Studies on a series of polymethine cyanine dyes and analogs (1-24) show that certain near-infrared cyanines are capable of damaging DNA in the absence of light and external reducing agents. Experimental results imply that in this DNA thermal cleavage, the cyanine reduces Cu(II) to Cu(I) which reacts with O2 to generate the reactive oxygen species (ROS) O2∙- and ∙OH. The formation of these ROS is also thought to be responsible for the irreversible bleaching of the dyes in aqueous solutions. A correlation between structural features and DNA thermal cleavage activity as well as dye bleaching is suggested. Long polymethine chains appear to confer instability to cyanines in aqueous solutions and further contribute to undesired thermal DNA cleavage. These drawbacks can be overcome by introducing an electron-withdrawing group to the polymethine bridge of the cyanine dye.

Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2009.

Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2009.

Point-of-care testing (POCT) devices have received increasing attention because of their potential to address the urgent need for quick and accurate diagnostic tools, especially in areas of personal care and clinical medicine. They offer several benefits over current diagnostic systems, including rapid diagnostic results in comparison to microbial cultures, simple interpretation of results, portability, and requiring no specialised laboratory equipment or technical training to operate. These are essential for diagnosing critical illnesses, such as sepsis, in areas of poor healthcare infrastructure. Sepsis, an innate physiological response to infection, is a growing problem worldwide with high associated costs and mortality rates, and affects a wide range of patients including neonates, infants, the elderly, and immunocompromised individuals. A literature review of the biomarkers of sepsis and the currently available diagnostic systems indicates the need for a biosensor capable of meeting the requirements of designing POCT systems and achieving detection of low concentrations of biomarkers. To meet these demands, two significant contributions to developing POCT platforms have been achieved and described in this thesis, including: 1) development of a colorimetric, magnetically separable biosensor that can be easily fabricated and demonstrates an easily identifiable colour response upon analyte detection, as well as the ability to capture and detection target biomarkers at low concentrations from complex solutions; and 2) tuning of the biosensor’s colorimetric response to achieve low detection limits, as well as demonstration of the versatility of the biosensor for sensing different target analytes. The developed biosensor in this work combines colour responsive polydiacetylenes and superparamagnetic iron oxide for the first time to achieve a biosensor capable of meeting these demands. The sensors exhibit identifiable colour responses to biomolecule detection, capture of a target analyte from complex solutions, sensing of different target analytes, a lower detection limit of 0.01 mg/mL, and rapid separation from solution with a common magnet. This work has been a significant demonstration of the capabilities of this biosensor as a new platform for POCT systems to diagnosis sepsis, and potentially other sensing applications.

This thesis covers the combination of two seperate work accomplished during the throughout the study. In the first part of the study, xanthene based artificial enzymes were synthesized, and kinetic hydrolysis studies done. Artificial enzyme design is an active field of supramolecular chemistry and metalloenzymes are attractive targets in such studies. Enzymatic catalysis is essentially a &lsquo / multifuctional&rsquo / catalysis. As part of our work, we designed and synthesized three novel xanthene derivatives. All three model contain Zn(II) in their active sites. Using the model substrate p-nitrophenyl acetate, we showed that the bifunctional model is at least an order of magnitude more active in catalyzing the hydrolysis of the substrate. Compared to the uncatalyzed hydrolysis reaction of the p-nitrophenyl ester at pH 7.0, the bifunctional model complex showed a 5714-fold rate acceleration. The second part of the thesis involves the design of a dimeric calixpyrrole as a chromogenic chemosensor. Anions are involved in a large number of biological processes and there is an interest in developing molecular sensors for these charged species. The calixpyrroles are a class of old but new heterocalixarene analogues that show considerable promise in the area of anion sensing. In this work, we have designed, synthesized and characterized a calixpyrrole-dimer anion sensor for its anion binding strength. The dimer forms stable complexes with p-nitrophenolate ion. This formed complex is used as a colorimetric sensor by displacing the chromogenic anion with the addition of various anions. like fluoride and acetate. The receptor shows strong affinity and high selectivity for fluoride anion, and also show reasonable affinity toward acetate. Thus, effective optical sensing of biochemically relevant these anions is accomplished using the calixpyrrole dimer.

Milk contains high concentrations of calcium. It occurs in two forms, a free ionic form, and calcium associated with milk proteins (caseins). The latter association is called colloidal calcium phosphate. New Zealand Dairy Foods of Takanini is marketing a range of commercial milks in supermarkets. The company uses ultra filtration to concentrate milk proteins and calcium in different milk products. During ultra filtration, the fraction that is retained by the membrane is rich in calcium bound to proteins and the portion that passes through the membrane is richer in the free ionic form. The company wanted to develop a quick and an economical method that can be applied in industrial settings to determine calcium in both these fractions and in other milk products. This research aimed to develop a quick, wet chemistry method to measure calcium in milk fractions and to trial it in an industrial environment. Two methods, the so-called EDTA method and the atomic absorption spectrophotometric method (AA) were trialled as potential reference methods against which to compare results obtained by the method to be developed. The AA method was chosen due to its ease, accuracy and precision. (This could not be selected as the industrial method for a number of reasons.) A colorimetric method was favoured over other contenders. Two colorimetric dyes, Arsenazo I and o-cresolphthalein-complexone (CPC) were chosen to work with. Arsenazo I forms a purple complex with calcium in a suitable buffer at a range of pHs. o-Cresolphthalein-complexone also forms purple-coloured complexes at alkaline pHs. During method development with Arsenazo I, different buffers were trialled and a NaOH/ KCl buffer was selected for further development at pH 12. The method worked well during the development phase but with some inconsistent results at times. o-Cresolphthalein-complexone formed clear purple complexes with Clark and Lubs and 2-amino-2-methylpropanol (AMP) buffers. The key advantage of the CPC dye with AMP buffer was that when 8-hydroxyquinoline was included in the reaction mixture, it successfully masked coloured complex formation due to CPC with magnesium, which is present in milk at about 1/3 the calcium concentration. This effect did not work with Arsenazo I. However, the results obtained with the CPC method were lower than claimed values of most milks trialled during development. Both methods were compared for their precision and it was found that CPC method has better precision and was chosen for further development. To improve the accuracy and precision, various denaturing reagents were used to (hypothetically) release calcium from the caseins. Trichloroacetic acid at 25 % was more effective than the several other denaturing treatments tested. The finalised CPC method, using trichloroacetic acid, AMP and 8-hydroxyquinoline, was then used to monitor calcium concentration over four months in three milk products, skim, Xtra (retentate) and permeate. For all milks, the CPC values were lower than the AA reference values, and the values reported by a commercial analytical laboratory. The reasons for this are discussed, as are other changes in calcium concentration in the three milks throughout the trial. The correlation between the CPC and AA values was poor for Xtra, better for skim, and best for permeate. A chemical model to explain this is discussed. The method developed is cheap and quick, and sample and reagent preparation is simple. The method could be applied in an industrial environment, but a proportionality factor would have to be applied to account for the difference in mean values between the CPC and AA methods.

Milk contains high concentrations of calcium. It occurs in two forms, a free ionic form, and calcium associated with milk proteins (caseins). The latter association is called colloidal calcium phosphate. New Zealand Dairy Foods of Takanini is marketing a range of commercial milks in supermarkets. The company uses ultra filtration to concentrate milk proteins and calcium in different milk products. During ultra filtration, the fraction that is retained by the membrane is rich in calcium bound to proteins and the portion that passes through the membrane is richer in the free ionic form. The company wanted to develop a quick and an economical method that can be applied in industrial settings to determine calcium in both these fractions and in other milk products. This research aimed to develop a quick, wet chemistry method to measure calcium in milk fractions and to trial it in an industrial environment. Two methods, the so-called EDTA method and the atomic absorption spectrophotometric method (AA) were trialled as potential reference methods against which to compare results obtained by the method to be developed. The AA method was chosen due to its ease, accuracy and precision. (This could not be selected as the industrial method for a number of reasons.) A colorimetric method was favoured over other contenders. Two colorimetric dyes, Arsenazo I and o-cresolphthalein-complexone (CPC) were chosen to work with. Arsenazo I forms a purple complex with calcium in a suitable buffer at a range of pHs. o-Cresolphthalein-complexone also forms purple-coloured complexes at alkaline pHs. During method development with Arsenazo I, different buffers were trialled and a NaOH/ KCl buffer was selected for further development at pH 12. The method worked well during the development phase but with some inconsistent results at times. o-Cresolphthalein-complexone formed clear purple complexes with Clark and Lubs and 2-amino-2-methylpropanol (AMP) buffers. The key advantage of the CPC dye with AMP buffer was that when 8-hydroxyquinoline was included in the reaction mixture, it successfully masked coloured complex formation due to CPC with magnesium, which is present in milk at about 1/3 the calcium concentration. This effect did not work with Arsenazo I. However, the results obtained with the CPC method were lower than claimed values of most milks trialled during development. Both methods were compared for their precision and it was found that CPC method has better precision and was chosen for further development. To improve the accuracy and precision, various denaturing reagents were used to (hypothetically) release calcium from the caseins. Trichloroacetic acid at 25 % was more effective than the several other denaturing treatments tested. The finalised CPC method, using trichloroacetic acid, AMP and 8-hydroxyquinoline, was then used to monitor calcium concentration over four months in three milk products, skim, Xtra (retentate) and permeate. For all milks, the CPC values were lower than the AA reference values, and the values reported by a commercial analytical laboratory. The reasons for this are discussed, as are other changes in calcium concentration in the three milks throughout the trial. The correlation between the CPC and AA values was poor for Xtra, better for skim, and best for permeate. A chemical model to explain this is discussed. The method developed is cheap and quick, and sample and reagent preparation is simple. The method could be applied in an industrial environment, but a proportionality factor would have to be applied to account for the difference in mean values between the CPC and AA methods.

Neste estudo apresenta-se a síntese de duas amostras de nanopartículas de ferrita de níquel, denominadas C-NiFe2O4 e NiFe2O4, através de um método simples, de baixo custo e ambientalmente amigável. Estudos morfológicos, estruturais, eletrônicos, ópticos e magnéticos foram realizados com o intuito de caracterizar as propriedades desses materiais para que possibilitassem, além de maior grau de conhecimento, sua aplicação como sensores colorimétricos para detecção de ácido ascórbico e peróxido de hidrogênio. Mediante a análise térmica dos precursores, foi possível determinar os intervalos de temperatura de decomposição, assim como a temperatura ótima de formação das nanopartículas. A amostra NiFe2O4 é ferromagnética e corresponde a uma fase cúbica de espinélio inverso. Os dados de difração de raios X, espectroscopia Mössbauer e o modelo iônico sugerem a presença de um certo grau de substituição, possuindo em sua estrutura um cátion divalente como agente dopante. As nanopartículas de C-NiFe2O4 foram utilizadas como catalisador na oxidação do 3,3',5,5'-tetrametilbenzidina (TMB) em meio ácido para formar uma solução azul sem adição de outro reagente. Como resultado foi utilizado como sensor colorimétrico para detecção de ácido ascórbico, visto que este reduz o complexo de transferência de carga, TMBOX, novamente para TMB. A calibração analítica apresentou uma faixa linear entre 1-20 μM para a concentração de ácido ascórbico, com limite de detecção (3/m) de 0,93 μM. A determinação em suplementos de vitamina C através do método de adição de padrão mostrou a eficiência do sensor para detectar ácido ascórbico em amostras reais. Já a amostra de NiFe2O4 demonstrou atividade catalítica semelhante as peroxidases naturais, oxidando o TMB na presença de H2O2 para formar TMBOX, que dá coloração azul a solução. Dessa forma, NiFe2O4 foi utilizado em um sensor colorimétrico para detecção de H2O2 e a calibração analítica revelou duas faixas lineares, uma entre 2,28 - 28,60 μM e a outra entre 28,60 μM - 114,20 μM. O limite de detecção (3/m) foi de 1,94 μM. Ambos os métodos apresentaram boa repetibilidade, com coeficiente de variação de 3,5% e 4% respectivamente. / This study presents the synthesis of two samples of nickel ferrite nanoparticles, termed C-NiFe2O4 and NiFe2O4, through a simple, low cost and environmentally friendly method. Morphological, structural, electronic, optical and magnetic studies were carried out with the aim of characterizing the properties of these materials, which allowed the application of colorimetric sensors for the detection of ascorbic acid and hydrogen peroxide. Through the thermal analysis of the precursors, it was possible to determine the decomposition temperature ranges, as well as the optimum temperature of formation of the nanoparticles. The sample NiFe2O4 is ferromagnetic and corresponds to a cubic phase of inverse spinel. The X-ray diffraction data, Mössbauer spectroscopy and the ionic model suggest the presence of a certain degree of substitution, having in its structure a divalent cation as a doping agent. The C-NiFe2O4 nanoparticles were used as catalysts in the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in acidic medium to form a blue solution without addition of another reagent. As a result, it was used as a colorimetric sensor for the detection of ascorbic acid, as it reduces the charge transfer complex, TMBOX, again to TMB. The analytical calibration showed a linear range between 1-20 μM for the concentration of ascorbic acid, with a detection limit (3 /m) of 0.93 μM. The determination of vitamin C supplements using the standard addition method showed the efficiency of the sensor to detect ascorbic acid in actual samples. Already NiFe2O4 sample demonstrated catalytic activity similar to natural peroxidases, oxidizing the TMB in the presence of H2O2 to form TMBOX, which gives blue coloration to the solution. Thus, NiFe2O4 was used in a colorimetric sensor to detect H2O2, and the analytical calibration revealed two linear ranges, one between 2.28 - 28.60 μM and the other between 28.60 μM - 114.20 μM. The detection limit (3 /m) was 1.94 μM. Both methods presented good repeatability, with a coefficient of variation of 3.5% and 4% respectively.

A avaliação de uma estrutura danificada por incêndios usualmente inicia por observações visuais do concreto, incluindo sua mudança de cor. A mudança de cor observada no concreto exposto a altas temperaturas persiste após seu resfriamento, constituindo-se em uma ferramenta importante para uma avaliação preliminar do nível de deterioração do concreto, pois essas mudanças podem ser relacionadas com as temperaturas as quais o mesmo foi exposto. Com o objetivo de avaliar as mudanças de cor e a degradação térmica de concretos potencialmente encontrados em estruturas no estado, foram estudados concretos de resistência convencional, moldados com materiais usualmente empregados no RS. Foram utilizadas três relações água/cimento, empregando-se o cimento CPIV, agregado graúdo granítico e basáltico. Os espécimes moldados foram submetidos às temperaturas de 200°C, 400°C, 600°C e 900°C, utilizando-se como base uma taxa de aquecimento baseada na curva padrão “Temperatura-Tempo”. Após o aquecimento, os espécimes foram resfriados lentamente, no interior do forno, e bruscamente, com aspersão de água. A degradação térmica do concreto foi avaliada através de ensaios de resistência à compressão, módulo de elasticidade e ultra-som. Para a avaliação das mudanças de cor foi utilizada metodologia colorimétrica, método mais consistente do que uma avaliação visual subjetiva. Observou-se queda de resistência à compressão e do módulo de elasticidade do concreto, conforme o aumento da temperatura de exposição. O ensaio de ultra-som mostrou-se bastante efetivo para detectar micro-fissuração do concreto, apresentando fatores de redução da velocidade de propagação mais semelhantes aos fatores de redução do módulo de elasticidade do que da resistência à compressão, mostrando a sensibilidade e potencialidade do método. As maiores diferenças colorimétricas foram obtidas nos concretos expostos às temperaturas mais altas, acima de 600°C, cujos níveis de percepção podem ser classificados como facilmente distinguíveis e muito grandes, o que pôde ser confirmado pela análise visual dos concretos, na qual foi observado o surgimento de uma cor amarelada. Considera-se, portanto, viável a identificação dos níveis de temperatura de exposição do concreto através das diferenças colorimétricas, especialmente para altas temperaturas de exposição, e, portanto, de maior interesse, já que levam a níveis de degradação mais acentuados. / The assessment of fire damaged concrete structures usually starts with visual observation of concrete, including his color change. The observed color change in high temperatures exposed concrete remains after cooling, consisting in a important tool for a preliminar assessment of concrete deterioration degree, therefore this changes could be related with the exposed temperatures. With the objective of assessing the color changes and thermal degradation of concretes potentially finding out in state’s structures, it was studied in this work normal-strength concretes made with materials usually finding in RS state. The concretes were made with three w/c ratio, with Pozzolanic cement (CPIV), granitic e basaltic coarse aggregate. The molded specimens were subjected to temperatures of 200°C, 400°C, 600°C e 900°C, with utilization of the standard fire curve (ISO 834). After heating, the specimens were allowed to a slow cool in the furnace, and quickly with water spread. The concrete thermal degradation was assessed with compressive strength test, elasticity modulus and pulse velocity measurements. The color changes was assessed by colorimetric methodology, a more consistent method than a subjective visual assessment. It was observed concrete loss of compressive strength and elasticity modulus with de increment of the exposure temperature. The pulse velocity test showed itself as a very effective for detecting concrete micro-cracks, showing reducing factors, as exposure temperature, more likely the elasticity modulus reducing factors than the compressive strength, indicating method sensibility and potentiality. The larger colorimetric differences were obtained on concretes exposed at higher temperatures, above 600°C, witch perceptions levels can be confirmed by concretes visual analyses, where was observed the appeared of a buff color. Can be consider, thus, viable to make the identification of concrete exposed temperatures levels through colorimetric differences, specially for higher exposure temperatures, end, thus, of major interest, since they conduce to more accentuated degradation levels.

Neste estudo apresenta-se a síntese de duas amostras de nanopartículas de ferrita de níquel, denominadas C-NiFe2O4 e NiFe2O4, através de um método simples, de baixo custo e ambientalmente amigável. Estudos morfológicos, estruturais, eletrônicos, ópticos e magnéticos foram realizados com o intuito de caracterizar as propriedades desses materiais para que possibilitassem, além de maior grau de conhecimento, sua aplicação como sensores colorimétricos para detecção de ácido ascórbico e peróxido de hidrogênio. Mediante a análise térmica dos precursores, foi possível determinar os intervalos de temperatura de decomposição, assim como a temperatura ótima de formação das nanopartículas. A amostra NiFe2O4 é ferromagnética e corresponde a uma fase cúbica de espinélio inverso. Os dados de difração de raios X, espectroscopia Mössbauer e o modelo iônico sugerem a presença de um certo grau de substituição, possuindo em sua estrutura um cátion divalente como agente dopante. As nanopartículas de C-NiFe2O4 foram utilizadas como catalisador na oxidação do 3,3',5,5'-tetrametilbenzidina (TMB) em meio ácido para formar uma solução azul sem adição de outro reagente. Como resultado foi utilizado como sensor colorimétrico para detecção de ácido ascórbico, visto que este reduz o complexo de transferência de carga, TMBOX, novamente para TMB. A calibração analítica apresentou uma faixa linear entre 1-20 μM para a concentração de ácido ascórbico, com limite de detecção (3/m) de 0,93 μM. A determinação em suplementos de vitamina C através do método de adição de padrão mostrou a eficiência do sensor para detectar ácido ascórbico em amostras reais. Já a amostra de NiFe2O4 demonstrou atividade catalítica semelhante as peroxidases naturais, oxidando o TMB na presença de H2O2 para formar TMBOX, que dá coloração azul a solução. Dessa forma, NiFe2O4 foi utilizado em um sensor colorimétrico para detecção de H2O2 e a calibração analítica revelou duas faixas lineares, uma entre 2,28 - 28,60 μM e a outra entre 28,60 μM - 114,20 μM. O limite de detecção (3/m) foi de 1,94 μM. Ambos os métodos apresentaram boa repetibilidade, com coeficiente de variação de 3,5% e 4% respectivamente. / This study presents the synthesis of two samples of nickel ferrite nanoparticles, termed C-NiFe2O4 and NiFe2O4, through a simple, low cost and environmentally friendly method. Morphological, structural, electronic, optical and magnetic studies were carried out with the aim of characterizing the properties of these materials, which allowed the application of colorimetric sensors for the detection of ascorbic acid and hydrogen peroxide. Through the thermal analysis of the precursors, it was possible to determine the decomposition temperature ranges, as well as the optimum temperature of formation of the nanoparticles. The sample NiFe2O4 is ferromagnetic and corresponds to a cubic phase of inverse spinel. The X-ray diffraction data, Mössbauer spectroscopy and the ionic model suggest the presence of a certain degree of substitution, having in its structure a divalent cation as a doping agent. The C-NiFe2O4 nanoparticles were used as catalysts in the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in acidic medium to form a blue solution without addition of another reagent. As a result, it was used as a colorimetric sensor for the detection of ascorbic acid, as it reduces the charge transfer complex, TMBOX, again to TMB. The analytical calibration showed a linear range between 1-20 μM for the concentration of ascorbic acid, with a detection limit (3 /m) of 0.93 μM. The determination of vitamin C supplements using the standard addition method showed the efficiency of the sensor to detect ascorbic acid in actual samples. Already NiFe2O4 sample demonstrated catalytic activity similar to natural peroxidases, oxidizing the TMB in the presence of H2O2 to form TMBOX, which gives blue coloration to the solution. Thus, NiFe2O4 was used in a colorimetric sensor to detect H2O2, and the analytical calibration revealed two linear ranges, one between 2.28 - 28.60 μM and the other between 28.60 μM - 114.20 μM. The detection limit (3 /m) was 1.94 μM. Both methods presented good repeatability, with a coefficient of variation of 3.5% and 4% respectively.