Just 160 atoms have been made to tie themselves into the smallest version of the pentafoil knot ever made. It鈥檚 also the most complicated knot ever achieved by a single molecule.
The knot, also known as the cinquefoil or Solomon鈥檚 knot, is a 鈥減rime鈥� knot鈥�. Its woven star shape contains five crossing points and cannot be built from smaller knots, similar to the way a prime number cannot be the product of smaller numbers. A version of the pentafoil knot features on the flags of Ethiopia and Morocco, giving it cultural as well as mathematical significance.
Chemists have previously created a prime knot called a trefoil, which has three crossing points. and colleagues at the University of Edinburgh, UK, wove the pentafoil using 鈥渘eedles鈥� made of positively charged iron ions attached to long, skinny organic-molecule 鈥渢hreads鈥�.
Advertisement
When the researchers added negatively charged chloride ions, these ions became hubs, each attracting exactly five needle-and-thread compounds. In the process of arranging themselves around the central hub, the metal ions folded the organic molecules over one another, braiding them into a woven star shape. Finally, chemical bonds formed that connected the strands at the points of the star, turning the whole arrangement into a single molecule.
Some day, the researchers would like to knit a whole surface of knotted molecules. 鈥淧erhaps we could make a chain-mail type of material in which, just like a suit of armour, you鈥檝e got a very strong but very flexible material,鈥� says Leigh.