Covalent Attachment and Detachment by Reactive DESI of Sequence-Coded Polymer Taggants.

The use of sequence-defined polymers is an interesting emerging solution for materials identification and traceability. Indeed, a very large amount of identification sequences can be created using a limited alphabet of coded monomers. However, in all reported studies, sequence-defined taggants are usually included in a host material by noncovalent adsorption or entrapment, which may lead to leakage, aggregation, or degradation. To avoid these problems, sequence-defined polymers are covalently attached in the present work to the mesh of model materials, namely acrylamide hydrogels. To do so, sequence-coded polyurethanes containing a disulfide linker and a terminal methacrylamide moiety are synthesized by stepwise solid-phase synthesis. These methacrylamide macromonomers are afterward copolymerized with acrylamide and bisacrylamide in order to achieve cross-linked hydrogels containing covalently-bound polyurethane taggants. It is shown herein that these taggants can be selectively detached from the hydrogel mesh by reactive desorption electrospray ionization. Using dithiothreitol the disulfide linker that links the taggant to the gel can be selectively cleaved. Ultimately, the released taggants can be decoded by tandem mass spectrometry.

Optimal conditions for tandem mass spectrometric sequencing of information-containing nitrogen-substituted polyurethanes.

RATIONALE: To prevent solubility issues faced with sequence-defined polyurethanes, a new family of digital polyurethanes was conceived with the alkyl coding chain held by the carbamate nitrogen (N) atom and CH3 instead of OH as the ϖ termination. This led to different dissociation mechanisms that were explored prior to optimizing tandem mass spectrometric (MS/MS) sequencing. METHODS: N-Substituted polyurethanes (N-R PUs) were dissolved in methanol and subjected to collision-induced dissociation (CID) as deprotonated chains in the negative ion mode, and as ammonium and sodium adducts in the positive ion mode, using electrospray ionization (ESI) as the ionization technique. Their dissociation behavior was thoroughly investigated using a quadrupole time-of-flight (QTOF) instrument in order to provide accurate mass measurements to support proposed fragmentation mechanisms. RESULTS: While O-(CO) bonds were broken in N-H PUs, the CH2 -O linkage between repeating units was cleaved upon CID of N-R PUs. This main process occurred either from deprotonated molecules or from cationized chains but was followed by different rearrangements, producing up to four product ion series. Yet, MS/MS spectra could be drastically simplified for precursor ions having their acidic α group methylated, as was found to spontaneously occur upon storage in methanol. CONCLUSIONS: Using experimental conditions aimed at avoiding any reactive proton in precursor ions (no acidic end-groups and alkali adduction), full coverage sequence of N-R PUs was successfully achieved with the single ion series observed in MS/MS, opening a promising perspective for reading large amounts of information stored in these dyad-encoded polymers.

Efficient Protocol for the Synthesis of "N-Coded" Oligo- and Poly(N-Substituted Urethanes).

Sequence-defined poly(N-substituted urethanes) were synthesized via a solid-phase iterative protocol including two successive orthogonal coupling steps: the formation of an activated carbonate and its chemoselective reaction with the secondary amine group of amino alcohol building blocks. This simple method was used to write binary information on the formed polymers using four-coded molecules, 2-(methylamino)ethanol, 2-(ethylamino)ethanol, 2-(propylamino)ethanol, and 2-(butylamino)ethanol, symbolizing binary dyads 00, 01, 10, and 11, respectively. The method is fast and allows synthesis of uniform oligomers and polymers with controlled lengths (4-mer to 28-mer) and digital information sequences. Furthermore, the coded poly(N-substituted urethanes) were easily characterized by electrospray mass spectrometry and decoded by tandem mass spectrometry. Overall, these digital macromolecules offer interesting advantages over conventional sequence-coded polyurethanes, i.e., synthesis of longer chains, reduced synthesis times, and better solubility and processing in common organic solvents.