Cleft-like hexaamine ligands containing large hetero-aromatic moieties as receptors for both anions and metal cations

Carla Bazzicalupi, Andrea Bencini, Emanuela Berni, Antonio Bianchi, Patrizia Fornasari, Claudia Giorgi, Andrea Masotti, Piero Paoletti, Barbara Valtancoli

Research output: Contribution to journalArticlepeer-review

Abstract

Ligands L1 and L2 contain two ethylenediamine chains linked to the 2,9 and 6,6' positions of phenanthroline and bipyridyl, respectively. Their molecular architecture defines a coordinative 'cleft,' a potential binding site for metals and anionic species. Their coordination properties toward Zn(II), Cd(II) and Pb(II) were studied by means of potentiometric, microcalorimetric and UV-vis spectrophotometric measurements. In the [ML]2+ complexes (L = L1 or L2), the metal is enveloped inside the ligand cleft, as shown by the crystal structure of the [ZnL2]2+ cation. On the other hand, the analysis of the thermodynamic data for metal complexation reveals that in the [ML]2+ complexes some nitrogen donors are weakly bound, or not bound, to the metal, owing to the presence of a rigid heteroaromatic unit, which leads to a stiffening of the ligands. Both L1 and L2, in their protonated forms, behave as multifunctional receptors for the nucleotide anions at neutral or slightly acidic p H, giving 1:1 complexes. Binding of diphosphate, triphosphate, ATP and ADP was studied by means of potentiometry and 1H and 31p NMR spectroscopy. Charge-charge and hydrogen bonding interactions take place between the polyphosphate chain of nucleotides and the polyammonium groups of L1 and L2, whereas the adenine moiety shows charge-dipole interactions with the ammonium groups and π-stacking with the heteroaromatic units of the receptors.

Original languageEnglish
Pages (from-to)432-443
Number of pages12
JournalJournal of Physical Organic Chemistry
Volume14
Issue number7
DOIs
Publication statusPublished - Jul 2001

Keywords

  • Anion coordination
  • Metal coordination
  • Molecular recognition
  • Nucleotides
  • Polyamine
  • Proton binding
  • Supramolecular chemistry

ASJC Scopus subject areas

  • Organic Chemistry
  • Physical and Theoretical Chemistry

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