Nina D. Stepina

Total reflection X-ray fluorescence study of Langmuir monolayers on water surface

X-ray total external reflection fluorescence has been applied to detect an angular dependence of fluorescence yield modulated by evanescent/X-ray standing wave pattern from metal-rich organic monolayer alone on water surface. Theoretical consideration reveals that electric field intensity in a molecular monolayer is completely determined by an area per one molecule value that can be obtained from pressure-area isotherm. This allows getting an ion position inside a monolayer from the corresponding fluorescence angular dependence. The possibilities of the technique have been used at the SR beamline ID10B (ESRF) to characterize Langmuir monolayers of phthalocyanines and cyclolinear polyorganosiloxanes formed on air/water interface.

X-ray fluorescence methods for investigations of lipid/protein membrane models

The protective effect of the bisphosphonate drug xydiphone (K,Na-ethidronate) on membrane-bound enzyme damaged by lead ions has been studied. A protein/lipid film of Ca-ATPase/phosphatedylethanolamine deposited on a silicon substrate was used as a model system. The position of lead ions within the molecular film before and after the xydiphone treatment was determined using the total-reflection X-ray fluorescence method. This technique is based on the simultaneous measurement of the X-ray reflection and the yield of the fluorescence radiation excited by X-ray inelastic scattering. The possibility of directly locating lead ions is the main advantage of this approach. Xydiphone has been found to effectively eliminate lead ions that have been incorporated into Ca-ATPase molecules during a preliminary incubation in lead acetate solution. The lead ions that were bound at the sites of the Ca-ATPase attachment to the phospholipid monolayer have proved to be inaccessible for xydiphone. A preliminary incubation of Ca-ATPase in the xydiphone solution precluded the incorporation of lead ions into the protein.

Langmuir monolayers on water surface investigated by X-ray total reflection fluorescence

Abstract Langmuir monolayers of metal-rich phthalocyanines (Pc) and phospholipid at air/water interface have been studied by X-ray total reflection fluorescence at SR beam line ID 10B (ESRF). Experimental fluorescence angular dependences from “heavy” ions of a monolayer alone on water surface modulated by evanescent wave/X-ray standing wave pattern have been detected for the first time, are in good agreement with calculations and provide information about the position of metal ions in organic molecule with respect to water surface.

Total external reflection X-ray fluorescence analysis of protein-metal ion interactions in biological systems

This paper presents the results of an investigation into hemoglobin-based protein films that were formed on a liquid surface. X-ray standing wave measurements were performed at the ID 10 beamline of the European Synchrotron Radiation Facility (ESRF) and at the Langmuir station of the Kurchatov Synchrotron Radiation Source. It was found that the ability of the protein to bind metal ions is substantially increased due to the conformational rearrangements of protein macromolecules caused by various damaging effects. The elemental composition of protein preparations, which were isolated from children and adults with chronic metabolic diseases accompanied by endogenous intoxication, was analyzed. The results of the investigations offer evidence that an increase in the ligand-binding properties of the protein molecules, which was observed in model experiments using protein films, is a common trait and corresponds to in vivo processes accompanying metabolic disturbances in the body.

Ordering phenomena in composite monolayers and Langmuir–Blodgett films

Abstract The phenomenon of monolayer and Langmuir–Blodgett (LB) film stabilization via interaction with water soluble substrates like polyacrylic acid is studied. Hydrogen bonds (H-bonds) are shown to be responsible for the formation of composite monolayers based on tertiary amines and polyacid. An important influence of the contact time (before the compression) and amine amount spread on the subphase on the monolayer density is shown to be related to the diffusion of the polymer molecules up to the subphase surface. The structure of monolayers is found to depend on the amount of polyacid dissolved in water as well as on the order of introduction of the polymer into the water subphase (before or after compression). Composite monolayers based on the preprepared amine monolayer show the most dense and well aligned structure. This results in the formation of double layered LB films with highly periodic structures where polyacid amine residues are located between thin layers of H-bonded polyacid and aligned normally to the film plane. This binding of monolayers with water soluble polymers seems to be very important for the deposition of monolayers on the solid substrates and LB film preparation particularly when monolayers based on individual compounds cannot be transferred.

Composite gas-separating membranes with polymerized LB films

Abstract Composite gas-separating membranes were prepared by deposition of multibilayer diacetylene Langmuir-Blodgett (LB) films onto a poly(dimethylsiloxane) membrane. Local measurements of gas permeability with the surface resolution of 0.2 cm2 show that LB modification increases both membrane permeability to O2 and He gases and dispersion of local permeability over the membrane surface. A poly (diacetylene) LB film increases the selectivity of O 2 N 2 and He N 2 separation by 1.5 and 1.2 times, respectively. The potential of LB films in the improvement of gas separation is discussed.

DISTINCT EFFECT OF XENOBIOTICS ON THE METAL-BINDING PROPERTIES OF PROTEIN MOLECULES

The X-ray standing-wave method was applied to study the elemental composition and molecular organization of ordered protein films of alkaline phosphatase exposed to different xenobiotics (drug compounds, lead). Binding of metal ions from triply distilled water to protein molecules has been experimentally observed. Definite differences in the arrangement of impurity metal ions in the films have been established. The considerable enhancement of protein-metal interactions is attributed to partial rearrangement of the protein native structure, induced by xenobiotics.

Possibilities of surface-sensitive X-ray methods for studying the molecular mechanisms of interaction of nanoparticles with model membranes

The processes of structural rearrangement in a model membrane, i.e., an arachic acid monolayer formed on a colloidal solution of cerium dioxide or magnetite, are studied in situ in real time by the methods of X-ray standing waves and 2D diffraction. It is shown that the character of the interaction of nanoparticles with the monolayer is determined by their nature and sizes and depends on the conditions of nanoparticle synthesis. In particular, the structure formation in the monolayer–particle system is greatly affected by the stabilizer (citric acid), which is introduced into the colloidal solution during synthesis.

Organic monolayers and lipid–protein nanostructures on solid and liquid surfaces studied by TR-XSW technique

24 European Crystallographic Meeting, ECM24, Marrakech, 2007 Page s220 Acta Cryst. (2007). A63, s220 MS25 P01 Organic monolayers and lipid-protein nanostructures on solid and liquid surfaces studied by TR-XSW technique. S.I.Zheludeva, N.N.Novikova, N.D.Stepina, E.A.Yurieva,E.Yu.Tereschenko, O.V. Konovalov*, Shubnikov Institute of crystallography RAS, Moscow, Russia. * Europian Synchrotron radiation facility (ESRF), Grenoble, France.