Allosteric Supramolecular Receptors and Catalysts

Tren-Capped Hexaphyrin Zinc Complexes: Interplaying Molecular Recognition, Möbius Aromaticity, and Chirality

“…It is worth to stress the straightforward access to these capped hexaphyrins obtained in only three steps from a 5-(aryl)dipyrromethane. In contrast to their Möbius aromatic precursors 3 and 6, the three capped hexaphyrins 4, 5 and 8 exhibit typical features of Hückel antiaromatic [28]hexaphyrins within a rectangular topology. Indeed, while HRMS analysis confirmed 28π-electron species, UV-vis spectroscopy revealed highly broaden bands between 400 to 650 nm (Figure 3 and SI) and Q-like bands were not observed at higher wavelength.…”

“…These data traduce a general tendency of triply bridged Scheme 2. Synthesis of tren-capped [28]hexaphyrins 4, 5, 7, and 8, and oxidation of compounds 4, 5 and 8 in their 26π aromatic counterparts 9, 10 and 11. Conditions: i) acryloyl chloride, DIPEA, THF, -50 °C, 41 % (2 steps); ii) tren, CHCl3/CH3OH 1:9, 45 °C, 41 % (4); iii) Me-tren, CHCl3/CH3OH 1:9, 45 °C, 67 % (5); iv) 3-(chloromethyl)benzoyl chloride, Et3N, THF, 0 °C, 46 % (2 steps); v) NaI, DIPEA, THF, 70 °C then tren, not characterized (7); vi) NaI, DIPEA, THF, reflux then Me-tren, 50 °C, 55 % (8); vii) DDQ, CDCl3/CD3OD 9:1 or CDCl3 (9 and 11); (viii) DDQ, CHCl3, 82 % (10).…”

“…the tren unit (allosteric site) and the Zn-dipyrin unit (two-ligand binding site). 27,28 Considering these findings, several remarkable features have to be highlighted: (i) ligand 8 shows a total selectivity of metallation for the hexaphyrin vs. the tren binding site; (ii) the metallation process at a dipyrrin site is instantaneous at room temperature, suggesting an assistance mechanism of the tren unit; (iii) in contrast to all Möbius hexaphyrin metal complexes reported to date, the herein described Möbius complex does not involve β-CH activation of the inverted central pyrrole but features a NNNO coordination sphere (vide infra); (iv) the cooperative binding of two exogeneous ligands (amino and acetato), that triggers conformational restriction of a Möbius hexaphyrin metal complex, is unprecedented. 29 The planar-to-singly-twisted topological change allows antiaromatic-to-aromatic transformation; (v) the tren cap provides a basic site that can be selectively protonated without hexaphyrin demetallation.…”

Conformational Control of Energy Transfer: A Mechanism for Biocompatible Nanocrystal‐Based Sensors

“…Oligonucleotide conformational switches triggered by other simple stimuli have been characterized, [12] along with DNA-based aptamers that exhibit a conformational change on binding non-nucleotide targets, [19] while the field of supramolecular chemistry has provided a host of synthetic receptors that undergo a conformational change on guest binding. [20] The sensor design reported here demonstrates that any of these systems may be harnessed in a NC-nanomachine sensor. Achieving control over nanoconstruct stoichiometry is a key challenge that now must be addressed.…”

Metal‐Ion‐Regulated Miniature DNA‐Binding Proteins Based on GCN4 and Non‐native Regulation Sites

“…Rebek and coworkers first took advantage of the reorientation of 2,2'-bipyridine substituents on metal-ion complexation, to introduce an allosteric regulation site into a crown ether, thus regulating its alkali-metal-ion binding capacity. [20] The metal switching behaviour of substituted bipyridine and terpyridine has subsequently found many applications, primarily in aprotic solvents, [20][21][22][23] and has been introduced into a range of macromolecular synthetic (e.g., polymers) [24] and biological structures (e.g., DNA). [25] Despite the latter there are no reports of their introduction into peptides and their subsequent switching behaviour, beyond the work by Kelly and co-workers who introduced a bipyridine unit into a peptide backbone and reported that Cu II coordination triggers a transoid-to-cisoid conformational change, but only under basic conditions (pH 9.5).…”