Infrared multiple photon dissociation spectroscopy of sodium and potassium chlorate anions

The structures of gas‐phase, metal chlorate anions with the formula [M(ClO₃)₂]^?, M = Na and K, were determined using tandem mass spectrometry and infrared multiple photon dissociation (IRMPD) spectroscopy. Structural assignments for both anions are based on comparisons of the experimental vibrational spectra for the two species with those predicted by density functional theory (DFT) and involve conformations that feature either bidentate or tridentate coordination of the cation by chlorate. Our results strongly suggest that a structure in which both chlorate anions are bidentate ligands is preferred for [Na(ClO₃)₂]^?. However, for [K(ClO₃)₂]^? the best agreement between experimental and theoretical spectra is obtained from a composite of predicted spectra for which the chlorate anions are either both bidentate or both tridentate ligands. In general, we find that the overall accuracy of DFT calculations for prediction of IR spectra is dependent on both functional and basis set, with best agreement achieved using frequencies generated at the B3LYP/6‐311+g(3df) level of theory. Copyright © 2009 John Wiley & Sons, Ltd.     

Probing the interaction of the potassium channel modulating KCNE1 in lipid bilayers via solid‐state NMR spectroscopy

KCNE1 is known to modulate the voltage‐gated potassium channel α subunit KCNQ1 to generate slowly activating potassium currents. This potassium channel is essential for the cardiac action potential that mediates a heartbeat as well as the potassium ion homeostasis in the inner ear. Therefore, it is important to know the structure and dynamics of KCNE1 to better understand its modulatory role. Previously, the Sanders group solved the three‐dimensional structure of KCNE1 in LMPG micelles, which yielded a better understanding of this KCNQ1/KCNE1 channel activity. However, research in the Lorigan group showed different structural properties of KCNE1 when incorporated into POPC/POPG lipid bilayers as opposed to LMPG micelles. It is hence necessary to study the structure of KCNE1 in a more native‐like environment such as multi‐lamellar vesicles. In this study, the dynamics of lipid bilayers upon incorporation of the membrane protein KCNE1 were investigated using ³¹P solid‐state nuclear magnetic resonance (NMR) spectroscopy. Specifically, the protein/lipid interaction was studied at varying molar ratios of protein to lipid content. The static ³¹P NMR and T₁ relaxation time were investigated. The ³¹P NMR powder spectra indicated significant perturbations of KCNE1 on the phospholipid headgroups of multi‐lamellar vesicles as shown from the changes in the ³¹P spectral line shape and the chemical shift anisotropy line width. ³¹P T₁ relaxation times were shown to be reversely proportional to the molar ratios of KCNE1 incorporated. The ³¹P NMR data clearly indicate that KCNE1 interacts with the membrane. Copyright © 2017 John Wiley & Sons, Ltd.     

Zur Bestimmunz der Oxyfetts?uren

Ohne Zusammenfassung     

Thin‐layer chromatography and mass spectrometry coupled using proximal probe thermal desorption with electrospray or atmospheric pressure chemical ionization

An atmospheric pressure proximal probe thermal desorption sampling method coupled with secondary ionization by electrospray or atmospheric pressure chemical ionization was demonstrated for the mass spectrometric analysis of a diverse set of compounds (dyestuffs, pharmaceuticals, explosives and pesticides) separated on various high‐performance thin‐layer chromatography plates. Line scans along or through development lanes on the plates were carried out by moving the plate relative to a stationary heated probe positioned close to or just touching the stationary phase surface. Vapors of the compounds thermally desorbed from the surface were drawn into the ionization region of a combined electrospray ionization/atmospheric pressure chemical ionization source where they merged with reagent ions and/or charged droplets from a corona discharge or an electrospray emitter and were ionized. The ionized components were then drawn through the atmospheric pressure sampling orifice into the vacuum region of a triple quadrupole mass spectrometer and detected using full scan, single ion monitoring, or selected reaction monitoring mode. Studies of variable parameters and performance metrics including the proximal probe temperature, gas flow rate into the ionization region, surface scan speed, read‐out resolution, detection limits, and surface type are discussed. Published in 2010 by John Wiley & Sons, Ltd.     

X-ray crystal structure of cis-{(±)-6,6′-[[1,1′-biphenyl]-2,2′-diylbis(oxy)]bis–dibenzo[d,f][1,3,2]dioxaphosphepin} diiodoplatinum(II)·dichloromethane

Bis(dibenzo[d,f][1,3,2]dixoaphosphepin) ligands are extensively used in catalysts for asymmetric alkene hydroformylation; however, few crystal structures of complexes of these ligands have been reported. In this paper, the synthesis and X-ray crystal structure of cis-{(±)-6,6-[[1,1-biphenyl]-2,2-diylbis(oxy)]bis-dibenzo[d,f][1,3,2]dioxaphosphepin} diiodoplatinum (II)·dichloromethane are presented. This complex crystallizes in the triclinic space group P1¯ with a = 12.0842(2,3) b = 12.6993(15) c = 13.2801(18) Å; = 85.852(10), = 76.723(13), = 72.400(12)°, V = 1890.7(10) ų and Z = 4. The diastereomer that has crystallized has an R*R*R*(S*S*S*) configuration. This X-ray crystal structure supports previous observations that bis(phosphite) ligands with bridging groups derived from 2,2-biphenol can exhibit a wide range of bite angles (>20°).     

Maximum estimates for oblique derivative problems with right hand side in L p , p<n

If u is a solution of the second order elliptic differential equation Lu=f in some Lipschitz domain in ⁿ , we estimate the maximum of u in terms of some oblique derivative prescribed on the boundary of the domain and in terms of the L ^p norm of f with p<n.     

Characterization and use of a Raman liquid-core waveguide sensor using preconcentration principles

A novel Raman sensor using a liquid-core optical waveguide is reported, implementing a Teflon-AF 2400 tube filled with water. An aqueous analyte mixture of benzene, toluene and p-xylene was introduced using a 1000 μl sample loop to the liquid-core waveguide (LCW) sensor and the analytes were preconcentrated on the inside surface of the waveguide tubing. The analytes were then eluted from the waveguide using an acetonitrile-water solvent mixture injected via a 30 μl eluting solvent loop. The preconcentration factor was experimentally determined to be 14-fold, in reasonable agreement with the theoretical preconcentration factor of 33 based upon the sample volume to elution volume ratio. Raman spectra of benzene, toluene and p-xylene were obtained during elution. It was found that analytically useful Raman signals for benzene, toluene and p-xylene were obtained at 992, 1004 and 1206 cm⁻¹, respectively. The relative standard deviation of the method was 3% for three replicate measurements. The limit of detection (LOD) was determined to be 730 ppb (parts per billion by volume) for benzene, exceptional for a system that does not resort to surface enhancement or resonance Raman approaches. The Raman spectra of these test analytes were evaluated for qualitative and quantitative analysis utility.     

Determining the scope of the organolanthanide-catalyzed, sequential intramolecular amination/cyclization reaction: formation of substituted quinolizidines, indolizidines, and pyrrolizidines

The scope of the lanthanide-mediated, intramolecular amination/cyclization reaction was determined for the formation of substituted quinolizidines, indolizidines, and pyrrolizidines. A methyl group was installed at diverse positions in the substrates to determine the sense and magnitude of diastereoselection. High diastereoselectivity (>20:1) was achieved for the formation of some quinolizidines and indolizidines. The sense of relative asymmetric induction was contrary to previously studied systems, and although some questions remain, a rationalization for these results is put forward.     

An overview of some recent developments in ionization methods for mass spectrometry

An overview of some recent advances in ionization sources for mass spectrometry is presented. Limitations were set so that the overview covers ionization techniques relevant to organic and biological analysis that have appeared in the literature since the year 2000. No effort is made to be comprehensive. Rather, a broad sweep overview of author-subjective highlights among a wide variety of sources is presented. These ionization sources include electron ionization, chemical ionization, various atmospheric plasma ionization sources, laser desorption sources, sonic spray and electrospray ionization sources.