A German chemist has constructed a mathematical method to describe the geometric structure of knotted molecules.

Dirk Andrae, a theoretical chemist at Universität Bielefeld, argues that any monomer that forms a linear polymer can be expected to exist in a knotted structure which, once formed, is likely to be stable. 

Andrae has proposed a mathematical procedure that can be used together with force field or quantum mechanical methods to obtain the geometric arrangement of a knotted molecule. Once the structure is known, standard quantum chemical methods could be used to study the knot's electronic structure, he said.

Knots and links are familiar to us all in everyday life, but they are also found at the molecular level in synthetic compounds, proteins and some forms of DNA.  This is the motivation for studying the chemical theory of molecular knots, said Andrae. The areas of topological and supramolecular chemistry are of key importance for nanotechnology, according to Andrae, so understanding the possibilities for new knots and links and designing new synthetic strategies to realise these are crucial.

'Of course, this will require suitable tools to be available,' said Andrae. Currently the synthesis of knotted and linked molecules relies on self-assembly and template effects. Andrae speculates that a 'surface template technique' could be developed to synthesise new molecular knots and links. He envisages that molecular chains of a desired length could be attached to a surface that is covered with suitable linker groups in a controlled and ordered manner, gradually forming a knot which can then be detached from the surface.

Caroline A Moore