Yun-Xiang Xu

Vesicles and organogels from foldamers: a solvent-modulated self-assembling process.

Nonamphiphilic, hydrogen-bonded hydrazide foldamers appended with four or six long flexible chains were revealed to spontaneously assemble to form vesicles in methanol and organogels in aliphatic hydrocarbons. SEM, AFM, TEM, DLS, and fluorescence microscopy were all used to identify the structures of the vesicles. It was proposed that intermolecular pi stacking of the folded frameworks and hydrogen bonding of the amide units in the appended chains induced the molecules to produce cylindrical aggregates. In polar methanol, these aggregates packed together to generate one-layered vesicles owing to hydrophobically induced entanglement of the peripheral chains, while in nonpolar hydrocarbons, the peripheral chains entwined across stacked cylinders to form three-dimensional networks and thus immobilize the liquid molecules.

Folding of aromatic amide-based oligomers induced by benzene-1,3,5-tricarboxylate anion in DMSO.

In this paper, we describe the folding of a series of linear arylamide oligomers in DMSO that is induced by benzene-1,3,5-tricarboxylate anion. The oligomers are comprised of naphthalene-2,7-diamine and 1,3,5-benzenetricarboxylic acid segments with two (tert-butoxycarbonylamino) groups at the ends and two to four hydrophilic N,N-bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)amino groups at one side of the backbones. (2D NOESY) (1)H NMR, fluorescence and UV-vis studies indicate that the oligomers do not adopt defined conformations in DMSO but fold into compact structures in the presence of the anion. It is revealed that the folded conformation is induced by intermolecular hydrogen bonds between the amide and aromatic hydrogen atoms of the oligomers and the oxygen atoms of the anion. (1)H NMR and UV-vis titrations support a 1:1 binding stoichiometry, and the associated constants are determined, which are found to increase with the elongation of the oligomers.

Self-assembly of vesicles from amphiphilic aromatic amide-based oligomers.

A novel class of linear arylamide oligomers has been designed and synthesized from naphthalene-2,7-diamine and benzene-1,3,5-tricarboxylic acid segments. The molecules carry two (tert-butoxycarbonylamino) groups at the ends and one to three hydrophilic N,N-bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)amino groups at one side of the backbone. The oligomers self-assembled into vesicular structures in methanol as a result of ordered stacking of the oligomeric amide backbones, which were evidenced by SEM, AFM, TEM, and fluorescent micrography experiments. It was also found that the tert-butoxycarbonylamino groups at the ends played an important role in promoting the ordered stacking of the backbones. Structural factors that affected the self-assembly of the oligomers were investigated. A two-layer model that was supported by TEM has been proposed for the formation of the vesicular structures, which was driven by both the hydrogen bonding and aromatic stacking.

Hydrogen bonding-driven highly stable homoduplexes formed by benzene/naphthalene amide oligomers

This paper describes the dimerization of aromatic amide oligomers in chloroform. The oligomers were prepared by step-by-step coupling of benzene-m-dicarboxylic acid and naphthalene-2,7-diamine. Triethylene glycol chains were introduced into the 5-position of the benzene rings to provide solubility in organic solvents. 1H NMR investigations revealed that, although shorter oligomers did not exhibit good dimerization ability, longer oligomers with five or more amide units could form stable homoduplexes which were stabilized by intermolecular multiple N–H⋯OC hydrogen bonds. The association constants (Ka) of the 3-, 4- and 5-mer oligomers were determined using 1H NMR dilution experiments, while the Ka values of a 5-mer oligomer and a 7-mer oligomer, which were appended with two or one pyrene unit, were also evaluated using fluorescent dilution experiments. The results showed that the stability of the homoduplexes of the aromatic amide oligomers is nearly linearly related to the number of their amide units, and a Ka of 3.0 × 107 M−1 was determined for the 7-mer oligomer.

Controllable self-assemblies of micro/nano-tubes and vesicles from arylamides and their applications as templates to fabricate Pt micro/nano-tubes and hollow Pt nanospheres

A novel class of nonamphiphilic aromatic amides (T1–T3) have been designed and synthesized from naphthalene-2,7-diamine or 2-amino-naphthalene and a 5-hydroxy-isophthalic acid segment, which is revealed to selectively assemble into vesicular or tubular architectures, depending on the solvents and concentrations. T1 and T2 form vesicles in methanol, but can be converted into micro/nano-tubes when water is added and further gelate the binary solvent when the concentration is high enough. In contrast, T3 self-assembles into fine tubular structures in methanol, but can be transformed into vesicles upon being diluted or adding chloroform. The morphology transition has been investigated by SEM, AFM, TEM and fluorescent microscopy, which also reveal that microtubes of large size are formed through the fusion of vesicles of small size, which is driven by the cooperative hydrogen bonding and aromatic stacking interactions, as evidenced by the X-ray investigation on an analogue of T3. The novel organic micro/nano-tubes and vesicles are further used to template the fabrication of Pt micro/nano-tubes or hollow Pt spheres by in situ reduction of the absorbed K2PtCl4 with ascorbic acid, as confirmed by SEM, TEM and EDX analyses.