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41.
David W. Allen Ian W. Nowell Lorraine A. March Brian F. Taylor 《Tetrahedron letters》1982,23(51):5479-5482
Tertiary phosphines react with -halobenzaldimines and -bromodiarylazo compounds, under mild conditions in the presence of a metal ion catalyst, with displacement of the halogen to form the related arylphosphonium salts. The corresponding -haloaryl compounds do not undergo these reactions. 相似文献
42.
Aqueous latex/ceramic nanoparticle dispersions: colloidal stability and coating properties 总被引:3,自引:0,他引:3
Sun J Velamakanni BV Gerberich WW Francis LF 《Journal of colloid and interface science》2004,280(2):2303-399
The effect of pH on the colloidal stability of aqueous dispersions containing antimony-doped tin oxide (ATO) or indium tin oxide (ITO) nanoparticles and poly(vinyl acetate-acrylic) copolymer (PVAc-co-acrylic) latex particles was investigated using experimental observations and Derjiaguin, Landau, Verwey and Overbeek (DLVO) theory. The microstructure, electrical properties and optical properties of composite coatings prepared from various dispersions were also studied. Zeta potential measurements revealed that the isoelectric point (IEP) of ATO nanoparticles was below pH 2.0, that of ITO nanoparticles was at pH approximately 6.0 and that of PVAc-co-acrylic latex was at pH approximately 2.0. ATO/PVAc-co-acrylic dispersions prepared at pH 3 were stable, but those prepared at pH 1.5 formed aggregates, which settled quickly with time. DLVO theory predictions are in accord with these results. Stable ITO/PVAc-co-acrylic dispersions are obtained at a pH of 3.0 and 11.0, but dispersions are not stable at a pH of 6.0, the IEP of ITO. At a pH of 3.0, DLVO results predict attraction between ITO particles and latex particles. Dispersion pH affected the microstructures and properties of ATO (or ITO)/PVAc-co-acrylic coatings. Suspensions that formed aggregates produced coatings with lower percolation thresholds and lower transparencies than those produced from stable suspensions. 相似文献
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We incorporate basic genetics into an AIDS model. We illustrate that if a homozygote is immune to the disease or is resistant to the effects of the disease, the corresponding allele goes to fixation. On the other hand, if the heterozygote is immune to the disease or is resistant to the effects of the disease, polymorphism usually occurs. 相似文献
45.
Cao R Gu Z Hsu L Patterson GD Armitage BA 《Journal of the American Chemical Society》2003,125(34):10250-10256
We describe the synthesis and characterization of a thermoreversibly cross-linked biopolymer microgel based on protein, DNA, and peptide nucleic acid (PNA) components. The DNA assembles into a trifunctional three-way junction (TWJ) with single-stranded overhangs. PNA oligomers complementary to these overhangs and bearing terminal biotin groups hybridize to the DNA TWJ and simultaneously bind to the tetrafunctional protein avidin, leading to a cross-linked system. Dynamic light scattering experiments reveal that micron-sized particles are formed. Static light scattering was used to characterize the internal structure of these microgels, which were found to have a fractal dimension of 1.85, indicative of a loose network structure. Heating disrupts the weakest component in the system, namely the PNA-DNA hybrid, resulting in dissolution of the microgel, while cooling restores the hydrogen bonding leading to reassembly of the microgel. Variation of the nucleotide sequence permits tuning of the gelation temperature with fine control. 相似文献
46.
Ralph A. Messing Lorraine F. Bialousz Raymond E. Lindner 《Applied biochemistry and biotechnology》1976,1(2):151-158
Lactose (β-galactosidase) derived fromAspergillus niger was immobilized on controlledpore silica with an average pore diameter of 425 Å. The coupling of this enzyme to the surface of the silica was accomplished by reacting the surface of the silica with o-dianisidine followed by the functionalization of the residual amine with glutaraldehyde or with nitrite to form the diazonium salt. The PH profiles of the immobilized enzymes were determined and compared. Continuous reactor studies of the glutaraldehyde-functionalized, immobilized enzyme indicated a half-life of 52 days at 50°C with a 5% lactose feed at pH 3.5. 相似文献
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Anderson LB Ouellette AJ Eaton-Rye J Maderia M MacCoss MJ Yates JR Barry BA 《Journal of the American Chemical Society》2004,126(27):8399-8405
In oxygenic photosynthesis, photosystem II (PSII) carries out the oxidation of water and reduction of plastoquinone. Three PSII subunits contain reactive groups that covalently bind amines and phenylhydrazine. It has been proposed that these reactive groups are carbonyl-containing, co- or post-translationally modified amino acids. To identify modified amino acid residues in one of the PSII subunits (CP47), tandem mass spectrometry was performed. Modified residues were affinity-tagged with either biotin-LC-hydrazide or biocytin hydrazide, which are known to label carbonyl groups. The affinity-tagged subunit was isolated by denaturing gel electrophoresis, and tryptic peptides were then subjected to affinity purification and tandem mass spectrometry. This procedure identified a hydrazide-labeled peptide, which has the sequence XKEGR. This result is supported by quantitative results acquired from peptide mapping and methylamine labeling. The gene sequence and these tandem data predict that the first amino acid, X, which is labeled with the hydrazide reagent, is a modified form of aspartic acid. On the basis of these data, we propose that D348 of the CP47 subunit is post- or co-translationally modified to give a novel amino acid side chain, aspartyl aldehyde. 相似文献