ORGN 613 |
| Metal cofactor for protein involve in stabilizing enzyme catalysis and activating many essential life processes such as respiration and photosynthesis. There continues to be a high demand for synthetic compounds that selectively bind metals. We predicted that host-[2]rotaxanes (HRs) would selectively bind metals with high affinities since the wheel can adjust its position upon metal ion association. Benzyl-18-crown-6 (B18C6) was used as one blocking group to house a ion. Carboxylic acids of varying lengths were added to the wheel to determine the extent to which they could enhance metal ion association. Extraction assays were performed to provide a measure of binding strength and selectivity. We found that HRs can bind metals to a greater extent than B18C6, and the existence or nature of the carboxylic acid can effect complex stability. For example, extremely large association constants for ion binding in CHCl3 were determined in the transfer of Mg2+•picrate2 from water into CHCl3 for the acid containing rotaxanes (KA ~ 1013 M-1). The difference in the binding free energy for these complexes as compared to the binding of the same metal by B18C6 is on the order of 9 kcal/mol. We are currently modifying the HRs to selectively bind other metal ions. The ability of carboxylates of varying lengths, which are attached to the wheel, to enhance metal ion association was investigated. |
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Materials, Devices and Switches, Metal-Mediated Reactions, Asymmetric Reactions, Total Synthesis, Biologically-Related Molecules and Processes
7:00 PM-9:00 PM, Wednesday, April 9, 2008 Morial Convention Center -- La Louisiane, Blrm. C, Poster
Division of Organic Chemistry |