Sílvia Costa - Academia.edu (original) (raw)

Papers by Sílvia Costa

Research paper thumbnail of Electron-Transfer Kinetics in Sulfonated Aluminum Phthalocyanines/Cytochrome c Complexes

The Journal of Physical Chemistry B, 2004

Sulfonated aluminum phthalocyanines interact with cytochrome c forming complexes in aqueous solut... more Sulfonated aluminum phthalocyanines interact with cytochrome c forming complexes in aqueous solutions. The binding of these dyes was probed using fluorescence techniques (steady-state spectroscopy and timecorrelated single photon counting), which enable the calculation of the equilibrium binding constants. The fluorescence of the complex is relatively low (φ) 0.07) due to an electron-transfer process from the phthalocyanine singlet-excited state to the cytochrome c. The binding constant determines the amount of fluorescence and is quite high for the tetrasulfonated aluminum phthalocyanine (3.3 × 10 5 M-1) while those for the disulfonated and monosulfonated aluminum phthalocyanines are one order of magnitude smaller. The fluorescence decays suggest more than one location for the dye adsorbed in the protein, which is affected by electrostatic interactions, leading to nonexponential decays.

Research paper thumbnail of Transient effects in charge-transfer diffusion-controlled processes in nonionic micelles

The Journal of Physical Chemistry, 1980

The quenching of the fluorescence of benzyl 9-anthroate (Bz-9-Ant), benzyl 1-pyrenoate (Bz-1-Pn),... more The quenching of the fluorescence of benzyl 9-anthroate (Bz-9-Ant), benzyl 1-pyrenoate (Bz-1-Pn), and benzyl 2-naphthoate (Bz-2-Np) by triethylamine (TEA) and dimethylaniline (DMA) was studied in nonionic micelles of Triton X 100. The determination of the equilibrium constants between the aqueous and micellar phase [K, = 0.8 (TEA) and K, = 30 (DMA)] allowed the evaluation of the effective quencher concentration. Fluorescence studies in steady-state and transient conditions showed the existence of transient effects which enabled calculation of reactional distances (R? and an effective diffusion coefficient (D'eff). The results are explained on the basis of a charge-transfer diffusion-controlled process consistent with the correlation of 12, and R' with parameters associated with charge-transfer phenomena.

Research paper thumbnail of Steady-State Fluorescence Quenching Kinetics of Water-Soluble Zinc Porphyrins in Reversed Micelles

Journal of the Chemical Society-Faraday Transactions Ii, 1986

ABSTRACT

Research paper thumbnail of Probing the interface polarity of AOT reversed micelles using centro-symmetrical squaraine molecules

Physical Chemistry Chemical Physics, 1999

Page 1. Probing the interface polarity of AOT reversed micelles using centro-symmetrical squarain... more Page 1. Probing the interface polarity of AOT reversed micelles using centro-symmetrical squaraine molecules Ce sar AT Laia and S• lvia MB Costa* Centro de Estrutural, Complexo 1, Instituto Superior 1049-001 L isboa, Qu• mica T e cnico, Portugal. ...

Research paper thumbnail of Mechanism of photosensitized reduction of tetrazolium blue I. homogeneous solvent: ethanol

Journal of Photochemistry and Photobiology A: Chemistry, 1993

Research paper thumbnail of Diffusion coefficients of tetrazolium blue in homogeneous and micellar solutions

International Journal of Thermophysics, 1991

Diffusion coefficients of the electron acceptor dye tetrazolium blue were measured by the Taylor ... more Diffusion coefficients of the electron acceptor dye tetrazolium blue were measured by the Taylor dispersion method, with an accuracy better than 4%, in two solvents: (i) a homogeneous one-aqueous phosphate buffer, 0.1 M, pH=7.0 (medium I); and (ii) a heterogeneous one-nonionic micelles of Triton X-100, 2.0 mM (where M stands for mol·dm-3), in the same aqueous phosphate buffer (medium II).

Research paper thumbnail of A critical evaluation of partition constants in nonionic micelles

The Journal of Physical Chemistry, 1987

Transient and steady-state methods, used in the study of fluorescence quenching of excited n-(9-a... more Transient and steady-state methods, used in the study of fluorescence quenching of excited n-(9-anthroyloxy)stearic acids (n = 2, 6 , 9, 12) by N,N-dimethylaniline, DMA, and triethylamine, TEA, in nonionic micelles of Triton X-100, enabled the evaluation of quencher partition constants (K,) which range from 20 to 100 for DMA and from 0.9 to 3.1 for TEA. The values of K p are characteristic of probe (or similar probe location)/quencher pair. The changes obtained in the values of these partition constants reflect the increase in the effective amine concentration with the position of the carbon atom in the chain to which the chromophore is attached and are in good agreement with the location of the functional probes nAS at different depths in micelles of Triton X-100. Changes observed in the values of K p indicate that these micelles are not homogeneous and consequently that the physical meaning of K p is not rigorously that of a partition constant.

Research paper thumbnail of The quenching of excited aromatic esters by triethylamine

Journal of Photochemistry, 1979

The interaction of excited aromatic esters with tertiary aliphatic amines, triethylamine (TEA) an... more The interaction of excited aromatic esters with tertiary aliphatic amines, triethylamine (TEA) and diazobicyclo 12.2.23 octane has been investigated. In non-polar solvents the fluorescence quenching that is observed is accompanied in most cases by an exciplex emission when TEA is the quencher, whereas the radical anions of the esters are detected in polar solvents. The large dipole moments found for the exciplexes (9-16 debye) and the correlation of the bimolecular rate constant k, with the half-wave potential of the excited esters and the ionization potentials of the amines show that a charge transfer mechanism is operative in these systems.

Research paper thumbnail of Denaturation of a Recombinant Cutinase from Fusarium solani in AOT-iso-Octane Reverse Micelles: a Steady-State Fluorescence Study

Photochemistry and Photobiology, 1996

Near UV absorbance and fluorescence spectroscopy show conformational changes of a recombinant cut... more Near UV absorbance and fluorescence spectroscopy show conformational changes of a recombinant cutinase from Fusarium solani incorporated in sodium-di-2-ethylhexyl sulfosuccinate (A0T)-iso-octane reversed micelles with W, = [H,O]/[AOT] = 20. Excitation spectra were ...

Research paper thumbnail of The use of the n-(9-anthroyloxy) stearic acid to probe the water content of sodium dodecyl sulfate, dodecyltimethylammonium chloride, and triton X-100 micelles

Journal of Colloid and Interface Science, 1991

Quenching of the n-(9-anthroyloxy) stearic acids (n = 2, 6, 9, and 12) fluorescence by water is u... more Quenching of the n-(9-anthroyloxy) stearic acids (n = 2, 6, 9, and 12) fluorescence by water is used to evaluate the water content in the vicinity of the anthroate chromophore in micelles of sodium dodecyl sulfate (SDS), dodecyltrimethylammonium chloride (DTAC), and Triton X-100. The mean locations of the probes in the three micelles are evaluated from the ring current effects of the anthracene ring on the ~H-NMR resonances of the surfactant protons. It is found that there is practically no water in the hydrocarbon core of the Triton X-100 and the DTAC micelles while in SDS micelles water seems to penetrate further down to the/3 carbon of the surfactant molecule. Water concentrations obtained from fluorescence decays are compared with those obtained from the response of the emission spectra of the same probes to changes in the solvent polarity.

Research paper thumbnail of Structural Effect of Reversed Micelles of AOT over a Recombinant Cutinase from Fusarium solani pisi. A Steady State Fluorescence Study

Annals of the New York Academy of Sciences, 1995

Research paper thumbnail of Kinetics of fluorescence quenching of n(9-anthroyloxy) stearic acids by tertiary amines in non-ionic micelles of Triton X-100

Journal of the Chemical Society, Faraday Transactions, 1990

ABSTRACT

Research paper thumbnail of Dynamics of Excited Charge-Transfer Complexes in Non Ionic Micelles

Journal of Photochemistry, 1978

Bcciplexeshavebeenwellcharacterizedarrltheir khwztlcsare~ established(i) (*) ihslIl@esf3lventf3. ... more Bcciplexeshavebeenwellcharacterizedarrltheir khwztlcsare~ established(i) (*) ihslIl@esf3lventf3. Recently %aU3(3) hasrepo&zilon~physicalandchanicalproper ties0f&arq~transfer~lexeainulk!ellarsys~. wF===t a3mmmlcationreportsastudyofthe~offl~_ oence of araaaticesterabytriethylamLneinnan-ianicmiaelles, using trahsientandsteaay-state fluoresaeru=e mw. IntheSptf3WStUdl&,the acmptm mlecules are benzyl9-anama* (1) and (1) A.

Research paper thumbnail of Spectroscopy of photoinduced charge-transfer reactions between tetrasulfonated aluminium phthalocyanine and methyl viologenDedicated to the memory of Nobel Laureate, Lord George Porter FRSC FRS OM

Photochemical & Photobiological Sciences, 2003

Interactions between tetrasulfonated aluminium phthalocyanine (AlPcTS4-) and methyl viologen (Mv2... more Interactions between tetrasulfonated aluminium phthalocyanine (AlPcTS4-) and methyl viologen (Mv2+) have been studied in water and ethanol solutions using several experimental techniques. UV-visible absorption and fluorescence spectroscopies show that ion-pair complexes occur in ethanol, disappearing in more polar environments such as water. Time-resolved fluorescence spectroscopy (picosecond timescale) reveals the existence of several emissive species in ethanol solutions, of which one of the components is attributed to the charge-transfer complex (AlPcTS4-)(Mv2+)2, another to higher-order aggregates and yet another to the isolated AlPcTS4- molecule. The AlPcTS4- emission is quenched by Mv2+, leading to transient diffusion in the fluorescence decay kinetics. On the other hand, the emissive complex has an exponential decay with a relatively long lifetime (above 1 ns). Time-resolved absorption measurements did not reveal the existence of radicals in aqueous solution, even on the picosecond timescale. The spectra reveal the presence of excited singlet state AlPcTS4-, which decays via the triplet excited state back to the ground state.

Research paper thumbnail of Behaviour of the water-soluble meso-tetra (4-methylpyridyl) porphine in mixed monolayers and in Langmuir���Blodgett films

... Amélia M. Gonçalves da Silva*, Maria Isabel Viseu*, Rute IS Romão and Sílvia MB Costa. Centro... more ... Amélia M. Gonçalves da Silva*, Maria Isabel Viseu*, Rute IS Romão and Sílvia MB Costa. Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, 1049–001, Lisboa, Portugal. ... The authors acknowledge Ms. P. Antunes for performing some experiments. ...

Research paper thumbnail of Spectroscopy of photoinduced charge-transfer reactions between tetrasulfonated aluminium phthalocyanine and methyl viologen

Interactions between tetrasulfonated aluminium phthalocyanine (AlPcTS4-) and methyl viologen (Mv2... more Interactions between tetrasulfonated aluminium phthalocyanine (AlPcTS4-) and methyl viologen (Mv2+) have been studied in water and ethanol solutions using several experimental techniques. UV-visible absorption and fluorescence spectroscopies show that ion-pair complexes occur in ethanol, disappearing in more polar environments such as water. Time-resolved fluorescence spectroscopy (picosecond timescale) reveals the existence of several emissive species in ethanol solutions, of which one of the components is attributed to the charge-transfer complex (AlPcTS4-)(Mv2+)2, another to higher-order aggregates and yet another to the isolated AlPcTS4- molecule. The AlPcTS4- emission is quenched by Mv2+, leading to transient diffusion in the fluorescence decay kinetics. On the other hand, the emissive complex has an exponential decay with a relatively long lifetime (above 1 ns). Time-resolved absorption measurements did not reveal the existence of radicals in aqueous solution, even on the picosecond timescale. The spectra reveal the presence of excited singlet state AlPcTS4-, which decays via the triplet excited state back to the ground state.

Research paper thumbnail of Steady state and dynamic quenching of zinc tetramethylpyridylporphyrin by methyl viologen ion pairs. Salt effects

New J. Chem., 2002

New J. Chem., 2002, 26, 1774-1783 DOI:10.1039/B206789G (Paper). Steady state and dynamic quenchin... more New J. Chem., 2002, 26, 1774-1783 DOI:10.1039/B206789G (Paper). Steady state and dynamic quenching of zinc tetramethylpyridylporphyrin by methyl viologen ion pairs. Salt effects. Denisio M. Togashi* and Sílvia MB Costa. ...

Research paper thumbnail of Probing the interface polarity of AOT reversed micelles using centro-symmetrical squaraine molecules

Page 1. Probing the interface polarity of AOT reversed micelles using centro-symmetrical squarain... more Page 1. Probing the interface polarity of AOT reversed micelles using centro-symmetrical squaraine molecules Ce sar AT Laia and S• lvia MB Costa* Centro de Estrutural, Complexo 1, Instituto Superior 1049-001 L isboa, Qu• mica T e cnico, Portugal. ...

Research paper thumbnail of Hydrogen bonding effects in the photophysics of a drug, Piroxicam, in homogeneous media and dioxane–water mixtures

Page 1. Hydrogen bonding e†ects in the photophysics of a drug, Piroxicam, in homogeneous media an... more Page 1. Hydrogen bonding e†ects in the photophysics of a drug, Piroxicam, in homogeneous media and dioxane–water mixtures Suzana M. Andrade and S• lvia MB Costa* Centro de Estrutural, Complexo 1, Instituto Superior 1049-001 L isboa Codex, Qu• mica T e cnico, ...

Research paper thumbnail of Thermal unfolding of proteins at high pH range studied by UV absorbance

This work describes a methodology to monitor protein unfolding by using the well known changes in... more This work describes a methodology to monitor protein unfolding by using the well known changes in tyrosine absorbance with the ionization of the side chain phenol group. It can be applied to proteins that are functionally active at pH values higher than 9.0 where the current UV differential spectroscopy technique can not be used. The simplicity and facility of the proposed methodology (only two absorbance measurements have to be acquired) can make it very useful namely for technological applications. Thermal unfolding of cutinase and a-chymotrypsin were followed using this methodology and the thermodynamic stability data was obtained assuming a two-state mechanism. The transition from the folded to the unfolded state was further confirmed by fluorescence maxima for both proteins proving the validity of the methodology based on UV measurements.

Research paper thumbnail of Electron-Transfer Kinetics in Sulfonated Aluminum Phthalocyanines/Cytochrome c Complexes

The Journal of Physical Chemistry B, 2004

Sulfonated aluminum phthalocyanines interact with cytochrome c forming complexes in aqueous solut... more Sulfonated aluminum phthalocyanines interact with cytochrome c forming complexes in aqueous solutions. The binding of these dyes was probed using fluorescence techniques (steady-state spectroscopy and timecorrelated single photon counting), which enable the calculation of the equilibrium binding constants. The fluorescence of the complex is relatively low (φ) 0.07) due to an electron-transfer process from the phthalocyanine singlet-excited state to the cytochrome c. The binding constant determines the amount of fluorescence and is quite high for the tetrasulfonated aluminum phthalocyanine (3.3 × 10 5 M-1) while those for the disulfonated and monosulfonated aluminum phthalocyanines are one order of magnitude smaller. The fluorescence decays suggest more than one location for the dye adsorbed in the protein, which is affected by electrostatic interactions, leading to nonexponential decays.

Research paper thumbnail of Transient effects in charge-transfer diffusion-controlled processes in nonionic micelles

The Journal of Physical Chemistry, 1980

The quenching of the fluorescence of benzyl 9-anthroate (Bz-9-Ant), benzyl 1-pyrenoate (Bz-1-Pn),... more The quenching of the fluorescence of benzyl 9-anthroate (Bz-9-Ant), benzyl 1-pyrenoate (Bz-1-Pn), and benzyl 2-naphthoate (Bz-2-Np) by triethylamine (TEA) and dimethylaniline (DMA) was studied in nonionic micelles of Triton X 100. The determination of the equilibrium constants between the aqueous and micellar phase [K, = 0.8 (TEA) and K, = 30 (DMA)] allowed the evaluation of the effective quencher concentration. Fluorescence studies in steady-state and transient conditions showed the existence of transient effects which enabled calculation of reactional distances (R? and an effective diffusion coefficient (D'eff). The results are explained on the basis of a charge-transfer diffusion-controlled process consistent with the correlation of 12, and R' with parameters associated with charge-transfer phenomena.

Research paper thumbnail of Steady-State Fluorescence Quenching Kinetics of Water-Soluble Zinc Porphyrins in Reversed Micelles

Journal of the Chemical Society-Faraday Transactions Ii, 1986

ABSTRACT

Research paper thumbnail of Probing the interface polarity of AOT reversed micelles using centro-symmetrical squaraine molecules

Physical Chemistry Chemical Physics, 1999

Page 1. Probing the interface polarity of AOT reversed micelles using centro-symmetrical squarain... more Page 1. Probing the interface polarity of AOT reversed micelles using centro-symmetrical squaraine molecules Ce sar AT Laia and S• lvia MB Costa* Centro de Estrutural, Complexo 1, Instituto Superior 1049-001 L isboa, Qu• mica T e cnico, Portugal. ...

Research paper thumbnail of Mechanism of photosensitized reduction of tetrazolium blue I. homogeneous solvent: ethanol

Journal of Photochemistry and Photobiology A: Chemistry, 1993

Research paper thumbnail of Diffusion coefficients of tetrazolium blue in homogeneous and micellar solutions

International Journal of Thermophysics, 1991

Diffusion coefficients of the electron acceptor dye tetrazolium blue were measured by the Taylor ... more Diffusion coefficients of the electron acceptor dye tetrazolium blue were measured by the Taylor dispersion method, with an accuracy better than 4%, in two solvents: (i) a homogeneous one-aqueous phosphate buffer, 0.1 M, pH=7.0 (medium I); and (ii) a heterogeneous one-nonionic micelles of Triton X-100, 2.0 mM (where M stands for mol·dm-3), in the same aqueous phosphate buffer (medium II).

Research paper thumbnail of A critical evaluation of partition constants in nonionic micelles

The Journal of Physical Chemistry, 1987

Transient and steady-state methods, used in the study of fluorescence quenching of excited n-(9-a... more Transient and steady-state methods, used in the study of fluorescence quenching of excited n-(9-anthroyloxy)stearic acids (n = 2, 6 , 9, 12) by N,N-dimethylaniline, DMA, and triethylamine, TEA, in nonionic micelles of Triton X-100, enabled the evaluation of quencher partition constants (K,) which range from 20 to 100 for DMA and from 0.9 to 3.1 for TEA. The values of K p are characteristic of probe (or similar probe location)/quencher pair. The changes obtained in the values of these partition constants reflect the increase in the effective amine concentration with the position of the carbon atom in the chain to which the chromophore is attached and are in good agreement with the location of the functional probes nAS at different depths in micelles of Triton X-100. Changes observed in the values of K p indicate that these micelles are not homogeneous and consequently that the physical meaning of K p is not rigorously that of a partition constant.

Research paper thumbnail of The quenching of excited aromatic esters by triethylamine

Journal of Photochemistry, 1979

The interaction of excited aromatic esters with tertiary aliphatic amines, triethylamine (TEA) an... more The interaction of excited aromatic esters with tertiary aliphatic amines, triethylamine (TEA) and diazobicyclo 12.2.23 octane has been investigated. In non-polar solvents the fluorescence quenching that is observed is accompanied in most cases by an exciplex emission when TEA is the quencher, whereas the radical anions of the esters are detected in polar solvents. The large dipole moments found for the exciplexes (9-16 debye) and the correlation of the bimolecular rate constant k, with the half-wave potential of the excited esters and the ionization potentials of the amines show that a charge transfer mechanism is operative in these systems.

Research paper thumbnail of Denaturation of a Recombinant Cutinase from Fusarium solani in AOT-iso-Octane Reverse Micelles: a Steady-State Fluorescence Study

Photochemistry and Photobiology, 1996

Near UV absorbance and fluorescence spectroscopy show conformational changes of a recombinant cut... more Near UV absorbance and fluorescence spectroscopy show conformational changes of a recombinant cutinase from Fusarium solani incorporated in sodium-di-2-ethylhexyl sulfosuccinate (A0T)-iso-octane reversed micelles with W, = [H,O]/[AOT] = 20. Excitation spectra were ...

Research paper thumbnail of The use of the n-(9-anthroyloxy) stearic acid to probe the water content of sodium dodecyl sulfate, dodecyltimethylammonium chloride, and triton X-100 micelles

Journal of Colloid and Interface Science, 1991

Quenching of the n-(9-anthroyloxy) stearic acids (n = 2, 6, 9, and 12) fluorescence by water is u... more Quenching of the n-(9-anthroyloxy) stearic acids (n = 2, 6, 9, and 12) fluorescence by water is used to evaluate the water content in the vicinity of the anthroate chromophore in micelles of sodium dodecyl sulfate (SDS), dodecyltrimethylammonium chloride (DTAC), and Triton X-100. The mean locations of the probes in the three micelles are evaluated from the ring current effects of the anthracene ring on the ~H-NMR resonances of the surfactant protons. It is found that there is practically no water in the hydrocarbon core of the Triton X-100 and the DTAC micelles while in SDS micelles water seems to penetrate further down to the/3 carbon of the surfactant molecule. Water concentrations obtained from fluorescence decays are compared with those obtained from the response of the emission spectra of the same probes to changes in the solvent polarity.

Research paper thumbnail of Structural Effect of Reversed Micelles of AOT over a Recombinant Cutinase from Fusarium solani pisi. A Steady State Fluorescence Study

Annals of the New York Academy of Sciences, 1995

Research paper thumbnail of Kinetics of fluorescence quenching of n(9-anthroyloxy) stearic acids by tertiary amines in non-ionic micelles of Triton X-100

Journal of the Chemical Society, Faraday Transactions, 1990

ABSTRACT

Research paper thumbnail of Dynamics of Excited Charge-Transfer Complexes in Non Ionic Micelles

Journal of Photochemistry, 1978

Bcciplexeshavebeenwellcharacterizedarrltheir khwztlcsare~ established(i) (*) ihslIl@esf3lventf3. ... more Bcciplexeshavebeenwellcharacterizedarrltheir khwztlcsare~ established(i) (*) ihslIl@esf3lventf3. Recently %aU3(3) hasrepo&zilon~physicalandchanicalproper ties0f&arq~transfer~lexeainulk!ellarsys~. wF===t a3mmmlcationreportsastudyofthe~offl~_ oence of araaaticesterabytriethylamLneinnan-ianicmiaelles, using trahsientandsteaay-state fluoresaeru=e mw. IntheSptf3WStUdl&,the acmptm mlecules are benzyl9-anama* (1) and (1) A.

Research paper thumbnail of Spectroscopy of photoinduced charge-transfer reactions between tetrasulfonated aluminium phthalocyanine and methyl viologenDedicated to the memory of Nobel Laureate, Lord George Porter FRSC FRS OM

Photochemical & Photobiological Sciences, 2003

Interactions between tetrasulfonated aluminium phthalocyanine (AlPcTS4-) and methyl viologen (Mv2... more Interactions between tetrasulfonated aluminium phthalocyanine (AlPcTS4-) and methyl viologen (Mv2+) have been studied in water and ethanol solutions using several experimental techniques. UV-visible absorption and fluorescence spectroscopies show that ion-pair complexes occur in ethanol, disappearing in more polar environments such as water. Time-resolved fluorescence spectroscopy (picosecond timescale) reveals the existence of several emissive species in ethanol solutions, of which one of the components is attributed to the charge-transfer complex (AlPcTS4-)(Mv2+)2, another to higher-order aggregates and yet another to the isolated AlPcTS4- molecule. The AlPcTS4- emission is quenched by Mv2+, leading to transient diffusion in the fluorescence decay kinetics. On the other hand, the emissive complex has an exponential decay with a relatively long lifetime (above 1 ns). Time-resolved absorption measurements did not reveal the existence of radicals in aqueous solution, even on the picosecond timescale. The spectra reveal the presence of excited singlet state AlPcTS4-, which decays via the triplet excited state back to the ground state.

Research paper thumbnail of Behaviour of the water-soluble meso-tetra (4-methylpyridyl) porphine in mixed monolayers and in Langmuir���Blodgett films

... Amélia M. Gonçalves da Silva*, Maria Isabel Viseu*, Rute IS Romão and Sílvia MB Costa. Centro... more ... Amélia M. Gonçalves da Silva*, Maria Isabel Viseu*, Rute IS Romão and Sílvia MB Costa. Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, 1049–001, Lisboa, Portugal. ... The authors acknowledge Ms. P. Antunes for performing some experiments. ...

Research paper thumbnail of Spectroscopy of photoinduced charge-transfer reactions between tetrasulfonated aluminium phthalocyanine and methyl viologen

Interactions between tetrasulfonated aluminium phthalocyanine (AlPcTS4-) and methyl viologen (Mv2... more Interactions between tetrasulfonated aluminium phthalocyanine (AlPcTS4-) and methyl viologen (Mv2+) have been studied in water and ethanol solutions using several experimental techniques. UV-visible absorption and fluorescence spectroscopies show that ion-pair complexes occur in ethanol, disappearing in more polar environments such as water. Time-resolved fluorescence spectroscopy (picosecond timescale) reveals the existence of several emissive species in ethanol solutions, of which one of the components is attributed to the charge-transfer complex (AlPcTS4-)(Mv2+)2, another to higher-order aggregates and yet another to the isolated AlPcTS4- molecule. The AlPcTS4- emission is quenched by Mv2+, leading to transient diffusion in the fluorescence decay kinetics. On the other hand, the emissive complex has an exponential decay with a relatively long lifetime (above 1 ns). Time-resolved absorption measurements did not reveal the existence of radicals in aqueous solution, even on the picosecond timescale. The spectra reveal the presence of excited singlet state AlPcTS4-, which decays via the triplet excited state back to the ground state.

Research paper thumbnail of Steady state and dynamic quenching of zinc tetramethylpyridylporphyrin by methyl viologen ion pairs. Salt effects

New J. Chem., 2002

New J. Chem., 2002, 26, 1774-1783 DOI:10.1039/B206789G (Paper). Steady state and dynamic quenchin... more New J. Chem., 2002, 26, 1774-1783 DOI:10.1039/B206789G (Paper). Steady state and dynamic quenching of zinc tetramethylpyridylporphyrin by methyl viologen ion pairs. Salt effects. Denisio M. Togashi* and Sílvia MB Costa. ...

Research paper thumbnail of Probing the interface polarity of AOT reversed micelles using centro-symmetrical squaraine molecules

Page 1. Probing the interface polarity of AOT reversed micelles using centro-symmetrical squarain... more Page 1. Probing the interface polarity of AOT reversed micelles using centro-symmetrical squaraine molecules Ce sar AT Laia and S• lvia MB Costa* Centro de Estrutural, Complexo 1, Instituto Superior 1049-001 L isboa, Qu• mica T e cnico, Portugal. ...

Research paper thumbnail of Hydrogen bonding effects in the photophysics of a drug, Piroxicam, in homogeneous media and dioxane–water mixtures

Page 1. Hydrogen bonding e†ects in the photophysics of a drug, Piroxicam, in homogeneous media an... more Page 1. Hydrogen bonding e†ects in the photophysics of a drug, Piroxicam, in homogeneous media and dioxane–water mixtures Suzana M. Andrade and S• lvia MB Costa* Centro de Estrutural, Complexo 1, Instituto Superior 1049-001 L isboa Codex, Qu• mica T e cnico, ...

Research paper thumbnail of Thermal unfolding of proteins at high pH range studied by UV absorbance

This work describes a methodology to monitor protein unfolding by using the well known changes in... more This work describes a methodology to monitor protein unfolding by using the well known changes in tyrosine absorbance with the ionization of the side chain phenol group. It can be applied to proteins that are functionally active at pH values higher than 9.0 where the current UV differential spectroscopy technique can not be used. The simplicity and facility of the proposed methodology (only two absorbance measurements have to be acquired) can make it very useful namely for technological applications. Thermal unfolding of cutinase and a-chymotrypsin were followed using this methodology and the thermodynamic stability data was obtained assuming a two-state mechanism. The transition from the folded to the unfolded state was further confirmed by fluorescence maxima for both proteins proving the validity of the methodology based on UV measurements.