Rotaxane | EPFL Graph Search

A rotaxane () is a mechanically interlocked molecular architecture consisting of a dumbbell-shaped molecule which is threaded through a macrocycle (see graphical representation). The two components of a rotaxane are kinetically trapped since the ends of the dumbbell (often called stoppers) are larger than the internal diameter of the ring and prevent dissociation (unthreading) of the components since this would require significant distortion of the covalent bonds. Much of the research concerning rotaxanes and other mechanically interlocked molecular architectures, such as catenanes, has been focused on their efficient synthesis or their utilization as artificial molecular machines. However, examples of rotaxane substructure have been found in naturally occurring peptides, including: cystine knot peptides, cyclotides or lasso-peptides such as microcin J25. Synthesis The earliest reported synthesis of a rotaxane in 1967 relied on the statistical probability that if two h

Self-assembly of boron-based supramolecular structures

Nicolas Christinat

This work describes the synthesis and characterization of boronic acid-based supramolecular structures. Macrocycles, dendritic structures, polymers, rotaxanes, and cages were assembled using four types of reversible reactions. The key point of the strategy is the parallel utilization of two –or more– of these reactions. Initially, aryl and alkylboronic acids were condensed with dihydroxypyridine ligands to give tetrameric or pentameric macrocycles, in which four or five boronate esters are connected by dative B-N bonds. These macrocycles were then used as scaffolds for the assembly of more complex structures from the multicomponent reaction of formyl functionalized boronic acids, with dihydroxypyridine ligands and primary amines. Dendritic structures having a tetrameric or pentameric macrocyclic core and four, five, eight, or ten amine-derived groups in their periphery were obtained. Three-component reactions were further used to prepare boronate ester polymers from aryl boronic acids, 1,2,4,5-tetrahydroxybenzene and either 1,2-di(4-pyridyl)ethylene or 4,4'-dipyridine. Crystallographic analyses show that the bis(dioxaborole) units are connected by dipyridyl linkers via dative B-N interactions. A computational study provides evidence that the polymers are strongly colored due to efficient intrastrand charge transfer excitations from the tetraoxobenzene to the dipyridyl linker. This latter property was used to assemble the first boron-based rotaxanes from 1,2-di(4-pyridyl)ethylene, catechol, 3,5-bis(trifluoromethyl)phenylboronic acid and 1,5-dinaphto-38-crown-10 or bis-p-phenylene-34-crown-10. In the last part of this work, boronate ester condensations were combined with imine condensations to build organic macrocycles and cages. The former interaction was also used together with metal-ligand interactions to prepare rhenium-based macrocycles. Finally, a nanometer-sized macrocycle was obtained in one step from four chemically distinct building blocks via the simultaneous utilization of the three reversible reactions.

EPFL2008

Self-assembly of boron-based supramolecular structures

Nicolas Christinat

EPFL2008