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1.
Litharge, the red tetragonal form of lead oxide α-PbO and massicot, the yellow orthorhombic form β-PbO, are synthesized from
lead(II) salts in aqueous media at elevated temperatures. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were
used to characterize the size, morphology, and crystallographic structural forms of the products. The role of impurities in
the experimental synthesis of the materials and microstructural variations in the final products are described. The implications
of these observations regarding the synthesis of different conducting lead oxides and other related materials are discussed.
PACS 71.20.Ps; 72.80.Jc; 74.62.Bf; 74.62.Dh; 75.50.Tt 相似文献
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Tobacco protein separation by aqueous two-phase extraction 总被引:13,自引:0,他引:13
Tobacco has long been considered as a host to produce large quantity of high-valued recombinant proteins. However, dealing with large quantities of biomass is a challenge for downstream processing. Aqueous two-phase extraction (ATPE) has been widely used in purifying proteins from various sources. It is a protein-friendly process and can be scaled up easily. In this paper, ATPE was studied for its applicability to recombinant protein purification from tobacco with egg white lysozyme as the model protein. Separate experiments with poly(ethylene glycol) (PEG)-salt-tobacco extract and PEG-salt-lysozyme were carried out to determine the partition behavior of tobacco protein and lysozyme, respectively. Two-level fractional factorial designs were used to study the effects of factors such as, PEG molecular mass, PEG concentration, the concentration of phase forming salt, sodium chloride concentration and pH, on protein partitioning. The results showed that, among the studied systems, PEG-sodium sulfate system was most suitable for lysozyme purification. Detailed experiments were conducted by spiking lysozyme into the tobacco extract. The conditions with highest selectivity of lysozyme over native tobacco protein were determined using a response surface design. The purification factor was further improved by decreasing the phase ratio along the tie line corresponding to the phase compositions with the highest selectivity. Under selected conditions the lysozyme yield was predicted to be 87% with a purification factor of 4 and concentration factor of 14. From this study, ATPE was shown to be suitable for initial protein recovery and partial purification from transgenic tobacco. 相似文献
5.
Gusev AI Wilkinson WR Proctor A Hercules DM 《Analytical and bioanalytical chemistry》1996,354(4):455-463
The protocol and various matrices were examined for quantification of biomolecules in both the low ca. 1200 amu and mid mass 6000-12000 amu ranges using an internal standard. Comparative studies of different matrices of MALDI quantitative analysis showed that the best accuracy and standard curve linearity were obtained for two matrices: (a) 2,5-dihydroxybenzoic acid (DHB) combined with a comatrix of fucose and 5-methoxysalicylic acid (MSA) and (b) ferulic acid/fucose. In the low mass range, the quantitative limit was in the 30 fmol range and in the mid mass range the quantitative limit was in the 250 fmol range. Linear response was observed over 2-3 decades of analyte concentration. The relative error of the standard curve slope was 1.3-1.8% with correlation coefficients of 0.996-0.998.The main problem for quantitative measurement was suppression of the signal of the less concentrated component (analyte or internal standard) by the more concentrated component. The effect was identified with saturation of the matrix by the analyte. The threshold of matrix saturation was found to be in the range of 1/(3000-5000) analyte/matrix molar ratio. To avoid matrix saturation the (analyte+internal standard) to matrix molar ratio should be below this threshold. Thus the internal standard concentration should be as low as possible.DHB/MSA/fucose and ferulic acid/fucose matrices demonstrated good accuracy and linearity for standard curves even when the internal standard had chemical properties different from the analyte. However, use of an internal standard with different chemical properties requires highly stable instrumental parameters as well as constant (analyte+internal standard)/matrix molar ratio for all samples. 相似文献
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C.T. Mortimer M.P. Wilkinson J. Burgess R.D.W. Kemmitt N. Morton 《Journal of organometallic chemistry》1979,171(3):369-371
The enthalpy, ΔH = ?64.7 ± 4 kJ mol?1, for the reaction Pt(PPh3)2(η-C2H4)(s) + pcbd(g) → Pt(PPh3)2(η-pcbd)(s) + C2H4(g) where pcbd is 3-phenylcyclobutene-1,2-dione, , has been measured calorimetrically. The Ptolefin bond in this complex is slightly stronger than that in Pt(PPh3)2(η-PhCHCH2). 相似文献
8.
The unseeded non-hydrolytic sol-gel synthesis of ZrW2O8 and ZrMo2O8 produces trigonal ZrM2O8 (M = W, Mo) at 740 and 300–400°C, respectively. Cubic ZrW2O8 can be prepared using non-hydrolytic sol-gel methods by seeding with small amounts of preprepared cubic material, and the formation of the trigonal polymorph can be suppressed completely. Seeds with a small particle size are necessary for the preparation of cubic ZrW2O8. In contrast, seeding of ZrMo2O8 gels with either cubic ZrMo2O8 or cubic ZrW2O8 only lowers the temperature at which the trigonal phase crystallizes. 相似文献
9.
L. Viaene D. Meerschaut M. Van Der Auweraer F. C. De Schryver F. Wilkinson 《Research on Chemical Intermediates》1995,21(7):711-723
The absorption and fluorescence of 16-(1-pyrene)-hexadecanoicacid adsorbed on silica have been investigated. Time-resolved transient diffuse reflectance spectra were recorded following pulsed nanosecond laser excitation at 355 nm of pyrene, 1-methylpyrene and 16-(1-pyrene)-hexadecanoicacid adsorbed on silica. In addition to a rapidly decaying transient, absorbing at 420 nm assigned as the triplet state, and of the radical cation, absorbing at 460 nm, another long living transient species absorbing at 420 nm was observed for 16-(1-pyrene)-hexadecanoic acid. The decay is reversible but complete recovery takes several hours. Although no definitive assignment could be made for this transient several possibilities are discussed. The radical cations of the investigated molecules are formed by a biphotonic process. The non-exponential decay of the radical cations could be analyzed in the framework of a Gaussian distribution of free energy barriers. 相似文献
10.
Raman spectra of a series of alkali-halide/BH?4 (and BD?4 crystals have been obtained. These spectra show some interesting examples of Fermi resonance type interactions between the stretching mode levels and overtone and combination band levels of the bending modes. Two resonances will be considered: (i) that between ν1 and 2ν4(A1), and (ii) that between ν3, 2ν4 (F2) and (ν2+ν4) (F2).The F2 resonance between ν3, 2ν4 and ν2+ν4 appears in the infrared spectrum and it has been studied on several occasions. However the equivalent Raman spectrum is of interest because the relative intensities of the bands are significantly different to those shown by the infrared spectrum.In the A1 (and E) Raman spectrum of the stretching mode region there are two strong bands for each for the 10B and 11B isotopes. The ν1 would not be expected to show any 10B and 11B splitting, but the observed bands are both closely resonating mixtures of ν1 and 2ν4(A1). In fact the analysis shows that the stronger band has the higher proportion of 2ν4 character, and the larger isotopic shift of the more intense band can then be seen to be reasonable. 相似文献