Transformation of Nano-Size Titanium Dioxide Particles in the Gastrointestinal Tract and Its Role in the Transfer of Nanoparticles through the Intestinal Barrier.

In this work, the size transformation of the TiO2 nanofraction from pharmaceutical grade E171 powder was studied during its transit through the gastrointestinal tract (GIT). It was shown that pharmaceutical-grade TiO2 powder contained about 0.68% (w/w) of particles smaller than 240 nm in diameter. In the observed GIT transit process the TiO2 nanoparticles were agglomerated up to 150-200 nm in simulated salivary fluid, with gradual agglomerate enlargement up to 300-600 nm and more than 1 micron in simulated gastric fluid. In the intestinal fluid the reverse process occurred, involving a decrease of agglomerates accompanied by the formation of a small fraction with ~50 nm average size. This fraction can be further involved in the histohematic transport process. The acidity degree (pH) and mineral composition of solutions, as well as the transit speed along the gastrointestinal tract, influence the nature of the particle transformation significantly. The rapid passing between the gastrointestinal tract sections creates conditions for a decrease in part of the TiO2 particles, up to 100 nm, and may be associated with the violation of the structural and functional integrity of the intestinal mucus layer.

Indolicidin analogs with broad-spectrum antimicrobial activity and low hemolytic activity.

To create a broad-spectrum peptide biocide, we synthesized 45 analogs of antimicrobial peptide indolicidin (H-Ile-Leu-Pro-Trp-Lys-Trp-Pro-Trp-Trp-Pro-Trp-Arg-Arg-NH2). Among them the peptides H-Ile-Leu-Pro-(2-Me)Phe-Lys-(2-Me)Phe-Pro-(2-Me)Phe-(2-Me)Phe-Pro-(2-Me)Phe-Arg-Arg-NH2 and HN2-(CH2)10-Ile-Leu-Pro-D-Phe-Lys-D-Phe-Pro-D-Phe-D-Phe-Pro-D-Phe-Arg-Arg-NH2 have the broadest spectrum of antimicrobial activity and the lowest hemolytic activity. They are active against all 11 tested strains of Gram-positive bacteria, Gram-negative bacteria and fungi with MIC50 from 0.9 to 6.1 µg/ml (0.5 to 3.2 µM), being up to 3 times more active than indolicidin, and are at least 1.8 times less hemolytically active than indolicidin (reached the detection limit). These peptides are patented and could be used for further drug development as antimicrobials.

Remote epitaxy using graphene enables growth of stress-free GaN.

The properties of group III-Nitrides (III-N) such as a large direct bandgap, high melting point, and high breakdown voltage make them very attractive for optoelectronic applications. However, conventional epitaxy on SiC and sapphire substrates results in strained and defective films with consequently poor device performance. In this work, by studying the nucleation of GaN on graphene/SiC by MOVPE, we unambiguously demonstrate the possibility of remote van der Waals epitaxy. By choosing the appropriate growth conditions, GaN crystals can grow either in-plane misoriented or fully epitaxial to the substrate. The adhesion forces across the GaN and graphene interface are very weak and the micron-scale nuclei can be easily moved around. The combined use of x-ray diffraction and transmission electron microscopy demonstrate the growth of stress-free and dislocation-free crystals. The high quality of the crystals was further confirmed by photoluminescence measurements. First principles calculations additionally highlighted the importance of the polarity of the underlying substrate. This work lays the first brick towards the synthesis of high quality III-N thin films grown via van der Waals epitaxy.

Anti-Influenza Activity of Enterocin B In vitro and Protective Effect of Bacteriocinogenic Enterococcal Probiotic Strain on Influenza Infection in Mouse Model.

In spite of scientific evidence demonstrating the antiviral activity of lactic-acids bacteria, little is known about the mechanism of their action. Previously, several bacteriocins isolated from lactic acid bacteria (LAB) and some other microorganisms were reported as having antiviral activity in vitro. In the present study, chemically synthetized enterocin B (EntB) and the strain E. faecium L3, known as the producer of this peptide, were tested for activity against influenza viruses. The inhibition of cytopathic effect of А/Perth/16/2009(H3N2) and A/South Africa/3626/2013(H1N1) pdm influenza viruses in MDCK cells by chemically synthetized EntB was revealed. The EntB demonstrated antiviral activity at a concentration of 2.5-5 µg/ml depending on the dose of viruses. This peptide exhibited low toxicity in MDCK cells, causing partial damage of the monolayer of the cells only at a concentration above 10 µg/ml. It was also shown, that strain E. faecium L3-protected mice from lethal A/South Africa/3626/2013(H1N1) pdm infection. We speculate that this protective effect of enterococci may be associated with the specific action of enterocin B, which possesses antiviral activity in vitro.

Propagation of combustion waves in the shell-core energetic materials with external heat losses.

In this paper, the properties and stability of combustion waves propagating in the composite solid energetic material of the shell-core type are numerically investigated within the one-dimensional diffusive-thermal model with heat losses to the surroundings. The flame speed is calculated as a function of the parameters of the model. The boundaries of stability are determined in the space of parameters by solving the linear stability problem and direct integration of the governing non-stationary equations. The results are compared with the characteristics of the combustion waves in pure solid fuel. It is demonstrated that a stable travelling combustion wave solution can exist for the parameters of the model for which the flame front propagation is unstable in pure solid fuel and it can propagate several times faster even in the presence of significant heat losses.

Binding of Synthetic LKEKK Peptide to Human T-Lymphocytes.

The synthetic peptide LKEKK corresponding to sequence 16-20 of human thymosin-α1 and 131-135 of human interferon-α2 was labeled with tritium to specific activity 28 Ci/mol. The [3H]LKEKK bound with high affinity (Kd = 3.7 ± 0.3 nM) to donor blood T-lymphocytes. Treatment of cells with trypsin or proteinase K did not abolish [3H]LKEKK binding, suggesting the non-protein nature of the peptide receptor. The binding was inhibited by thymosin-α1, interferon-α2, and cholera toxin B subunit (Ki = 2.0 ± 0.3, 2.2 ± 0.2, and 3.6 ± 0.3 nM, respectively). Using [3H]LKEKK, we demonstrated the existence of a non-protein receptor common for thymosin-α1, interferon-α2, and cholera toxin B-subunit on donor blood T-lymphocytes.

Instability and Spontaneous Reconstruction of Few-Monolayer Thick GaN Graphitic Structures.

Two-dimensional (2D) semiconductors are a very hot topic in solid state science and technology. In addition to van der Waals solids that can be easily formed into 2D layers, it was argued that single layers of nominally 3D tetrahedrally bonded semiconductors, such as GaN or ZnO, also become flat in the monolayer limit; the planar structure was also proposed for few-layers of such materials. In this work, using first-principles calculations, we demonstrate that contrary to the existing consensus the graphitic structure of few-layer GaN is unstable and spontaneously reconstructs into a structure that remains hexagonal in plane but with covalent interlayer bonds that form alternating octagonal and square (8|4 Haeckelite) rings with pronounced in-plane anisotropy. Of special interest is the transformation of the band gap from indirect in planar GaN toward direct in the Haeckelite phase, making Haeckelite few-layer GaN an appealing material for flexible nano-optoelectronics.

[Investigation of the Influence of Angiogenesis on Tumor Growth with the Use of a Mathematical Model].

A mathematical model of tumor growth is developed taking into account angiogenesis. Malignant cells under metabolic stress produce vascular endothelium growth factor that stimulates angiogenesis, increasing nutrient influx in tumor. The model takes into account the migration and proliferation dichotomy in the malignant cells depending on nutrient concentration. Convective fluxes originated due to active tumor cell proliferation in compact dense tissue are also considered. The computational analysis of the model has demonstrated that diffusive tumor growth rate does not depend on angiogenesis while for non-invasive tumors angiogenesis can significantly alter tumor growth, although it is not able to stop it completely. The causes and significance of the result for estimation of the antitumor efficacy of antiangiogenic therapy are discussed.

Understanding Phase-Change Memory Alloys from a Chemical Perspective.

Phase-change memories (PCM) are associated with reversible ultra-fast low-energy crystal-to-amorphous switching in GeTe-based alloys co-existing with the high stability of the two phases at ambient temperature, a unique property that has been recently explained by the high fragility of the glass-forming liquid phase, where the activation barrier for crystallisation drastically increases as the temperature decreases from the glass-transition to room temperature. At the same time the atomistic dynamics of the phase-change process and the associated changes in the nature of bonding have remained unknown. In this work we demonstrate that key to this behavior is the formation of transient three-center bonds in the excited state that is enabled due to the presence of lone-pair electrons. Our findings additionally reveal previously ignored fundamental similarities between the mechanisms of reversible photoinduced structural changes in chalcogenide glasses and phase-change alloys and offer new insights into the development of efficient PCM materials.

Study of band inversion in the PbxSn1-xTe class of topological crystalline insulators using x-ray absorption spectroscopy.

Pb(x)Sn(1-x)Te and Pb(x)Sn(1-x)Se crystals belong to the class of topological crystalline insulators where topological protection is achieved due to crystal symmetry rather than time-reversal symmetry. In this work, we make use of selection rules in the x-ray absorption process to experimentally detect band inversion along the PbTe(Se)-SnTe(Se) tie-lines. The observed significant change in the ratio of intensities of L1 and L3 transitions along the tie-line demonstrates that x-ray absorption can be a useful tool to study band inversion in topological insulators.

[Evaluation of the placental morphofunctional state in perinatal HIV transmission].

The paper presents the results of investigating the mechanisms of placental insufficiency and transplacental infection of infants born to HIV-infected mothers who have received specific antiretroviral therapy mothers and who have not.

[Simulation of the competition for light in forest stands of the same age].

A model simulating the growth and interaction of trees during their competition for light has been proposed and verified. Qualitative analys of the model behavior at various values of parameters determining the tree growth rate has been performed. The model verification shows a sufficiently high accuracy of the model approximation of empirical tree growth data. To study interspecific interactions in forest communities, some computing experiments on the development of mixed forest stands, represented by the main forest-forming wood species of the Far East, have been carried out.

Influence of synthetic peptide inducers on antibacterial activity of enterococci.

Antibacterial activity of probiotic enterococci is often related to the production of bacteriocins. There is a variety of Enterococcus faecium strains which synthesise one or several enterocins including A, B, P, 96, L50AB and others. In this work we have analysed the probiotic strain E. faecium L3 whose genome contained the genes encoding enterocins А, В and a three-component regulatory system. All these genes were found to be expressed in enterococcal strain L3. Antimicrobial activity of the strain tested on the strains of Listeria monocytogenes and Streptococcus agalactiae was pheromone dependent. Chemically synthesised cyclic peptides (analogues and shorter derivates of EntF) with different molecular structures were able to increase the antagonistic activity of the strain E. faecium L3 in contrast to the strain E. faecium SF68, which does nоt have genes encoding enterocins А and В.

Interfacial phase-change memory.

Phase-change memory technology relies on the electrical and optical properties of certain materials changing substantially when the atomic structure of the material is altered by heating or some other excitation process. For example, switching the composite Ge(2)Sb(2)Te(5) (GST) alloy from its covalently bonded amorphous phase to its resonantly bonded metastable cubic crystalline phase decreases the resistivity by three orders of magnitude, and also increases reflectivity across the visible spectrum. Moreover, phase-change memory based on GST is scalable, and is therefore a candidate to replace Flash memory for non-volatile data storage applications. The energy needed to switch between the two phases depends on the intrinsic properties of the phase-change material and the device architecture; this energy is usually supplied by laser or electrical pulses. The switching energy for GST can be reduced by limiting the movement of the atoms to a single dimension, thus substantially reducing the entropic losses associated with the phase-change process. In particular, aligning the c-axis of a hexagonal Sb(2)Te(3) layer and the 〈111〉 direction of a cubic GeTe layer in a superlattice structure creates a material in which Ge atoms can switch between octahedral sites and lower-coordination sites at the interface of the superlattice layers. Here we demonstrate GeTe/Sb(2)Te(3) interfacial phase-change memory (IPCM) data storage devices with reduced switching energies, improved write-erase cycle lifetimes and faster switching speeds.

Distortion-triggered loss of long-range order in solids with bonding energy hierarchy.

An amorphous-to-crystal transition in phase-change materials like Ge-Sb-Te is widely used for data storage. The basic principle is to take advantage of the property contrast between the crystalline and amorphous states to encode information; amorphization is believed to be caused by melting the materials with an intense laser or electrical pulse and subsequently quenching the melt. Here, we demonstrate that distortions in the crystalline phase may trigger a collapse of long-range order, generating the amorphous phase without going through the liquid state. We further show that the principal change in optical properties occurs during the distortion of the still crystalline structure, upsetting yet another commonly held belief that attributes the change in properties to the loss of long-range order. Furthermore, our results suggest a way to lower energy consumption by condensing phase change inducing energy into shorter pulses or through the use of coherent phonon excitation.

Dendrimer D5 is a vector for peptide transport to brain cells.

Dendrimers are a new class of nonviral vectors for gene or drug transport. Dendrimer capacity to penetrate through the blood-brain barrier remaines little studied. Biotinylated polylysine dendrimer D5, similarly to human growth hormone biotinylated fragment covalently bound to D5 dendrimer, penetrates through the blood-brain barrier and accumulates in Drosophila brain after injection into the abdomen. Hence, D5 dendrimer can serve as a vector for peptide transport to brain cells.

Expression of thrombospondin-1 gene mRNA and protein in the placenta in gestosis.

The expression of TSP-1 gene mRNA and TSP-1 protein in the placental tissue was studied during normal pregnancy and in gestosis. The formation of placental tissue in normal gestation was associated with expression of TSP-1 gene mRNA and of TSP-1 protein. Gestosis was associated with inflammatory reaction in the placenta characterized by increased counts of lymphocytes and macrophages in the villous stroma and involution degenerative changes in tissue. Disorders in placental villi maturation and branching in gestosis were paralleled by hyperexpression of TSP-1 gene mRNA by placental cells and hyperexpression of TSP-1 protein predominating in the stromal elements of terminal villi and near villous vessels.

[Experimental study of candidate vaccines against variable or quasi-species pathogenes: multiepitopic synthetic peptide antigenes and new receptor-guiding adjuvants].

The short multiepitopic synthetic peptides from the sequences of hypervariable area of V3-loope of gp120 of HIV don't induce anti-peptides antibodies production in mice themselves. We prepared the potent immunogen by noncovalent conjugations of the multitude peptides with pure peptidoglycans from cell wall of Salmonella typhi. The sera from immunized mice have the anti-peptides antibody titers (3-5) x 10(5) in ELISA, as high as Freund's adjuvant is of use.

Toward the ultimate limit of phase change in Ge(2)Sb(2)Te(5).

The limit to which the phase change memory material Ge(2)Sb(2)Te(5) can be scaled toward the smallest possible memory cell is investigated using structural and optical methodologies. The encapsulation material surrounding the Ge(2)Sb(2)Te(5) has an increasingly dominant effect on the material's ability to change phase, and a profound increase in the crystallization temperature is observed when the Ge(2)Sb(2)Te(5) layer is less than 6 nm thick. We have found that the increased crystallization temperature originates from compressive stress exerted from the encapsulation material. By minimizing the stress, we have maintained the bulk crystallization temperature in Ge(2)Sb(2)Te(5) films just 2 nm thick.