Investigation of molecular mechanisms of action of chelating drugs on protein-lipid model membranes by X-ray fluorescence

Protein-lipid films based on the enzyme alkaline phosphatase were subjected to the action of chelating drugs, which are used for accelerating the removal of heavy metals from the human body, and the elemental composition of the resulting films was investigated. Total-reflection X-ray fluorescence measurements were performed at the Berlin Electron Storage Ring Company for Synchrotron Radiation (BESSY) in Germany. A comparative estimation of the protective effect of four drugs (EDTA, succimer, xydiphone, and mediphon) on membrane-bound enzymes damaged by lead ions was made. The changes in the elemental composition of the protein-lipid films caused by high doses of chelating drugs were investigated. It was shown that state-of-the-art X-ray techniques can, in principle, be used to develop new methods for the in vitro evaluation of the efficiency of drugs, providing differential data on their actions.     

Synchrotron X-ray diffraction study of the structure of oral stratum corneum model lipid membranes

Membranes modeling the lipid fraction of the mucous membrane of the human oral cavity have been studied by X-ray synchrotron diffraction. Ternary systems, composed of a mixture of sphingomyelin, dipalmitoylphosphatidylcholine, and dipalmitoylphosphatidylethanolamine with component weight ratios of 1: 2: 2 and 1: 2: 1, have lamellar structures in the gel phase at the physiological temperature (37°C). An inverted hexagonal phase is formed in the system with 40% dipalmitoylphosphatidylethanolamine in the temperature range of 60–70°C. This phase coexists with the liquid-crystalline lamellar phase in a narrow temperature range and completely surpresses the lamellar phase with an increase in temperature to 80°C. Multi-component oral stratum corneum membranes are characterized by several lamellar phases at 20–37°C and the coexistence of one or several lamellar phases with inverted hexagonal phase at 80–90°C.     

Electron crystallography as an informative method for studying the structure of nanoparticles

The overwhelming majority of modern nanotechnologies deal with nanoparticles owing to the great variety of their unusual properties, which make them irreplaceable in various fields of science and technology. Since the physical properties of nanoparticles depend on their composition, structure, and shape, the problem of monitoring these parameters both after and during formation of nanoparticles is very important. Methods of electron crystallography are most informative and appropriate for studying and monitoring nanoparticle parameters. In this review, we briefly report the main modern methods based on the use of electron diffraction and electron microscopy, along with examples of their applications for nanoparticles, to solve a number of urgent structural problems of nanomaterials science.     

Capabilities of X-ray topography for studying interfacial instabilities during directional solidification

X-ray topography is very sensitive to segregation inhomogeneities. It is shown that the related contrasts can be used for revealing, over large distances, different features of the instabilities of the growth interface. Additional information can be obtained from orientation contrast. The capabilities of the method are illustrated on In doped GaAs.     

Planar lattices of magnetic nanoparticles with antiferromagnetic interaction

Square lattices of magnetic nanoparticles undergoing dipole–dipole and antiferromagnetic exchange interactions have been investigated. The main types of equilibrium states with zero and nonzero total magnetic moments have been revealed. It is shown that transitions between different equilibrium states may occur by means of a uniform magnetic field due to the presence of configuration bistability. Orientational transitions between equilibrium states under the action of a magnetic-field pulse on the system and transient oscillation processes have been studied.     

Comparative analysis of methods for studying internal stresses in crystals

The possibilities provided by the main polarization optical methods of studying internal stresses in differently oriented plates prepared from cubic crystals are compared. A promising method for obtaining exhaustive information on the stressed state of an object, including the trajectories and the values of the principal stresses, is described.     

Development of methods for ultrasonic scanning of X-ray wavelength

The method for X-ray wavelength tuning using an adaptive element (a quartz monolithic resonator modulated by a standing longitudinal low-frequency ultrasonic wave) has been proposed and implemented. This method is characterized by high tuning accuracy and possibility of scanning X-ray beam parameters with a time resolution of up to 3 μs.     

Investigation of the interaction of dimethyl sulfoxide with lipid membranes by small-angle neutron scattering

The influence of dimethyl sulfoxide (CH₃)₂SO (DMSO) on the structure of membranes of 1,2-dimiristoyl-sn-glycero-3-phosphatidylcholine (DMPC) in an excess of a water-DMSO solvent is investigated over a wide range of DMSO molar concentrations 0.0 ≤ X _DMSO ≤ 1.0 at temperatures T = 12.5 and 55°C. The dependences of the repeat distance d of multilamellar membranes and the thickness d _b of single vesicles on the molar concentration X _DMSO in the L _β’ gel and L _α liquid-crystalline phases are determined by small-angle neutron scattering. The intermembrane distance d _s is determined from the repeat distance d and the membrane thickness d _b. It is shown that an increase in the molar concentration X _DMSO leads to a considerable decrease in the intermembrane distance and that, at X _DMSO = 0.4, the neighboring membranes are virtually in steric contact with each other. The use of the deuterated phospholipid (DMSO-D6) and the contrast variation method makes it possible, for the first time, to determine the number of DMSO molecules strongly bound to the membrane.     

X-ray and molecular mechanics studies on the crystal and molecular structure of the leucoacetate of ventilatone A

Molecular details of the leucoacetate of ventilatone A have been obtained by X-ray crystallographic and molecular mechanics calculations. In the crystalline state (space group P1,Z=2) the two independent molecules of the asymmetric unit appear to be disordered as some unusual geometrical features are evident. As these two molecules are related by a pseudo center of symmetry details of space group assignment are presented. Evidence of bond order in the molecules is supported by previously published spectroscopic data.     

On the Theory of X-ray Diffraction Interferometry in Single Crystals. Peculiarities of Effect and Possibilities of Application

Crystallography Reports - A new version of X-ray diffraction interferometer in a single crystal is studied theoretically. This device is similar to the Young interferometer with two slits, but,...     

X-ray microscopy of track membranes and biological objects in the soft-and hard-wavelength ranges

The methods used to obtain X-ray images of track membranes and various biological objects in the soft (20 nm) and hard (0.2–0.02 nm) wavelength ranges have been considered. In the range of soft X-rays, the images were obtained in a Schwarzshild microscope. In the spectral range of hard X-ray radiation, various methods were used including the use of Fresnel zone plates, asymmetric reflecting crystals, X-ray microradiography and microtomography.     

A molecular model for the vibrational modes in chalcogenide glasses

We demonstrate the use of molecular models for calculating the optic mode frequencies in elemental and compound chalcogenide glasses. Our model gives good agreement with the optic mode frequencies reported for As₂Se₃, and for the polymeric fraction in liquid S and amorphous Se and Te. The model is not applicable to amorphous Si and Ge and III–V semiconductors.     

Development of methods of X-ray diffraction analysis for determining the composition and structure of sillenite-family crystals

A methodology for refining the crystal structure of sillenites of nominal composition Bi₂₄ M ₂O₄₀ based on the choice of the correct initial model and thermal atomic parameters is reported. The validity of the approach proposed is demonstrated by examples of crystals with M = Si, Fe, or V, for which the real composition is found with allowance for the composition of each structural site. Individual structural details are confirmed by IR and Raman spectroscopy data.     

Solution of the inverse problem for reconstructing the real structure of materials from the data of different X-ray methods

A software program has been developed for joint solution of the inverse problem on the basis of the X-ray diffractometry and reflectometry data. A system of basic objects supporting some functions of automatic data flow processing in the program and oriented to mathematical calculations has been created. It is shown by the example of experimental data for an In _x Ga_{1 ? x} As-In _y Al_{1 ? y} As/InP(001) sample that joint fitting of X-ray diffractometry and reflectometry curves makes it possible to reconstruct the model parameters of a multilayer with smaller rms errors. The data were processed taking into account the angular dependences of the background intensity and the aperture factors stemming from the geometry of the experiment.     

Reflectometer for studying the surface of liquid systems

To study the free surface of liquids, a Reverans reflectometer with a vertical neutron scattering plane has been designed and is fabricated at Petersburg Nuclear Physics Institute. This reflectometer is intended to investigate surfaces and interfaces in liquid magnetic or nonmagnetic systems. The principles of reflectometer operation are described. The general view of the reflectometer with ready units is presented and its main technical parameters are given. The results of preliminary tests are reported.     

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.     

Application of X-ray diffraction methods in the study of micrometer-sized porous Si layers

An X-ray analysis of porous silicon layers (Sb-doped n ⁺-Si(111)) obtained by anodic oxidation for different times with a current of 50 mA/cm² is performed by the methods of double-crystal rocking curves and total external reflection. A nondestructive method for monitoring the stationary process of the formation of micrometer-sized porous silicon layers and estimating their porosity and thickness is proposed. The parameters obtained for porous silicon layers with a thickness of ～6 μm are confirmed by the joint processing of diffraction curves for the 111 and 333 reflections on the basis of the developed model of dynamic scattering from layers while taking into account the strain profiles Δd(z)/d, the static Debye-Waller factor f(z), and the porosity P(z). The advantages and drawbacks of the proposed method are discussed.     

Peculiarities of aluminium interaction with Ga85In15 eutectics as evidenced by X-ray synchrotron diagnostics

A set of X-ray synchrotron techniques, viz., diffraction, EXAFS/XANES spectroscopy and microtomography, is applied to elucidate microstructural changes in a technical aluminium alloy treated with GaIn eutectics. Such a treatment gives rise simultaneously to a prominent enbrittlement of the material and its activation towards reaction with water with the hydrogen evolution. The latter fact makes the activated aluminium a promising energy carrier for the small-scale hydrogen energetics. It is demonstrated that both phenomena are caused by the fast diffusion of the eutectics along intergrain boundaries and microcracks throughout the bulk of polycrystalline Al. The diffusion is promoted by the formation of (Al-Ga-In) solid solution in near-surface regions of Al crystalline grains. The progressive loss of activity of aluminium treated with GaIn eutectics upon a prolonged storage in humid air is due to the decomposition of the eutectics accompanied by the segregation of indium metal and partial gallium oxidation.