Abstract
Melamine oligomers composed of repeating triazine-piperidine units and equipped with phenol and phosphine oxide side-chains form H-bonded duplexes. The melamine backbone provides sufficient rigidity to prevent intramolecular folding of oligomers up to three recognition units in length, leading to reliable duplex formation between sequence complementary oligomers. NMR spectroscopy and isothermal titration calorimetry (ITC) were used to characterize the self-assembly properties of the oligomers. For length-complementary homo-oligomers, duplex formation in toluene is characterized by an increase in stability of an order of magnitude for every base-pair added to the chain. NMR spectra of dilute solutions of the AD 2-mer show that intramolecular H-bonding between neighboring recognition units on the chain (1,2-folding) does not occur. NMR spectra of dilute solutions of both the AAD and the ADD 3-mer show that 1,3-folding does not take place either. ITC was used to characterize interactions between all pairwise combinations of the six different 3-mer sequences, and the sequence complementary duplexes are approximately an order of magnitude more stable than duplexes with a single base mismatch. High-fidelity duplex formation combined with the synthetic accessibility of the monomer building blocks makes these systems attractive targets for further investigation.
Highlights
The molecular nanotechnology found in nature is based on linear oligomers, where function is encoded by the sequence of monomer building blocks
The H-bond donor and acceptor building blocks were synthesized from secondary amines 2 and 4, which have isobutyl solubilizing groups
Secondary amine 2 was obtained by protection of 3-hydroxybenzaldehyde using triisopropylsilyl chloride, followed by reductive amination with isobutylamine (Scheme 1)
Summary
The molecular nanotechnology found in nature is based on linear oligomers, where function is encoded by the sequence of monomer building blocks. The limiting bound chemical shifts of the two complexes are very similar, which indicates that AD·AD forms a duplex with both phosphine oxide groups involved in intermolecular H-bonds.
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