Obtenção de géis eletroativos a partir de polipirrol e pectina cítrica

Abstract

Resumo: Neste trabalho foram preparados hidrogeis a partir de pectina citrica e polipirrol (PPy). Foram estudas comparativamente a pectina bruta (PND) e dialisada (PD). A caracterizacao das amostras revelou diferencas em sua massa molar media, polidispersividade, teor proteico e grau de metoxilacao. A amostra PD e mais metoxilada, menos polidispersa, tem maior massa molar media e teor proteico. Em consequencia, as propriedades em solucao sao diferentes, sendo que a PD e mais viscosa. Tanto a PND quanto a PD foram empregadas como agente de estabilizacao na sintese de polipirrol em meio aquoso. A formacao do polipirrol foi acompanhada por UV-Vis pelo crescimento da intensidade das bandas em 450 e 800 nm. O potencial zeta das particulas de PPy estabilizadas por PND (PND-PPy) e por PD (PD-PPy) e negativo (¡V 25 mV), justificando a estabilidade das dispersoes, por no minimo um mes. A partir das amostras PND-PPy e PD-PPy, foram preparados hidrogeis, por reticulacao da matriz pectica com CaCl2. Geis preparados na ausencia de PPy foram tambem estudados comparativamente. Por espectroscopia Raman, evidenciou-se que o PPy encontra-se mais oxidado na presenca de PND em comparacao a PD. Ainda, as propriedades de perda de agua (sinerese) a 25 „aC e 1„aC demonstraram o melhor desempenho dos geis empregando PND e na presenca de PPy. Quando imersos em fluido de pH simulado gastrico (FSG, pH 1,2) e intestinal (FSI, pH 6,8), os geis na presenca de PPy intumesceram ate 25% da sua massa em pH 1,2 e perderam completamente sua integridade fisica em pH 6,8. As caracterizacoes eletroquimicas por voltametria ciclica e espectroscopia de impedancia eletroquimica mostraram que os hidrogeis formados a partir de pectina e polipirrol sao eletroativos e condutores. Visando futuras aplicacoes, o sistema que apresentou a melhor combinacao de propriedades foi o obtido com pectina citrica dialisada e polipirrol (PND-PPy). Palavras-chave: pectina, polipirrol, hidrogel, dialise e eletroatividade.

Abstract: Hydrogels were prepared from citric pectin and polypyrrole (PPy). Raw pectin (PND) and dialysed pectin (PD) were comparatively studied. The characterization of both samples revealed differences in their molar weight, polydispersity, protein content and methoxylation degree. The sample PD has a higher methoxylation degree, is less polydisperse, has a higher molar weight and protein content. As a consequence, the solution properties of both samples differ, being the PD the more viscous. Both PND and PD were employed as stabilizers during the synthesis of polypyrrole in aqueous medium. The formation of PPy was accompanied through UV-Vis by the increase in the intensity of the bands at 450 and 800 nm. Zeta potential of the as-formed particles, stabilized by either PND (PND-PPy) or PD (PD-PPy) resulted negative (- 25 mV), explaining the high stability of the dispersions for at least one month. The dispersions, PND-PPy and PD-PPy, were used to prepare hydrogels by crosslinking with CaCl2. For comparative purposes, gels in the absence of PPy were also prepared. By Raman spectroscopy it was evidenced that PPy are more oxidized in the presence of PND, when compared to PD. Also, the loss of water behavior (syneresis) at 1 „aC and 25 „aC demonstrated that the better results were obtained with PD in the presence of PPy. When immersed in simulated gastric (FSG, pH 1.2) and intestinal (FSI, pH 6.8) pHs, the hydrogels prepared with PPy have swollen up to 25 wt% in pH 1.2 and have completely lost their physical integrity at pH 6.8. The electrochemical characterization by cyclic voltammetry and electrochemical impedance spectroscopy showed that hydrogels formed from pectin and polypyrrole are electroactive and present conductivity. Prospecting future applications, the system that presented the better combination of properties was PND-PPy. Keywords: pectin, polypyrrole, hydrogel, dialysis and electroactivity.