Ricerc@Sapienza

Second-order rate constants of the aminolysis of 2-cyano-2-phenylpropanoic anhydride 3 by a series of N-methylanilines differently substituted in the aromatic moiety (4a-d) were measured in dichloromethane. The common reaction product of aminolysis is 2-cyano-2-phenylpropanoic acid 1, which is known to be an effective fuel for acid-base driven molecular machines, but cannot be used in molar excess with respect to the machine.

Back and forth motions of the acid–base-operated molecular switch 1 are photo-controlled by irradiation of a solution, which also contains the photolabile pre-fuel 4. The photo-stimulated deprotection of the pre-fuel produces controlled amounts of acid 2, the base-promoted decarboxylation of which fuels the back and forth motions of the Sauvage-type [2]-catenane-based molecular switch. Because switch 1 and pre-fuel 4 do not interact in the absence of irradiation, an excess of the latter with respect to 1 can be added to the solution from the beginning.

The back and forth motions of a crown-ether based wheel along the axis of a bistable rotaxane are triggered by the decarboxylation of 2-cyano-2-phenylpropanoic acid and detected by the oscillation of the EPR nitrogen splitting of a dialkyl nitroxide function mounted within the macrocyclic ring. When the p-Cl derivative of the acid is used, back and forth motions are accelerated. Conversely, with p-CH3 and p-OCH3 derivatives, the back motion is strongly inhibited by the insurgence of collateral radical reactions.