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Estudo da interacção do decavanadato com bicamadas lipídicas
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Abstract(s)
O vanádio é um metal de transição de grande interesse nas áreas da química,
bioquímica, bem como das ciências da vida e da saúde, em consequência de se terem
descoberto acções benéficas dos compostos contendo vanádio, com acção anti-diabética
e anti-cancerígena, a realçar de entre outros efeitos farmacológicos. A espécie
decamérica do vanádio, também designada decavanadato, tem sido alvo de muitos
estudos no desenvolvimento de fármacos no combate dessas doenças. Porém, tendo em
conta que o decavanadato é uma espécie bastante estável a pH ácido e estruturalmente
compacta, tem gerado alguma controvérsia sobre o modo como este actua ou interage
com as membranas biológicas. Por conseguinte, a elucidação da interacção do
oligómero decamérico de vanádio com modelos de membranas biológicas, reveste-se de
importância acrescida para a compreensão dos mecanismos subjacentes às acções como
anti-diabéticos ou anti-cancerígenos. Os lipossomas são o sistema de membrana que
melhor simula os estudos envolvendo membranas biológicas. Tendo em atenção a sua
dimensão, as vesículas unilamelares grandes (LUV – large unilamelar vesicles), são os
mais indicados para efectuar este estudo. Sendo assim, o objectivo deste trabalho
experimental, foi o de verificar se o decavanadato interage com bicamadas lipídicas
unilamelares.
Determinou-se o tempo de desoligomerização do decavanadato em água, de
modo a estabelecer a escala temporal possível para os estudos de interacção. Verificouse
que o decavanadato é mais estável quanto mais baixo for o pH e a temperatura, e
quanto maior for a concentração de vanádio em solução. A partir dos resultados obtidos
é possível verificar que a 25ºC, o decavanadato (1mM) a pH 5.84, o valor médio para o
tempo de meia-vida é de 22h45±1h45, enquanto a pH 7.53 o tempo de meia-vida médio
é somente de 7h30±1h30.
Para se poder verificar se o decavanadato interage com bicamadas lipídicas, é
necessário utilizar uma sonda de fluorescência que o decavanadato consiga quenchar,
neste caso será o 7-nitrobenz-2-oxa-1,3-diazole-4-yl (NBD). Verificou-se então que a
constante de quenching do NBD pelo decavanadato em água é 1,677×1012 M−1s−1. Em
seguida inseriu-se a sonda lipídica em LUV e observou-se que, também neste caso, o
decavanadato é capaz de quenchar a sonda NBD, sendo a constante de quenching 7,20×1010 M−1s−1. Desta forma, a ocorrência de quenching comprova que o
decavanadato interage com bicamadas lipídicas zwiteriónicas.
Vanadium is a transition metal of great interest in the areas of chemistry, biochemistry, as well as in the for health and life sciences, as resulting from benefic action of vanadium containing compounds displaying anti-diabetic and anti-cancer actions, standing out from other pharmacological effects. The decameric specie of vanadium, termed decavanadate, has been the target of many studies in the development of drugs to fight these sicknesses. However, considering that decavanadate is a very stable specie in acid pH and structurally compact, there has been some controversy about the way it acts or interacts with biological membranes. Therefore, the comprehension of the interaction between the decameric oligomers and biological model membranes is of great importance to the understanding of the mechanisms underlying to the anti-diabetic and anti-cancer actions. The liposomes are the membrane systems that best simulate biological membranes. Considering their dimension, large unilamellar vesicles (LUV), are the best indicated to pursue this study. The main goal of this experimental work was to verify if decavanadate interacts with unilamellar lipid bilayers. It was determined the deoligomerization characteristic time of the decavanadate in water, so that there could be established a temporal scale to use in the interaction studies. The result of this study established that the decavanadate is more stable at a low pH and temperature, and at a high concentration of vanadium in solution. Analyzing the results, it is fair to say that at 25ºC, and decavanadate (1mM) at pH=5.84, the average value of half-life time is 22h45±1h45, while at pH=7.53 the half-life time is only 7h30±1h30. To verify if decavanadate interacts with lipid bilayers, it is necessary to use a fluorescence probe that can be quenched by this vanadium oligomer. The chosen probe was 7-nitrobenz-2-oxa-1,3-diazole-4-yl (NBD). The value determined for of the quenching constant of the NBD in water solution is 1.677×1012 M−1s−1. The next procedure was the insertion of the probe in LUV, it was also observed that the decavanadate is capable of quenching the NBD probe, being the quenching constant found 7.20×1010 M−1s−1. Therefore, the occurrence of quenching proves that the decavanadate interacts with zwitterionic lipid bilayers.
Vanadium is a transition metal of great interest in the areas of chemistry, biochemistry, as well as in the for health and life sciences, as resulting from benefic action of vanadium containing compounds displaying anti-diabetic and anti-cancer actions, standing out from other pharmacological effects. The decameric specie of vanadium, termed decavanadate, has been the target of many studies in the development of drugs to fight these sicknesses. However, considering that decavanadate is a very stable specie in acid pH and structurally compact, there has been some controversy about the way it acts or interacts with biological membranes. Therefore, the comprehension of the interaction between the decameric oligomers and biological model membranes is of great importance to the understanding of the mechanisms underlying to the anti-diabetic and anti-cancer actions. The liposomes are the membrane systems that best simulate biological membranes. Considering their dimension, large unilamellar vesicles (LUV), are the best indicated to pursue this study. The main goal of this experimental work was to verify if decavanadate interacts with unilamellar lipid bilayers. It was determined the deoligomerization characteristic time of the decavanadate in water, so that there could be established a temporal scale to use in the interaction studies. The result of this study established that the decavanadate is more stable at a low pH and temperature, and at a high concentration of vanadium in solution. Analyzing the results, it is fair to say that at 25ºC, and decavanadate (1mM) at pH=5.84, the average value of half-life time is 22h45±1h45, while at pH=7.53 the half-life time is only 7h30±1h30. To verify if decavanadate interacts with lipid bilayers, it is necessary to use a fluorescence probe that can be quenched by this vanadium oligomer. The chosen probe was 7-nitrobenz-2-oxa-1,3-diazole-4-yl (NBD). The value determined for of the quenching constant of the NBD in water solution is 1.677×1012 M−1s−1. The next procedure was the insertion of the probe in LUV, it was also observed that the decavanadate is capable of quenching the NBD probe, being the quenching constant found 7.20×1010 M−1s−1. Therefore, the occurrence of quenching proves that the decavanadate interacts with zwitterionic lipid bilayers.
Description
Relatório de estágio de licenciatura, Bioquímica, Faculdade de Ciências e Tecnologia da Universidade do Algarve, 2009
Keywords
Decavanadato Biomembranas