V. T. Lebedev

Synthesis, extraction, and chromatographic purification of higher empty fullerenes and endohedral gadolinium metallofullerenes

Higher empty and endohedral gadolinium metallofullerenes were prepared by electric arc synthesis, isolated, and separated chromatographically to high degree of purity (99 wt %). The samples obtained were characterized by chromatography, optical spectroscopy, and mass spectrometry. According to small-angle neutron scattering data, the endohedral metallofullerenes in o-xylene form a molecular solution in which the molecules interact to form molecular pairs.

Study of the structure of carbon matrices for radionuclide encapsulation by small-angle neutron scattering

The structure of carbon matrices prepared from diphtalocyanines using pyrolysis to encapsulate metal atoms (Y, Sm, U) inside small pores is studied by small-angle neutron scattering. It is shown that the structure of the porous matrix at a scale of 100–102 nm is characterized by two levels — small pores with the characteristic radii of 3–7 nm aggregated into entities with sizes of 40–100 nm and higher. The scattering data fit the values of the sample density and the total volume of pores in the matrices.

Structural features of fullerene-containing star-shaped polystyrene molecules with Oligomer arms in solutions

The structure and conformational properties of star-shaped oligostyrenes containing fullerene C60 as a branching center and short arms with lengths at the level of the persistent length or a segment of a polystyrene chain are studied by small-angle neutron scattering in deuterotoluene. The gyration radii of linear precursor oligomers (∼0.4 and 0.6 nm) and corresponding star-shaped molecules (∼1.1 and 1.4 nm) are calculated under the Guinier approximation. The linear oligomer (4–5 units) is found to be a rodlike molecule; arms of star-shaped molecules based on it assume the straightened conformations as well. Linear oligomer chains composed of 6–7 units deviate from the rodlike shape and acquire a certain flexibility in solution, but oligomer chains grafted onto the C60 center preserve the extended conformations. There is no marked tendency toward screening of fullerene by radially extended arms. The number of branches in the star-shaped oligostyrenes corresponds to a functionality of f = 6 preset by the conditions of synthesis.

Amphiphilic star-shaped polymer with fullerene (C60) branching center and its micelle-forming properties in D2O solutions

A star-shaped amphiphilic polymer with arms of polystyrene and sodium salt of polymethacrylic acid on the common fullerene (C60) branching center was prepared by hydrolysis of polar chains in a heteroarm star-shaped fullerene (C60)-containing polymer. The micelle-forming properties of the amphiphilic polymer were examined by small-angle neutron scattering. Structure of solutions of the polymer in D2O is discussed.

Polarized-neutron scattering in aqueous solutions of fullerenols in a magnetic field

The aqueous solutions of mixtures (T = 25°C) of paramagnetic Gd@C82(OH)x and diamagnetic C82(OH)x fullerenols, where x ∼ 30, are studied via small-angle polarized-neutron scattering under the conditions of transition from diluted to concentrated systems whose solubility threshold is close to that of fullerenols. When the induction B of an external field varies from 0.001 to 1.0 T, the molecular correlation radius of solutions is RC ∼ 15–20 nm and the aggregation number reaches ∼5 × 104 with increasing fullerenol content (C = 0.04−2.0 wt %). Such changes are coupled with both paramagnetic Gd@C82(OH)x molecules and interactions between the induced diamagnetic moments of fullerenols introduced into aggregates.

Effect of annealing temperature on the structure of pyrolysates of diphthalocyanines of rare-earth elements: Neutron research

Small-angle neutron scattering is used to study the structure of carbon matrices—the pyrolysis products of diphthalocyanines with embedded metal atoms (Y, La, and Ce), synthesized at annealing temperatures of 800–1700°C. It is shown that the structure of the porous matrix on the scale of ∼100–102 nm is characterized by a level of small pores (3–10 nm in radius) and the next level of the structure is associated with the formation of their aggregates (above 100 nm in size). The quantity and size of the scattering objects increases sharply at annealing temperatures above 1000°C. The results are consistent with X-ray diffraction data.

Structure of the amorphous phase of pyrolisates of lanthanum diphthalocyanine according to X-ray scattering data

Data on X-ray diffraction in lanthanum diphthalocyanine pyrolysates synthesized at temperatures of 800–1800°С demonstrate the formation of an amorphous carbon phase with embedded lanthanum atoms. Low-temperature pyrolysis (800–900°С) creates layered carbon structures. Due to annealing at 1000°С, carbon integrates into globules whose number of atoms is m ~ 100. Such structures with gyration radii of Rg ~ 0.4–0.5 nm on the order of the precursor molecule size are synthesized in the temperature range of 1000–1800°С, and are stable in terms of size and mass. In this case, their density approaches that of graphite.

Structural features of films based on star-shaped fullerene-containing polystyrenes: Small-angle neutron-scattering study

The structuring of films based on regular six-arm and twelve-arm polystyrenes with the arm characteristics Mn = 118 × 103 and Mw/Mn = 1.06 and a fullerene (С60) branching center in a weakly swollen state in a mixture of deuterated solvents (90 vol % D-methanol and 10 vol % D-toluene) is studied by small-angle neutron scattering. Analogous studies are performed for films based on linear polystyrene (Mn = 280 × 103, Mw/Mn = 1.07) and its composites with fullerene С60 (0.5 wt %). It is shown that, during saturation of the samples with the solvent D-toluene, filling of the free volume that forms chain-transport channels that have gyration radii of the order of diameters of macromolecules and unite to form submicron and micron structures occurs. The degree of filling of the free volume, which is maximum for the linear polymer, becomes minimum for polystyrene with the inserted free fullerene. In addition, the transition from the linear polymer to the six-arm polymer is related to a smaller degree of filling of the free volume due to the formation of thinner migration channels. As the amount of arms in macromolecules is increased to 12, permeability of the polymer matrix improves because molecular order partially appears in accordance with the model of the densest packing of solid spheres.

Aggregation of iron-containing fullerenols in aqueous solutions

Endometallofullerenols Fe@C60(OH)30 were synthesized by a new procedure using a special molecular precursor in the course of electric arc evaporation of a composite carbon electrode. Aqueous solutions of fullerenols Fe@C60(OH)30 were studied by small-angle neutron scattering (SANS) and viscometry under the conditions of transition from dilute to concentrated systems in two media: acidic (pH 3.7) and weakly alkaline (pH 7.8). In a weakly alkaline medium, fullerenols form relatively dense clusters (correlation radius RC ~ 17 nm), and in acidic medium, less dense structures of size RC ~ 18 nm in the concentration interval с = 0.5–1.4 wt %. The mechanisms of aggregation of fullerenol molecules in aqueous solutions are discussed. The water-soluble derivatives Fe@C60(OH)30 obtained show promise for biomedical applications in magnetic resonance imaging as contrasting agents that are potentially less toxic than presently used contrasts based on gadolinium chelate complexes.

Small-angle neutron scattering study of composites based on poly(phenylene oxide) modified with hybrid starlike fullerene-containing macromolecules

Composite films based on poly(2,6-dimethyl-1,4-phenylene oxide) modified with a hybrid star-like polymer (1, 3, and 5 wt %) with a fullerene C60 branching center and polymer chain arms of various structures (nonpolar polystyrene and the polar poly(2-vinylpyridine)-block-poly(tert-butyl methacrylate) diblock copolymer) are investigated via small-angle neutron scattering. The data analysis for initially dry samples of the matrix polymer and composites and for samples dried after swelling in deuterated methanol shows that the latter samples fil diffusion channels, a circumstance that provides a high contrast between them and the protonated matrix. This fact allows the distribution of methanol in swollen membranes and the geometry of diffusion channels to be studied. It is found that the matrix polymer possesses highly branched channels. However, removal of the solvent from the swollen polymer results in partial disappearance of the channels and transformation of the polymer into a more homogeneous material. In the case of composites, in contrast, as the fraction of the starlike polymer is increased, a well-developed system of linear channels that survive after solvent removal is formed in the matrix.