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Molecular Pumps that drives a system away from equilibrium

By Chuyang Cheng, Hao Li, Weiguang Liu, Paul R. McGonigal, Nicolaas A. Vermeulen, Marco Frasconi, Chenfeng Ke, III William A. Goddard and J. F. Stoddart


A pressing goal for contemporary science is to build artificial mol. systems that can perform useful work. Here\ud we report a 'mol. pump' system that processes chem. energy (redox) to drive a macrocycle away from equil.,\ud from a low energy to a high energy state. A series of mol. rods were synthesized contg. 3,5-\ud dimethylpyridinium (Py +) and 4,4'-bipyridinium (BIPY 2+) units connected to a bulky steric stopper by chains\ud of different lengths. Cyclobis(paraquat-p-phenylene) (CBPQT 4+) is repelled by the Py + and BIPY 2+ initially;\ud however, upon redn. with activated zinc dust, Coulombic repulsion between Py + and CBPQT 2(+•) dramatically\ud decreases and a thermodynamically stable trisradical complex BIPY +•I CBPQT 2(+•) is formed within seconds.\ud Tris(4-bromophenyl)aminium hexachloridoantimonate (Magic Blue) was used to oxidize the radical cation\ud rapidly to the fully oxidized state. The electrostatic Py + barrier is recovered, causing the CBPQT 4+ ring to\ud shuttle on to the glycol/alkyl chain, for which it has little affinity. Dethreading from this high energy, metastable\ud [2]rotaxane state occurs slowly due to Coulombic repulsion between CBPQT 4+ and Py +/BIPY 2+.\ud Exptl. results and DFT calcns. show that the mol. pump can raise the potential energy of CBPQT 4+ up to 13\ud kcal/mol with an efficiency up to 8%

Year: 2013
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Provided by: Caltech Authors
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