title: Zn(II)-coordination and fluorescence studies of a new polyazamacrocycle incorporating 1H-pyrazole and naphthalene units.
abstract: The synthesis and Zn(2+) coordination properties of a new macrocycle (L1) obtained by dipodal (2 + 2) condensation of the polyamine 3-(naphthalen-2-ylmethyl)pentane-1,5-diamine with 1H-pyrazole-3,5-dicarbaldehyde are reported. pH-metric studies show that L1 bears five measurable protonation steps in the 2.0-11.0 pH range. Fluorescence emission studies indicate that the removal of the first proton from the H(5)L1(5+) species leads to a significant decrease in the emission due to a photoinduced electron transfer process. Addition of Zn(2+) promotes a boat-like conformation that approaches both fluorophores and facilitates the formation of an excimer which reaches its highest emission for a 1 : 1 Zn(2+) : L1 molar ratio. Density functional theory calculations support the experimental data and suggest that the protective effect of the Zn(2+) ion along with hydrogen bonding between the 1H-pyrazole moiety and one of the tertiary nitrogen atoms is responsible for this behaviour.
authors.affiliation: Instituto de Ciencia Molecular, Universidad de Valencia, Dr Moliner, 46100, Burjassot, Valencia, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Pitarch
authors.forename: M Paz
authors.initials: MP
authors.lastname: Clares
authors.forename: Raquel
authors.initials: R
authors.lastname: Belda
authors.forename: Rubén D
authors.initials: RD
authors.lastname: Costa
authors.forename: Pilar
authors.initials: P
authors.lastname: Navarro
authors.forename: Enrique
authors.initials: E
authors.lastname: Ortí
authors.forename: Conxa
authors.initials: C
authors.lastname: Soriano
authors.forename: Enrique
authors.initials: E
authors.lastname: García-España
mesh_terms: D003300:Copper / Q000737:chemistry; D055664:Electrochemical Techniques; D005453:Fluorescence; D005456:Fluorescent Dyes; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D047028:Macrocyclic Compounds / Q000737:chemistry*; D008968:Molecular Conformation; D015394:Molecular Structure; D009281:Naphthalenes / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D011073:Polyamines / Q000737:chemistry*; D011522:Protons; D011720:Pyrazoles / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: D005456:Fluorescent Dyes; D047028:Macrocyclic Compounds; D009281:Naphthalenes; D009942:Organometallic Compounds; D011073:Polyamines; D011522:Protons; D011720:Pyrazoles; C031721:naphthalene; C031280:pyrazole; D003300:Copper; D015032:Zinc