RESUMO
Nanoparticles with a mean hydrodynamic radius of 16 nm and low polydispersity (P.I. = 0.1) were spontaneously formed by the complexation of poly(ethylene oxide)-block-poly(L-glutamate) (PEO-b-PLGlu) with diminazene. Only one of two possible binding sites of each diminazene molecule was involved in complexation. As determined by UV-vis difference spectra measurements, the complex binding constant is on the order of 1-2 x 10(4) M(-1). Circular dichroism measurements showed that the highly water-soluble diminazene can induce and stabilize the alpha-helical secondary structure of a PLGlu block.
RESUMO
Superparamagnetic iron oxide particles (SPIO) of maghemite were prepared in aqueous solution and subsequently stabilized with polymers in two layer-by-layer deposition steps. The first layer around the maghemite core is formed by poly(ethylene imine) (PEI), and the second one is formed by poly(ethylene oxide)-block-poly(glutamic acid) (PEO-PGA). The hydrodynamic diameter of the particles increases stepwise from D(h) = 25 nm (parent) via 35 nm (PEI) to 46 nm (PEI plus PEO-PGA) due to stabilization. This is accompanied by a switching of their zeta-potentials from moderately positive (+28 mV) to highly positive (+50 mV) and finally slightly negative (-3 mV). By contrast, the polydispersity indexes of the particles remain constant (ca. 0.15). Mössbauer spectroscopy revealed that the iron oxide, which forms the core of the particles, is only present as Fe(III) in the form of superparamagnetic maghemite nanocrystals. The magnetic domains and the maghemite crystallites were found to be identical with a size of 12.0 +/- 0.5 nm. The coated maghemite nanoparticles were tested to be stable in water and in physiological salt solution for longer than 6 months. In contrast to novel methods for magnetic nanoparticle production, where organic solvents are necessary, the procedure proposed here can dispense with organic solvents. Magnetic resonance imaging (MRI) experiments on living rats indicate that the nanoparticles are useful as an MRI contrast agent.