RESUMO
The effects of the polymerization temperature and of voltammetric cycling on the chain length and the resistivity of polypyrrole films are investigated. The studies provide further proof for the existence of at least two different types of polypyrrole, the so-called PPy I and PPy II. As the electropolymerization of conjugated systems in contrast to normal polymerization reactions is a fully activated process, the generation of these different types of PPy depends on experimental parameters such as temperature or formation potentials. UV-vis measurements demonstrate that PPy II comprises significantly shorter chains than PPy I (8-12 vs 32-64 units); moreover, film conductivity is found to increase with the fraction of PPy II. This fraction is changed via the polymerization temperature as well as by cyclic voltammetry, both of which can induce a metal-insulator transition. The counter-intuitive relationship between resistivity and chain length is interpreted in terms of disorder-dominated transport, in which the shorter chains of PPy II support the formation of delocalized electronic states, thereby increasing the localization length. Thus, our results are in agreement with recent broadband reflectivity measurements.
RESUMO
3,3'-Dimethoxy-2,2'-bipyrrole (1) and 4,4'-dimethoxy-2,2'-bipyrrole (2) were obtained in short sequences and good yields from N-benzyl-3-hydroxypyrrole-2,4-dicarboxylic acid. The key intermediate leading to 1 is an N-benzyl-3-methoxypyrrole, which is dimerized by lithiation and oxidation with NiCl(2). The formation of 2 is achieved by a classical Ullmann coupling of diethyl 1-benzyl-2-bromo-4-methoxypyrrole-3,5-dicarboxylate. The N-benzyl protection groups of 1 and 2 are cleaved under reducing conditions with sodium in liquid ammonia. Both isomeric bipyrroles are extremely sensitive toward air. Compound 1 has a very low oxidation potential of 0.09 V against AgCl but film formation hardly occurs. On the other hand, compound 2 with a potential of 0.35 V readily forms stable polypyrrole films with anodic waves at -0.51 and -0.35 V and a cathodic wave at -0.77 V, the lowest potential ever observed for a p-doped polymer.
RESUMO
Géis de fase cúbica de monoleína e água têm sido propostos como sistemas de liberação de fármacos com diferentes características, incluindo moléculas protéicas e peptídicas. O presente trabalho estudou a incorporação de lactoferrina, usada como molécula protéica modelo em várias concentrações em géis de fase cúbica de monoleína e água. A influência da lactoferrina nos géis de monoleína/água foi avaliada por microscopia de luz polarizada e estudo de suas propriedades reológicas, asssim como estudos de liberação in vitro foram realizados. A fase cúbica foi observada na presença da lactoferrina sendo que esta proteína não modificou as transições de fase dos géis, quando observados ao microscópio de luz polarizada...
