780 research outputs found
Importance of Steric Influences in the Construction of Multicomponent Hybrid Polymetallic Clusters
The straightforward
room temperature synthesis of hybrid polymetallic manganese clusters
is investigated, exploiting complementary ligand combinations of <i>p</i>-<i>tert</i>-butylcalix[4]arene and salicylaldoximes.
Eight new [Mn<sup>III</sup><sub>7</sub>Mn<sup>II</sup>] clusters have
been prepared wherein the simple substitution of alkyl or aryl groups
at well-defined positions of the salicylaldoxime scaffold leads to
two distinct structure types that, while exhibiting the same general
topology, contain the unique Mn<sup>II</sup> ion in different positions.
Incorporation of a methyl, ethyl, or isopropyl group at the 3-position
of the aromatic skeleton or a phenyl group at the oximic carbon gives
structure type A that displays competing weak ferromagnetic and antiferromagnetic
interactions. Substitution of a methyl or ethyl group at the oximic
carbon atom invokes structure type B, incorporating an additional
bulky chloride or nitrate into the metallic core due to the smaller
steric imposition and position of the methyl or ethyl group. The distortion
of the cluster core is consequently enhanced, switching the magnetic
properties and resulting in single-molecule magnet behavior. The presence
of <i>tert</i>-butyl groups at the 3- and 5-positions of
the salicylaldoxime skeleton leads to a new [Mn<sup>IV</sup><sub>2</sub>Mn<sup>III</sup><sub>2</sub>] cluster that is found to be a single-molecule
magnet. The bulky <i>tert</i>-butyl group in the 3-position
is too large to facilitate Mn<sub>8</sub> cluster formation, and thus
assembly occurs by an alternative pathway. Characteristic bonding
modes of the constituent ligands are retained in every case, and the
results presented here give insight into the potential of ligand combinations
in future studies, highlighting the importance of steric factors in
evaluating their relevant compatibilities
Cell size influences inorganic carbon acquisition in artificially selected phytoplankton
Cell size influences the rate at which phytoplankton assimilate dissolved inorganic carbon (DIC), but it is unclear whether volume-specific carbon uptake should be greater in smaller or larger cells. On the one hand, Fick's Law predicts smaller cells to have a superior diffusive CO2 supply. On the other, larger cells may have greater scope to invest metabolic energy to upregulate active transport per unit area through CO2 -concentrating mechanisms (CCMs). Previous studies have focused on among-species comparisons, which complicates disentangling the role of cell size from other covarying traits. In this study, we investigated the DIC assimilation of the green alga Dunaliella tertiolecta after using artificial selection to evolve a 9.3-fold difference in cell volume. We compared CO2 affinity, external carbonic anhydrase (CAext ), isotopic signatures (δ13 C) and growth among size-selected lineages. Evolving cells to larger sizes led to an upregulation of CCMs that improved the DIC uptake of this species, with higher CO2 affinity, higher CAext and higher δ13 C. Larger cells also achieved faster growth and higher maximum biovolume densities. We showed that evolutionary shifts in cell size can alter the efficiency of DIC uptake systems to influence the fitness of a phytoplankton species
Increasing the dimensionality of cryogenic molecular coolers: Gd-based polymers and metal-organic frameworks
Trabajo presentado a la 5th International Conference on Molecular Materials (MolMat) celebrada en Barcelona (España) del 3 al 6 de julio de 2012.The magnetothermal properties of a coordination polymer and a metal-organic framework (MOF) based on Gd 3+ ions are reported. An equally large cryogenic magnetocaloric effect (MCE) is found, irrespective of the dimensionality. This combined with their robustness makes them appealing for widespread magnetic refrigeration applications. © 2012 The Royal Society of Chemistry.We are grateful to MINECO (contracts MAT2009-13977-C03, MAT2011-24284 and CSD2007-00010), EC (for a Marie Curie-IEF to GL), University of Granada (for a postdoctoral fellowship to MAP), and EPRSC for funding.Peer Reviewe
The true identity of the new world iguanid lizard liolaemus chillanensis Müller and Hellmich 1932 (Iguania: Liolaemidae) and description of a new species in the liolaemus elongatus group
Liolaemus is a particularly species-rich radiation of New World iguanid lizards from southern South America. Thanks to intense systematic and taxonomic research, the knowledge on its species-level diversity has increased rapidly over the past several years. The L. elongatus species-complex has received considerable attention and a remarkable case is Liolaemus chillanensis, a name that has been used for two different species that are sympatric in Termas de Chillán, central Chile. Since the holotype is lost, we propose that the first step to identify the true L. chillanensis is through the analysis of the original description. Then we provide a morphological and molecular characterization of L. chillanensis based on topotypes and a description of the taxon previously confused with it.Fil: Troncoso Palacios, Jaime. Universidad de Chile; ChileFil: Esquerré, Damien. The Australian National University; AustraliaFil: Urra, Félix A.. Universidad de Chile; ChileFil: Díaz, Hugo A.. Universidad de Chile; ChileFil: Castro Pastene, Carlos. Universidad de Concepción; ChileFil: Ruiz, Maria Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentin
EGF-R signaling through Fyn kinase disrupts the function of integrin α6β4 at hemidesmosomes: role in epithelial cell migration and carcinoma invasion
We have examined the mechanism and functional significance of hemidesmosome disassembly during normal epithelial cell migration and squamous carcinoma invasion. Our findings indicate that a fraction of EGF receptor (EGF-R) combines with the hemidesmosomal integrin α6β4 in both normal and neoplastic keratinocytes. Activation of the EGF-R causes tyrosine phosphorylation of the β4 cytoplasmic domain and disruption of hemidesmosomes. The Src family kinase inhibitors PP1 and PP2 prevent tyrosine phosphorylation of β4 and disassembly of hemidesmosomes without interfering with the activation of EGF-R. Coimmunoprecipitation experiments indicate that Fyn and, to a lesser extent, Yes combine with α6β4. By contrast, Src and Lck do not associate with α6β4 to a significant extent. A dominant negative form of Fyn, but not Src, prevents tyrosine phosphorylation of β4 and disassembly of hemidesmosomes. These observations suggest that the EGF-R causes disassembly of hemidesmosomes by activating Fyn, which in turn phosphorylates the β4 cytoplasmic domain. Neoplastic cells expressing dominant negative Fyn display increased hemidesmosomes and migrate poorly in vitro in response to EGF. Furthermore, dominant negative Fyn decreases the ability of squamous carcinoma cells to invade through Matrigel in vitro and to form lung metastases following intravenous injection in nude mice. These results suggest that disruption of hemidesmosomes mediated by Fyn is a prerequisite for normal keratinocyte migration and squamous carcinoma invasion
Kondo resonance effect on persistent currents through a quantum dot in a mesoscopic ring
The persistent current through a quantum dot inserted in a mesoscopic ring of
length L is studied. A cluster representing the dot and its vicinity is exactly
diagonalized and embedded into the rest of the ring. The Kondo resonance
provides a new channel for the current to flow. It is shown that due to scaling
properties, the persistent current at the Kondo regime is enhanced relative to
the current flowing either when the dot is at resonance or along a perfect ring
of same length. In the Kondo regime the current scales as , unlike
the scaling of a perfect ring. We discuss the possibility of detection
of the Kondo effect by means of a persistent current measurement.Comment: 11 pages, 3 Postscript figure
Ecosystem-bedrock interaction changes nutrient compartmentalization during early oxidative weathering
Ecosystem-bedrock interactions power the biogeochemical cycles of Earth's
shallow crust, supporting life, stimulating substrate transformation, and
spurring evolutionary innovation. While oxidative processes have dominated half
of terrestrial history, the relative contribution of the biosphere and its
chemical fingerprints on Earth's developing regolith are still poorly
constrained. Here, we report results from a two-year incipient weathering
experiment. We found that the mass release and compartmentalization of major
elements during weathering of granite, rhyolite, schist and basalt was
rock-specific and regulated by ecosystem components.
A tight interplay between physiological needs of different biota, mineral
dissolution rates, and substrate nutrient availability resulted in intricate
elemental distribution patterns. Biota accelerated CO2 mineralization over
abiotic controls as ecosystem complexity increased, and significantly modified
stoichiometry of mobilized elements. Microbial and fungal components inhibited
element leaching (23.4% and 7%), while plants increased leaching and biomass
retention by 63.4%. All biota left comparable biosignatures in the dissolved
weathering products. Nevertheless, the magnitude and allocation of weathered
fractions under abiotic and biotic treatments provide quantitative evidence for
the role of major biosphere components in the evolution of upper continental
crust, presenting critical information for large-scale biogeochemical models
and for the search for stable in situ biosignatures beyond Earth.Comment: 41 pages (MS, SI and Data), 16 figures (MS and SI), 6 tables (SI and
Data). Journal article manuscrip
Synthetic ability of dinuclear mesocates containing 1,3-bis(diazinecarboxamide)benzene bridging ligands to form complexes of increased nuclearity. Crystal structures, magnetic properties and theoretical studies
International audienceTriple stranded NiII2-metallacyclic complexes Na2.5[Ni2(bpcb)3]·0.5OH·18.5H2O (1) and Na2[Ni2(bpzcb)3]·16H2O (2), and double stranded CuII2-metallacyclic complexes [Cu2(bpcb)2(H2O)2]·8H2O (3) and [Cu2(bpzcb)2(H2O)2]·4H2O (4) have been assembled from the tailored bisbidentate bridging ligands, 1,3-bis(pyrimidine-2-carboxamide)benzene (H2bpcb) and 1,3-bis(pyrazine-2-carboxamide)benzene (H2bpzcb), and the corresponding nitrate salts of the metal ions. Following the “complex as ligand” strategy, 1 can be assembled with either Ni2+, Co2+ ions or the [Mn(acen)Cl] complex to afford unique, neutral, bent trinuclear molecules [MIINiII2(bpcb)3]·xH2O (5 and 6) and the 2D honeycomb-like complex (PPh4){[Ni2(bpcb)3]2[Mn(acen)]3} (7), respectively. In these cases, the Ni2 units are linked to the corresponding metal ions through amidate oxygen atoms and the outward nitrogen atom of one of the pyrimidine rings of the bcpb ligand. The assembly of 2 with Ln3+ ions (Ln3+ = Tb, Gd) leads to one dimensional complexes of formula [{[Ni2(bpzcb)3]Tb(H2O)5}(CF3SO3)·THF·5H2O]n (8) and [{[Ni2(bpzcb)3]Ln(H2O)4(NO3)}·2THF·nH2O]n (9 and 10) (Ln3+ = Gd and Tb), where the dinuclear Ni2 units are joined to two Ln3+ ions exclusively through amidate oxygen atoms of two different ligands. The analyses of the magnetic data indicate that 1–4 exhibit intradinuclear ferromagnetic interactions between the metal ions through a spin polarisation mechanism, as supported by DFT calculations. Trinuclear complexes 5 and 6 show predominant antiferromagnetic coupling, which is a result of an antiferromagnetic interaction between one of the Ni2+ ions of the Ni2 unit and the M2+ ion through the pyrimidine bridging fragment that is stronger than the polarised ferromagnetic interaction between the Ni2+ ions through the bpcb ligand in the dinuclear [Ni2(bpcb)3]2− moiety. Complex 7 shows a dominant antiferromagnetic interaction between the Ni2+ and Mn2+, whereas the Ni2Ln (Ln3+ = Gd, Tb) chain complexes present ferromagnetic interactions inside the Ni2 mesocate unit as well as between the Ni2+ ions of the Ni2 unit and the Ln3+ ions. The magnetic exchange interactions in these new materials have been experimentally analysed and supported by theoretical DFT studies
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