			Home About us Contact

Ion Groups (ion + groups)

Distribution by Scientific Domains

Chemistry	75%

Selected Abstracts

Mono and double polar [4 + 2+] Diels,Alder cycloaddition of acylium ions with O -heterodienes

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 2 2002
Eduardo C. Meurer
Abstract Gas-phase reactions of acylium ions with ,,,-unsaturated carbonyl compounds were investigated using pentaquadrupole multiple-stage mass spectrometry. With acrolein and metacrolein, CH3,C+O, CH2CH,C+O, C6H5,C+O, and (CH3)2N,C+O react to variable extents by mono and double polar [4 + 2+] Diels,Alder cycloaddition. With ethyl vinyl ketone, CH3,C+O reacts exclusively by proton transfer and C6H5,C+O forms only the mono cycloadduct whereas CH2CH,C+O and (CH3)2N,C+O reacts to great extents by mono and double cycloaddition. The positively charged acylium ions are activated O -heterodienophiles, and mono cycloaddition occurs readily across their C+O bonds to form resonance-stabilized 1,3-dioxinylium ions which, upon collisional activation, dissociate predominantly by retro-addition. The mono cycloadducts are also dienophiles activated by resonance-stabilized and chemically inert 1,3-dioxonium ion groups, hence they undergo a second cycloaddition across their polarized CC ring double bonds. 18O labeling and characteristic dissociations displayed by the double cycloadducts indicate the site and regioselectivity of double cycloaddition, which are corroborated by Becke3LYP/6,311++G(d,p) calculations. Most double cycloadducts dissociate by the loss of a RCO2COR1 molecule and by a pathway that reforms the acylium ion directly. The double cycloadduct of the thioacylium ion (CH3)2N,C+S with acrolein dissociates to (CH3)2N,C+O in a sulfur-by-oxygen replacement process intermediated by the cyclic monoadduct. The double cycloaddition can be viewed as a charge-remote type of polar [4 + 2+] Diels,Alder cycloaddition reaction. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Metal ion analysis using microchip CE with chemiluminescence detection based on 1,10-phenanthroline,hydrogen peroxide reaction

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 3 2009
Takahiro Nogami
Abstract We developed a microchip CE method with chemiluminescence (CL) detection using the reaction of 1,10-phenanthroline and hydrogen peroxide for separation and determination of metal ions, where the metal ions acted as catalysts for the CL reaction. The microchip consisted of two microchannels that crossed at the intersection and four reservoirs that accessed the ends of the channels. The metal ions in the sample solution migrated in the channel along with 1,10-phenanthroline included in a running solution, and then mixed with hydrogen peroxide in one of the reservoirs to emit CL. The light was detected with a photomultiplier tube located just above the reservoir. Two metal ion groups, the platinum metal group (Ru(III), Rh(III), Pd(II), Os(VIII), Ir(III), and Pt(IV)) and the fourth periodic transition metal group (Cu(II), Fe(II), Co(II), and Ni(II)) were examined using the present system. The lowest detection limit was observed for Os(VIII); Os(VIII) responded over the range of 7.5×10,12,1.0×10,8 M with the detection limit of 7.5×10,12 M (about 38 zmol) (S/N = 3). The mixed solution of Ru(III), Rh(III), Pd(II), Os(VIII), Ir(III), and Pt(IV) could be analyzed using this system within about 2.5 min. In addition, the system was applied to the determination of Cu(II) concentration in a city water supply. [source]

Swelling behavior of pH- and temperature-sensitive copolymers containing 2-hydroxy-ethyl methacrylate and N -vinyl-2-pyrrolidone crosslinked with new crosslinkers

POLYMER INTERNATIONAL, Issue 11 2004
Prof. Ayman M Atta
Abstract Copolymers of 2-hydroxyethyl methacrylate (HEMA) and N -vinyl-2-pyrrolidone (VP) and homopolymers of HEMA and VP were crosslinked in the presence of different mol% of melamine trimethacrylamide (MMAm) and melamine triacrylamide (MAAm) as crosslinkers by bulk radical polymerization. The resultant xerogels were characterized by extracting the soluble fractions and measuring the equilibrium water content. Lower critical solution transition temperatures (LCST) were measured by DSC. The properties of crosslinked HEMA and VP copolymers, VP and HEMA series were evaluated in terms of compositional drift of polymerization, heterogeneous crosslinking, and chemical structure of the relevant components. Soluble fractions of the crosslinked networks were reduced by varying the MAAm and MMAm concentrations. The influence of environmental conditions such as temperature and pH on the swelling behavior of these polymeric gels was investigated. The swelling behaviors of the resulting gels show pH sensitivity. This behavior is explained on the basis that amide groups of VP or crosslinkers could be hydrolyzed to form negatively charged carboxylate ion groups in the produced networks in response to an external pH variation. Copyright © 2004 Society of Chemical Industry [source]

Studies on azaspiracid biotoxins.

RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2002

In this report, the mass spectral analysis of azaspiracid biotoxins is described. Specifically, the collision-induced dissociation (CID) behavior and differences between CID spectra obtained on a triple-quadrupole, a quadrupole time-of-flight, and an ion-trap mass spectrometer are addressed here. The CID spectra obtained on the triple-quadrupole mass spectrometer allowed the classification of the major product ions of the five investigated compounds (AZA 1,5) into five distinct fragment ion groups, according to the backbone cleavage positions. Although the identification of unknown azaspiracids was difficult based on CID alone, the spectra provided sufficient structural information to allow confirmation of known azaspiracids in marine samples. Furthermore, we were able to detect two new azaspiracid analogs (AZA 1b and 6) in our samples and provide a preliminary structural analysis. The proposed dissociation pathways under tandem mass spectrometry (MS/MS) conditions were confirmed by a comparison with accurate mass data from electrospray quadrupole time-of-flight MS/MS experiments. Regular sequential MSn analysis on an ion-trap mass spectrometer was more restricted in comparison to the triple-quadrupole mass spectrometer, because the azaspiracids underwent multiple [M,+,H,,,nH2O]+ (n,=,1,6) losses from the precursor ion under CID. Thus, the structural information obtained from MSn experiments was somewhat limited. To overcome this limitation, we developed a wide-range excitation technique using a 180-u window that provided results comparable to the triple-quadrupole instrument. To demonstrate the potential of the method, we applied it to the analysis of degraded azaspiracids from mussel tissue extracts. Copyright © 2002 John Wiley & Sons, Ltd. [source]