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Representative Member (representative + member)
Selected AbstractsUnderstanding the Nature of the States Responsible for the Green Emission in Oxidized Poly(9,9-dialkylfluorene)s: Photophysics and Structural Studies of Linear Dialkylfluorene/Fluorenone Model CompoundsADVANCED FUNCTIONAL MATERIALS, Issue 13 2009Khai Leok Chan Abstract Here, the optical properties of a series of structurally well-defined model compounds for oxidatively degraded poly(dialkylfluorenes) (PFs) are reported. Specifically, linear compounds comprising one, two, or four dihexylfluorene (F) moieties together with one fluorenone (O) moiety placed either at the end or in the center of each chain (i.e., FO, FFO, FOF, FFOFF) are studied. The results support the recent observation that the photophysics of the fluorenone-centered "pentamer" (FFOFF) is most similar to that of oxidized PFs. They further demonstrate that molecule,molecule interaction is essential to activate the green emission band. Investigations by X-ray diffraction (XRD) identify the solid-state structure of a representative member of this class of compounds and reveal inter-molecular interaction through dipole,dipole coupling between neighboring fluorenone moieties. [source] A Model of Declining StandardsINTERNATIONAL ECONOMIC REVIEW, Issue 2 2000Joel Sobel This paper presents a model in which relative standing determines standards. There are three kinds of agents in the model: candidates who wish to pass a test, members of the elite who have passed the test, and the judge who decides who passes. In order to pass, a candidate's performance must be at least as good as the performance of a representative member of the elite. Without perturbations in the underlying data, the model predicts that standards will not change. Perturbations in the preferences used to judge candidates lead to a reduction in standards. [source] Escherichia coli Hsp31 functions as a holding chaperone that cooperates with the DnaK-DnaJ-GrpE system in the management of protein misfolding under severe stress conditionsMOLECULAR MICROBIOLOGY, Issue 3 2004Mirna Mujacic Summary Escherichia coli Hsp31 is a homodimeric protein that exhibits chaperone activity in vitro and is a representative member of a recently recognized family of heat shock proteins (Hsps). To gain insights on Hsp31 cellular function, we deleted the hchA gene from the MC4100 chromosome and combined the resulting null allele with lesions in other cytoplasmic chaperones. Although the hchA mutant only exhibited growth defects when cultivated at 48°C, loss of Hsp31 had a strong deleterious effect on the ability of cells to survive and recover from transient exposure to 50°C, and led to the enhanced aggregation of a subset of host proteins at this temperature. The absence of Hsp31 did not significantly affect the ability of the ClpB-DnaK-DnaJ-GrpE system to clear thermally aggregated proteins at 30°C suggesting that Hsp31 does not possess disaggregase activity. Although it had no effect on the growth of groES30, ,clpB or ,ibpAB cells at high temperatures, the hchA deletion aggravated the temperature sensitive phenotype of dnaK756 and grpE280 mutants and led to increased aggregation in stressed dnaK756 cells. On the basis of biochemical, structural and genetic data, we propose that Hsp31 acts as a modified holding chaperone that captures early unfolding intermediates under prolonged conditions of severe stress and releases them when cells return to physiological conditions. This additional line of defence would complement the roles of DnaK-DnaJ-GrpE, ClpB and IbpB in the management of thermally induced cellular protein misfolding. [source] Structure of Mycobacterium tuberculosis Rv2714, a representative of a duplicated gene family in ActinobacteriaACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 10 2009Martin Graña The gene Rv2714 from Mycobacterium tuberculosis, which codes for a hypothetical protein of unknown function, is a representative member of a gene family that is largely confined to the order Actinomycetales of Actinobacteria. Sequence analysis indicates the presence of two paralogous genes in most mycobacterial genomes and suggests that gene duplication was an ancient event in bacterial evolution. The crystal structure of Rv2714 has been determined at 2.6,Å resolution, revealing a trimer in which the topology of the protomer core is similar to that observed in a functionally diverse set of enzymes, including purine nucleoside phosphorylases, some carboxypeptidases, bacterial peptidyl-tRNA hydrolases and even the plastidic form of an intron splicing factor. However, some structural elements, such as a ,-hairpin insertion involved in protein oligomerization and a C-terminal ,-helical domain that serves as a lid to the putative substrate-binding (or ligand-binding) site, are only found in Rv2714 bacterial homologues and represent specific signatures of this protein family. [source] Life-history monographs of Japanese plants.PLANT SPECIES BIOLOGY, Issue 3 20079: Helonias orientalis (Thunb.) N. Tanaka (Liliaceae) Abstract The life-history characteristics of Helonias orientalis (Liliaceae) are described. The genus Helonias (Liliaceae), which includes Heloniopsis and Ypsilandra, is one of the representative members of the so-called Arcto-Tertiary Geoflora, with typical disjunct geographical ranges in eastern North America and eastern Asia, including the Japanese Islands to inland China and the Himalayan Mountains. The seasonal growth patterns of this evergreen perennial are most unique, showing different replacement patterns in foliage leaves, which are formed during two different seasons, once in late spring and again in late summer to autumn. Flowering occurs at different times of the year in populations that are located at different elevations. Lowland populations flower in late March to early April, whereas montane and subalpine,alpine populations bear flowers in early to mid-summer, June to August. Another outstanding feature of this species is that it produces tiny plantlets at the tips of the oldest (3-year-old) foliage leaves just before decaying. Survival rates of plantlets (ramets) are obviously much higher than that of the exceedingly minute seedlings (gamets), especially on the dark shady forest floor. Thus, populations in closed woodland habitats are primarily maintained by plantlets, that is, vegetative plantlet formation. The cost of seed production is dramatically higher in the subalpine,alpine populations compared with those of the lowland populations. [source] The new ternary phases of La3(Zn0.874Mg0.126)11 and Ce3(Zn0.863Mg0.137)11ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2010Volodymyr Pavlyuk The new ternary intermetallic title compounds, namely trilanthanum undeca(zinc/magnesium), La3(Zn0.874Mg0.126)11, (I), and tricerium undeca(zinc/magnesium), Ce3(Zn0.863Mg0.137)11, (II), are isostructural and crystallize in the orthorhombic La3Al11 structure type. These three phases belong to the same structural family, the representative members of which may be derived from the tetragonal BaAl4 structure type by a combination of internal deformation and multiple substitution. Compared to the structure of La3Al11, in (I), a significant decrease of 11.9% in the unit-cell b axis and an increase in the other two directions, of 3.6% along a and 5.2% along c, are observed. Such an atypical deformation is caused by the closer packing of atoms in the unit cell due to atom shifts that reflect strengthening of metallic-type bonding. This structural change is also manifested in a significant difference in the coordination around the smaller atoms at the 8l Wyckoff position (site symmetry m). The Al atom in La3Al11 is in a tricapped trigonal prismatic environment (coordination number 9), while the Zn atoms in (I) and (II) are situated in a tetragonal antiprism with two added atoms (coordination number 10). [source] Discovery of Potent Vascular Endothelial Growth Factor Receptor-2 InhibitorsCHEMMEDCHEM, Issue 1 2010Athanasios Papakyriakou Dr. Abstract Substantial evidence over the last decades has implicated uncontrolled angiogenesis with various pathological states, including cancer. Vascular endothelial growth factor (VEGF) plays a critical role in its regulation. Because the tyrosine kinase VEGF receptor-2 (VEGFR-2) is the major mediator of the mitogenic, angiogenic, and permeability-enhancing effects of VEGF, it has become one of the most profound anti-angiogenesis targets. Inspired by the anthranilamide class of VEGFR-2 inhibitors, we performed a computational analysis of some potent representative members, using docking and molecular dynamics calculations. Based on the observations drawn from introducing the effect of the receptor's flexibility in implicit aqueous environment, we designed, synthesized, and characterized several new analogues of related scaffolds with modifications in their steric and electronic characteristics. In,vitro evaluation of these compounds revealed several novel VEGFR-2 inhibitors that are less cytotoxic and more potent than the parent compounds. [source] | |||||||||||||