Induced-fit catalysis of corannulene bowl-to-bowl inversion

Abstract

Stereoelectronic complementarity between the active site of an enzyme and the transition state of a reaction is one of the tenets of enzyme catalysis. This report illustrates the principles of enzyme catalysis (first proposed by Pauling and Jencks) through a well-defined model system that has been fully characterized crystallographically, computationally and kinetically. Catalysis of the bowl-to-bowl inversion processes that pertain to corannulene is achieved by combining ground-state destabilization and transition-state stabilization within the cavity of an extended tetracationic cyclophane. This synthetic receptor fulfils a role reminiscent of a catalytic antibody by stabilizing the planar transition state for the bowl-to-bowl inversion of (ethyl)corannulene (which accelerates this process by a factor of ten at room temperature) by an induced-fit mechanism first formulated by Koshland.

Chiral Buckybowl Molecules

“…Siegel and co-workers studied the bowl-to-bowl inversion of corannulene 1 and ethylcorannulene derivatives mediated by extended tetracationic cyclophane (Figure 8) [22,30]. This synthetic host forms a supramolecular complex with 1 and ethylcorannulene via induced fit, and the bowl-to-bowl inversion process was accelerated by a factor of 10 at room temperature.…”

“…and co-workers found that sumanene 2 attached with a mono-iodo substituent induces a slightly deeper bowl depth and a higher bowl inversion energy compared with other sumanene derivatives because of its steric effect, whereas the electronic effects caused by formyl and nitro substituents induced a shallower bowl depth and a lower bowl inversion energy [20]. Siegel and co-workers studied the bowl-to-bowl inversion of corannulene 1 and ethylcorannulene derivatives mediated by extended tetracationic cyclophane (Figure 8) [22,30]. This synthetic host forms a supramolecular complex with 1 and ethylcorannulene via induced fit, and the bowl-to-bowl inversion process was accelerated by a factor of 10 at room temperature.…”

“…Comparison of energy profile of bowl-to-bowl inversion of corannulene 1 (black) and tetracationic cyclophane: 1, complex (green) in Me2CO; absolute contributions of ground-state (GS) destabilization (0.5 kcal mol −1 ) and transition-state (TS) stabilization (2.0 kcal mol −1 ) to the overall energy-barrier decrease (ΔΔG ‡ catalysis) of the bowl-to-bowl inversion process of 1 inside the tetracationic cyclophane calculated by DFT (B97D/Def2-TZVPP). Reprinted from [22]. © 2014 Nature Publishing Group.…”

“…Unsubstituted buckybowls 1 and 2 are not chiral due to the presence of the reflection symmetry with respect to the mirror planes containing the rotational axis to show C 5v and C 3v symmetry, respectively. Introducing the addends may break the reflection symmetry to cause chirality, and alter their properties, such as bowl-to-bowl inversion [12][13][14][15][16][17][18][19][20][21][22], chirality [12,17,19,23], bowl depth [14,19,20], crystal structure [19,24,25], molecular recognition [2,26,27,51] and supramolecular assembly [3,[28][29][30]52,53] behavior, metal complexation [23,[31][32][33][34][35][36], electronic conductivity [19,37,38], and so on. Although the chirality is an important element in three-dimensional curved π-electron systems, thus far there have been no reports of the enantioselective synthetic control of the bowl chirality.…”

“…Further extension of the π-conjugation of these chiral enantioenriched buckybowls leads to homochiral carbon nanotubes, and these chiral carbon materials create new perspectives in chiral catalysis, chiral sensing, chiral separation sciences, etc. [15][16][17][18][19][20][21][22][23][24][25][26][27]. A better understanding of bowl chirality will help researchers find a good way to control the chiral self-assembly of carbon nanotubes (CNTs) or fullerenes, which have already exhibited exciting potential as next-generation functional materials [28][29][30][31][32][33][34][35][36][37][38].…”