A Tetra-Porphyrin Host Exhibiting Interannular Cooperativity |
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| Authors: | Dr Rhys B Murphy Dr Duc-Truc Pham Assoc?Prof Martin R Johnston |
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| Institution: | 1. Flinders Institute for Nanoscale Science and Technology, College of Science and Engineering, Flinders University, Bedford Park, Adelaide, Australia;2. Department of Chemistry, The University of Adelaide, Adelaide, Australia |
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| Abstract: | Recently identified as another form of cooperativity, interannular cooperativity is rarely observed in supramolecular chemistry. A tetra-porphyrin molecular tweezer with two bis-porphyrin binding sites is reported that exhibits archetypal interannular cooperativity when complexing 1,4-diazabicyclo2.2.2]octane (DABCO). The UV/Vis titration data best supported a 1:2 plus 2:2 plus 1:4 complexation model (host:guest), giving K12=6.32×1013 m ?2, K22=3.04×1020 m ?3, and K14=1.92×1016 m ?4 in CHCl3. The NMR titration data supported the formation of two sandwich species, including tetra-porphyrin?(DABCO)2 as the major species, although there are speciation differences between UV/Vis and NMR concentrations. Using statistical analysis, interannular cooperativity (γ) for tetra-porphyrin?(DABCO)2 was determined to be negative (γ=2.41×10?3), which may be explained by DABCO being too small to be optimally bound simultaneously at both bis-porphyrin binding sites. |
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| Keywords: | association constants cooperativity effects porphyrinoids statistical analysis supramolecular chemistry |
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