[5]Rotaxane and [5]Pseudorotaxane Based on Cucurbit[6]uril and Anchored to a Meso-tetraphenyl Porphyrin

A bistable CB6-based [3]rotaxane with two recognition sites has been prepared very efficiently in a high yield synthesis through CB6 catalyzed 1,3-dipolar cycloaddition; this rotaxane behaves as a reversible molecular switch and exhibits conformational changes caused by the movement of rings under base, acid and heat stimuli from one location to the other.Mechanically interlocked molecules assembled through host-guest chemistry, such as rotaxanes and catenanes, containing more than one recognition site are proving to have great potential for the construction of molecular switches and motors. In these systems, the ring of the molecule can shuttle under external stimulus (chemical, electrochemical or photochemical) from one location to others. 1 In doing this, they convert chemical, electrochemical or photochemical energy into mechanical energy. To date, many elegantly designed rotaxanes and catenanes have been reported. 2 When appropriately designed, bistable [3]rotaxanes in particular have great potential to act as stimuli-responsive artificial molecular muscles. However, there are only a few examples of rotaxanes which resemble linear artificial molecular muscles. [3][4][5] In these systems, the expansion and contraction caused by the movements of the hosts from one recognition site to the other can be monitored via spectroscopic methods ( 1 H NMR, UV-Vis and fluorescence), and cyclic voltammetry.Cucurbit[6]uril (CB6) and its homologues are among the hosts, which can be used in the preparation of rotaxanes. Cucurbituril is prepared from the acid condensation of glycoluril and formaldehyde; it has a hydrophobic cavity, along with two matching hydrophilic carbonyl portals. [6][7][8] Owing to these structural features, CB6 binds well with protonated mono-and di-aminoalkanes mainly through ion-dipole interactions and the hydrophobic effect. Moreover, CB6 has been shown to catalyze 1,3-dipolar cycloaddition between properly functionalized alkyne and azide groups to yield 1,4-disubstituted triazoles. A number of rotaxanes and polyrotaxanes have been designed and synthesized by using the catalytic effect of CB6. [9][10][11][12] There are a number of examples of CB6-based bistable [2]rotaxanes which behave as molecular switches. 13 However, to the best of our knowledge, there is no example of a CB-based bistable [3]rotaxane mimicking the behaviour of artificial molecular muscles. Here, we report the design, synthesis and the reversible switching processes of a CB6 based [3]rotaxane. This rotaxane is prepared very efficiently by CB6-catalyzed 1,3-dipolar cycloaddition in a high yield; it is composed of two CB6s and a dumbbell with two recognition sites, namely diaminotriazole and dodecamethylene, a flexible spacer, which is long enough to accommodate more than one CB6. The movement of CB6s which can be triggered by base, acid and heat causes a large conformation change of this rotaxane. This has been investigated by 1 H NMR spectroscopy.[3]Rotaxane was synthesized according to Scheme 1 by following the procedures des...

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“…11,12 It was fully characterized by spectroscopic techniques ( 1 H, 13 C NMR and FT-IR), and elemental analysis.…”

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confidence: 99%

Molecular switch based on a cucurbit[6]uril containing bistable [3]rotaxane

et al. 2007

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“…[11,13] The products were characterized by using spectroscopic techniques ( 1 H, 13 C NMR, and FTIR) and elemental analysis.…”

Section: Resultsmentioning

confidence: 99%

“…[10][11][12][13] All other reagents and solvents were of commercial reagent grade and were used without further purification, except where noted. NMR spectra were recorded by using a Bruker Avance DPX-400 MHz spectrometer.…”

Section: Methodsmentioning

confidence: 99%

“…Cucurbiturils have a hydrophobic cavity and two identical hydrophilic carbonyl portals. [6][7][8][9][10][11][12][13] CB6 binds well to protonated mono-and diaminoalkanes as a result of these structural features, mainly through ion-dipole interactions and the hydrophobic effect.…”

Section: Introductionmentioning

confidence: 99%

“…[8][9][10][11] There are also a number of examples of CB6-based bistable [2]rotaxanes that behave as molecular switches. [12] The properties of rotaxanes and pseudorotaxanes in other applications can be best exploited if their synthesis is straightforward and very efficient.…”

Section: Introductionmentioning

confidence: 99%

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pH‐Triggered Dethreading–Rethreading and Switching of Cucurbit[6]uril on Bistable [3]Pseudorotaxanes and [3]Rotaxanes

Tuncel

Katterle

2008

Chemistry A European J

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The CH bond activation of small alkanes by the gaseous MgO+. cation is probed by mass spectrometric means. In addition to H‐atom abstraction from methane, the MgO+. cation reacts with ethane, propane, n‐ and iso‐butane through several pathways, which can all be assigned to the occurrence of initial CH bond activations. Specifically, the formal CC bond cleavages observed are assigned to CH bond activation as the first step, followed by cleavage of a β‐CC bond concomitant with release of the corresponding alkyl radical. Kinetic modeling of the observed product distributions reveals a high preference of MgO+. for the attack of primary CH bonds. This feature represents a notable distinction of the main‐group metal oxide MgO+. from various transition‐metal oxide cations, which show a clear preference for the attack of secondary CH bonds. The results of complementary theoretical calculations indicate that the CH bond activation of larger alkanes by the MgO+. cation is subject to pronounced kinetic control.

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