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Fourier-transform Ion Cyclotron Resonance Mass Spectrometry (fourier-transform + ion_cyclotron_resonance_mass_spectrometry)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

Gas-phase radical,radical recombination reactions of nitroxides with substituted phenyl radicals

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2004
J. L. Heidbrink
Fourier-transform ion cyclotron resonance mass spectrometry has been used to examine gas-phase reactions of four different nitroxide free radicals with eight positively charged pyridyl and phenyl radicals (some containing a Cl, F, or CF3 substituent). All the radicals reacted rapidly (near collision rate) with nitroxides by radical,radical recombination. However, some of the radicals were also able to abstract a hydrogen atom from the nitroxide. The results establish that the efficiency (kreaction/kcollision) of hydrogen atom abstraction varies with the electrophilicity of the radical, and hence is attributable to polar effects (a lowering of the transition-state energy by an increase in its polar character). The efficiency of the recombination reaction is not sensitive to substituents, presumably due to a very low reaction barrier. Even so, after radical,radical recombination has occurred, the nitroxide adduct was found to fragment in different ways depending on the structure of the radical. For example, a cationic fragment was eliminated from the adducts of the more electrophilic radicals via oxygen anion abstraction by the radical (i.e., the nitroxide adduct cleaves heterolytically), whereas adducts of the less electrophilic radicals predominantly fragmented via homolytic cleavage (oxygen atom abstraction). Therefore, differences in the product branching ratios were found to be attributable to polar factors. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 216,229 2004 [source]

Studies of the intermolecular DNA triplexes of C+·GC and T·AT triplets by electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry

JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 2 2008
Cuihong Wan
Abstract Formation and stabilities of four 14-mer intermolecular DNA triplexes, consisting of third strands with repeating sequence CTCT, CCTT, CTT, or TTT, were studied by electrospray ionization Fourier-transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) in the gas phase. The gas-phase stabilities of the triplexes were compared with their CD spectra and melting behaviors in solution, and parallel correlation between two phases were obtained. In the presence of 20 mM NH4+ (pH 5.5), the formation of the TTT triplex was not detected in both solution and the gas phase. Other triplexes showed the same order, CTCT > CCTT > CTT, of ion abundances in mass spectra and Tm values in solution. The more stable triplexes are those that contained higher percentage of C+·GC triplets and an alternating CT sequence. However, the CCTT with the same C+·GC triplets as the CTCT showed a higher stability than the latter during the gas-phase dissociation. Furthermore, a biphasic triplex-to-duplex-to-single transition was detected in the gas phase, while a monophasic triplex-to-single dissociation was observed in solution. The present results reveal that hydrogen bonds and electrostatic interactions dominate in the gas phase, while base stacking and hydrophobic interactions dominate in solution to stabilize the triplexes. Moreover, weak acidic conditions (pH 5,6) promote the formation of the parallel triplexes. Copyright © 2007 John Wiley & Sons, Ltd. [source]

The Structure of a Novel Neutral Lipid,A from the Lipopolysaccharide of Bradyrhizobium elkanii Containing Three Mannose Units in the Backbone

CHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2010
Iwona Komaniecka Dr.
Abstract The chemical structure of the lipid,A of the lipopolysaccharide (LPS) from Bradyrhizobium elkanii USDA 76 (a member of the group of slow-growing rhizobia) has been established. It differed considerably from lipids,A of other Gram-negative bacteria, in that it completely lacks negatively charged groups (phosphate or uronic acid residues); the glucosamine (GlcpN) disaccharide backbone is replaced by one consisting of 2,3-dideoxy-2,3-diamino- D -glucopyranose (GlcpN3N) and it contains two long-chain fatty acids, which is unusual among rhizobia. The GlcpN3N disaccharide was further substituted by three D -mannopyranose (D -Manp) residues, together forming a pentasaccharide. To establish the structural details of this molecule, 1D and 2D,NMR spectroscopy, chemical composition analyses and high-resolution mass spectrometry methods (electrospray ionisation Fourier-transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) and tandem mass spectrometry (MS/MS)) were applied. By using 1D and 2D,NMR spectroscopy experiments, it was confirmed that one D -Manp was linked to C-1 of the reducing GlcpN3N and an ,-(1,6)-linked D -Manp disaccharide was located at C-4, of the non-reducing GlcpN3N (,-linkage). Fatty acid analysis identified 12:0(3-OH) and 14:0(3-OH), which were amide-linked to GlcpN3N. Other lipid,A constituents were long (,-1)-hydroxylated fatty acids with 26,33 carbon atoms, as well as their oxo forms (28:0(27-oxo) and 30:0(29-oxo)). The 28:0(27-OH) was the most abundant acyl residue. As confirmed by high-resolution mass spectrometry techniques, these long-chain fatty acids created two acyloxyacyl residues with the 3-hydroxy fatty acids. Thus, lipid,A from B. elkanii comprised six acyl residues. It was also shown that one of the acyloxyacyl residues could be further acylated by 3-hydroxybutyric acid (linked to the (,-1)-hydroxy group). [source]