Interactions of the AT1 antagonist valsartan with dipalmitoyl-phosphatidylcholine bilayers.

Valsartan is a marketed drug with high affinity to the type 1 angiotensin (AT1) receptor. It has been reported that AT1 antagonists may reach the receptor site by diffusion through the plasma membrane. For this reason we have applied a combination of differential scanning calorimetry (DSC), Raman spectroscopy and small and wide angle X-ray scattering (SAXS and WAXS) to investigate the interactions of valsartan with the model membrane of dipalmitoyl-phosphatidylcholine (DPPC). Hence, the thermal, dynamic and structural effects in bulk as well as local dynamic properties in the bilayers were studied with different valsartan concentrations ranging from 0 to 20 mol%. The DSC experimental results showed that valsartan causes a lowering and broadening of the phase transition. A splitting of the main transition is observed at high drug concentrations. In addition, valsartan causes an increase in enthalpy change of the main transition, which can be related to the induction of interdigitation of the lipid bilayers in the gel phase. Raman spectroscopy revealed distinct interactions between valsartan with the lipid interface localizing it in the polar head group region and in the upper part of the hydrophobic core. This localization of the drug molecule in the lipid bilayers supports the interdigitation view. SAXS measurements confirm a monotonous bilayer thinning in the fluid phase, associated with a steady increase of the root mean square fluctuation of the bilayers as the valsartan concentration is increased. At high drug concentrations these fluctuations are mainly governed by the electrostatic repulsion of neighboring membranes. Finally, valsartans' complex thermal and structural effects on DPPC bilayers are illustrated and discussed on a molecular level.

Mesostructured silica aerosol particles: comparison of gas-phase and powder deposit X-ray diffraction data.

We report on the characterization of mesostructured aerosol silica particles in the gas phase using in situ synchrotron small-angle X-ray scattering (SAXS) in order to unveil the influence of the basic production parameters. The investigated system was based on tetraethylorthosilicate (TEOS) as the inorganic precursor and on cetyltrimethyl-ammonium bromide (CTAB) as the surfactant. The heating temperature, surfactant to silicate ratio, and particle flow rate were thoroughly investigated, and for this purpose, an in-house-built aerosol reactor equipped with a special X-ray observation chamber was used. Complementary fine structural analysis was applied on dried deposits of the silica aerosols comprising direct Fourier transforms as well as simple two-phase model fits. This resulted in robust estimates for the silica wall thickness and surfactant core radius of the hexagonally ordered mesostructure. The particle shape and size distribution were examined by scanning electron microscopy (SEM). The quality of the inner nanostructure was revealed from an analysis of the peak width. The comparison of data from the gas phase and powder deposit shows that, in general, slower drying conditions (heating temperature about 80 °C) and a medium surfactant to Si ratio (about 0.14) lead to nanostructures of the best quality in terms of well-defined long-range organization.

Procedures for cryogenic X-ray ptychographic imaging of biological samples.

Biological sample-preparation procedures have been developed for imaging human chromosomes under cryogenic conditions. A new experimental setup, developed for imaging frozen samples using beamline I13 at Diamond Light Source, is described. This manuscript describes the equipment and experimental procedures as well as the authors' first ptychographic reconstructions using X-rays.