RESUMO
The self-assembly of well-defined polypeptide-based diblock copolymers into micelles and vesicles is presented. The stimuli-responsive behavior of polypeptides to pH and ionic strength is used to produce stimuli-responsive nanoparticles with controlled size and shape. Results focusing on micelles and vesicles obtained from polypeptide-based diblock copolymers that are particularly promising for biomedical applications are detailed by means of static and dynamic light scattering analysis, UV circular dichroism, NMR and small angle neutron scattering experiments. Also systems able to form vesicles with a narrow size distribution at basic and acid pH going through a single molecule intermediate state are presented. These nanoparticles are particularly interesting for encapsulation and delivery purpose at a controlled pH.
Assuntos
Cápsulas/química , Lipossomos/química , Nanoestruturas/química , Peptídeos/química , Veículos Farmacêuticos/química , Polímeros/química , Concentração de Íons de Hidrogênio , Teste de Materiais , Micelas , Nanoestruturas/ultraestrutura , Tamanho da PartículaRESUMO
This paper discusses the self-assembly of block copolymers into vesicular morphology. After a brief state of art of the field, a system based on an amphiphilic poly(butadiene)- b-poly(-L-glutamic acid) (PB- b-PGA) diblock copolymer in aqueous solution is discussed in detail. The aggregation behavior of this block copolymer has been investigated by means of fluorescence spectroscopy, dynamic (DLS) and static (SLS) light scattering as well as transmission electron microscopy (TEM). The diblock copolymer was found to form well-defined vesicles in water. The size of these so-called polymersomes or peptosomes could be reversibly manipulated as a function of both pH and ion strength. Depending on the pH of the aqueous solution, the hydrodynamic radii of these vesicles were found to vary from 100 nm to 150 nm. By cross-linking the 1,2-vinyl double bonds present in the polybutadiene block, the ability to transform a transient supramolecular self-organized aggregate into a permanent "shape-persistent stimuli-responsive nanoparticle" has been demonstrated.
Assuntos
Butadienos/química , Cristalização/métodos , Ácido Glutâmico/química , Lipossomos/química , Nanotecnologia/métodos , Nanotubos/química , Polímeros/química , Elastômeros , Concentração de Íons de Hidrogênio , Lipossomos/síntese química , Substâncias Macromoleculares , Teste de Materiais , Conformação Molecular , Tamanho da Partícula , Polímeros/síntese química , Estimulação Química , Tensoativos/síntese química , Tensoativos/química , Água/químicaRESUMO
The kinetics of transport phenomena generated by an electric field and leading to the formation of density gradients in suspensions of charged colloidal silica were studied by using various electrodes. The rate of approach to a steady-state density gradient was found to be much higher when using metallic electrodes (Cu, Fe, and Pt) in comparison with graphite (C) electrodes. Nevertheless, the initial rate with C electrodes was substantially increased by the addition of hydroquinone-quinone because the redox reactions, necessary for electrode-electrolyte current transfer, occur at lower potential compared with the electrolysis of water. On the other hand, the products of oxidation of hydroquinone which accumulate in the system bring about an important decrease of the zeta potential of silica particles and progressive deceleration of their electrophoretic mobility. A detailed study was carried out, by using thin-layer isoperichoric focusing, UV-vis spectrophotometry, and voltamperometry, to explain the observed phenomena which can interfere in electric polarization or focusing field-flow fractionation. Copyright 2000 Academic Press.