Two aromatic hydrazide haptamers have been prepared,with both consisting of two hydrogen bonded folded segments. Compared to their fully hydrogen bonded analogues,the flexibility of their backbones increases due to lack of one or two intramolecular hydrogen bonds at the middle aromatic unit. (2D) 1H NMR,circular dichroism and fluorescent studies revealed that both oligomers moderately complex n-octyl-α-L-glucopyranoside in chloroform.
The complexing behaviour of two linear compounds 1 and 2 toward the trifluoroacetic acid （TFA） salts of n-dodecylamine, di-n-octylamine, n-dodecyl D- and L-phenylalaninates （3, 4, and D- and L-5） in chloroform has been described. Compounds 1 and 2 consist of two folded amide moieties with two pyridyls at the terminals which are connected directly or with an acetylene linker. The rigidified folded moieties are stabilized by intramolecular hydrogen bonding, while the whole molecules can adopt an ＂S＂- or a ＂C＂-styled conformation depending on the relative orientation of the two rigidified moieties. ^1H NMR, UV-Vis, fluorescent and circular dichroism investigations revealed that 1 and 2 could bind primary and secondary ammonium cations with their ＂C＂-styled conformation. In the presence of 1 equiv, of TFA, the binding stability was increased significantly as a result of promoted formation of the ＂C＂-styled conformation due to the monoprotonation of the peripheral pyridyl units in 1 and 2. In contrast, the addition of 2 equiv, of TFA substantially weakened the binding stability because the ＂S＂-styled conformation was favored as a result of protonation of both of their pyridyl units. Moreover, remarkable induced circular dichroisms were also displayed for the complexes of 1 and 2 with chiral D- and L-5.
Three arylamide-bridged biscoumarin derivatives 1-3 have been designed and prepared. Compounds 1 and 2 are induced by the intramolecular N?H…O and N·H…F hydrogen bonding to possess a helical conformation,and 3 is induced to have an extended conformation. A comparison of their absorption and fluorescent spectra in a variety of solvents of a wide range of polarity with those of control compound 4 reveals that,for foldamers 1 and 2,the intramolecular hydrogen bonding and the helical conformations exist in most solvents,but do not exist or are very weak in DMF and DMSO.
LU ZhengQuanZHU YuanYuanLIN JianBinJIANG XiKuiLI ZhanTing
In a preliminary letter （Tetrahedron Lett. 2010, 51, 188）, we reported two new hydrazide-based quadruple hydrogen-bonding motifs, this is, two monopodal （la and lb） and five dipodal （2a, 2b and 3a--3c） aromatic hydrazide derivatives, and the formation of supramolecular polymers and vesicles from the dipodal motifs in hydrocarbons. In this paper, we present a full picture on the properties of these hydrogen-bonding motifs with an emphasis on their self-assembling behaviors in aqueous media. SEM, AFM, TEM and fluorescent micrographs indicate that all the dipodal compounds also form vesicles in polar methanol and water-methanol （up to 50% of water） mixtures. Control experiments show that lb does not form vesicles in same media. Addition of lb to the solution of the dipodal compounds inhibits the latter＇s capacity of forming vesicles. At high concentrations, 3b and 3c also gelate discrete solvents, including hydrocarbons, esters, methanol, and methanol-water mixture. Concentration-dependent SEM investigations reveal that the vesicles of 3b and 3c fuse to form gels and the gel of 3c can de-aggregate to form the vesicles reversibly.
