Polymorphism of amyloid β peptide in different environments: implications for membrane insertion and pore formation

Amyloid-β (Aβ) peptides are thought to be involved in neurodegenerative diseases such as Alzheimer's disease and Down's syndrome. They form a large number of polymorphic structures, including heterogeneous ionic pores in membranes as well as different types of fibrillar and globular structures on surfaces and in solution. Understanding the origin of these structures and the factors that influence their occurrence is of great biomedical interest because of the possible relationship between structure and pathogenicity. Here, we use atomic force microscopy (AFM) and molecular dynamics (MD) simulations to demonstrate that at room temperature a truncated Aβ peptide which is generated in vivo and shown to be toxic in vitro forms fibrillar structures on hydrophobic graphite surfaces, but not on hydrophilic mica or lipid bilayers. Our results suggest that the toxic pores and fibrillar polymorphic organizations can be explained in terms of the U-shaped β-strand-turn-β-strand structural motif observed for full length Aβ and other amyloids, as well as the physicochemical properties at the interfaces. The interactions of the hydrophobic, truncated Aβ with its environment illustrate that the universal amyloid motif can provide a link between the pore and fibrillar structures and indicate that surfaces with different physicochemical properties can shift the polymorphic landscape toward other conformational states.     

Co-introduction of transition metal ions into cationic positions of H-ZSM—5 by a solid-state reaction

Calcination of a mixture of H-ZSM—5 and CuCrO₄ in air was accompanied by migration of metal ions into zeolitic channels. Cu(II) and Cr(V) ions were located randomly as isolated cations with negligible dipole—dipole interaction. The consecutive interaction of H-ZSM—5 with CrO₃ and CuO resulted in the substitution of a significant number of Cr(V) ions by Cu(II) ions in cationic positions of H-ZSM—5. The interaction of H-ZSM—5 with V₂O₅ and CuO led to 90% substitution of V(IV) cations by Cu(II) cations. Reduction of this sample by H₂ at 400°C resulted in the migration of copper from zeolite channels and the cationic positions became vacant. The rise in temperature to 800°C in H₂ resulted in the remigration of V(IV) ions into cationic positions. Thus, thermal treatment of high-silica zeolites with transition metal compounds under different conditions may be accompanied by complex migration processes, redistribution and substitution of different polyvalent ions into cationic positions in the zeolite.     

Influence of contour scans on surface roughness and pore formation using Scalmalloy® manufactured by laser powder bed fusion (PBF-LB)

The scandium modified aluminium alloy Scalmalloy® is specifically developed for the use in laser-based powder bed fusion (PBF-LB). It is supposed to show potential in the production of lightweight structures due to its high specific strength compared to other aluminium alloys. A limiting factor is the high surface roughness of additively manufactured parts, which has a negative influence on its mechanical properties, especially under cyclic loads. In order to reduce the surface roughness, methods of design of experiments (DoE) are applied to develop contour parameters. Additionally, the formation of pores in keyhole-mode welding and strategies to reduce the porosity in the contour area are investigated. The surface roughness of vertical walls can be reduced down to Ra < 7 μm using contour scans with a line energy E_L >0.9 J mm⁻¹ but keyhole pores start to form applying E_L >0.6– 0.75 J mm⁻¹. Two contour parameter sets in different E_L-ranges are developed that can be used to reduce the surface roughness compared to parameter sets without contour scans, without increasing the porosity in the contour area. Their impact on the mechanical properties has to be further investigated.     

Mechanism of silver nano-particles formation on α-alumina using supercritical water

Supercritical water impregnation is a novel method, which utilizes high diffusivity of the fluid with hydrothermal synthesis allowing nano-particles to deposit on porous materials in well-dispersed condition. In this work, silver nano-particles were deposited on the surface of α-alumina supports using metal acetate solution. TEM-EDS analyses clearly identified the silver particle of two kinds, those deposited on α-alumina surface and those gathering in bulk phase. Their particle size distribution showed differences in propensity, implying that particle formation were via different mechanism. The difference in particle deposition mechanism was also confirmed from the results of other operational factors investigated. Furthermore, the mechanism of particle deposition to alumina support surface have been proposed based on the experimental results and reported observation of nucleation and particle growth steps during the hydrothermal synthesis. In addition, the mechanism of silver particle formation has been discussed in detail.     

Room temperature synthesis and formation process of α-NaYF4 nanocubes

In this article, α-NaYF₄ nanocubes were synthesized with a simple and environmentally friendly method at room temperature. The structure and morphology of the products were characterized by X-ray diffraction and scanning electron microscopy. The influence of the F^?/Y³⁺ molar ratio on the morphology of the products was examined. The products changed from spherical nanocrystals to cubic nanocrystals when the F^?/Y³⁺ molar ratio gradually increased from 4:1 to 16:1, and excessive F^? ions were necessary for the formation of regular NaYF₄ nanocubes in our synthesis procedure. The formation process of these α-NaYF₄ nanocrystals was traced via time-dependent experiments. Several nanometer-sized NaYF₄ nanocrystals changed into 100 nm sized NaYF₄ nanocrystals with prolonging of the reaction time. Additionally, the photoluminescence properties of Eu³⁺-doped samples were investigated. The excitation spectrum consists of the characteristic absorption peaks of Eu³⁺ corresponding to the direct excitation from the europium f-electrons. The charge-transfer band of Eu³⁺–F^? is not present in our measured range. The ⁵D₀ → ⁷F₁ transition is much stronger than the ⁵D₀ → ⁷F₂ transition in our samples.     

Softening of α-Ti by electrochemically introduced hydrogen

The substantial and permanent modification of the elastic and inelastic properties of α-Ti have been achieved by hydrogen charging with cathodic polarization in an alkaline solution at RT, with the effects being dependent on the hydrogen state of the metal. The decrease in the elastic modulus to values close to those characteristic for bones have been caused by the distortion of the Ti lattice due to the supersaturation of the solid solution with hydrogen and (or) due to the formation of hydride precursors and precipitates. The low, but still detectable decrease in the elastic modulus has been observed by the formation of a compact hydride layer. On the basis of a thorough examination of the effect of cathodic polarization on the formation and morphology of the hydride phase and on the state of the α-Ti lattice, the electrochemical parameters provided: (1) the presence of hydrogen in supersaturated solid solution, (2) the formation of hydride precipitates of various stoichiometry and (3) the formation of the compact hydride surface layer have been determined.Taking into account the hydrogen induced metal softening, the easiness of electrochemical alloying the metal with hydrogen and no health hazard produced by this element when dissolved in body liquids, the electrochemical hydrogen treatment of Ti implants can be considered as very promising.     

Encapsulation of α-cyano-4-hydroxycinnamic acid into a NaY zeolite

The faujasite zeolite structure was studied to investigate its suitability for development of new drug delivery systems (DDS). The sodium form (NaY) of the zeolite was used for encapsulation of α-cyano-4-hydroxycinnamic acid (CHC), an experimental anticancer drug used in colorectal cancer therapy. The DDS was prepared by diffusion in liquid phase of CHC as a guest in the void space of the host zeolite structure at pH 7.0. The molecular integrity of CHC in the encapsulation process was evaluated by proton nuclear magnetic resonance spectroscopy (¹H NMR) and Ultraviolet–Visible spectroscopy (UV–Vis). The new drug delivery system, CHC@NaY, was characterized by Fourier transform infrared spectroscopy and UV–Vis, chemical analysis, powder X-ray diffraction, and Scanning electron microscopy. Analysis of the data of the drug alone and encapsulated in NaY show that CHC and the zeolite framework preserved their original structure. The effect of the zeolite and DDS on HCT-15 human colon carcinoma cell line viability was evaluated. The encapsulation of CHC significantly increased its potency.     

Microstructure control of α-Sialon ceramics by seeding with α-Sialon particles

A proper powder preparation was used to develop -Sialon single crystals as seeds. The microstructure and fracture toughness of seed-containing -Sialon ceramics sintered by hot-pressing were investigated. The specimen without seeding consisted of fine grains and a small amount of coarse grains. Specimens seeded with -Sialon single crystal particles presented a large amount of elongated -Sialon grains. The aspect ratio and the amount of elongated -Sialon grains can be tailored by using different sizes and amounts of the seeds. The fracture toughness of seed-containing -Sialon ceramics is improved, which is attributed to grain pullout and bridging of elongated grains.     

The formation of metal antimonates by mechanical milling and the conversion of α-Sb2O4 to β-Sb2O4

The mechanical milling of -Fe₂O₃ or V₂O₅ with Sb₂O₃ results in the formation of small particle FeSbO₄ or VSbO₄. Milling also induces the conversion of cubic Sb₂O₃ to the orthorhombic modification and the transformation of -Sb₂O₄ to -Sb₂O₄. The milling-induced - to -Sb₂O₄ phase transition is even more facile in the presence of vanadium or iron.     

Optimization of the thermoelectric performance of α-MgAgSb-based materials by Zn-doping

Journal of Materials Science - Recently, α-MgAgSb-based materials have proved to be a kind of potential thermoelectric materials around room temperature. Here, a series of Zn-doped...     

Construction of two-dimensional hydrogen clusters on Au（111） directed by phthalocyanine molecules

Low-dimensional H2 aggregates have been successfully fabricated on Au（111） surfaces and investigated by means of low temperature scanning tunneling microscopy. We use manganese phthalocyanine （MnPc） molecules anchored on the Au（111） surface to efficiently collect and pin hydrogen molecules. A two-dimensional （2D） molecular hydrogen cluster is formed around the MnPc. The hydrogen cluster exhibits bias-dependent topography and spatial-dependent conductance spectra, which are rationalized by the exponentially decreasing threshold energy with distance from the central MnPc to activate the motion of the H2 molecules. This exponential drop reveals an interfacial phase behavior in the 2D cluster.     

Preparation of octacalcium phosphate by the hydrolysis of α-tricalcium phosphate

A new simple method of preparation for the thermodynamically unstable octacalcium phosphate [Ca₈H₂(PO₄)₆·5H₂O; OCP] has been developed using the hydrolysis of -Ca₃(PO₄)₂ instead of the conventional hydrolysis of CaHPO₄·2H₂O. The hydrolysis experiments were carried out by treating an -Ca₃(PO₄)₂(1 g)-H₂O(50 m) suspension for 3 h at temperatures in the range 40 to 80° C and at pHs in the range 3 to 7.5. The formation of OCR was limited to within a narrow region between formation regions of other phosphates. Favourable conditions for OCP preparation were, for example, 70° C, pH4.5 to 5.0 and 60° C, pH5.0. Particles of OCP were composed of tight aggregates of strip-like microcrystals growing probably along the [0 0 1] and (1 0 0) plane of the OCP structure. Nearly stoichiometric OCP was obtained under the most suitable conditions with good reproducibility. Pyrolytic processes of OCP were approximately consistent with the data published so far. However, the temperatures of the appearance and disappearance of pyrolytic crystalline phases and ionic species deviated slightly from the published data. Thermal dehydration up to 150° C without destruction of OCP and decomposition reactions above 300° C resulted in changes in surface area and average pore radius of OCP.     

Room-temperature ferromagnetic and photoluminescence properties of indium–tin-oxide nanoparticles synthesized by solid-state reaction

In the present study, indium–tin-oxide (ITO) nanoparticles were synthesized using solid-state reaction and studied for their structural, vibrational and magnetic properties. The ITO nanoparticles were prepared under reduced pressure, which can increase the oxygen vacancies in the samples. The X-ray diffraction studies confirmed singe-phase cubic bixbyite structure of ITO with average crystallite size of 47 nm. The lattice vibrational studies (FT-IR and Raman spectroscopy) at room temperature indicated that Sn ions were occupied in In₂O₃ lattice and gives corresponding active vibrational modes in the respective spectra. The magnetic studies at room temperature reveal the ferromagnetic nature of ITO and the strength of magnetization is superior to those of In₂O₃ and SnO₂. However, the magnetic studies at 100 K revealed reduced ferromagnetism, which could be attributed to reduced itinerary electrons at low temperature. Blue and blue–green emissions were found from the ITO nanoparticles, which could be due to vacancies or surface defects present in the system.     

Microwave-Assisted Aging of Organic–Inorganic Hybrid Nanocomposite of α-Naphthaleneacetate in the Lamella of Zn-Al-Layered Double Hydroxide

Microwave-assisted aging Zn-Al-layered double hydroxide with nitrate as the interlayer anion (ZANOL) and its nanohybrid with an organic moiety, -naphthaleneacetate (ZANAN), was done and the resulting properties of the materials compared. The results showed that intercalation of the -naphthaleneacetate (NAA) anion into the Zn-Al layered double hydroxide lamella is readily accomplished, resulting in the expansion of the interlayer spacing from 9.0 Å in the layered double hydroxide to 20.0 Å in the nanohybrid. This expansion accommodates the NAA anion of larger size than nitrate, as indicated by its molecular structure. For both methods, the resulting materials afforded a well-ordered organic–inorganic nanolayered structure. The Zn to Al ratio of the resulting nanocomposite is lower than the ratio present in the mother liquor at the beginning of the reaction, which implied less incorporation of aluminum ions from the mother liquor into the inorganic metal hydroxide layers. By using the microwave-assisted method, however, slightly more Al³⁺ ions were incorporated into the inorganic metal double hydroxide layers. In general, there is not much difference in the physicochemical properties of ZANANs aged by either the microwave or the conventional oil bath method. For both methods, longer aging time slightly enriched the organic content of the resulting nanohybrid and the inorganic Zn to Al ratio remained the same, independent of the aging time.     

Structure and Optical Behavior of Nanocomposite Hybrid Films of Well Monodispersed ZnO Nanoparticles into Poly （vinylpyrrolidone）

We fabricated an inorganic-polymeric photoluminescent thin film based on ZnO nanoparticles, which were grown directly in the poly（vinylpyrrolidone） （PVP） matrix. The microstructure, composition, thermal stability, and the temperature-dependent photoluminescence of the thin film were investigated. X-ray diffraction （XRD） and transmission electron microscopy （TEM） results indicated that all the ZnO nanoparticles with a polycrys talline hexagonal wurzite structure were well separated from each other and were dispersed in the polymeric matrix homogeneously and randomly. Raman spectrum （Raman） showed a typical resonant multi-phonon process within the hybrid thin film. The shifts of infrared bands for PVP in the hybrid film should be attributed to strong coulombic interaction between ZnO and polymeric matrix. The stability of the hybrid film and the effect of the perturbation of ZnO on the stability were determined by means of the thermogravimetric analysis （TG） and differential thermal analysis （DTA）. The ultraviolet-visible adsorption （UV-vis） showed distinct excitonic features. The photoluminescent spectrum （PL） of the ZnO nanoparticles modified by PVP molecules showed markedly enhanced ultraviolet emission and significantly reduced green emission, which was due to the Perfect surface passivation of ZnO nanoparticles. Temperature dependent photoluminescent spectrum studies suggested that the ultraviolet emission was associated with bound exciton recombination.     

Strength properties of ice–soil composites created by method of cryotropic gel formation

This paper considers the strengthening of both frozen soils and the soils after thawing in ice–soil composites generated by the method of cryotropic gel formation. The properties of the frozen soils (ice–soil composites) have to be improved for example in order to create reliable materials with low filtration factor for building weirs and other hydrotechnical constructions, which operate under a wide range of temperatures, including positive temperatures. The application of this method is very promising in terms of the creation of almost impermeable curtains for hydrotechnical structures in cold regions. It is very important that such elements are safe in both frozen and thawing conditions. Aqueous solutions of polyvinyl alcohol (PVA) are used for the formation of cryogels. This paper shows that the ice–soil composites, obtained by using the method of cryotropic gel formation, are sufficiently strong and watertight during thawing. Experimental data are provided.     

Synthesis, X-ray diffraction and solid-state 31P magic angle spinning NMR study of α-tricalcium orthophosphate

The effects of synthesis conditions on the quantitative preparation of -tricalcium phosphate (-TCP) have been investigated. The following parameters of the synthesis were considered: nature of the starting material-Ca-deficient hydroxyapatite, DAP, versus hydroxyapatite-anhydrous dicalcium phosphate mixtures (HAP-DCPA); Ca/P atomic ratio of the mixture, calcination temperature and time, and cooling rate. The yield and crystallinity of the final product have been estimated using X-ray diffraction (XRD) and solid state ³¹P magic angle spinning NMR (MAS-NMR) techniques. The results show that pure, well-crystallized -TCP powders exhibiting nearly ideal MAS-NMR spectra, can be obtained by reactive sintering of HAP-DCPA (Ca/P=1.50...1.52) mixtures, at 1400°C for 8 h. The broadening of MAS-NMR spectra can be used as an indicator of structural order in the final product. The -TCP yield with DAP was always less than 50%.     

Synthesis and alteration of α-LiFeO2 by mechanochemical processes

The effects of grinding on a stoichiometric mixture of LiOH · H₂O and -FeOOH were studied. It was found that, in the course of grinding, losses of structural water occurred and a phase structurally related to disordered -LiFeO₂ was formed. X-ray diffraction data suggest the occurrence of an ordered phase as intermediate and both -Fe₂O₃ and -Fe₂O₃ were undetected during the comminution process. A prolonged mechanical treatment of this mixture originated an elimination of Li⁺ from the -LiFeO₂ structure and the appearance of the spinel phase, -LiFe₅O₈. Additionally, the mechanical activation of a sample of -LiFeO₂ prepared at high temperatures also leads to a similar rearrangement of cations. The structural transformation is explained with the help of a model in which the vacancies of Li⁺ created during grinding promote the migration of the Fe³⁺ ions from octahedral to tetrahedral sites.