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41.
Ricardo H. Sestrem Richard Landers Marcia L.A. Temperini 《European Polymer Journal》2010,46(3):484-7804
Poly(ortho-phenylenediamine) and oligomers of ortho-phenylenediamine were chemically synthesized and characterized by UV-vis, 1H and 13C NMR, FTIR and resonance Raman spectroscopies. Polymerization of ortho-phenylenediamine in HCl medium with ammonium persulfate only leads the trimer compound, in disagreement with some previous reports. Nevertheless, in acetic acid medium it was possible to prepare a polymer constituted by ladder phenazinic segments with different protonation levels and quinonediimine rings (polyaniline-like). X-ray absorption at N K-edge (N K XANES), X-ray photoelectron (XPS) and Electron paramagnetic resonance (EPR) spectroscopies were used to determine the different kinds of nitrogen presents in this class of polymer. N K XANES spectrum of poly(ortho-phenylenediamine) shows the band of N nitrogen of non-protonated phenazinic rings at 398.2 eV. In addition, XPS and N K XANES data confirm the presence of different types of protonated nitrogens in the polymeric poly(ortho-phenylenediamine) chain and the EPR spectrum shows that the polymer has a very weak polaronic signal. 相似文献
42.
Anniversary Dates
75th anniversary of Vladimir K. Baev 相似文献43.
França EJ Andrade CG Furlaneto-Maia L Serpa R Oliveira MT Quesada RM Furlaneto MC 《Micron (Oxford, England : 1993)》2011,42(7):726-732
Candida tropicalis has been identified as one of the most prevalent pathogenic yeast species of the Candida-non-albicans (CNA) group. Study of switching in C. tropicalis has not been the subject of extensive research. Therefore, we investigated switching event and characterized the ultrastructural architecture of different phenotypes and biofilm produced in a C. tropicalis clinical strain. Cells switched heritably, reversibly, and at a high frequency between four phenotypes readily distinguishable by the shape of colonies formed on agar at 25°C. SEM analysis was used to verify the architecture of whole Candida colonies at ultrastructural level. The smooth phenotype (parental phenotype) colony showed a hemispherical shape character, while the semi-smooth was characterized by the presence of shallow marginal depressions. The ring and rough phenotypes exhibited more complex architecture and were characterized by the presence of deep central and peripheral depressions areas. The biofilm-forming ability varied among the switch phenotypes. After 12h incubation, the smooth phenotype formed less biofilm compared to the other phenotypes (P<0.05). The electron microscopy analysis revealed that filamentation (pseudohyphae) was associated with ring and rough colonies. The ultrastructural analysis allowed the observation of the arrangement of individual cells within the colonies. At the deep central and peripheral depressions areas of the ring and rough colonies extracellular material was seen in different arrangements. The data presented here open new avenues to study a possible role for extracellular material in the formation and maintenance of the architecture of switch phenotypes in C. tropicalis. It is therefore essential that more strains be investigated to determine the biological significance of extracellular material in C. tropicalis phenotypic switching phenomenon. 相似文献
44.
In this paper, we present a new hybrid algorithm for convex Mixed Integer Nonlinear Programming (MINLP). The proposed hybrid algorithm is an improved version of the classical nonlinear branch-and-bound (BB) procedure, where the enhancements are obtained with the application of the outer approximation algorithm on some nodes of the enumeration tree. The two methods are combined in such a way that each one collaborates to the convergence of the other. Computational experiments with benchmark instances of the MINLP problem show the good performance of the proposed algorithm, which is compared to the outer approximation algorithm, the nonlinear BB algorithm and the hybrid algorithm implemented in the solver Bonmin. 相似文献
45.
46.
Marcia Cristina Branciforti Vitor Sencadas Senentxu Lanceros‐Mendez Rinaldo Gregorio Jr. 《Journal of Polymer Science.Polymer Physics》2007,45(19):2793-2801
Oriented β‐phase films were obtained by utilizing two different techniques: conventional uniaxial drawing at 80 °C of predominantly α‐phase films, and by drawing almost exclusively β‐phase films obtained by crystallization at 60 °C from dimethylformamide (DMF) solution with subsequent pressing. Wide angle X‐ray diffraction (WAXD) and pole figure plots showed that with the conventional drawing technique films oriented at a ratio (R) of 5 still contained about 20% of phase α, a crystallinity degree of 40% and β‐phase crystallographic c ‐axis orientation factor of 0.655. Drawing at 90 °C and with R = 4 of originally β‐phase films results in exclusively β‐phase films with crystallinity degree of 45% and orientation factor of 0.885. Crystalline phase, crystallinity degree, and crystallographic c‐axis orientation factor of both phases were also determined for α‐phase oriented films obtained by drawing α‐phase films at 140 °C. For films drawn at 140 °C the α to β phase transition drops to about 22%. Reduction in crystallinity degree with increasing R is more pronounced at draw temperature of 140 °C compared with 80 °C. Moreover, for both phases the c ‐axis orientation parallel to the draw direction is higher at draw temperature of 140 °C than at 80 °C. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2793–2801, 2007 相似文献
47.
In several applications, underestimation of functions has proven to be a helpful tool for global optimization. In protein–ligand
docking problems as well as in protein structure prediction, single convex quadratic underestimators have been used to approximate
the location of the global minimum point. While this approach has been successful for basin-shaped functions, it is not suitable
for energy functions with more than one distinct local minimum with a large magnitude. Such functions may contain several
basin-shaped components and, thus, cannot be underfitted by a single convex underestimator. In this paper, we propose using
an underestimator composed of several negative Gaussian functions. Such an underestimator can be computed by solving a nonlinear
programming problem, which minimizes the error between the data points and the underestimator in the L
1 norm. Numerical results for simulated and actual docking energy functions are presented. 相似文献
48.
Hung Dang Marcia Levitus Miguel A Garcia-Garibay 《Journal of the American Chemical Society》2002,124(1):136-143
A simple procedure for the synthesis of cyclopentafused polycyclic aromatic hydrocarbons (CP-PAH) with Pd(PPh(3))(2)Cl(2) catalyst has been applied to the one-pot palladium(0)-catalyzed coupling of 9,10-dibromoanthracene (1) with 2-methyl-3-butyn-2-ol. Reactions carried out in refluxing benzene in the presence of CuSO(4)/Al(2)O(3) yielded 9,10-dialkynylanthracene 2a, alkynyl aceanthrylene 2b, and 2,7-disubstituted cyclopent[hi]aceanthrylene 2c in 13%, 23%, and 19% purified yields, respectively, with total conversions of 80-90%. Sealed tube reactions without copper at 110 degrees C improved the yield of 2c up to >75%. Single-crystal X-ray analyses of 2a and 2c reveal a three-dimensional hydrogen bonding network, producing a unique crystal packing. The packing structure of 2b is dominated by pi-pi stacking interactions between two aceanthrylene molecules. CP-PAHs 2b and 2c have potentially interesting fullerene-like photophysics. While the UV-vis and fluorescence spectra of 2a (Phi(F) = 0.87) show the characteristic vibronic structure of anthracene, the UV-vis spectra of ruby-red aceanthrylene 2b and greenish-black cyclopent[hi]aceanthrylene 2c extend well into the visible range. Isomers 2b and 2c showed no detectable fluorescence emission. Unlike fullerenes, compounds 2b and 2c are poor singlet oxygen sensitizers with measured (1)O(2) quantum yields of 0.02 and 0.06, respectively. As expected from a simple Hückel analysis, 2c has relatively low two-electron reduction potentials as determined by cyclic voltammetry. 相似文献
49.
Jason Ashmore Roger Bishop Donald C. Craig Marcia L. Scudder 《Journal of inclusion phenomena and macrocyclic chemistry》2011,71(3-4):297-302
The V-shaped racemic compound 4,12-dinitro-6,7,14,15-tetrahydro-6,14-methanocycloocta[1,2-b:5,6-b??]diquinoline 2 crystallises from solvents of differing water content as a centrosymmetric spheroidal hexamer in the form of a series of isostructural clusters (2)6·(water) x X-ray structures of these crystals in space group $ R\bar{3} $ show that they can exhibit an extent of hydration anywhere throughout the composition range x = 0 to 1. 相似文献
50.
Sperb F Werlang IC Margis-Pinheiro M Basso LA Santos DS Pasquali G 《Applied biochemistry and biotechnology》2011,165(2):652-665
Erythropoietin (EPO) is a hormone belonging to a group of hematopoietic growth factors that control the proliferation and
differentiation of bone marrow cells. It induces the production of erythrocytes, thereby increasing the amount of circulating
hemoglobin and oxygen. Previous attempts to transgenically express human EPO in plants failed to succeed because the plants
exhibited abnormal morphology and infertility. In the present work, we describe the generation of fertile transgenic tobacco
plants able to express a synthetic version of human EPO. A 582-bp fragment of the human EPO gene was synthesized using a PCR-based
method and ligated into pCR-Blunt. After sequencing, the human EPO fragment was transferred to pWUbi.tm1 and the expression
cassette was then transferred to the binary vector pWBVec4a. After Agrobacterium-mediated transformation of Nicotiana tabacum SR1 plants, integration of the transgene into T0 and T1 plant genomes was confirmed by PCR. The human EPO gene was found to be expressed in tobacco leaves at the mRNA and protein
levels. Self-crossing allowed us to obtain T1 plants exhibiting Mendelian segregation of the transgene. None of the plants presented any kind of malformation or deformity. 相似文献