In this research, we report the regioselective synthesis of methylene-bridged naphthalene oligomers from 2,6-dialkoxyl naphthanene and paraformaldehyde by using p-TsOH as the catalyst and CH2Cl2 as the solvent. The structures were characterized by NMR spectroscopy and X-ray crystallography. Their host–guest chemistry with organic cations was studied, and optimal naphthalene numbers in the oligomers were revealed for different guests. In addition, the reason for the unsuccessful synthesis of methylene-bridged naphthalene macrocycles was discussed.

•Poly(p-dioxanone) (PPDO) can form pseudo-polyrotaxanes (PPRs) with cyclodextrin (CD).•The formation of CD-PPRs was demonstrated using WAXD, 2DNMR, POM and FTIR analyses.•Both thermal stability and hydrophilicity of PPDO were improved via CD imprisoning.•The degradation behavior of PPDO can be controlled by the types and amounts of CDs.Novel pseudo-polyrotaxanes (PPRs) consisting of poly(p-dioxanone) (PPDO) and cyclodextrins (CDs) were obtained via heat-cool (H-C) cycles. The optimum preparation condition for achieving the highest yield was investigated, which was selected as follow: 3 times H-C cycles in 72 h of PPDO and CDs dissolved in DMF at 60 °C. The PPRs were further characterized by using wide-angle X-ray diffraction (WAXD), NMR, FT-IR, and thermogravimetric analysis (TGA). It was found that PPDO could be wrapped by CDs units. Compare to the single PPDO chain, the PPRs have better thermal stability. Moreover, the hydrophilicity of PPRs is also enhanced significantly determined by the water static contact angle tests. In addition, hydrolytic degradation experiments showed that the PPRs had unique degradation behaviors. The construction of the PPRs based on the PPDO and CDs would further expand the application of PPDO as biomaterials.

•A novel mono-6-O-(4-carbamoylmethoxy-benzoyl)-β-cyclodextrin was newly synthesized.•The self-assembly structure was constructed by mono-modified β-cyclodextrin.•A novel supramolecular structure displayed a ‘Yin-Yang’-like packing mode.A novel mono-modified β-cyclodextrin (β-CD) consisting of 4-carbamoylmethoxy-benzoyl unit at the primary side was synthesized and its self-assembly behavior was determined by X-ray crystallography and NMR spectroscopy. The crystal structure shows a ‘Yin-Yang’-like packing mode, in which the modified β-CD exhibits a channel superstructure formed by a tail-to-tail dimer as the repeating motif with the substituted group embedded within the hydrophobic cavity of the facing β-CD. The geometry of the substituted group is determined by the inclusion of the cavity and is further stabilized by two intermolecular hydrogen bonds between the carbonyl O atom and phenyl group. Furthermore, NMR ROESY investigation indicates that the self-assembly behavior of the substituted group within the β-CD cavity is retained in aqueous solution, and the effective binding constant Ka was calculated to be 1330 M−1 by means of 1H NMR titration according to iterative determination.

The inclusion complex of β-cyclodextrin with m-nitrophenoxyacetic acid was studied by single crystal X-ray diffraction, 2D NMR spectroscopy and semi-empirical methods AM1. The crystallographic study shows that two β-cyclodextrins are held together by hydrogen bonds to form head-to-head dimers. The disordered guest molecule adjusts itself to attain the most stable accommodation into the cavity in which the nitro group is located at the dimer interface while the carboxyl group is buried in the primary hydroxyl groups of β-cyclodextrin. The guest inside the cavity is disordered over two sites and exhibits mobility. Moreover, 2D NMR spectroscopy and theoretical study show the same inclusion behavior. In comparison to the inclusion complex of β-cyclodextrin with p-nitrophenoxyacetic acid, the host-guest stoichiometries are different, i.e., 2:1 for m-nitrophenoxyacetic acid and 1:1 for p-nitrophenoxyacetic acid, while the inclusion orientation and the packing pattern of the host are similar in both complexes.The inclusion behavior of β-cyclodextrin with m-nitrophenoxyacetic acid shows that β-cyclodextrin forms a 2:1 complex with m-nitrophenoxyacetic acid, in which the disordered guest molecule adjusts itself to attain the most stable accommodation into the cavity. In comparison to the inclusion complex of β-cyclodextrin with p-nitrophenoxyacetic acid, the host-guest stoichiometries are different, i.e., 2:1 for m-nitrophenoxyacetic acid and 1:1 for p-nitrophenoxyacetic acid, while the inclusion orientation and the packing pattern of the host are similar in both complexes.

The mono-modified β-cyclodextrin, 6-deoxy-6-(2-pyrimidinethio)-β-cyclodextrin, was synthesized and characterized. Its self-assembly behavior was measured in both solution and the solid state. The crystal structure shows that the pyrimidine group penetrates deeply into the hydrophobic cavity of the adjacent β-cyclodextrin from the second side, and the molecules are stacked along the twofold screw axis to form a head-to-tail helical columnar superstructure. Furthermore, the effective binding constant K and the aggregation number n were calculated to be 354 M−1 and 2.1, respectively, by means of 1H NMR spectroscopy titration. The results indicate that the intramolecular/intermolecular interactions are a critical factor in determining the self-assembly behavior.Graphical abstractThe binding ability and self-assembling behavior of supramolecule formed by 6-deoxy-6-(2-pyrimidinethio)-β-CD through the molecular interpenetration have been investigated in both solution and the solid state. The results show that the molecules are stacked along the twofold screw axis to form a herringbone-like pattern in which the pyrimidine substituent group successively penetrates into the adjacent β-CD cavity, which indicates that the intramolecular/intermolecular interactions play a key role in the formation of the helical supramolecule.Highlights► The crystal structure of pyrimidinethio-modified β-cyclodextrin. ► The conformation of pyrimidinethio-modified β-cyclodextrin in solution. ► The binding constant of pyrimidinethio-modified β-cyclodextrin was measured.

The supramolecular self-assembly formed by newly synthesized mono-6-(4-cyano-phenyl)-β-cyclodextrin through the molecular interpenetration has been investigated and compared in both solution and the solid state, which was characterized by X-ray crystallography, fourier transform infrared spectroscopy, NMR spectroscopy and atomic force microscopy. The crystal structure clearly revealed that the benzonitrile group is consecutively inserted into the adjacent cyclodextrin cavity from the second side, thus giving rise to an unusual interlocked helical supramolecular self-assembly in which the benzonitrile group acts as bridge between the cyclodextrin units. As compared with crystal, the conformation in aqueous solution indicates that the benzonitrile group prefer to be self-assembled included into another cavity from the second side of cyclodextrin to form the self-assembly.

The mono-modified β-cyclodextrin derivative, 6-O-(4-aminobenzoyl)-β-cyclodextrin (1), was synthesized and characterized. We compared its self-assembling behavior with structurally related β-cyclodextrin derivative, 6-O-(4-hydroxybenzoyl)-β-cyclodextrin (2), in aqueous solution and in the solid state using NMR spectroscopy and single crystal X-ray structure analysis. The two complexes displayed different self-assembling behaviors. Complex 1 formed a head-to-tail helical columnar superstructure in which the substituent group penetrated deeply into the hydrophobic cavity of the adjacent β-cyclodextrin from the second side and aligned along the screw axis, whereas 2 exhibited a channel superstructure with a tail-to-tail dimer as the repeating motif. Further NMR studies in aqueous solution supported the result of the solid state. The influence of substituent groups on the self-assembly behavior was examined in mono-modified β-cyclodextrins by means of substituting an amino group for a hydroxyl group, which indicates that the weak intermolecular interaction is a critical factor in determining the self-assembling behavior.

The inclusion complex (1) of with β-cyclodextrin-p-nitrophenoxyacetic acid was synthesized and characterized. Its inclusion behavior was investigated by means of X-ray crystallography and NMR spectroscopy in solution and in the solid state. The crystallographic study shows that one β-cyclodextrin co-crystallize with one p-nitrophenoxyacetic acid, and 17 water molecules in the Monoclinic system with unit cell constants: a = 18.6864(16), b = 24.961(2), c = 16.6644(14) Å, β = 105.129(5)°. Two β-cyclodextrins are held together by hydrogen bonds to form head-to-head dimers. The disordered guest molecule molulates itself to attain the most stable accommodation into the cavity in which the nitro group is located at the dimer interface while the carboxyl group buried in the primary hydroxyl groups of β-CD. The further 2D NMR spectroscopy investigation in solution supports the inclusion mode of the solid state.