Dalton Transactions from Jan 2007

Complexation of the triphosphate anion: tunigh the structure of cyclen based bacrotricycles with 1,3-dimethylbenzene and 2,6-dimethylpyridine linkers. A potentiometric and NMR study

Stéphanie Develay, Raphaël Tripier, Nicolas Bernier, Michel Le Baccon, Véronique Patinec, Guy Serratrice and Henri Handel

Dalton Trans., 2007, 1038 - 1046, DOI: 10.1039/b616862k

Abstract: The host–guest interaction between orthophosphate, pyrophosphate and triphosphate anions and three cyclen-based macrotricyclic ligands was investigated by potentiometric measurements and NMR spectroscopy. The ligands differ from one another by the nature of their spacers, which are 1,3-dimethylbenzene (TMC), 2,6-dimethylpyridine (TPyC) or a combination of the two (TMPyC). In aqueous solution, each ligand gave protonated species that further formed ternary complexes after binding with anions; these complexes were analyzed as a result of hydrogen bond formation and coulombic attraction between the organic host and the inorganic guest. The equilibrium constants found for all the detected species are reported and the selectivity, illustrated with species distribution diagrams, is discussed. The results unambiguously showed that the ligand possessing a single supplementary anchoring site (the pyridinyl spacer) exhibited the greatest affinity for the phosphate species in a large p[H] range.



Multidimensional NMR spectroscopy of the study of histone H4-Ni(II) interaction

Maria Antonietta Zoroddu, Massimiliano Peana and Serenella Medici

Dalton Trans., 2007, 379 - 384, DOI: 10.1039/b610725g

Abstract: The N-terminal 30-amino acid tail of histone H4, a nuclear protein, was studied as a model for the interaction of this protein with Ni(II) ions. The behaviour of the ends-blocked Ac-SGRGKGGKGLGKGGA₁₅K₁₆R₁₇H₁₈R₁₉KVLRDNIQGIT-Am fragment towards Ni(II) was analyzed with multidimensional NMR (1D, 2D TOCSY, NOESY) and UV-Vis spectroscopy. As expected, the coordination involved the imidazolic nitrogen of the His₁₈ residue and the three deprotonated amidic nitrogens of the His₁₈, Arg₁₇ and Lys₁₆ residues, respectively. A model for the structure of the complex was calculated from the inter-residual NOEs recorded in 2D NOESY spectra. The structure obtained shows that the interaction with the metal is responsible for deep changes in the conformation of the peptide, blocking the side chain of Arg₁₇ and Lys₁₆ residues above the coordination plane. These structural modifications may be physiologically relevant to the mechanism of nickel carcinogenesis.