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Cleft‐like hexaamine ligands containing large heteroaromatic moieties as receptors for both anions and metal cations
Author(s) -
Bazzicalupi Carla,
Bencini Andrea,
Berni Emanuela,
Bianchi Antonio,
Fornasari Patrizia,
Giorgi Claudia,
Masotti Andrea,
Paoletti Piero,
Valtancoli Barbara
Publication year - 2001
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.385
Subject(s) - chemistry , protonation , moiety , ethylenediamine , hydrogen bond , metal , stacking , potentiometric titration , crystallography , ligand (biochemistry) , stereochemistry , counterion , isostructural , non covalent interactions , inorganic chemistry , crystal structure , molecule , receptor , organic chemistry , ion , biochemistry
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 [M L ] 2+ complexes ( L = L1 or L2 ), the metal is enveloped inside the ligand cleft, as shown by the crystal structure of the [Zn L2 ] 2+ cation. On the other hand, the analysis of the thermodynamic data for metal complexation reveals that in the [M L ] 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 pH, giving 1:1 complexes. Binding of diphosphate, triphosphate, ATP and ADP was studied by means of potentiometry and 1 H and 31 P 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. Copyright © 2001 John Wiley & Sons, Ltd.