Structure of dextran–magnetite complex: relation between conformation of dextran chains covering core and its molecular weight

A homologous series of dextran–magnetite complex (DM) was synthesized using alkali-treated dextrans with various molecular weights from 1800 to 27 000. The structure of DM particles in water, particularly effect on molecular weight of dextran, was studied. The number of dextran chains binding to a core is possibly determined by the steric hindrance between dextran chains covering core. The conformation of dextran chains may change from a fully extended state to a random-coiled state with an increase in molecular weight.     

Dextran-magnetite complex: temperature dependence of its NMR relaxivity

The NMR relaxivity of proton by dextran-magnetite (DM) complex was examined at temperatures from 20 to 80 °C. The decrease in T ₁ relaxivity with increasing temperature is due to the thermal activation of motion of water molecules in and/or surrounding DM particle. The decrease in magnetization of magnetite core is the secondary effect. The temperature dependence of T ₁ relaxivity was found to depend on molecular weight of dextran. The motion of dextran chains binding to core may affect the thermal activation of heavy water interacted with dextran. The Arrhenius plots of T ₁ relaxivity showed different slopes at 20–40 °C and 50–80 °C, while, no change in slope was observed for Fe(NO₃)₃, CuSO₄ and Gd-DTPA solutions.     

Pressureless sintering of SiC-TiC composites with improved fracture toughness

Composites of SiC-TiC containing up to 45 wt% of dispersed TiC particles were pressureless sintered to 97% of theoretical density at temperatures between 1850°C and 1950°C with Al₂O₃ and Y₂O₃ additions. An in situ-toughened microstructure, consisted of uniformly distributed elongated -SiC grains, matrixlike TiC grains, and yttrium aluminum garnet (YAG) as a grain boundary phase, was developed via pressureless sintering route in the composites sintered at 1900°C. The fracture toughness of SiC-30 wt% TiC composites sintered at 1900°C for 2 h was as high as 7.8 MPa·m^1/2, owing to the bridging and crack deflection by the elongated -SiC grains.     

Characterization of shock-hardened Al-8090 alloy

The structure and mechanical properties of Al-Li8090 alloy, that was dynamically deformed and then age hardened, were studied as a function of the changes in the nature and amount of precipitates produced. A comparison was made between two groups of samples, one group that was solution heat treated (SHT) and quenched from 530°C before the dynamic deformation and the other group that was dynamically deformed in the as-received (AR) condition. The higher values for microhardness and ultimate tensile strength observed (138 and 140 VHN, and 405 and 458 MPa, respectively), subsequent to shock treatment (ST), have been attributed to the increase in dislocation density and grain-boundary precipitation produced due to shock deformation. Dislocations and grain boundaries were assumed to act as precipitation sites and an increase in dislocation density, due to ST, was expected to increase precipitation density of (Al₃Li), S(Al₂CuMg), and T₁(Al₂CuLi) phases which, in turn, are expected to increase strength properties of the alloy. Differential scanning calorimetry showed that, for the species that precipitate below 180°C, (Al₃Li) and GP zones, an increase in the amount of deformation increased the precipitation temperatures. However, for the species that precipitate at 197°C, S(Al₂CuMg), an increase in the amount of deformation produced a decrease in its precipitation temperature. These results have been partially confirmed by the activation energy calculations for temperatures below 197 °C, which show a decrease of precipitation energies with an increase in the amount of deformation. Activation energies calculated from ageing curves showed that when ageing at low temperature (165–180 °C range), activation energies for the precipitation process are decreased upon increase in cold work. Shock treatment of SHT samples exhibited decreased activation energy values of precipitation, from 36.14 kcal mol^–1 for the SHT sample to 24.18, 24.08, and 21.00 kcal mol^–1 for SHT + ST samples 1, 2, and 3, respectively (corresponding to 1, 2, and 3 sheets of explosive). Activation energies of precipitation for AR + ST samples showed even lower values; 9.45, 9.95, and 8.21 kcal mol^–1 for samples 4, 5, and 6, respectively. These activation energies strongly corroborate the role of defect substructure on the age-hardening kinetics of this alloy.     

Effect of dextran as a run buffer additive in drug-protein binding studies using capillary electrophoresis frontal analysis

The study of drug-protein interactions by capillary electrophoresis frontal analysis requires establishment of a sufficient mobility difference between the mobility of the ligand and protein. The potential utility of dextran as a run buffer additive to manipulate the electrophoretic mobilities of low molecular weight ligands and protein in capillary electrophoresis frontal analysis binding studies was assessed. It was demonstrated that dextran was effective in improving the separation between the ligands warfarin and flurbiprofen and human serum albumin. Separation of ligand and protein increased with the concentration of added dextran (0-7.5% (w/w)), while molecular weight of the additive (70,000-2,000,000) only had a minor effect. The effect of dextran addition on viscosity and electrophoretic and electroosmotic mobilites was systematically studied. Optimal frontal analysis settings were a compromise between achieving satisfactory separation and acceptable analysis times without loss of plateau peak conditions. No effect of dextran upon the drug-human serum albumin interactions could be detected for the model ligands. Introduction of dextran into the electrophoresis buffer expands the applicability of capillary electrophoresis frontal analysis in drug research to binding interactions between proteins and low molecular weight ligands possessing similar electrophoretic mobilities.     

Some elevated temperature mechanical properties of Magnox AL80

The influence of grain-boundary hydride (MgH₂) precipitation on the mechanical properties of Magnox AL80 has been investigated by carrying out slow tensile and fatigue tests. The presence of hydride precipitates at some grain boundaries was found to have a detrimental effect on the slow tensile ductilities at the lower end (20 to 40% h^–1) of the range of strain rates used (20 to 2000% h^–1) at 250° C and at 20% h–1 at 300° C. Grain-boundary cavities caused by the dissociation of the hydride precipitates were introduced either byin situ thermal treatment prior to testing at 250° C or by testing at higher temperatures and also resulted in lower tensile ductilities at slow strain rates. The fatigue lives of Magnox AL80 were not significantly influenced by the presence of grain-boundary hydride precipitates or cavities due to the dissociation of the precipitates. This is due to the majority of the boundaries being unsuitably oriented to experience high shear stresses. Long-term ageing at 450° C was found to reduce the subsequent fatigue strength at that temperature and this effect is associated with the boundaries becoming more prone to migration during fatigue cycling.     

Immunosensor for detection of inhibitory neurotransmitter gamma-aminobutyric acid using quartz crystal microbalance

A piezoelectric immunosensor for sensing the low molecular weight neurotransmitter gamma-aminobutyric acid (GABA), one of two major inhibitory neurotransmitters in the central nervous system, is described. The sensing interface consists of a dextran layer covalently attached to a self-assembled monolayer of thiolamine compound on the surface of gold electrodes of the crystals. The dextran layer is further modified with GABA molecules to act as the biosensing layer. The affinity binding of monoclonal anti-GABA antibody on the modified piezoelectric crystals is studied in real time without any additional labels. The equilibrium association constant, K(eq) for binding between anti-GABA antibody and GABA molecules is 14.5 microg x mL (-1). The detection limit for anti-GABA is approximately 10 nM. The sensitivity of the sensor at a concentration corresponding to half-maximal response is 13.6 ng/mL x Hz. The functionalized sensor substrate is subsequently used for competitive determination of different concentrations of free GABA (range of 5 microM-50 mM) in PBS-BSA buffer. The detection limit of the immunosensor for sensing GABA with maximum sensitivity is approximately 42 microM.     

Synthesis of α-alumina powder with internal nanostructures from Al13-cluster

Nanostructured α-alumina powder was synthesized by precipitation and calcination of Al₁₃-clusters that were formed by the hydrolysis of Al³⁺ions with hydroxide. The Al₁₃-clusters were precipitated with oxalic acid by two-stage and one-stage precipitation techniques. The precipitates were calcined in air at 1100 °C. The resulting α-alumina particles were characterized using particle size analyzer, X-ray diffraction (XRD) and transmission electron microscope (TEM). The pH and precipitation technique were found to influence the microstructural features of the α-alumina powder produced. Alumina with more extensive nanostructures inside the grain can be produced through the two-stage precipitation technique.     

Microstructure and mechanical properties of ZrB2-SiC composites

A ZrB₂-based composite containing 20 vol.% nanosized SiC particles (ZSN) was fabricated at 1900 °C for 30 min under a uniaxed load of 30 MPa by hot-pressing. The microstructure and mechanical properties of the composite were investigated. It was shown that the grain growth of ZrB₂ matrix was effectively suppressed by submicrosized SiC particles located along the grain boundaries. In addition, the mechanical properties of ZSN composite were strongly improved by incorporating the nanosized SiC particles into a ZrB₂ matrix, especially for flexural strength (925 ± 28 MPa) and fracture toughness (6.4 ± 0.3 MPa•m^1/2), which was much higher than that of monolithic ZrB₂ and ZrB₂-based composite with microsized SiC particles, respectively. The formation of intragranular nanostructures plays an important role in the strengthening and toughening of ZrB₂ ceramic.     

Morphology of aluminum phosphate by the Al-EDTA mediated particle formation in aqueous solutions at high temperatures

The morphology of aluminum phosphate, formed by homogeneous precipitation in aqueous solutions using Al-ethylenediaminetetraacetic acid (Al-EDTA) complex in the presence of H₂O₂, was investigated under several temperature conditions, and pH, Al-EDTA, and H₂O₂ concentrations. Spherical particles of AlPO₄·xH₂O (x = 1.04-1.90) were formed at pH 4-8 at 125-200 °C. Since nonspherical precipitates were observed in the absence of EDTA or H₂O₂, the formation of the spherical particles at pH 4-8 is attributed to the slow release of Al³⁺ ions by the degradation and/or dissociation of Al-EDTA with H₂O₂ under hydrothermal conditions. The size of the spherical particles obtained with Al-EDTA depends on the concentration of the Al-EDTA chelate and H₂O₂, and also on temperature; the size distribution of the particles decreased significantly with the H₂O₂ concentration and temperature.     

Molecular weight dependence on bioavailability of FITC-dextran after administration of self-dissolving micropile to rat skin

Background: Self-dissolving micropiles (SDMPs) have been evaluated with macromolecular drugs like insulin and erythropoietin as a new percutaneous drug delivery system. To study the molecular weight dependence on the absorption of macromolecular drugs through the skin after administration of SDMPs, four kinds of SDMP were prepared using fluorescein isothiocyanate-labeled dextrans (FDs) having a molecular weight of 10, 20, 40, and 70 kDa. Method: In in vitro release experiments there were no significant differences on their release rates in the four SDMPs. The dependence of molecular weight of FD on the permeability coefficient was studied in the in vitro permeation experiment. Histological study on the skin after administration of FD SDMP (5.0 mg/kg) to rat was performed for 24 hours. In vivo experiment using rats resulted in slower absorption rate of FD-40 and FD-70 SDMP (5.0 mg/kg). Results: The permeability coefficient was 4.59, 4.69, 3.38, and 1.43 × 10^?4 cm/h for FD-10, 20, 40, and 70, respectively. Histological examination showed that yellow color was still observed at 6 h after administration of FD-40, and FD‐70 showed yellow color even at 24 h. Bioavailabilities of FDs from SDMP were 99.4 ± 6.93%, 88.3 ± 7.05%, 45.7 ± 4.77%, and 16.0 ± 1.15% for FD-10, 20, 40, and 70, and the dependency on molecular weight dependence was clearly observed. Conclusion: These observations supported that bioavailabilities of FD from SDMP decreased as the molecular weight of FD increased to more than 40 kDa.     

Mechanical properties and microstructures of co-precipitation derived tetragonal Y2O3-ZrO2-Al2O3 composites

Y-TZP Al₂O₃ specimens (2.5 mol% Y₂O₃-ZrO₂ and 5 to 30 wt% Al₂ 03) were prepared from coprecipitated powders and their mechanical properties were studied. The addition of alumina to Y-TZP improves the attainable density of the materials after sintering at 1500° C and reduces the degradation of their densities due to porosity formation when the materials are sintered above 1500° C. Near theoretical density could be achieved for most of the samples after HIPing at 1500° C for 1/2 h at 200 M Pa pressure. The fracture strength of the HIPed specimens was in the range 2.0 to 2.4 GPa and the stress intensity factor was in the range 3.5 to 6.0 MPa m^1/2. The mechanical strength of the materials was not degraded seriously after autoclaving in water at 175° C for 24 h. The surface layer of transformed monoclinic zirconia was less than 70 m thick even after autoclaving at 175° C for 5 days.     

Coating of hydroxyapatite on metal plates using thermal dissociation of calcium-EDTA chelate in phosphate solutions under hydrothermal conditions

Coating of hydroxyapatite on various metal plates was carried out by a homogeneous precipitation technique using hydrothermal reactions in Ca(edta)^2-–NaH₂PO₄ at 140–200°C and pH 3.4–10.0. Hydroxyapatite films were formed on the surface of the iron plates in solutions at an initial pH above 4.7, whereas aggregates consisting of needle-like hydroxyapatite crystal radiating from a point in the form of flower deposited as islands on the surface of aluminum, copper and titanium plates. The upper part of the film formed on the surface of the iron plates consisted of needle-like hydroxyapatite particles whereas the bottom of the film consisted of spherical hydroxyapatite particles. The length of the needle-like hydroxyapatite particles increased with decreasing concentration of Ca(edta)^2-.     

Precipitation hardening and recrystallization in Cu-4% to 7% Ni-3% Al alloys

The effects of microstructure on mechanical properties in three cold-worked Cu-4% to 7% Ni-3% Al alloys have been investigated by changing ageing time at 500 °C. Hardness and strength in the Cu-7% Ni-3% Al and Cu-5.5% Ni-3% Al alloys increase with ageing time and have maximum values at an ageing time of 10³–10⁴s at 500 °C, then decrease. During ageing of Cu-7% Ni-3% Al at 500 °C, the coherent Ni₃Al phase was first precipitated out and later incoherent NiAl phase was formed. Ni₃Al formed during the initial stage of ageing is likely to be a transient phase. The increases in hardness and strength are due to the precipitation of coherent Ni₃Al phase. Coherent Ni₃Al particles are effective in increasing the strength and retarding the recrystallization process. On the other hand, the hardness and strength in the Cu-4% Ni-3% Al alloy gradually declined with ageing time. Only incoherent NiAl phase was formed during ageing at 500 °C. Decreases in hardness and strength in the Cu-4% Ni-3% Al alloy are attributed to softening during recovery and recrystallization, because incoherent NiAl particles have an insufficient effect to increase the strength.     

Fabrication of multilayered Au/silica/gadolinium compound core–shell particles and their imaging properties

The present work proposes a preparation method for multilayered Au nanoparticle/silica/gadolinium compound core–shell (Au/SiO₂/GdC) particles. Silica-coated Au core–shell (Au/SiO₂) particles with a size of 38.0?nm were prepared by a sol-gel reaction in the presence of the Au nanoparticles with a size of 15.5?nm. Multilayered Au/SiO₂/GdC particles with sizes of ca. 35–52?nm were prepared by a homogeneous precipitation reaction in the presence of Au/SiO₂ particles. The computed tomography (CT) value of the Au/SiO₂/GdC colloid solution containing 4.3?×?10^?2?M Au was 344.1?HU: Its converted CT value (CT divided by Au concentration) was as large as 8.0?×?10³?HU/M. The r₁ value of the Au/SiO₂/GdC colloid solution was as large as 3.5?mM^?1?s^?1.     

Dilute Solution Behavior of Dendrimers and Polysaccharides: SEC, ESI-MS, and Computer Modeling

Dendrimers, the most highly branched structures achievable, have found numerous uses in the chemical, biological, and pharmaceutical fields. We have employed size exclusion chromatography (SEC) with universal calibration to determine molecular weight averages, distributions, intrinsic viscosities, and structural parameters of Starburst dendrimers, dextrans, and the starch degradation polysaccharides known as maltodextrins. Comparisons have been made in the dilute solution behavior of dendrimers and polysaccharides with equivalent weight-average molecular weights. Intrinsic viscosities decreased in the order [η](dextran) > [η](dextrin) > [η](dendrimer). While the difference between dendrimer and polysaccharides may be attributed to the higher branching of the former, which leads to a higher chain density in solution, the difference between dextran and dextrin is likely a result of the variation in solution behavior of α-(1→6) vs α-(1→4) linked carbohydrates. The solution behavior of the maltodextrins studied indicates that debranching in their manufacture appears to have been more thorough than in that of β-limiting dextrins studied by other groups. Comparison of molecular radii obtained from SEC data to radii from molecular dynamics studies show Starburst dendrimers behave as θ-stars with functionality between 1 and 4. Additionally, electrospray ionization mass spectrometry was employed to determine M(w), M(n), and PD of Astramol dendrimers.     

Synthesis of polycrystalline zirconia fibre with organozirconium precursor

Polycrystalline zirconia fibre was successfully synthesized by pyrolysis of preceramic fibre formed from an organozirconium compound. Dibutoxybis(2, 4-pentadionato)zirconium (BPZ) was polymerized at 150° C and 10² Pa, yielding a viscous polymeric product. The infrared absorption bands of the Zr-O bond changed from separate to coalesced bands after polymerization. The signals of the¹³C NMR spectrum of BPZ changed from sharp singlets to multiplets after polymerization. The molecular weight of the polymer was between 400 and 1000. The viscosity of polymer was 580 Pa sec at 30° C and a shear rate of 1.0 sec^–1. The polymer viscosity decreased with increased temperature from 30 to 60° C. The precursor polymer pyrolysed at 400° C in air was amorphous to X-rays, and crystallized in a mixture of monoclinic and tetragonal phases at 450° C. Tetragonal zirconia was synthesized from the polymer including 4.3 mol % yttrium compound (2.2 mol % yttria) after heat treatment at 1200° C for 1 h. The precursor fibres were pyrolysed to yield fine-grained fibres of tetragonal zirconia at 1200° C for 1 h.     

Study on the interaction of phthalate esters to human serum albumin by steady-state and time-resolved fluorescence and circular dichroism spectroscopy

Phthalate esters (PAEs) are globally pervasive contaminants that are considered to be endocrine disruptor chemicals and toxic environmental priority pollutants. In this paper, the interactions between PAEs and human serum albumin (HSA) were examined by molecular modelling, steady state and time-resolved fluorescence, ultraviolet-visible spectroscopy (UV-vis) and circular dichroism spectroscopy (CD). The association constants between PAEs and HSA were determined using the Stern-Volmer and Scatchard equations. The binding of dimethyl phthalate (DMP) to HSA has a single class of binding site and its binding constants (K) are 4.08 × 10³, 3.97 × 10³, 3.45 × 10³, and 3.20 × 10³ L mol⁻¹ at 289, 296, 303, and 310 K, respectively. The Stern-Volmer and Scatchard plots both had two regression curves for HSA-butylbenzyl phthalate (BBP) and HSA-di-2-ethylhexyl phthalate (DEHP), which indicated that these bindings were via two types of binding sites: the numbers of binding site for the first type were lower than for the second type. The binding constants of the first type binding site were higher than those of the second type binding site at corresponding temperatures, the results suggesting that the first type of binding site had high affinity and the second binding site involved other sites with lower binding affinity and selectivity. The thermodynamic parameters of the binding reactions (ΔG°, ΔH° and ΔS°) were measured, and they indicated the presences of hydrophobic forces and hydrogen interactions in the PAEs-HSA interactions, which agreed well with the results from molecular modelling. The alterations of protein secondary structure in the presence of PAEs were confirmed by UV-vis and CD spectroscopy. The time-resolved fluorescence study showed that the lifetime of Trp residue of HSA decreased after the addition of PAEs, which implied that the Trp residue of HSA was the main binding site.     

Reinforcement of molten carbonate fuel cell matrixes by adding rod-shaped γ-LiAlO2 particles

Improvement in strength of -LiAlO₂ matrixes for a molten carbonate fuel cell (MCFC) via addition of rod-shaped -LiAlO₂ particles has been investigated. The rod-shaped -LiAlO₂ particles with the aspect ratio of 9–15 were obtained by heat-treating rod-shaped -LiAlO₂ particles at 800 °C for 3 h, synthesized from the reaction mixture of LiOH--Al₂O₃-NaOH. The -form was very stable for more than 700 h in a molten carbonate environment at 650 °C, while the -form showed both a phase change from - to -LiAlO₂ and a morphology change from rod- to bipyramid-shapes. The average pore size and the porosity of the matrix (550 m thickness) fabricated by tape-casting of the slurry with weight ratio 1.0 of rod-shaped -LiAlO₂ particles to commercial -LiAlO₂ powders (2.0 m dia.) were about 0.12 m and 54%, respectively, after being heat-treated at 650 °C for 2 h. The strength (197 g_f/mm²) of the rod- shaped particle reinforced matrixes was enhanced more than twice as much as that of the non-reinforced -LiAlO₂ matrixes (91 g_f/mm²).