Rotaxane 2010/06/02 Tobe Lab. Furutani Hajime
Contents • What isRotaxane? • History -First Synthesis -Host-Guest Chemistry -Improved Synthetic Method • Applications of Rotaxane -Rotaxane Specific Mobility -Molecular Switch -Molecular Machine • My Project -Chirality -Rotaxane Specific Chirality -My Project
What is Rotaxane ? A rotaxaneis a supramolecule consisting of a “dumbbell shaped axle” molecule and a “ring” molecule. ring dumbbell Rotaxane The dumbbell threads into cavity of the ring molecule. There are no strong chemical bond between the two components The ring molecule is impossible to slip out.
History-First Synthesis- probabilistic method end-cap thread Harrison, S. et al.J. Am. Chem. Soc. , 1967, 89, 5723-5724 rotaxane Repetition of above thread-end-cap processes 70 times afforded resulted rotaxanes in only 6% yield. Holes of molecular rings is too small to be threaded. The quite low probability makes rotaxane synthesis difficult. How about using “temporary covalent bonding” ?
History-First Synthesis- Schill, G. et al. 1967; Jus.Liebigs Ann. Chem.1969, 53, 721 This synthesis needed many steps , and resulted in not good yield. In general, rotaxaneswere… 1. difficult to be synthesized. 2. interested only in their structure. Progresses of “Host-Guest Chemistry” improved the situation dramatically.
History-Host-Guest Chemistry- A molecule binds another molecule using weak interaction. + Weak and Attractive Interaction Host Guest Host-Guest If a ring can bind an axle, a subsequentcapping reaction gives a rotaxane. + capping Guest-Axle Rotaxane Host-Guest “Pseudo” rotaxane Host-Ring
History-Improved Synthetic Method- Crown ethers are well-known as ring-shaped “host” molecules. Crown ether Lone pair on oxgen Electron negativity Crown ethers capture cations in their cavities. If axles have cationic moieties, crownethers capture the axles very efficiently. 22% yield D. H. Busch et al.J. Chem. Soc., Chem. Commun , 1995, 89, 1289-1291
Applications of Rotaxane-RotaxaneSpecific Mobility- Improvements of rotaxane syntheses make advanced researches on rotaxane specific properties easily. One of the most important properties is “mobility”. shuttling In above scheme, the ring moves along the axle freely. Because of this property, rotaxanesare expected to be prime candidate of molecular switches, molecular memories and more advanced machines.
Applications of Rotaxane-Molecular Switch- If a rotaxane consists of a ring and an axle having two cationic moieties, the ring locates on one of the cationic units. A position of a ring can be controlled by external stimuli. J. F. Stoddart et al.J. Am. Chem. Soc. , 1998, 120, 11932-11942 This positional control is elementary operation for “molecular switch” and ”molecular memory”
Applications of Rotaxane-Molecular Machine- Shuttling motion induced by UV light emittion lifted a drop up . The rotaxane worked as a transport machine. D. A. Leigh et al.Nat. Mater , 2005, 4, 704-710
My Project-Chirality- Molecules sometimes have right-handed or left-handed properties. * * Central chirality If a molecule in a mirror is not superimposable to an original molecule, the molecule is ”chiral”. Helicity Planar chirality Axial chirality
My Project-Rotaxane Specific Chirality- Achiral ring Achiral axle A rotaxane consisting of an achiral ring and an achiral axle sometimes has chirality. Chiralrotaxane
My Project I’ve been investigating in a rotaxane which can interconvert between right and left handed-properties. And the rotaxane can change the interconversion frequency by photo or thermal stimuli. Left-Handed Right-Handed I’ll talk in detail on presentation next semester.
Summary ・A rotaxaneis a supramolecule consisting of a “dumbbell shaped axle”molecule and a “ring” molecule. ・Synthetic methods of supramolecules having threaded structure were well improved accompanying with Host-Guest chemistry ・Rotaxanes have high flexibility of mobility. ・Rotaxanes are expected to be prime candidate for molecular machines. ・Rotaxanes sometimes have rotaxane-specific chirality. ・I’ve been investigating in a rotaxane which interconverts between enantiomers.