E. Yu. Tereshchenko

In situ study of the growth and degradation processes in tetragonal lysozyme crystals on a silicon substrate by high-resolution X-ray diffractometry

The results of an in situ study of the growth of tetragonal lysozyme crystals by high-resolution X-ray diffractometry are considered. The crystals are grown by the sitting-drop method on crystalline silicon substrates of different types: both on smooth substrates and substrates with artificial surface-relief structures using graphoepitaxy. The crystals are grown in a special hermetically closed crystallization cell, which enables one to obtain images with an optical microscope and perform in situ X-ray diffraction studies in the course of crystal growth. Measurements for lysozyme crystals were carried out in different stages of the crystallization process, including crystal nucleation and growth, developed crystals, the degradation of the crystal structure, and complete destruction.

X-ray and synchrotron methods in studies of cultural heritage sites

X-ray and synchrotron methods that are most widely used in studies of cultural heritage objects (including archaeological sites)—X-ray diffraction analysis, X-ray spectroscopy, and visualization techniques— have been considered. The reported examples show high efficiency and informativeness of natural science studies when solving most diverse problems of archaeology, history, the study of art, museology, etc.

The pathways of silver nanoparticles formation by Mycobacterium smegmatis.

325 The nanoparticles composed of reduced metal atoms have become recently a subject of intense studd ies. Due to their unique properties, these nanopartii cles are widely used in modern fundamental and applied technologies [1]. Microorganisms form metal nanoparticles by reduction of the corresponding ions to the neutral state by various cell products [2]. Reducc tion of the metal cations during usual chemical proo cesses is followed by the formation of the nanopartii cles or aggregates; after penetration into the cell, the granules are formed that are encapsulated in vesicles. If reduction of the toxic ions occurs outside of the cytoplasm, the nanoparticles may be concentrated at the cell surface [3]. The goal of this study was to analyze the formation of weakly coagulating silver nanoparticles with similar sizes by Mycobacterium smegmatis cells. M. smegmatis was chosen as the object of the study because its microbiological, physiological, genetic, and biochemm ical properties, as well as the chemical composition and surface architecture of the cell, are well known [4–6]. Due to the specific structure of the cell enve lope, mycobacteria are resistant to organic and inorr ganic toxic agents [5]. One of the peculiarities of the envelope structure in M. smegmatis and other representatives of this genus is the presence of an outer bilayer membrane containing mycolic acids and lipids. However, this membrane diff feres significantly from the outer membrane of Gramm negative bacteria [7, 8]. M. smegmatis transport proo teins porins, which mediate transition of various moll ecules (including antibiotics) through the outer hydrophobic layers of the cell envelope [4, 6, 9], are of a special interest. Since mspAdeficient mutants exhibit an enhanced resistance to toxic metal ions, one could suggest their transport into the cell to be medii ated by these proteins [10]. Unlike ions, metal nanoo particles are transported into the mycobacteria cells with difficulty: small gold nanoparticles (d = 3.7 nm) were shown to bind within the porin channel, and larger ones (d = 17 nm), within the outer part of the protein [11]. Thus, both the study of nanoparticle formation by microorganisms (as a mechanism of resistance to the metal ion toxic effects [3]) and comparative study of the effects of the two metal forms on microbial cells are of theoretical and practical interest. We have carr ried out these studies previously. Here, we present the results of the studies of nanoparticles formation during the treatment …

Structure of porphyrin-fullerene dyad monolayer on the water surface and solid substrate

Monolayers of porphyrin-fullerene dyad TBD6a were formed on the surface of a water subphase and then transported on a solid substrate by the Langmuir-Schaefer method. A simulation was performed for the structure of a single molecule and for a molecular monolayer, according to the area per molecule in the monolayer formed, which was calculated based on an analysis of the π-A isotherm. A unit cell was chosen for the proposed molecular packing (a = 1.54 nm, b = 1.50 nm, c = 1.75 nm, α = 80.0°, β = 90.0°, and γ = 90.0°), and the atomic coordinates were calculated. A comparison of the interplanar spacings and diffraction peak intensities in the experimental and calculated (for the unit cell proposed) diffraction patterns indicates that a platelike texture is formed in the monolayer and that the crystal structure of the domains corresponds to the model chosen.

The Influence of Macrocyclic Tetraamine Immobilization in Langmuir Monolayers on Complex Formation Selectivity

Selective complex formation in Langmuir dicetyl cyclene monolayers on the surface of aqueous solutions of Cu(II), Ni(II), and Zn(II) salts and their mixtures was studied. The effect of selectivity “inversion” of diphilic cyclene immobilized in monolayers on the surface of solutions of a mixture of copper(II) and nickel(II) salts was observed; the inversion was induced by a change in subphase pH. An analysis of the isotherms of monolayer compression and X-ray fluorescence spectra of the corresponding Langmuir-Blodgett films showed that subphase acidification caused a gradual transition from the selective formation of copper-containing macrocyclic complexes to selective complex formation between the ligand and nickel ions. The effect observed was not characteristic of complex formation with similar unsubstituted tetraamines in bulk solution. The phenomenon was interpreted from the point of view of specific conformational transitions of the diphilic macroring in the two-dimensional system organized at the interphase boundary.

Integument structure in ornithischian dinosaurs (Hypsilophodontia, Ornithopoda) from the Late Jurassic of Transbaikalia

Integumentary structures of ornithischain dinosaurs of the taxon Hypsilophodontia (Ornithopoda) from the Ukureiskaya Formation (Upper Jurassic) of the Kulinda locality (Transbaikal Region, Russia) are described in detail. It is shown that members of this group had so-called bristle scales, integumentary appendages previously unknown in ornithischian dinosaurs. These are relatively small horn plates embedded in the skin, the distal margin of which has several long, flat, and probably constantly growing bristles. The monobristle variant of bristle scale is probably homologous to the protofeather of theropods; if this is the case, it is possible to reconstruct the protofeather as an elongated and constantly growing scale.

Comparison of the data of X-ray microtomography and fluorescence analysis in the study of bone-tissue structure

The possibility of localizing clusters of heavy atoms is substantiated by comparing the data of X-ray microtomography at different wavelengths, scanning electron microscopy, and X-ray fluorescence analysis. The proximal tail vertebrae of Turner’s thick-toed gecko (Chondrodactylus turneri) have been investigated for the first time by both histological and physical methods, including X-ray microtomography at different wavelengths and elemental analysis. This complex methodology of study made it possible to reveal the regions of accumulation of heavy elements in the aforementioned bones of Turner’s thick-toed gecko.

Investigation of the thermal diffusion during the formation of a quasicrystalline phase in thin Al-Pd-Re films

The layer mixing during the formation of the Al70Pd20Re10 icosahedral quasicrystalline phase in thin (55 nm) Al-Pd-Re layered film systems subjected to vacuum annealing has been studied. It is shown that a combined layer of Pd and Al atoms (with the Al3Pd2 phase dominating) is formed in the first stage (at 350°C), while the rhenium layer remains invariable. In the second annealing stage (at 450°C), the β′-AlPd phase is formed and the Re layer is diffused. In the third stage (700°C), Pd and Re atoms are uniformly distributed throughout the film with the formation of a quasicrystalline phase.

Complex Study of the Spearhead Superficial Crust from Burial Mound no. 1 near Novosvobodnaya Village

A complex study of a spearhead dated back to IV mill. BC from burial mound no. 1 near Novosvobodnaya village (collection of the State Historical Museum) and, in particular, the material of spearhead superficial crust has been performed. The elemental and phase composition of the metal of spearhead and the superficial crust on its surface have been determined by scanning electron microscopy, jointly with energydispersive X-ray microanalysis and X-ray phase analysis. A comparative analysis of the results of studying the spearhead superficial crust and similar crusts on other artifacts from the mounds near Novosvobodnaya village suggest natural origin of the crust on copper‒arsenic artifacts.

Thermal stability of organic layered systems based on lead stearate

The structural variation in multilayer Langmuir-Blodgett films of lead stearate caused by heat treatment under different conditions in the temperature range 20–100°C is investigated by X-ray reflectometry and high-resolution electron diffraction. Successive annealing of the samples is shown to not alter the initial layered structure at temperatures of 60, 80, and 100°C; partial disturbance of the layered structure occurs upon successive annealing at 80°C and 100°C. Significant disturbance of the structure is observed when the films are heated immediately to 100°C. In all these cases, the orthorhombic (pseudomonoclinic) lattice, with the lattice constants: a = 0.496, b = 0.738, c = 9.60 nm, α = β = γ = 90°, space group P2/1b, formed by transferring monolayers onto the substrate is retained in the crystalline domains of the film.