Photoemission study of onionlike carbons produced by annealing nanodiamonds

Photoelectron spectroscopy has been used to study the products resulting from high temperature phase transformation of nanodiamonds (ND). Depending on the temperature of annealing various particles with a diamond core covered by nanometer sized fullerene-like shells, and onionlike carbon (OLC) were formed. Analysis of the C1s photoemission lines of the intermediates of ND transformation, prepared at temperatures of 1420 and 1600 K and then exposed to atmosphere, reveals the presence of oxygen-containing groups and both sp2 and sp3 carbon. The sp2 component for these samples has binding energies of 284.70±0.05 eV (for the sample prepared at 1420 K) and 284.50±0.05 eV (for the sample prepared at 1600 K). A difference of 1.3±0.1 eV in the binding energy of the sp3 and sp2 components was observed. The sp2 component for OLC prepared at 1800, 1900, and 2140 K has a binding energy of 284.45±0.05 eV. The shift towards higher binding energies of the sp2 component of the samples prepared at lower temperatures is explained by significant curvature of graphite layers formed in the initial stages of graphitization. The observed increase in density of states at the Fermi level for the samples prepared at 1600, 1800, and 1900 K is associated with an accumulation of different types of defects in the curved graphite layers during graphitization of diamond. The Lorentzian widths of C1s photoemission lines from OLC are large compared with those of HOPG. The possible reasons for this broadening are discussed

Photoemission spectroscopy of clean and potassium-intercalated carbon onions

Hollow onionlike carbon (OLC), generated by annealing nanodiamond at 2140 K, has been studied by core-level and valence-band photoemission spectroscopy. Upon intercalation with potassium, core and valence states of the OLC show an almost rigid shift to higher binding energies, and the density of states at the Fermi level (EF) is observed to increase. An asymmetric broadening of the C1s line from the OLC as intercalation proceeds indicates an increase in electron-hole pair excitations. Both core and valence-band spectra are consistent with charge transfer from the intercalated potassium to the OLC, and support the conclusion that the electronic structure of the carbon onions bears strong similarity to that of graphite, although differences do exist. In consequence the conclusion can be drawn that these species behave as graphite ``nanocrystals'' rather than as large fullerene molecules

Possible Mechanisms of Axonal Transport Disturbances in Mouse Spinal Motoneurons Induced by Hypogravity

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. The data obtained by transcriptome analysis of lumbar spinal cord segments, sciatic nerve, and the respiratory diaphragm of the mice performed after a space flight on board Bion-M1 biosatellite were processed by bioinformatic methods aimed at elucidation of the regularities in hypogravity-induced transcriptome changes in various compartments of motor neurons. The study revealed abnormalities of axonal transport in spinal motor neurons provoked by weightlessness. These data agree with the results of electron microscopy examination of the spinal cord in experimental animals. In space group mice sacrificed on the landing day, the content of perinuclear ribosomes in lumbar motoneurons surpassed that in control mice or in the recovery group examined 1 week after the flight. The data corroborate our hypothesis on contribution of axonal transport disturbances into pathogenesis of hypogravity motor syndrome. They can be employed as a launching pad for further study of hypogravity-triggered motor disorder mechanisms in order to elaborate the preventive therapy against the development of hypogravity motor syndrome in space flights

Morphological changes in myelinated fibers of the spinal cord and the sciatic nerve in mice after modeling of the hypogravity and the approach of their correction by preventive gene therapy

Earlier, in mice after a 30-day space flight on the Bion-M1 biosatellite, we found signs of a negative effect of weightlessness on the structure of myelinated fibers of the spinal cord tracts; these findings indicate their involvement in the pathogenesis of hypogravitational motor syndrome (HMS). In the present study, under conditions of hypogravity modeling by the hindlimb unloading, we obtained data on destructive changes in the myelinated fibers of the motor posterior corticospinal tract (tractus corticospinalis posterior), sensitive anterior spinocerebellar tract (tractus spinocerebellaris anterior), and the gracile fascicle (fasciculus gracilis), as well as in the tibial fascicle (fasciculus tibialis) of the sciatic nerve of mice 30 days after unloading. The obtained data confirm our hypothesis on the role of disturbance in the processes of myelination of nerve fibers during the development of HMS, both during space flight and under conditions of simulating hypogravity on Earth. Morphometric analysis after a 7-day period of readaptation did not reveal signs of restoration of pathological changes in myelinated fibers that arose after 30 days of hanging. However, preventive gene therapy (administration of a gene construct providing the synthesis of recombinant vascular endothelial growth factor, glial cell line-derived neurotrophic factor, and neural cell adhesion molecule, prior to hindlimb unloading) has been shown to be effective in the preservation of myelinated fibers in projection anterior spininocerebellar tract, compared with control animals that did not receive gene therapy. The research carried out at this stage gives ground to make a preliminary conclusion about the advisability of developing methods of preventive gene therapy to prevent the development of GDS during long-term space flights