Transition from the Compact to the Dense Phase of Two-Dimensional Polymers

We present a unifying picture of the compact, dense, and dilute phases of two-dimensional polymers. The lattice dependence of the scaling exponents for compact polymers is reconciled with their universality in the dense and dilute cases. In particular, we show that violations of the fully packing constraint in the compact phase can be interpreted as magnetic screening in the associated Coulomb gas, which induces a flow to either the dense or the dilute phase. When more than one flavor of polymers is present the flow away from the compact phase leads to a decoupling of the flavors, and the central charge decreases by an integer. If charge asymmetry develops, the polymer flavors may independently flow to either of the two noncompact phases.     

Workshop on Timing Modes for Low-Emittance Storage Rings

A three-day workshop was held in Lund, Sweden, from March 25 to 27, 2015, with a focus on timing modes for low-emittance storage rings. The MAX IV Laboratory, currently under construction in Lund, will provide a 1.5 GeV storage ring for soft X-rays and a 3 GeV storage ring with an ultralow emittance down to 0.2 nm rad for hard X-rays [1 M. Eriksson, Proceedings of 2011 PAC, TUOBS4, 737–741 (2011). [Google Scholar]]. Both rings are designed to operate with a uniform multibunch filling pattern with a 100 MHz RF system and employ passive harmonic cavities [2 Å. Andersson, Proceedings of IPAC 2011, MOPC051, 193–195 (2011). [Google Scholar]] to damp instabilities and increase the Touschek lifetime. For the 3 GeV ring, the harmonic cavities are also required to conserve the ultralow emittance at high bunch charge [3 S. C. Leemann, Phys. Rev. ST Accel. Beams 17, 050705 (2014).[Crossref] , [Google Scholar]]. The facility will include a short pulse facility delivering 100 fs FWHM X-ray pulses at a repetition rate of 100 Hz.     

Triphenylene analogues with B2N2C2 cores: synthesis, structure, redox behavior, and photophysical properties

A series of alkyl (1-3), aryl (6), and benzo-annulated (4, 5) heteroaromatic triphenylene analogues with B(2)N(2)C(2) cores have been synthesized via chelation of pyridazine derivatives using difunctional Lewis acidic diborabiphenyl precursors. In contrast to triphenylene, NICS(1) calculations on 1 suggested high aromaticities for the central (-11.3 ppm) and outer borabenzene rings (-7.7 ppm), along with nonaromatic behavior for the pyridazine ring (-0.7 ppm). Crystal structure analyses supported this analysis. When the a- and c-faces of the pyridazine moiety were free of substitution (1, 3), planar structures resulted, but upon substitution, a twisted B(2)N(2)C(2) core was observed due to steric repulsion of neighboring hydrogen atoms (e.g., 5). The increase of steric bulk from H (1) to (i)Pr (3) in the planar species was found to result in a dimeric, head-to-tail herringbone packing motif, held together by close intermolecular B...N interactions of 3.39 Angstrom. One-electron reduction by Cp(2)Co was found to afford the radical anions of 3 and 5, which were characterized by broad, featureless singlets in the EPR spectra; [3](.)(-)[Cp(2)Co](+) was characterized by X-ray crystallography. While the planar structures (1-4) were observed to possess weak fluorescence (Phi(F) = 0.02-0.08) with either yellow-orange (ca. 555 nm) or green emission (521 nm), the twisted structures (5, 6) were found to be nonfluorescent.     

On definition and measurement of extinction cross section

Following the recent analyses of extinction by Berg et al. [J Opt Soc Am A 2008;25:1504–1513; J Opt Soc. Am A 2008;25:1514–1520], we show that although it is possible to define and measure the extinction cross section for a single particle using a detector of light facing the incident beam, this requires certain theoretical assumptions and experimental precautions.     

Kohlenhydrate

Ohne Zusammenfassung     

Solvolysis of (Z)-5-trimethylstannyl 2-adamantyl p-bromobenzenesulfonate: mechanistic implications of a record-breaking secondary alpha-deuterium kinetic isotope effect for an SN1 substrate

The secondary alpha-deuterium kinetic isotope effect (alpha-kie) for the solvolysis of (Z)-5-trimethylstannyl 2-adamantyl p-bromobenzenesulfonate in 97% w/w aqueous 2,2,2-trifluoroethanol (97T) at 25 degrees C has been measured (k(H)/k(D) = 1.33). The alpha-kie is abnormally high compared to the value of 1.23 for the corresponding limiting S(N)1 solvolysis of 2-adamantyl p-bromobenzenesulfonate, which proceeds via an extended ion-pair mechanism. A novel mechanism for the solvolysis of the tin compound is proposed that accommodates not only the high alpha-kie but also the absence of internal return.     

Cathelicidins--nature's attempt at combinatorial chemistry

Cathelicidins are a family of diverse antimicrobial peptides found in granules of mammalian neutrophils. Cathelicidins are active against a broad range of microbes in different environments. Aside from their antimicrobial activity, cathelicidins possess other biological properties including cytotoxic activity towards mammalian cells. Several studies have shown that the amino acid sequence of cathelicidins can be modified to temper undesired properties, such as hemolytic and cytotoxic activity, and at the same time maintain antimicrobial activity. These properties make cathelicidins ideal templates in combinatorial chemistry for designing de novo antimicrobial peptides for therapeutic use. However, one of the major challenges will be to screen these peptides in experimentally relevant models that reflect the environments in which the peptides should be therapeutically active.