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Communication

Harnessing the Energy of Molecular Recognition in a Nanomachine Having a Photochemical On/Off Switch

Supporting Info

Roger J. Coulston,^† Hideki Onagi,^† Stephen F. Lincoln,^‡ and Christopher J. Easton*^†^§

Research School of Chemistry, Australian National University, Canberra ACT 0200, Australia, School of Chemistry and Physics, University of Adelaide, Adelaide SA 5005, Australia, and ARC Centre of Excellence in Free Radical Chemistry and Biotechnology

J. Am. Chem. Soc., 2006, 128 (46), pp 14750–14751

DOI: 10.1021/ja0651761

Publication Date (Web): October 26, 2006

†

Australian National University.

‡

University of Adelaide.

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

ARC Centre of Excellence in Free Radical Chemistry and Biotechnology.

, easton@rsc.anu.edu.au

Abstract

6^A-Deoxy-6^A-(N-methyl-3-phenylpropionamido)-β-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 °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-6^A-Deoxy-6^A-(N-methylcinnamido)-β-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.