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https://hdl.handle.net/1959.11/1590
Title: | The effects of catenation on the acidity constants of porphyrin [2]catenanes | Contributor(s): | Gunter, Maxwell John (author); Farquhar, Sandra (author); Jeynes, Tyrone (author) | Publication Date: | 2003 | Handle Link: | https://hdl.handle.net/1959.11/1590 | Abstract: | The acidity constants (pKa₃ and pKa₄) of a series of porphyrins and their corresponding [2]catenanes where the porphyrin is over-arched with a hydroquinol or naphthoquinol polyether strap and mechanically linked to a bipyridinium macrocycle cyclobis-paraquat(4,4'-biphenylene), are calculated from acid-base titration data. As the length of the strap decreases from tetraethylene through triethylene to diethylene, the pKa values decrease, and the separation between pKa₃ and pKa₄ increases. In the diethylene glycol strapped derivatives, only the monocation is accessible above pH = 0. The trend in values reflects the ease of protonation which becomes increasingly difficult as the coulombic repulsions between the protonated porphyrin and the tetracationic macrocycle becomes more severe, as a consequence of enforced proximity of the two charged centres. On protonation, any electronic interactions between the interlinked subunits is replaced by strong electrostatic repulsions. This is alleviated by a 90˚ rotation of the tetracation and a movement away from the porphyrin; such a reorientation is possible only in the longer strapped derivatives, and is prevented in the "tight" analogues. | Publication Type: | Journal Article | Source of Publication: | Journal of Porphyrins and Phthalocyanines, 7(10), p. 667-673 | Publisher: | World Scientific Publishing Co Pte Ltd | Place of Publication: | Singapore | ISSN: | 1099-1409 1088-4246 |
Fields of Research (FoR) 2008: | 030302 Nanochemistry and Supramolecular Chemistry | Peer Reviewed: | Yes | HERDC Category Description: | C1 Refereed Article in a Scholarly Journal | Publisher/associated links: | http://www.u-bourgogne.fr/jpp/base_article/index.php?abs=667&n=10&v=07 |
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Appears in Collections: | Journal Article |
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