Collection method for chemical particulates on surfaces with detection using thermal desorption-ion trap mass spectrometry

Successful analysis of particulate/low vapor pressure analytes such as explosives and toxic chemicals, and commercial pesticides require new sampling tools that enable detection of these analytes using current vapor phase detection instruments. We describe a sampling approach that uses stainless steel screens coated with a sticky polydimethyl siloxane (PDMS) coating to capture particulates from surfaces. Preliminary results for the collection of dimethyl methylphosphonate (DMMP) sorbed onto silica gel (SG) particulates (DMMP/SG) from a surface with subsequent analysis by thermal desorption-cylindrical ion trap mass spectrometry (TD-CITMS) are reported.     

Atmospheric pressure chemical ionization of alkanes,alkenes, and cycloalkanes

Normal and cyclic alkanes and alkenes form stable gas-phase ions in air at atmospheric pressure from 40 to 200°C when moisture is below 1 ppm. Ionization of alkanes in a ⁶³Ni source favored charge transfer over proton transfer through pathways involving [M?1]⁺ and [M?3]⁺ ions. Ion mobility spectra for alkanes showed sharp and symmetrical profiles while spectra for alkenes suggested fragmentation. Ion identifications were made by using mass spectrometry, and ionization pathways were supported by using deuterated analogs of alkanes and alkenes. Alkanes were ionized seemingly through a hydrogen abstraction pathway and did not proceed through an alkene intermediate. New methods for interpretation of mobility spectra utilizing ion mobility spectrometry, atmospheric pressure chemical ionization mass spectrometry, chemical ionization mass spectrometry, and ion mobility spectrometry-mass spectrometry data were demonstrated.     

The Reactivities of Iminoboranes with Carbenes: BN Isosteres of Carbene–Alkyne Adducts

The first examples of adducts of cyclic alkyl(amino) carbenes (CAAC) and N‐heterocyclic carbenes (NHCs) with iminoboranes have been synthesized and isolated at low temperature (?45 °C). The adducts show short B?N bonds and planarity at boron, mimicking the structures of the isoelectronic imine functionality. When di‐tert‐butyliminoborane was reacted with 1,3‐bis(isopropyl)imidazol‐2‐ylidene (IPr), the initially formed Lewis acid–base adduct quickly rearranged to form a new carbene substituted with an aminoborane at the 4‐position. Warming the iminoborane–CAAC adduct to room temperature resulted in an intramolecular cyclization to give a bicyclic 1,2‐azaborilidine compound.     

Exclusive π Encapsulation of Light Alkali Metal Cations by a Neutral Molecule

Cation–π interactions are one of the most important classes of noncovalent bonding, and are seen throughout biology, chemistry, and materials science. However, in almost every documented case, these interactions play only a supporting role to much stronger covalent or dative bonds, thus making examples of exclusive cation–π bonding exceedingly rare. In this study, a neutral diboryne molecule is found to encapsulate the light alkali metal cations Li⁺ and Na⁺ in the absence of a net charge, covalent bonds, or lone‐pair donor groups. The resulting encapsulation complexes are, to our knowledge, the first structurally authenticated species in which a neutral molecule binds the light alkali metals exclusively through cation–π interactions.     

Generation of 1,2-azaboretidines via reduction of ADC borane adducts

Reaction of the acyclic (diamino)carbene (ADC) :C(NiPr₂)₂ (1) with different dihaloboranes of the type RBX₂ (R = Mes, Dur; X = Cl, Br) smoothly afforded a novel class of ADC-stabilized borane adducts. For MesBBr₂ however, the reaction did not stop at the adduct level, but an uncommon rearrangement process occurred, which eventually resulted in the formation of a 5-membered boracycle after elimination of mesitylene. Chemical reduction of the ADC borane adducts by KC₈ selectively yielded air stable 1,2-azaboretidines. Detailed DFT studies suggest a reduction mechanism involving a highly reactive borylene intermediate, which is converted into the boracycles via a rearrangement/C–H activation sequence.     

Correlative Cellular Mass Spectrometry Imaging and Amperometry Show Dose Dependent Changes in Lipid Composition and Exocytosis

Aberrant functioning of the proteasome has been associated with crucial pathologic conditions including neurodegeneration. Yet, the complex underlying causes at the cellular level remain unclear and there are conflicting reports of neuroprotective to neurodegenerative effects of proteasomal inhibitors such as lactacystin that are utilised as models for neurodegenerative diseases. The conflicting results may be associated with different dose regimes of lactacystin and hence we have performed a dose dependent study of the effects of lactacystin to identify concurrent changes in the cell membrane lipid profile and the dynamics of exocytosis using a combination of surface sensitive mass spectrometry and single cell amperometry. Significant changes of negatively charged lipids were associated with different lactacystin doses that showed a weak correlation with exocytosis while changes in PE and PE−O lipids showed dose dependent changes correlated with initial pore formation and total release of vesicle content respectively.     

Quantifying Intracellular Single Vesicular Catecholamine Concentration with Open Carbon Nanopipettes to Unveil the Effect of L-DOPA on Vesicular Structure

Understanding the regulatory mechanisms of exocytosis is essential for uncovering the pathologies of neuronal disorders and developing related pharmaceuticals. In this work intracellular vesicle impact electrochemical cytometry (IVIEC) measurements with different-sized (50–500 nm radius) open carbon nanopipettes (CNPs) were performed to quantify the vesicular content and release kinetics of specific vesicle populations grouped by orifice sizes. Intracellular vesicles with radius below 100 nm were captured and narrowed between 50 and 100 nm. On the basis of this, single vesicular catecholamine concentrations in the intracellular environment were quantified as 0.23–1.1 M. Our results with L-3,4-dihydroxyphenylalanine (L-DOPA)-exposure indicate that L-DOPA regulates exocytosis by increasing the dense core size and vesicular content while catecholamine concentrations did not show obvious alterations. These were all achieved simultaneously and relatively noninvasively with open CNPs.     

ChemInform Abstract: Pressure‐Induced Phase Transitions of β‐Type Pyrochlore CsTaWO6.

Polycrystalline CsTaWO₆ is prepared by calcination of stoichiometric amounts of Cs₂CO₃, Ta₂O₅, and WO₃ in air (1.