Hai-Yu Hu

Chiral induction in phenanthroline-derived oligoamide foldamers: an acid- and base-controllable switch in helical molecular strands.

A series of phenanthroline-derived oligoamides bearing a chiral (R)-phenethylamino end group were synthesized that displayed chiral helical induction and subsequently formed one-hand helical foldamers in solution. Moreover, an acid- and base-controllable switch in the helical molecular strands was observed, which has been demonstrated by NMR, UV-vis, and circular dichroism spectroscopy.

Folding-Induced Selective Hydrogenation of Helical 9,10-Anthraquinone Analogues

The first selective catalytic hydrogenation induced by the artificial helix based on oligo(phenanthroline dicarboxamide)s containing a 9,10-anthraquinone subunit is described. Due to the steric hindrance within the helically folded oligomers, the selective reductions of the anthraquinone units were completely different from those of model substrates, which subsequently mimicked the enzyme catalysis for preventing some reactions from occurring.

Supramolecular substitution reactions between hydrazide-based molecular duplex strands: complexation induced nonsymmetry and dynamic behavior.

Supramolecular substitution reactions between hydrazide-based oligomers 1a- c and 2a- c were systematically investigated. Each oligomer existed as hydrogen-bonding mediated molecular duplex strands or a polymeric zipper structure in apolar solvents. But when another oligomer with complementary hydrogen bonding sites was added, a heterodimer structure formed due to supramolecular substitution reaction driven by the formation of more hydrogen bonds, which was evidenced by NMR experiments, sometimes gel-sol transition. When a nonsymmetric oligomer and a symmetric oligomer were involved, complexation-induced nonsymmetry was observed. When two nonsymmetric oligomers were involved, two hydrogen-bonded isomers were observed in solution. Variable-temperature (1)H NMR experiments further revealed unique dynamic behavior for the individual oligomer and the complexes. When diacetyl-terminated oligomer 1c was involved, slides perpendicular to hydrogen bonds between two constituent molecules were observed, which led to complicated (1)H NMR spectra at lower temperature; otherwise, high selectivity was obtained. Combined with the results we reported previously, a detailed picture of the structure-property relationship for our hydrazide-based oligomers was depicted, which would provide guidelines for the design of hydrazide-based fine-tuning functional materials.

Conformationally constrained aromatic oligoamide foldamers with supersecondary structure motifs

The design, synthesis, and structural studies of aromatic foldamers based on oligo(phenanthroline dicarboxamide)s that displayed supersecondary structure motifs have been described. Governed by a combined conformational restriction, the foldamers adopted well defined and compact 3D structures, which have been validated by UV/Vis, NMR spectra, and X-ray crystal analysis. The results presented here would offer a useful route for the de novo design of aromatic oligoamide foldamers with distinctive structural architectures.

Probing the Dynamic Environment-Associated Conformational Conversion from Secondary to Supersecondary Structures in Oligo(phenanthroline dicarboxamide)s

The special structural features of the oligo(phenanthroline dicarboxamide)s and their dynamic environment-associated conformational conversion from secondary helical structure to supersecondary helix-turn structure, owing to the conversion of the CONH bond from s-cis form to s-trans form, have been experimentally and theoretically characterized by X-ray crystallographic, variable-temperature (1)H NMR, variable-temperature circular dichroism techniques, and computational studies. It has been demonstrated that the solvent effects together with intramolecular hydrogen bonds and pi-pi stacking play a key role in stabilizing both the secondary and supersecondary structures. Furthermore, by introducing the intramolecular F...H-N hydrogen bond to restrict the rotation about the CONH-aryl bonds, the oligomers 6 and 7 have been synthesized, which showed well-defined and predictable secondary helical conformations in solution and in the solid state.

Selective recognition of specific G-quadruplex vs. duplex DNA by a phenanthroline derivative

A key problem in designing G-quadruplex ligand is how to discriminate quadruplex DNA specifically from other DNAs, searching ligands targeted at special G-quadruplex structure with high selectivity is a major challenge. Herein, a phenanthrolin-dicarboxylate ester (PD) is proved to exhibit selectivity toward parallel and hybrid G-quadruplex structures with propeller and edge-wise loops, over duplex DNA and antiparallel quadruplex structure with diagonal loop. Such preferred binding of PD to these special G-quadruplex structures is possibly resulted from steric hindrance of: (1) the four substituent groups in PD molecule which prevent close interaction with duplex DNA and (2) the diagonal loop above the G-tetrads in antiparallel G-quadruplex which hinder face-to-face stacking of planar phenanthrolin ring to G-tetrads. In line with its stabilizing ability of G-quadruplex, PD molecule exhibit a inhibitory ability telomerase activity, as well as the potent cytotoxic activity against several human cancer cell lines, which makes it an interesting anti-tumor drug lead.

Stabilizing G-Quadruplex DNA by a Scissors-Shaped Binaphthyl Derivative through the Entangling Mode: Cooperation of Binaphthylene and the Ethoxy Chain

A scissors-shaped binaphthyl derivative (NPA) has been found to stabilize the G-quadruplex by intertwisting the whole G-quadruplex with two long chains, through the cooperation of the two functional groups: binaphthylene and the ethoxy chain. Moreover, NPA exhibits a good inhibitory effect of telomerase activity as well as excellent cytotoxic activity against HepG-2 human liver cancer cells.