Mechanically interlocked daisy-chain-like structures as multidimensional molecular muscles

• Published in: Nature chemistry Vol. 9; no. 2; pp. 128 - 134
• Main Authors: Chang, Jia-Cheng, Tseng, Shin-Han, Lai, Chien-Chen, Liu, Yi-Hung, Peng, Shie-Ming, Chiu, Sheng-Hsien
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-02-2017; Nature Publishing Group
• Subjects: 140/131; 140/58; 639/638/541/964; 639/638/541/966; Analytical Chemistry; Biochemistry; Chemistry; Chemistry/Food Science; Inorganic Chemistry; Muscles; Organic Chemistry; Physical Chemistry; Rigidity; Taiwan
• ISSN: 1755-4330; 1755-4349
• DOI: 10.1038/nchem.2608

Daisy chains (DCs) are garlands of flowers that can be worn as bracelets and necklaces. As a result of their beautiful interlocked structures and possible muscle-like motions, cyclic molecular DCs ([
cn
]DCs, where
n
is the number of repeating units) have long been attractive synthetic targets for supramolecular chemists. Herein we report artificial molecular muscles that—unlike one-dimensional (1D) biological muscles—contract and stretch in 2D or 3D. These systems have the structures of [
c3
]- and [
c4
]DCs with subcomponents that operate as molecular switches, powered through the addition or removal of Zn
2+
ions to impart muscle-like behaviour. We assembled these [
c3
]- and [
c4
]DCs selectively by exploiting structural rigidity, coordination geometries and bond rotational barriers that disfavoured the formation of smaller homologues. The switching phenomena of our [
c3
]- and [
c4
]DCs resulted in the contracted molecular muscles stretching by approximately 23 and 36%, respectively, comparable to the value (27%) for linear biological muscles.
By exploiting structural rigidity, coordination geometries and bond rotational barriers that disfavour the formation of smaller homologues, molecular switches based on [
c3
] and [
c4
]daisy chains have been assembled selectively; they display muscle-like motion in multiple dimensions with changes in length of approximately 23% and 36%, respectively.