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; Springer Nature; Nature Publishing Group
• Subjects: 140/131; 140/58; 639/638/541/964; 639/638/541/966; Analytical Chemistry; Biochemistry; Chemistry; Chemistry, Multidisciplinary; Chemistry/Food Science; Inorganic Chemistry; Muscles; Organic Chemistry; Physical Chemistry; Physical Sciences; Rigidity; Science & Technology; Taiwan; POLYMERS; CONTRACTION; JANUS; DIMER; PH; ROTAXANE; DRIVEN; MACHINE
• 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.