In order to improve their MS/MS sequencing, structure of sequence-controlled synthetic polymers can be optimized based on considerations regarding their fragmentation behavior in collision-induced dissociation conditions, as demonstrated here for two digitally encoded polymer families. In poly(triazole amide)s, the main dissociation route proceeded via cleavage of the amide bond in each monomer, hence allowing the chains to be safely sequenced. However, a competitive cleavage of an ether bond in a tri(ethylene glycol) spacer placed between each coding moiety complicated MS/MS spectra while not bringing new structural information. Changing the tri(ethylene glycol) spacer to an alkyl group of the same size allowed this unwanted fragmentation pathway to be avoided, hence greatly simplifying the MS/MS reading step for such undecyl-based poly(triazole amide)s. In poly(alkoxyamine phosphodiester)s, a single dissociation pathway was achieved with repeating units containing an alkoxyamine linkage, which, by very low dissociation energy, made any other chemical bonds MS/MS-silent. Structure of these polymers was further tailored to enhance the stability of those precursor ions with a negatively charged phosphate group per monomer in order to improve their MS/MS readability. Increasing the size of both the alkyl coding moiety and the nitroxide spacer allowed sufficient distance between phosphate groups for all of them to be deprotonated simultaneously. Because the charge state of product ions increased with their polymerization degree, MS/MS spectra typically exhibited groups of fragments at one or the other side of the precursor ion depending on the original α or ω end-group they contain, allowing sequence reconstruction in a straightforward manner. Graphical Abstract ᅟ.
Keywords: Coded monomer sequence; Information-containing macromolecules; MS/MS; Polymer sequencing; Sequence-controlled polymers.