The mass spectra of aluminum isopropoxide

The mass spectra of aluminum isopropoxide show that polymers, [Al(OC₃H₇)₃]_x where x = 1 to 7, can be present in the vapor and are, therefore, probably present in the bulk sample. The polymeric composition of the vapor depends on the previous history of the sample. Exact mass measurements on many of the ions along with data on a number of metastable peaks support the proposed fragmentation mechanisms. Loss of 102 mass units between intense peaks in the mass range above 500 a.m.u. leads to the suggestion that the higher polymers may be used as high mass marking substances.     

Chrysomelidial by chromyl chloride oxidation: A revised structure for gastrolactone

Non-conjugated $\text{gem}$-dialkylated alkenes were oxidized to aldehydes in the presence of α,β-unsaturated carbonyl functional groups, providing a new synthesis of $\text{1}$ and a synthesis of $\text{2}$ that led to a revised structure for gastrolactone.     

Quantitative variability in the 252Cf plasma desorption mass spectra of triglycerides and waxes

A series of mixtures of solid triglycerides and waxes are examined using ²⁵²Cf plasma desorption mass spectrometry. The relative abundances of diagnostic ions are found to vary with sample preparation, handling, and composition. It is proposed that the less efficiently packing, shorter chain, compounds are forced to the analysis site, i.e. the surface. This takes place at varying rates that reflect the bulk properties of the mixture as revealed by its phase diagram and thermal history. Mixtures that remain liquids during analysis show ion abundances correctly reflecting their composition. Mixtures of isotopomeric glycerides also show normal ion abundances.     

Structural assignment of isomeric 2-(2-quinolinyl)-1H-indene-1,3(2H)-dione mono- and disulfonic acids by liquid chromatography electrospray and atmospheric pressure chemical ionization tandem mass spectrometry

Positionally isomeric 2-(2-quinolinyl)-1H-indene-1,3(2H)-dione mono- and disulfonic acids give rise to similar electrospray ionization (ESI) and atmosphere pressure chemical ionization (APCI) mass spectra, which show very abundant MH(+) ions and negligible fragmentation. The MH(+) ions of these isomeric acids exhibit notably different behavior under collision-induced dissociation (CID) conditions. The acids with a sulfonic group at position 8' in the quinoline moiety, adjacent to the N-atom, exhibit highly abundant [MH - H(2)SO(3)](+) ions (m/z 272 for the mono- and m/z 352 for the disulfonic acids), which are of lower abundance in the CID spectra of isomers with the SO(3)H group at other positions, remote from the nitrogen atom. The latter isomers undergo efficient eliminations of SO(3) and HSO(3). The isomeric diacids with one SO(3)H group at position 4 of the indene-1,3(2H)-dione moiety, adjacent to one of the carbonyl groups, undergo highly efficient elimination of H(2)O. Mechanistic pathways, involving interactions between adjacent groups, are proposed for the above regiospecific fragmentations. Pronounced different behavior has been also observed in negative ion tandem mass spectrometric measurements of the sulfonic acids. The distinctive behavior of the isomeric acids was strongly pronounced when the measurements were performed with an ion trap mass spectrometer (LCQ), and much less so with a triple-stage quadrupole instrument (TSQ).     

Plasma desorption mass spectrometry of transition metal complexes of thio- and selenosemicarbazones of 2-acetylpyridines

Summary Californium-252 plasma desorption mass spectra were recorded for complexes of the anions of various thio-and seleno-semicarbazones of 3-acetylpyridines(1–4) with the transition metal ions iron(III) and cobalt(II). Positive ion spectra gave clear evidence of the cation present and fragmentation with loss of ligands or parts of ligands was straightforward. Negative ion spectra likewise provided evidence of the intact anion except with tetracoordinate metal halide systems [MX₄]^– which lost one or more halide atoms. Evidence of fragmentation of the ligand and recombination of the fragments with the metal ion was also observed in the negative ion mode. Spectra were used to revise the structure of a complex previously reported as [FeLCl₂]⁽¹⁾ to [FeL₂]⁺[FeCl₄]^–.     

Elektroanalyse

Ohne Zusammenfassung     

Intramolecular cross-linking experiments on cytochrome c and ribonuclease A using an isotope multiplet method.

Mass spectral analysis of tryptic digests of cross-linked proteins offers considerable promise as a simple technique to probe protein structure and study protein-protein interactions. We describe the use of a 1:1 mixture of isotopically labeled and unlabeled cross-linkers, disuccinimidyladipate (DSA) and dimethyladipimidate (DMA), to enhance visualization of cross-linked peptides in a tryptic digest. Optimized intramolecular reactions of cytochrome c and ribonuclease A (RNase A) with DSA yielded an average of two cross-links per protein molecule. After digestion of the cross-linked cytochrome c with trypsin and analysis by liquid chromatography/mass spectrometry (LC/MS) and matrix-assisted laser desorption/ionization (MALDI), eight modified peptides, five cross-linked and two end-capped, were detected by virtue of their doublet character. An eighth modified peptide's identity remained ambiguous because of its inability to fragment. The lysine-lysine distance constraints obtained are discussed in the context of the known NMR and X-ray structures of cytochrome c. Analysis of cross-linked RNase A by LC/MS and MALDI yielded nine modified peptides, four of which were modified twice, as indicated by the isotopic triplets. Although seven of these peptides contained cross-links, few distance constraints were gained due to the fact that the cross-linked products were variations of modification of the same three lysine residues.     

Infrared Multiple Photon Dissociation Action Spectroscopy and Theoretical Studies of Diethyl Phosphate Complexes: Effects of Protonation and Sodium Cationization on Structure

The gas-phase structures of deprotonated, protonated, and sodium-cationized complexes of diethyl phosphate (DEP) including [DEP − H]⁻, [DEP + H]⁺, [DEP + Na]⁺, and [DEP − H + 2Na]⁺ are examined via infrared multiple photon dissociation (IRMPD) action spectroscopy using tunable IR radiation generated by a free electron laser, a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) with an electrospray ionization (ESI) source, and theoretical electronic structure calculations. Measured IRMPD spectra are compared to linear IR spectra calculated at the B3LYP/6-31G(d,p) level of theory to identify the structures accessed in the experimental studies. For comparison, theoretical studies of neutral complexes are also performed. These experiments and calculations suggest that specific geometric changes occur upon the binding of protons and/or sodium cations, including changes correlating to nucleic acid backbone geometry, specifically P–O bond lengths and ∠OPO bond angles. Information from these observations may be used to gain insight into the structures of more complex systems, such as nucleotides and solvated nucleic acids.