Rigidified Cavitand Hosts in Water: Bent Guests, Shape Selectivity, and Encapsulation

Abstract

We report the synthesis and characterization of two water-soluble container compounds (cavitand hosts) with rigidified open ends. One cavitand uses four (CH2)4’s as spacers to bridge the adjacent walls, while another cavitand uses four CH2CH2OCH2CH2’s bridges and features a wider open end. The spacers preorganize the deep cavitands into vase-like, receptive shapes and prevent their unfolding to the unreceptive kite-like conformation. Cycloalkane guests (C6–C8) and small n-alkanes (C5–C7) form 1:1 complexes with the cavitands and move freely in the cavitands’ spaces. Hydrophilic compounds 1,4-dioxane, tetrahydrofuran, tetrahydropyran, pyridine, and 1-methylimidazole also showed good binding affinity to the new cavitands. Longer alkanes (C11–C14) and n-alcohols (C11–C16) are taken up with a −CH3 group fixed at the bottom of the cavity and the groups near the rim in compressed conformations. The methylene bridges appear to divide the cavitand into a narrow hydrophobic compartment and a broader space with exposure to the aqueous medium. Longer alkane guests (C15–C18), N,N-dimethyl­dioctylammonium, and dioctylamine induce the formation of capsules (2:1 host:guest complexes). The new cavitands showed selectivity for p/m-cresol isomers and xylene isomers. The cavitand with CH2CH2OCH2CH2 bridges bound long-chain α,ω-diols (C13–C15) and diamines in folded, U-shaped conformations with polar functions exposed to the aqueous medium. It was used to separate o-xylene from its isomers by using simple extraction procedures.

Recent Advances in the Applications of Water‐soluble Resorcinarene‐based Deep Cavitands

“…[34] To control the shape and size of the container's cavity and suppress the kite conformers, a new water-soluble dynamic cavitand H8 with covalently bridged benzimidazolones at the upper rim was prepared (Figure 9). [35] In contrast to dynamic cavitands H1 and H2, the flexible spacers of cavitand H8 cannot fold to the unreceptive kite shape. The motions of the walls are somewhat reduced, resulting in altered recognition properties.…”

“… [34] To control the shape and size of the container's cavity and suppress the kite conformers, a new water‐soluble dynamic cavitand H8 with covalently bridged benzimidazolones at the upper rim was prepared (Figure 9 ). [35] …”

Binding and Assembly of a Benzotriazole Cavitand in Water

“…Hydrogen bonding of benzimidazolone rims was introduced for dimerization in organic media, [17][18][19] while polar groups on the feet allow them to form capsules in water. [20] Simple hydrophobic interactions [9,[21][22][23][24][25][26][27] or their combination with electrostatic interactions [28] were also effective at creating capsules; even halogen [29,30] and chalcogen bonding [31] were incorporated for assembly by Diederich. These host/guest capsular assemblies are stable in both organic and aqueous [32] media.…”

Chirality Induction in a Hydrophilic Metallohelicate

“…The imitation of such naturally occurring systems by water-soluble artificial receptors has been studied for a long time. [1][2][3][4][5][6][7][8] The hydrophobic interior of artificial receptors, such as molecular capsules, can incorporate sizable molecules. Binding events can be detected spectroscopically and therefore used as chemical sensors.…”

“…Preorganized cavities in protein receptors recognize specific substrates, which regulates the protein structures and functionalities. The imitation of such naturally occurring systems by water‐soluble artificial receptors has been studied for a long time [1–8] . The hydrophobic interior of artificial receptors, such as molecular capsules, can incorporate sizable molecules.…”