Chemical characterization of diaspirin cross-linked hemoglobin polymerized with poly(ethylene glycol)

A lack of specificity associated with chemical modification methods used in the preparation of certain hemoglobin (Hb)-based oxygen carriers (HBOCs) may alter Hb structure and function, as amino acids located in critical regions (e.g., alpha-beta interfaces and the 2,3-DPG binding pocket) may unintentionally be targeted. Hb protein surface modifications with various poly(ethylene glycol) (PEG) derivatives have been used as conjugating and polymerizing agents with the intent of improving reaction site specificity/reproducibility and ultimately reducing the untoward hypertensive response due to nitric oxide scavenging by smaller molecular size tetrameric species (i.e., 64 kDa) in HBOC solutions. Previous experiments performed in our laboratory have evaluated the influence of polymerization of diaspirin alpha-alpha cross-linked Hb (alphaalpha-DBBF-Hb) with a bifunctional modified PEG, bis(maleoylglycylamide) PEG (BMAA-PEG), in terms of oxygen carrying capacity, redox properties, hypertensive response, and renal clearance in rats. The data presented in this paper specifically evaluate the influence of BMAA-PEG on alphaalpha-DBBF-Hb (Poly-alphaalpha-DBBF-Hb) to identify molecular weight distribution, protein conformation, and site-specific modification, as well as to provide insight into the previously determined in vitro and in vivo functional and vasoactive characteristics of this HBOC. Chemical analysis performed herein reveals nonspecific modifications induced by BMAA-PEG that result in the full modification of alphaalpha-DBBF-Hb leaving no tetrameric cross-linked starting material in solution. These data are inconsistent with the continuing assumption that molecular size (i.e., 64 kDa) has a direct influence on HBOC-mediated vasoactivity and that other protective strategies should be considered to control blood pressure imbalances.     

Electrochemical synthesis and characterization of conducting copolymer: poly(o-anisidine-co-o-toluidine)

Copolymerization of o-anisidine and o-toluidine was achieved electrochemically in aqueous solution containing H₂SO₄ as supporting electrolyte. The copolymer compositions can be altered by varying the monomer feed ratios during electrosynthesis. The films were electropolymerized in solution containing monomers in various ratio (0.025–0.1 M) and 1 M sulphuric acid as electrolyte by applying sequential linear potential scan rate 50 mV/s between −0.2 to 1.0 V. versus Ag/AgCl electrode. The copolymers were characterized by cyclic voltammetric, conductivity measurement, UV-Visible spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA).     

Synthesis and characterization of cross-linked silicone thin films by pulsed laser ablation deposition (PLAD)

Stable, uniform and cross-linked silicone films have been synthesized by pulsed laser ablation deposition (PLAD) for the first time. A KrF excimer (248 nm) laser was used in the synthesis. The effect of incident energy density on the deposited film chemistry was examined in depth. The surface analysis showed that at low energy densities (100–150 mJ/cm²), smooth, hydrophobic films similar in structure to the starting cross-linked silicone elastomer were obtained. Beyond 200 mJ/cm², hydrophilic films with oxygen contents much higher than the starting polymer were obtained. These films also exhibited a more particulate texture suggesting ablation of particles and/or polymeric clusters from the silicone target. The results demonstrate that the PLAD process may prove valuable for the preparation of cross-linked silicone thin films with tailored properties. Received: 27 June 2001 / Accepted: 17 July 2001     

Optical and mechanical characterization of evaporated SiO(2) layers. Long-term evolution

Numerous characterizations were performed on 120-nm thick evaporated SiO(2) layers in order to understand how their features change as a function of deposition conditions and time. Density decreases with increasing deposition pressure. It governs all the layer properties (refractive index, hardness, and stress). In situ stress measurements show that stress can be divided into intrinsic and water-induced components, respectively linked to local density (outside the pores) and porosity. Intrinsic stress increase with decreasing pressure is explained by a diminution of the Si-O-Si bond angle (IR measurements). Long-term evolution is characterized by stress relaxation related to Si-O-Si strained bond hydrolysis.     

Large-area vapor-phase growth and characterization of MoS(2) atomic layers on a SiO(2) substrate

Atomic-layered MoS(2) is synthesized directly on SiO(2) substrates by a scalable chemical vapor deposition method. The large-scale synthesis of an atomic-layered semiconductor directly on a dielectric layer paves the way for many facile device fabrication possibilities, expanding the important family of useful mono- or few-layer materials that possess exceptional properties, such as graphene and hexagonal boron nitride (h-BN).     

Investigation of copper layers deposited by CVD using Cu(I)hfac(TMVS) precursor

Chemical vapour deposition (CVD) of copper on titanium-coated substrates was performed in a stainless steel reactor using copper(I) hexafluoroacetylacetonate trimethylvinylsilane (Cu(I)hfac(TMVS)) as a precursor and nitrogen (N₂) as carrier gas. Film resistivity, film composition and surface morphology were studied in relation to deposition temperature, process pressure and process gas flow ratio. The lowest resistivity value obtained was around 2 μΩcm. In addition, cross-sectional examination of the copper films, using a LEO SEM imaging system, indicated increased film porosity at higher deposition temperatures. An optimum carrier gas flow rate was determined: higher carrier gas flow rates caused excessive dilution of the copper precursor, whilst lower carrier gas flow rates weakened the transport of the copper precursor to the substrate. XRD data revealed formation of copper oxide (Cu₂O) if annealing temperatures exceeded 450∘C for a period of 30 min.FIB/TEM imaging revealed that CVD copper offers better conformality and viafilling than PVD copper in trenches 0.25 μm wide and 0.5 μm deep. CVD copper layers, passivated by a spin-on-glass dielectric, were shown to have reduced surface migration of copper atoms, compared to unpassivated layers. Copper films with a predominantly (111) orientation were found to exhibit a longer electromigration lifetime than copper films with mixed (111) and (200) orientations.     

Synthesis and characterization of TiC-reinforced iron-based composites Part I On synthesis and microstructural characterization

The present investigation establishes a liquid processing route where thermit based reactions have been used to synthesize in-situ TiC-reinforced Fe-based composites in a single step. The main raw material used is siliceous sand, which is a waste product of aluminum extraction plants. A dispersion of TiC in Fe-based matrix has been obtained by aluminothermic reduction of siliceous sand, containing oxides of different elements like iron, titanium, silicon etc., in the presence of carbon. The reduction is highly exothermic in nature and leads to a self-propagating high-temperature synthesis (SHS) of the Fe-TiC composites. The matrix structure and volume fraction of TiC of the composites have been found to depend upon the amount of carbon added in the charge. It has been found that microstructures of Fe-TiC composites are not stable at high temperature due to the nonstoichiometric nature of TiC particles.     

东方龙虱(雄性)抱握足形态学及吸附特性

研究了东方龙虱(雄性)抱握足上吸附脚掌的形态结构、吸附机制及其在2种不同表面的吸附特性。扫描电镜观察发现其吸附脚掌由4排吸附结构及其外围的吸附刚毛群构成,其吸附结构由约15个“鞋垫”状微吸盘平行并排构成一体。吸附机制为微吸盘的真空负压吸附和刚毛群的范德华力粘附。实验测定吸附脚掌在东方龙虱鞘翅表面和玻璃表面产生的最大法向吸附力为53.3 mN,最大切向吸附力为213.5 mN。在2种表面上(干、湿状态)其切向吸附力均远大于法向吸附力,大约是法向吸附力的6～8倍,同时吸附脚掌在湿表面的切向吸附力比干表面大得多,法向吸附力却相反。法向吸附力主要由刚毛群的范德华力产生,而切向吸附力由真空吸附和范德华力共同产生。     

Microwave synthesis and physical characterization of tin(II) phosphate glasses

Tin phosphate glasses in the SnO–P₂O₅ binary diagram have been prepared by using a domestic microwave-heating device. Microwaves provide an extremely facile and automatically temperature-controlled route to the synthesis of glasses due to the specific dielectric properties of each chemical composition. Typical melting time is no longer than 10 min, limiting the oxidation of Sn²⁺ and the melt can be quenched into glass. The glass transition temperature increases with the SnO content confirming the depolymerization of the vitreous network, as expected by the relative fraction of the different Q ⁿ structural units deduced from NMR experiments. Concerning the mechanical properties, the Vickers hardness and the fracture toughness decrease while the thermal expansion coefficient and the different elastic moduli remain constants. These results confirm that those characteristics are not very sensible to structural considerations. On the contrary, the chemical durability of Sn₂P₂O₇, determined from the weight loss method, is 300 times higher than that of Sn(PO₃)₂. Furthermore, Sn₂P₂O₇ is the only glass composition that exhibits a devitrification phenomenon leading to the low-temperature phase of the crystalline tin(II) pyrophosphate.     

Computer-aided fault tree synthesis I (system modeling and causal trees)

This paper is devoted to fault tree synthesis and is split up into three parts. Part I starts with the introduction of component models that show all fault propagation through the components and fault initiation by the components in both directions (upstream and downstream). Subsequently, it is shown how to create system models that interconnect a system's components and environmental variables. Then a fault tree construction algorithm is introduced which is able to generate fault trees from the given system and component models in two steps. First a causal tree is constructed showing the propagation paths for all basic events leading to any deviation in the top parameter. All control loops (feedback and feedforward loops) in this causal tree must be traced prior to any fault tree construction since they might prevent some faults from reaching the top parameter. They consequently require a special treatment. Part I ends showing how to adapt the causal trees for these loops. Part II discusses the final step of the fault tree construction algorithm, i.e. it shows how fault trees can be abstracted from the causal diagram and ends with a comprehensive example. Finally, Part III discusses a method for real-time fault location which is based on the causal tree construction procedure introducted in Part I.     

Behaviour of photopolymerized silicate-glass-fibre-reinforced dimethacrylate composites subjected to hydrothermal ageing: Part I Steady-state sorption characteristics

Steady-state water sorption due to hydrothermal ageing (37 °C) was determined via gravimetric methods for both an unreinforced dimethacrylate copolymer network and for composites of the copolymer reinforced with two different silicate yarn products – S2-glass® and quartz. The copolymer sorbed 4.9±0.3 wt%, and the composites sorbed 0.5–2.5 wt%. For the two types of composites, two different positive linear correlations were established between the sorption gain and the copolymer content in the composites. In the case of the S2-glass® composites, the sorption gain was fully explained in terms of sorption in the copolymer; and normalization of these data by the mass fraction of copolymer yielded a constant sorption value matching that of the unreinforced copolymer. After normalizing the data for the quartz composites, an additional positive correlation was established between the water gain (per unit weight of copolymer) and the linear density of interfacial surface area. For both types of composites the sorption response was stable over a three-month ageing period. © 1998 Chapman & Hall     

Green nanocomposites: synthesis and characterization

A series of intercalated and exfoliated nanocomposites montmorillonite-ulvan was prepared. Ulvan, extracted from the green algae, is a water-soluble polysaccharide biopolymer. Depending on the drying process, air or freeze drying, ulvan were inserted in the interlayer space or adsorbed on the both sides of inorganic layers. The crystallization of water molecules bounded to the ulvan induced the delamination of the layers during the lyophilization. Thermogravimetric experiments show a high percentage (approximately 51%) of organic matter for the freeze dried samples and a lowest one (approximately 17%) for the air dried solids. X-Ray Diffraction patterns exhibit a d(001) varying with the content of organic matter. When the delamination occurs, the (001) reflection disappears. Transmission electron microscopy micrographs show individual layers for the highest amount of ulvan.     

Chemical synthesis and characterization of magnesium substituted amorphous calcium phosphate (MG-ACP)

Amorphous calcium phosphate (ACP) was synthesized by a simple aqueous precipitation using CaCl₂ and Na₃PO₄ in the presence of MgCl₂ to ensure the formation of the ACP phase at room temperature. Magnesium substituted ACP phases corresponding to two different compositions representing the two most prominent calcium phosphate phases (hydroxyapatite: Ca + Mg/P = 1.67 and tricalcium phosphate: Ca + Mg/P = 1.5) were synthesized by this simple approach. Both compositions of ACP phases resulted in their transformation into β-tricalcium phosphate upon heat treatment in air at 600 °C. X-ray diffraction (XRD), heat treatment, scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) and Brunauer-Emmett-Teller (BET) analyses were used to characterize the phase, thermal stability, surface area, and morphology of the synthesized ACP powders corresponding to the two different nominal Ca/P compositions. Although it is known that α-TCP is the phase that appears upon heat treatment at 600 °C unsubstituted ACP, substitution of magnesium ion in ACP (both TCP and HA composition) stabilized the structure of β-TCMP phase at 600 °C. Moreover, FT-IR analysis revealed that the ACP phase regardless of the composition, exhibited characteristic bands corresponding to that of HA, with the exception of the ACP corresponding to HA composition which exhibited a prominent OH vibrational mode.     

药物缓释材料聚(乳酸-丙氨酸)的直接法合成与表征

直接以外消旋乳酸(LA)、L-丙氨酸(Ala)为原料[n(LA):n(Ala)=9:1],采用熔融聚合法合成药物缓释材料聚(乳酸-丙氨酸)共聚物[P(LA-co-Ala)],并用特性黏数、FTIR、1H NMR、GPC、DSC、XRD等手段进行系统表征.熔融共聚中采用一次投料并分次预聚,可生成重均相对分子质量(Mw)达3200(分散度Mw/Mn＝1.23)的共聚物,相对分子质量可以达到丙交酯开环共聚法的水平.首次报道了P(LA-co-Ala)]药物缓释材料的DSC与XRD表征结果,其与聚外消旋乳酸(PDLLA)相比,共聚物具有较低的Tg、Tm和结晶度.新方法步骤少、操作简便,且成本更加低廉.