Polyamines containing naphthyl groups as pH-regulated molecular machines driven by light

A series of compounds made up by linking methylnaphthalene fragments at both ends of different polyamine chains have shown to behave as pH-regulated molecular machines driven by light and fluorescence emission studies have proved the formation of an excimer between the two naphthalene units whose appearance, fluorescence intensity and decay times depend on the pH value of the media.Albelda Gimeno, Maria Teresa, [email protected] ; Garcia-España Monsonis, Enrique, [email protected] ; Soriano Soto, Concepción, [email protected]

Synthesis and H+, Cu2+, and Zn2+ Coordination Behavior of a Bis(fluorophoric) Bibrachial Lariat Aza-Crown

The synthesis, protonation behavior, and Cu2+ and Zn2+ coordination chemistry of the novel bibrachial aza lariat ether (naphthalen-1-ylmethyl)[2-(20-{2-[(naphthalen-1-ylmethyl)amino]ethyl}-3,6,9,17,20,23,29,30-octaazatricyclo[23.3.1.1*11,15*]triaconta-1(29),11(30),12,14,25,27-hexaen-6-yl)ethyl]amine (L) are discussed. The macrocycle, which has two aminoethyl naphthyl moieties symmetrically appended to a 2:2 azapyridinophane structure, displays, in the pH range 2−11, six protonation steps that correspond to the protonation of the secondary amino groups. Steady-state fluorescence measurements show emissions due to the monomer and to the excimer formed between the two naphthalene fragments of the macrocycle. The time-resolved fluorescence data, obtained by the time-correlated single photon counting technique, show that a significant percentage of excimer is preformed as ground-state dimers. The ligand L forms with the metal ions Cu2+ and Zn2+ mono- and dinuclear complexes in aqueous solution. The influence of metal coordination in the fluorescence emission of L is analyzed. The acid−base, coordination capabilities, and emissive behavior of L are compared with those presented by its synthetic precursor L1, which has a tripodal tris(2-aminoethyl)amine structure functionalized at one of its terminal amino groups with a naphthyl moiet

Binuclear Cu2+ complex mediated discrimination between L-glutamate and L-aspartate in water

L-Glutamate and L-aspartate selectivity is achieved by the action of two Cu2+ metal ions rightly disposed in a cyclophanetype macrocyclic framework; electrochemical sensing of glutamate has been achieved by adsorption of the copper complexes on graphite electrodes.Verdejo Viu, Begoña, [email protected] ; Domenech Carbo, Antonio, [email protected] ; Jimenez Garcia, Hermas Rafael, [email protected] ; Soriano Soto, Concepción, [email protected] ; Garcia-España Monsonis, Enrique, [email protected]

Specific interaction of citrate with bis(fluorophoric) bibrachial lariat aza-crown in comparison with the other components of the Krebs cycle

Clares Garcia, M. Paz, [email protected] ; Garcia-España Monsonis, Enrique, [email protected] ; Soriano Soto, Concepcion, [email protected] ; Tejero Toquero, Roberto, [email protected]

Synthesis and photophysical properties of dansyl-based polyamine ligands and their Zn(II) complexes

The synthesis, potentiometric studies and photophysical properties of two new polyamine ligands (L1 and L2) possessing the dansyl chromophore were studied in aqueous 0.15 M NaCl. The compounds show the absorption and emissions bands characteristic of the dansylamide fluorophore and both present intramolecular excited state proton transfer at intermediate pH ranges. One of the ligands (L2) strongly coordinates Zn(II) leading to fluorescence quenching. A model compound (L3) of the dansyl moiety was also investigated.http://www.sciencedirect.com/science/article/B6TG5-4MB4DV1-2/1/45cafbcee9a8df7daddd765512437ca

Switching from intramolecular energy transfer to intramolecular electron transfer by the action of pH and Zn2+ co-ordination

http://www.sciencedirect.com/science/article/B6TFN-44SKJK4-4/1/7cd5958d3acd1757d2b3a88517f1d55

Intramolecular Excimer Formation in a Tripodal Polyamine Receptor Containing Three Naphthalene Fluorophores

A comprehensive investigation on the energetics and dynamics of a new fluorescent sensor constituted by a tripodal polyamine receptor containing three naphthalene fluorophores, compound L, is reported. The influence of external factors such as the solvent, hydrogen ion concentration, and temperature in the photophysics of the sensor is discussed. The temperature dependence of monomer/excimer interconversion of L revealed an average percentage relative sensitivity of 4.5%/°C thus portending its use as a temperature sensor. The activation energy for excimer formation (E1 = 12 kJ mol-1) and dissociation (E-1 = 57 kJ mol-1), entropy change (ΔS = −128 J K-1 mol-1), and the binding energy of the excimer (ΔH = 45 kJ mol-1) were obtained in water at acidic pH values and ethanol (E1 = 15 kJ mol-1, E-1 = 40 kJ mol-1, ΔS = −61 J K-1 mol-1, and ΔH = 25 kJ mol-1). The dependence of the kinetic and thermodynamic parameters on the dielectric constant of the medium and on the degree of protonation of the polyamine chain was interpreted in terms of the excimer destabilization provoked by the electrostatic repulsion between the positively charged chains

Energetics and Dynamics of Naphthalene Polyaminic Derivatives. Influence of Structural Design in the Balance Static vs Dynamic Excimer Formation

Two new fluorescent macrocyclic structures bearing two naphthalene (Np) units at both ends of a cyclic polyaminic chain were investigated with potentiometric, fluorescence (steady-state and time-resolved) and laser flash photolysis techniques. The fluorescence emission studies show the presence of an excimer species whose formation depends on the protonation state of the polyamine chains implying the existence of a bending movement (occurring in both the ground and in the first singlet excited state), which allows the two naphthalene units to approach and interact. For comparison purposes, one bis-chromophoric compound containing a rigid chain (piperazine unit) was also investigated. Its emission spectra shows a unique band decaying single exponentially thus showing that no excimer is formed. With the two new ligands, excimer formation occurs in all situations even at very acidic pH values when the protonation of the polyamine bridges is extensive. Coexistence of ground-state dimers with dynamic excimers was established based on steady-state and time-resolved fluorescence data. The energetics of excimer formation and dissociation were determined in ethanol and water. Different methods of decay analysis (independent decay deconvolution, global analysis and excimer deconvolution with monomer) were used to extract the kinetic (rate constants for excimer formation, dissociation, and decay) and thermodynamic parameters. In ethanol and acidified ethanol:water mixtures, an additional short decay time was found to exist and assigned to a dimer, whose presence is assumed to be responsible by the decrease in activation energy for excimer formation in this solvent. The results are globally discussed in terms of the small architectural differences that can induce significant changes in the photophysical behavior of the three studied compounds

A New ZnIITweezer Pyridine-Naphthalene System - An Off-On-Off System Working in a Biological pH Window

The synthesis, protonation behaviour and Zn2+ coordination chemistry of a new photoactive polyamine exhibiting ldquooff-on-offrdquo fluorescence is presented. Addition of Zn2+ reduces the width of the fluorescence window, which is centred around physiological pH, and sharply enhances the emission intensity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005

Spectroscopy and Coordination Chemistry of a New Bisnaphthalene−Bisphenanthroline Ligand Displaying a Sensing Ability for Metal Cations

A new fluorescent macrocyclic structure (L1) bearing two naphthalene units at both ends of a cyclic polyaminic chain containing two phenanthroline units was investigated with potentiometric and fluorescence (steady-state and time-resolved) techniques. The fluorescence emission spectra show the simultaneous presence of three bands: a short wavelength emission band (naphthalene monomer), a middle emission band (phenanthroline emission), and a long-wavelength band. All three bands were found to be dependent on the protonation state of the macrocyclic unit (including the polyaminic and phenanthroline structures). The existence of the long-wavelength emission band is discussed and is shown to imply that a bending movement involving the two phenanthroline units leads to excimer formation. This is determined by comparison with the excimer emission formed by intermolecular association of 1,10-phenanthroline. With ligand L1, excimer formation occurs only at pH values above 4. At very acidic pH values, the protonation of the polyamine bridges is extensive leading to a rigidity of the system that precludes the bending movement. The interaction with metal cations Zn(II) and Cu(II) was also investigated. Excimer formation is, in these situations, increased with Zn(II) and decreased with Cu(II). The long-emission band is shown to present a different wavelength maximum, depending on the metal, which can be considered as a characteristic to validate the use of ligand L1 as a sensor for a given metal