A Tetra‐Porphyrin Host Exhibiting Interannular Cooperativity

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 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.

Supramolecular Self-Assembly of Porphyrin and Metallosurfactant as a Drug Nanocontainer Design

“…The most significant high-field shift in this methyl group in a mixture with a three-fold excess of LaSurf compared to mixtures with a four-and ten-fold excess confirms the strong complexation in the mixture near the stoichiometric ratio TSPP:LaSurf = 1:2. Furthermore, a separate resonance appears between the signals of the protons of DABCO fragments at ~3.15 ppm, which is probably related to the so-called DABCO sandwich resonance as a result of being surrounded by two TSPP molecules [68]. In this sandwich the methylene units of hexadecyl tails of LaSurf, depending on the location between two TSPP molecules, undergo different high-field displacements.…”