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Successive Addition (successive + addition)
Selected AbstractsCa2+ -dependent in vitro contractility of a precipitate isolated from an extract of the heliozoon Actinophrys solCYTOSKELETON, Issue 2 2006Mikihiko Arikawa Abstract Contraction of axopodia in actinophrid heliozoons (protozoa) is induced by a unique contractile structure, the "contractile tubules structure (CTS)". We have previously shown that a cell homogenate of the heliozoon Actinophrys sol yields a precipitate on addition of Ca2+ that is mainly composed of filamentous structures morphologically identical to the CTS. In this study, to further characterize the nature of the CTS in vitro, biochemical and physiological properties of the precipitate were examined. SDS-PAGE analysis showed that the Ca2+ -induced precipitate was composed of many proteins, and that no proteins in the precipitate showed any detectable changes in electrophoretic mobility on addition of Ca2+. Addition of extraneous proteins such as bovine serum albumin to the cell homogenate resulted in cosedimentation of the proteins with the Ca2+ -induced precipitate, suggesting that the CTS has a high affinity for other proteins that are not related to precipitate formation. Appearance and disappearance of the precipitate were repeatedly induced by alternating addition of Ca2+ and EGTA, and its protein composition remained unchanged even after repeated cycles. When adhered to a glass surface, the precipitate showed Ca2+ -dependent contractility with a threshold of 10,100 nM, and this contractility was not inhibited by colchicine or cytochalasin B. The precipitate repeatedly contracted and relaxed with successive addition and removal of Ca2+, indicating that the contraction was controlled by Ca2+ alone with no need for any other energy supply. From our characterization of the precipitate, we concluded that its Ca2+ -dependent formation and contraction are associated with the unique contractile organelle, the "contractile tubules structure". Cell Motil. Cytoskeleton 2006. © 2005 Wiley-Liss, Inc. [source] The evolutionary history of crustacean segmentation: a fossil-based perspectiveEVOLUTION AND DEVELOPMENT, Issue 6 2005Dieter Waloszek Summary The evolution of segmentation in Crustacea, that is, the formation of sclerotized and jointed body somites and arrangement of somites into tagmata, is viewed in light of historical traits and functional constraints. The set of Early to Late Cambrian ,Orsten' arthropods have informed our current views of crustacean evolution considerably. These three-dimensionally preserved fossils document ancient morphologies, as opposed to purely hypothetical models and, because of the unusual preservation of larval stages, provide us with unparalleled insight into the morphogenesis of body somites and their structural equipment. The variety of evolutionary levels represented in the ,Orsten' including lobopodians, tardigrades, and pentastomids also allows phylogenetic interpretations far beyond the Crustacea. The ,Orsten' evidence and data from representatives of the Lower Cambrian Chengjiang biota in southwestern China, including phylogenetically earlier forms, form the major source of our morphology-based review of structural and functional developments that led toward the Crustacea. The principal strategy of arthropods is the simultaneous development of head somites, as expressed in a basal "head larva," and a successive addition of postcephalic somites from a preterminal budding zone with progressive maturation of metameric structures. This can be recognized in the developmental patterns of extant and fossil representatives of several euarthropod taxa, particularly crustaceans, trilobites, and chelicerates (at least basally). The development of these taxa points to an early somite-poor and free-living hatching stage. Embryonic development to a late stage within an egg, as occurring in recent onychophorans and certain in-group euarthropods, is regarded as achieved several times convergently. [source] Recycled carbon fiber filled polyethylene compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2008Tony McNally Abstract Composites of recycled carbon fiber (CF) with up to 30 wt % loading with polyethylene (PE) were prepared via melt compounding. The morphology of the composites and the degree of dispersion of the CF in the PE matrix was examined using scanning electron microscopy, and revealed the CF to be highly dispersed at all loadings and strong interfacial adhesion to exist between the CF and PE. Raman and FTIR spectroscopy were used to characterize the surface chemistry and potential bonding sites of recycled CF. Both the Young's modulus and ultimate tensile stress increased with increasing CF loading, but the percentage stress at break was unchanged up to 5 wt % loading, then decreased with further successive addition of CF. The effect of CF on the elastic modulus of PE was examined using the Halpin-Tsai and modified Cox models, the former giving a better fit with the values determined experimentally. The electrical conductivity of the PE matrix was enhanced by about 11 orders of magnitude on addition of recycled CF with a percolation threshold of 7 and 15 wt % for 500-,m and 3-mm thick samples. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Identification and Biosynthesis of an Aggregation Pheromone of the Storage Mite Chortoglyphus arcuatusCHEMBIOCHEM, Issue 11 2004Stefan Schulz Prof. Abstract In an effort to identify new pheromones from mites, the headspace of undisturbed colonies of the storage mite Chortoglyphus arcuatus was analyzed by GC-MS by use of a closed-loop stripping apparatus (CLSA) or solid-phase microextraction (SPME). The major compound emitted from the mites is (4R,6R,8R)-4,6,8-trimethyldecan-2-one (4R,6R,8R - 8). The structure was elucidated by analysis of the mass spectrum, synthesis of authentic samples, and gas chromatography on a chiral phase. Bioassays show that this compound, for which we propose the trivial name chortolure, is an aggregation pheromone for both sexes of this species. Several related compounds are released in smaller amounts by the mites. The alarm pheromones of these mites, neral and geranial, can only be found in total extracts of the mites, in which 8 occurs only in minute amounts. The method of sampling is therefore crucial for pheromone identification. Feeding experiments with deuterated propionate showed that chortolure is a polyketide, formed by successive addition of four propionate units to an acetate starter. [source] Solid-State Gas Sensors Developed from Functional Difluoroboradiazaindacene DyesCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2009Raymond Ziessel Dr. Abstract This article describes the synthesis and characterization of several new difluoroboradiazaindacene (BODIPYÔ) dyes functionalized at the central 8-position by a phenyliodo, phenylheptynoate or phenylheptynoic fragment and at the 3- or 3/5-position(s) by 4-dimethylaminophenylstyryl residue(s). Single-crystal structural determinations confirm the planarity of the dyes, while the absorption and fluorescence spectroscopic properties are highly sensitive to the state of protonation (or alkylation) of the terminal anilino donor group(s). Reversible color tuning from green to blue for absorption and from colorless (i.e., near-IR region) to red for fluorescence is obtained on successive addition of acid and base. The difunctionalized derivative is especially interesting in this respect and shows two well-resolved pKa values of 5.10 and 3.04 in acetonitrile. Addition of the first proton causes only small spectral changes and deactivates the molecule towards addition of the second proton. It is this latter step that accommodates the large change in absorption and emission properties, due to the reversible extinction of the intramolecular charge-transfer character inherent to this type of dye. The main focus of the work is the covalent anchoring of the dyes to inert, porous polyacrylate beads so as to form a solid-state sensor suitable for analysis of gases or flowing liquids. The final material is highly stable,its performance is undiminished after more than one year,and fully reversible over many cycles. The sensitivity is such that reactions can be followed by the naked eye and the detection limit is about 600,ppb for HCl and about 80,ppb for ammonia. Trace amounts of diphosgene can be detected, as can alkylating agents. The sensing action is indiscriminate and also operates when the beads are dispersed in aqueous media. Ce manuscrit décrit la synthèse et la caractérisation de nouvelles sondes fluorescentes communément appelées BODIPY qui ont été ciselées en position centrale par un groupe phényl-iodo, phénylheptynoate ou phénylheptanoic acide et en positions 5 ou 3/5 avec des fragments 4-diméthylaminostyryle. Ces derniers fragments favorisent une excellente conjugaison qui est à l'origine de la couleur verte des sondes. Des structures moléculaires obtenues par diffraction aux rayon X sur monocristal confirment la planarité des ces objets, tandis que les propriétés d'absorption et de fluorescence sont sensibles à la protonation ou l'alkylation des groupements aminés terminaux. Un changement de couleur réversible du vert au bleu par absorption et de l'invisible au rouge en fluorescence est obtenu en présence d'un flux d'air pimenté avec des traces d'acides. La réversibilité est observée en présence de traces de base. Le dérivé di-fonctionnalisé est particulièrement intéressant dans la mesure ou deux pKa sont bien résolus à 5,10 et 3,04 unités dans l'acétonitrile. L'addition du premier proton induits des changements spectroscopiques modestes et diminue la basicité du deuxième groupe amino. Cette dernière protonation induit des changements majeurs en absorption et émission et inhibe le transfert de charge intramoléculaire. L'intérêt majeur de ces sondes réside dans leur potentiel d'être lié de façon covalente à des billes de polymères et d'utiliser ces billes pour la détection d'éléments toxiques dans des effluents gazeux. En particulier il a été démontré que la détection visuelle de trace de HCl (environ 600 ppb) ou d'ammoniaque (environ 80 ppb) est possible sans l'utilisation de systèmes de détection particuliers. De façon similaire des traces de diphosgène et d'autre agent vésicant et alkylant est possible. Ces systèmes sont très stables (durée supérieure à un an) et fonctionnent également en phase aqueuse. Aucune sélectivité de détection n'a été obtenue mais conceptuellement les systèmes sont particulièrement sensibles et peuvent être modifiés à façon. [source] Tandem Exploitation of Helix pomatia Glycosyltransferases: Facile Syntheses of H-Antigen-Bearing OligosaccharidesCHEMISTRY - A EUROPEAN JOURNAL, Issue 25 2007Hagen Bretting Prof. Abstract Snails from the family Helicidae produce in their albumen glands a highly branched galactan, which consists almost exclusively of D - and L -galactose. The D -Gal residues are glycosydically ,(1,6)- or ,(1,3)-linked, whereas the L -Gal moieties are attached ,(1,2). Up until the present time, two ,(1,6)- D -galactosyl transferases and one ,(1,2)- L -galactosyl transferase have been identified in a membrane preparation of these glands. These were used to synthesise various oligosaccharides by successive addition of the NDP-activated (NDP=nucleoside-5,-diphosphate) D -Gal or L -Fuc moieties, up to a heptasaccharide by starting from the disaccharide D -Gal-,(1,3)- D -Gal-,(1,OMe. Even larger oligosaccharides up to a tridecasaccharide were obtained by starting with the hexasaccharide D -Gal-[,(1,3)- D -Gal]4 -,(1,4)- D -Glc as an acceptor substrate. This tandem exploitation process has high potential for the easy introduction of D -Gal and L -Fuc residues into a great variety of oligosaccharides, which can be used in ligand/acceptor studies. [source] Block copolymerizations of higher 1-olefins with traditional polar monomers using metallocene-type single component lanthanide initiatorsPOLYMER INTERNATIONAL, Issue 8 2004Hajime Yasuda Abstract Block copolymerizations of 1-pentene or 1-hexene with methyl methacrylate or ,-caprolactone were explored using [Me2Si(2-SiMe3 -4- t -BuMe2SiC5H2)2YH]2 (1) or [Me2Si(2-SiMe3 -4- t -BuC5H2)2SmH]2 (2) as an initiator in toluene or in neat mixtures by the successive additions of monomers in this order. Random copolymerizations of 1-pentene with 1-hexene, and random copolymerization of ethylene with 1-hexene were also performed using 1 as an initiator. Copyright © 2004 Society of Chemical Industry [source] Expression of merA, amoA and hao in continuously cultured Nitrosomonas europaea cells exposed to zinc chloride additionsBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2009Tyler S. Radniecki Abstract The effects of ZnCl2 additions on a mercuric reductase, merA, ammonia monooxygenase, amoA, and hydroxylamine (NH2OH) oxidoreductase, hao, gene expression were examined in continuously cultured Nitrosomonas europaea cells. The reactor was operated for 85 days with a 6.9 d hydraulic retention time and with four successive additions of ZnCl2 achieving maximum concentrations from 3 to 90 µM Zn2+. Continuously cultured N. europaea cells were more resistant to Zn2+ inhibition than previously examined batch cultured cells due to the presence of Mg2+ in the growth media, suggesting that Zn2+ enters the cell through Mg2+ import channels. The maximum merA up-regulation was 45-fold and expression increased with increases in Zn2+ concentration and decreased as Zn2+ concentrations decreased. Although Zn2+ irreversibly inactivated ammonia oxidation in N. europaea, the addition of either 600 µM CuSO4 or 2250 µM MgSO4 protected N. europaea from ZnCl2 inhibition, indicating a competition between Zn2+ and Cu2+/Mg2+ for uptake and/or AMO active sites. Since ZnCl2 inhibition is irreversible and amoA was up-regulated at 30 and 90 µM additions, it is hypothesized that de novo synthesis of the AMO enzyme is needed to overcome inhibition. The up-regulation of merA during exposure to non-inhibitory Zn2+ levels indicates that merA is an excellent early warning signal for Zn2+ inhibition. Biotechnol. Bioeng. 2009;102: 546,553. © 2008 Wiley Periodicals, Inc. [source] | ||||||||||||||||