# Molecular shuttle

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thumbnail|200px|An example of a molecular shuttle where the macrocyle (green) moves between two stations (yellow).
A   '''molecular shuttle''' in [supramolecular chemistry](/source/supramolecular_chemistry) is a special type of [molecular machine](/source/molecular_machine) capable of [shuttling](/source/Shuttle_(weaving)) molecules or ions from one location to another. This field is of relevance to [nanotechnology](/source/nanotechnology) in its quest for nanoscale electronic components and also to [biology](/source/biology) where many biochemical functions are based on molecular shuttles. Academic interest also exists for synthetic molecular shuttles, the first prototype reported in 1991 based on a [rotaxane](/source/rotaxane).<ref name="AnelliSpencer1991">{{cite journal|last1=Anelli|first1=Pier Lucio|last2=Spencer|first2=Neil|last3=Stoddart|first3=J. Fraser|title=A molecular shuttle|journal=Journal of the American Chemical Society|volume=113|issue=13|year=1991|pages=5131–5133|issn=0002-7863|doi=10.1021/ja00013a096|doi-access=free|pmid=27715028 |bibcode=1991JAChS.113.5131A }}</ref>

This device is based on a molecular thread composed of an [ethyleneglycol](/source/ethyleneglycol) chain interrupted by two [arene](/source/arene_compound) groups acting as so-called '''stations'''. The terminal units (or '''stoppers''') on this wire are bulky [triisopropylsilyl](/source/triisopropylsilyl) groups. The '''bead''' is a tetracationic [cyclophane](/source/cyclophane) based on two [bipyridine](/source/bipyridine) groups and two [para-phenylene](/source/phenylene) groups. The bead is locked to one of the stations by [pi-pi interaction](/source/pi-pi_interaction)s but since the [activation energy](/source/activation_energy) for migration from one station to the other station is only 13 [kcal](/source/Calorie)/[mol](/source/mole_(unit)) (54 [kJ](/source/kilojoule)/mol) the bead shuttles between them. The stoppers prevent the bead from slipping from the thread. Chemical synthesis of this device is based on [molecular self-assembly](/source/molecular_self-assembly) from a preformed thread and two bead fragments (32% [chemical yield](/source/chemical_yield)). 

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In certain [molecular switch](/source/molecular_switch)es the two stations are non-degenerate.

==References==
{{Reflist}}

Category:Supramolecular chemistry
Category:Molecular machines

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Adapted from the Wikipedia article [Molecular shuttle](https://en.wikipedia.org/wiki/Molecular_shuttle) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Molecular_shuttle?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.