Natural polycationic membrane-active peptides typically lack disulfide bonds and exhibit fusion, cell-penetrating, antimicrobial activities. They are mostly unordered in solution, but adopt a helical ...structure, when bound to phospholipid membranes. Structurally different are cardiotoxins (or cytotoxins, CTs) from cobra venom. They are fully β- structured molecules, characterized by the three-finger fold (TFF). Affinity of CTs to lipid bilayer was shown to depend on amino acid sequence in the tips of the three loops. In the present review, CT-membrane interactions are analyzed through the prism of data on binding of the toxins to phospholipid liposomes and detergent micelles, as well as their structural and computational studies in membrane mimicking environments. We assess different hydrophobicity scales to compare membrane partitioning of various CTs and their membrane effects. A comparison of hydrophobic/hydrophilic properties of CTs and linear polycationic peptides provides a key to their biological activity and creates a fundamental basis for rational design of new membrane-interacting compounds, including new promising drugs. For instance, from the viewpoint of the data obtained on model lipid membranes, cytotoxic activity of CTs against cancer cells is discussed.
Fibrin is a well-known tool in tissue engineering, but the structure of its modifications created to improve its properties remains undiscussed despite its importance,
in designing biomaterials that ...ensure cell migration and lumenogenesis. We sought to uncover the structural aspects of PEGylated fibrin hydrogels shown to contribute to angiogenesis. The analysis of the small-angle X-ray scattering (SAXS) data and
modeling revealed that the PEGylation of fibrinogen led to the formation of oligomeric species, which are larger at a higher PEG : fibrinogen molar ratio. The improvement of optical properties was provided by the decrease in aggregates' sizes and also by retaining the bound water. Compared to the native fibrin, the structure of the 5 : 1 PEGylated fibrin gel consisted of homogenously distributed flexible fibrils with a smaller space between them. Moreover, as arginylglycylaspartic acid (RGD) sites may be partly bound to PEG-NHS or masked because of the oligomerization, the number of adhesion sites may be slightly reduced that may provide the better cell migration and formation of continuous capillary-like structures.
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IJS, KILJ, NUK, UL, UM, UPUK
In this paper hydrodynamic processes arisen in the silica under laser action are analyzed numerically. Exactly these processes determine the development of fracture of optical fiber under the action ...of high-intense laser beams. The mathematical model describing the wave processes inside the core and cover of an optical fiber is proposed. It is shown that the basic mechanism of high-speed fracture wave propagation is related to the plasma expansion into the cold silica. At the same time, the transverse waves define the development of the plasma bubble and as a result the destruction of the optical fiber core. Obtained hydrodynamic mechanisms are basic for a wide class of scenarios related to the interaction of high-energy fluxes with solid medium.
•Hydrodynamic processes involved in laser-induced silica fracture are overviewed.•A mathematical model is proposed to describe wave processes in silica.•The fracture is mainly due to the expansion of hot plasma into the cold silica.•The plasma bubble structure is affected by transverse shock and rarefaction waves.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this paper a set of models is considered to describe the mechanism of ultra fast plasma propagation in silicon dioxide waveguide under the action of intense laser pulse. In particular, the paths ...via which the energy is absorbed are analyzed. For the first time, the absorption in the region ahead of the primary plasma front related to the medium fracture by the shock wave with magnitude greater than 30kbar is taken into account on the base of recently obtained experimental data. And it is clearly shown that this effect defines the propagation of the absorption wave with a speed ~3km/s that was observed experimentally and did not get an explanation yet. It is also shown that the competition between the energy absorption behind the shock wave and momentum losses due to transverse expansion defines the oscillations in the speed of absorption wave. The spatial period of oscillations depends unequivocally on the absorption length in the fractured region as well as on the fragments size. Obtained results can provide an interpretation of the unique experimental data on high-speed fracture of optical fibers under the action of intense laser pulse.
•A set of models is proposed for ultra-fast laser plasma propagation in silicon dioxide.•Compression-induced fracture causes transparency loss ahead of the primary plasma front.•Ultra-fast plasma front propagates in oscillatory manner.•The average plasma front speed is estimated as 3 km/s.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The propagation of an optical discharge (OD) along hollow-core optical fibers (HCFs) is investigated experimentally. Silica-based revolver-type HCFs filled with atmospheric air were used as test ...samples. We observed that the average propagation velocity of an OD along the HCF (VAV) depends on the properties of the medium around the silica structure of the fiber. It is shown that the value of VAV changes by approximately a factor of three, depending on whether the optical discharge is moving along a polymer coated or uncoated fiber. The value of VAV practically does not change when the polymer is replaced by an immersion liquid (such as glycerol) or liquid gallium. By analyzing the destruction region's patterns that appear in the fiber cladding after an OD propagation, we propose the physical picture of the phenomenon.
In this work the graphitization and thermal stability of detonation nanodiamonds were studied. Received data showed that the temperature of graphitization of nanodiamond particles lies in wide range ...and the temperature of graphitization beginning depend on the particle size. It is established the influence of heating rate on the size of nanodiamond conglomerates. The analysis of literature shows that the graphitization processes take place at irradiation. Depending on the type and irradiation dose the point defects, amorphous and graphite phases can form in the diamond structure. Annealing of irradiation samples showed the defect structure restore to ideal lattice and the release of stored energy.
The behavior of detonation nano- and microdiamonds at increased temperatures is studied by synchronous thermal analysis, X-ray diffraction analysis, and scanning electron microscopy. The X-ray ...analysis of survived samples shows that a part of the nanodiamond is stable under heating to 1500°C. At the heating to 600°C, we see the decreasing of nanodiamond phase. Appearance of graphite phase isn't observed in the sample up to 1500°C. However, in the range Bragg angle 20-32° after heating to 1500°C, the x-ray amorphous graphite-like phase is observed. The analysis of microphotographs of samples before and after heating showed the influence of heating rate on the parameters of powder particles. A high thermal stability of detonation microdiamonds (above 1500°C) is established. Literature data on the radiation stability of diamond are analyzed. It is established that the character of the diamond damage depends on the type and dose of the irradiation.
Detonation nanodiamonds are produced at utilization of high explosives. When an explosive blasts in a water environment, the detonation products contain microdiamonds, and in a gaseous medium, ...nanodiamonds. It is known that with decreasing size the influence of the surface energy of particles on their properties increases. Thus, it is interesting to compare the properties of detonation nano and microdiamonds. In this study, we have examined the thermal stability of diamond materials by synchronous thermal analysis. The experiments were performed at atmospheric pressure in argon flow for different heating rates in a range from room temperature to 1500 °C. Samples of initial and annealed micro and nanomaterials were studied using electron microscopy, x-ray and x-ray-fluorescence analysis. It was established that thermal and structural properties of micro and nanodiamonds differ substantially.
The detonation nanodiamond is a new perspective material. Ammunition recycling with use of high explosives and obtaining nanodiamond as the result of the detonation synthesis have given a new ...motivation for searching of their application areas. In this work nanodiamond powder has been investigated by the method of synchronous thermal analysis. Experiments have been carried out at atmospheric pressure in the environment of argon. Nanodiamond powder has been heated in the closed corundum crucible at the temperature range of 30-1500 °C. The heating rates were varied from 2 K min to 20 K min. After the heat treatment, the samples have been studied by the x-ray diffraction and the electron microscopy. As one of the results of this work, it has been found that the detonation nanodiamond has not started the transition into graphite at the temperature below 800 °C.
In this work, porous media are studied using silicone rubber with glass microspheres as an example. There were investigated three types of silicon rubber samples featuring different concentrations ...and sizes of microspheres: non-porous silicon rubber, porous silicon rubber with calibrated glass microspheres and porous silicon rubber with glass microspheres having a wide range of sizes. The density of the samples was 0.99, 0.55 and 0.48 g/cm3, accordingly. Investigating spall strength under pulse tension shows that the destruction beginning threshold of the samples in question is quite low. For the non-porous sample, it is around 30 MPa, for the porous ones it is an order of magnitude lower. The spall plate does not come off the sample after the beginning of destruction. The ability of the free surface velocity to change in such a way is typical for materials with a low destruction threshold.
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