title: Exploring the binding ability of phenanthroline-based polyammonium receptors for anions: hints for design of selective chemosensors for nucleotides.
abstract: The synthesis of receptor 2,6,10,14,18-pentaaza[20]-21,34-phenanthrolinophane (L1), containing a pentaamine chain linking the 2,9 positions of a phenanthroline unit, is reported. The protonation features of L1 and of receptor 2,6,10,14,18,22-hexaaza[23]-24,37-phenanthrolinophane (L2) have been studied by means of potentiometric, (1)H NMR, and spectrofluorimetric measurements; this study points out that the fluorescent emission of both receptors depends on the protonation state of the polyamine chain. In fact, the receptors are emissive only at neutral or acidic pH values, where all the aliphatic amine groups are protonated. Potentiometric titrations show that L2 is able to bind selectively ATP over TTP, CTP, and GTP. This selectivity is lost in the case of L1. (1)H and (31)P NMR measurements and molecular mechanics calculations show that the phosphate chains of nucleotides give strong electrostatic and hydrogen-bonding interactions with the ammonium groups of the protonated receptors, while the nucleobases interact either via pi-stacking with phenanthroline or via hydrogen bonding with the ammonium groups. Of note, MM calculations suggest that all nucleotides interact in an inclusive fashion. In fact, in all adducts the phosphate chain is enclosed within the receptor cavities. This structural feature is confirmed by the crystal structure of the [(H(6)L2)(2)(TTP)(2)(H(2)O)(2)](4+) adduct. Fluorescence emission measurements at different pH values show that L2 is also able to ratiometrically sense ATP in a narrow pH range, thanks to emission quenching due to a photoinduced electron transfer (PET) process from an amine group of the receptor to the excited phenanthroline.
authors.affiliation: Dipartimento di Chimica, Università di Firenze, Via della Lastruccia, 3, 50019 Sesto Fiorentino, Firenze, Italy.
authors.forename: Carla
authors.initials: C
authors.lastname: Bazzicalupi
authors.forename: Andrea
authors.initials: A
authors.lastname: Bencini
authors.forename: Silvia
authors.initials: S
authors.lastname: Biagini
authors.forename: Enrico
authors.initials: E
authors.lastname: Faggi
authors.forename: Stefano
authors.initials: S
authors.lastname: Meini
authors.forename: Claudia
authors.initials: C
authors.lastname: Giorgi
authors.forename: Alessio
authors.initials: A
authors.lastname: Spepi
authors.forename: Barbara
authors.initials: B
authors.lastname: Valtancoli
mesh_terms: D000838:Anions / Q000737:chemistry; D001665:Binding Sites; D005456:Fluorescent Dyes / Q000737:chemistry*; D006860:Hydrogen Bonding; D009711:Nucleotides / Q000737:chemistry*; D010618:Phenanthrolines / Q000138:chemical synthesis / Q000737:chemistry*; D000644:Quaternary Ammonium Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D055672:Static Electricity
chemical_list: C545377:2,6,10,14,18-pentaaza(20)-21,34-phenanthrolinophane; D000838:Anions; D005456:Fluorescent Dyes; D009711:Nucleotides; D010618:Phenanthrolines; D000644:Quaternary Ammonium Compounds