Two triptycene rotators have been covalently linked to the backbone of a quinquepyridine (QPY) foldamer at the second and fourth pyridine rings, respectively, to form molecular spur gears. The studies revealed that a QPY foldamer as a stator can reversibly control the intermeshed and demeshed states of molecular spur gears due to the linear-to-helical conformational switching triggered by complexation/decomplexation.

Foldamers 1–4 incorporating different terminal substituents have been designed and synthesized for binding halide anions. 1H NMR titration experiments carried out in DMSO-d6/CDCl3 (15/85, v/v) demonstrated that the short oligo(aryltriazole)s backbone 1 could not bind halide anions unless that amide H-bond donors were incorporated at the termini of the oligomer. Terminal substituents on oligo(aryltriazoleamide)s foldamers 2–4 display a considerable influence on the binding affinities of the foldamers for halide anions. Large steric hindrance of the terminal substituents was found to be unfavorable for binding halide anions, but aromatic π-π interactions between two terminal substituents are capable of stabilizing the conformation of foldamers thus giving rise to an enhancement in the binding strengths. However, the terminal substituents were found to hardly affect the binding selectivity in the studied cases.Download high-res image (118KB)Download full-size image

A novel aryl-triazole foldamer incorporating a 1,8-naphthalimide motif was designed and synthesized. 1H NMR, UV-vis and fluorescence spectroscopic titration experiments with halide anions (Cl−, Br−, I−) demonstrated that the π–π stacking interaction of 1,8-naphthalimide building blocks could largely enhance the folding and anion binding of the foldamer.

In artificial molecular devices, flexible, linear chains typically exhibit very weak capability in inhibiting molecular motion. Herein, we describe the dynamic properties of a series of molecular turnstiles consisting of a rigid frame and a phenyl rotator flanked with linear alkoxymethyl substituents. The long, flexible substituents act as elastic baffles to inhibit the rotations of the rotator at medium to fast speeds on the NMR time scale. When the rotator moves slowly, the substituents become more relaxed, thus obtaining an opportunity to completely thread through the cavity of the turnstiles. These findings reveal a basic but missing correlation between steric hindrance and speed of motion for flexible, linear chains in dynamic molecular devices, thus opening up a new direction toward molecular machines with more elaborate dynamic functions.

•A new aryl-triazole receptor incorporating ethynyl spacer was readily constructed.•These receptors bind various anions with high affinities but a low selectivity.•These results may provide a new application of anion abstraction in sewage treatment.•Improve our insights into anion binding properties and design novel anion receptors.A new aryl-triazole receptor incorporating ethynyl spacer was readily constructed. By using UV–Vis spectroscopic titration, the foldamers were proved to be capable of binding various shaped anions (nBu4N+A−, A = Cl, Br, I, NO3, HSO4, H2PO4 and AcO) with high affinities but a low selectivity.

Based on the selective reduction of nitro group to hydroxylamine or amino group by nitroreductase in the presence of NADPH as an electron donor, a near-infrared ratiometric fluorescent probe CyNNO2 was designed and synthesized. CyNNO2 containing a p-nitrobenzyl moiety as a reactive group can selectively respond to nitroreductase with a ratiometric fluorescence signal output. The limit of detection for nitroreductase is 0.0058 ng/mL. Moreover, the probe can be used to image the endogenous nitroreductase in A549 cells under hypoxic condition.

A family of novel molecular turnstiles 1–3 composed of two stators with pyridyl binding sites and a different-sized triptycene rotor was synthesized. The molecular turnstiles behave in an open state at room temperature in the absence of metal ions but display significantly different closed states in the presence of Ag+ and Pd2+. The Ag+-mediated turnstiles 1–3Ag exhibited closed states but unreadable bistability at ambient temperature because the Ag+-mediated macrocyclic framework is not able to restrict the rotations of the rotors; while temperature was decreased, the macrocyclic frameworks became stable enough to halt the rotations of the rotors, eventually leading to the readable closed states for 1–3Ag. In contrast, Pd2+-mediated macrocyclic frameworks are stable, giving rise to a detectable closed state of turnstiles 1–3Pd in a wide range of temperatures. These findings have also been supported by DFT calculations.

A series of N2,N6-bis(triptycene-9-yl)pyridine-2,6-dicarboxamides 1–4 were designed and synthesized. Due to rotational constraint of the 2,6-diamidopyridine bridge, the triptycene components in the systems are held together. X-ray structures of 1–4 show that the molecules adopt a gear-like geometry in the solid states. DFT (B3LYP/6-31G(d)) calculations predict the gear-like C2 conformation as global minimum structures for 1 and 2 and suggest that, through a slippage transition process, rotation of one triptycene component would give rise to a rocking vibration of the counter component due to the barrier for rotation of the triptycene components. VT NMR studies on 1–4 show that the pair of triptycene components undergo ceaseless slippage at room temperature but nearly freeze at temperatures as low as 183 K. Decreasing the temperature freezes the slippage between triptycene components as well, thus producing the appearance of phase isomers of 3 and 4. The dynamic features of the studied molecules indicate that this kind of molecule is able to function as a kind of molecular transmission device for transforming the mode of motion from rotation to rocking vibration.

Preorganized aryltriazole foldamers 1 and 2 were designed and synthesized. NMR studies and X-ray analysis demonstrate that 1 adopts a crescent conformation driven by a series of continuous hydrogen bonds at the periphery of the foldamer, whereas 2 displays a coil conformation. NMR titrations reveal that the affinities of fully preorganized foldamer 1 for halogen anions are much stronger that those of partially preorganized foldamer 2. Furthermore, it is found that such full preorganization makes 1 an effective transmembrane transporter for the chloride anion across a lipid bilayer.