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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 96 (1993), S. 32-39 
    ISSN: 1432-1939
    Keywords: Formicidae ; Leptothorax ; Queen polymorphism ; Wing reduction ; Colony founding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In two nearctic ants, Leptothorax canadensis and Leptothorax sp. A, young queens may either found their own nest solitarily after mating or seek adoption into an established colony. Whether a queen disperses or not is associated with genetically determined queen morphology in Leptothorax sp. A. Whereas a majority of winged queens attempt solitary colony founding after mating, most wingless, intermorphic queens return to their maternal nests and new colonies are founded by budding after hibernation. The latter strategy appears to be correlated with patchy, isolated habitats, whereas in extended boreal forests dispersal on the wing is probably more common. Alternative dispersal strategies strongly affect the average number of queens per colony and seasonal fluctuations of colony structure.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Behavioral ecology and sociobiology 45 (1999), S. 151-159 
    ISSN: 1432-0762
    Keywords: Key words Reproductive competition ; Ants ; Aggression ; Dominance rank ; Fertility recognition ; Leptothorax
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In most species of advanced eusocial insects, the partitioning of reproduction between nestmates is thought to be regulated by means of primer pheromones or other chemical cues, which presumably influence the behavior of co-queens and workers such that they maximize their own inclusive fitness. Here we show that in multi-queen colonies of the Nearctic ant, Leptothorax sp. A, physical dominance in concert with chemical cues, which signal the ovarian development of a queen, are used to control reproduction of competing queens and to influence worker behavior. The analysis of ranks obtained during two fighting periods in the annual colony cycle revealed a strong link between individual aggressiveness of a queen and her fertility. During the adoption of newly mated queens in autumn, the resident, egg-laying α-queen was more likely to start aggression first and keep her high rank position compared to the fighting period after hibernation. We suggest that this is proximately caused by the α-queen having much stronger developed ovaries in autumn than the young queens, whereas after hibernation, the ovaries of all queens are similarly inactive. Interactions during the first weeks after the end of hibernation and intrinsic, individual differences in aggressiveness appear to be crucial for the dominance rank achieved later. Queens which were allowed to become fertile when their nestmate queens still were kept under prolonged hibernation, were immediately socially dominant over the latter when all queens were reunited, though no aggression occurred. In another experiment, queen antagonism was prevented by spatial separation in different parts of the same nest and all queens began to lay eggs. Workers stayed preferentially with queens with high actual fecundity rather than with those which had had high social status before separation. This and further evidence suggest that ovarian status is communicated, most likely by a chemical cue perceived by co-queens and workers, affects the direction of their aggressive behavior, and allows them to discriminate among queens.
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  • 3
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ESR and cyclic voltammetry investigations show that isomerization of the radical cation of cis-1,1′-azonorbornane (cis-1) to the trans-radical ion proceeds too fast in solution for direct investigation of the cis-radical ion even at -78°. The facile isomerization of the radical cation is in agreement with PM3 calculations proposing an activation barrier of only 17 kJ/mol. As a consequence, quantitative cis → trans isomerization of 1,1′-azonorbornane can effectively be accomplished by addition of catalytic amounts of one-electron oxidants. This is the first evidence for a radical-cation-catalyzed cis → trans isomerization of azo compounds.
    Additional Material: 2 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 75 (1992), S. 2307-2316 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Seven redox stages, the dication 12+, the radical cation \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {{+}\kern-4pt {.}\kern-2pt }}$\end{document}, the neutral 1, the radical anion \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {{\relbar}\kern-4pt {.}\kern-2pt }}$\end{document}, the dianion 12-, the radical trianion \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {3{\relbar}\kern-4pt {.}\kern-2pt }}$\end{document}\end{document}, and the tetraanion 14-, are indicated by cyclic voltammetry for the bisphane 1, in which the benzene decks of two lateral paracyclophane moieties are orthogonal to the plane of anthracene framework. In \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {{+}\kern-4pt {.}\kern-2pt }}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {{\relbar}\kern-4pt {.}\kern-2pt }}$\end{document}, the unpaired electron is accommodated into the central anthracene subsystem, and the same statement holds for the two positive or negative charges in 12+ and 12-. Formation of \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {3{\relbar}\kern-4pt {.}\kern-2pt }}$\end{document}\end{document} and 1- occurs through admission of additional electrons one-by-one into the two paracyclophane moieties flanking the doubly charged anthracene subsystem in 12-. The above-postulated, successive release or uptake of electrons by the individual parts of the bisphane is in perfect accord with the hyperfine data determined by ESR and ENDOR spectroscopy for \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {{+}\kern-4pt {.}\kern-2pt }}$\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {{\relbar}\kern-4pt {.}\kern-2pt }}$\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$1^{\scriptstyle {3{\relbar}\kern-4pt {.}\kern-2pt }}$\end{document}\end{document}, as well as for radical ions of suitable reference compounds.
    Additional Material: 6 Ill.
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  • 5
    ISSN: 0947-3440
    Keywords: Cyano compounds, conjugated ; Phenylacetylenes ; Radical anions ; Electrochemistry ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of phenylacetylenes 4a-h with copper(I) acetate (5) and TCNE (tetracyanoethylene) in THF/acetonitrile gave 4-phenyl-1-buten-3-yne-1,1,2-tricarbonitriles 6a-h. 4i did not react to give 6i. The phenylacetylenes 4b-i were prepared by a two-step synthesis starting from the corresponding phenyl halides 1b-i. The tricyanoacrylates 8 were synthesized from the corresponding cyanoacetates 7, TCNE and catalytic amounts of pyridine in THF. - Cyclovoltammetric investigations showed that the butenynes 6 and the tricyanoacrylates 8 are strong electron acceptors which can be easily reduced. The radical anions 6·- are unstable in aceto-nitrile and react irreversibly with 6 to give oligomeric anions 6n·-. Only 4-(2,4,6-trimethoxyphenyl)-1-buten-3-yne-1,1,2-tricarbonitrile (6h) is reduced to a radical anion 6h·- which associates with 6h in a reversible follow-up process to form a dimeric anion 6h2·-. By contrast, the tricyanoacrylates 8 can be reversibly reduced to their respective radical anions and dianions.
    Additional Material: 5 Ill.
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  • 6
    ISSN: 0947-3440
    Keywords: Carotenoids ; C26—C70 β-carotenes ; Cyclic voltammetry ; Photoelectron spectroscopy ; Semiempirical calculations ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper, we report on the synthesis of β-carotenes of variable chain length with between 5 and 23 double bonds (1-7). These oligoenes were prepared by McMurry and Wittig reactions. The tetradecapreno-β-carotene 7 would seem to be the longest β-carotene yet reported. Furthermore, we investigated the electronic properties using cyclic voltammetry and photoelectron spectroscopy (UPS) to generate open-shell and closed-shell ions of carotenoids in solution and in the solid state, respectively. With increasing chain length (≥ 11 double bonds), even the generation of tetracations and tetraanions could be observed by cyclic voltammetry. Extending the number of conjugated bonds causes the potentials to converge to limiting values. All electron-transfer processes occur in one-electron steps, which are close to each other in pairs. The potential difference between the first oxidation potential and the first reduction potential is a linear function of the reciprocal chain length. Despite the different techniques used (CV and UPS) and the different condensed phases, there is an excellent correspondence between the energies of the radical cation states generated by the two methods. This shows that the radical cation formation is principally determined by the chain length. The structures of the ion states were investigated using semiempirical methods at the NDDO level. Charge delocalization and bond relaxation are not identical and do not utilize the same number or the same kind of atoms. It can be shown that from the length of 20 double bonds onwards, the effective conjugation length for doubly-charged cations converges slowly to a limiting value.
    Additional Material: 10 Ill.
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