Temperature‐Dependent Left‐ and Right‐Twisted Conformational Changes in 1 : 1 Host‐Guest Systems: Theoretical Modeling and Chiroptical Simulations

• Published in: Angewandte Chemie 2025-01, Vol.137 (1), p.n/a
• Main Authors: Suzuki, Nozomu, Taura, Daisuke, Furuta, Yusuke, Ono, Yudai, Miyagi, Senri, Kameda, Ryota, Haino, Takeharu
• Format: Article
• Language: English
• Subjects: Calixarenes; Chemical equilibrium; Chemical synthesis; Chiral materials; Chirality; Circular dichroism; Dichroism; Host-Guest Systems; Molecular Recognition; NMR; Non-Covalent Interactions; Nuclear magnetic resonance; Porphyrins; Temperature dependence; Titration; Twisted Conformations
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.202413340

An efficient strategy for high‐performance chiral materials is to design and synthesize host molecules with left‐ and right‐ (M‐ and P‐)twisted conformations and to control their twisted conformations. For this, a quantitative analysis is required to describe the chiroptical inversion, chiral transfer, and chiral recognition in the host‐guest systems, which is generally performed using circular dichroism (CD) and/or proton nuclear magnetic resonance (1H NMR) spectroscopies. However, the mass‐balance model that considers the M‐ and P‐twisted conformations has not yet been established. In this study, we derived the novel equations based on the mass‐balance model for the 1 : 1 host‐guest systems. Then, we further applied them to analyze the 1 : 1 host‐guest systems for the achiral calixarene‐based capsule molecule, achiral dimeric zinc porphyrin tweezer molecule, and chiral pillar[5]arene with the chiral and/or achiral guest molecules by using the data obtained from the CD titration, variable temperature CD (VT−CD), and 1H NMR experiments. The thermodynamic parameters (ΔH and ΔS), equilibrium constants (K), and molar CD (Δϵ) in the 1 : 1 host‐guest systems could be successfully determined by the theoretical analyses using the derived equations. Novel equations based on the mass‐balance model were applied to analyze 1 : 1 host‐guest systems for achiral and chiral host molecules with left‐ and right‐twisted conformations (HM and HP) and chiral and achiral guest molecules (GX). Theoretical analysis for the variable temperature circular dichroism (VT−CD) experiments resulted in the successful determination of the thermodynamic parameters, equilibrium constants (K), and molar CD values.