End-group rearrangements in poly(propylene sulfide) matrix-assisted laser desorption/ionization time-of-flight analysis. Experimental evidence and possible mechanisms

RATIONALE Polysulfides [poly(1,2-alkylene sulfides)] are oxidation-responsive polymers that are finding application in drug release and biomaterials. The precise knowledge of their macromolecular characteristics is of the essence in view of their application to biological systems. METHODS Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) with and without silver trifluoroacetate was used to characterize a series of polymers with increasing molecular weight in the range 10004000 g/mol and with low polydispersity (<1.12). RESULTS Well-resolved peaks and accurate mass-measured values were obtained using a 2-(4-hydroxyphenylazo)benzoic acid (HABA) matrix, but significant fragmentations took place in the absence of silver as a cationizing reagent. Elimination reactions appeared to occur at terminal groups and limited depolymerization could be recorded. Interestingly, the most common fragmentation pathway seemed to be based on an as-yet-unreported process of hydrogen transfer requiring the presence both of ester groups and of thioethers. CONCLUSIONS The use of an appropriate cationizing reagent (silver trifluoroacetate) appeared to suppress end-group eliminations; we hypothesize that this action is based on the involvement of the terminal groups in silver chelation. Copyright (c) 2012 John Wiley & Sons, Ltd.