S.I. Zheludeva

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.

X-ray total external reflection fluorescence study of LB films on solid substrate

The distribution of heavy ions inside a thin LB film and the structure perfection of organic layers have been studied by registering fluorescence excited by X-ray evanescent/standing wave fields under conditions of total external reflection. The possibility of the application of new complicated artificial multilayer systems as substrates for structure characterization of LB films deposited on them was revealed.

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 reflection X-ray fluorescence study of organic nanostructures ☆

Abstract X-ray scattering techniques based on total external fluorescence study and development of X-ray standing wave method are presented and used for characterization of organic nanostructure Langmuir–Blodgett films of fatty acid salts and phospholipids. Spectral selectivity of data obtained allows us to detect structure position of different ions in organic systems, to obtain information about interdiffusion at the interfaces, about ion permeation through organic bilayers, thus allowing us to develop models of biomembranes.

X-ray Standing Waves in X-ray Specular Reflection and Fluorescence Study of Nano-Films

The analysis of the wavefield intensity distribution connected with X-ray standing wave (XRSW) generation above the mirror surface at total reflection (TR) is presented for a vacuum/film/substrate sample along with experimental examples for organic and inorganic films for cases where the refractive index of the film is greater than that of the substrate. The thickness of an ultra-thin film may be estimated from the value of the XRSW period formed above the film/substrate interface at TR. In some cases, the thickness of an ultra-thin film may be roughly obtained just from the form of the X-ray reflection curve at incident angles smaller than the critical angle of the substrate. It is demonstrated that interference phenomena at TR, leading to waveguide mode formation inside the layered structure and responsible for a modulation of the X-ray reflection and fluorescence angular dependence, can be used for characterization of nano-films.

X-ray standing waves in bragg diffraction and in total reflection regions using Langmuir-Blodgett multilayers

Abstract A Langmuir-Blodgett heterostructure composed of 100 monolayers of leadstearate and one monolayer of barium behenate has been utilized to generate long-range standing waves in two different angular regions. The first corresponds to the Bragg peak from the layered structure and the second to the total reflection region. In this second region the period of the standing wave is a function of the incident angle.

Ion permeation through Langmuir-Blodgett layers investigated by total external reflection and fluorescence study

Abstract Combined measurements of X-ray reflectivity and characteristic fluorescence yield from investigated ions excited by the primary beam give a unique opportunity for determination of the ion position in the organic system in the direction normal to the surface. This technique has been applied to study the possibility of K + ion permeation from a solution into arachidic acid/valinomycin mixed L-B films. It was found that potassium ions are organized in clusters inside the L-B film.

X-ray fluorescence studies for the elemental composition and molecular organization of protein films on the surface of the liquid subphase

This paper reports on the results of the investigation of protein films that are based on alkaline phosphatase and glucose oxidase enzymes and formed on the surface of the liquid subphase. The experimental studies have been performed using total external reflection X-ray fluorescence spectrometry at the European Synchrotron Radiation Facility (Grenoble, France). The self-organization processes that occur in protein systems on the surface of the liquid subphase under the conditions where the protein molecules retain their mobility have been investigated using X-ray fluorescence measurements for the first time.

X-ray standing waves in LSM for characterization of ultra-thin films

New aspects of the advantages of layered synthetic microstructures (LSM) as X-ray standing wave (XSW) generators are discussed. One of them-the possibility to prepare a standing wave pattern with any necessary period by varying the LSM parameters-was applied for structure characterization of a thin organic Langmuir Blodgett film of the same period as the LSM substrate. Another one-the opportunity to determine the ultra-thin film thickness in the case when it is smaller than the XSW period-was demonstrated in the investigation of Fe and Ni films on top of the LSM. The thickness of the carbon layer was also determined without direct measurement of the fluorescence yield from carbon.