The melting processes of various Pt–Pd nanoparticles (binary alloy, core–shell,
D
≤ 4.0 nm) with different percent platinum atom content are investigated via the molecular dynamics using the embedded ...atom method potential in order to establish the thermal stability of simulated particle structure. In accordance with the data obtained, the most thermally stable are Pt–Pd nanoalloys with a diameter above 2.0 nm and core–shell Pd@Pt particles. As is shown, heating of binary Pt–Pd cluster alloys with the particle diameters less than 2.0 nm may cause the transition to pentagonal symmetry structures and core–shell-like complex formations.
Microglial cells are the main HIV-1 targets in the central nervous system (CNS) and constitute an important reservoir of latently infected cells. Establishment and persistence of these reservoirs ...rely on the chromatin structure of the integrated proviruses. We have previously demonstrated that the cellular cofactor CTIP2 forces heterochromatin formation and HIV-1 gene silencing by recruiting HDAC and HMT activities at the integrated viral promoter. In the present work, we report that the histone demethylase LSD1 represses HIV-1 transcription and viral expression in a synergistic manner with CTIP2. We show that recruitment of LSD1 at the HIV-1 proximal promoter is associated with both H3K4me3 and H3K9me3 epigenetic marks. Finally, our data suggest that LSD1-induced H3K4 trimethylation is linked to hSET1 recruitment at the integrated provirus.
Mainly regulated at the transcriptional level, the cellular cyclin-dependent kinase inhibitor, CDKN1A/p21(WAF1) (p21), is a major cell cycle regulator of the response to DNA damage, senescence and ...tumor suppression. Here, we report that COUP-TF-interacting protein 2 (CTIP2), recruited to the p21 gene promoter, silenced p21 gene transcription through interactions with histone deacetylases and methyltransferases. Importantly, treatment with the specific SUV39H1 inhibitor, chaetocin, repressed histone H3 lysine 9 trimethylation at the p21 gene promoter, stimulated p21 gene expression and induced cell cycle arrest. In addition, CTIP2 and SUV39H1 were recruited to the silenced p21 gene promoter to cooperatively inhibit p21 gene transcription. Induction of p21(WAF1) gene upon human immunodeficiency virus 1 (HIV-1) infection benefits viral expression in macrophages. Here, we report that CTIP2 further abolishes Vpr-mediated stimulation of p21, thereby indirectly contributing to HIV-1 latency. Altogether, our results suggest that CTIP2 is a constitutive p21 gene suppressor that cooperates with SUV39H1 and histone methylation to silence the p21 gene transcription.
The catalytic activity of Pt clusters is dependent not only on the nanoparticle size and its composition, but also on its internal structure. To determine the real structure of the nanoparticles used ...in catalysis, the boundaries of the thermal structure stability of Pt clusters to 8.0 nm in diameter interacting with carbon substrates of two types: a fixed α-graphite plane and a mobile substrate with the diamond structure. The effect of a substrate on the processes melting of Pt nanoclusters is estimated. The role of the cooling rate in the formation of the internal structure of Pt clusters during crystallization is studied. The regularities obtained in the case of “free” Pt clusters and Pt clusters on a substrate are compared. It is concluded that platinum nanoparticles with diameter
D
≤ 4.0 nm disposed on a carbon substrate conserve the initial fcc structure during cooling.
The molecular dynamics method with the modified tight-binding (TB-SMA) potential has been used to study thermal stability of the initial fcc phase in perfect silver clusters to 2 nm in diameter. ...Dimensional boundaries of nanoparticles, at which the internal atomic configuration changes upon heating, have been determined using the molecular dynamics simulation. It has been shown that the temperature factor can cause the transition from the initial fcc phase to other structural modifications, including those with pentagonal symmetry, in small Ag clusters. It has been demonstrated that “magic” numbers play an important role in the formation of the internal structure of silver clusters.
The applicability of individual Ni, Cu, Au, Pt, and Pd nanoclusters as data bits in next generation memory devices constructed on the phase-change carrier principle is studied. To this end, based on ...the modified tight-binding potential (TB-SMA), structure formation from the melt of nanoparticles of these metals to 10 nm in diameter was simulated by the molecular dynamics method. The effect of various crystallization conditions on the formation of the internal structures of Ni, Cu, Au, Pt, and Pd nanoclusters is studied. The stability boundaries of various crystalline isomers are analyzed. The obtained systematic features are compared for nanoparticles of copper, nickel, gold, platinum, and palladium of identical sizes. It is concluded that platinum nanoclusters of diameter
D
> 8 nm are the best materials among studied metals for producing memory elements based on phase transitions.
Peculiar features of heat capacity for Cu and Ni nanoclusters Gafner, S. L.; Redel, L. V.; Gafner, Yu. Ya ...
Journal of nanoparticle research : an interdisciplinary forum for nanoscale science and technology,
12/2011, Letnik:
13, Številka:
12
Journal Article
The heat capacity of copper and nickel clusters (from 2 to 6 nm in diameter) was investigated in the temperature range 200–800 K using molecular dynamics method and a modified tight-binding ...potential. The simulation results demonstrate a very good agreement with the available experimental data at
T
= 200 K and a fairy good agreement at higher temperatures. A number of regular trends are revealed in computer experiments which agree with the corresponding theoretical predictions. A conclusion is made that in the case of single free clusters the heat capacity may exceed the capacity of the corresponding bulk material. It is found that at 200 K, the copper nanocluster (
D
= 6 nm) heat capacity is higher by 10% and for nickel cluster by 13%. The difference diminishes with increasing the nanoparticles size proportionally to the relative number of surface atoms. A conclusion is made that very high values of the nanostructure heat capacity observed in laboratory experiments should not be attributed to free clusters, i.e., the effect in question is caused by other reasons.
The heat capacity of ideal nickel, copper, gold, aluminum, and palladium fcc clusters with diameter of up to 6 nm has been studied in the temperature range of 150–800 K in terms of the ...molecular-dynamics theory using a tight-binding potential. The heat capacity of individual metallic nanoclusters has been found to exceed that characteristic of the bulk state, but by no more than 16–20%, even in the case of very small clusters. To explain the discrepancy between the simulated data and the experimental results on the compacted metals, aluminum and palladium samples with 80% theoretical density have also been investigated. Based on the simulation results and analysis of the experimental data, it has been established that the increased heat capacity of the compacted nanomaterials does not depend on the enhanced heat capacity of the individual clusters but rather, can be due to either the disordered state of the nanomaterial or a significant content of impurities (mainly, hydrogen).
Limits of thermal stability of the original fcc phase in gold clusters up to 3.5 nm in diameter have been studied. The simulation carried out by the molecular-dynamics method using a modified TB-SMA ...tight-binding potential has shown that in small Au clusters under the effect of the temperature factor there occurs a transition from the original fcc phase to other structural modifications, including those with a pentagonal symmetry. As the size of gold nanoparticles increases, the polytypic-transition temperature shifts toward the melting temperature of the cluster. The results obtained are compared with the data for copper and nickel nanoparticles with similar sizes. It has been shown that, in the case of nickel and copper clusters, it is the transition from the fcc phase into structures with a pentagonal symmetry, which are not found in the bulk state, that is the governing factor; the gold clusters demonstrate a much more intricate behavior.
On the basis of our former simulations, we conclude that the heat capacity in the case of isolated free clusters can exceed that of a bulk material. It was found that at T=200K the increase in the Cu ...nanocluster heat capacity (D = 6nm) was only 10%, decreasing with growing nanoparticle proportionally to the reduction in the fraction of surface atoms. Thus, the considerably larger heat capacities of copper nanostructures observed in the experimental works cannot be related to the characteristics of free clusters. In our view, these properties of a nanomaterial can be associated with the degree of agglomeration of its constituent particles, i.e., the interphase boundaries and the increase in the root-mean-square displacements of atoms on the combined surface of the interconnected nanoclusters can have a strong effect. To test the above hypothesis, we took copper clusters of various sizes (4071-15149 atoms) that we produced when simulating the synthesis of Cu nanoparticles. Thus, in our molecular-dynamics experiments using a tight-binding potential at high temperatures, we failed to properly assess the role of the interphase boundaries in calculating the heat capacity of nanoparticles. The reason was the mass diffusion of Cu atoms to impart an energetically more favorable shape and structure to the cluster. At low temperatures, the heat capacity of the clusters exceeded that of the bulk same by a value from 10% to 17%. Consequently, the Cu clusters produced in direct experiments cannot be immediately applied in devices using the thermal energy of such clusters, because their external shape and internal structure are nonideal.
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