N. D. Stepina

Structure of cellulose Acetobacter xylinum

The data are presented on optimization of cellulose synthesis by Acetobacter xylinum (strain VKM V-880) and the structural characteristics of A. xylinum cellulose gel film synthesized during static cultivation. The structural changes caused by the removal of water from gel films are established and the structural organization of macromolecular chains in cellulose A. xylinum is studied.

Construction and X-ray reflectivity study of self-assembled lysozyme/polyion multilayers

Abstract The process of multilayer assembly via layer-by-layer deposition of linear polyions and lysozyme have been studied. The films were fabricated on glass slides by alternate electrostatic adsorption of anionic poly(styrenesulfonate) (PSS), cationic poly(allylamine) (PAA) polyions and hen egg-white lysozyme. The multilayer build-up was monitored by the small-angle X-ray diffraction method. X-ray reflectivity curves from the films measured at different steps of the assembly reveal Kiessig fringes. From their periodicity the film thickness was calculated. The growth step for a PSS/PAA bilayer equals 37 A. The thickness of the lysozyme layer equals 45 A, which is close to dimensions of the lysozyme molecule determined by X-ray crystallography. An analysis of surface charges of the lysozyme molecule shows some preferentially positive charged regions, which are the most probable sites of interactions with negatively charged PSS.

Epitaxy of CdS and PbS on Langmuir layers

The results of a structural study of CdS and PbS nanocrystals grown from solutions under a Langmuir monolayer of a fatty acid are presented, and the influence of the geometric and stereochemical factors on the mutual orientation of the monolayer and the nanocrystals grown are considered.

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.

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.

Formation of Langmuir-Blodgett films in solutions of comblike polymers

The structures have been analyzed of the monolayers of comblike precursor polymers of polyimides and mixed cellulose esters formed at the water/air interface and of the Langmuir-Blodgett films obtained by transfer of these condensed monolayers onto solid substrates. The important factors that ensure the structure control and supramolecular organization of these monolayers and films are established.

Model of packing of cellulose acetomyristinate in Langmuir-Blodgett films

The variation of the structural characteristics in the transition from a block polymer to a Langmuir-Blodgett film has been investigated for cellulose acetomyristinate by the methods of X-ray diffraction analysis. The effect of length and number of acid residues on the diffraction pattern of block cellulose acetomyristinate is studied. The role of acyl substituent in the formation of an ordered structure of multilayer Langmuir-Blodgett films is established. A model of packing of cellulose acetomyristinate molecules in the Y-type films is suggested. The model is based on a two-domain structure in which close-packed myristic-acid residues are located either normally or at a certain angle to the plane of glucoside rings on one side of the polymer chain.

Structural localization of trace amounts of impurity ions in Langmuir-Blodgett films by the X-ray standing wave method

The molecular organization of Langmuir-Blodgett films based on the liquid crystal europium complex has been studied by the X-ray standing-wave method at the synchrotron radiation source BESSY (Germany). Analysis of the experimental data obtained made it possible to determine the composition of the organic multilayer nanosystems and localize the position of metal ions incorporated in organic layers from the aqueous subphase during film deposition. It is shown that, despite the low content of metal ions in the aqueous subphase (no higher than 10−7 mol/l), their incorporation into the Langmuir layer affects the molecular film organization significantly.

On the supramolecular organization of Langmuir-Blodgett cellulose acetovalerate films

Abstract The conditions of the deposition of the mixed cellulose acetovalerate ester Langmuir–Blodgett (LB) films are studied. The structure of films is examined by X-ray and electron diffraction methods, and atomic force microscopy. It was shown that LB films reveal the Y-type layer structure. A comparison between the macromolecule packing in LB films and macrofilms (bulk) was done. Modeling of the cellulose acetovalerate mono- and multilayer organization on the basis of the π–A isotherms and structural data was realized.

Structural features of Fab fragments of rheumatoid factor IgM-RF in solution

The structural features of the Fab fragments of monoclonal (Waldenström’s disease) immunoglobulin M (IgM) and rheumatoid immunoglobulin M (IgM-RF) were studied by a complex of methods, including small-angle X-ray scattering (SAXS), electron spin resonance (ESR), and mass spectrometry (MS). The Fab-RF fragment was demonstrated to be much more flexible in the region of interdomain contacts, the molecular weights and the shapes of the Fab and Fab-RF macromolecules in solution being only slightly different. According to the ESR data, the rotational correlation time for a spin label introduced into the peptide sequence for Fab is twice as large as that for Fab-RF (21±2 and 11±1 ns, respectively), whereas the molecular weights of these fragments differ by only 0.5% (mass-spectrometric data), which correlates with the results of molecular-shape modeling by small-angle X-ray scattering. The conclusion about the higher flexibility of the Fab-RF fragment contributes to an understanding of the specificity of interactions between the rheumatoid factor and the antigens of the own organism.