746 research outputs found

    Dialing in single-site reactivity of a supported calixarene-protected tetrairidium cluster catalyst.

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    A closed Ir4 carbonyl cluster, 1, comprising a tetrahedral metal frame and three sterically bulky tert-butyl-calix[4]arene(OPr)3(OCH2PPh2) (Ph = phenyl; Pr = propyl) ligands at the basal plane, was characterized with variable-temperature 13C NMR spectroscopy, which show the absence of scrambling of the CO ligands at temperatures up to 313 K. This demonstration of distinct sites for the CO ligands was found to extend to the reactivity and catalytic properties, as shown by selective decarbonylation in a reaction with trimethylamine N-oxide (TMAO) as an oxidant, which, reacting in the presence of ethylene, leads to the selective bonding of an ethyl ligand at the apical Ir site. These clusters were supported intact on porous silica and found to catalyze ethylene hydrogenation, and a comparison of the kinetics of the single-hydrogenation reaction and steady-state hydrogenation catalysis demonstrates a unique single-site catalyst-with each site having the same catalytic activity. Reaction orders in the catalytic ethylene hydrogenation reaction of approximately 1/2 and 0 for H2 and C2H4, respectively, nearly match those for conventional noble-metal catalysts. In contrast to oxidative decarbonylation, thermal desorption of CO from silica-supported cluster 1 occurred exclusively at the basal plane, giving rise to sites that do not react with ethylene and are catalytically inactive for ethylene hydrogenation. The evidence of distinctive sites on the cluster catalyst leads to a model that links to hydrogen-transfer catalysis on metals-involving some surface sites that bond to both hydrocarbon and hydrogen and are catalytically engaged (so-called "*" sites) and others, at the basal plane, which bond hydrogen and CO but not hydrocarbon and are reservoir sites (so-called "S" sites)

    The physiological ecology of the specialist lagoon amphipod, Gammarus insensibilis

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    Coastal lagoons are habitats of conservation importance. The characteristic fauna of lagoons includes a number of specialist species, some of which are scheduled for protection. Work on the conservation of coastal lagoons has suggested that detailed information on the ecology of lagoon specialist species is essential to ensure management strategies are relevant to the lagoonal species. This study addresses this issue by providing information about the monthly reproductive investment and energy-balance as well as interactions with parasites for the specialist lagoon amphipod, Gammarus insensibilis (Stock). For comparison information is also presented on the reproductive investment of the lagoonal isopod Idotea chelipes (Pallas). Gilkicker lagoon on the south coast of England, UK, from which the majority of samples were taken, demonstrated environmental variability characteristic of coastal lagoons. Annually, temperature varied between 2 and 28 °C and salinity fluctuated between extremes of 24 and 39. The Lymington-Keyhaven lagoons, also on the south coast of England, demonstrated similar variation. This has implications for Gammarus insensibilis, and effects on reproductive investment were evident. The amphipod was shown to employ a continuous reproductive strategy but while the overall investment, expressed as clutch volume, remained relatively stable over the course of the year, the individual components varied. In the summer, when weight-specific embryo number was at its highest with a mean of 13 embryos mg dry wt.-1 the mean size of the individual embryos was small (0.032 mm3). The opposite was true in the winter months, with mean brood sizes as low as 6 embryos mg dry wt.-1 while mean embryo volume was larger, at 0.04 mm3. Idotea chelipes demonstrated a more seasonal reproductive strategy in which winter reproductive output was low. The environmental variability also had effects on the metabolic rates of individual amphipods with temperature related increases in feeding and respiration rates in the summer months. Scope For Growth (SFG), a measure of net energy availability to the organism, was variable during the year and was unrelated to temperature and salinity. Lowest SFG occurred in spring in conjunction with peak reproductive output. This suggested that the amphipods were well adapted to the environmental variation of the lagoon and that it was reproductive investment that represented an important cost to the organism. Eighty four percent of G. insensibilis from Gilkicker were shown to be infected by microphallid trematode parasites. Reproductive investment was negatively affected, with a 36.6 % reduction in weight-specific brood size associated with higher degrees of infection. Respiration rates were also reduced in the infected organisms. The high prevalence of the parasites and the related effects on the host suggest that trematode infection should be considered, alongside the characteristic habitat variability, as an important aspect of the ecology of lagoons

    Partition of Land and Mineral Rights

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    Flat fiber: the flexible format for distributed lab-on-a-chip

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    Integrated optical devices offer dense, multifunctional capability in a single robust package but are rarely considered compatible with the fields of remote or distributed sensing or long-haul 'one-dimensional' fibers. Here we aim to change that by introducing a 'flat-fiber' process that combines the advantages of existing low-cost fiber drawing with the functionality of planar lightwave circuits in a novel hybrid format. By taking this approach, we hope to extend beyond the limitations of traditional planar and fiber substrates - allowing exotic material compositions, device layouts, and local sensing functions to be distributed over extended distances with no coupling or compatibility concerns in highly functional distributed lab-on-a-chip devices

    Deep-water observation of scalloped hammerhead Sphyrna lewini in the western Indian Ocean off Tanzania

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    A scalloped hammerhead Sphyrna lewini was observed opportunistically from a remotely operated vehicle 1 m off the seabed at 1042 m depth, during hydrocarbon exploration activities in the Ruvuma Basin off Tanzania. The observation, which occurred during night hours, is the deepest accurately recorded for this species and the first deep-water record for the Indian Ocean. The record adds support for the occurrence in deep water during night hours being a widespread and possibly common behaviour in this species, and further expands a small but growing literature that meso- and bathypelagic environments may be of greater importance to elasmobranchs previously considered to be primarily epipelagic

    Copper maturation of nitrous oxide reductase in Paracoccus denitrificans

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    Nitrous oxide (N2O) is an important greenhouse gas that is also responsible for stratospheric ozone depletion [1, 2]. Human activity is the main source of N2O due to the use of fertilisers in agriculture. Nitrous oxide reductase (N2OR) is the only enzyme to destroy N2O as part of a biological process termed denitrification. This enzyme has a unique catalytic CuZ centre, an electron transfer CuA centre and a high demand for Cu with 12 atoms required per functional dimer. A previous transcriptomic study revealed that two putative Cu chaperones, ScoB and PCuC were upregulated under Cu limiting conditions [3]. Here we demonstrate that ScoB/PCuC is a high-affinity Cu system essential for N2O respiration. Deletion of scoB causes N2O accumulation under anoxic and Cu-limited growth. N2O respiration could be restored complementation in trans with recombinant full-length, or soluble, periplasmic ScoB proteins (ScoBFL and ScoBsol, respectively). ScoBsol was biochemically characterised and found to be a monomeric protein of _25 kDa that can bind Cu1+ or Cu2+ with an apparent KD value within the subfemtomolar range. In contrast, PCuC is a multidomain protein with a Ycn-like N-terminal domain [4], and a PCuAC-like C-terminal domain [5]. Recombinant periplasmic proteins for each individual domain and full-length protein were generated (i.e., PCuCNt, PCuCCt and PCuCFL). The pcuC deletion strain has an N2O-genic phenotype. Only complementation in trans with PCuCFL restored N2O reduction under anaerobic and Cu-limited conditions. In addition, the crystallographic structure of Cu-bound PCuCNt was solved to a resolution of 1.5 Ă… revealing a trimeric protein of _56 kDa with a novel histidine brace metal binding site. PCuCNt can bind 1+ or 2+ and competition assays with 1+ chelators revealed that metallation occurs with femtomolar affinity. Analysis of YcnI-type proteins revealed the presence of two defined families. Family A contains a HX22HX101W consensus Cu-binding motif and was principally found among alphaproteobacteria, while Family B contain a HX22DX90WX13H motif and are distributed in actinobacteria and firmicutes. The Cu-bound structure of PCuCCt was also solved to a resolution of 1.6 Ă… and reveals a _18 kDa monomer that contains a defined H(M)X10MX21HXM Cu-binding site that can bind Cu1+ with subfemtomolar affinity. Further biochemical studies of native PCuC confirmed that the full-length protein forms a _100 kDa homotrimer in solution regardless of metallation state, with the N-terminal domain driving oligomerization exposing individual C-terminal domains to bulk solution through a flexible linker region. Each trimer can bind up to 6 Cu atoms with binding affinities within the subfemtomolar range. Finally, the maturation of the Cu centres of N2OR was studied in P. denitrificans WT, scoB and pcuC deletion strains. A periplasmic and readily isolatable affinity-tagged N2OR protein was expressed in cis under two different Cu regimes in P. denitrificans. N2OR purified from WT cells grown under anaerobic and Cu-limited conditions only contained a recognisable CuA centre. However, N2OR from scoB and pcuC mutants lacked both Cu-centres, had significantly lower Cu content and impaired enzymatic activity. A model for the metallation process of the CuA centre of N2OR by the high affinity Cu-maturation system ScoB/PCuC has been proposed

    Deep-sea life of Tanzania

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    A haloarchaeal ferredoxin electron donor that plays an essential role in nitrate assimilation

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    In the absence of ammonium, many organisms, including the halophilic archaeon Haloferax volcanii DS2 (DM3757), may assimilate inorganic nitrogen from nitrate or nitrite, using a ferredoxin-dependent assimilatory NO3-/NO2- reductase pathway. The small acidic ferredoxin Hv-Fd plays an essential role in the electron transfer cascade required for assimilatory nitrate and nitrite reduction by the cytoplasmic NarB- and NirA-type reductases respectively. UV–visible absorbance and EPR spectroscopic characterization of purified Hv-Fd demonstrate that this protein binds a single [2Fe–2S] cluster, and potentiometric titration reveals that the cluster shares similar redox properties with those present in plant-type ferredoxins
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