RESUMO
We describe a new synthetic approach to regioregular monodisperse oligo(3-alkylthiophene)s allowing for simple separation of regioregular material in gram quantities. The number of repeat units follows the Fibonacci numbers up to a length of 21. In a small adaption of this approach, introduction of a protecting group was used to synthesize an oligo(3-hexylthiophene) with 36 repeating units, the longest regioregular 3-hexylthiophene oligomer synthesized to date.
RESUMO
Conjugated polymer chains have many degrees of conformational freedom and interact weakly with each other, resulting in complex microstructures in the solid state. Understanding charge transport in such systems, which have amorphous and ordered phases exhibiting varying degrees of order, has proved difficult owing to the contribution of electronic processes at various length scales. The growing technological appeal of these semiconductors makes such fundamental knowledge extremely important for materials and process design. We propose a unified model of how charge carriers travel in conjugated polymer films. We show that in high-molecular-weight semiconducting polymers the limiting charge transport step is trapping caused by lattice disorder, and that short-range intermolecular aggregation is sufficient for efficient long-range charge transport. This generalization explains the seemingly contradicting high performance of recently reported, poorly ordered polymers and suggests molecular design strategies to further improve the performance of future generations of organic electronic materials.
RESUMO
BACKGROUND: Poly(ethylene imine) (PEI) is a widely used transfection reagent for mammalian cells, but in vivo application of PEI 25 kDa is restricted by its toxicity. Low molecular weight (LMW) PEI is less toxic, but also less efficient than its high molecular weight equivalent, and prone to aggregation. METHOD: A set of polymers was synthesized by coupling poly(ethylene glycol) (PEG) that contained either C(16/18) -chains (Cx-EO) or butyl-poly(propylene oxide)-co-poly(ethylene glycol) (ButPP). Critical micelle concentration (CMC) was determined for copolymers. Polyplexes were characterized by DNA binding ability, polyplex size and aggregation, hemolysis, and cytotoxicity. Transfection efficiency was tested in vitro and in vivo in mouse lungs. RESULTS: Copolymers formed stable complexes with DNA, and showed enhanced complex stability in isotonic solution for at least 1 h. CMC was determined for Cx-EO-PEI 4.7 and 8.3 at 0.0019 and 0.0037 mM, respectively; membrane activity in a haemolysis assay was demonstrated for ButPP-PEI: both factors possibly enhance endosomal escape effect after PEGylation. IC(50) values of all synthesized polymers were in the range 6-33 ng/ml. Transfection efficiency of unmodified LMW-PEIs was equivalent or better than that of PEI 25 as a result of aggregation in vitro. Cells treated with polyplexes of amphiphilic polymers showed reduced transfection compared to PEI 25. After instillation in mouse lungs, highest transfection efficiency was demonstrated with Cx-EO copolymer of lowest molecular weight PEI. CONCLUSIONS: A new set of polymers with low toxicity and high stability was synthesized, which contains promising candidates for pulmonary gene transfer, as documented by in vivo experiments in mice.
