2 research outputs found
Guest-Triggered Zn<sup>II</sup> Translocation and Supramolecular Nuclearity Control in Calix[6]arene-Based Complexes
Two
new polytopic ligands based on a calix[6]Âarene scaffold were synthesized.
The truncated cone-shaped calixarene was functionalized at its small
rim by a tris-imidazole site, aimed at generating a tetrahedral Zn<sup>II</sup> complex, where a fourth labile site inside the cavity is
accessible through the funnel provided by its large rim. Tridentate
aza ligands (either two or three) were then grafted at this large
rim (the entrance of the cavity). Zn<sup>II</sup> coordination studies,
monitored by <sup>1</sup>H NMR spectroscopy, showed unprecedented
behavior in this family of heteropolytopic ligands. Indeed, it gives
access to complexes of various nuclearities in acetonitrile, where
zinc binding is under the supramolecular control of the guest. It
is first shown that, in the absence of a good guest donor (a primary
amine), Zn<sup>II</sup> binding is favored at the large rim where
two tridentate nitrogenous groups can form an octahedral complex.
The addition of a long guest such as heptylamine induces the quantitative
translocation of the Zn<sup>II</sup> ion from the large rim octahedral
(<i>O</i><sub>h</sub>) site to the small rim tetrahedral
(<i>T</i><sub>d</sub>) site provided by the trisimidazole
core and the guest ligand. With 2 equiv of Zn<sup>II</sup>, well-defined
dinuclear complexes were obtained and isolated, with one Zn<sup>II</sup> ion bound at each rim. Interestingly, it is shown that the binding
mode at the large rim is under the supramolecular control of the guest
bound at the small rim (with short guests, the <i>O</i><sub>h</sub> environment is obtained at the large rim, whereas long guests
disrupt this core through an induced-fit process); the partially included
and dangling alkyl chain opens the large rim (entrance of the cavity)
and pushes apart the tridentate moieties. As a result, a guest-induced
switch of Zn<sup>II</sup> binding mode occurs and frees one of the
tridentate groups from coordination, allowing further extension of
the complex nuclearity
Additional file 1: of Autonomous multi-joint soft exosuit with augmentation-power-based control parameter tuning reduces energy cost of loaded walking
Variability of positive augmentation power and work with cadence. (PDF 285 kb