Raquel Correia - Academia.edu (original) (raw)

Papers by Raquel Correia

Research paper thumbnail of SUPPL. MAT. Aggregation/disaggregation of chlorophyll a in model phospholipid–detergent vesicles and micelles

Photochemical and Photobiological Sciences

The photosynthetic pigments of higher plants exist in complex oligomeric states, which are diffic... more The photosynthetic pigments of higher plants exist in complex oligomeric states, which are difficult to study in vivo. To investigate aggregation processes of chlorophyll a (Chl a), we used an in vitro reconstitution procedure, with this pigment incorporated into liposomes of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), micelles and pre-micelle media of the detergent n-dodecyltrimethylammonium chloride (DTAC), and mixed, spontaneous, DMPC–DTAC vesicles and micelles. Chl a oligomers were characterized by UV-visible absorption, steady-state and time-resolved fluorescence, and fluorescence lifetime imaging microscopy. Equivalent diameters of the colloidal structures were obtained by fluorescence correlation spectroscopy. In DMPC liposomes and DMPC–DTAC vesicles and micelles, three fluorescence lifetimes indicated the coexistence of Chl a monomers (≈5 ns) and oligomers (≈1–2 to ≈0.1 ns). The increase in DTAC amount, in the mixed system, induces a progressive solubilization of DMP...

Research paper thumbnail of Graphical Abstract 1

Research paper thumbnail of SUPPLEMENTARY MATERIAL for the paper Spontaneous Vesicles, Disks, Threadlike and Spherical Micelles found in the Solubilization of DMPC Liposomes by the Detergent DTAC

Research paper thumbnail of Aggregation/disaggregation of chlorophyll a in model phospholipid–detergent vesicles and micelles

Photochemical & Photobiological Sciences, 2014

The photosynthetic pigments of higher plants exist in complex oligomeric states, which are diffic... more The photosynthetic pigments of higher plants exist in complex oligomeric states, which are difficult to study in vivo. To investigate aggregation processes of chlorophyll a (Chl a), we used an in vitro reconstitution procedure, with this pigment incorporated into liposomes of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), micelles and pre-micelle media of the detergent n-dodecyltrimethylammonium chloride (DTAC), and mixed, spontaneous, DMPC-DTAC vesicles and micelles. Chl a oligomers were characterized by UV-visible absorption, steady-state and time-resolved fluorescence, and fluorescence lifetime imaging microscopy. Equivalent diameters of the colloidal structures were obtained by fluorescence correlation spectroscopy. In DMPC liposomes and DMPC-DTAC vesicles and micelles, three fluorescence lifetimes indicated the coexistence of Chl a monomers (≈5 ns) and oligomers (≈1-2 to ≈0.1 ns). The increase in DTAC amount, in the mixed system, induces a progressive solubilization of DMPC liposomes (from vesicles to micelles) and simultaneous disruption of Chl a aggregates; in pure DTAC micelles, mostly monomers were found. The present work aims for a better understanding of chlorophyll-chlorophyll (Chl-Chl), Chl-lipid, and Chl-detergent interactions in spontaneous colloidal micro-and nanostructures. † Electronic supplementary information (ESI) available: (1) Turbidity correction of electronic absorption spectra of chlorophyll a in DMPC-DTAC media; (2) parameters of electronic absorption spectra of chlorophyll a in DMPC-DTAC media;

Research paper thumbnail of Aggregation and disaggregation of anionic aluminum phthalocyanines in cationic pre-micelle and micelle media: A fluorescence study

Journal of Photochemistry and Photobiology A: Chemistry, 2012

The interactions of two anionic aluminum phthalocyanines (Pcs), the tetrasulfonated (AlPcS 4 ) an... more The interactions of two anionic aluminum phthalocyanines (Pcs), the tetrasulfonated (AlPcS 4 ) and the monosulfonated (AlPcS 1 ) species, with the cationic detergent n-dodecyltrimethylammonium chloride (DTAC) were investigated. These studies were performed by UV-visible absorption, steady-state and transient-state fluorescence, fluorescence lifetime imaging microscopy (FLIM), and fluorescence correlation spectroscopy (FCS). For both AlPcS 4 and AlPcS 1 , large complexes of Pc-DTAC were formed at low surfactant concentrations, in the pre-micelle range. These complexes were visualized by the FLIM technique, directly in a drop of the sample. As the DTAC concentration increased, the size of the complexes decreased significantly. Above the detergent critical micelle concentration (CMC ≈ 22 mM), highly fluorescent monomers of both AlPcS 4 and AlPcS 1 were found to be strongly bound to the DTAC micelles surface: large equilibrium binding constants, K b = 3.5 × 10 5 and 6.2 × 10 4 , were obtained for AlPcS 4 and AlPcS 1 , respectively. The aggregation/disaggregation behavior of phthalocyanines likely results from a delicate balance in the system, between hydrophobic attractions (Pc-Pc) and electrostatic attractions (anionic Pc macrocycles -cationic DTAC headgroups) and repulsions (between anionic sulfonated groups of Pc macrocycles).

Research paper thumbnail of Time evolution of the thermotropic behavior of spontaneous liposomes and disks of the DMPC–DTAC aqueous system

Journal of Colloid and Interface Science, 2010

In this work, solubilization of the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMP... more In this work, solubilization of the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) by the cationic detergent n-dodecyltrimethylammonium chloride (DTAC) was studied in aqueous solution, at a fixed DMPC concentration and variable detergent:lipid (D:L) molar ratios. The colloidal nanostructures present in different stages of the solubilization process were characterized using micro-differential scanning calorimetry (DSC) and dynamic light scattering (DLS) techniques. For total (analytical) D:L molar ratios below %1, DTAC monomers incorporate into the DMPC liposome bilayers, forming smaller and more fluid vesicles than pure DMPC liposomes. At D:L % 1-2, vesicles begin to rupture, coexisting with intact vesicles and bilayer fragments. At D:L % 2-12.5, discoidal and spherical micelles are formed and coexist with vesicles; a slow structural rearrangement of the system, monitored in successive DSC heating/cooling cycles, was observed, and is reported for the first time. Finally, for D:L above %15-20, the bilayers are completely dissolved, and the main aggregates in solution become spherical micelles, which slowly evolve to cylindrical (threadlike) micelles. Based on the dependence of the temperature and enthalpy of transitions on the total D:L molar ratio, at constant DMPC concentration, a schematic model, showing the different colloidal nanostructures present in the solubilization process, is proposed.

Research paper thumbnail of Spontaneous vesicles, disks, threadlike and spherical micelles found in the solubilization of DMPC liposomes by the detergent DTAC

Journal of Colloid and Interface Science, 2012

The spontaneous colloidal nanostructures formed in water by the zwitterionic phospholipid DMPC (1... more The spontaneous colloidal nanostructures formed in water by the zwitterionic phospholipid DMPC (1,2dimyristoyl-sn-glycero-3-phosphocholine) with the cationic detergent DTAC (n-dodecyltrimethylammonium chloride) were investigated at a fixed DMPC concentration and variable detergent:lipid total molar ratios (D:L). Apparent (neutral-sphere-equivalent) hydrodynamic diameters (U e ) of liposomes and micelles were obtained by dynamic light scattering (DLS). Fluorescence lifetime imaging microscopy (FLIM), using chlorophyll-a as a probe, showed the morphology of giant vesicles and threadlike micelles. Micro-differential scanning calorimetry (micro-DSC) detected the presence of bilayers, in vesicles and discoidal micelles (disks). Pure DMPC liposomes are multilamellar and polydisperse (U e % 100-10,000 nm). As D:L increased, smaller vesicles were found, due to the bigger spontaneous curvature of the bilayer: at D:L = 1, ULVs (unilamellar vesicles; U e % 100 nm) appeared and, at D:L = 2-10, ULVs coexisted with disks (U e % 30 nm). Bilayers totally disappeared at D:L P 15, giving rise to spheroidal (U e % 2-16 nm) and threadlike (U e % 100-10,000 nm) micelles. A quasi-equilibrium structural diagram for the DMPC-DTAC-water system shows equivalent diameters of the scattering nanoparticles as a function of D:L. The results obtained herein for the system DMPC-DTAC show the role of electrostatic interactions in the formation of the mixed structures.

Research paper thumbnail of Time evolution of monomers and aggregates of a polymethine dye probe the dynamics of model vesicles and micelles

Journal of Photochemistry and Photobiology A: Chemistry, 2014

ABSTRACT An anionic polymethine dye (a fluoro-oxonol abbreviated FDID), which forms monomers and ... more ABSTRACT An anionic polymethine dye (a fluoro-oxonol abbreviated FDID), which forms monomers and oligomers according to the surrounding medium, is used in this work to probe the stability and dynamics of bicationic colloidal nanostructures, namely micelles and vesicles. Using pure water as the reference solvent (medium 1), five aqueous colloidal media of the lipid-detergent system DDAB-DTAC (didodecyldimethylammonium bromide-dodecyltrimethylammonium chloride) were analyzed: pre-micelle DTAC media (2); pure DTAC micelles (3); DDAB-DTAC micelles (4); DDAB-DTAC vesicles (5); and pure DDAB vesicles (6). In systems 4-6, containing the double-chained DDAB, FDID showed a slow-dynamics disaggregation, H-aggregates monomers. The kinetics of this transition was followed by running UV-vis absorption spectra along time. The transition lifetimes tau increased in the order tau(medium 3) << tau(media4,5) < tau(medium6) reflecting the much faster mobility of the single-chained DTA(+) long ion, as compared to that of the more hydrophobic, double-chained, DDA(+). This paper showed that FDID can probe the exchanging dynamics of the DDA(+)/DTA(+) long cations between the water phase and the colloidal nanostructures.

Research paper thumbnail of Unfolding Kinetics of β-Lactoglobulin Induced by Surfactant and Denaturant: A Stopped-Flow/Fluorescence Study

Biophysical Journal, 2007

The b/a transition of b-lactoglobulin, a globular protein abundant in the milk of several mammals... more The b/a transition of b-lactoglobulin, a globular protein abundant in the milk of several mammals, is investigated in this work. This transition, induced by the cationic surfactant dodecyltrimethylammonium chloride (DTAC), is accompanied by partial unfolding of the protein. In this work, unfolding of bovine b-lactoglobulin in DTAC is compared with its unfolding induced by the chemical denaturant guanidine hydrochloride (GnHCl). The final protein states attained in the two media have quite different secondary structure: in DTAC the a-helical content increases, leading to the so-called a-state; in GnHCl the amount of ordered secondary-structure decreases, resulting in a random coil-rich final state (denatured, or D, state). To obtain information on both mechanistic routes, in DTAC and GnHCl, and to characterize intermediates, the kinetics of unfolding were investigated in the two media. Equilibrium and kinetic data show the partial accumulation of an on-pathway intermediate in each unfolding route: in DTAC, an intermediate (I 1 ) with mostly native secondary structure but loose tertiary structure appears between the native (b) and a-states; in GnHCl, another intermediate (I 2 ) appears between states b and D. Kinetic rate constants follow a linear Chevron-plot representation in GnHCl, but show a more complex mechanism in DTAC, which acts like a stronger binding species.

Research paper thumbnail of SUPPL. MAT. Aggregation/disaggregation of chlorophyll a in model phospholipid–detergent vesicles and micelles

Photochemical and Photobiological Sciences

The photosynthetic pigments of higher plants exist in complex oligomeric states, which are diffic... more The photosynthetic pigments of higher plants exist in complex oligomeric states, which are difficult to study in vivo. To investigate aggregation processes of chlorophyll a (Chl a), we used an in vitro reconstitution procedure, with this pigment incorporated into liposomes of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), micelles and pre-micelle media of the detergent n-dodecyltrimethylammonium chloride (DTAC), and mixed, spontaneous, DMPC–DTAC vesicles and micelles. Chl a oligomers were characterized by UV-visible absorption, steady-state and time-resolved fluorescence, and fluorescence lifetime imaging microscopy. Equivalent diameters of the colloidal structures were obtained by fluorescence correlation spectroscopy. In DMPC liposomes and DMPC–DTAC vesicles and micelles, three fluorescence lifetimes indicated the coexistence of Chl a monomers (≈5 ns) and oligomers (≈1–2 to ≈0.1 ns). The increase in DTAC amount, in the mixed system, induces a progressive solubilization of DMP...

Research paper thumbnail of Graphical Abstract 1

Research paper thumbnail of SUPPLEMENTARY MATERIAL for the paper Spontaneous Vesicles, Disks, Threadlike and Spherical Micelles found in the Solubilization of DMPC Liposomes by the Detergent DTAC

Research paper thumbnail of Aggregation/disaggregation of chlorophyll a in model phospholipid–detergent vesicles and micelles

Photochemical & Photobiological Sciences, 2014

The photosynthetic pigments of higher plants exist in complex oligomeric states, which are diffic... more The photosynthetic pigments of higher plants exist in complex oligomeric states, which are difficult to study in vivo. To investigate aggregation processes of chlorophyll a (Chl a), we used an in vitro reconstitution procedure, with this pigment incorporated into liposomes of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), micelles and pre-micelle media of the detergent n-dodecyltrimethylammonium chloride (DTAC), and mixed, spontaneous, DMPC-DTAC vesicles and micelles. Chl a oligomers were characterized by UV-visible absorption, steady-state and time-resolved fluorescence, and fluorescence lifetime imaging microscopy. Equivalent diameters of the colloidal structures were obtained by fluorescence correlation spectroscopy. In DMPC liposomes and DMPC-DTAC vesicles and micelles, three fluorescence lifetimes indicated the coexistence of Chl a monomers (≈5 ns) and oligomers (≈1-2 to ≈0.1 ns). The increase in DTAC amount, in the mixed system, induces a progressive solubilization of DMPC liposomes (from vesicles to micelles) and simultaneous disruption of Chl a aggregates; in pure DTAC micelles, mostly monomers were found. The present work aims for a better understanding of chlorophyll-chlorophyll (Chl-Chl), Chl-lipid, and Chl-detergent interactions in spontaneous colloidal micro-and nanostructures. † Electronic supplementary information (ESI) available: (1) Turbidity correction of electronic absorption spectra of chlorophyll a in DMPC-DTAC media; (2) parameters of electronic absorption spectra of chlorophyll a in DMPC-DTAC media;

Research paper thumbnail of Aggregation and disaggregation of anionic aluminum phthalocyanines in cationic pre-micelle and micelle media: A fluorescence study

Journal of Photochemistry and Photobiology A: Chemistry, 2012

The interactions of two anionic aluminum phthalocyanines (Pcs), the tetrasulfonated (AlPcS 4 ) an... more The interactions of two anionic aluminum phthalocyanines (Pcs), the tetrasulfonated (AlPcS 4 ) and the monosulfonated (AlPcS 1 ) species, with the cationic detergent n-dodecyltrimethylammonium chloride (DTAC) were investigated. These studies were performed by UV-visible absorption, steady-state and transient-state fluorescence, fluorescence lifetime imaging microscopy (FLIM), and fluorescence correlation spectroscopy (FCS). For both AlPcS 4 and AlPcS 1 , large complexes of Pc-DTAC were formed at low surfactant concentrations, in the pre-micelle range. These complexes were visualized by the FLIM technique, directly in a drop of the sample. As the DTAC concentration increased, the size of the complexes decreased significantly. Above the detergent critical micelle concentration (CMC ≈ 22 mM), highly fluorescent monomers of both AlPcS 4 and AlPcS 1 were found to be strongly bound to the DTAC micelles surface: large equilibrium binding constants, K b = 3.5 × 10 5 and 6.2 × 10 4 , were obtained for AlPcS 4 and AlPcS 1 , respectively. The aggregation/disaggregation behavior of phthalocyanines likely results from a delicate balance in the system, between hydrophobic attractions (Pc-Pc) and electrostatic attractions (anionic Pc macrocycles -cationic DTAC headgroups) and repulsions (between anionic sulfonated groups of Pc macrocycles).

Research paper thumbnail of Time evolution of the thermotropic behavior of spontaneous liposomes and disks of the DMPC–DTAC aqueous system

Journal of Colloid and Interface Science, 2010

In this work, solubilization of the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMP... more In this work, solubilization of the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) by the cationic detergent n-dodecyltrimethylammonium chloride (DTAC) was studied in aqueous solution, at a fixed DMPC concentration and variable detergent:lipid (D:L) molar ratios. The colloidal nanostructures present in different stages of the solubilization process were characterized using micro-differential scanning calorimetry (DSC) and dynamic light scattering (DLS) techniques. For total (analytical) D:L molar ratios below %1, DTAC monomers incorporate into the DMPC liposome bilayers, forming smaller and more fluid vesicles than pure DMPC liposomes. At D:L % 1-2, vesicles begin to rupture, coexisting with intact vesicles and bilayer fragments. At D:L % 2-12.5, discoidal and spherical micelles are formed and coexist with vesicles; a slow structural rearrangement of the system, monitored in successive DSC heating/cooling cycles, was observed, and is reported for the first time. Finally, for D:L above %15-20, the bilayers are completely dissolved, and the main aggregates in solution become spherical micelles, which slowly evolve to cylindrical (threadlike) micelles. Based on the dependence of the temperature and enthalpy of transitions on the total D:L molar ratio, at constant DMPC concentration, a schematic model, showing the different colloidal nanostructures present in the solubilization process, is proposed.

Research paper thumbnail of Spontaneous vesicles, disks, threadlike and spherical micelles found in the solubilization of DMPC liposomes by the detergent DTAC

Journal of Colloid and Interface Science, 2012

The spontaneous colloidal nanostructures formed in water by the zwitterionic phospholipid DMPC (1... more The spontaneous colloidal nanostructures formed in water by the zwitterionic phospholipid DMPC (1,2dimyristoyl-sn-glycero-3-phosphocholine) with the cationic detergent DTAC (n-dodecyltrimethylammonium chloride) were investigated at a fixed DMPC concentration and variable detergent:lipid total molar ratios (D:L). Apparent (neutral-sphere-equivalent) hydrodynamic diameters (U e ) of liposomes and micelles were obtained by dynamic light scattering (DLS). Fluorescence lifetime imaging microscopy (FLIM), using chlorophyll-a as a probe, showed the morphology of giant vesicles and threadlike micelles. Micro-differential scanning calorimetry (micro-DSC) detected the presence of bilayers, in vesicles and discoidal micelles (disks). Pure DMPC liposomes are multilamellar and polydisperse (U e % 100-10,000 nm). As D:L increased, smaller vesicles were found, due to the bigger spontaneous curvature of the bilayer: at D:L = 1, ULVs (unilamellar vesicles; U e % 100 nm) appeared and, at D:L = 2-10, ULVs coexisted with disks (U e % 30 nm). Bilayers totally disappeared at D:L P 15, giving rise to spheroidal (U e % 2-16 nm) and threadlike (U e % 100-10,000 nm) micelles. A quasi-equilibrium structural diagram for the DMPC-DTAC-water system shows equivalent diameters of the scattering nanoparticles as a function of D:L. The results obtained herein for the system DMPC-DTAC show the role of electrostatic interactions in the formation of the mixed structures.

Research paper thumbnail of Time evolution of monomers and aggregates of a polymethine dye probe the dynamics of model vesicles and micelles

Journal of Photochemistry and Photobiology A: Chemistry, 2014

ABSTRACT An anionic polymethine dye (a fluoro-oxonol abbreviated FDID), which forms monomers and ... more ABSTRACT An anionic polymethine dye (a fluoro-oxonol abbreviated FDID), which forms monomers and oligomers according to the surrounding medium, is used in this work to probe the stability and dynamics of bicationic colloidal nanostructures, namely micelles and vesicles. Using pure water as the reference solvent (medium 1), five aqueous colloidal media of the lipid-detergent system DDAB-DTAC (didodecyldimethylammonium bromide-dodecyltrimethylammonium chloride) were analyzed: pre-micelle DTAC media (2); pure DTAC micelles (3); DDAB-DTAC micelles (4); DDAB-DTAC vesicles (5); and pure DDAB vesicles (6). In systems 4-6, containing the double-chained DDAB, FDID showed a slow-dynamics disaggregation, H-aggregates monomers. The kinetics of this transition was followed by running UV-vis absorption spectra along time. The transition lifetimes tau increased in the order tau(medium 3) << tau(media4,5) < tau(medium6) reflecting the much faster mobility of the single-chained DTA(+) long ion, as compared to that of the more hydrophobic, double-chained, DDA(+). This paper showed that FDID can probe the exchanging dynamics of the DDA(+)/DTA(+) long cations between the water phase and the colloidal nanostructures.

Research paper thumbnail of Unfolding Kinetics of β-Lactoglobulin Induced by Surfactant and Denaturant: A Stopped-Flow/Fluorescence Study

Biophysical Journal, 2007

The b/a transition of b-lactoglobulin, a globular protein abundant in the milk of several mammals... more The b/a transition of b-lactoglobulin, a globular protein abundant in the milk of several mammals, is investigated in this work. This transition, induced by the cationic surfactant dodecyltrimethylammonium chloride (DTAC), is accompanied by partial unfolding of the protein. In this work, unfolding of bovine b-lactoglobulin in DTAC is compared with its unfolding induced by the chemical denaturant guanidine hydrochloride (GnHCl). The final protein states attained in the two media have quite different secondary structure: in DTAC the a-helical content increases, leading to the so-called a-state; in GnHCl the amount of ordered secondary-structure decreases, resulting in a random coil-rich final state (denatured, or D, state). To obtain information on both mechanistic routes, in DTAC and GnHCl, and to characterize intermediates, the kinetics of unfolding were investigated in the two media. Equilibrium and kinetic data show the partial accumulation of an on-pathway intermediate in each unfolding route: in DTAC, an intermediate (I 1 ) with mostly native secondary structure but loose tertiary structure appears between the native (b) and a-states; in GnHCl, another intermediate (I 2 ) appears between states b and D. Kinetic rate constants follow a linear Chevron-plot representation in GnHCl, but show a more complex mechanism in DTAC, which acts like a stronger binding species.