| Research Abstract |
1. We have previously first developed a molecular machine, a light-powered chiral molecular motor of six-membered ring type. However, the thermal rotation step was slow, and therefore the speed up of motor rotation has been required.
2. In this research, we have synthesized the chiral and novel molecular motor of five-membered ring type, (2S,2'S)-(M,M)-trans-(-)-4a, and have clarified the mechanism and dynamics of the motor rotation by CD spectroscopy. Chiral ketone (S)-(+)-8 was synthesized by the CSDP acid method, and its absolute configuration was determined by X-ray crystallography. The compound (S)-(+)-8 was subjected to the McMurry reaction giving the chiral molecular motor, (2S,2'S)-(M,M)-trans-(-)-4a, in 26% yield. From the absolute configuration determined and CD spectrum, it was found that the absolute configurations of motor trans-(-)-4a and other isomers reported by the Feringa group were incorrect.
3. The photochemical and thermal rotation steps of the molecular motor, trans-(-)-4a, were traced by CD spectroscopy clarifying the motor rotation dynamics ; the activation energy of the thermal rotation step of unstable motor isomer, (2S,2'S)-(P,P)-trans-4d, was 16.8 kcal/mol, which is ca. 8 kcal/mol lower than that of the molecular motor of six-membered ring type. We have thus succeeded in constructing the molecular motor of high speed rotation.
4. We have next studied the continuous rotation of the molecular motor trans-(-)-4a by CD spectroscopy. Even after 10 times rotation, the CD intensity of the motor molecule remained almost unchanged, indicating that this molecular motor is durable for such continuous rotation.
5. In addition, we have first succeeded in crystallization of a chiral C60 fullerene derivative and also in determination of its absolute configuration by X-ray crystallography at the SPring 8.
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