Differentiation of isobaric compounds using chemical ionization reaction mass spectrometry

The technique of proton transfer reaction mass spectrometry (PTR-MS) couples a proton transfer reagent, usually H3O+, with a drift tube and mass spectrometer to determine concentrations of volatile organic compounds. Here we describe a first attempt to use chemical ionization (CI) reagents other than proton transfer species inside a PTR-MS instrument. The ability to switch to other types of CI reagents provides an extra dimension to the technique. This capability is demonstrated by focusing on the ability to distinguish several isobaric aldehydes and ketones, including the atmospherically important molecules methacrolein and methyl vinyl ketone. Two CI reagents were selected, H3O+ and NO+, both being cleanly generated in a low intensity radioactive source prior to injection into the drift tube. By recording spectra with both of these reagents, the contributions from different isobaric molecules can be separated by virtue of their unique spectrometric 'fingerprints'. The work demonstrates that this form of instrumentation is not restricted to proton transfer reagents and is the basis of a more general technique, chemical ionization reaction mass spectrometry (CIRMS).     

Monodromy and K-theory of Schubert curves via generalized jeu de taquin

We establish a combinatorial connection between the real geometry and the K-theory of complex Schubert curves \(S(\lambda _\bullet )\), which are one-dimensional Schubert problems defined with respect to flags osculating the rational normal curve. In Levinson (One-dimensional Schubert problems with respect to osculating flags, 2016, doi: 10.4153/CJM-2015-061-1), it was shown that the real geometry of these curves is described by the orbits of a map \(\omega \) on skew tableaux, defined as the commutator of jeu de taquin rectification and promotion. In particular, the real locus of the Schubert curve is naturally a covering space of \({\mathbb {RP}}^1\), with \(\omega \) as the monodromy operator. We provide a fast, local algorithm for computing \(\omega \) without rectifying the skew tableau and show that certain steps in our algorithm are in bijective correspondence with Pechenik and Yong’s genomic tableaux (Pechenik and Yong in Genomic tableaux, 2016. arXiv:1603.08490), which enumerate the K-theoretic Littlewood–Richardson coefficient associated to the Schubert curve. We then give purely combinatorial proofs of several numerical results involving the K-theory and real geometry of \(S(\lambda _\bullet )\).     

A dynamic disorder‐linked reversible phase transition in a new chloroform solvate of cis‐dichloridobis(triethylphosphane)platinum(II)

The title compound, cis‐dichloridobis(triethylphosphane)platinum(II) chloroform monosolvate, [PtCl₂(C₆H₁₅P)₂]·CHCl₃, has been obtained from ligand scrambling in the cis‐[PtCl₂(Cyp₂PCl)(PEt₃)] (Cyp = cyclopentyl) system in CHCl₃ solvent. Unlike the two previously reported unsolvated polymorphs, which are both monoclinic, the compound crystallizes in an orthorhombic setting. Furthermore, the system exhibits a reversible temperature‐dependent structural phase transition, coupling a reduction in anisotropic displacement parameters and a reduction in crystallographic symmetry on cooling. The high‐temperature phase adopts space group Pnma with the complex and solvent molecules sitting across a crystallographic mirror plane (Z′ = 0.5). The low‐temperature phase adopts the space group P2₁2₁2₁ with Z′ = 1.     

The kinetics of the nitrate radical self-reaction

This article describes the first direct determination of the rate coefficient for the self-reaction between two NO₃ radicals. A laser photolysis technique was used to generate NO₃, and time-resolved decays of NO₃ were followed after stopping the photolysis. The products of the reaction are inferred to be NO₂ and O₂. The derived rate coefficient at room temperature for the self-reaction of (2.3 ± 0.8) ×10^?16 cm³ molecule^?1s^?1 is in excellent agreement with the only other data, which were obtained in an indirect study. Consideration is given to the magnitude and influence of secondary chemistry and to the participation of FO in the chemistry of the NO₃ buildup phase. The studies were conducted over a pressure range of 8 to 100 torr in helium. No clear pressure dependence was observed, and some tentative inferences are drawn both from this result and from the absolute magnitude of the rate coefficient about the mechanism of the reaction. There is apparently no role for the reaction in the chemistry of the atmosphere. © 1993 John Wiley & Sons, Inc.     

The synthesis of XTT: A new tetrazolium reagent that is bioreducible to a water-soluble formazan

A new tetrazolium salt, XTT, has been synthesized. XTT is reduced by a considerable variety of cell lines to a water-soluble formazan. XTT appears to merit further investigation as a reagent for broader application to cell culture assay systems.