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Digital polymers are uniform macromolecules that store monomer-based binary sequences. Molecularly stored information is usually extracted from the polymer by a tandem mass spectrometry (MS/MS) measurement, in which the coded chains are fragmented to reveal each bit (i.e. basic coded monomer unit) of the sequence. Here, we show that data-extraction can be greatly simplified by favoring the formation of MS/MS fragments containing two bits instead of one. In order to do so, digital poly(alkoxyamine phosphodiester)s, containing binary dyads in each repeat unit, were prepared by an orthogonal solid-phase approach involving successive phosphoramidite and radical-radical coupling steps. Three different sets of monomers were considered to build these polymers. In all cases, four coded building blocks-two hydroxy-nitroxides and two phosphoramidite monomers-were required to build the dyads. Among the three studied monomer sets, one combination allowed synthesis of uniform sequence-coded polymers. The resulting polymers led to clear dyad-containing fragments in MS/MS and could therefore be efficiently decoded. Additionally, an algorithm was created to detect specific dyad fragments, thus enabling automated sequencing.
Cavallo et al. (Tue,) studied this question.