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Hideki Onagi

Publications and source records attributed to Hideki Onagi.

6 recordsLinked to original sources
PubMed2006

Harnessing the energy of molecular recognition in a nanomachine having a photochemical on/off switch.

6A-Deoxy-6A-(N-methyl-3-phenylpropionamido)-beta-cyclodextrin operates as a molecular machine, where the amide group serves as a torsion bar to harness the work output resulting from extraction of 1-adamantanol and consequent complexation of the aryl substituent by the cyclodextrin, when the latter behave as the piston and cylinder, respectively, of a molecular pump. At 25 degrees C, the complexation changes the ratio of the amide (Z)- and (E)-isomers from 2.4:1 to 25:1, on which basis the work performed on the amide bond is calculated to be 1.4 kcal mol-1. trans-6A-Deoxy-6A-(N-methylcinnamido)-beta-cyclodextrin and the cis isomer function as a more advanced version of the machine, with the alkene moiety serving as a photochemical on/off switch. Irradiation at 300 nm converts the trans cinnamide to the cis isomer, while the reverse process occurs at 254 nm. With the cis isomer there is little interaction of the phenyl group with the cyclodextrin cavity, so in that mode the machine is turned off. By contrast, complexation of the aryl substituent by the cyclodextrin occurs with the trans cinnamide and changes the ratio of the amide (Z)- and (E)-isomers from 2.6:1 to 100:1. Consequently, in this mode the machine is turned on, and the work harnessed by the amide bond is 2.1 kcal mol-1.

Journal Article↗
PubMed2004

Molecular reactors and machines: applications, potential, and limitations.

Molecular reactors are miniature vessels for the assembly of reactants at the molecular level, in order to change the nature of chemical transformations. It seems probable that those that will find most immediate applications are those that change product ratios or give products which would not readily form in the absence of the reactors, and thereby afford easy access to materials that are otherwise difficult to obtain. Molecular machines consist of interrelated parts with separate functions and perform some kind of work, at the molecular level. Practical examples are likely to be relatively uncomplicated and not based on individual functions of single-molecule devices. Instead they will probably rely on extensive redundancy of the molecular components and their interactions and reactions, as well as of the machines themselves.

Journal Article↗
PubMed2003

Separated and aligned molecular fibres in solid state self-assemblies of cyclodextrin [2]rotaxanes.

The conformations of two [2]rotaxanes, each comprising alpha-cyclodextrin as the rotor, a stilbene as the axle and 2,4,6-trinitrophenyl substituents as the capping groups, have been examined in solution and in the solid state, using (1)H NMR spectroscopy and X-ray crystallography, respectively. In solution, introducing substituents onto the stilbene prevents the cyclodextrin from being localized over one end of the axle. Instead the cyclodextrin moves back and forth along the substituted stilbene. In the solid state, the axles of the rotaxanes form extended molecular fibres that are separated from each other and aligned along a single axis. The molecular fibres are strikingly similar to those formed by the axle component of one of the rotaxanes in the absence of the cyclodextrin, but in the latter case they are neither separated nor all aligned.

Crystallography, X-Ray↗
PubMed2003

Installation of a ratchet tooth and pawl to restrict rotation in a cyclodextrin rotaxane.

Eight new [2]rotaxanes have been prepared, incorporating an alpha-cyclodextrin as the rotor, a stilbene as the axle, and trinitrophenyl substituents as capping groups. Strategies have been devised to elaborate these by linking the rotor to the axle, to produce two new [1]rotaxanes. Rotational motion in a selection of these rotaxanes has been investigated through the application of two-dimensional NMR spectroscopy by performing TOCSY, DQF-COSY, ROESY and HMQC experiments. This has shown that a methoxyl group incorporated on the stilbene and a succinamide joining the stilbene and the cyclodextrin behave analogously to a ratchet tooth and pawl, respectively, to restrict rotation.

Amides↗