In Search of Wasserman's Catenane.

We repeat the earliest claimed [2]catenane synthesis, reported by Wasserman over 60 years ago, in order to ascertain whether or not a nontemplate, statistical synthesis by acyloin macrocyclization does indeed form mechanically interlocked rings. The lack of direct experimental evidence for Wasserman's catenane has led to it being described as a "prophetic compound", a technical term used in patents for claimed molecules that have not yet been synthesized. Contemporary synthetic methods were used to reconstruct Wasserman's deuterium-labeled macrocycle and other building blocks on the 10-100 g reaction scale necessary to generate, in principle, ∼1 mg of catenane. Modern spectrometric and spectroscopic tools and chemical techniques (including tandem mass spectrometry, deuterium nuclear magnetic resonance (NMR) spectroscopy, and fluorescent tag labeling) were brought to bear in an effort to detect, isolate, and prove the structure of a putative [2]catenane consisting of a 34-membered cyclic hydrocarbon mechanically linked with a 34-membered cyclic α-hydroxyketone.

Switched "On" Transient Fluorescence Output from a Pulsed-Fuel Molecular Ratchet.

We report the synthesis and operation of a molecular energy ratchet that transports a crown ether from solution onto a thread, along the axle, over a fluorophore, and off the other end of the thread back into bulk solution, all in response to a single pulse of a chemical fuel (CCl3CO2H). The fluorophore is a pyrene residue whose fluorescence is normally prevented by photoinduced electron transfer (PET) to a nearby N-methyltriazolium group. However, crown ether binding to the N-methyltriazolium site inhibits the PET, switching on pyrene fluorescence under UV irradiation. Each pulse of fuel results in a single ratchet cycle of transient fluorescence (encompassing threading, transport to the N-methyltriazolium site, and then dethreading), with the onset of the fluorescent time period determined by the amount of fuel in each pulse and the end-point determined by the concentration of the reagents for the disulfide exchange reaction. The system provides a potential alternative signaling approach for artificial molecular machines that read symbols from sequence-encoded molecular tapes.