A new glycorotaxane molecular machine based on an anilinium and a triazolium station

International audienceA glycorotaxane molecular machine: The mannosyl [2]rotaxane shuttle contains an original triazolium station, an anilinium station, and a mannoside stopper. The mild synthesis of the [2]rotaxane can be carried out by a templated approach using a two-step sequence: 1) “click chemistry” and 2) N-methylation of the 1,2,3-triazole. The dibenzo[24]crown-8 (DB24C8) has a better affinity for the anilinium station than for the triazolium one. After deprotonation, the DB24C8 moves around the triazolium station

Cover Picture: Controlling the Chair Conformation of a Mannopyranose in a Large-Amplitude [2]Rotaxane Molecular Machine (Chem. Eur. J. 21/2009)

Cover pictureInternational audienceA domino effect from one extremity to the other is observed in a large‐amplitude mannosyl [2]rotaxane molecular machine. In their Communication on page 5186 ff., F. Coutrot and E. Busseron describe the efficient preparation of new [2]rotaxane molecular machines containing anilinium and either mono‐ or disubstituted pyridinium amide stations. In the case of the disubstituted pyridinium amide, the macrocycle shuttles from the anilinium to the pyridinium upon deprotonation and causes an impressive flipping of the chair conformation of the glucidic moiety

N-Benzyltriazolium as both Molecular Station and Barrier in [2]Rotaxane Molecular Machines

International audienceA two-station [2]rotaxane, consisting of a dibenzo-24-crown-8 macrocycle which surrounds a molecular axle containing an anilinium and a mono-substituted pyridinium amide molecular stations, has been synthesized via the alkyne-azide "click chemistry". The subsequent N-benzylation of the triazole moiety, which is located in the middle of the threaded axle, was then envisaged. In addition to affording a third molecular station (i.e. a triazolium station) for the macrocycle dibenzo-24-crown-8 (DB24C8), it was found that the benzyl moiety behaves as a kinetic molecular barrier which prevents the DB24C8 from shuttling along the molecular encircled axle from one extremity to the other. Depending on where the DB24C8 is initially located, the N-benzylation of the triazole allows to trap the DB24C8 either on the "left" or the "right" side of the thread with respect to the triazolium station. The presence of the benzyl barrier thus affords two different three-station [2]rotaxane molecular machines, in which some of co conformational states remain unbalanced and not at the equilibrium

Controlling the Chair Conformation of a Mannopyranose in a Large-Amplitude [2]Rotaxane Molecular Machine

International audienceMolecular machines boarding now! Molecular machines containing dibenzo[24]crown-8 (DB24C8) and based on an anilinium and a pyridinium amide station have been prepared. The DB24C8 shuttles upon variation of pH and interacts differently with the pyridinium amide station depending on its substitution. When the DB24C8 sits around the disubstituted amide, the conformation of the pyranose changes from 1C4 to 4C1

Very Contracted to Extended co-Conformations with or without Oscillations in Two-and Three-Station[c2]Daisy Chains

International audienceThe syntheses of various two- and three-station mannosyl [c2]daisy chains, based on a dibenzo-24-crown- 8 macrocyclic moiety and an ammonium, a triazolium, and a mono- or disubstituted pyridinium amide station, are reported. The ability of thesemolecules to act asmolecular machine based mimetics has been further studied by 1H NMR studies. In all the protonated ammonium states, the interwoven rotaxane dimers adopt an extended co-conformation. However, carbamoylation of the ammonium station led to many different other [c2]daisy chain co-conformations, depending on the other molecular stations belonging to the axle. In the two-station [c2]daisy chains containing an ammonium and a mono- or disubstituted pyridinium amide station, two large-amplitude relative movements of the interwoven components were noticed and afforded either an extended and a contracted or very contracted statewith, in the latter case, an impressive chairlike conformational flipping of themannopyranose from 1C4 to 4C1. In the case of the three-station-based [c2]daisy chains containing an ammonium, a triazolium, and disubstituted pyridinium amide, an extended and a half-contracted molecular state could be obtained because of the stronger affinity of the dibenzo-24-crown-8 part for, respectively, the ammonium, the triazolium, and the disubstituted pyridinium amide. Eventually, with axles comprising an ammonium, a triazolium, and a monosubstituted pyridinium amide, an extended conformation was noticed in the protonated state whereas a continuous oscillation between half-contracted and contracted states, in fastexchange on the NMR time scale, was triggered by carbamoylation. Variations of the solvent or the temperature allow the modification of the population of each co-conformer. Thermodynamic data provided a small free Gibbs energy ΔG of 2.1 kJ 3 mol-1 between the two translational isomers at 298 K

A very efficient synthesis of a mannosyl orthoester [2]rotaxane and mannosidic [2]rotaxanes

International audienc

Bistable or Oscillating State Depending on Station and Temperature in Three-Station Glycorotaxane Molecular Machines

International audienceHigh-yield, straightforward synthesis of two- and three-station [2]rotaxane molecular machines based on an anilinium, a triazolium, and a mono- or disubstituted pyridinium amide station is reported. In the case of the pH-sensitive two-station molecular machines, large-amplitude movement of the macrocycle occurred. However, the presence of an intermediate third station led, after deprotonation of the anilinium station, and depending on the substitution of the pyridinium amide, either to exclusive localization of the macrocycle around the triazolium station or to oscillatory shuttling of the macrocycle between the triazolium and monosubstituted pyridinium amide station. Variable-temperature 1H NMR investigation of the oscillating system was performed in CD2Cl2. The exchange between the two stations proved to be fast on the NMR timescale for all considered temperatures (298–193 K). Interestingly, decreasing the temperature displaced the equilibrium between the two translational isomers until a unique location of the macrocycle around the monosubstituted pyridinium amide station was reached. Thermodynamic constants K were evaluated at each temperature: the thermodynamic parameters ΔH and ΔS were extracted from a Van′t Hoff plot, and provided the Gibbs energy ΔG. Arrhenius and Eyring plots afforded kinetic parameters, namely, energies of activation Ea, enthalpies of activation ΔH≠, and entropies of activation ΔS≠. The ΔG values deduced from kinetic parameters match very well with the ΔG values determined from thermodynamic parameters. In addition, whereas signal coalescence of pyridinium hydrogen atoms located next to the amide bond was observed at 205 K in the oscillating rotaxane and at 203 K in the two-station rotaxane with a unique location of the macrocycle around the pyridinium amide, no separation of 1H NMR signals of the considered hydrogen atoms was seen in the corresponding nonencapsulated thread. It is suggested that the macrocycle acts as a molecular brake for the rotation of the pyridinium–amide bond when it interacts by hydrogen bonding with both the amide NH and the pyridinium hydrogen atoms at the same time

A new pH-switchable dimannosyl[c2]daisy chain molecular machine

International audienc