E. V. Shtykova

Poly(acrylamide) gels with embedded magnetite nanoparticles

Magnetic gels are a new class of soft polymer materials with their properties controlled by magnetic fields. A method was developed for the preparation of magnetite nanoparticles in a matrix of poly(acrylamide) gel. Synthesis of the magnetic spinel iron oxide Fe3O4 in a matrix of poly(acrylamide) gel was performed via coprecipitation of Fe(II) and Fe(III) in alkaline medium. The effects of the cross-link density, the concentration of polymer and salt in the swollen network during preparation on the composition, structure and properties of the magnetic gels were studied by electronography, TEM and small-angle X-ray scattering (SAXS). The crystalline lattice of the particles was determined as magnetite. The average size of the particles, d, calculated from the half-width of the diffraction peaks, is of the order of 10 nm. The obtained data demonstrate a marked difference in size distribution of magnetic particles in gels of different structure.

Size distributions of metal nanoparticles in polyelectrolyte gels

Small-angle x-ray scattering is used to study size distributions of noble metal nanoparticles embedded in polyelectrolyte hydrogels with oppositely charged surfactants. A procedure is proposed to subtract matrix scattering and to extract pure scattering due to the nanoparticles allowing to evaluate their size distribution functions by means of a regularization technique. Two kinds of collapsed gel-surfactant complexes were studied: a complex of a cationic gel of poly(diallyldimethylammonium chloride) with an anionic surfactant sodium dodecyl sulfate (PDADMACl/SDS), and that of an anionic gel of poly(methacrylic acid) with a cationic surfactant cetylpyridinium chloride (PMA/CPC). Addition of a gold compound (HAuCl4⋅3H2O) to the PDADMACl/SDS system forms the metal compound clusters and leads to a partial distortion of the gel structure. After subsequent reduction of the gold compound with sodium borohydride (NaBH4) ordering in the gel disappears and gold nanoparticles are formed. Their size distribution inc...

Small-angle X-ray scattering reveals hollow nanostructures in iota- and kappa-carrageenan/surfactant complexes

Complexes of polyelectrolyte gels with oppositely charged surfactants form ordered polymer matrices with unique structure properties, which can be used in a wide range of medical, chemical and physical applications. Ordered matrices made of natural components are of special interest for medical and biological purposes. In the present study, self-organised complexes of native - and -carrageenans formed with oppositely charged cetylpyridinium chloride (CPC) are prepared and structurally characterised using small-angle X-ray scattering (SAXS). Starting from the molar ratio CPC/(charge of carrrageenan) of 0.2, the carrageenan gel shrinks and ordered motifs in its internal structure are formed. The internal order in the sample is reflected by the Bragg peaks in the scattering patterns which permit to compute periodicity and characteristic sizes of the ordered regions. Moreover, strong central scattering appears and the calculated fractal dimensions indicate that these regions are organised in well defined clusters. The periodicity of the ordered motifs computed from the Bragg peaks in the scattering patterns corresponds to the width of the surfactant bilayer (about 4.0 nm) for all the complexes. The crystallite size ranges from 25 nm to 40 nm depending on the type of carrageenan and on the amount of CPC. A model of the ordered fragments is proposed whereby the carrageenan/surfactant bilayers are regularly packed at the walls of hollow cylindric clusters with the outer radius of about 8 nm and height 40 nm. More detailed ab initio models indicate that these particles are formed by bent worm-like substructures with the cross-section coinciding to the thickness of the carrageenan/CPC bilayer. Thanks to a higher charge density per monomer, -carrageenans form more regular structures than -carrageenans.

Determination of the size and phase composition of silver nanoparticles in a gel film of bacterial cellulose by small-angle X-ray scattering, electron diffraction, and electron microscopy

The nanoscale structural features in a composite (gel film of Acetobacter Xylinum cellulose with adsorbed silver nanoparticles, stabilized by N-polyvinylpyrrolidone) have been investigated by small-angle X-ray scattering. The size distributions of inhomogeneities in the porous structure of the cellulose matrix and the size distributions of silver nanoparticles in the composite have been determined. It is shown that the sizes of synthesized nanoparticles correlate with the sizes of inhomogeneities in the gel film. Particles of larger size (with radii up to 100 nm) have also been found. Electron microscopy of thin cross sections of a dried composite layer showed that large particles are located on the cellulose layer surface. Electron diffraction revealed a crystal structure of silver nanoparticles in the composite.

Synthesis of Ag and Cu-chitosan metal-polymer nanocomposites in supercritical carbon dioxide medium and study of their structure and antimicrobial activity

This paper is dedicated to the design of efficient antimicrobial pharmaceuticals based on chitosan. Chitosan with a deacetylation degree of 0.98 preliminarily treated with supercritical carbon dioxide (scCO2) was impregnated with organometallic complexes (silver cyclooctadiene(hexafluoroacetylacetonate) and copper hexafluoroacetylacetonate) from an scCO2 solution followed by reduction with hydrogen to form metal-chitosan composites. Their structure was studied by small-angle X-ray scattering (SAXS). A narrow virtually monodisperse size distribution with a preferable particle size of 1–3 nm was found for silver and a wider polymodal size distribution with a particle size of up to 1–40 nm was revealed for copper. An X-ray fluorescent analysis showed the content of silver and copper metal to be 6 and 4.6%, respectively. The composites prepared by fluid technology were tested for antimicrobial activity toward bacteria S. epidermidis, E. coli, and a spore form of bacteria B. cereus in comparison with Cu2+-chitosan complexes obtained by the routine solution procedure. Ag0-chitosan nanocomposites were found to show bactericidal activity toward all the noted bacteria and spore forms, whereas Cu2+-chitosan complexes exhibit bacteriostatic activity toward the above bacteria and a lack of bactericidal properties toward the spore forms. The reasons for the bactericidal activity of the prepared composites are discussed.

Small-angle X-ray scattering, synchrotron radiation, and the structure of bio- and nanosystems

Small-angle X-ray scattering is a universal diffraction method for studying the supra-atomic structure of matter. The potential of this technique has greatly increased in recent years due to the development of bright synchrotron radiation sources. The extensive use of these sources, in combination with new techniques for analyzing scattering data and structure modeling, made small-angle scattering one of the most effective analytical methods for studying nanoscale structures. In this review, after a brief outline of the basic principles of small-angle scattering by isotropic dispersed nanosystems, we consider two areas of nanodiagnostics, in which the progress in the small-angle experiment and the latest techniques for interpreting scattering data has become pronounced in recent years. These areas—the analysis of the structure of biological macromolecules in a solution and structural studies of metal nanoparticles synthesized in polymer and aqueous media—are illustrated by examples of practical biological and nanotechnologycal applications.

Structure of composites prepared via polypyrrole synthesis in supercritical CO2 on microporous polyethylene

The synthesis of polypyrrole in supercritical carbon dioxide in the presence of the microporous polyethylene has been studied. Formation of polymer composites based on polypyrrole and polyethylene has been demonstrated. The structure of the test samples has been investigated by vibrational spectroscopy, SAXS, and atomic force and scanning electron microscopy. It has been discovered that the oxidized structure of polypyrrole forms during the synthesis under supercritical conditions.

Solution structures of human immunoglobulins IgG and IgM and rheumatoid factor IgM-RF

The low-resolution structures of human immunoglobulins M (IgM) and G (IgG) and the rheumatoid factor (IgM-RF) in solution were determined from synchrotron-radiation small-angle X-ray scattering by the method of dummy atom modeling (bead models). The structural models of IgM determined on the assumption that the molecule has a fivefold symmetry axis are in good agreement with the atomic structure of this protein proposed earlier. The molecular structure of the rheumatoid factor IgM-RF reconstructed by dummy atom modeling differs from the model of the IgM molecule: the F(ab)2 regions in the IgM-RF pentamer are asymmetric. This result confirms the earlier assumption that these regions in IgM-RF are different both structurally and biochemically. The typical shape of the IgG molecule in solution was demonstrated to be closer to the Y type, with the maximum size being larger than the size of the known crystallographic models.

Small-Angle X-ray Scattering Study of the Structure of Self-Organized Polymer Matrices and Formation of Imbedded Metal Nanoparticles

The structures of self-organizing polymer matrices based on collapsed gels and polyoctadecylsiloxanes have been studied by the methods of conventional and anomalous X-ray small-angle scattering with the use of the laboratory and synchrotron sources of X-ray radiation. The process of formation of metal nanoparticles in such matrices is also studied, their size distributions are calculated, and the models of localization of these particles in the polymer matrices are suggested. It is shown that growth of metal particles is controlled by the structure of the polymer network and is limited by the dimensions of its cells. The electron-density profiles of polycondensed octadecylsiloxane matrices are also calculated.

Structure of mono- and bimetallic heterogeneous catalysts based on noble metals obtained by means of fluid technology and metal-vapor synthesis

Monometallic nanocomposites are obtained with the use of supercritical carbon dioxide (fluid technique) and metal-vapor synthesis (MVS), while bimetallic nanocomposites of Pt and Au noble metals and γ-Al2O3 oxide matrix are synthesized by a combination of these two methods. The structures, concentrations, and chemical states of metal atoms in composites are studied by means of small-angle X-ray scattering (SAXS), transparent electron microscopy (TEM), X-ray fluorescent analysis (XFA), and X-ray photoelectron spectroscopy (XPS). The neutral state of metal atoms in clusters is shown by XPS and their size distribution is found according to SAXS; as is shown, it is determined by the pore sizes of the oxide matrices and lies in the range of 1 to 50 nm. The obtained composites manifest themselves as effective catalysts in the oxidation of CO to CO2.