Armelle Buzy

Mass spectral characterization of the thermal degradation of poly(propylene oxide) by electrospray and matrix-assisted laser desorption ionization

Abstract The thermal degradation of poly(propylene oxide) (PPO), M n = 2000, can be characterized by electrospray (ESI) and matrix-assisted laser desorption ionization (MALDI). ESI and MALDI spectra of partially degraded PPO provide strong support for the thermal degradation pathway previously suggested by Griffiths et al. and Lemaire et al. Although these pathways differ in detail, it is not possible to distinguish between them from the masses of the resultant degradation species. Gel permeation chromatography data indicate that both mass spectrometric methods emphasize the presence of low-mass material, particularly in the degraded samples. This is attributed to the different sensitivities of the two techniques and some in situ fragmentation during mass spectrometric analysis.

A mechanism for the loss of 60 u from peptides containing an arginine residue at the C-terminus

The loss of 60 u from protonated peptide ions containing an arginine residue at the C-terminus has been investigated by means of low energy tandem mass spectrometry. The lowest energy conformation of singly charged bradykinin is thought to involve a salt-bridge structure, which may lead to the formation of two isomeric forms. It is thought that one isomer retains the ionizing proton at the C-terminal end of the peptide, leading to the formation of the [bn−1 + H + OH]+ fragment ion, and the other isomer retains the charge at the N-terminus, leading to the formation of the [M + H − 60]+ fragment ion. It was found that the formation of the [M + H − 60]+ ion occurs only from singly charged precursor ions. In addition, the loss of 60 u occurs from peptides in which the charge is localized at the N-terminus. These results indicate that the mechanism of formation of the [M + H − 60]+ ion may be driven by a charge-remote process.

The application of electrospray ionisation and tandem mass spectrometry to the analysis of polymer additives

Electrospray ionisation (ESI) has been employed in conjunction with tandem mass spectrometry (MS/MS) on a tandem quadrupole mass spectrometer for the analysis of five common organic polymer additives. The distribution of fragment ions and molecule ions observed in the mass spectra was found to be highly dependent on the skimmer cone voltage that was used, especially for the additives of lowest molecular weight (relative molecular mass). The skimmer cone voltage and the collision energy were very important in determining the envelope of fragment ions that were seen in the collision induced dissociation (CID) spectra. Mechanisms and fragmentation pathways have been proposed for many of the product ions that were observed in the CID spectra.

Electrospray ionization mass spectrometric study of oligomeric linear polysulfides : characterization of repeat units, end groups and fragmentation pathways

Abstract Electrospray ionization mass spectrometry is shown to offer excellent characterization of linear oligomeric polysulfides H(SC2H4OCH2OC2H4S)nH with n = 1–24. Analysis of the mass spectra reveals the presence of individual oligomers, the presence in certain oligomers of repeat units containing additional oxyalkylene groups (and in some cases a monosulfide link rather than disulfide) and the presence of end groups such as epoxy. The attachment of polyacrylates during cure can also be detected. Assignments of individual peaks can be confirmed by collision-induced decomposition and precursor ion experiments: the fragmentation pathways are relatively few except for linear polysulfides of complex structure. The best signal-to-noise conditions are achieved with low-to-medium cone voltages and a mobile phase of acetone containing 0.5% KI.

Mass spectral characterization of oligomeric polysulfides by electrospray ionization combined with collision-induced decomposition

Abstract Polysulfide oligomers H(SC 2 H 4 OCH 2 OC 2 H 4 S) n H with n = 1–24 can be characterized by electrospray ionization mass spectrometry. Samples prepared by the conventional method are shown to contain up to eight series of oligomers differing in structure by one of a small group of variants in one (or sometimes two) of the repeat units, e.g. with one less S atom or an additional CH 2 O group. The composition of individual ions can be confirmed by collision-induced decomposition of cationized polysulfides, which yields unambiguous spectra of the fragmented ions.

Mass spectral characterization of linear and cyclic forms of oligomeric nitrated polyethers by electrospray ionization: specific cationization effects in cyclic polyethers

Abstract Electrospray ionization mass spectrometry provides a highly detailed picture of the various species present in the high energy material poly(3-nitratomethyl-3-methyloxetane), also known as polynimmo. Polynimmo contains up to 18 cyclic oligomers in addition to the dominant tetramer, the highest species detected containing 22 repeat units. Linear oligomers from the tetramer up to species of mass 3200 Da are detected, affording the characterization of several new combinations of end groups X, Y in X-[nimmo] n -Y. Various cations can be used to generate the cationized species, and highly specific cation cyclic oligomer interactions are apparent in the adducts with Na + , K + , NH 4 + and H + : some of these can be rationalized through molecular modelling calculations. The cone voltage applied in the e.s.i. experiment is highly significant in influencing the relative abundances of high- and low-molecular mass ions and in the relative amounts of H + and NH 4 + adducts in cationization experiments with NH 4 Cl. Despite giving highly accurate relative molar masses of individual species within polynimmo, the e.s.i. technique fails to give accurate molecular mass distributions, especially as no doubly- or triply-charged ions are found.

Electrospray ionisation mass spectrometry (ESI MS) of poly(methyl methacrylate) and acrylic statistical copolymers

ESI MS is found to an effective tool for the analysis of poly(methyl methacrylate); optimum conditions involve the use of K+ counter ion at relatively high cone voltage; ESI MS is used for end-group and copolymer compositional analysis.

Electrospray ionisation studies of the interaction of N,N'-dicyclohexylcarbodiimide with ceroid lipofuscinosis protein (subunit c)

N,N′-dicyclohexylcarbodiimide (DCCD) interacts with isolated ceroid lipofuscinosis protein (CLP), a model for subunit c. The products are (a) CLP–DCCD adduct (+206 Da), presumably by addition at Glu-58; (b) acetyl–CLP–DCCD (+42 Da + 206 Da); (c) acetyl–CLP (+42 Da). Under specific conditions, additional DCCD adducts are formed; CLP–DCCD–DCCD (+206 Da + 206 Da) and acetyl–CLP–DCCD–DCCD (+42 Da + 206 Da + 206 Da). Acetylation utilises the acetate present in CLP preparations as a buffer and the site is shown to be located within amino acids 1–9 (probably Lys-7 or N-terminal aspartate). Acetyl–CLP is shown to be the primary product but, in addition, acylation by other fatty acids (myristate, palmitate, oleate and stearate) can be demonstrated in low acetate concentrations. Oligomycin is shown to modify some interactions of CLP with DCCD but venturicidin has little or no effect.