Anion binding modes in meso-substituted hexapyrrolic calix[4]pyrrole isomers

J Am Chem Soc. 2014 Jan 29;136(4):1520-5. doi: 10.1021/ja411391c. Epub 2014 Jan 17.

Abstract

We report on the synthesis of a new receptor for anions, meso-substituted hexapyrrolic calix[4]pyrrole 1. The calix[4]pyrrole's core features two additional pyrrole side-arms suspended above or below the calix[4]pyrrole core. This hexapyrrolic calix[4]pyrrole 1 is formed as cis- and trans-configurational isomers, the structures of which have been determined by single crystal X-ray diffraction. The anion binding experiments revealed interesting difference in the binding mode: The cis-1 isomer binds anions in a mixed binding mode featuring a combination of hydrogen bonding and anion-π interactions resulting in an unexpected strong binding. On the other hand, the trans-1 isomer displays only hydrogen bonding and lower affinity for anions. This is unexpected as one would assume both isomers to display the same binding modes. Overall, the titrations of 1 using UV spectrophotometry and NMR titrations by anions reveal that cis-isomer 1 displays higher affinity (10(5)-10(6) M(-1)) and cross-reactivity for anions, while the trans-isomer 1 shows a more selective response to anions. Such differences in binding mode in configurational isomers are so far unexplored and a feature deserving further study.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Anions / chemistry
  • Binding Sites
  • Calixarenes / chemical synthesis
  • Calixarenes / chemistry*
  • Crystallography, X-Ray
  • Models, Molecular
  • Molecular Conformation
  • Porphyrins / chemical synthesis
  • Porphyrins / chemistry*
  • Stereoisomerism

Substances

  • Anions
  • Porphyrins
  • calix(4)pyrrole
  • Calixarenes