The structure, slip systems, and microhardness of C-60 crystals

The structure and microplasticity of high-purity fullerite C-60 have been investigated comprehensively. The crystalline structure, lattice parameters, and phase transitions have been studied by x-ray diffractometry in the temperature range 30-293 K. It is found that the temperature corresponding to the orientational order-disorder phase transition is T-c = 260 K. A considerable number of regions with stacking faults discovered in the samples leads to blurring of the fcc-->sc phase transition in the temperature interval T-c+/-3 K. The a(T) dependences of the lattice parameter display peculiarities at the following characteristic temperatures: T-c at which the lattice parameter jump Delta a/a = 3.3 x 10(-3) is observed, and the temperatures T-0 similar or equal to 155 K, and T-g similar or equal to 95 K which are associated with the beginning and end of molecular orientation freezing. It is shown that the formation of orientational glass is accompanied by a considerable increase in the width of x-ray reflections. The slip geometry and the temperature dependence of microhardness H-V are studied in the temperature interval 81-293 K. It is shown that a system of the {111}[110] type is the only slip system in the fee and sc phases, The value of H-V depends on the indentation plane: H-V(111)>H-V(100). Below T-c, the microhardness increases abruptly (by approximately 30%). The temperature interval of this anomaly decreases after annealing of the crystal in vacuum. At T<T-0, the H-V(T) dependence becomes much stronger. It is shown that the hardness of C-60 normalized to the elastic shear modulus is higher than the hardness of typical molecular crystals at comparable homologic temperatures

CORRELATION OF LOW-TEMPERATURE MICROPLASTICITY ANOMALIES WITH STRUCTURE TRANSFORMATIONS IN C-60 CRYSTALS

Structure, microhardness and slip systems were studied on C-60 crystals of high purity in the temperature range 30-290 K, which includes the fcc --> sc phase transition at T-c = 260 K and the orientational glass region T < 100 K. A step-like change of both the lattice parameter and the microhardness was recorded when passing through T-c, as well as the formation of slip lines near the indentations in both phases. The slip system <110>{111}, operative at room temperature in the FEC phase, is shown to retain its activity below T-c, in the sc phase. In the region where the orientation glass is formed, we have found a kink-like anomaly on the microhardness vs temperature curve; this anomaly correlates with a weak anomaly in the temperature dependence of the lattice parameter. Assumptions are Formulated concerning the chancier ol the dislocation motion in C-60 crystals, which make it possible to explain the microplasticity anomalies observed

TEM and HREM of diamond crystals grown on Si tips: structure and results of ion-beam-treatment.

Diamond single crystals were grown on the silicon whiskers by a hot filament chemical vapor deposition technique at the filament temperature about 2100 degrees C and the temperature of support 800 degrees C. Specimens were examined by SEM, TEM, HRTEM and SAED. When the filament temperature was about 1900 degrees C globular polycrystalline diamond particles were grown. At a support temperature more then 800 degrees C SiC nanoparticles were formed. To investigate the ion etching process of the silicon tip/diamond system, tips were treated with an Ar(+) beam with energy up to 30 kV. The results depend on fluence: at 4 x 10(18)ion/cm(2) diamonds and partially Si tips were destroyed, amorphous layer was formed (sometimes with nanometric size fragments of diamond); at 1 x 10(18)ion/cm(2) sharpened diamonds (radius of curvature about 20 nm) covered with amorphous layer (radius about 80 nm) probably with nanoclusters of diamond were observed; at 4.4 x 10(17) ion/cm(2) there was no visible tip sharpening but formation of amorphous thick layer occurred. The emission characteristics of Si tips covered with diamond were improved due to ion treatment. Since such tips in our case were covered with amorphous layer containing nanometric size fragments of diamond, we suppose this layer is responsible for electron emission improvement

Current Genome Editing Tools in Gene Therapy: New Approaches to Treat Cancer

Genotoxic stress inflicted by anti-cancer drugs causes DNA breaks and genome instability. DNA double strand breaks induced by irradiation or pharmacological inhibition of Topoisomerase II activate ATM (ataxia-telangiectasia-mutated) kinase signalling pathway that in turn triggers cell cycle arrest and DNA repair. ATM-dependent gamma-phosphorylation of histone H2Ax and other histone modifications, including ubiquitnylation, promote exchange of histones and recruitment of DNA damage response (DDR) and repair proteins. Signal transduction pathways, besides DDR itself, also control expression of genes whose products cause cell cycle arrest and/or apoptosis thus ultimately affecting the sensitivity of cells to genotoxic stress. In this study, using a number of experimental approaches we provide evidence that lysine-specific methyltransferase (KMT) Set7/9 affects DDR and DNA repair, at least in part, by regulating the expression of an E3 ubiquitin ligase, Mdm2. Furthermore, we show that Set7/9 physically interacts with Mdm2. Several cancer cell lines with inverse expression of Set7/9 and Mdm2 displayed diminished survival in response to genotoxic stress. These findings are signified by our bioinformatics studies suggesting that the unleashed expression of Mdm2 in cancer patients with diminished expression of Set7/9 is associated with poor survival outcome