Thermodynamic, Spectroscopic, and Structural Studies of Complexation of Phenol- and Pyridine-Armed Macrocyclic Ligands with Univalent Metal Ions

Log K, ΔH, and ΔS values for interactions of a series of pyridinoazacrown ethers each bearing a phenol arm (2−6) and two macrocycles each bearing a pyridine arm (7, 8) with Na^+, K^+, Tl^+, and Ag^+ have been determined in absolute methanol at 25 °C by calorimetric titration. In each case, the complex stability has the sequence Na^+ < K^+ < Tl^+ ≪ Ag^+. The phenol-armed macrocycles exhibit selectivity of more than 4 orders of magnitude for Ag^+ over Na^+, K^+, and Tl^+. Attachment of a pendant phenol arm having various substituents to parent macrocycle 1 increases the binding abilities of the resulting ligands. Substituents on the para position of the phenol arm have an appreciable effect on cation-binding constants. Good Hammett correlations are found by plotting log K values vs σ_p for interactions of five phenol-armed macrocyclic ligands (2−6) with Na^+, K^+, and Tl^+. The complexation has been characterized by means of ^1H NMR and UV−visible spectroscopic, and X-ray crystallographic methods. The crystal data for Na^+−3:  formula, [Na(C_(23)H_(28.5)N_3O_5)](ClO_4)_(0.5); space group, P^1̄; a = 9.400(9) Å, b = 11.467(10) Å, c = 12.281(11) Å, α = 77.22(7)°, β = 87.73(7)°, γ = 86.39(7)°, V = 1288(2) Å^3, and Z = 2. The study indicates that the phenol OH group of 2−6 is capable of forming an intramolecular hydrogen bond with the macroring nitrogen atom and that the complexation in absolute methanol generally does not deprotonate these phenols. In the crystal structure of the Na^+−3 complex, the Na^+ is coordinated to all seven of the donor atoms of the ligand and two Na^+−3 complexes join together to form a dimer. The dimer contains an intermolecular hydrogen bond formed between the phenol hydrogen atom of one ligand and the phenolate group of a centrosymmetrically related ligand and two π−π stacking interactions between the electron-deficient pyridine ring of one molecule and the electron-rich phenol ring of the other

Thermodynamic, Spectroscopic, and Structural Studies of Complexation of Phenol- and Pyridine-Armed Macrocyclic Ligands with Univalent Metal Ions

Log K, ΔH, and ΔS values for interactions of a series of pyridinoazacrown ethers each bearing a phenol arm (2−6) and two macrocycles each bearing a pyridine arm (7, 8) with Na^+, K^+, Tl^+, and Ag^+ have been determined in absolute methanol at 25 °C by calorimetric titration. In each case, the complex stability has the sequence Na^+ < K^+ < Tl^+ ≪ Ag^+. The phenol-armed macrocycles exhibit selectivity of more than 4 orders of magnitude for Ag^+ over Na^+, K^+, and Tl^+. Attachment of a pendant phenol arm having various substituents to parent macrocycle 1 increases the binding abilities of the resulting ligands. Substituents on the para position of the phenol arm have an appreciable effect on cation-binding constants. Good Hammett correlations are found by plotting log K values vs σ_p for interactions of five phenol-armed macrocyclic ligands (2−6) with Na^+, K^+, and Tl^+. The complexation has been characterized by means of ^1H NMR and UV−visible spectroscopic, and X-ray crystallographic methods. The crystal data for Na^+−3:  formula, [Na(C_(23)H_(28.5)N_3O_5)](ClO_4)_(0.5); space group, P^1̄; a = 9.400(9) Å, b = 11.467(10) Å, c = 12.281(11) Å, α = 77.22(7)°, β = 87.73(7)°, γ = 86.39(7)°, V = 1288(2) Å^3, and Z = 2. The study indicates that the phenol OH group of 2−6 is capable of forming an intramolecular hydrogen bond with the macroring nitrogen atom and that the complexation in absolute methanol generally does not deprotonate these phenols. In the crystal structure of the Na^+−3 complex, the Na^+ is coordinated to all seven of the donor atoms of the ligand and two Na^+−3 complexes join together to form a dimer. The dimer contains an intermolecular hydrogen bond formed between the phenol hydrogen atom of one ligand and the phenolate group of a centrosymmetrically related ligand and two π−π stacking interactions between the electron-deficient pyridine ring of one molecule and the electron-rich phenol ring of the other

Orbital-selective Mott transitions: Heavy fermions and beyond

Quantum phase transitions in metals are often accompanied by violations of Fermi liquid behavior in the quantum critical regime. Particularly fascinating are transitions beyond the Landau-Ginzburg-Wilson concept of a local order parameter. The breakdown of the Kondo effect in heavy-fermion metals constitutes a prime example of such a transition. Here, the strongly correlated f electrons become localized and disappear from the Fermi surface, implying that the transition is equivalent to an orbital-selective Mott transition, as has been discussed for multi-band transition-metal oxides. In this article, available theoretical descriptions for orbital-selective Mott transitions will be reviewed, with an emphasis on conceptual aspects like the distinction between different low-temperature phases and the structure of the global phase diagram. Selected results for quantum critical properties will be listed as well. Finally, a brief overview is given on experiments which have been interpreted in terms of orbital-selective Mott physics.Comment: 29 pages, 4 figs, mini-review prepared for a special issue of JLT

Winning Fights Induces Hyperaggression via the Action of the Biogenic Amine Octopamine in Crickets

Winning an agonistic interaction against a conspecific is known to heighten aggressiveness, but the underlying events and mechanism are poorly understood. We quantified the effect of experiencing successive wins on aggression in adult male crickets (Gryllus bimaculatus) by staging knockout tournaments and investigated its dependence on biogenic amines by treatment with amine receptor antagonists. For an inter-fight interval of 5 min, fights between winners escalated to higher levels of aggression and lasted significantly longer than the preceding round. This winner effect is transient, and no longer evident for an inter-fight interval of 20 min, indicating that it does not result from selecting individuals that were hyper-aggressive from the outset. A winner effect was also evident in crickets that experienced wins without physical exertion, or that engaged in fights that were interrupted before a win was experienced. Finally, the winner effect was abolished by prior treatment with epinastine, a highly selective octopamine receptor blocker, but not by propranolol, a ß-adrenergic receptor antagonist, nor by yohimbine, an insect tyramine receptor blocker nor by fluphenazine an insect dopamine-receptor blocker. Taken together our study in the cricket indicates that the physical exertion of fighting, together with some rewarding aspect of the actual winning experience, leads to a transient increase in aggressive motivation via activation of the octopaminergic system, the invertebrate equivalent to the adrenergic system of vertebrates

Prevalence of Influenza A viruses in wild migratory birds in Alaska: Patterns of variation in detection at a crossroads of intercontinental flyways

<p>Abstract</p> <p>Background</p> <p>The global spread of the highly pathogenic avian influenza H5N1 virus has stimulated interest in a better understanding of the mechanisms of H5N1 dispersal, including the potential role of migratory birds as carriers. Although wild birds have been found dead during H5N1 outbreaks, evidence suggests that others have survived natural infections, and recent studies have shown several species of ducks capable of surviving experimental inoculations of H5N1 and shedding virus. To investigate the possibility of migratory birds as a means of H5N1 dispersal into North America, we monitored for the virus in a surveillance program based on the risk that wild birds may carry the virus from Asia.</p> <p>Results</p> <p>Of 16,797 birds sampled in Alaska between May 2006 and March 2007, low pathogenic avian influenza viruses were detected in 1.7% by rRT-PCR but no highly pathogenic viruses were found. Our data suggest that prevalence varied among sampling locations, species (highest in waterfowl, lowest in passerines), ages (juveniles higher than adults), sexes (males higher than females), date (highest in autumn), and analytical technique (rRT-PCR prevalence = 1.7%; virus isolation prevalence = 1.5%).</p> <p>Conclusion</p> <p>The prevalence of low pathogenic avian influenza viruses isolated from wild birds depends on biological, temporal, and geographical factors, as well as testing methods. Future studies should control for, or sample across, these sources of variation to allow direct comparison of prevalence rates.</p

Comparative analysis of co-processed starches prepared by three different methods

Co-processing is currently of interest in the generation of high-functionality excipients for tablet formulation. In the present study, comparative analysis of the powder and tableting properties of three co-processed starches prepared by three different methods was carried out. The co-processed excipients consisting of maize starch (90%), acacia gum (7.5%) and colloidal silicon dioxide (2.5%) were prepared by co-dispersion (SAS-CD), co-fusion (SAS-CF) and co-granulation (SAS-CG). Powder properties of each co-processed excipient were characterized by measuring particle size, flow indices, particle density, dilution potential and lubricant sensitivity ratio. Heckel and Walker models were used to evaluate the compaction behaviour of the three co-processed starches. Tablets were produced with paracetamol as the model drug by direct compression on an eccentric Tablet Press fitted with 12 mm flat-faced punches and compressed at 216 MPa. The tablets were stored at room temperature for 24 h prior to evaluation. The results revealed that co-granulated co-processed excipient (SAS-CG) gave relatively better properties in terms of flow, compressibility, dilution potential, deformation, disintegration, crushing strength and friability. This study has shown that the method of co-processing influences the powder and tableting properties of the co-processed excipient

Comparative analysis of co-processed starches prepared by three different methods

Co-processing is currently of interest in the generation of high-functionality excipients for tablet formulation. In the present study, comparative analysis of the powder and tableting properties of three co-processed starches prepared by three different methods was carried out. The co-processed excipients consisting of maize starch (90%), acacia gum (7.5%) and colloidal silicon dioxide (2.5%) were prepared by co-dispersion (SAS-CD), co-fusion (SAS-CF) and co-granulation (SAS-CG). Powder properties of each co-processed excipient were characterized by measuring particle size, flow indices, particle density, dilution potential and lubricant sensitivity ratio. Heckel and Walker models were used to evaluate the compaction behaviour of the three co-processed starches. Tablets were produced with paracetamol as the model drug by direct compression on an eccentric Tablet Press fitted with 12 mm flat-faced punches and compressed at 216 MPa. The tablets were stored at room temperature for 24 h prior to evaluation. The results revealed that co-granulated co-processed excipient (SAS-CG) gave relatively better properties in terms of flow, compressibility, dilution potential, deformation, disintegration, crushing strength and friability. This study has shown that the method of co-processing influences the powder and tableting properties of the co-processed excipient

The medical threat of mamba envenoming in sub-Saharan Africa revealed by genus-wide analysis of venom composition, toxicity and antivenomics profiling of available antivenoms

Mambas (genus Dendroaspis) are among the most feared of the medically important elapid snakes found in sub-Saharan Africa, but many facets of their biology, including the diversity of venom composition, remain relatively understudied. Here, we present a reconstruction of mamba phylogeny, alongside genus-wide venom gland transcriptomic and high-resolution top-down venomic analyses. Whereas the green mambas, D. viridis, D. angusticeps, D. j. jamesoni and D. j. kaimosae, express 3FTx-predominant venoms, black mamba (D. polylepis) venom is dominated by dendrotoxins I and K. The divergent terrestrial ecology of D. polylepis compared to the arboreal niche occupied by all other mambas makes it plausible that this major difference in venom composition is due to dietary variation. The pattern of intrageneric venom variability across Dendroaspis represented a valuable opportunity to investigate, in a genus-wide context, the variant toxicity of the venom, and the degree of paraspecific cross-reactivity between antivenoms and mamba venoms. To this end, the immunological profiles of the five mamba venoms were assessed against a panel of commercial antivenoms generated for the sub-Saharan Africa market. This study provides a genus-wide overview of which available antivenoms may be more efficacious in neutralising human envenomings caused by mambas, irrespective of the species responsible. The information gathered in this study lays the foundations for rationalising the notably different potency and pharmacological profiles of Dendroaspis venoms at locus resolution. This understanding will allow selection and design of toxin immunogens with a view to generating a safer and more efficacious pan-specific antivenom against any mamba envenomation

Reply to Nielsen et al. social mindfulness is associated with countries’ environmental performance and individual environmental concern

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