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Abstract
The self-assembly of organic molecules has increasing potential for a range of applications including catalysis, drug delivery and tissue engineering. This work focused on the development of N-glyoxylamides as a scaffold with enhanced gelation and self-assembly properties. The N-glyoxylamides can be obtained via ring-opening reactions of N-acylisatins or N-sulfonylisatins with a range of alkyl amines. In addition, anion recognition capacity of N-glyoxylamides was also investigated.
N-Glyoxylamides bearing a long hydrophobic alkyl side chain on either the glyoxylamide or amide side of the molecule were found to have enhanced self-assembly properties in solution and solid state when compared to the parent compound which favoured a dimeric conformation. The self-assembly process was dictated by a synergistic action of hydrogen bonding, π-π stacking of the aromatic groups and van der Waals interactions between alkyl chains. Conversely, N-glyoxylamides bearing hydrophobic alkyl side chains on both sides of the molecule were found to possess weaker aggregation and gelation abilities than N-glyoxylamides possessing only one alkyl side chain. Bis-glyoxylamides similarly exhibited minimal association and aggregation abilities in solution but clearly demonstrated well-defined self-assembly in the solid state, with both strong and weak molecular interactions playing key roles in stabilizing the self-assembled structures.
Increasing attention has focused upon the development of anion receptors due to the environmental consequences and human health effects that arise from the presence of excess anions. N-Glyoxylamides bearing a pendant 4-nitrophenyl and 2,4-dinitrophenyl groups were synthesised where the two NH groups acted as anion binding sites and the nitrophenyl moiety acted as a signalling group. These compounds proved to be selective colorimetric sensors of CNˉ and Fˉ in acetone and formed complexes with HSO4ˉ, Clˉ, Brˉ, NO2ˉ and NO3ˉ. The N- mononitrophenylglyoxylic amide showed excellent selectivity for HSO4ˉ and formed a 1:1 host-guest complex with Clˉ in both solution and solid states.
A fluorescence-based anion sensor was prepared via the ring-opening reaction of N-acetylisatin with 9,10-diaminomethylanthracene. This N-glyoxylamide with the pendant anthracene amide exhibited selective recognition of CNˉ, Fˉ and H2PO4ˉ in dimethyl sulfoxide over other examined anions, such as Clˉ, NO2ˉ, ClO4ˉ, HSO4ˉ and HPO4ˉ.