Autor(es): Cruz, Diana Sofia de Melo Gonçalves da
Data: 2010
Identificador Persistente: http://hdl.handle.net/10451/3671
Origem: Repositório da Universidade de Lisboa
Assunto(s): Nanopartículas de prata; Biosíntese; Lúcia Lima; Erva de S. Roberto; Teses de mestrado - 2010
Tese de mestrado, Bioquímica, Universidade de Lisboa, Faculdade de Ciências, 2010
O objectivo principal deste estudo foi o desenvolvimento de um metodo biologico simples de sintese de nanoparticulas de prata (AgNPs) utilizando extractos aquosos de Lucia Lima e Erva de S. Roberto como agentes redutores. Investigou-se se factores como a temperatura e a concentracao de extracto influenciam a forma e a velocidade de formacao das AgNPs obtidas. Por ultimo tentou-se identificar o(s) composto(s) que levam a formacao e estabilizacao das AgNPs bem como a percentagem de reducao dos ioes Ag+. Ambos os extractos estudados podem ser eficientemente utilizados na sintese de AgNPs. Atraves da espectroscopia de UV-Vis foi possivel determinar a presenca de AgNPs esfericas pela obtencao de uma banda de absorcao a ~430 nm devido a uma banda de ressonancia plasmonica superficial (SPR) para o caso da sintese de AgNPs com extracto de Lucia Lima. Para o extracto de Erva de S. Roberto esta banda SPR sofre um desdobramento em duas bandas SPR, a primeira centrada entre 360 e 400 nm e a segunda centrada entre 420 e 520 nm, devido a obtencao de particulas esfericas e anisotropicas (nao esfericas). As formas e tamanhos das AgNPs foram verificados atraves de estudos de microscopia electronica (TEM), onde se observaram particulas esfericas e anisotropicas com tamanho entre 15 e 30 nm, nao variando significativamente com a concentracao de extracto ou temperatura de reaccao. Verificou-se que a velocidade de formacao das AgNPs aumenta com o aumento da temperatura de reaccao, onde a 25 °C se obtem AgNPs apos 3h de reaccao, atingindo uma estabilizacao as 24h, enquanto que a 95 °C a formacao das AgNPs requer apenas 15 min de reaccao. As particulas obtidas sao cristalinas e com crescimento preferencial (111), resultados determinados por estudos de difraccao de raios-X (XRD). Atraves de estudos de cromatografia liquida de alta pressao (HPLC) e espectroscopia de infravermelhos (FTIR-ATR) verificou-se que o extracto de Lucia Lima contem 4 compostos maioritarios, como verbascosido, isoverbascosido, lutelina-7-Odiglucuronido e crisoeriol-7-O-diglucuronido, e que o isoverbascosido e o principal responsavel pela formacao e estabilizacao das AgNPs. Para o caso do extracto de Erva de S. Roberto, este contem 5 compostos maioritarios, acido sinaptico glucuronisado, acido galico, acido elagico, quercitrina e cianidina (estudo efectuado anteriormente). No entanto, nao se conseguiu determinar o(s) composto(s) responsaveis pela formacao das AgNPs. Podemos sugerir que sera uma contribuicao de todos os compostos presentes no extracto, possivelmente da quercitrina e do acido galico. A taxa de reducao dos ioes Ag+ foi determinada por espectroscopia de absorcao atomica. Para o caso do extracto de Lucia Lima foi cerca de 45% para a sintese a 25 °C e 85% para a sintese a 95 °C. Para a Erva de S. Roberto a taxa de reducao do ioes Ag+ foi de 70% em ambas as temperaturas.
The main purpose of this study was the development of a simple biological method for the synthesis of silver nanoparticles (AgNPs) using aqueous leaf extracts of Lemon Verbena (Lippia citriodora) and Geranium (Geranium Robertianum) as reducing agents. We investigate the role of factors such as synthesis temperature and extract concentration that can influence the AgNPs synthesis rate, size and shape. At last we tried to identify the compounds that are responsible for AgNPs formation and stabilization as well as reduction rate of Ag+ ions. Both extracts that were studied can be efficiently used in the synthesis of silver nanoparticles. Through UV-Vis spectroscopy it was possible to verify the presence of spherical AgNPs due to the appearance of an absorption band at approximately 430 nm related with the surface plasmon ressonance band (SPR), for synthesis using Lemon Verbena extract. For the synthesis of AgNPs with Geranium extract, the SPR band suffers a split in two SPR bands, the first centered between 360 and 400 nm, and the second between 420 and 520 nm, due to the formation of spherical and anisotropic particles (non spherical). The shapes and sizes of AgNPs were assessed through TEM studies, and it was observed spherical and anisotropic particles with diameters sizes between 15 and 30 nm. Time, temperature and extract concentration did not influence significantly the shape and size of AgNPs. Althougth, the kinetic of AgNPs formation increased with the increase of temperature, were at 25 °C, AgNPs were obtained within 3h, with stabilization at 24h, and at 95 °C the AgNPs were detected after 15 minutes of reaction. The DRX studies confirmed that the silver particles are crystalline with preferential growth at (111). Through liquid chromatographic and infrared spectroscopic methods we determined that Lemon Verbena extract possesses four main compounds, verbascoside, isoverbascoside, luteolin- and chrysoeriol-7-O-diglucoronide, being isoverbascoside the compound responsible for AgNPs formation and stabilization. In the case of Geranium Robertianum contains five main compounds, synaptic acid, gallic acid, elagic acid, quercitrin and cyanidin but it was not possible to determine which compound is mainly responsible for AgNPs formation and stabilization, all compounds present in the extract contribute to the reduction of silver ions, and most probably the quercitrin and gallic acid play a key role on the synthesis of AgNPs. The reduction rate of Ag+ ions was determined by atomic absorption spectroscopy. For Lippia citriodora it was obtained 45% of ion reduction at 25 °C and 85% for synthesis at 95 °C. For Geranium Robertianum it was obtained 70% at both temperatures.
