Molecular Machine Wrap

Taking a new twist on molecular machines, an international team of chemists has created a molecular shuttle by wrapping a helical molecule around a dumbbell-shaped molecule (Science, DOI: 10.1126/science.1200143). The resulting assembly is akin to a rotaxane—a pair of mechanically interlocked molecules in which a dumbbell-shaped molecule is threaded through a macrocycle. But in the case of the new shuttle, the helix can unwind itself from the dumbbell. Project leaders Hua Jiang of the Chinese Academy of Sciences and Ivan Huc of France’s University of Bordeaux were inspired to build the device by the dynamic behavior of biological molecular machines, which slowly assemble and disassemble but rapidly do work when all their components are in place. In Jiang and Huc’s molecular shuttle, an oligomeric aromatic amide—a molecular tape—forms a helix around a hydrocarbon rod equipped with bulky substituents at each end and carbonyl anchor points for hydrogen bonding. Although winding and unwinding of the helix is slow, once in place the helix quickly shuttles up and down the rod between different hydrogen-bonding sites. “This modular design and dynamic assembly open up promising capabilities in molecular machinery,” the researchers note.