Organocatalytic hydroacylation of unactivated alkenes

N-Heterocyclic carbenes interact with aldehydes to generate the Breslow intermediate, a rendering of the prototypical electrophile into a nucleophile (umpolung). Recent work has indicated that these intermediates may also add to simple, unpolarized alkenes. The use of a chiral precatalyst leads to the generation of the derived adducts with high yields and very high selectivities.     

Just add tetrazole: 5-(2-pyrrolo)tetrazoles are simple, highly potent anion recognition elements

We report a novel pyrrolo-tetrazole motif that encodes anion binding orders of magnitude stronger than closely related systems and suggests the general utility of amide-tetrazole exchanges for creating simple, high-affinity anion binders.     

Observation of a two-dimensional halogen-bonded cocrystal at sub-monolayer coverage using synchrotron X-ray diffraction

The formation of two-dimensional halogen-bonded layers of 4,4'-bipyridyl and 1,4-diiodotetrafluorobenzene was observed on a graphite surface at sub-monolayer coverage using synchrotron X-ray diffraction; the use of the diffraction technique enabled, for the first time, the measurement of I···N halogen bonding distances in a two-dimensional cocrystal and the identification of the halogen bonding interaction in the monolayer.     

Hydrogen bonding topology influences gelating properties of malonamides

Preparation, structural characterisation and topology of hydrogen bonding networks of bis(phenylglycinol)malonamide, as well as its Cα mono- and dialkyl-substituted derivatives are described. Their hydrogen bonding motifs are described in view of their gelling properties. Topology of hydrogen bonding typical of malonamide gelators is compared with those of well-examined oxalamide gelators.     

Recognition properties of carboxylic acid bioisosteres: anion binding by tetrazoles, aryl sulfonamides, and acyl sulfonamides on a calix[4]arene scaffold

Tetrazoles and acyl sulfonamides are functional groups that are common in medicinal chemistry but virtually unexplored as recognition elements in supramolecular chemistry. We report here on the anion binding properties of these highly acidic N-H functional groups. We have prepared two new calixarene-based tetrazole-containing hosts, as well as new acetyl sulfonamide and benzoyl sulfonamide hosts. We also report on analogous hosts bearing the better-known aryl sulfonamide functional group as a point of comparison. We find that these hosts are competent anion binders and that the recognition of anions by these groups is highly dependent on their conformational preferences. We also report in detail on the preferred molecular shape of each acid bioisostere as determined by calculations and structural database surveys, and discuss how these shapes impact binding in the context of the reported hosts.     

Stabilization of domain walls between traveling waves by nonlinear mode coupling in Taylor-Couette flow

We present a new mechanism that allows the stable existence of domain walls between oppositely traveling waves in pattern-forming systems far from onset. It involves a nonlinear mode coupling that results directly from the nonlinearities in the underlying momentum balance. Our work provides the first observation and explanation of such strongly nonlinearly driven domain walls that separate structured states by a phase generating or annihilating defect. Furthermore, the influence of a symmetry breaking externally imposed flow on the wave domains and the domain walls is studied. The results are obtained for vortex waves in the Taylor-Couette system by combining numerical simulations of the full Navier-Stokes equations and experimental measurements.     

Direct Identification of Urinary Tract Pathogens by MALDI-TOF/TOF Analysis and De Novo Peptide Sequencing

For mass spectrometry-based diagnostics of microorganisms, matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is currently routinely used to identify urinary tract pathogens. However, it requires a lengthy culture step for accurate pathogen identification, and is limited by a relatively small number of available species in peptide spectral libraries (≤3329). Here, we propose a method for pathogen identification that overcomes the above limitations, and utilizes the MALDI-TOF/TOF MS instrument. Tandem mass spectra of the analyzed peptides were obtained by chemically activated fragmentation, which allowed mass spectrometry analysis in negative and positive ion modes. Peptide sequences were elucidated de novo, and aligned with the non-redundant National Center for Biotechnology Information Reference Sequence Database (NCBInr). For data analysis, we developed a custom program package that predicted peptide sequences from the negative and positive MS/MS spectra. The main advantage of this method over a conventional MALDI-TOF MS peptide analysis is identification in less than 24 h without a cultivation step. Compared to the limited identification with peptide spectra libraries, the NCBI database derived from genome sequencing currently contains 20,917 bacterial species, and is constantly expanding. This paper presents an accurate method that is used to identify pathogens grown on agar plates, and those isolated directly from urine samples, with high accuracy.     

Mechanochemical Desymmetrization of Unbiased Bis- and Tris-alkynes to Access 3,5-Isoxazoles-Alkyne Adducts and Unsymmetrical Bis-3,5-isoxazoles**

A mechanochemical desymmetrization of symmetrical bis- and tris-alkynes by a controlled 1,3-dipolar cycloaddition reaction using nitrile oxide dipoles (NOs). This operationally simple protocol allows access to 3,5-isoxazole-alkyne adducts from easily prepared or commercially available symmetrical bis- and tris-alkynes in moderate to excellent yields. In addition, we have highlighted the synthetic utility of 3,5-isoxazole-alkyne by developing a route to access, for the first time, β-ketoenamine-alkyne derivatives, and unsymmetrical bis-3,5-isoxazoles.     

Estimation of Slow Crack Growth Behavior in Polyethylene after Stepwise Isothermal Crystallization

The use of analytical methods to estimate the SCG resistance of PE pipe materials has been suggested due to the fact that the slow crack growth (SCG) behavior of polyethylene (PE) is governed by structural parameters such as molecular weight and side chains. In the research project presented here, the molecular structure of several commercially available polyethylene-high density (PE-HD) materials was analyzed using a modified stepwise isothermal segregation (SIS) technique and compared with results from fracture mechanics experiments. A good correlation between the SIS results and SCG rates was found. It turned out that the modified SIS technique is a fast and simple method and could be used to assess SCG resistance in PE.