Self-assembly Behaviors And Characteristic Of Low Molecular Mass Organogels Based On -C=O…H-N- Hydrogen Bonding.

We report on the self-assembly of a new two-component hydrogel of thymidine (T) and melamine (M) which formed supramolecular complex (≥0.1%, w/v) based on intermolecular hydrogen-bonding. The complexes can form stable gels due toπ-satcking. We designed and synthesized unsymmetrical bi-dihydrazide derivatives: ethyl Oxalyl acid - (3, 4, 5- trialkoxybenzoyl)-hydrazide Bn (n=4, 12, 16) and N', N'-bis [4-octadecylox-ybenzamido] pyromellitic diimide F8, and the molecular structures were confirmed by 1H NMR, FT-IR spectroscopy and Elemental Analysis. SEM, 1H NMR, Fourier transform infrared (FT-IR) spectroscopy and wide angle X-ray diffraction (WAXD) were used to investigate their self-assembly behaviour and the results were outlined as follows:The 3D morphologies were tuned by changing the molar ratio of T and M in aqueous medium from 3/1 to 1/3 above the critical gelation concentrations (CGC) of 0.1 wt%. The xerogels showed rod, sheet and flower structures as observed under SEM depending on the molar ratios of T and M. Fourier transform infrared (FT-IR) spectroscopy and wide angle X-ray diffraction (WAXD) studies confirmed that the thymidine and melamine form supramolecular complexes through intermolecular hydrogen-bonding between -C=O…H-N-. The morphology and WAXD patterns of the xerogels are different for different complexes indicating different modes of self-assembly in TM complexes. During gel formation, the two building units assembled together into aggregates. With the increase of the ratio of M/T, the backbone shapes changed from rod to sheet to curling slices, and the contents of free N–H groups increased, therefore providing a way to control gel formation and stability. It was found that thymidine/melamine can self-assemble into tubular structures with nanometric dimensions in aqueous solution. The present system may open a newpath to accelerate the development of one-dimensional or three-dimensional molecular assembly systems taking advantage of DNA-based functions, leading to the creation of novel multiple dimensional functional nanomaterials.FTIR spectroscopy revealed that intermolecular H-bonds are the main driving force for the formation of supramolecules in Bn. The gelling ability, the morphologies, and packing structures were significantly influenced by the length of the alkoxy chains. Bn can gel either DMF at higher concentrations or DMSO. B16 showed weak gelation ability in DMF and DMSO. In addition, B16 are effective gelators for ethanol and methanol.The synthesis and self-assembly of a new hydrazide derivative, e.g. N', N'-bis [4-octadecyloxy-benzamido] pyromellitic diimide F8, were investigated. It formed gels in several apolar organic solvents such as benzene and 1, 2-dichloroethane.Based on the SEM observations, FT-IR and 1H NMR spectroscopy results, it was demonstrated that intermolecular hydrogen bonding originating from the–N–H group and O=C– group existed in F8. Furthermore, F8 was shown to exhibit sensing of the polar, positional isomers of dihydroxybenzene by virtue of its different color change. This unique system may provide an insight in designing molecular machines as well as chemical sensors. We investigated the colorimetric system by UV/Vis, 1H NMR and 1H NMR NOESY spectra and con?rmed that the intermolecular donor–acceptor interaction between F8 and the isomers resulted in the spontaneous colorimetric sensing. We also found even 5.6×10?3M of the dihydroxybenzene (0.62 mg of 2a) could be sensed by 0.1 mM of F8. Therefore, recognition property of F8 is quite attractive, considering that the conventional recognition in solution requires 10–100 equivalents of the analyte for sensing with the naked eyes.