Issue 42, 2010

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

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 (1H NMR, 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+.

Graphical abstract: Binding of H+ and Zn(ii) ions with a new fluorescent macrocyclic phenanthrolinophane

Supplementary files

Article information

Article type
Paper
Submitted
24 May 2010
Accepted
28 Jul 2010
First published
04 Oct 2010

Dalton Trans., 2010,39, 10128-10136

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 and B. Valtancoli, Dalton Trans., 2010, 39, 10128 DOI: 10.1039/C0DT00534G

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