A Tetra‐Porphyrin Host Exhibiting Interannular Cooperativity. Issue 56 (10th September 2019)

• Record Type: Journal Article
• Authors: Murphy, Rhys B.; Pham, Duc‐Truc; Johnston, Martin R.
• Is Part Of: Chemistry. Volume 25:Issue 56(2019)
• Page Start: 13037
• Page End: 13043
• Publication Date: 2019-09-10
• Subjects: association constants -- cooperativity effects -- porphyrinoids -- statistical analysis -- supramolecular chemistry; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201903636
• Languages: English
• ISSNs: 0947-6539

Abstract

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‐diazabicyclo[2.2.2]octane (DABCO). The UV/Vis titration data best supported a 1:2 plus 2:2 plus 1:4 complexation model (host:guest), giving K 12 =6.32×10 13 m −2, K 22 =3.04×10 20 m −3, and K 14 =1.92×10 16 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. Abstract : Not something you see everyday : A rare form of cooperativity, namely interannular, was observed within a host containing four zinc porphyrins at two different complexation sites linked by a rigid alicyclic backbone. 1, 4‐Diazabicyclo[2.2.2]octane (DABCO) complexation was negatively cooperative, as shown from a statistical analysis of UV/Vis‐determined association constants.