Hypercharge annihilation

Aspects of the process K^?p → Λ + pions for K^? mesons of momentum 8.25 GeV/c are examined. It is shown that the hypercharge annihilation process can be effectively separated into off-shell baryon (B?B) and strangeness (K?K) annihilation. Both annihilation regions have many features in common and show strong similarities to on-shell annihilation processes; some differences are also noted.     

Synthesis and characterization of luminescent rod-coil block copolymers by atom transfer radical polymerization: utilization of novel end-functionalized terfluorenes as macroinitiators

Two novel, rigid, photoluminescent, substituted terfluorene derivatives were synthesized by utilizing direct bromination and Suzuki coupling reactions. These oligomers were used as initiators for the atom transfer radical polymerization (ATRP) of styrene and tert-butyl acrylate. Thus, diblock and triblock rod-coil block copolymers were prepared with well-defined structure, as far as their size and shape is concerned. Molecular weights up to approximately 21 000 and polydispersity indices not exceeding 1.5 in most cases were obtained. The copolymers emit blue light in solution, and their luminescence properties remain practically invariable when passing from solution to the solid state. No ground-state aggregation or excimer formation were observed in the solid state, even after annealing at high temperatures.     

Improved cyclodextrin-based receptors for camptothecin by inverse virtual screening

We report the computer-aided optimization of a synthetic receptor for a given guest molecule, based on inverse virtual screening of receptor libraries. As an example, a virtual set of beta-cyclodextrin (beta-CD) derivatives was generated as receptor candidates for the anticancer drug camptothecin. We applied the two docking tools AutoDock and GlamDock to generate camptothecin complexes of every candidate receptor. Scoring functions were used to rank all generated complexes. From the 10 % top-ranking candidates nine were selected for experimental validation. They were synthesized by reaction of heptakis-[6-deoxy-6-iodo]-beta-CD with a thiol compound to form the hepta-substituted beta-CDs. The stabilities of the camptothecin complexes obtained from solubility measurements of five of the nine CD derivatives were significantly higher than for any other CD derivative known from literature. The remaining four CD derivatives were insoluble in water. In addition, corresponding mono-substituted CD derivatives were synthesized that also showed improved binding constants. Among them the 9-H-purine derivative was the best, being comparable to the investigated hepta-substituted beta-CDs. Since the measured binding free energies correlated satisfactorily with the calculated scores, the applied scoring functions appeared to be appropriate for the selection of promising candidates for receptor synthesis.     

Synthesis of coil‐rod‐coil block copolymers with the aid of anionic polymerization

A two step synthetic procedure towards model coil‐rod‐coil triblock copolymers was developed. In the first step, α,ω‐bromo‐functionalized oligophenylenes (rod part) were modified to anionic bifunctional initiators. In the second step, flexible chains were grown from both ends of the rod part by an anionic polymerization procedure leading to polystyrene‐rod‐polystyrene and/or poly(2‐vinyl pyridine)‐rod‐poly(2‐vinyl pyridine) triblock copolymers. Characterization of the final products by gel permeation chromatography, NMR spectroscopy, light scattering, Raman spectroscopy and differential scanning calorimetry demonstrated that well‐defined coil‐rod‐coilblock copolymers can be synthesized.     

Phosphonated fully aromatic polyethers for PEMFCs applications

New homopolymers and copolymers based on aromatic polyethers bearing side diphosphonate and diphosphonic groups have been synthesized. These synthetic efforts resulted in homo and copolymers of high thermal stability but moderate molecular weights. To evaluate the influence of the immobilized phosphonate ester and phosphonic acid moieties on polymer electrolyte membranes for fuel cells applications, blends of the newly synthesized homo and copolymers with a pyridine‐based aromatic polyether were prepared. These blends were miscible with high glass transition temperatures and high thermal stabilities. Furthermore, the introduction of these groups to a polymeric backbone significantly increases the doping ability in phosphoric acid compared to the net matrix as well as the ionic conductivity for high doping levels. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2817–2827, 2010     

pH‐responsive photoluminescence properties of a water‐soluble copolymer containing quinoline groups in aqueous solution

The synthesis of a water‐soluble copolymer containing quinoline groups, P(DMAM‐co‐SDPQ), through free radical copolymerization of N,N‐dimethylacrylamide, DMAM, with 2,4‐diphenyl‐6‐(4‐vinylphenyl)quinoline, SDPQ, is presented and the optical properties of the final product are investigated in aqueous solution as a function of pH. It is found that the emission peak of SDPQ is red‐shifted from 411 to 484 nm with decreasing pH, due to the protonation of quinoline groups at low pH, suggesting that this copolymer may function as a luminescent pH‐indicator. Moreover, the copolymer exhibits the characteristics of a luminescent pH‐detector within the pH range 2 < pH < 4, as in this pH region the ratio of the emission intensity at 411 nm over that at 484 nm changes linearly in a logarithmic scale with the pH of the solution. Finally, the formation of less polar quinoline clusters in the aqueous P(DMAM‐co‐SDPQ) solution upon increasing pH was detected through Nile red probing. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2078–2083, 2010     

Coarse-grained model simulations of mixed-lipid systems: composition and line tension of a stabilized bilayer edge

Bilayer disks and ribbons composed of a mixture of short- and long-tail phospholipids have been studied by molecular dynamics with a coarse-grained model. The effects of system composition on the edge structure, composition, and line tension were analyzed. Increases in the fraction of short-tail lipids tend to decrease the line tension (i.e., stabilize the edge) but not eliminate it. The short-tail lipid is generally enriched at the curved rim forming the bilayer edge, with an excess of 3 to 4 molecules per nanometer (relative to the bulk), but complete segregation was not observed. In all mixtures, a region depleted in the short-tail component occurs just before the edge, corresponding to a bulge in the bilayer thickness. The bulge and depletion are more prominent as the bilayer composition shifts toward a majority of short-tail lipids. In one case, a net excess of long-tail lipids at the edge was demonstrated, suggesting that certain circumstances give rise to a "segregation inversion" in which the long-tail lipid behaves as an edge stabilizer.     

Thermally stable blue emitting terfluorene block copolymers

Spectroscopic and morphological studies on a series of rod-coil block copolymers containing terfluorene segments as the rigid blocks and polystyrene as the flexible parts demonstrate an increase in the photoluminescence intensity and the exciton lifetime as well as formation of isolated spheres as thin films upon thermal annealing in air (200 degrees C for 30 min). Moreover, no appearance of the low energy emission band centered at 520 nm was found after the same thermal treatment which permits these copolymers to emit pure blue light.     

Time-dependent Cu-induced gelation of poly(ethylene-alt-maleic acid) in aqueous solution

The complexation of Cu²⁺ ions with an alternating copolymer of maleic acid (MAc) and ethylene in aqueous solution was followed through turbidimetry and absorption spectrophotometry as a function of the polymer concentration and the metal ion-to-polymer molar ratio, r. The introduction of Cu²⁺ ions was performed in aqueous solution through neutralization of the polyacid with Cu(OH)₂ powder. A gelation window between homogeneous and phase-separated solutions was observed in the phase diagram of the polymer/Cu²⁺ mixture and the viscoelastic properties of the hydrogels were evaluated through rheology measurements. It is found that the stiffness of the hydrogels can be tuned by the polymer concentration and the mixing ratio r. Moreover, the stiffness of the hydrogels increases substantially with time. In fact, this time evolution may be as long as one month or longer if the composition of the aqueous solution is close to the gelation threshold. The gelation properties can be qualitatively explained from the possible formation of binuclear polymer/Cu²⁺ complexes in aqueous solutions, as indicated from the absorption spectroscopy results.     

Evidence for a narrow peak in Ksoπ±π+π- at 2.6 gev in 12 gev/cpp interactions

We report the evidence for a narrow charged peak (5.5 s.d.), which we suggest calling the I, in the 6-prong-V⁰ topology of $\text{p}$p interactions at 12 GeV/c. The mass, widht and the product of cross section σ_I times the branching ratio BR into the final state (K_s^oτ±τ⁺τ^? are found to be: $\text{M}{}_{\mathrm{I}}\text{=2.60 ±}\text{0.01}\text{GeV}\text{/}\text{c}{}^2$, $\text{Γ}{}_{\mathrm{I}}\text{?}\text{0.018}\text{GeV}\text{/}\text{c}{}^2$, σ_I·BR≈20 μbarn