Short communication controlling LC-SPE-NMR systems

There are several stages of the LC-SPE-NMR process that should be monitored closely to ensure an efficient isolation and concentration of the target analyte, for instance analyte break-through and compound transfer from the LC-SPE to the NMR probe. In this study, analyte break-through monitoring was performed with a UV detector and a mass spectrometer placed after the SPE unit. Easy break-through was a problem when attempting multiple trapping of various compounds using C18 SPE cartridges with the original commercial system. However, on lowering the flow rate over the SPE system and using SPE cartridges packed with porous carbon, the number of trappings possible increased five-fold. To increase control over the on-line SPE-NMR transfer, a gradient pump-UV system was used to elute compounds trapped on an SPE to an NMR probe. The analyte band was placed in the active volume of the probe by a stop-flow mechanism. The modified LC-SPE system was also coupled with off-line NMR analysis for determination of a degradation product of the insecticide monuron, present in the low ppm range.     

Purity determination as needed for the realisation of primary standards for elemental determination: status of international comparability

Within the National Metrology Institutes (NMIs) and designated laboratories, an interlaboratory comparison, CCQM-P107, was conducted to verify the degree of international comparability concerning the results of purity analysis. The mass fractions of Ag, Bi, Cd, Cr, Ni, Tl at the lower mg/kg-level in a high purity zinc material were determined, but the real measurand in metrological sense was the sum of the six mass fractions. Homogeneity was investigated by glow discharge mass spectrometry, reference values were obtained using isotope dilution mass spectrometry. Six NMIs participated, contributing eight independent data sets. The agreement amongst the results of the participants, their median and the agreement with the reference values were usually excellent and in almost all cases below the target uncertainty of 30% relative. In this manner, the accuracy of results and the comparability between the participants was demonstrated to be established.     

Genotyping of Francisella tularensis, the causative agent of tularemia

Francisella tularensis is a facultative, intracellular, zoonotic pathogen and the causative agent of tularemia. Historically, F. tularensis has been subdivided into subspecies on the basis of phenotypic traits, including biochemical reactivity and virulence. More recently, a number of genotypic methods, ranging from relatively insensitive methods to full genome sequencing, have been used to investigate genetic diversity within F. tularensis. These analyses indicate that F. tularensis is a pathogen of low sequence diversity with pair-wise average nucleotide identities > 99.2% across subspecies. Nonetheless, genomic rearrangements and sequence deletions exist between and within F. tularensis subspecies, creating polymorphisms detectable by genotyping methods. Genetic subpopulations intermediate to the subspecies and strain level have been identified within F. tularensis subsp. tularensis and F. tularensis subsp. holarctica by several different typing methods. These genetic subpopulations have been associated with differences in disease severity, geographic distribution, and transmission patterns. For example, one F. tularensis subsp. tularensis subpopulation has been found to be significantly associated with mortality in humans. Additionally, genotypic analyses of Francisella spp. have provided information for use in the rational design of strain panels for validation of F. tularensis diagnostic tests. This review provides a guide to the various F. tularensis genotyping methods.     

Solution Structure of a Locked Nucleic Acid Modified Quadruplex: Introducing the V4 Folding Topology

Sharp curves : The structure of a locked nucleic acid modified telomeric sequence from Oxytricha nova displays a remarkable folding topology, distinct from the native O. nova quadruplex. Each guanine stretch folds back in a V‐shaped turn that puts the first and fourth guanines in the same tetrad, looping over a tetrad with a sharp turn in the DNA backbone, showing how subtle interplay between sequence and conformation defines the folding topology.

     

Chemistry surrounding monomeric copper(I) methyl, phenyl, anilido, ethoxide, and phenoxide complexes supported by N-heterocyclic carbene ligands: reactivity consistent with both early and late transition metal systems

Monomeric copper(I) alkyl complexes that possess the N-heterocyclic carbene (NHC) ligands IPr, SIPr, and IMes [IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene, IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] react with amines or alcohols to release alkane and form the corresponding monomeric copper(I) amido, alkoxide, or aryloxide complexes. Thermal decomposition reactions of (NHC)Cu(I) methyl complexes at temperatures between 100 and 130 degrees C produce methane, ethane, and ethylene. The reactions of (NHC)Cu(NHPh) complexes with bromoethane reveal increasing nucleophilic reactivity at the anilido ligand in the order (SIPr)Cu(NHPh) < (IPr)Cu(NHPh) < (IMes)Cu(NHPh) < (dtbpe)Cu(NHPh) [dtbpe = 1,2-bis(di-tert-butylphosphino)ethane]. DFT calculations suggest that the HOMO for the series of Cu anilido complexes is localized primarily on the amido nitrogen with some ppi(anilido)-dpi(Cu) pi-character. [(IPr)Cu(mu-H)]2 and (IPr)Cu(Ph) react with aniline to quantitatively produce (IPr)Cu(NHPh)/dihydrogen and (IPr)Cu(NHPh)/benzene, respectively. Analysis of the DFT calculations reveals that the conversion of [(IPr)Cu(mu-H)]2 and aniline to (IPr)Cu(NHPh) and dihydrogen is favorable with DeltaH approximately -7 kcal/mol and DeltaG approximately -9 kcal/mol.     

Observation of attraction between dark solitons

We demonstrate a dramatic change in the interaction forces between dark solitons in nonlocal nonlinear media. We present what we believe is the first experimental evidence of attraction of dark solitons. Our results indicate that attraction should be observable in other nonlocal systems, such as Bose-Einstein condensates with repulsive long-range interparticle interaction.     

The pinnacle set of a permutation

The peak set of a permutation records the indices of its peaks. These sets have been studied in a variety of contexts, including recent work by Billey, Burdzy, and Sagan, which enumerated permutations with prescribed peak sets. In this article, we look at a natural analogue of the peak set of a permutation, instead recording the values of the peaks. We define the “pinnacle set” of a permutation $w$ to be the set $\{w\left(i\right):i\text{ is a peak of}w\}$. Although peak sets and pinnacle sets mark the same phenomenon for a given permutation, the behaviors of these sets differ in notable ways as distributions over the symmetric group. In the work below, we characterize admissible pinnacle sets and study various enumerative questions related to these objects.     

Tragoponol, a dimeric dihydroisocoumarin from Tragopogon porrifolius L.

A phytochemical re-investigation of Tragopogon porrifolius L. (Asteraceae) yielded (7S,15S)-2,4,12-trihydroxy-7-(4-hydroxyphenyl)-10-methoxy-15-(4-methoxyphenyl)-7,8,15,16-tetrahydrodibenzo[c,i][1,7]dioxacyclododecine-5,13-dione, named tragoponol, a dimeric dihydroisocoumarin.The compound, which represents the first of its kind, is comprised of the open-chained forms of two different mono-methoxylated dihydroisocoumarin moieties, scorzocreticin and hongkongenin, which are connected via two ester bonds to form a macrolide with two lactone moieties featuring a 12-membered ring. The structure of the nearly symmetrical compound was established by HR mass spectrometry, CD measurements, and extensive 1D and 2D NMR experiments.