Orientation of the DMPC unilamellar vesicle system in the magnetic field: SANS study

We present the results of a small angle neutron scattering investigation on a unilamellar DMPC vesicle system during the application of a magnetic field. The presence of the strong magnetic field, elongate the vesicles along the field and cause a change in the shape of the particles. This circumstance is caused by the presence of a small anisotropy in the magnetic susceptibility parallel and perpendicular to the long axes of phospholipid molecules. Our obtained results indicate the importance of some relevant parameters such as the vesicle dimension and concentrations. More specifically under the action of a strong magnetic field (H = 4 T) small (50 nm diameter) vesicles show a shape modification from sphere to ellipsoid. On the other hand the increase in vesicle dimensions (up to 200 nm diameter) as well as at the higher DMPC concentration (i.e. C = 5% w/w) vesicle magnetic deformation is hindered. The main structural modification of the system has been explained as the effect of increasing of the effective "steric stability" for the system against the deforming action of an external perturbation. The use of magnetic forces can be seen as a promising tool for non-invasive manipulation of biological membranes and supramolecular assemblies in solutions. (C) 2007 Elsevier B.V. All rights reserved.