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2006
Lodeiro, C, Lima JC, Parola AJ, de Melo JSS, Capelo JL, Covelo B, Tamayo A, Pedras B.  2006.  Intramolecular excimer formation and sensing behavior of new fluorimetric probes and their interactions with metal cations and barbituric acids, 2006. Sensors and Actuators B-Chemical. 115:276-286. Abstract

A new family of compounds able to promote host-guest interactions with specific molecules (e.g., cyanuric and parabanic acids) and to coordinate metal ions, namely Zn(II) and Cu(II), has been synthesized and fully characterized. The new probes derive from the attachment of two methylaminopyrene units to the carbonyl precursor 2,6-bis(2-formylphenoxymethyl)pyridine. Its signalling properties result from the fluorescence emission properties, which reveal the existence of intramolecular excimer formation. The compounds have showed to be highly sensitive to the solvent and hydrogen ion concentration of the medium. Depending on these, different monomer-to-excimer fluorescence ratio is displayed by the two probes. The compound with a single pyrene unit revealed absence of excimer formation and was used as model compound. The overall results are discussed on the basis of the studied probes as potentially revealing molecular movements, off-on-off fluorescent photoinduced electron transfer (PET), host-guest interactions with specific compounds and of sensing metal ions. (c) 2005 Elsevier B.V. All rights reserved.

Bazzicalupi, C, Bencini A, Bianchi A, Borsari L, Danesi A, Giorgi C, Lodeiro C, Mariani P, Pina F, Santarelli S, Tamayo A, Valtancoli B.  2006.  Basicity and coordination properties of a new phenanthroline-based bis- macrocyclic receptor. Dalton Transactions. :4000-4010., Number 33 Abstract
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Bazzicalupi, C, Bencini A, Bianchi A, Borsari L, Danesi A, Giorgi C, Mariani P, Pina F, Santarelli S, Valtancoli B.  2006.  Coordination features of a terpyridine-containing polyamine receptor. Effect of protonation on the photophysical properties of the complexes. Dalton Transactions. :5743-5752., Number 48 Abstract
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de Melo, SJ, Rondao R, Burrows HD, Melo MJ, Navaratnam S, Edge R, Voss G.  2006.  Photophysics of an indigo derivative (keto and leuco structures) with singular properties. Journal of Physical Chemistry A. 110:13653-13661., Number 51 Abstract
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de Melo, SSJ, Rondao R, Burrows HD, Melo MJ, Navaratnam S, Edge R, Voss G.  2006.  Spectral and photophysical studies of substituted indigo derivatives in their keto forms. Chemphyschem. 7:2303-2311., Number 11 Abstract
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Gago, S, Dias AS, Monteiro B, Pillinger M, Valente AA, Santos TM, Goncalves IS.  2006.  Synthesis and characterization of layered double hydroxides intercalated by an oxomolybdenum complex. Journal of Physics and Chemistry of Solids. 67:1011-1015., Number 5-6 Abstract
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2005
Pina, J, de Melo JS, Pina F, Lodeiro C, Lima JC, Parola AJ, Soriano C, Clares MP, Albelda MT, Aucejo R, Garcia-Espana E.  2005.  Spectroscopy and coordination chemistry bisnaphthalene-bisphenanthroline ligand of a new displaying a sensing ability for metal cations, 2005. Inorganic Chemistry. 44:7449-7458. Abstract

A new fluorescent macrocyclic structure (0) 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.

Galindo, F, Lima JC, Luis SV, Melo MJ, Parola AJ, Pina F.  2005.  Water/humidity and ammonia sensor, based on a polymer hydrogel matrix containing a fluorescent flavylium compound, 2005. Journal of Materials Chemistry. 15:2840-2847. Abstract

Flavylium compounds can conveniently be encapsulated in water permeable cross-linked poly(2-hydroxyethyl methacrylate) ( PHEMA) polymer hydrogel matrices. The polymer is also permeable to gases, for example ammonia and hydrogen chloride. The ability of the polymer to concentrate water from the surrounding atmosphere was demonstrated. The absorption and emission spectra of the encapsulated flavylium compounds are very dependent on the pH, and by consequence ammonia ( or hydrogen chloride) can be easily detected. The intensity of the fluorescence emission of the flavylium cation (AH+ species obtained in acidic media) is very dependent on the water content due to the efficient excited state proton transfer involving the AH(+)* excited state and water. The combination of flavylium emission sensitivity to water and ability of the polymer to concentrate water from the surrounding atmosphere, confers this material potential utility as a humidity sensor with high sensitivity.

da Silva, PF, Lima JC, Freitas AA, Shimizu K, Macanita AL, Quina FH.  2005.  Charge-transfer complexation as a general phenomenon in the copigmentation of anthocyanins. Journal of Physical Chemistry a. 109:7329-7338., Number 32 Abstract
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Noronha, MC, Lima JC, Santos H, Macanita AL.  2005.  The discrimination of tyrosine residues in ribonuclease A by picosecond time-resolved fluorescence spectroscopy. Febs Journal. 272:382. Abstract
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Aucejo, R, Alarcon J, Garcia-Espana E, Llinares JM, Marchin KL, Soriano C, Lodeiro C, Bernardo MA, Pina F, Pina J, de Melo JS.  2005.  A new Zn-II tweezer pyridine-naphthalene system - An off-on-off system working in a biological pH window. European Journal of Inorganic Chemistry. :4301-4308., Number 21 Abstract
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Costa, T, Miguel MG, Lindman B, Schillen K, Lima JC, de Melo JS.  2005.  Self-assembly of a hydrophobically modified naphthalene-labeled poly(acrylic acid) polyelectrolyte in water: Organic solvent mixtures followed by steady-state and time-resolved fluorescence. Journal of Physical Chemistry B. 109:3243-3251., Number 8 Abstract
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2004
Bencini, A, Berni E, Bianchi A, Fornasari P, Giorgi C, Lima JC, Lodeiro C, Melo MJ, de Melo JS, Parola AJ, Pina F, Pina J, Valtancoli B.  2004.  A fluorescent chemosensor for Zn(II). Exciplex formation in solution and the solid state, 2004. Dalton Transactions. :2180-2187. Abstract

The macrocyclic phenanthrolinophane 2,9-[2,5,8-triaza-5-(N-anthracene-9-methylamino) ethyl]-[9]-1,10-henanthrolinophane(L) bearing a pendant arm containing a coordinating amine and an anthracene group forms stable complexes with Zn(II), Cd(II) and Hg(II) in solution. Stability constants of these complexes were determined in 0.10 mol dm(-3) NMe4Cl H2O-MeCN (1:1, v/v) solution at 298.1+/-0.1 K by means of potentiometric (pH metric) titration. The fluorescence emission properties of these complexes were studied in this solvent. For the Zn(II) complex, steady-state and time-resolved fluorescence studies were performed in ethanol solution and in the solid state. In solution, intramolecular pi-stacking interaction between phenanthroline and anthracene in the ground state and exciplex emission in the excited state were observed. From the temperature dependence of the photostationary ratio (I-Exc/I-M), the activation energy for the exciplex formation (E-a) and the binding energy of the exciplex (-DeltaH) were determined. The crystal structure of the [ZnLBr](ClO4).H2O compound was resolved, showing that in the solid state both intra- and inter-molecular pi-stacking interactions are present. Such interactions were also evidenced by UV-vis absorption and emission spectra in the solid state. The absorption spectrum of a thin film of the solid complex is red-shifted compared with the solution spectra, whereas its emission spectrum reveals the unique featureless exciplex band, blue shifted compared with the solution. In conjunction with X-ray data the solid-state data was interpreted as being due to a new exciplex where no pi-stacking (full overlap of the pi-electron cloud of the two chromophores-anthracene and phenanthroline) is observed. L is a fluorescent chemosensor able to signal Zn(II) in presence of Cd(II) and Hg(II), since the last two metal ions do not give rise either to the formation of pi-stacking complexes or to exciplex emission in solution.

Alarcon, J, Aucejo R, Albelda MT, Alves S, Clares MP, Garcia-Espana E, Lodeiro C, Marchin KL, Parola AJ, Pina F, de Melo JS, Soriano C.  2004.  Fluorescent type II materials from naphthylmethyl polyamine precursors, 2004. Supramolecular Chemistry. 16:573-580. Abstract

Speciation studies in aqueous solution on the interaction Of Cu2+ and Zn2+ with a series of polyaminic ligands N-naphthalen-1-ylmethyl-N'-[2-[(naphthalen-1-ylmethyl)- amino]-ethyl)-ethane-l,2-diamine (LI), N-naphthalen-lylmethyl-iV-(2-{2-[(naphthalen-1-ylmethyl)-amino]-ethyl- amino]-ethyl)-ethane-l,2-diamine (L2) and N-naphthalen-1-ylmethyl-N'-[2-(2-{2-[(naphthalen-1-ylmethyl)-amino]- ethylamino)-ethylamino)-ethyl]-ethane-1,2-diamine (L3) containing two naphthylmethyl groups at their termini and N-1-(2-{2-[(naphthalen-1-ylmethyl)-amino]-ethyl-amino)-ethyl)-ethane-1,2-diamine (L4) containing just one naphthylmethyl group have been carried out at 298.1 K in 0.15 mol dm (-3) NaCl. In the case of the tetraamines L2 and L4, their coordination capabilities towards Cd2+, Ni2+, Co2+ and Pb2+ have also been considered. The stability constants follow the general Irving-Williams sequence. The steady-state fluorescence emission studies on the interaction with metal ions show that while Cu2+ produces a chelation enhancement of the quenching (CHEQ), the interaction with Zn2+ leads to a chelation enhancement of the fluorescence (CHEF). Finally, ligands L1, L2 and L3 have been successfully covalently attached to silica surfaces and some preliminary results of their emissive properties are given.

Moncada, MC, Fernandez D, Lima JC, Parola AJ, Lodeiro C, Folgosa F, Melo MJ, Pina F.  2004.  Multistate properties of 7-(N,N-diethylamino)-4 '-hydroxyflavylium. An example of an unidirectional reaction cycle driven by pH, 2004. Organic & Biomolecular Chemistry. 2:2802-2808. Abstract

The synthetic flavylium salt 7-(N,N-diethylamino)-4'-hydroxyflavylium tetrafluoroborate gives rise in aqueous solution to a complex network of chemical reactions driven by pH. The system was studied by H-1 NMR, single crystal X-ray diffraction, steady state and transient UV-Vis spectrophotometry as well as stopped flow. The crystal structure shows a high degree of coplanarity between the pyrylium system and the phenyl group in position 2. Thermodynamic and kinetic constants for the pH dependent network of chemical reactions were obtained. The introduction of an amino group in position 7 allows formation of protonated species leading, in particular, to a tautomeric form of the protonated cis-chalcone, CcH(+), whose absorption spectra is rather red shifted, in comparison with the correspondent protonated trans-chalcone, CtH(+). The CcH(+) species can be rapidly converted into the flavylium cation through a first order process with lifetime of 0.2 s at pH = 2.35. This new reaction channel confers this compound a peculiar behaviour in acidic media, allowing to define an unidirectional pH driven reaction cycle.

Moncada, MC, Parola AJ, Lodeiro C, Pina F, Maestri M, Balzani V.  2004.  Multistate/multifunctional behaviour of 4 '-hydroxy-6-nitroflavylium: A write-lock/read/unlock/enable-erase/erase cycle driven by light and pH stimulation, 2004. Chemistry-a European Journal. 10:1519-1526. Abstract

We have investigated the network of reactions observed for the photochromic 4'-hydroxy-6-nitroflavylium compound in aqueous solutions upon pH changes (including pH jump and stopped flow experiments) and light excitation. The changes observed in the NMR and UV/Vis spectra allowed identification of ten different forms in which this compound can be transformed depending on the experimental conditions. Equilibrium and kinetic constants have been determined. Compared with other members of the flavylium family, 4'-hydroxy-6-nitroflavylium is characterized by a large cis --> trans isomerization barrier, and a very efficient hydration reaction. These peculiar features allow writing, reading, storing and erasing photonic information on 4'-hydroxy-6-nitroflavylium by a novel cyclic process that involves the following steps: write-lock/read/unlock/enable-erase/erase.

Clares, MP, Aguilar J, Aucejo R, Lodeiro C, Albelda MT, Pina F, Lima JC, Parola AJ, Pina J, de Melo JS, Soriano C, Garcia-Espana E.  2004.  Synthesis and H+, Cu2+, and Zn2+ coordination behavior of a bis(fluorophoric) bibrachial lariat aza-crown, 2004. Inorganic Chemistry. 43:6114-6122. Abstract

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 moiety.

Moncada, MC, Pina F, Roque A, Parola AJ, Maestri M, Balzani V.  2004.  Tuning the photochromic properties of a flavylium compound by pH, 2004. European Journal of Organic Chemistry. :304-312. Abstract

We studied the intricate pH- and light-dependent network of the thermal and photochemical reactions of the 4'-(dimethylamino) -7-hydroxyflavylium ion by continuous irradiation, flash photolysis, H-1 NMR spectroscopy, and stopped flow analysis. The distribution of the various forms at the pH-dependent thermodynamic equilibrium and the rates of several interconversion processes were measured. The most interesting feature of this multistate/multifunctional system is related to the possibility of pH-tuning the colour change caused by photoirradiation, because the cis-chalcone isomer, obtained from the photoisomerization of the trans-chalcone form, is spontaneously transformed into coloured species (flavylium. cation and quinoidal base) at low values of pH, but reverts back to the uncoloured trans-chalcone at high values of pH because of the low energy barrier between the cis and trans chalcone isomers. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).

da Silva, PF, Lima JC, Quina FH, Macanita AL.  2004.  Excited-state electron transfer in anthocyanins and related flavylium salts. Journal of Physical Chemistry a. 108:10133-10140., Number 46 Abstract
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Faustino, P, Miranda A, Silva MD, Alves C, Pinanco I, Ferreira C, Seixas MT, Pina F, Romao L.  2004.  Hb Yaounde beta 134(H12)Val -> Ala in association with Hb C beta 6(A3)Glu -> Lys in a Caucasian Portuguese family. Hemoglobin. 28:229-235., Number 3 Abstract
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Noronha, M, Lima JC, Lamosa P, Santos H, Maycock C, Ventura R, Macanita AL.  2004.  Intramolecular fluorescence quenching of tyrosine by the peptide alpha-carbonyl group revisited. Journal of Physical Chemistry a. 108:2155-2166., Number 12 Abstract
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Moncada, MC, Fernandez D, Lima JC, Parola AJ, Lodeiro C, Folgosa F, Melo MJ, Pina F.  2004.  Multistate properties of 7-(N,N-diethylamino)-4 '-hydroxyflavylium. An example of an unidirectional reaction cycle driven by pH. Organic & Biomolecular Chemistry. 2:2802-2808., Number 19 Abstract
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de Melo, JS, Moura AP, Melo MJ.  2004.  Photophysical and spectroscopic studies of Indigo derivatives in their keto and leuco forms. Journal of Physical Chemistry A. 108:6975-6981., Number 34 Abstract
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