256 research outputs found
Scientific substantiation and development of innovative processes for the extraction of zirconium and rare earth elements in the deep and comprehensive treatment of eudialyte concentrate
Based on a package of modern analysis methods, the influence of various acids and energy effects on the morphology, elemental composition, structural and chemical transformations of the mineral surface, and the efficiency of eudialyte concentrate leaching was studied. The mechanism and the optimal conditions and specific features of the destruction of eudialyte and rock minerals and the extraction of zirconium and REE under the influence of various acids, powerful nanosecond pulses, dielectric barrier discharge, electrochemical processing, mechanochemical activation and ultrasound were revealed. The mechanism of formation and the optimal conditions for the dispersion of silica gel, depending on the methods and parameters of energy effects, was theoretically and experimentally substantiated. A combined three-stage circuit of nitric acid leaching of eudialyte concentrate with ultrasonic treatment of the suspension, providing 97.1 % extraction of zirconium and 94.5 % REE, were scientifically substantiated and tested. The conditions for the selective deposition of zirconium and REE were theoretically and experimentally substantiated
Paradoxical lipid dependence of pores formed by the Escherichia coli α-hemolysin in planar phospholipid bilayer membranes
α-Hemolysin (HlyA) is an extracellular protein toxin (117 kDa) secreted by Escherichia coli that targets the plasma membranes of eukaryotic cells. We studied the interaction of this toxin with membranes using planar phospholipid bilayers. For all lipid mixtures tested, addition of nanomolar concentrations of toxin resulted in an increase of membrane conductance and a decrease in membrane stability. HlyA decreased membrane lifetime up to three orders of magnitude in a voltage-dependent manner. Using a theory for lipidic pore formation, we analyzed these data to quantify how HlyA diminished the line tension of the membrane (i.e., the energy required to form the edge of a new pore). However, in contrast to the expectation that adding the positive curvature agent lysophosphatidylcholine would synergistically lower line tension, its addition significantly stabilized HlyA-treated membranes. HlyA also appeared to thicken bilayers to which it was added. We discuss these results in terms of models for proteolipidic pores.Facultad de Ciencias ExactasInstituto de Investigaciones Bioquímicas de La Plat
Mineralogical and technological features and patterns of selective disintegration of ferruginous quartzites of the Mikhailovskoye deposit
The growing demand for ferrous metallurgy products necessitates the introduction of technologies that increase the efficiency of the processing of iron-bearing raw materials. A promising trend in this area is the implementation of solutions based on the possibility of selective disintegration of ores. The purpose of this work was to establish the laws of selective disintegration of ferruginous quartzites based on the results of the study of mineralogical and technological properties of raw materials. We present data on the study of mineralogical and technological features of ferruginous quartzites of the Mikhailovskoye deposit. The data were obtained using X-ray fluorescence analysis and automated mineralogical analysis. Based on studies of the nature of dissemination and the size of grains of rock-forming and ore minerals, the tasks of ore preparation are formulated. The parameters for the iron and silicon oxide distribution by grain-size classes in the grinding products were established during the study. Based on empirical dependences, the grain size of grinding was predicted, at which the most effective release of intergrowths of ore minerals and their minimum transition to the size class of –44 µm should be achieved
Paradoxical lipid dependence of pores formed by the Escherichia coli α-hemolysin in planar phospholipid bilayer membranes
α-Hemolysin (HlyA) is an extracellular protein toxin (117 kDa) secreted by Escherichia coli that targets the plasma membranes of eukaryotic cells. We studied the interaction of this toxin with membranes using planar phospholipid bilayers. For all lipid mixtures tested, addition of nanomolar concentrations of toxin resulted in an increase of membrane conductance and a decrease in membrane stability. HlyA decreased membrane lifetime up to three orders of magnitude in a voltage-dependent manner. Using a theory for lipidic pore formation, we analyzed these data to quantify how HlyA diminished the line tension of the membrane (i.e., the energy required to form the edge of a new pore). However, in contrast to the expectation that adding the positive curvature agent lysophosphatidylcholine would synergistically lower line tension, its addition significantly stabilized HlyA-treated membranes. HlyA also appeared to thicken bilayers to which it was added. We discuss these results in terms of models for proteolipidic pores.Facultad de Ciencias ExactasInstituto de Investigaciones Bioquímicas de La Plat
Field theoretic study of bilayer membrane fusion: I. Hemifusion mechanism
Self-consistent field theory is used to determine structural and energetic
properties of metastable intermediates and unstable transition states involved
in the standard stalk mechanism of bilayer membrane fusion. A microscopic model
of flexible amphiphilic chains dissolved in hydrophilic solvent is employed to
describe these self-assembled structures. We find that the barrier to formation
of the initial stalk is much smaller than previously estimated by
phenomenological theories. Therefore its creation it is not the rate limiting
process. The barrier which is relevant is associated with the rather limited
radial expansion of the stalk into a hemifusion diaphragm. It is strongly
affected by the architecture of the amphiphile, decreasing as the effective
spontaneous curvature of the amphiphile is made more negative. It is also
reduced when the tension is increased. At high tension the fusion pore, created
when a hole forms in the hemifusion diaphragm, expands without bound. At very
low membrane tension, small fusion pores can be trapped in a flickering
metastable state. Successful fusion is severely limited by the architecture of
the lipids. If the effective spontaneous curvature is not sufficiently
negative, fusion does not occur because metastable stalks, whose existence is a
seemingly necessary prerequisite, do not form at all. However if the
spontaneous curvature is too negative, stalks are so stable that fusion does
not occur because the system is unstable either to a phase of stable radial
stalks, or to an inverted-hexagonal phase induced by stable linear stalks. Our
results on the architecture and tension needed for successful fusion are
summarized in a phase diagram.Comment: in press, Biophys.J. accepted versio
The contribution of PA-X to the virulence of pandemic 2009 H1N1 and highly pathogenic H5N1 avian influenza viruses
PA-X is a novel protein encoded by PA mRNA and is found to decrease the pathogenicity of pandemic 1918 H1N1 virus in mice. However, the importance of PA-X proteins in current epidemiologically important influenza A virus strains is not known. In this study, we report on the pathogenicity and pathological effects of PA-X deficient 2009 pandemic H1N1 (pH1N1) and highly pathogenic avian influenza H5N1 viruses. We found that loss of PA-X expression in pH1N1 and H5N1 viruses increased viral replication and apoptosis in A549 cells and increased virulence and host inflammatory response in mice. In addition, PA-X deficient pH1N1 and H5N1 viruses up-regulated PA mRNA and protein synthesis and increased viral polymerase activity. Loss of PA-X was also accompanied by accelerated nuclear accumulation of PA protein and reduced suppression of PA on non-viral protein expression. Our study highlights the effects of PA-X on the moderation of viral pathogenesis and pathogenicity
The temperature dependence of lipid membrane permeability, its quantized nature, and the influence of anesthetics
We investigate the permeability of lipid membranes for fluorescence dyes and
ions. We find that permeability reaches a maximum close to the chain melting
transition of the membranes. Close to transitions, fluctuations in area and
compressibility are high, leading to an increased likelihood of spontaneous
lipid pore formation. Fluorescence Correlation Spectroscopy (FCS) reveals the
permeability for rhodamine dyes across 100 nm vesicles. Using FCS, we find that
the permeability of vesicle membranes for fluorescence dyes is within error
proportional to the excess heat capacity. To estimate defect size we measure
the conductance of solvent-free planar lipid bilayer. Microscopically, we show
that permeation events appear as quantized current events. Further, we
demonstrate that anesthetics lead to a change in membrane permeability that can
be predicted from their effect on heat capacity profiles. Depending on
temperature, the permeability can be enhanced or reduced. We demonstrate that
anesthetics decrease channel conductance and ultimately lead to 'blocking' of
the lipid pores in experiments performed at or above the chain melting
transition. Our data suggest that the macroscopic increase in permeability
close to transitions and microscopic lipid channel formation are the same
physical process.Comment: 12 pages, 6 figure
- …