet voidaan korvata johdepolymeereillä (eli muoveilla). Sähkönjohtavuuden lisäksi johdepolymeereillä on myös ionijohtavuutta. Näiden erityislaatuisten ominaisuuksien yhdistelmä on mahdollistanut mm. sensorimateriaalin kehittämisen, sillä kemiallinen tieto voidaan kääntää mitattavaksi sähköiseksi signaaliksi. Tämä taas omalta osaltaan mahdollistaisi nopeiden, halpojen ja herkkien sensorien valmistuksen, mm. diagnostiikkaan. Tässä väitöksessä on tutkittu sähkökemiallisesti valmistettuja N- ja rengassubstituoituja polyaniliinikalvoja. Polyaniliini (PANI) on yksi eniten tutkituista johdepolymeereistä. Se on stabiili ja helppo valmistaa. Substituoidut polyaniliinit ovat herättäneet vain kohtalaista tieteellistä kiinnostusta, lähinnä, koska niiden sähköinen johdekyky on alhaisempi kuin PANIn. Myös niiden valmistus voi olla vaikeaa. Substituoidut molekyylit PANI-ketjussa mahdollistavat kuitenkin, että niihin voi liittää uusia molekyylejä, esim. ioniherkkiä ryhmiä. Kovalentisti sitoutuneilla selektiivisillä molekyyleillä saadaan tehtyä stabiileja, herkkiä ja selektiivisiä sensorimateriaaleja. Väitöksessä käytettyjen polymeerien karakterisointi on tärkeää, jotta niiden erityisominaisuuksia pystyttäisiin ymmärtämään paremmin ja myös kehittämään sopivia tulevaisuuden sensorimateriaaleja.