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Monitoring intracellular pH using ratiometric fluorescent probes can provide further insights into various biological processes including many diseases. Although ratiometric fluorescent probes with dual emission can efficiently exclude interferences (probe concentration, instrumental efficiency, and environmental conditions) compared with traditional off-on fluorescent probes, development of pH-responsive fluorescent probes with dual emission remains relatively unexplored and challenging. Herein we reported a new hemicyanine-based ratiometric fluorescent probe 1 with a hydroxyl group. The probe 1 exhibits dual emission and shows a real-time and selective fluorescence response to micro-environmental pH conditions in a range of 6.0 âˆ¼ 8.0. Further studies revealed that 1 could exclusively enter and accumulate into mitochondria and monitor the pH micro-environmental conditions through fluorescence imaging in HepG2 cells. We suggest that this probe might be used as a probe to elucidate the role of pH in many physiological processes.

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Despite dramatic advances in the template-directed synthesis of archetypal [2]rotaxanes, higher order rotaxanes with multiple molecular components (rings or dumbbells) are relatively daunting subjects owing to their synthetic challenges. With unique interlocked architectures, higher order rotaxanes have found applications in artificial molecular machines. In this feature article, we will focus on the recent advances in higher order rotaxanes with well-defined structures. Different types of rotaxane architectures will be described, and their synthetic approaches will be highlighted. Moreover, the stimuli-responsive molecular motion with increasing complexity in these diverse architectures will also be discussed.

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Complexation between a triptycene-derived macrotricyclic polyether containing two dibenzo-[30]-crown-10 cavities and different functionalized paraquat derivatives, diquat, and a 2,7-diazapyrenium salt in both solution and solid state was investigated in detail. It was found that depending on the guests with different terminal functional groups and structures, the macrotricyclic polyether could form 1:1 or 1:2 complexes with the guests in different complexation modes in solution and also in the solid state. Especially, the conformation of the macrotricyclic polyether was efficiently adjusted by the encapsulated guests, which was to some extent similar to substrate-induced fit of enzymes. Moreover, the binding and releasing of the guests in the complexes could be controlled by potassium ions.

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The asymmetric unit of the title compound, C(9)H(9)NO(2)·2H(2)O, comprises two independent organic mol-ecules and four water mol-ecules of crystallization. The heterocyclic rings are not planar: in one mol-ecule, the C atom bearing the O atom and the adjacent methyl-ene C atom are displaced by 0.320 (3) and 0.677 (3) Å, respectively, from the other eight atoms of the fused ring system. Equivalent values of 0.243 (3) and 0.659 (3) Šapply to the second mol-ecule. In the crystal, the components are linked by N-H⋯O and O-H⋯O hydrogen bonds, forming a three-dimensional network.

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In the title compound, C(15)H(13)FN(2)O(3)·CH(3)OH, the dihedral angle between the benzene rings of the benzohydrazone mol-ecule is 5.3 (3)°. The C atom of the meth-oxy group is almost coplanar with its attached ring [deviation = 0.017 (2) Å]. The r.m.s. deviation of the 21 non-H atoms of the hydrazone mol-ecule is 0.106 Å. In the crystal, the components are linked by O(m)-H⋯O(h), N(h)-H⋯O(m) and O(h)-H⋯O(h) (m = methanol and h = hydrazone) hydrogen bonds, forming (001) layers.

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In the title compound, C(26)H(24)Br(2)N(2)O(2), the central naphthalene system carries two Br atoms and two -CH(2)CH(2)NHC(6)H(5) substituents. The phenyl rings of the latter residues are inclined at 74.17 (17) and 51.4 (2)° with respect to the naphthalene ring system. Each alkyl chain adopts a fully extended all-cis conformation with respect to the naphthalene and phenyl rings [N-C-C-O torsion angles = 68.6 (4) and 60.5 (4)°]. In the crystal, one of the N-H groups forms bifurcated N-H⋯(Br,O) hydrogen bonds, which link the mol-ecules into inversion-related dimers. The centrosymmetric dimers are aggregated via pairs of C-H⋯π inter-actions into sheets parallel to (110).

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A new triptycene-derived macrotricyclic host containing two dibenzo-[18]-crown-6 moieties was synthesized and shown to form 1:1 complexes with paraquat derivatives in solution, in which the guests all thread the central cavity of the host. However, it was interestingly found that, depending on the paraquat derivatives with different functional groups, the host can form stable 1:1 or 1:2 complexes in different complexation modes in the solid state, which is significantly different from those of the macrotricyclic host containing two dibenzo-[24]-crown-8 moieties. The formation of the complexes was also proved by the ESI MS and electrochemical experiments. Moreover, it was found that the binding and release of the guests in the complexes could be easily controlled by the addition and removal of lithium ions.

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A new triptycene-based macrotricyclic host containing two dibenzo-30 crown-10 moieties (1) has been synthesized. It could form a 1:2 stable complex 1 x 3(2) with (9-anthracylmethyl)benzylammonium salt (3) in both solution and solid state, in which the 9-anthracyl groups were selectively positioned inside the cavity of the host. Moreover, the complexation and disassociation of complex 1 x 3(2) could be chemically controlled by the addition of base and acid. It was also found that Ba(2+) ion could considerably induce the fluorescence enhancement of complex 1 x 3(2), which might thus be utilized as a selective supramolecular fluorescence probe for Ba(2+) ion. Fluorescence and (1)H NMR spectroscopic titrations further showed that the complexation between complex 1 x 3(2) and barium ions underwent a two-step process.

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The triptycene-based macrotricyclic host containing two dibenzo-[24]-crown-8 moieties has been found to form stable 1:1 or 1:2 complexes in different complexation modes with different functional paraquat derivatives and secondary ammonium salts in solution and in the solid state. Consequently, the alkyl-substituted paraquat derivatives thread the lateral crown cavities of the host to form 1:1 complexes. It was interestingly found that the paraquat derivatives containing two beta-hydroxyethyl or gamma-hydroxypropyl groups form 1:2 complexes, in which two guests thread the central cavity of the host. Other paraquat derivatives containing terminal hydroxy, methoxy, 9-anthracylmethyl, and amide groups were included in the cavity of the host to form 1:1 complexes. Moreover, the host also forms a 1:2 complex with two 9-anthracylmethylbenzylammonium salts, in which the 9-anthracyl groups were selectively positioned outside the lateral crown cavities. The competition complexation process between the host and two different guests (the propyl-substituted paraquat derivative and a dibenzylammonium salt) could be chemically controlled.

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Triptycene-based cylindrical macrotricyclic polyether 1 has been proved to be an efficient host for the complexation with diquaternary salts in solution and in the solid state. Moreover, it was also found that binding and release of the guest molecules could be easily controlled by the addition and removal of potassium ions.

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Corrections are made to the name of the author and the address in Zhong [Acta Cryst. (2007), E63, o4446].[This corrects the article DOI: 10.1107/S1600536807050040.].

RESUMEN

[reaction: see text] It was found that a cylindrical macrotricyclic host containing two dibenzo[24]crown-8 cavities could self-assemble with two dibenzylammonium salts to form a stable 1:2 complex in solution and in the solid state, in which multiple hydrogen-bonding and pi-pi stacking interactions between the host and the guest played an important role. Furthermore, a series of dendritic pseudorotaxanes were constructed and structurally studied.

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[reaction: see text] A novel triptycene-based cylindrical macrotricyclic polyether containing two dibenzo[24]crown-8 cavities has been synthesized and proved to be a highly efficient host for the complexation with paraquat derivatives. Consequently, a new kind of very stable pseudorotaxane-type complex was formed in solution and in the solid state.

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