Knotting and Threading of Molecules: Chemistry and Chirality of Molecular Knots and Their Assemblies

Abstract

How and why do molecules tangle or thread? Investigations of molecular knots (knotanes) may shed some light on the mechanisms of (supra)molecular templation and the folding of molecules that result in intertwining. The topological chirality of these fascinating molecules leads to new types of isomerism and paves the way to nanosized molecular motors. Their preparation and derivatization makes high demands on modern synthetic methods and analytical separation since molecular knots are formed in a more or less planned design based on metal coordination or hydrogen-bonding patterns. This Review describes the development of templation techniques for the synthesis of knotanes and their chiral resolution as well as their selective functionalization and use as building blocks in the synthesis of higher knotane assemblies. Such assemblies can possess linear, branched, or even macrocyclic structures which, on the one hand, introduce unprecedented isomeric compositions that arise from multiple topological stereogenic units and, on the other, define new types of artificial macromolecules beyond polymers and dendritic species.

Molekulare Knoten

“…[116] Vçgtle und Lukin berichteten, dass das dynamische Verhalten seines Kleeblattknotens lçsungsmittelabhängig ist, in anderen Solvenzien als DMSO fand eine langsame dynamische Bewegung statt (erkennbar durch Signalverbreiterung in den NMR-Spektren). [117] …”

“…Vçgtle fand heraus,d ass eine dünne Schicht eines organischen Kleeblattknotens Octan adsorbieren kann. [117] Tr abolsis Kleeblattknoten (Schema 10) kçnnen transmetalliert werden, und es ist mçglich, das Anion in der zentralen Kavitäta uszutauschen (über Bindung von I À ,N 3 À , SCN À und NO 3 À wurde berichtet). [90,91] [120] Simulationen haben auch gezeigt, dass einige Knoten die bevorzugten Selbstassemblierungsprodukte von Lçsungen helicaler Bausteine mit "klebrigen" Enden sind.…”

C22H46: The smallest open 31-knotted alkane by computer-aided design

“…1a) are present everywhere in daily life (ropes, ties, art, etc. ); nevertheless, these intertwining designs are also found at the extreme opposite boundaries of the universe as gigantic galactic knots [4,5] or nanoscience devices such as knotted proteins [6,7], synthesized molecular knots [8][9][10], etc. Landmark works were the introduction of knot topology in the field of chemistry [11], the thermodynamics [12] of knot formation and the first reported synthesis [13] of a molecular knot.…”

A grid-enabled algorithm yields figure-eight molecular knot

“…Molecular knots are also referred to by some chemists as 'knotanes'. The term knotane was coined by Lukin and Vögtle [1] by analogy with rotaxane and catenane. Knotanes are increasingly found in nature (knotted proteins [2,3] and DNA [4]), while synthesised molecular knots [5,6] along with catenanes and rotaxanes have been proposed as parts of potential molecular machines [7 -9] or scaffolds [10] for drug carriers.…”