Binding of H+ and Zn(II) ions with a new fluorescent macrocyclic phenanthrolinophane.

Bazzicalupi, Carla; Biagini, S.; Bianchi, Antonio; Faggi, E.; Gratteri, Paola; Mariani, Palma Maria; Pina, F.; Valtancoli, Barbara

doi:10.1039/c0dt00534g

The new macrocyclic ligand 1,9(4,7)-diphenanthroline-3,7,11,15-tetraazacyclohexadecaphane (L) was synthesized by a 2 : 2 reaction of 1,10-phenanthroline-4,7-dialdehyde with 1,3-diaminopropane, followed by reduction with NaBH4. L contains two phenanthroline groups linked together by two 1,3-diaminopropane chains in such a way that the heteroaromatic nitrogen atoms point outside the ligand cavity. The ligand structure defines two pairs of identical compartments displaying a specific ability in the binding of protons (1,3-diaminopropane) and metal ions (phenanthroline). Protonation and Zn(II) coordination were studied by means of potentiometric and spectroscopic (1HNMR, UV-vis, fluorescence) techniques. Both protonation and Zn(II) coordination consistently affect the fluorescence emission properties of L, giving rise to enhancement or quenching of the emission, depending on the species involved. L becomes emissive upon protonation, but the formation of the highly protonated species, in particular the fully protonated [H6L]6+, quenches the emission. The mono- and dinuclear Zn(II) complexes of the unprotonated ligand are non-emissive, like free L, while Zn(II) binding to [HL]+ activates the emission. The most interesting aspect, however, is the chelation enhancement of quenching (CHEQ) observed upon Zn(II) binding to [H2L]2+ and [H4L]4+, being among the few examples of CHEQ effect observed for Zn(II) complexes. Hydrogen bonding between a metal coordinated water molecule and a phenanthroline group seems to be responsible for the CHEQ observed for [ZnH2L]4+.

Binding of H+ and Zn(II) ions with a new fluorescent macrocyclic phenanthrolinophane / C. Bazzicalupi; S. Biagini; A. Bianchi; E. Faggi; P. Gratteri; P. Mariani; F. Pina; B. Valtancoli. - In: DALTON TRANSACTIONS. - ISSN 1477-9226. - STAMPA. - 39(2010), pp. 10128-10136. [10.1039/c0dt00534g]

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Titolo:	Binding of H+ and Zn(II) ions with a new fluorescent macrocyclic phenanthrolinophane.
Autori di Ateneo:	BAZZICALUPI, CARLA S. Biagini BIANCHI, ANTONIO E. Faggi GRATTERI, PAOLA MARIANI, PALMA MARIA F. Pina VALTANCOLI, BARBARA mostra contributor esterni nascondi contributor esterni
Autori:	BAZZICALUPI, CARLA; S. Biagini; BIANCHI, ANTONIO; E. Faggi; GRATTERI, PAOLA; MARIANI, PALMA MARIA; F. Pina; VALTANCOLI, BARBARA
Anno di registrazione:	2010
Rivista:	DALTON TRANSACTIONS
Volume:	39
Pagina iniziale:	10128
Pagina finale:	10136
Abstract:	The new macrocyclic ligand 1,9(4,7)-diphenanthroline-3,7,11,15-tetraazacyclohexadecaphane (L) was synthesized by a 2 : 2 reaction of 1,10-phenanthroline-4,7-dialdehyde with 1,3-diaminopropane, followed by reduction with NaBH4. L contains two phenanthroline groups linked together by two 1,3-diaminopropane chains in such a way that the heteroaromatic nitrogen atoms point outside the ligand cavity. The ligand structure defines two pairs of identical compartments displaying a specific ability in the binding of protons (1,3-diaminopropane) and metal ions (phenanthroline). Protonation and Zn(II) coordination were studied by means of potentiometric and spectroscopic (1HNMR, UV-vis, fluorescence) techniques. Both protonation and Zn(II) coordination consistently affect the fluorescence emission properties of L, giving rise to enhancement or quenching of the emission, depending on the species involved. L becomes emissive upon protonation, but the formation of the highly protonated species, in particular the fully protonated [H6L]6+, quenches the emission. The mono- and dinuclear Zn(II) complexes of the unprotonated ligand are non-emissive, like free L, while Zn(II) binding to [HL]+ activates the emission. The most interesting aspect, however, is the chelation enhancement of quenching (CHEQ) observed upon Zn(II) binding to [H2L]2+ and [H4L]4+, being among the few examples of CHEQ effect observed for Zn(II) complexes. Hydrogen bonding between a metal coordinated water molecule and a phenanthroline group seems to be responsible for the CHEQ observed for [ZnH2L]4+.
Handle:	http://hdl.handle.net/2158/395575
Appare nelle tipologie:	1a - Articolo su rivista

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