Chemical sequencing of sequence-defined polymers by controlled degradation : studies and applications
Sequence-defined polymers are a promising platform of discovery for the fields of biomimetics, self-assembly, catalysis, and information storage. The power of these polymers lies in their primary structure, which can beget complex chemical processes. Here we report the solution-phase and the high-yielding solid-phase syntheses of discrete oligourethanes and methods for their chain-end depolymerization for sequencing, resulting in rapid and robust characterization of this class of oligomers and polymers, without the use of MS/MS. Crucial to the sequencing is the inherent reactivity of the terminal alcohol to “unzip” the oligomers, in a controlled and iterative fashion, releasing each monomer as a 2-oxazolidinone. The process utilizes the effective molarity of the terminal alcohol, as well as the steric compression of the sidechain methylenes to control the rate of cyclization. It was observed that these macromolecules do not auto-depolymerize at room temperature or in the absence of base, and are generally stable to hydrolysis. The mechanism of depolymerization was confirmed as a 5-exo-trig intramolecular cyclization, and is capable of tolerating a wide diversity of sidechain functionalities as well as crude or complex sample mixtures. This robust immolative self-sequencing paradigm was utilized in the development of a complete workflow for the encoding and decoding of digital information within the macromolecular sequence-defined urethanes. Within the encoding and decoding schema, a highly configurable software was developed that is capable taking any information and converting it to the preferred positional numeral system (such as hexadecimal), which can then be synthesized into the urethanes, and ultimately sequenced back to decode the molecular information. A parallel synthesis methodology was developed for the simultaneous synthesis of numerous sequence-defined urethanes, and utilized to synthesize 18 unique 10-mer oligourethanes that encoded a passage from Jane Austen’s Mansfield Park. A parallel sequencing methodology was developed to simultaneously sequence all 18 oligomers, where the data were fed into our decoding software and the information transformed back to its original state. Currently, we are working to advance the sequencing methodology to allow multiple urethanes to be stored and sequenced within the same solution, utilizing isotopic labelling as unique mass tags for their discreet characterization. Ultimately, we plan to use this technology for cryptography and steganography, wherein we imbed and store a 256-bit molecular cipher key. Only upon extraction, sequencing, and decoding can the encrypted information be accessed.