Biomedical subjects

M J Bedzyk

Publications and source records attributed to M J Bedzyk.

5 recordsLinked to original sources

PubMed1994

Lattice location of trace elements within minerals and at their surfaces with X-ray standing waves.

The x-ray standing waves generated by dynamical Bragg diffraction were used to directly measure lattice locations of trace elements within and at the surface of a mineral single crystal. These high-precision measurements were made on natural Iceland spar calcite cleaved along the (1014) plane and reacted with a dilute aqueous lead solution. Within the bulk crystal, naturally occurring trace manganese was found within (1014) planes, consistent with its substitution for calcium. At the crystal surface, sorbed lead was found to be highly ordered and mostly within (1014) planes. This demonstrates a powerful application of synchrotron radiation in the earth and environmental sciences.

Calcium↗

PubMed1992

Resonance-enhanced x-rays in thin films: a structure probe for membranes and surface layers.

An x-ray resonance effect in an organic thin film on an x-ray reflecting mirror is reported. The resonance effect is the result of interference between reflected and refracted x-rays at the air-organic thin film interface and occurs at incident angles slightly above the critical angle of the film. In excellent agreement with theory, the primary resonant x-ray electric field that is confined in the organic thin film is approximately 20 times as intense as the electric field of the incident beam when measured at a position close to the center of the film. Resonance-enhanced x-rays can be used to characterize the internal structure of Langmuir-Blodgett thin film membranes. This effect may also find use in x-ray-based thin film devices and in the structural analysis of adlayers and surfaces that have thus far proved difficult, if not impossible, to study because of sensitivity limitations.

Electron Probe Microanalysis↗

PubMed1991

Structural studies of membranes and surface layers up to 1,000 A thick using X-ray standing waves.

The X-ray standing wave (XSW) method, developed in the 1960s, was used originally to determine heavy atom positions in and on silicon and germanium single crystals. An X-ray standing wave generated by the interference of coherent incident and reflected beams excites X-ray fluorescence from the heavy atom, the intensity of which as a function of incident angle provides an indication of the atom's distance from the X-ray reflecting surface. The availability of X-ray mirrors and the ability to prepare layered synthetic microstructures has made possible the study of biologically relevant structures using the XSW technique on length scales of typically tens to hundreds of ångströms, allowing heavy atoms in such structures to be located with ångström or subångström resolution. Many model biological systems (such as Langmuir-Blodgett films, which mimic membranes) require access to still larger scales, but it is not obvious that an XSW will remain coherent over such length scales. Here we report studies of a lipid multilayer system using the XSW method, in which we have been able to locate the metal atoms in a zinc arachidate bilayer with ångström resolution at a distance of almost 1,000 A above the surface of a gold mirror. Our results indicate that the XSW technique should be useful for structural studies of supramolecular aggregates, receptor-ligand interactions and multi-membrane stacks, in which length scales of this order are encountered.

Arachidonic Acids↗

PubMed1990

Diffuse-double layer at a membrane-aqueous interface measured with x-ray standing waves.

The ion distribution in an electrolyte solution in contact with a charged polymerized phospholipid membrane was directly measured with long-period x-ray standing waves. The 27-angstrom-thick lipid monolayer was supported on a tungsten/silicon mirror. X-ray standing waves were generated above the mirror surface by total external reflection of a 9.8-kiloelectron volt x-ray beam from a synchrotron undulator. The membrane surface, which contained negatively charged phosphate headgroups, was bathed in a dilute ZnCl2 solution. The concentration of Zn2+ in the condensed layer at the membrane surface and the Zn2+ distribution in the diffuse layer were measured as a function of headgroup charge. The Debye length of the diffuse layer varied between 3 and 58 angstroms. The results qualitatively agree with the Gouy-Chapman-Stern model.

Chemical Phenomena↗

PubMed1988

X-ray standing waves: a molecular yardstick for biological membranes.

Structural information on an atomic scale has been obtained for a Langmuir-Blodgett (LB) trilayer system by means of long-period x-ray standing waves. The LB trilayer of zinc and cadmium arachidate was deposited on a layered synthetic microstructure (LSM) consisting of 200 tungsten/silicon layer pairs with a 25 A period. A 30 A thermally induced inward collapse of the zinc atom layer that was initially located in the LB trilayer at 53 A above the LSM surface has been observed. The mean position and width of the zinc atom layer was determined with a precision of +/- 0.3 A.

Membranes↗