Three Tales of Supramolecular Analytical Chemistry

Acyclic Cucurbit[n]uril‐Type Receptors: Aromatic Wall Extension Enhances Binding Affinity, Delivers Helical Chirality, and Enables Fluorescence Sensing

“…Scheme 1a lso shows as chematic representation of ah elical conformation of M3 that could occur due to steric clashes between the anthracene walls. [35] The presented 1 Ha nd 13 CNMR data is also consistentw ith a rapidly equilibrating mixture of both senses of helical chirality. In order to gauget he self-association and dynamic properties of M3 in water we first performed ad ilution experiment monitored by 1 HNMR ( Figure S5).…”

“…Subsequently,m ethylene bridgedg lycoluril tetramer (Tet) was allowedt or eact with W2 under acidic conditions (TFA/Ac 2 O, 1:1) at 110 8Ci nasealed tube to deliver crude M3 (Scheme 1) after precipitation with acetone.P urification of M3 wasa chieved by repeated washing of the crude materialw ith MeOH, followed by size exclusion chromatography (Sephadex G25) using H 2 Oa se luent to afford M3 in 7.4 % yield. Host M3 was characterized by 1 HNMR, 13 resonances for C 2v -symmetric M3 due to accidentald egeneracy of the two CH 3 resonances. Scheme 1a lso shows as chematic representation of ah elical conformation of M3 that could occur due to steric clashes between the anthracene walls.…”

“…M3 (M2) displays higher affinity toward 24 than 6 (M3:3 4.5-fold; M2: 29.0-fold). Ac onsideration of the homologous series of guests (6,13,11,14,a nd finally 23)t hat contain hydrophobic moieties of different size and width is also instructive. Acrosst his series, M3 is am ore potent host than M2 (6:1 .7-fold; 13:5 .7fold; 11:1.25-fold; 14:2.0-fold; 23:1 12-fold) andt he selectivity becomes higher as the size/width of the guest exceeds the volumeo ft he smaller M2 hosts cavity.C B [8] was previously observedt ob ind 23 much stronger than CB [7] due to am ore pronounced cavity size mismatch.…”

“…1-3 and 6; 10 and 11; 12 and 13; 15 and 16)p resumably due in part to differences in M3•guest K a .D iscrimination between diammonium guestsw ith different hydrophobic moieties (e.g. 6,11,13,14,23)i sa lso efficient. One subset of guests that cannotb ed iscriminateda re compounds 8, 9,a nd 14,w hich contain electronic deficientp yridinium units whichf ully quencha nd therefore eliminate the difference in fluorescenceo ft hose M3•guest complexes.I ti sw orth emphasizing that the LDA plots were createdu sing as ingle host (M3)a to nly three concentrations.…”

“…molecular containers) occupies ac entral role in the field of supramolecular chemistry because the preorganization inherent to macrocyclic scaffolds generally results in high affinity and selectivity.S ome of the mostp opular classes of macrocyclic receptors include the crown ethers, [1c] cryptands, [1b] cyclodextrins, [6] calixarenes, [7] cyclophanes, [1a, 3a, 8] cavitands, [9] pillararenes, [10] as well as cages self-assembledb y H-bonding, the hydrophobic effect, and metal-ligand interactions. [9c, 11] Macrocycles are at the heart of solutions to societally important problemsi ncluding the formulation of insoluble drugs, [6] the household product Febreeze TM , [12] glucose monitors, [13] sequestrants for nuclear waste ions, [14] and the removal of contaminants from water sources. [15] Amongst thesem olecular containers, cucurbit[n]urils (CB[n], Figure 1) [16] have distin-guishedt hemselves due to their ability to form high affinity CB [n]•guest complexesi nh ighly selective and stimuli responsive processes in aqueous solution.…”