Long-distance magnetic coupling in dinuclear copper(II) complexes with oligo-para-phenylenediamine bridging ligands

Two novel dinuclear copper(II) complexes of formulae [Cu₂(tren)₂(bpda)](ClO₄)₄ (2) and [Cu₂(tren)₂(tpda)](ClO₄)₄ (3) containing the tripodal tris(2-aminoethyl)amine (tren) terminal ligand and the 4,4′-biphenylenediamine (bpda) and 4,4″-p-terphenylenediamine (tpda) bridging ligands have been synthesized and structurally, spectroscopically, and magnetically characterized. Their experimentally available electronic spectroscopic and magnetic properties have been reasonably reproduced by DFT and TDDFT calculations. Single crystal X-ray diffraction analysis of 2 shows the presence of dicopper(II) cations where the bpda bridging ligand adopts a bismonodentate coordination mode toward two [Cu(tren)]²⁺ units with an overall non-planar, orthogonal anti configuration of the N-Cu-N threefold axis of the trigonal bipyramidal Cu^II ions and the biphenylene group. The electronic absorption spectra of 2 and 3 in acetonitrile reveal the presence of four moderately weak d-d transitions characteristic of a slightly distorted trigonal bipyramid stereochemistry of the Cu^II ions. TDDFT calculations on 2 identify these transitions as those taking place between the four lower-lying, doubly occupied a₂ (d_yz)², b₂ (d_xz)², b₁ (d_xy)², and a₁ (d_x²-y²)² orbitals and the upper, singly occupied a₁ (d_z²)¹ orbital of each trigonal bipyramidal Cu^II ion. Variable-temperature magnetic susceptibility measurements of 2 and 3 show the occurrence of moderate (J = −8.5 cm⁻¹) to weak intramolecular antiferromagnetic couplings (J = −2.0 cm^-1) [H = −JS₁·S₂ with S₁ = S₂ = S_Cu = ½] inspite of the relatively large copper-copper separation across the para-substituted biphenylene- (r = 12.3 Å) and terphenylenediamine (r = 16.4 Å) bridges, respectively. DFT calculations on 2 and 3 support the occurrence of a spin polarization mechanism for the propagation of the exchange interaction between the two unpaired electrons occupying the d_z² orbital of each trigonal bipyramidal Cu^II ion through the predominantly π-type orbital pathway of the oligo-p-phenylenediamine bridges, as reported earlier for the parent compound [Cu₂(tren)₂(ppda)](ClO₄)₄·2H₂O (1) with the 1,4-phenylenediamine (ppda) bridging ligand. Finally, a rather slow exponential decay of the antiferromagnetic coupling (-J) with the number of phenylene repeat units, -(C₆H₄)_n- (n = 1-3), has been found both experimentally and theoretically along this series of oligo-p-phenylenediamine-bridged dicopper(II) complexes. These results further support the ability of linear π-conjugated oligo-p-phenylene spacers to transmit the exchange interaction between the unpaired electrons of the two Cu^II centers with intermetallic distances in the range of 7.5-16.4 Å.     

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry analysis of oligosaccharides and oligosaccharide alditols obtained by hydrolysis of agaroses and carrageenans, two important types of red seaweed polysaccharides

MALDI-TOF mass spectrometry analyses of several oligosaccharides (aldoses) and oligosaccharide alditols derived from agaroses, kappa- and iota-carrageenans using different matrices (2,5-dihydroxybenzoic acid, nor-harmane, ferulic acid, and the ionic liquid matrices 2,5-dihydroxybenzoic acid-n-butylamine and ferulic acid-n-butylamine) were conducted. These carbohydrates were selected as model compounds to study the MALDI prompt and post-source decay (PSD) fragmentation processes of both families of oligosaccharides. Sulfated alditols showed in the negative-ion mode the molecular ion as [M−Na]⁻ together with the species yielded by their prompt fragmentation (mainly desulfation) while the sulfated oligosaccharides (aldoses) showed mainly glycosidic prompt fragmentation (glycosidic C-cleavages and desulfation). Non-sulfated aldoses and alditols, which could only be analyzed in positive-ion mode ([M+Na]⁺), did not suffer any prompt fragmentation. The former yielded cross-ring fragmentation in the PSD mode. Best results were obtained by using 2,5-dihydroxybenzoic acid and/or nor-harmane as matrices for all the compounds studied.     

WHEN DO ADAPTIVE PLASTICITY AND GENETIC EVOLUTION PREVENT EXTINCTION OF A DENSITY‐REGULATED POPULATION?

We study the dynamics of evolutionary recovery after an abrupt environmental shift in a density‐regulated population with evolving plasticity. Maladaptation to the new environment initially causes the population to decline, until adaptive phenotypic plasticity and genetic evolution restore positive population growth rate. We assume that selection on a quantitative trait is density‐independent and that the initial cost of plasticity is much lower than the benefit of the initial plastic response. The initial partially adaptive plasticity reduces the effective magnitude of the environmental shift, whereas evolution of plasticity increases the rate of adaptation. Both effects greatly facilitate population persistence. In contrast, density dependence of population growth always hinders persistence. With θ‐logistic population regulation, a lower value of θ produces a faster initial population decline and a higher extinction risk.     

BcsKC Is an Essential Protein for the Type VI Secretion System Activity in Burkholderia cenocepacia That Forms an Outer Membrane Complex with BcsLB

The type VI secretion system (T6SS) contributes to the virulence of Burkholderia cenocepacia, an opportunistic pathogen causing serious chronic infections in patients with cystic fibrosis. BcsK_C is a highly conserved protein among the T6SSs in Gram-negative bacteria. Here, we show that BcsK_C is required for Hcp secretion and cytoskeletal redistribution in macrophages upon bacterial infection. These two phenotypes are associated with a functional T6SS in B. cenocepacia. Experiments employing a bacterial two-hybrid system and pulldown assays demonstrated that BcsK_C interacts with BcsL_B, another conserved T6SS component. Internal deletions within BcsK_C revealed that its N-terminal domain is necessary and sufficient for interaction with BcsL_B. Fractionation experiments showed that BcsK_C can be in the cytosol or tightly associated with the outer membrane and that BcsK_C and BcsL_B form a high molecular weight complex anchored to the outer membrane that requires BcsF_H (a ClpV homolog) to be assembled. Together, our data show that BcsK_C/BcsL_B interaction is essential for the T6SS activity in B. cenocepacia.     

The internet as a research tool in the study of associative learning: an example from overshadowing

The present study aimed to replicate an associative learning effect, overshadowing, both in the traditional laboratory conditions and over the internet. The experimental task required participants to predict an outcome based on the presence of several cues. When a cue that was always trained together with a second cue was presented on isolation at test, the expectancy of the outcome was impaired, which revealed overshadowing. This experimental task was performed by undergraduate students (N=106) in the laboratory and by a different set of anonymous participants over the internet (N=91). Similar levels of overshadowing were obtained in both locations. These similarities show that web-delivered experiments can be used as a complement of traditional experiments.     

Role of the septin Cdc10 in the virulence of Candida albicans

The relationship between the morphology and virulence of Candida albicans has aroused interest in the study of the proteins involved in its morphogenesis. We present virulence data for one important element in fungal morphogenesis-septins. We disrupted CaCDC10 and studied the virulence in a mouse infection model and the different steps followed by the fungus during the infection: adherence to epithelial cells, organ colonisation, macrophage phagocytosis, and host survival. We found the altered subcellular localisation of Int1--a C. albicans adhesin- in the septin null mutants. The Int1 mislocalisation and the defects in the cell wall of defective CaCdc10 strains permit us to propose a model for explaining the biological meaning of the absence of virulence presented by these septin mutants.     

Sinorhizobium fredii HH103 mutants affected in capsular polysaccharide (KPS) are impaired for nodulation with soybean and Cajanus cajan

The Sinorhizobium fredii HH103 rkp-1 region, which is involved in capsular polysaccharides (KPS) production, was isolated and sequenced. The organization of the S. fredii genes identified, rkpUAGHIJ and kpsF3, was identical to that described for S. meliloti 1021 but different from that of S. meliloti AK631. The long rkpA gene (7.5 kb) of S. fredii HH103 and S. meliloti 1021 appears as a fusion of six clustered AK631 genes, rkpABCDEF. S. fredii HH103-Rif(r) mutants affected in rkpH or rkpG were constructed. An exoA mutant unable to produce exopolysaccharide (EPS) and a double mutant exoA rkpH also were obtained. Glycine max (soybean) and Cajanus cajan (pigeon pea) plants inoculated with the rkpH, rkpG, and rkpH exoA derivatives of S. fredii HH103 showed reduced nodulation and severe symptoms of nitrogen starvation. The symbiotic capacity of the exoA mutant was not significantly altered. All these results indicate that KPS, but not EPS, is of crucial importance for the symbiotic capacity of S. fredii HH103-Rif(r). S. meliloti strains that produce only EPS or KPS are still effective with alfalfa. In S. fredii HH103, however, EPS and KPS are not equivalent, because mutants in rkp genes are symbiotically impaired regardless of whether or not EPS is produced.     

Neural ensemble coding of satiety states

The motivation to start or terminate a meal involves the continual updating of information on current body status by central gustatory and reward systems. Previous electrophysiological and neuroimaging investigations revealed region-specific decreases in activity as the subject's state transitions from hunger to satiety. By implanting bundles of microelectrodes in the lateral hypothalamus, orbitofrontal cortex, insular cortex, and amygdala of hungry rats that voluntarily eat to satiety, we have measured the behavior of neuronal populations through the different phases of a complete feeding cycle (hunger-satiety-hunger). Our data show that while most satiety-sensitive units preferentially responded to a unique hunger phase within a cycle, neuronal populations integrated single-unit information in order to reflect the animal's motivational state across the entire cycle, with higher activity levels during the hunger phases. This distributed population code might constitute a neural mechanism underlying meal initiation under different metabolic states.     

Antioxidant responses of cortex neurons to iron loading

Brain cells have a highly active oxidative metabolism, yet they contain only low to moderate superoxide dismutase and catalase activities. Thus, their antioxidant defenses rely mainly on cellular reduced glutathione levels. In this work, in cortical neurons we characterized viability and changes in reduced and oxidized glutathione levels in response to a protocol of iron accumulation. We found that massive death occurred after 2 days in culture with 10 microM Fe. Surviving cells developed an adaptative response that included increased synthesis of GSH and the maintenance of a glutathione-based reduction potential. These results highlight the fundamental role of glutathione homeostasis in the antioxidant response and provide novel insights into the adaptative mechanisms of neurons subjected to progressive iron loads.