Abstract
Pressure represents a clean tuning parameter for traversing the complex phase diagrams of interacting electron systems, and as such has proved of key importance in the study of quantum ...materials. Application of controlled uniaxial pressure has recently been shown to more than double the transition temperature of the unconventional superconductor Sr
2
RuO
4
, leading to a pronounced peak in
T
c
versus strain whose origin is still under active debate. Here we develop a simple and compact method to passively apply large uniaxial pressures in restricted sample environments, and utilise this to study the evolution of the electronic structure of Sr
2
RuO
4
using angle-resolved photoemission. We directly visualise how uniaxial stress drives a Lifshitz transition of the γ-band Fermi surface, pointing to the key role of strain-tuning its associated van Hove singularity to the Fermi level in mediating the peak in
T
c
. Our measurements provide stringent constraints for theoretical models of the strain-tuned electronic structure evolution of Sr
2
RuO
4
. More generally, our experimental approach opens the door to future studies of strain-tuned phase transitions not only using photoemission but also other experimental techniques where large pressure cells or piezoelectric-based devices may be difficult to implement.
The influence exerted by addition of 3-(methacryloyloxy) propyltrimethoxysilane (MPTMOS) on the porosity and size of silica particles synthesized in a water-ethanol-ammonia-tetraethoxysilane (TEOS) ...mixture by the Stöber-Fink-Bohn method with the subsequent calcination in oxygen at 400 °C was studied. A set of particles was synthesized at the same relative amounts of the starting reagents and at the same temperature of the reaction mixture. It was shown that as the amount of MPTMOS in the TEOS + MPTMOS precursor is raised from 0 to 12.5 mol%, the final size of the resulting SiO2 particles decreases from ∼400 to ∼10 nm, which is presumably due to the increase in the number of nucleation centers by several orders of magnitude. It was found that the particles have micropores, which are presumably formed upon removal of methacryloyloxypropyl groups by calcination. As the MPTMOS:TEOS molar ratio is raised, the micropore volume and the apparent specific surface area of the particles first grow and reach values of 0.15 сm3 g−1 (350 m2 g−1), and then decrease to 0.05 сm3 g−1 (100 m2 g−1) because the particle size (∼10 nm) becomes comparable with the pore size (1–2 nm). Upon addition of one more porogen, cetyltrimethylammonium bromide (CTAB), to the reaction mixture, the micropore volume and the apparent specific surface area of the particles substantially increase to become 0.25 cm3 g−1 and 600 m2 g−1, correspondingly, and the particle size rises to 50 nm. Probably, mesopores formed upon oxidation of CTAB micelles and micropores are mutually connected and form a common network within the particles. The total pore volume and the specific surface area of the particles determined by BET reach values of 1.05 cm3 g−1 and 1200 m2 g−1, respectively.
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•The Stöber method was used to synthesize microporous SiO2 particles from TEOS and MPTMOS.•On replacing 12.5 mol% TEOS with MPTMOS, the size of SiO2 particles becomes 40 times smaller.•The SiO2 particles have a specific surface area determined by BET of up to 1200 m2 g−1.
This work is devoted to the study of magnetic Fe3O4 nanoparticles doubly coated with carbon. First, Fe3O4@C nanoparticles were synthesized by thermal decomposition. Then these synthesized ...nanoparticles, 20–30 nm in size were processed in a solution of glucose at 200 °C during 12 h, which led to an unexpected phenomenon—the nanoparticles self-assembled into large conglomerates of a regular shape of about 300 nm in size. The morphology and features of the magnetic properties of the obtained hybrid nanoparticles were characterized by transmission electron microscopy, differential thermo-gravimetric analysis, vibrating sample magnetometer, magnetic circular dichroism and Mössbauer spectroscopy. It was shown that the magnetic core of Fe3O4@C nanoparticles was nano-crystalline, corresponding to the Fe3O4 phase. The Fe3O4@C@C nanoparticles presumably contain Fe3O4 phase (80%) with admixture of maghemite (20%), the thickness of the carbon shell in the first case was of about 2–4 nm. The formation of very large nanoparticle conglomerates with a linear size up to 300 nm and of the same regular shape is a remarkable peculiarity of the Fe3O4@C@C nanoparticles. Adsorption of organic dyes from water by the studied nanoparticles was also studied. The best candidates for the removal of dyes were Fe3O4@C@C nanoparticles. The kinetic data showed that the adsorption processes were associated with the pseudo-second order mechanism for cationic dye methylene blue (MB) and anionic dye Congo red (CR). The equilibrium data were more consistent with the Langmuir isotherm and were perfectly described by the Langmuir–Freundlich model.
Submicrometer spherical micro-mesoporous SiO2 particles have been synthesized with a Brunauer–Emmett–Teller specific surface area of up to 1600 m2 g−1, comparable with that of nanoporous carbon ...materials. The particles are constituted by densely packed SiO2 channels, similarly to materials of the MCM-41 type. The particles have two pore subsystems: monodisperse cylindrical mesopores with controllably varied average diameter (2.5–3.5 nm) and micropores supposedly situated within the walls of the SiO2 channels and between their outer surfaces. The particles with combined micro-mesoporous structure are obtained by hydrolysis of a mixture of tetraethoxysilane (TEOS) and 3-(methacryloyloxy)propyltrimethoxysilane (MPTMOS) with molar ratio 5:1 in an alcoholic–aqueous–ammonia medium containing surfactant (cetyltrimethylammonium bromide + 1,3,5-trimethylbenzene). Negatively charged products of hydrolysis of silica precursors (TEOS and MPTMOS) are condensed near the positively charged amino groups situated on the surface of the cylindrical micelles of surfactant forming SiO2 layer containing hydrophilic methacryloyloxypropyl (MP) groups in the interior. Due to the Van der Waals forces, these micelles coated with a SiO2 layer are organized into surfactant–silica clusters forming identical spherical aggregates. Removing of surfactant micelles and MP groups leads to formation of mesopores and micropores consequently.
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•Micro-mesoporous SiO2 particles are obtained by single-step soft-template synthesis.•Porous SiO2 particles have a Brunauer-Emmett-Teller specific surface area of up to 1600 m2 g−1.•Submicrometer porous SiO2 particles have a spherical shape and a narrow size distribution.
A series of new organic ligands (5Z,5Z′)-2,2′-(alkane-α,ω-diyldiselenyl)-bis-5-(2-pyridylmethylene)-3,5-dihydro-4H-imidazol-4-ones (L) consisting of two ...5-(2-pyridylmethylene)-3,5-dihydro-4H-imidazol-4-one units linked with polymethylene chains of various lengths (n = 2–10, where n is the number of CH2 units) have been synthesized. The reactions of these ligands with CuCl2·2H2O and CuClO4·6H2O gave Cu2+ or Cu1+ containing mono- and binuclear complexes with Cu2LClx (x = 2–4) or CuL(ClO4)y (y = 1, 2) composition. It was shown that the agents reducing Cu2+ to Cu1+ in the course of complex formation can be both a ligand and an organic solvent in which the reaction is carried out. This fundamentally distinguishes the selenium-containing ligands L from their previously described sulfur analogs, which by themselves are not capable of reducing Cu2+ during complexation under the same conditions. A higher cytotoxicity and reasonable selectivity to cancer cell lines for synthesized complexes of selenium-containing ligands was shown; unlike sulfur analogs, ligands L themselves demonstrate a high cytotoxicity, comparable in some cases to the toxicity of copper-containing complexes.
Non-identical copies of mitochondrial DNA (mtDNA) compete with each other within a cell and the ultimate variant of mtDNA present depends on their relative replication rates. Using yeast
cells as a ...model, we studied the effects of mitochondrial inhibitors on the competition between wild-type mtDNA and mutant selfish mtDNA in heteroplasmic zygotes. We found that decreasing mitochondrial transmembrane potential by adding uncouplers or valinomycin changes the competition outcomes in favor of the wild-type mtDNA. This effect was significantly lower in cells with disrupted mitochondria fission or repression of the autophagy-related genes
,
or
, implying that heteroplasmic zygotes activate mitochondrial degradation in response to the depolarization. Moreover, the rate of mitochondrially targeted GFP turnover was higher in zygotes treated with uncoupler than in haploid cells or untreated zygotes. Finally, we showed that vacuoles of zygotes with uncoupler-activated autophagy contained DNA. Taken together, our data demonstrate that mitochondrial depolarization inhibits clonal expansion of selfish mtDNA and this effect depends on mitochondrial fission and autophagy. These observations suggest an activation of mitochondria quality control mechanisms in heteroplasmic yeast zygotes.
Triterpene glycosides are a diverse group of plant secondary metabolites, consisting of a sterol-like aglycon and one or several sugar groups. A number of triterpene glycosides show membranolytic ...activity, and, therefore, are considered to be promising antimicrobial drugs. However, the interrelation between their structure, biological activities, and target membrane lipid composition remains elusive. Here we studied the antifungal effects of four Panax triterpene glycosides (ginsenosides) with sugar moieties at the C-3 (ginsenosides Rg3, Rh2), C-20 (compound K), and both (ginsenoside F2) positions in Saccharomyces cerevisiae mutants with altered sterol plasma membrane composition. We observed reduced cytostatic activity of the Rg3 and compound K in the UPC2-1 strain with high membrane sterol content. Moreover, LAM gene deletion reduced yeast resistance to Rg3 and digitonin, another saponin with glycosylated aglycon in the C-3 position. LAM genes encode plasma membrane-anchored StARkin superfamily-member sterol transporters. We also showed that the deletion of the ERG6 gene that inhibits ergosterol biosynthesis at the stage of zymosterol increased the cytostatic effects of Rg3 and Rh2, but not the other two tested ginsenosides. At the same time, in silico simulation revealed that the substitution of ergosterol with zymosterol in the membrane changes the spatial orientation of Rg3 and Rh2 in the membranes. These results imply that the plasma membrane sterol composition defines its interaction with triterpene glycoside depending on their glycoside group position. Our results also suggest that the biological role of membrane-anchored StARkin family protein is to protect eukaryotic cells from triterpenes glycosylated at the C-3 position.
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•StARkin family genes provide the yeast ginsenoside Rg3 and digitonin resistance.•ERG6 deletion reduces yeast resistance to C-3 glycosylated ginsenosides Rg3 and Rh2.•In our computer-simulated membrane model, ergosterol-to-zymosterol substitution changes Rg3 localization.
A series of new organic ligands (5
,5
')-2,2'-(alkane-α,ω-diyldiselenyl)-bis-5-(2-pyridylmethylene)-3,5-dihydro-4
-imidazol-4-ones (L) consisting of two 5-(2-pyridylmethylene)-3,5-dihydro-4
...-imidazol-4-one units linked with polymethylene chains of various lengths (
= 2-10, where
is the number of CH
units) have been synthesized. The reactions of these ligands with CuCl
·2H
O and CuClO
·6H
O gave Cu
or Cu
containing mono- and binuclear complexes with Cu
LCl
(
= 2-4) or CuL(ClO
)
(
= 1, 2) composition. It was shown that the agents reducing Cu
to Cu
in the course of complex formation can be both a ligand and an organic solvent in which the reaction is carried out. This fundamentally distinguishes the selenium-containing ligands L from their previously described sulfur analogs, which by themselves are not capable of reducing Cu
during complexation under the same conditions. A higher cytotoxicity and reasonable selectivity to cancer cell lines for synthesized complexes of selenium-containing ligands was shown; unlike sulfur analogs, ligands L themselves demonstrate a high cytotoxicity, comparable in some cases to the toxicity of copper-containing complexes.
Purpose
Design and characterization of a new inductively driven wireless coil (WLC) for wrist imaging at 1.5 T with high homogeneity operating due to focusing the B1 field of a birdcage body coil.
...Methods
The WLC design has been proposed based on a volumetric self‐resonant periodic structure of inductively coupled split‐loop resonators with structural capacitance. The WLC was optimized and studied regarding radiofrequency fields and interaction to the birdcage coil (BC) by electromagnetic simulations. The manufactured WLC was characterized by on‐bench measurements and in vivo and phantom study in comparison to a standard cable‐connected receive‐only coil.
Results
The WLC placed into BC gave the measured
B1+ increase of the latter by 8.6 times for the same accepted power. The phantom and in vivo wrist imaging showed that the BC in receiving with the WLC inside reached equal or higher signal‐to‐noise ratio than the conventional clinical setup comprising the transmit‐only BC and a commercial receive‐only flex‐coil and created no artifacts. Simulations and on‐bench measurements proved safety in terms of specific absorption rate and reflected transmit power.
Conclusions
The results showed that the proposed WLC could be an alternative to standard cable‐connected receive coils in clinical magnetic resonance imaging. As an example, with no cable connection, the WLC allowed wrist imaging on a 1.5 T clinical machine using a full‐body BC for transmitting and receive with the desired signal‐to‐noise ratio, image quality, and safety.
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