Laser-assisted synthesis of superparamagnetic Fe@Au core-shell nanoparticles

A novel method combining wet chemistry for synthesis of an Fe core, 532 nm laser irradiation of Fe nanoparticles and Au powder in liquid medium for deposition of an Au shell, and sequential magnetic extraction/acid washing for purification has been developed to fabricate oxidation-resistant Fe@Au magnetic core-shell nanoparticles. The nanoparticles have been extensively characterized at various stages during and up to several months after completion of the synthesis by a suite of electron microscopy techniques (HRTEM, HAADF STEM, EDX), X-ray diffraction (XRD), UV-vis spectroscopy, inductively coupled plasma atomic emission spectroscopy, and magnetometry. The surface plasmon resonance of the Fe@Au nanoparticles is red shifted and much broadened as compared with that of pure colloidal nano-gold, which is explained to be predominantly a shell-thickness effect. The Au shell consists of partially fused approximately 3-nm-diameter fcc Au nanoparticles (lattice interplanar distance, d = 2.36 A). The 18-nm-diameter magnetic core is bcc Fe single domain (d = 2.03 A). The nanoparticles are superparamagnetic at room temperature (300 K) with a blocking temperature, T(b), of approximately 170 K. After 4 months of shelf storage in normal laboratory conditions, their mass magnetization per Fe content was measured to be 210 emu/g, approximately 96% of the Fe bulk value.     

CHARACTERIZATION OF CARBON BLACK FILLED POLYMERS USING SMALL ANGLE X-RAY SCATTERING AND TRANSMISSION ELECTRON MICROSCOPY: A COMPARATIVE STUDY

Carbon black (CB) is often incorporated in polymeric materials in order to modify their properties. The final properties of composite materials containing CB depend on, among other things, the nature of the carbon black, its concentration and its degree of dispersion. Therefore, there is a need to accurately characterize the degree of dispersion of carbon black in polymers. Although techniques based on optical microscopy can be used for detecting large agglomerates, they do not have the resolution to accurately quantify dispersions of particles having diameters less than 0.25 microns. Small angle X-ray scattering (SAXS) has the potential of being a useful and efficient tool for characterizing dispersions on length scales ranging from the order of 0.01 to 0.1 micron. The method is quick and provides an average value of the average agglomerate size through indirect measurements of the correlation length and the inner specific surface area. On the other hand. Transmission Electron Microscopy (TEM) allows for the direct visualization of the dispersion and measurements of each individual agglomerate. When coupled with computerized image analysis, size distributions of the agglomerates can be generated. In this article, characterization of model dispersions of carbon black using both SAXS and TEM are presented and a correlation between the two techniques are discussed.     

XPS study of the effect of the conditions of peptide chemisorption to gold and silver coated polymer surfaces

Chemisorption of peptides and active moieties onto gold and silver coated surfaces is an attractive method for studying the effect of fundamental surface properties on biological interactions. In theory, the monolayers formed have a high density of the active group of interest, and the relatively mild conditions associated with chemisorption should allow biological activity to be maintained. While the conditions for chemisorption are widely reported in the literature, significant differences exist between research groups and the effects of changing these conditions on the resultant surface have not been fully examined. Furthermore, comparisons have not been made between gold and silver as potential substrates in these applications. In the current work, glutathione and cysteine were chemisorbed onto gold- and silver-coated polymers. The effect of varying the chemisorption conditions was evaluated by XPS analysis of the resultant surfaces. Factors identified as having potentially significant effects on chemisorption procedure included chemisorption time, peptide concentration, peptide, pH of the chemisorption solution, mixing and material of the incubation container. Factor significance was evaluated using a two level fractional factorial design of experiments (DOE), with sulfur content determined by XPS used as a measure of chemisorption effectiveness. Significant differences were noted between the silver and gold-coated surfaces, with a higher amount of sulfur and hence, by inference, peptide found in general on silver surfaces reacted under identical conditions. On the gold surfaces, peptide concentration, peptide type, and chemisorption time were found to have a significant effect on the composition of the resulting surface. On the silver surfaces, factor specific differences were not as significant but there were a number of two factor interactions. The results provide further evidence of the differences in interactions with thiol between silver and gold and suggest that changes in the chemisorption conditions can dramatically affect the resultant surface composition.     

Synthesis of two series of pyrazolic analogues of the marine alkaloids granulatimide and isogranulatimide as potent Checkpoint 1 kinase inhibitors

Two series of regioisomeric pyrazolic analogues of the marine alkaloids granulatimide and isogranulatimide were prepared. The synthesis of the first series was based on the condensation reaction of diversely 5-substituted 3-bromoindoles with pyrazole followed by addition of the intermediates on dibromomaleimide, the so-obtained acyclic adducts being finally photochemically cyclised to the desired analogues. Compounds of the second series were obtained by reacting different 5-substituted-indole-3-glyoxylates with N-Boc-pyrazole-3-acetamide and subsequent photochemical cyclisation of the adducts.     

Introduction of bismuth into the highT c superconductor La2−x Sr x CuO4−y

Novel high-T _c superconductors La_2–x Bi _x Sr _x–x CuO_4–y have been isolated and studied. The influence of the experimental conditions of synthesis on the superconductivity has been especially studied for the composition La_1.7Bi_0.1Sr_0.2CuO_4–y ; it is shown thatT _c decreases as oxygen is introduced into the matrix, likely due to the partial oxidation of Bi(III) to Bi(V). The highT _c value observed for one sample (T _c 42 K), as compared withT _c 38 K of La_1.8Sr_0.2CuO_4–y suggests that bismuth is also a potential candidate for improving the superconducting properties in these oxides.     

Superconductivity in the Bi - Sr - Cu - O system

During the investigation of the system Bi–Sr–Cu–O a novel family of superconducting oxides, close to the composition Sr₂Bi₂Cu₂O₇₊ has been isolated, with a midpoint critical temperature ranging from 7 K to 22 K. The X-ray diffraction and high-resolution electron microscopy studies have shown its relationships with perovskite and demonstrated its bidimensional character. The possible relationships of this lamellar oxide with Aurivillius phases is discussed.     

Step-scan photoacoustic fourier transform and X-rays photoelectron spectroscopy of oil sands fine tailings: new structural insights.

The chemical and physical properties of clay suspensions from oil sands have profound effect not only on the bitumen extraction process but also on the tailing treatment and reclamation. Step-scan Photoacoustic Fourier Transform Infrared (S2PAS-FTIR) has been used to characterize the properties of clay suspensions. The photoacoustic spectral features of the fine solids (FS) fraction were found to vary drastically with the modulation frequency. This is attributed to the increase in the relative amount of bitumen-like matter in the bulk. A similar behavior was observed on the bi-wetted solid (BWS) fraction, in spite of the fact that the variation as a function of the modulation frequency is less significant. No such change is observed on hydrophobic solid (HPS) sample. These observations allow us to refine our pictorial image of the bitumen fraction materials structure.     

Poly(β-hydroxyalkanoates): Biorefinery polymers in search of applications

Poly(β-hydroxyalkanoates) are nature's high molecular weight thermoplastic polyesters. They occur as storage granules in a variety of bacteria. From a plastics, film, and fibres perspective, the statistically random copolyesters based on β-hydroxybutyrate (HB) and β-hydroxyvalerate (HV) repeating units have high potential for commercial exploitation because of their biodegradability. They provide a range of melting points from 180°C down to 80°C and all compositions exhibit high crystallinity due to isodimorphism. The latter is due to the similar crystalline conformations of poly(β-hydroxybutyrate) (PHB) and poly(β-hydroxyvalerate) (PHV). The nascent granules of a 21 mole % HV copolyester sample in freeze-dried bacterial cells were examined by ¹³C solid-state NMR. A disorder in the HV ethyl side group was noted but backbone carbons for HB and HV units showed evidence of crystalline order which was confirmed by x-ray diffraction. In keeping with the isodimorphous properties of this system, electron diffraction of copolyester single crystals for compositions up to 21 mole % HV confirmed a lattice expansion previously observed for bulk crystallized P(HB-co-HV). Solution or melt crystallized films showed decreasing rates of crystallization with increasing HV content. Homogeneous blends of PHB with P(HB-co-HV) could be formed which showed a single melting peak by differential scanning calorimetry. The potential of P(HB-co-HV) as a source of value-added small molecules is discussed. Depending on the method of degradation (i.e., chemical or pyrolytic) chiral synthons or vinylic small molecules are obtainable in nearly quantitative yields. Because their physical properties resemble those of polyolefins this family of chiral thermoplastics will probably find wide use in biomedical applications where compatibility and absorbability are essential features.