title: Strong Static Magnetic Fields Increase the Gel Signal in Partially Hydrated DPPC/DMPC Membranes.
abstract: NIt was recently reported that static magnetic fields increase lipid order in the hydrophobic membrane core of dehydrated native plant plasma membranes [Poinapen, Soft Matter 9:6804-6813, 2013]. As plasma membranes are multicomponent, highly complex structures, in order to elucidate the origin of this effect, we prepared model membranes consisting of a lipid species with low and high melting temperature. By controlling the temperature, bilayers coexisting of small gel and fluid domains were prepared as a basic model for the plasma membrane core. We studied molecular order in mixed lipid membranes made of dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) using neutron diffraction in the presence of strong static magnetic fields up to 3.5 T. The contribution of the hydrophobic membrane core was highlighted through deuterium labeling the lipid acyl chains. There was no observable effect on lipid organization in fluid or gel domains at high hydration of the membranes. However, lipid order was found to be enhanced at a reduced relative humidity of 43%: a magnetic field of 3.5 T led to an increase of the gel signal in the diffraction patterns of 5%. While all biological materials have weak diamagnetic properties, the corresponding energy is too small to compete against thermal disorder or viscous effects in the case of lipid molecules. We tentatively propose that the interaction between the fatty acid chains' electric moment and the external magnetic field is driving the lipid tails in the hydrophobic membrane core into a better ordered state.
authors.affiliation: Department of Physics and Astronomy, McMaster University, Hamilton, ON, L8S 4M1, Canada. tangj43@mcmaster.ca.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Tang
authors.affiliation: Department of Physics and Astronomy, McMaster University, Hamilton, ON, L8S 4M1, Canada. alsoprj@mcmaster.ca.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Alsop
authors.affiliation: JCNS, Forschungszentrum Jülich, Outstation at ILL, 38042 Grenoble, France. schmalzl@ill.eu.
authors.forename: Karin
authors.initials: K
authors.lastname: Schmalzl
authors.affiliation: Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, ON, L8S 4K1, Canada. epand@mcmaster.ca.
authors.forename: Richard M
authors.initials: RM
authors.lastname: Epand
authors.affiliation: Department of Physics and Astronomy, McMaster University, Hamilton, ON, L8S 4M1, Canada. rheinstadter@mcmaster.ca.
authors.forename: Maikel C
authors.initials: MC
authors.lastname: Rheinstädter
keywords: biomagnetism; effect of magnetic fields on membranes; lipid membranes; membrane electric dipole moment; membrane magnetic moment; neutron diffraction