816 resultados para Electrochemical etching
Resumo:
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.
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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.
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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.
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Bis-(µ2-oxo)-tetrakis{[1-feniltriazene-1,3-diil)-2-(phenyltriazenil)benzene copper(II) is a tetranuclear complex which shows four Cu(II) ions coordinated by four 1,2-bis(phenyltriazene)benzene bridged ligands, with one diazoaminic deprotonated chain, and two O2- ligands. The complex reduces at E1/2 = -0.95 V vs Fc+/Fc, a two electrons process. Cyclic voltammetric and spectroelectrochemical studies showed a reversible process. When immobilized on carbon paste electrode, the complex electrocatalyses the reduction of O2 dissolved on aqueous solution at -0.3 V vs SCE potential. The obtained current shows linearity with O2 concentration.
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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.
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Electrocoagulation is a process in which wastewater is treated under electrical current. Coagulant is formed during the process through the metal anode dissolution to respective ions which react with hydroxyl ions released in cathode. These metal hydroxides form complexes with pollutant ions. Pollutants are removed among metal hydroxide precipitates. This study was concentrated on describing chemistry and device structures in which electrochemical treatment operations are based on. Studied pollutants were nitrogen compounds, sulphate, trivalent and pentavalent arsenic, heavy metals, phosphate, fluoride, chloride, and bromide. In experimental part, removal of ammonium, nitrate, and sulphate during electrochemical treatment was studied separately. Main objective of this study was to find suitable metal plate material for ammonium, nitrate, and sulphate removal, respectively. Also other parameters such as pH of solution, concentration of pollutant and sodium chloride, and current density were optimized. According to this study the most suitable material for ammonium and sulphate removal by electrochemical treatment was stainless steel. Respectively, iron was the optimum material for nitrate removal. Rise in the pH of solution at the final stage of electrochemical treatment of ammonium, nitrate, and sulphate was detected. Conductivities of solutions decreased during ammonium removal in electrochemical processes. When nitrate and sulphate were removed electrochemically conductivities of solutions increased. Concentrations of residual metals in electrochemically treated solutions were not significant. Based on this study electrochemical treatment processes are recommended to be used in treatment of industrial wastewaters. Treatment conditions should be optimized for each wastewater matrix.
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Polarization curves experimentally obtained in the electro-dissolution of iron in a 1 M H2SO4 solution using a rotating disc as the working electrode present a current instability region within the range of applied voltage in which the current is controlled by mass transport in the electrolyte. According to the literature (Barcia et. al., 1992) the electro-dissolution process leads to the existence of a viscosity gradient in the interface metal-solution, which leads to a velocity field quantitatively different form the one developed in uniform viscosity conditions and may affect the stability of the hydrodynamic field. The purpose of this work is to investigate whether a steady viscosity profile, depending on the distance to the electrode surface, affects the stability properties of the classic velocity field near a rotating disc. Two classes of perturbations are considered: perturbations monotonically varying along the radial direction, and perturbations periodically modulated along the radial direction. The results show that the hydrodynamic field is always stable with respect to the first class of perturbations and that the neutral stability curves are modified by the presence of a viscosity gradient in the second case, in the sense of reducing the critical Reynolds number beyond which perturbations are amplified. This result supports the hypothesis that the current oscillations observed in the polarization curve may originate from a hydrodynamic instability.
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The primary aim of these investigations was to probe the spectroscopic, electrochemical, biological and single crystal X-ray diffraction studies of some selected transition metal complexes of 4N-monosubstituted thiosemicarbazones. Transition metal complexes with thiosemicarbazones exhibit a wide range of stereochemistries and possess potential biological activity. Metal complexes of thiosemicarbazones are proved to have improved pharmacological and therapeutic effects. The studies are conducted to bring about a fair understanding of the structure activity relationship and to develop certain effective and economical metal-based antimicrobial agents. Study showed that the thiosemicarbazones have antibacterial, antiviral and antiproliferative properties and hence used against tuberculosis, leprosy, psoriasis, rheumatism, trypanosomiasis and coccidiosis. Certain thiosemicarbazones showed a selective inhibition of HSV and HIV infections. The insolubility of most thiosemicarbazones in water causes difficulty in the oral administration in clinical practice. Transition metal complexes are found to have more activity than uncombined thiosemicarbazones. They exhibit a variety of denticity and can be varied by proper substitution. The stereochemistry assumed by the thiosemicarbazones during the coordination with transition metal ions depends on the factors such as preparative conditions and availability of additional bonding site in the ligand moiety and charge of the ligand. The resulting complexes exhibited a wide range of stereochemistries and have biomimic activity and potential application as sensors.
Resumo:
The primary aim of these investigations was to probe the spectroscopic, electrochemical, biological and single crystal X-ray diffraction studies of some selected transition metal complexes of 4N-monosubstituted thiosemicarbazones. Transition metal complexes with thiosemicarbazones exhibit a wide range of stereochemistries and possess potential biological activity. Metal complexes of thiosemicarbazones are proved to have improved pharmacological and therapeutic effects. The studies are conducted to bring about a fair understanding of the structure activity relationship and to develop certain effective and economical metal-based antimicrobial agents. Study showed that the thiosemicarbazones have antibacterial, antiviral and antiproliferative properties and hence used against tuberculosis, leprosy, psoriasis, rheumatism, trypanosomiasis and coccidiosis. Certain thiosemicarbazones showed a selective inhibition of HSV and HIV infections. The insolubility of most thiosemicarbazones in water causes difficulty in the oral administration in clinical practice. Transition metal complexes are found to have more activity than uncombined thiosemicarbazones. They exhibit a variety of denticity and can be varied by proper substitution. The stereochemistry assumed by the thiosemicarbazones during the coordination with transition metal ions depends on the factors such as preparative conditions and availability of additional bonding site in the ligand moiety and charge of the ligand. The resulting complexes exhibited a wide range of stereochemistries and have biomimic activity and potential application as sensors
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A metalloporphyrin incorporated carbon paste sensor has been developed for the determination of metronidazole benzoate (MTZB). Zn(II) complex of 5,10,15,20-tetrakis (3-methoxy-4-hydroxy phenyl) porphyrin (TMHPP) was used as the active material. The MTZB gave a well-defined reduction peak at - 0.713V in 0.1 mol l -1 phosphate buffer solution of pH around 7. Compared with bare carbon paste electrode (CPE), the TMHPP Zn(II) modified electrode significantly enhanced the reduction peak current of MTZB as well as lowered its reduction potential. Under optimum conditions the reduction peak current was proportional to MTZB concentration over the range 1×10-3 mol1-1 to 1×10-5mol1-1. The detection limit was found to be 4.36×10-6mol1-1 . This sensor has been successfully applied for the determination of MTZB in pharmaceutical formulations and urine samples.
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Poly(6-tert-butyl-3,4-dihydro-2H-1,3-benzoxazine) was synthesized by thermally activated cationic ring opening polymerization. The structure of the polymer was confirmed by spectral and thermal studies. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) were estimated using cyclic voltammetry and optical absorption. Modulated photocurrent measurement technique was employed to study the spectral and field dependence of photocurrent. Photocurrent of the order of 1.5 micro A/m2 was obtained for polymer at a biasing electric field of 40 V/mico m.
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Voltammetric sensors are an important class of electrochemical sensors in which the analytical information is obtained from the measurement of current obtained as a result of electrochemical oxidation/reduction.This current is proportional to the concentration of the analyte.Chemically modified electrodes(CMEs) have great significance as important analytical tools for the electrochemical determination of pharmaceuticals.The modification of electrode results in efficient determination of electro-active biomolecules at very lower potential without its major interferences.The operation mechanism of CMEs depends on the properties of the modifier materials that are used to promote selectivity towards the target analytes.Modified electrodes can be prepared by deposition of various compounds such as organic compounds ,conducting polymers,metal oxides,etc. on the various electrode surfaces.The thesis presents the development ,electrochemical characterization and analytical application studies of eight voltammetric sensors developed for six drugs viz.,Ambroxol,Sulfamethoxazole,PAM Chloride, Lamivudine,Metronidazole and Nimesulide.The modification techniques adopted as part of the present work include Multiwalled Carbon Nanotube(MWCNT) based modification.Electropolymerisation and Gold Nanoparticle (AuNP) based modifications.
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The design and development of an evanescent wave sensor to determine the etching rate of the core of an optical fibre is discussed in this paper. The working of the device is based on the principle of propagation and loss of the evanescent wave in the cladding region of the fibre. The fraction of light intensity creeping out of the core of an uncladded fibre is a function of the core radius. As this radius decreases, the evanescent wave coupling to the medium surrounding the core enhances. This results in a decrease of the transmitted light intensity through the fibre. This technique is useful to design and fabricate optical fibres with different core geometries.