Alkane lengths determine encapsulation rates and equilibria |
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Authors: | Jiang Wei Ajami Dariush Rebek Julius |
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Institution: | Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, United States. |
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Abstract: | A cylindrical capsule provides an environment for straight-chain alkanes that can properly fill the space through extended or compressed conformations. The encapsulation rates of a series of alkanes were examined and found to be dependent on guest length: the rates of uptake are C(9) > C(10) > C(11), while complex stability is in the reverse order, C(11) > C(10) > C(9). Direct competition experiments, pairwise or between all 3 alkanes, maintain this order as the longer alkanes sequentially displace the shorter ones. The distribution of species with time provides a clock for this complex system, which combines elements of self-sorting phenomena and dynamic combinatorial chemistry. The clock can be stopped by replacing the alkanes with the superior guest 4,4'-dimethylazobenzene, then restarted by irradiation. |
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