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October 16, 2006
Volume 84, Number 42
p. 11

Supramolecular Chemistry

Molecules Get Suited Up

Novel assembly features one molecule clothed with another

Bethany Halford

Sometimes even molecules need to dress for success. Chemists at the University of California, Los Angeles, and London's Imperial College have come up with a new class of mechanically interlocked structures called suitanes. As the name suggests, the compounds feature one molecule dressed in another, with no covalent link between the two (Angew. Chem. Int. Ed. 2006, 45, 6665).

Angewandte Chemie
Dressed For Success A suit[2]ane, depicted in both ball-and-stick and space-filling models, has an hourglass "body" consisting of a slim core (yellow) between buxom anthracene units (blue). The "suit" (red) is made from crown ethers knitted together with aryl amines via imine formation.

A suitane's basic components consist of a single-molecule "body" with two or more rigid limbs and a close-fitting, all-in-one suit molecule that encompasses the body's torso. The body molecule's limbs protrude outward from the suit, just as arms and legs stick out of real-world clothes. Shorts are a good human-scale analogy for a suit[3]ane because three so-called limbs—two legs and a torso—poke out from the clothing; a T-shirt is analogous to a suit[4]ane; and the one-piece infant romper known as a onesie is akin to a suit[5]ane.

"The inspiration for the name came from looking at my grandson in a onesie, an American term I had never heard of before," says UCLA chemistry professor and Scotland native J. Fraser Stoddart.

Working in collaboration with David J. Williams' lab at Imperial College, chemists in Stoddart's group synthesized a suit[2]ane, the simplest assembly in the class. With the help of computational chemistry, they decided the ideal body molecule would possess a rigid hourglass figure. The suit portion of the assembly would need to be flexible enough to slip onto the body easily. Once the body was dressed, size, shape, and a specific molecular recognition motif would hold the suit, or components of the suit, in place.

The group based the body of their suit[2]ane on a slim phenyl waist flanked by two bulky anthracene units on either side. On the other side of the anthracene moieties, they placed a secondary ammonium salt intended to hydrogen bond with pyridine units in two complex crown ether structures that make up most of the suit.

The researchers then dressed the molecule in two steps. First, they threaded crown ethers onto both ends of the body. Next, they synthetically stitched the suit up with two equivalents of p-phenylenediamine, which formed imines with aldehyde units that were part of the crown ether. The assembly's integrity remained stable, even after a month in solution at 70 °C, indicating they had indeed made an interlocked compound.

The group plans to use the same template-directed approach to make more complex suitanes. "Discovering the way to dress a molecule with another one is a prelude to constructing artificial systems reminiscent of the living cell," Stoddart says.

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