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A Tetra‐Porphyrin Host Exhibiting Interannular Cooperativity
Author(s) -
Murphy Rhys B.,
Pham DucTruc,
Johnston Martin R.
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201903636
Subject(s) - dabco , cooperativity , porphyrin , supramolecular chemistry , chemistry , octane , titration , tetra , cooperative binding , stereochemistry , crystallography , photochemistry , binding site , medicinal chemistry , inorganic chemistry , organic chemistry , crystal structure , biochemistry
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 CHCl 3 . 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.