705281-64-7

Upstream product

• 24424-99-5 di-tert-butyl dicarbonate 

Downstream Products

• 705281-66-9 C₆₆H₇₂N₁₂O₆ 
• 705281-65-8 C₆₆H₇₂Cl₃N₃O₆ 

Relevant academic research and scientific papers

Operating molecular elevators

Inspired by the concept of multivalency in living systems, two mechanically interlocked molecules have been conceived that incorporate not once or twice but thrice the features of a pH-switchable [2]rotaxane with two orthogonal recognition sites for dibenzo[24]crown-8 (DB24C8), and 2,3-dinaphtho[24]crown-8 (DN24C8)-one a dialkylammonium ion (CH2NH2 +CH2) and the other a bipyridinium dication (BIPY 2+). Whereas at low pH, the CH2NH2 +CH2 sites bind the DB24C8/DN24C8 macrocycles preferentially, at high pH, deprotonation occurs with loss of hydrogen bonding and the macrocycles will move to the BIPY2+ sites, where they can acquire some stabilizing [π-π] stacking interactions. Such mechanically interlocked molecules have been assembled from a trifurcated rig-like component wherein the dumbbell-like components of three [2]rotaxanes have one of their ends fused onto alternate positions (1,3,5) around a benzenoid core. The rig is mechanically interlocked by a platform based on a tritopic receptor, wherein either three benzo[24]crown-8 or three 2,3-naphtho[24]crown-8 macrocycles are fused onto a hexaoxatriphenylene core. The synthesis of these molecular elevators involves 1:1 complexation, followed by stoppering, i.e., feet are added to the rig. 1H NMR spectroscopy and cyclic voltammetry, aided and abetted by absorption spectroscopy, have been employed to unravel the details of the mechanism by which the rig and platform components move on the alternate addition of base and acid. For each molecular elevator, the platform operates by taking three distinct steps associated with each of the three deprotonation/reprotonation processes. Thus, molecular elevators are more reminiscent of a legged animal than they are of passengers on freight elevators.

A Mechanically Interlocked Bundle

The prototype of an artificial molecular machine consisting of a trisammonium tricationic component interlocked with a tris(crown ether) component to form a molecular bundle with averaged C3ν symmetry has been designed and synthesized. The system is based on noncovalent interactions, which include 1) N+-H...O hydrogen bonds; 2) C-H...O interactions between the CH2NH2 +CH2 protons on three dibenzylammonium-ion-containing arms, which are attached symmetrically to a benzenoid core, and three dibenzo[24]crown-8 macrorings fused onto a triphenylene core; and 3) π...π stacking interactions between the aromatic cores. The template-directed synthesis of the mechanically interlocked, triply threaded bundle involves post-assembly covalent modification, that is, the efficient conversion of three azide functions at the ends of the arms of the bound and threaded trication into bulky triazole stoppers, after 1,3-dipolar cycloaddition with di-tert-butylacetylenedicarboxylate to the extremely strong 1:1 adduct that is formed in dichloromethane/acetonitrile (3:2), on account of a cluster effect associated with the paucivalent adduct. Evidence for the averaged C3ν symmetry of the molecular bundle comes from absorption and luminescence data, as well as from electrochemical experiments, 1H NMR spectroscopy, and mass spectrometry. The photophysical properties of the mechanically interlocked bundle are very similar to those of the super-bundle that precedes the formation of the bundle in the process of supra-molecular assistance to covalent synthesis. Although weak non-nucleophilic bases (e.g., nBu3N and iPr2NEt) fail to deprotonate the bundle, the strong tBuOK does, as indicated by both luminescence and 1H NMR spectroscopy. While deprotonation undoubtedly loosens up the interlocked structure of the molecular bundle by replacing relatively strong N+-H...O hydrogen bonds by much weaker N-H...O ones, the π...π stacking interactions ensure that any structural changes are inconsequential, particularly when the temperature of the solution of the neutral molecular bundle in dichloromethane is cooled down to considerably below room temperature.