title: Monitoring x-ray beam damage on lipid films by an integrated Brewster angle microscope/x-ray diffractometer.
abstract: We describe an integrated Brewster angle microscope (BAM), Langmuir trough, and grazing incidence x-ray diffraction assembly. The integration of these three techniques allows for the direct observation of radiative beam damage to a lipid monolayer at the air-water interface. Although beam damage has been seen in x-ray measurements, it has not been directly observed in situ at the micron scale. Using this integrated assembly, we examined the effects of radiative beam damage on Langmuir monolayers of 1,2-dimyristoyl-sn-glycero-3-[phospho-L-serine] (DMPS), 1:1 DMPS:1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, and 1:1 DMPS:1,2-dioleoyl-sn-glycero-3-phosphocholine held at a constant surface pressure. For constant surface pressure experiments, we observed a marked decrease in the surface area of the film upon exposure to the beam due to photodissociation. For a condensed lipid film, a change in refractive index of the film was observed post-beam-exposure, indicating areas of damage. For DMPS in an oxygenated environment, the Bragg peak intensity decreased with beam exposure. In mixed monolayer systems, with saturated and unsaturated lipids, an increase in the number of small saturated lipid domains was seen as the unsaturated lipid was preferentially damaged and lost from the monolayer. We show that BAM is a highly effective technique for in situ observation of the effects of radiative damage at the air/water interface during a synchrotron experiment.
authors.affiliation: Department of Chemistry, The University of Chicago, Chicago, Illinois 60637, USA.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Danauskas
authors.forename: Maria K
authors.initials: MK
authors.lastname: Ratajczak
authors.forename: Yuji
authors.initials: Y
authors.lastname: Ishitsuka
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Gebhardt
authors.forename: David
authors.initials: D
authors.lastname: Schultz
authors.forename: Mati
authors.initials: M
authors.lastname: Meron
authors.forename: Binhua
authors.initials: B
authors.lastname: Lin
authors.forename: Ka Yee C
authors.initials: KY
authors.lastname: Lee
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D008051:Lipid Bilayers / Q000737:chemistry* / Q000528:radiation effects*; D008422:Materials Testing / Q000295:instrumentation* / Q000379:methods; D008567:Membranes, Artificial; D008859:Microscopy, Polarization / Q000295:instrumentation* / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013048:Specimen Handling / Q000295:instrumentation*; D018511:Systems Integration; D014961:X-Ray Diffraction / Q000295:instrumentation* / Q000379:methods; D014965:X-Rays
chemical_list: D008051:Lipid Bilayers; D008567:Membranes, Artificial