The high-intensity reflectometer of the Jülich Centre for Neutron Science: MARIA.

MARIA (magnetism reflectometer with high incident angle) is a world class vertical sample reflectometer dedicated to the investigation of thin films in the fields of magnetism, soft matter and biology. The elliptical vertically focusing guide allows one to measure small samples with a typical size of 1 × 1 cm very efficiently. The double-bounce polarizer and the in situ pumped 3He SEOP (spin-exchange optical pumping) neutron spin filter cell for analysing the polarization of the reflected neutron beam can be moved into the beam in seconds. The polarized flux of MARIA amounts to 5 × 107 n (s cm2)-1 at the sample position with a horizontally collimated beam of 3 mrad, a wavelength of λ = 4.5 Šand a wavelength resolution of Δλ/λ = 10%. In the non-polarized mode a flux of 1.2 × 108 n (s cm2)-1 is achieved in this configuration. MARIA is also capable of grazing-incidence small-angle neutron scattering measurements, using a pinhole collimation with two four-segment slits and an absorber that prevents the focusing of the elliptical guide in the vertical direction.

Studies on the adsorption and desorption of mitoxantrone to lauric acid/albumin coated iron oxide nanoparticles.

A rational use of superparamagnetic iron oxide nanoparticles (SPIONs) in drug delivery, diagnostics, and other biomedical applications requires deep understanding of the molecular drug adsorption/desorption mechanisms for proper design of new pharmaceutical formulations. The adsorption and desorption of the cytostatic Mitoxantrone (MTO) to lauric acid-albumin hybrid coated particles SPIONs (SEONLA-HSA) was studied by Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), surface titration, release experiments and small-angle neutron and X-ray scattering. Such MTO-loaded nanoparticles have shown very promising results in in vivo animal models before, while the exact binding mechanism of the drug was unknown. SEONLA-HSA formulations have shown better stability under drug loading in comparison with uncoated nanoparticle and sustainable drug release to compare with protein solution. Adsorption of MTO to SEONLA-HSA leads to decreasing of absolute value of zeta potential and repulsive interaction among particles, which points to the location of separate molecules of MTO on the outer surface of LA-HSA shell.

The low resolution structure of ApoA1 in spherical high density lipoprotein revealed by small angle neutron scattering.

Spherical high density lipoprotein (sHDL), a key player in reverse cholesterol transport and the most abundant form of HDL, is associated with cardiovascular diseases. Small angle neutron scattering with contrast variation was used to determine the solution structure of protein and lipid components of reconstituted sHDL. Apolipoprotein A1, the major protein of sHDL, forms a hollow structure that cradles a central compact lipid core. Three apoA1 chains are arranged within the low resolution structure of the protein component as one of three possible global architectures: (i) a helical dimer with a hairpin (HdHp), (ii) three hairpins (3Hp), or (iii) an integrated trimer (iT) in which the three apoA1 monomers mutually associate over a portion of the sHDL surface. Cross-linking and mass spectrometry analyses help to discriminate among the three molecular models and are most consistent with the HdHp overall architecture of apoA1 within sHDL.

Congruency between biophysical data from multiple platforms and molecular dynamics simulation of the double-super helix model of nascent high-density lipoprotein.

The predicted structure and molecular trajectories from >80 ns molecular dynamics simulation of the solvated Double-Super Helix (DSH) model of nascent high-density lipoprotein (HDL) were determined and compared with experimental data on reconstituted nascent HDL obtained from multiple biophysical platforms, including small angle neutron scattering (SANS) with contrast variation, hydrogen-deuterium exchange tandem mass spectrometry (H/D-MS/MS), nuclear magnetic resonance spectroscopy (NMR), cross-linking tandem mass spectrometry (MS/MS), fluorescence resonance energy transfer (FRET), electron spin resonance spectroscopy (ESR), and electron microscopy. In general, biophysical constraints experimentally derived from the multiple platforms agree with the same quantities evaluated using the simulation trajectory. Notably, key structural features postulated for the recent DSH model of nascent HDL are retained during the simulation, including (1) the superhelical conformation of the antiparallel apolipoprotein A1 (apoA1) chains, (2) the lipid micellar-pseudolamellar organization, and (3) the solvent-exposed Solar Flare loops, proposed sites of interaction with LCAT (lecithin cholesteryl acyltransferase). Analysis of salt bridge persistence during simulation provides insights into structural features of apoA1 that forms the backbone of the lipoprotein. The combination of molecular dynamics simulation and experimental data from a broad range of biophysical platforms serves as a powerful approach to studying large macromolecular assemblies such as lipoproteins. This application to nascent HDL validates the DSH model proposed earlier and suggests new structural details of nascent HDL.