Multiple interactions in the self-association of porphyrin discotic mesogens

The conformational preferences and the self-associational behaviors of two hemin-derived porphyrin compounds, a tetramethyl ester and a liquid crystalline tetrakis(3,5-didodecyloxyphenyl)ester, have been studied by UV/vis and (1)H NMR spectroscopy in solution. Results indicate that the 3,5-didodecyloxyphenyl units play an important role in both the conformational and the self-associational behaviors of the mesomorphic tetraester. In the monomeric, nonassociated species, the two propionic 3,5-didodecyloxyphenyl esters establish mutual CH/pi interactions that restrict the fluctuative behavior of the chains. In the dimeric, self-associated species, intermolecular CH/pi interactions occur in addition to the pi-pi stacking of the porphyrin cores. The temperature-dependent addition of side CH/pi interactions to the pi-pi stacking of the porphyrin rings accounts for the observed tightening and for the slower dynamics of the dimeric structure. The relationship between the self-associational behavior and the mesomorphism of the hemin-derived porphyrin tetraesters is also discussed.     

Topological estimator of block entanglement for Heisenberg antiferromagnets

We introduce a computable estimator of block entanglement entropy for many-body spin systems admitting total singlet ground states. Building on a simple geometrical interpretation of entanglement entropy of the so-called valence bond states, this estimator is defined as the average number of common singlets to two subsystems of spins. We show that our estimator possesses the characteristic scaling properties of the block entanglement entropy in critical and noncritical one-dimensional Heisenberg systems. We invoke this new measure to examine entanglement scaling in the two-dimensional Heisenberg model on a square lattice revealing an "area law" for the gapped phase and a logarithmic correction to this law in the gapless phase.     

Structural Study of O-Specific Polysaccharides of Proteus

Abstract

Proteus bacteria are important human opportunistic pathogens which frequently cause urinary tract infections. According to Bergey's Manual of Systematic Bacteriology,¹ this genus includes three species: P. mirabilis, P. vulgaris, and P. myxofaciens. A novel species of P. penneri has been recently proposed^2,3 for strains formerly called P. vulgaris biogroup I. Proteus is an antigenically heterogeneous group of bacteria, and this is mainly associated with diverse composition and structures of O-specific polysaccharide chains of outer-membrane lipopolysaccharides (O-antigens). The Kauffman-Perch serological classification⁴ of P. mirabilis and P. vulgaris includes 49 O-serogroups. However, a number of S-strains remain unclassified,⁵ including strains of P. penneri.     

Physical Science in Barcelona

We provide a tour of Barcelona, Catalonia, Spain, following four routes through the city and one elsewhere in the city and beyond, focusing on sites of importance in physics. Route 1 covers the Old Town, its Gothic Quarter, Plaça del Rei, Plaça de Sant Jaume, and Jewish Quarter. Route 2 identifies sites on and close to La Rambla, the main promenade in the city. Route 3 goes from the medieval shipyards to the Board of Commerce to Citadel Park. Route 4 concentrates on the Extension (Eixample) and covers the restored University, the Industrial University, and the new campus of the University of Barcelona. Elsewhere in the city and beyond are the Fabra Observatory; the Plaça de les Glòries with its large steel sculpture depicting the meridian arc from Dunkirk to Barcelona; Montjuïc, the site of the National Art Museum of Catalonia; and the National Museum of Science and Technology in Terrassa.     

Contact separation and failure analysis of a rotating thermo-elastoplastic shrink-fit assembly

Gas turbine propulsion and aircraft engines involve a great number of rotating shrink-fit assemblies. In presence of high-speed rotations and thermal effects, the reliability of such components with respect to contact separation and failure occurrences needs to be analyzed in the very early design of those structures. In particular, engineers and designers are to prescribe an adequate shrink interference to ensure a structural safe life for a given range of operating conditions. This paper is devoted to the determination of those critical contact and plastic states. To that end, a thermo-elastic–plastic analytical model of a rotating shrink-fit assembly is studied. The stress distributions and contact/plasticity/failure conditions are then derived analytically. In the last part, the determination of the safe operating domain and optimum shrink interference is illustrated through a numerical example.     

Trace analysis of endectocides in milk by high performance liquid chromatography with fluorescence detection

An analytical method has been developed for the simultaneous determination of the following endectocide drugs in milk: ivermectin, abamectin, doramectin, moxidectin, eprinomectin, emamectin and nemadectin. Samples were extracted with acetonitrile, purified with solid-phase extraction on a reversed phase C₈, derivatised with N-methylimidazole, trifluoroacetic anhydride and acetic acid to a stable fluorescent derivative, and were further analysed by gradient high performance liquid chromatography (HPLC) on an endcapped reversed phase Supelcosil LC-8-DB. The derivatisation step was mathematically optimised and the method was validated according to the requirements of Commission Decision 2002/657/EC, using fortified raw bovine milk. Mean recovery was between 78 and 98%. The repeatability (CV_r) and within-laboratory reproducibility (CV_W) ranged from 4.6 to 13.4% and from 6.6 to 14.5%, respectively. Decision limits (CCα) for analytes with MRL values, namely eprinomectin and moxidectin, were determined to be 24.8 and 50.6 μg kg⁻¹, respectively. CCα values for unauthorised endectocides ranged from 0.1 to 0.2 μg kg⁻¹. Due to high acceptability regarding the required criteria and applicability to ovine and caprine milk, giving similar results, this multi-analyte method has been successfully implemented in pharmacokinetic research studies as well as statutory residue monitoring in Slovenia.     

Chiral N-phosphino sulfinamide ligands in rhodium(I)-catalyzed [2+2+2] cycloaddition reactions

The combination of cationic rhodium(I) complexes with N-phosphino tert-butylsulfinamides (PNSO) ligands is efficient for catalytic intra- and intermolecular [2+2+2] cycloaddition reactions. PNSO ligands are a new class of chiral bidentate ligands, which have the characteristic of combining the easily accessible sulfur chirality with the coordinating capacity of phosphorous. Cycloaddition of open-chained and macrocyclic E-enediynes with these chiral complexes have proved to be highly efficient in terms of yields, giving moderate enantiomeric excesses of the corresponding cyclohexadiene derivatives. In addition Rh(I)/PNSO complexes catalyzed the intermolecular cycloaddition of diynes with monoalkynes in mild reaction conditions and short reaction times.     

Size Selection During Crystallization of Oppositely Charged Nanoparticles

Opposites attract (selectively) : Oppositely charged nanoparticles characterized by different size distributions form 3D supracrystals (see figure) only if the distributions overlap. Crystal quality decreases rapidly with decreasing degree of overlap, and, irrespective of the ratio of particle diameters/charges, no crystals are observed for non‐overlapping distributions.