Hydrogen-bonded oligoamide duplexes as programmable molecular recognition units: A systematic approach towards directed self-assembly and controlled non-covalent synthesis

Association units with high strength and specificity are getting increasing attention in the construction of well-defined selfassembling systems, which are making controlled non-covalent synthesis a reality. A class of hydrogen-bonded duplexes consisting of oligoamide strands carrying various combinations (sequences) of hydrogen-bond donors and acceptors has exhibited superb ability as intermolecular association units. These duplexes are featured by programmable sequence-specificity, predictable binding strength, ready synthetic availability and modifiability. With association constants ranging from ~104 to 109M-1, these hydrogen-bonded duplexes offer a diverse set of association units capable of specifying intermolecular association in a controlled and directed manner. The efficacy of these molecules as molecular assembler has already been demonstrated by a number of examples such as the construction of supramolecular block copolymers, the templation of β-sheets, directed chemical reactions such as olefin metathesis and disulfide exchange. By integrating hydrogen bonding with dynamic covalent interactions, covalently linked duplexes are formed sequence-specifically in a selfassembling fashion in highly competitive media, which represents a major progress in creating association units combining the strength of covalent bonds and the specificity of multiple hydrogen bonds. Recently, hydrogen-bonded and/or covalent crosslinked duplexes have been found to serve as gelators for organic solvents, which may open a new avenue for developing novel materials.