23,099 research outputs found
Evidence for the decay B0→J/ψω and measurement of the relative branching fractions of meson decays to J/ψη and J/ψη′
No full textFirst evidence of the B 0 → J / ψ ω decay is found and the B s 0 → J / ψ η and B s 0 → J / ψ η ′ decays are studied using a dataset corresponding to an integrated luminosity of 1.0 fb -1 collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV. The branching fractions of these decays are measured relative to that of the B 0 → J / ψ ρ 0 decay:frac(B (B 0 → J / ψ ω), B (B 0 → J / ψ ρ 0)) = 0.89 ± 0.19 (stat) - 0.13 + 0.07 (syst),frac(B (B s 0 → J / ψ η), B (B 0 → J / ψ ρ 0)) = 14.0 ± 1.2 (stat) - 1.5 + 1.1 (syst) - 1.0 + 1.1 (frac(f d, f s)),frac(B (B s 0 → J / ψ η ′), B (B 0 → J / ψ ρ 0)) = 12.7 ± 1.1 (stat) - 1.3 + 0.5 (syst) - 0.9 + 1.0 (frac(f d, f s)), where the last uncertainty is due to the knowledge of f d / f s, the ratio of b-quark hadronization factors that accounts for the different production rate of B 0 and B s 0 mesons. The ratio of the branching fractions of B s 0 → J / ψ η ′ and B s 0 → J / ψ η decays is measured to befrac(B (B s 0 → J / ψ η ′), B (B s 0 → J / ψ η)) = 0.90 ± 0.09 (stat) - 0.02 + 0.06 (syst)
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
eine Analyse von Ultrastruktur, Phylogenie und Kospeziation
No full textThe complex mechanisms leading to a tripartite symbiosis involving bacteria,
flagellates, and host termites are not yet fully understood. While the
flagellates are known to play a major role in the degradation of the
cellulosic food of the termites, in most cases, the functions of the diverse
flagellate-associated bacteria are completely obscure. Unambiguous
identification of the mostly uncultivable prokaryotes and eukaryotes is an
important step in understanding the mutual interactions between the two
partners. For this purpose, in the studies described in my thesis,
morphological investigations (light microscopy and electron microscopy) were
combined with molecular phylogenetic analyses (full-cycle-rRNA approach). In
two earlier light microscopy studies, other authors reported contradicting
numbers of devescovinid flagellates occurring in the hindgut of the dry-wood
termite Incisitermes marginipennis. We clearly and unambiguously documented
the presence of only one devescovinid species (Metadevescovina modica)
inhabiting the gut of I. marginipennis using a combination of various light
and electron microscopy techniques and molecular phylogenetic analysis of the
small subunit (SSU) rRNA gene sequences. Moreover, we confirmed the validity
of the genus Metadevescovina, which had long been discussed as being the same
as the genus Devescovina; monophyly of each of the genera was revealed by
molecular phylogenetic analyses. Metadevescovina could not be distinguished
from Devescovina solely by morphological characteristics of the flagellates
themselves, but the two flagellate genera could be differentiated by examining
their bacterial symbionts. The cell surface of Metadevescovina flagellates is
densely colonized with spirochetes, and that of Devescovina flagellates is
densely covered with filamentous bacteria affiliated to the Bacteroidales.
Molecular phylogenetic analyses of Devescovina spp. and their bacterial
symbionts from a wide range of Kalotermitidae revealed that the termites
acquired two bacterial symbionts by two different routes: vertical
transmission and horizontal transmission. The ectosymbionts of Devescovina
spp. form a monophyletic group within the Bacteroidales (“Candidatus
Armantifilum devescovinae”). Congruence analyses of the phylogenetic trees of
Devescovina spp. and “Candidatus Armantifilum devescovinae” documented a
strict cospeciation of the partners, which indicated an obligate symbiosis,
leading to a vertical transmission of the bacteria within their host lineages.
The ‘Endomicrobia’ endosymbionts of Devescovina spp. are most closely related
to endosymbionts of phylogenetically unrelated termite gut flagellates, which
indicated that these symbionts were acquired by horizontal transmission
between different flagellate species present in the same termite gut. In a
further study documented in this thesis, the multiple symbionts of the
flagellate Joenia annectens from the dry-wood termite Kalotermes flavicollis
were identified, localized using a full-cycle-rRNA approach, and
morphologically described at the ultrastructural level. Two populations of J.
annectens could be distinguished not only by their SSU rRNA gene sequences
(0.8% sequence divergence), but also by differences in their assemblages of
bacterial symbionts. Each of the flagellate populations hosted
phylogenetically distinct ectosymbionts from the phylum Bacteroidetes, while a
single phylotype of ‘Endomicrobia’ was consistently associated with only one
of the host phylotypes. However, not all individuals were colonized, once
again corroborating that ‘Endomicrobia’ are not always cospeciating with their
host lineages. The results reported in my thesis provide important information
about the specificity of the symbioses between termite gut flagellates and
their bacterial symbionts. This information is necessary for further studies
of the function of these symbioses. A possible involvement of bacterial
symbionts in the nitrogen metabolism of the host flagellates is discussed.Die komplexen Mechanismen, welche der Dreiersymbiose zwischen Bakterien,
Flagellaten und ihren Wirtstermiten zugrundeliegen, sind bis heute noch
weitgehend unverstanden. Während den Flagellaten eine wesentliche Rolle beim
Abbau der cellulosehaltigen Nahrung der Termiten zugeschrieben wird, sind die
Funktionen der diversen, mit den Flagellaten assoziierten Bakterien in den
meisten Fällen komplett unbekannt. Ein wichtiger Schritt für die Erforschung
der wechselseitigen Beziehungen zwischen den in der Regel nicht kultivierbaren
pro- und eukaryotischen Symbionten stellt deren eindeutige Identifizierung
dar. Dazu wurden in den vorliegenden Studien morphologische Untersuchungen
(Licht- und Elektronenmikroskopie) beider Partner mit molekular-
phylogenetischen Analysen kombiniert (full-cycle-rRNA approach). In zwei
vorangegangenen lichtmikroskopischen Studien anderer Autoren wurde für die
Trockenholztermite Incisitermes marginipennis eine widersprüchliche
Artenanzahl von devescoviniden Flagellaten dokumentiert. Durch den Einsatz
verschiedener licht- und elektronenmikroskopischer Techniken sowie durch die
Analyse der Sequenzvariabilität der Gene der kleinen ribosomalen Untereinheit
(SSU rRNA) konnten wir in der vorliegenden Arbeit eindeutig zeigen, dass I.
marginipennis lediglich eine Art devescovinider Flagellaten (Metadevescovina
modica) im Darm beherbergt. Gleichzeitig konnten wir die Gültigkeit der
Gattung Metadevescovina, welche bis zum heutigen Tag stark umstritten war und
häufig als Synonym zu Devescovina angesehen wurde, bestätigen.
Molekularphylogenetische Analysen zeigten, dass beide Gattungen jeweils eine
separate monophyletische Gruppe bilden. Eine Unterscheidung der beiden
Gattungen an Hand morphologischer Merkmale der Flagellaten selbst war nicht
möglich, konnte jedoch unter Berücksichtigung ihrer bakteriellen Symbionten
erfolgen. Während Flagellaten der Gattung Metadevescovina einen dichten Besatz
von Spirochaeten auf ihrer Oberfläche zeigen, sind Devescovina spp.
vollständig von filamentösen Bakterien bedeckt, welche den Bacteroidales
zugeordnet werden. Molekularphylogenetische Analysen von Devescovina spp. von
verschiedenen Vertretern der Kalotermitidae und ihren bakteriellen Symbionten
ergaben zwei verschiedene Szenarien bezüglich des Erwerbs dieser Symbionten:
Eine vertikale Weitergabe und eine horizontale Weitergabe. Es konnte gezeigt
werden, dass die Ektosymbionten eine monophyletische Gruppe innerhalb der
Bacteroidales bilden („Candidatus Armantifilum devescovinae“).
Kongruenzanalysen der Stammbäume von Devescovina spp. und „Candidatus
Armantifilum devescovinae“ dokumentierten eine strikte Kospeziation der
Partner. Eine obligate Symbiose der beiden Partner, und somit eine vertikale
Weitergabe der Bakterien innerhalb ihrer Wirtsflagellaten, konnte demnach
belegt werden. Der Erwerb von Symbionten durch horizontale Weitergabe von
anderen Wirtsflagellaten wurde dagegen für die im Zytoplasma vorkommenden
‚Endomicrobia‘ dokumentiert. Hier waren die nächsten Verwandten der mit den
Devescovina spp. assoziierten ‚Endomicrobia‘ Endosymbionten von phylogenetisch
nicht verwandten Termitenflagellaten. In einer weiteren Studie dieser Arbeit
wurden die multiplen Symbionten des Flagellaten Joenia annectens aus der
Trockenholztermite Kalotermes flavicollis identifiziert und lokalisiert (full-
cycle-rRNA approach). Ultrastrukturelle Untersuchungen ermöglichten eine
morphologische Beschreibung der gefundenen Phylotypen. Basierend auf den
Assoziationen mit phylogenetisch verschiedenen Symbionten konnten zwei
Populationen von J. annectens unterschieden werden. Gestützt wurde das
Ergebnis durch die Analyse der SSU rRNA Gensequenzen von J. annectens (0,8%
Sequenzunterschied zwischen beiden Populationen). Beide
Flagellatenpopulationen waren jeweils mit eigenen Ektosymbionten des Phylums
Bacteroidetes assoziiert. Dahingegen beherbergte nur eine der beiden
Populationen von J. annectens einen Vertreter der ‚Endomicrobia‘ im
Zytoplasma. Das Fehlen von ‚Endomicrobia‘-Symbionten bei vielen Flagellaten
der gleichen Population zeigt ein weiteres Beispiel dafür, dass diese
Symbionten nicht immer mit ihren Wirtsflagellaten kospeziieren. Die Ergebnisse
meiner Arbeit haben wichtige Erkenntnisse zur Spezifität der Symbiosen
zwischen Termitenflagellaten und ihrer bakteriellen Symbionten gebracht. Sie
stellen somit eine Grundvoraussetzung für die anstehende Erforschung der
funktionellen Aspekte dieser Symbiosen dar. Eine Beteiligung der bakteriellen
Symbionten am Stickstoffstoffwechsel der Flagellaten wird diskutiert
Early Diversification of Membrane Intrinsic Proteins (MIPs) in Eukaryotes
No full textAbstract Membrane intrinsic proteins (MIPs), including aquaporins (AQPs) and aquaglyceroporins (GLPs), form an ancient family of transporters for water and small solutes across biological membranes. The evolutionary history and functions of MIPs have been extensively studied in vertebrates and land plants, but their widespread presence across the eukaryotic tree of life suggests both a more complex evolutionary history and a broader set of functions than previously thought. That said, the early evolution of MIPs remains obscure. The presence of one GLP and four AQP clades across both bacteria and archaea suggests that the first eukaryotes could have possessed up to five MIPs. Here, we report on a previously unknown richness in MIP diversity across all major eukaryotic lineages, including unicellular eukaryotes, which make up the bulk of eukaryotic diversity. Three MIP clades have likely deep evolutionary origins, dating back to the last eukaryotic common ancestor (LECA), and support the presence of a complex MIP repertoire in early eukaryotes. Overall, our findings highlight the growing complexity of the reconstructed LECA genome: the dynamic evolutionary history of MIPs was set in motion when eukaryotes were in their infancy followed by radiative bursts across all main eukaryotic lineages.Open-Access-Publikationsfonds 202
Measurement of the branching fraction
No full textThe B
0
s
→ J/ψK
0
S
branching fraction is measured in a data sample corresponding to 0.41 fb−1
of integrated luminosity collected with the LHCb detector at the LHC. This channel is sensitive to
the penguin contributions affecting the sin 2β measurement from B
0
→ J/ψK
0
S
. The time-integrated
branching fraction is measured to be B(B
0
s
→ J/ψK
0
S
) = (1.83±0.28)×10−5
. This is the most precise
measurement to date
Aquatic hyphomycetes in Catamaran Brook: colonization dynamics, seasonal patterns, and logging effects
No full textAquatic fungal colonization dynamics and seasonal patterns were investigated in two sites in Catamaran Brook, New Brunswick, Canada, as part of a larger study to evaluate logging effects on a salmon stream. Four leaf-pack trials were conducted between May 1995 and Dec 1996 to determine species composition of the fungal community, the seasonal pattern of colonization on decaying maple leaves, and what effects, if any, invertebrate feeding and logging activities might have on community structure. Contrary to expectation, neither mesh size (i.e., invertebrate presence or absence) nor preliminary logging activity (road construction near one site) had a consistent effect on community structure. Time of immersion of the leaves in the stream, followed by season, were the major factors controlling community structure. Spore production and species diversity measures were highest during the middle part of the colonization period (generally 4-8 wk of immersion in summer trials and 2-4 wk immersion in the autumn trial), and were also higher in the autumn (Sep to Dec) than in the summer trials. Forty-five species of hyphomycetes were recorded during the study period, although 6 taxa (Alatospora acuminata, Anguillospora filiformis, Articulospora tetracladia, Geniculospora inflata, Lunulospora cymbiformis, and a sigmoid species, probably Flagellospora curvula) made up nearly 95% of all identified spores. A total of 35 species were found during the autumn trial, compared to 27 in each of the two summer trials, and 25 during a winter trial. Colonization dynamics also varied with season, but generally there were three main colonization patterns; some taxa were only present or showed highest abundance very early in the colonization period, most arrived or peaked during intermediate stages of leaf decay, and a few were characteristic of the latest stages.PT: J; CR: AKRIDGE RE, 1987, MYCOLOGIA, V79, P228 BARLOCHER F, 1974, J ECOL, V62, P761 BARLOCHER F, 1980, OECOLOGIA, V47, P303 BARLOCHER F, 1982, CAN J BOT, V60, P1487 BARLOCHER F, 1983, OIKOS, V41, P205 BARLOCHER F, 1992, ECOLOGY AQUATIC HYPH BARLOCHER F, 1992, ECOLOGY AQUATIC HYPH, P38 BARLOCHER F, 1995, ARCH HYDROBIOL, V133, P457 BERMINGHAM S, 1996, J APPL ECOL, V33, P1311 CHAMIER AC, 1984, OECOLOGIA, V64, P92 CUNJAK RA, 1990, 1751 DEP FISH OC CUNJAK RA, 1993, 1914 DEP FISH OC CUNJAK RA, 1995, CANADIAN SPECIAL PUB, V123, P191 ERMAN NA, 1995, J KANSAS ENTOMOL SOC, V68, P50 FABRE E, 1998, CAN J BOT, V76, P115 GARNETT H, 1998, THESIS MOUNT ALLISON GESSNER MO, 1993, MYCOL RES, V97, P163 GESSNER MO, 1994, ECOLOGY, V75, P1807 GONCZOL J, 1989, NOVA HEDWIGIA, V48, P391 INGOLD CT, 1975, SCI PUBLICATION, V30 IQBAL SH, 1973, T BRIT MYCOLOGICAL S, V61, P331 KAUSHIK NK, 1971, ARCH HYDROBIOL, V68, P465 MAHARNING AR, 1996, MYCOLOGIA, V88, P80 MALTBY L, 1991, WATER RES, V25, P247 MANLY BFJ, 1986, MULTIVARIATE STAT ME MARVANOVA L, 1985, BOT J LINN SOC, V91, P1 MARVANOVA L, 1997, ROPICAL MYCOLOGY, P170 NILSSON S, 1964, SYMBOLAE BOTANICAE U, V18, P1 RAVIRAJA NS, 1998, FRESHWATER BIOL, V39, P537 RAVIRAJA NS, 1998, FUNGAL DIVERS, V1, P179 RODRIGUES AP, 1997, SYDOWIA, V49, P160 RONG Q, 1995, HYDROBIOLOGIA, V316, P173 SANDERS PF, 1979, T BRIT MYCOLOGICAL S, V73, P103 SHEARER CA, 1983, MYCOLOGIA, V75, P498 SHEARER CA, 1985, T BRIT MYCOL SOC, V84, P489 SMITH B, 1996, OIKOS, V76, P70 SUBERKROPP K, 1984, T BRIT MYCOL SOC, V82, P53 SUBERKROPP K, 1992, FUNGAL COMMUNITY ITS, P729 SUBERKROPP K, 1992, J N AMER BENTHOL SOC, V11, P165 SUBERKROPP K, 1995, ECOLOGY, V76, P1433; NR: 40; TC: 11; J9: MYCOLOGIA; PG: 13; GA: 280XZSource type: Electronic(1
Transformation of the endostyle of the anadromous sea lamprey, Petromyzon-marinus L, during metamorphosis .2. Electron-microscopy
No full textPT: J; CR: BARRINGTON EJW, 1956, Q J MICROSC SCI, V97, P393 BARRINGTON EJW, 1975, INTRO GENERAL COMP E BEAMISH FWH, 1975, J ZOOL, V177, P57 BENCOSME SA, 1959, J BIOPHYS BIOCHEM CY, V5, P508 CHENG H, 1974, AM J ANAT, V141, P537 CLEMENTSMERLINI M, 1960, J MORPHOL, V106, P337 COLEMAN R, 1968, GEN COMP ENDOCR, V10, P34 CORDIER AC, 1976, AM J ANAT, V146, P339 DAEMS WT, 1969, LYSOSOMES, V1, P64 EGEBERG J, 1965, Z ZELLFORSCH MIKROSK, V68, P102 ETKIN W, 1968, METAMORPHOSIS PROBLE, P313 FINSTAD J, 1964, J EXP MED, V120, P1151 FOX H, 1970, J EMBRYOL EXP MORPH, V24, P139 FOX H, 1973, Z ZELLFORSCH, V130, P371 FUJITA H, 1966, Z ZELLFORSCH MIKROSK, V73, P559 FUJITA H, 1968, GEN COMP ENDOCR, V11, P111 FUJITA H, 1969, Z ZELLFORSCH, V98, P525 FUJITA H, 1972, ARCH HISTOL JAPON, V34, P109 FUJITA H, 1975, ARCH HISTOL JPN, V37, P277 FUJITA H, 1975, INT REV CYTOL, V40, P197 GOOD RA, 1972, BIOL LAMPREYS, V2, P405 GORBMAN A, 1962, TXB COMP ENDOCRINOLO HELMINEN HJ, 1971, J ULTRASTRUCT RES, V36, P708 HENDERSON NE, 1971, GEN COMP ENDOCR, V16, P409 HILFER SR, 1964, J MORPHOL, V115, P135 HILFER SR, 1977, J CELL BIOL, V75, P446 HOHEISEL G, 1969, GEGENBAURS MORPHOL J, V114, P204 HOHEISEL G, 1970, MORPHOL JB, V114, P337 HOURDRY J, 1969, Z ZELLFORSCH MIKR AN, V101, P527 JAMIESON JD, 1977, INT CELL BIOL, P308 KLINCK GH, 1970, LAB INVEST, V22, P2 KRAENVZEL F, 1933, ARCH BIOL LIEGE, V44, P469 KRUPP PP, 1977, ANAT REC, V187, P495 LANZING WJR, 1959, STUDIES RIVER LAMPRE LEACH JW, 1939, J MORPHOL, V65, P549 LUFT JH, 1961, J BIOPHYS BIOCH CYTO, V9, P409 MANASEK FJ, 1969, J EMBRYOL EXP MORPH, V21, P271 MARINE D, 1913, J EXP MED, V17, P379 MILLONIG G, 1961, J APPL PHYS, V32, P1637 MOLLENHAUER HH, 1964, STAIN TECHNOL, V39, P111 MORRIS GP, 1979, CELL TISSUE RES, V196, P449 NEUENSCHWANDER P, 1972, Z ZELLFORSCH MIKROSK, V130, P553 NEVE P, 1965, J MICROSC-PARIS, V4, P811 NICKERSON PA, 1970, J CELL BIOL, V47, P277 NOVIKOFF AB, 1976, CELLS ORGANELLES NUNEZ EA, 1967, J CELL BIOL, V2, P404 NUNEZ EA, 1976, ANAT REC, V184, P133 OLIN P, 1970, ENDOCRINOLOGY, V87, P1000 OLIVEREAU M, 1952, ARCH ANAT MICROSC EX, V41, P1 OOI EC, 1976, CAN J ZOOL, V54, P1449 OOI EC, 1979, AM J ANAT, V154, P57 PEEK WD, 1979, J MORPHOL, V160, P143 PIPAN N, 1976, CYTOBIOLOGIE, V13, P435 POLLARD B, 1966, PHYLOGENY IMMUNITY, P88 REMY L, 1977, J ULTRASTRUCT RES, V61, P243 REYNOLDS ES, 1963, J CELL BIOL, V17, P208 ROITT IM, 1971, ESSENTIAL IMMUNOLOGY, P211 ROMERT P, 1973, Z ANAT ENTWICKLUNGS, V139, P319 SELJELID R, 1967, J ULTRASTRUCT RES, V17, P195 SELJELID R, 1967, J ULTRASTRUCT RES, V17, P401 SETOGUTI T, 1973, Z ZELLFORSCH MIKROSK, V137, P195 SHEPARD TH, 1967, J CLIN ENDOCR METAB, V27, P945 SHIVELY JN, 1969, AM J VET RES, V30, P219 STERBA G, 1953, WISS Z F SCHILLER MN, V3, P1 STERBA G, 1953, WISS Z F SCHILLER MN, V3, P239 STERBA G, 1961, INT REV GES HYDROBIO, V46, P105 STERBA G, 1962, HDB BINNENFISCHEREI, V3, P263 THIELE J, 1976, CELL TISSUE RES, V168, P133 WATSON ML, 1958, J BIOPHYS BIOCHEM CY, V4, P475 WESSELLS NK, 1971, SCIENCE, V171, P135 WETZEL BK, 1969, ENDOCRINOLOGY, V84, P563 WISSIG SL, 1960, J BIOPHYS BIOCHEM CY, V7, P419 WOLLMAN SH, 1969, LYSOSOMES BIOLOGY PA, V2, P483 WRIGHT G, 1978, AM J ANAT, V152, P263 WRIGHT GM, 1976, GEN COMP ENDOCR, V30, P243 WRIGHT GM, 1977, J EXP ZOOL, V202, P27 WRIGHT GM, 1978, THESIS U TORONTO, P70 YOUSON JH, 1977, CAN J ZOOL, V55, P469 YOUSON JH, 1979, CAN J ZOOL, V57, P1808 YOUSON JH, 1980, CAN J FISH AQUAT SCI, V37; NR: 80; TC: 21; J9: J MORPHOL; PG: 27; GA: KT943Source type: Electronic(1
Measurement of the CP-violating phase \phi s in Bs->J/\psi\pi+\pi- decays
No full textMeasurement of the mixing-induced CP-violating phase phi_s in Bs decays is of prime importance in probing new physics. Here 7421 +/- 105 signal events from the dominantly CP-odd final state J/\psi pi+ pi- are selected in 1/fb of pp collision data collected at sqrt{s} = 7 TeV with the LHCb detector. A time-dependent fit to the data yields a value of phi_s=-0.019^{+0.173+0.004}_{-0.174-0.003} rad, consistent with the Standard Model expectation. No evidence of direct CP violation is found
Catalytic P-H activation by Ti and Zr catalysts
No full textCatalytic dehydrocoupling of phosphines was investigated using the anionic zirconocene trihydride salts [Cp*Zr-2(mu-H)(3)Li](3) (1a) or [Cp*Zr-2(mu-H)(3)K(thf)(4)] (1b), and the metallocycles [CpTi(NPtBu3)(CH2)(4)] (6) and [Cp*M(NPtBu3)(CH2)(4)] (M = Ti 20, Zr 21) as catalyst precursors. Dehydrocoupling of primary phosphines RPH2 (R = Ph, C6H2Me3, Cy, C10H7) gave both dehydrocoupled dimers RP(H)P(H)R or cyclic oligophosphines (RP)(n) (n = 4, 5) while reaction of tBu(3)C(6)H(2)PH(2) gave the phosphaindoline tBu(2)(Me2CCH2)C6H2PH (9). Stoichiometric reactions of these catalyst precursors with primary phosphines afforded [Cp*Zr-2((PR)(2))H][K(thf)(4)] (R = Ph 2, Cy 3, C6H2Me3 4), [Cp*Zr-2((PPh)(3))H] [K(thf)(4)] (5), [CpTi(NPtBu3)(PPh)(3)] (7) and [CpTi(NPtBu3)(mu-PHPh)](2) (8), while reaction of 6 with (C(6)H(2)tBu3)PH2 in the presence of PMe3 afforded [CpTi(NPtBu3)(PMe3)(p(C(6)H(2)tBu(3))] (10). The secondary phosphines Ph2PH and (PhHPCH2)(2)CH2 also undergo dehydrocoupling affording (Ph2P)(2) and (PhPCH2)(2)CH2. The bisphosphines (CH2PH2)(2) and C6H4(PH2)(2) are dehydrocoupled to give (PCH2CH2PH)(2) (12) and (C6H4P(PH))(2) (13) while prolonged reaction of 13 gave (C6H4P2)(8) (14). The analogous bisphosphine Me2C6H4(PH)(2) (17) was prepared and dehydrocoupling catalysis afforded (Me2C6H2P(PH))(2) (18) and subsequently [(Me2C6H2P2)(2)(mu-Me2C6H2P2)](2) (19). Stoichiometric reactions with these bisphosphines gave [Cp*Zr-2(H)(PH)(2)C6H4] [Li(thf)(4)] (22), [Cp*Ti(NPtBu3)(PH)(2)C6H4](2) (23) and [Cp*Ti(NPtBu3)(PH)(2)C6H4] (24). 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A metathesis model for the dehydrogenative coupling of amines with alcohols and esters into carboxamides by milsteins [Ru(PNN)(CO)(H)] catalysts
No full textMilsteins [Ru(PNN)(CO)(H)] catalyst (1-Ru) is known to mediate the dehydrogenative coupling of alcohols into esters. When it is used in alcohol-amine mixtures it catalyzes carboxamide formation selectively over esters and imines. The given chemistry is generally accepted to follow metal-ligand cooperation (MLC) mechanisms involving hemiacetals and hemiaminals as intermediates. Using electronic structure DFT methods we investigate alternative, more direct OR-H and NHR-H metal-acyl metathesis routes to coupling that circumvent the intermediacy of the hemiacetal and the hemiaminal. The newly proposed mechanism involves formation of hemiacetaloxide and hemiaminaloxide ion-pairs by addition of an aldehyde (from metal-catalyzed alcohol dehydrogenation) to an octahedral ruthenium-alkoxide or ruthenium-amide intermediate (from alcohol or amine addition to 1-Ru), followed by simple rearrangement (slippage) within the intact ion-pairs to transfer a hydride from the hemiacetaloxide or hemiaminaloxide to the metal. We show that the computed potential energy surfaces that are sometimes invoked to support the MLC mechanism correspond to indirect routes to metathesis. Both the ion-pair and the MLC routes predict the dehydrogenative coupling of ethanol and methanol into methyl acetate to be kinetically much more favored than the kinetics of formation of N-methylacetamide from ethanol and methylamine. However, the calculations provide evidence for the accessibility of a low energy NHR-OR metathesis path that would amidate the ester into the experimentally observed thermodynamically more favored carboxamide product. 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