Tandem mass spectrometry of electrosprayed polyhedral oligomeric silsesquioxane compounds with different substituents
Article first published online: 21 FEB 2012
Copyright © 2012 John Wiley & Sons, Ltd.
Rapid Communications in Mass Spectrometry
Volume 26, Issue 7, pages 765–774, 15 April 2012
How to Cite
Fouquet, T., Phan, T. N. T. and Charles, L. (2012), Tandem mass spectrometry of electrosprayed polyhedral oligomeric silsesquioxane compounds with different substituents. Rapid Commun. Mass Spectrom., 26: 765–774. doi: 10.1002/rcm.6159
- Issue published online: 15 FEB 2012
- Article first published online: 21 FEB 2012
- Manuscript Revised: 9 JAN 2012
- Manuscript Accepted: 9 JAN 2012
- Manuscript Received: 28 NOV 2011
Polyhedral oligomeric silsesquioxanes (POSSs), defined as [RSiO3/2]n with R designating an organic substituent, were considered here as models of highly cross-linked polysiloxanes, to be further used as references in tandem mass spectrometric characterization of plasma polymers of hexamethyldisiloxane, expected to be composed of organic polydimethylsiloxane (PDMS) and inorganic (SiOx) silica-based parts. The collision-induced dissociation (CID) behavior of [RSiO3/2]8 compounds was then studied as a function of the R substituent.
POSS compounds were produced in the gas phase as ammonium adducts and the product ions generated upon CID, amongst which was the protonated precursor, were accurately mass measured in an orthogonal acceleration time-of-flight mass analyzer.
The presence of eight propylamine substituents was shown to induce sequential dehydration of the protonated precursor, ultimately leading to a complete unfolding of the POSS cage. Similar opening of the octahedron structure in the protonated molecule substituted with OSi(CH3)3, OSiH(CH3)2 or OH (formed upon methanolysis of dimethylsiloxy substituents) was proposed to account for the product ions generated during their CID. Sequential charge-remote transfers of a methyl group (and of H in the case of dimethylsiloxy substituents) from one substituent group to a neighboring one was shown to lead to a linear co-oligomeric chain composed of randomly distributed siloxy-based monomers.
All the peaks observed in CID could be accounted for by applying dissociation reactions typically occurring in protonated polysiloxane-like oligomers. The large number of product ions observed in MS/MS was found to result from the variety of possible structural rearrangements, producing numerous linear isomeric forms of the dissociating species. Copyright © 2012 John Wiley & Sons, Ltd.