title: Polyamine receptors containing dipyridine or phenanthroline units: clues for the design of fluorescent chemosensors for metal ions.
abstract: The synthesis of the macrocyclic receptor L1, which contains a tetraamine chain linking the 6,6'-positions of a 2,2'-dipyridine moiety, is reported. Its basicity properties and complexation features toward Cu(II), Zn(II), Cd(II) and Pb(II) have been studied in aqueous solutions by means of potentiometric, UV/Vis spectroscopy and fluorescence emission measurements and compared with those of ligand L2, in which a 1,10-phenanthroline moiety replaces the dipyridine unit of L1. In metal coordination, L1 shows a marked selectivity toward Cd(II) over Zn(II) and Pb(II). The crystal structures of its metal complexes shows that L1 possesses a preferential tetradentate binding site for metal cations, composed of the dipyridine unit and the two adjacent benzylic amine groups. This binding site has the proper dimension and conformation to selectively coordinate the Cd(II) ion, as confirmed by DFT calculations carried out on the complexes. This coordinative zone is lost in L2. The rigidity of phenanthroline does not allow the simultaneous binding of both the benzylic amine groups to Zn(II) and Cd(II) and, in fact, one benzylic amine is not coordinated to these metal cations. The fluorescence emission properties of the L1 and L2 complexes are strongly pH dependent. Only the Zn(II) and Cd(II) complexes with L1 display fluorescence emission at neutral pH. This feature is related to the formation in solution at pH 7 of emissive protonated complexes of the type [M(H(x)L)]((2+x)+) (x=1-3), in which all the nitrogen donors are involved in metal or proton binding. The emissive characteristics of these protonated complexes are confirmed by the fluorescence emission spectra collected on the [Zn(HL1)Br][ClO(4)](2) and [Cd(HL1)Br][ClO(4)](2) solid compounds dissolved in CH(3)CN. Conversely, the Zn(II) and Cd(II) complexes with L2 are not emissive; in fact, they contain a benzylic amine group not involved in metal or proton binding that can quench the fluorescence emission of the fluorophore, thanks to a photoinduced electron-transfer process.
authors.affiliation: Department of Chemistry, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze (Italy), Fax: (+39) 0554573364.
authors.forename: Carla
authors.initials: C
authors.lastname: Bazzicalupi
authors.affiliation: Department of Chemistry, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze (Italy), Fax: (+39) 0554573364.
authors.forename: Andrea
authors.initials: A
authors.lastname: Bencini
authors.affiliation: Department of Chemistry, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze (Italy), Fax: (+39) 0554573364.
authors.forename: Silvia
authors.initials: S
authors.lastname: Biagini
authors.affiliation: Department of Chemistry, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze (Italy), Fax: (+39) 0554573364.
authors.forename: Antonio
authors.initials: A
authors.lastname: Bianchi
authors.affiliation: Department of Chemistry, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze (Italy), Fax: (+39) 0554573364.
authors.forename: Enrico
authors.initials: E
authors.lastname: Faggi
authors.affiliation: Department of Chemistry, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze (Italy), Fax: (+39) 0554573364.
authors.forename: Claudia
authors.initials: C
authors.lastname: Giorgi
authors.affiliation: Department of Chemistry, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze (Italy), Fax: (+39) 0554573364.
authors.forename: Melania
authors.initials: M
authors.lastname: Marchetta
authors.affiliation: Department of Chemistry, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze (Italy), Fax: (+39) 0554573364.
authors.forename: Federico
authors.initials: F
authors.lastname: Totti
authors.affiliation: Department of Chemistry, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze (Italy), Fax: (+39) 0554573364.
authors.forename: Barbara
authors.initials: B
authors.lastname: Valtancoli
mesh_terms: D015082:2,2'-Dipyridyl / Q000031:analogs & derivatives / Q000737:chemistry; D002104:Cadmium / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000138:chemical synthesis* / Q000737:chemistry; D007854:Lead / Q000737:chemistry*; D015394:Molecular Structure; D010618:Phenanthrolines / Q000737:chemistry*; D011073:Polyamines / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: D005456:Fluorescent Dyes; D010618:Phenanthrolines; D011073:Polyamines; D002104:Cadmium; D007854:Lead; D015082:2,2'-Dipyridyl; D003300:Copper; D015032:Zinc