Adaptive Chirality of an Achiral Cage: Chirality Transfer, Induction, and Circularly Polarized Luminescence through Aqueous Host–Guest Complexation

Abstract

Chirality transfer, induction, and circularly polarized luminescence (CPL) using supramolecular hosts, such as macrocycles and cages, have been explored for wide-ranging applications in chiral recognition, sensing, catalysis, and chiroptical functional materials. Herein, we report the adaptive chirality of an achiral tetraphenylethene (TPE)-based octacationic cage (1) induced by binding with enantiopure deoxynucleotides (A, T, C, and G) through host-guest (H-G) complexation inwater. The hydrophobic cavity of the cage efficiently stabilizes the hydrogen-bonded dimerization of deoxynucleotides (A 2 , T 2 , C 2 , and G 2 ) to form H-G complexes in 1∶2 ratios. Given the photophysical properties and dynamic rotational conformation of the TPE units of the cage, cage⊃ deoxynucleotide complexes exhibited excellent chiroptical properties based on chirality transfer and induction from the chiral guest to the achiral host. For this supramolecular system, the cage showed a unique adaptive chirality of the double clockwise-typed (PP) rotational conformation of the two TPE units, which was induced by chiral guests (e.g., A 2 , T 2 , C 2 , and G 2 ) through H-G complexation in water. Furthermore, the adaptive chirality of the cage⊃deoxynucleotide complexes successfully induced CPL signals in homogeneous aqueous solutions. This study provides insights for the construction of adaptive chirality from an achiral TPE-based octacationic cage with dynamic conformational nature, and might facilitate further design of chiral functional materials for several applications, such as chiral recognition, sensing, displays, catalysis, and other chiral fluorescent supramolecular systems based on aqueous H-G complexation.

Stabilization and Multiple-Responsive Recognition of Natural Base Pairs in Water by a Cationic Cage

“…Similarly, CD spectra of 1 (20 μM) with a 1:1 mixture of G and C also exhibited two new negative CD signals centered at 330 nm (g abs ≈ −2.7 × 10 −4 ) and 395 nm (g abs ≈ -2.8 × 10 −4 ), and stronger negative/positive CD signals at 200-250 nm (g abs(220 nm) ≈ −4.40 × 10 −4 ) and 250-300 nm (g abs (280 nm) ≈ 1.8 × 10 −4 ) when compared with free guests (Figure 4b and Supporting Information Table S4). Based on previous reports [18][19][20]31,33,34 and theoretical calculations (Supporting Information Figure S18), the negative Cotton effect in the 300-450 nm region is attributed to the P-rotational conformation of TPE units, strongly suggesting that P-rotational conformation of TPE units on the chiral host-guest complexes is preferential. Energyminimized structures of possible chiral host-guest complexes show that the dynamic conformation transformation from MP-1/MM-1 to PP-1 is an energy-favored process when a cage binds with base pairs (Supporting Information Figure S19).…”

“…[12][13][14][15] The water-soluble tetraphenylethene (TPE)-based octacationic cage (1) possesses remarkable absorption, excellent fluorescence, and adaptive chirality (Scheme 1a, top). [16][17][18][19][20] Based on the left-handed (M) and right-handed (P) rotational conformation of two TPE units (Scheme 1a, bottom), in theory, 1 can have three conformational isomers. including mesomeric PM-1 and a pair of racemic MM-1 and PP-1.…”

“…However, this TPE-based achiral cage can preferentially adopt one of the chiral conformations (PP or MM) to exhibit adaptive chirality via efficient through-space chirality transfer between cage and guests when binding with chiral guests. 19 Therefore, an achiral cage 1 with dynamically adaptive features could be an ideal host for recognizing chiral biomolecules or bioassemblies with chiroptical responses.…”

Advances in Chirality Sensing with Macrocyclic Molecules

“…These macrocyclic molecules could thus recognize biomolecules, such as nucleotides and DNA, through multiple orthogonal responses, which improves the accuracy of detection and identification of biomolecules in biocompatible media. TPE units have been introduced into an octa-cationic cage to give a meso-racemic compound because the two TPE cells in the cage adopt P and M helical conformations simultaneously [36]. Because of the existence of eight electron-defective pyridine rings, cage 22 was able to recognize electron-rich guest molecules well through C-H .…”

Hollow and highly diastereoselective face-rotating polyhedra constructed through rationally engineered facial units

“… 10 On the other hand, introducing chiral guests may also enable the chirality transfer to the cage hosts, templating the formation of specific diastereoisomers. 11 In both cases, however, the intervention of extra components, e.g. metal salts and chiral small molecules, is required.…”