Gustavo Miguel - Academia.edu (original) (raw)
Papers by Gustavo Miguel
The Journal of Physical Chemistry C, 2009
ABSTRACT The molecular organization and the domain morphology of an anionic matrix dimyristoyl−ph... more ABSTRACT The molecular organization and the domain morphology of an anionic matrix dimyristoyl−phosphatidic acid (DMPA) as influenced by the presence of a cationic water-soluble methylene blue (MB) have been studied by using Brewster angle microscopy and reflection spectroscopy at the air−water interface. Mixed monolayers of DMPA:MB, molar ratios 5:1 and 1:1, were formed by the cospreading method. BAM images show particular domain morphologies as a function of the MB density in the mixed film: circular domains for DMPA:MB = 5:1, and domains with hexagonal shape for DMPA:MB = 1:1. The reflection measurements during the compression process of the mixed films reveal a blue shift of the visible band with respect to that of the MB monomer. This blue shift is larger for the DMPA:MB = 5:1 in comparison with that for the 1:1 monolayer, despite lower MB density. By using the extended dipole model, we demonstrate that such blue shift is due to the formation of a 2D hexagonal network of MB molecules underneath the DMPA monolayer in the mixed 1:1 film, while it is due to infinite linear aggregates in the 5:1 monolayer. BAM domain textures have been simulated by using the Fresnel equations for biaxial anisotropic materials. The results fit correctly the predictions of the extended dipole model.
The Journal of Physical Chemistry B, 2010
A series of [2]rotaxane materials, in which [60]fullerene is linked to a macrocycle and ferrocene... more A series of [2]rotaxane materials, in which [60]fullerene is linked to a macrocycle and ferrocene (Fc) moieties are placed at the termini of a thread, both of which possess a central Cu(I)-1,10-phenanthroline [Cu(phen)(2)](+) complex, were synthesized by self-assembly using Sauvage metal template methodology. Two types of threads were constructed, one with terminal ester linkages, and a second with terminal 1,2,3-triazole linkages derived from Cu(I)-catalyzed "click" 1,3-cycloaddition reactions. Model compounds lacking the fullerene moiety were prepared in an analogous manner. The ability of the interlocked Fc-[Cu(phen)(2)](+)-C(60) hybrids to undergo electron transfer upon photoexcitation in benzonitrile, dichloromethane, and ortho-dichlorobenzene was investigated by means of time-resolved fluorescence and transient absorption spectroscopy, using excitation wavelengths directed at the fullerene and [Cu(phen)(2)](+) subunits. The energies of the electronic excited states and charge separated (CS) states that might be formed upon photoexcitation were determined from spectroscopic and electrochemical data. These studies showed that MLCT excited states of the copper complex in the fullerenerotaxanes were quenched by electron transfer to the fullerene in benzonitrile, resulting in charge separated states with oxidized copper and reduced fullerene moieties, (Fc)(2)-[Cu(phen)(2)](2+)-C(60)(•-). Even though electron transfer from Fc to the oxidized copper complex is predicted to be exergonic by 0.16 to 0.20 eV, no unequivocal evidence in support of such a process was obtained. The conclusion that Fc plays no role in the photoinduced processes in our systems rests on the lack of enhancement of the lifetime of the charge separated state, as measured by decay of C(60)(•-) at ∼1000 nm, since one-electron oxidized Fc is very difficult to detect spectroscopically in the 500-800 nm spectral region.
![Research paper thumbnail of J-Aggregation of a Water-Soluble Tetracationic Porphyrin in Mixed LB Films with a Calix[8]arene Carboxylic Acid Derivative](https://attachments.academia-assets.com/39383865/thumbnails/1.jpg)
](Langmuir, 2007
The molecular organization of a mixed film, containing a water-soluble tetracationic porphyrin (T... more The molecular organization of a mixed film, containing a water-soluble tetracationic porphyrin (TMPyP) and a p-tert-butyl calix[8]arene octacarboxylic acid derivative (C8A), at the air-water interface and on a solid support (LB film), has been investigated. Although the TMPyP aggregation was not detected at the air-water interface, TMPyP J-aggregates have been found in the LB films (Y-type). Unlike tetraanionic porphyrins, for example TSPP, the TMPyP J-aggregates are not induced by a zwitterion formation. The TMPyP J-aggregation is a result of a "double comb" configuration, where porphyrins from opposite layers are interwoven in a linear infinite J-aggregate. Our results confirm that TMPyP molecules tend to self-aggregate strongly, provided the electrostatic repulsions of their peripheral groups are cancelled by the anionic groups of the C8A matrix.
![Research paper thumbnail of [2]Catenanes Decorated with Porphyrin and [60]Fullerene Groups: Design, Convergent Synthesis, and Photoinduced Processes](https://attachments.academia-assets.com/42294886/thumbnails/1.jpg)
](Journal of the American Chemical Society, 2010
A new class of [2]catenanes containing zinc(II)-porphyrin (ZnP) and/or [60]fullerene (C(60)) as a... more A new class of [2]catenanes containing zinc(II)-porphyrin (ZnP) and/or [60]fullerene (C(60)) as appended groups has been prepared. A complete description of the convergent synthetic approach based on Cu(I) template methodology and "click" 1,3-dipolar cycloaddition chemistry is described. This new electron donor-acceptor catenane family has been subjected to extensive spectroscopic, computational, electrochemical and photophysical studies. (1)H NMR spectroscopy and computational analysis have revealed that the ZnP-C(60)-[2]catenane adopts an extended conformation with the chromophores as far as possible from each other. A detailed photophysical investigation has revealed that upon irradiation the ZnP singlet excited state initially transfers energy to the (phenanthroline)(2)-Cu(I) complex core, producing a metal-to-ligand charge transfer (MLCT) excited state, which in turn transfers an electron to the C(60) group, generating the ZnP-[Cu(phen)(2)](2+)-C(60)(*-) charge-separated state. A further charge shift from the [Cu(phen)(2)](2+) complex to the ZnP subunit, competitive with decay to the ground state, leads to the isoenergetic long distance ZnP(*+)-[Cu(phen)(2)](+)-C(60)(*-) charge-separated radical pair state, which slowly decays back to the ground state on the microsecond time scale. The slow rate of back-electron transfer indicates that in this interlocked system, as in previously studied covalently linked ZnP-C(60) hybrid materials, this process occurs in the Marcus-inverted region.
Journal of Materials Chemistry, 2008
A novel pseudospherical fluorinated iridium(III) derivative, Ir-dye/PF 6 , [Ir(F 2 -ppy) 2 (bpy)]... more A novel pseudospherical fluorinated iridium(III) derivative, Ir-dye/PF 6 , [Ir(F 2 -ppy) 2 (bpy)]PF 6 (F 2 -ppy ¼ 2-(2,4-difluoro)phenylpyridine, bpy ¼ 2,2 0 -bipyridine), has been organized by using a lipid matrix, DMPA (dimyristoyl-phosphatidic acid), in several molar ratios at the air-water interface. The molecular organization of both components and the degree of miscibility in the different mixed films have been inferred by surface techniques such as p-A isotherms, ellipsometry, reflection spectroscopy, Brewster angle microscopy (BAM), and IR spectroscopy for the LB films, additionally the results have been discussed according to the additivity rule. The equimolecular Ir-dye/DMPA mixture leads to a totally miscible, stable and homogeneous monolayer. Any surplus of DMPA with respect to the 1 : 1 ratio segregates under compression while forming domains. By varying the surface concentration of DMPA in the mixture we demonstrate that the Ir-dye can be confined to certain regions of the 2D patterned structure formed at the air-water interface. The fraction of surface containing the photofunctional complex can be controlled by both the fraction of lipid in the initial co-spread mixture and the surface pressure applied to the film. Finally, the additivity rule has been applied, for the first time to our knowledge, to simulate the ellipsotherms of mixed monolayers.
Journal of Colloid and Interface Science, 2007
In this work, organized mixed monolayers containing a cationic water-insoluble iridium(III) compl... more In this work, organized mixed monolayers containing a cationic water-insoluble iridium(III) complex, Ir-dye, [Ir(ppy) 2 (tmphen)]PF 6 , (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline, and ppy = 2-phenylpyridine), and an anionic lipid matrix, DMPA, dimyristoyl-phosphatidic acid, with different molar proportions, were formed by the co-spreading method at the air-water interface. The presence of the dye at the interface, as well as the molecular organization of the mixed films, is deduced from surface techniques such as π -A isotherms, Brewster angle microscopy (BAM) and reflection spectroscopy. The results obtained remark the formation of an equimolar mixed film, Ir-dye/DMPA = 1:1. BAM images reveal a whole homogeneous monolayer, with gradually increasing reflectivity along the compression process up to reaching the collapse of this equimolecular monolayer at π ≈ 37 mN m −1 . Increasing the molar ratio of DMPA in the mixture, the excess of lipid molecules organizes themselves forming dark flower-like domains of pure DMPA at high surface pressures, coexisting with the mixed Ir-dye/DMPA = 1:1 monolayer. On the other hand, unstable mixed monolayers are obtained by using an initial dye surface concentration higher than the equimolecular one. These mixed Langmuir monolayers have been successfully transferred onto solid substrates by the LB (Langmuir-Blodgett) technique.
Biophysical Journal, 2014
proteins consistent with single-particle tracking data. For system (2), we perform drug-trial exp... more proteins consistent with single-particle tracking data. For system (2), we perform drug-trial experiments on living COS-7 cells to show that kICS can quantify the degree to which the drugs will affect kinetic binding/unbinding rates. By labeling the glycolipid membrane receptor GM1 with a fluorescent cholera toxin B-subunit, we show that cytoskeleton perturbations with the drug cytochalasin D result in significant changes (k u = 0.013 5 0.004 s À1 to 0.08 5 0.02 s À1 ) to the undocking rate of GM1 to the actin cytoskeleton. With these two proof-of-concept experiments, we pave the way to using kICS as an efficient and reliable method to elucidate kinetic binding rates and transport dynamics parameters for studies in biomembranes.
The Journal of Physical Chemistry C, 2009
ABSTRACT The molecular organization and the domain morphology of an anionic matrix dimyristoyl−ph... more ABSTRACT The molecular organization and the domain morphology of an anionic matrix dimyristoyl−phosphatidic acid (DMPA) as influenced by the presence of a cationic water-soluble methylene blue (MB) have been studied by using Brewster angle microscopy and reflection spectroscopy at the air−water interface. Mixed monolayers of DMPA:MB, molar ratios 5:1 and 1:1, were formed by the cospreading method. BAM images show particular domain morphologies as a function of the MB density in the mixed film: circular domains for DMPA:MB = 5:1, and domains with hexagonal shape for DMPA:MB = 1:1. The reflection measurements during the compression process of the mixed films reveal a blue shift of the visible band with respect to that of the MB monomer. This blue shift is larger for the DMPA:MB = 5:1 in comparison with that for the 1:1 monolayer, despite lower MB density. By using the extended dipole model, we demonstrate that such blue shift is due to the formation of a 2D hexagonal network of MB molecules underneath the DMPA monolayer in the mixed 1:1 film, while it is due to infinite linear aggregates in the 5:1 monolayer. BAM domain textures have been simulated by using the Fresnel equations for biaxial anisotropic materials. The results fit correctly the predictions of the extended dipole model.
The Journal of Physical Chemistry B, 2010
A series of [2]rotaxane materials, in which [60]fullerene is linked to a macrocycle and ferrocene... more A series of [2]rotaxane materials, in which [60]fullerene is linked to a macrocycle and ferrocene (Fc) moieties are placed at the termini of a thread, both of which possess a central Cu(I)-1,10-phenanthroline [Cu(phen)(2)](+) complex, were synthesized by self-assembly using Sauvage metal template methodology. Two types of threads were constructed, one with terminal ester linkages, and a second with terminal 1,2,3-triazole linkages derived from Cu(I)-catalyzed "click" 1,3-cycloaddition reactions. Model compounds lacking the fullerene moiety were prepared in an analogous manner. The ability of the interlocked Fc-[Cu(phen)(2)](+)-C(60) hybrids to undergo electron transfer upon photoexcitation in benzonitrile, dichloromethane, and ortho-dichlorobenzene was investigated by means of time-resolved fluorescence and transient absorption spectroscopy, using excitation wavelengths directed at the fullerene and [Cu(phen)(2)](+) subunits. The energies of the electronic excited states and charge separated (CS) states that might be formed upon photoexcitation were determined from spectroscopic and electrochemical data. These studies showed that MLCT excited states of the copper complex in the fullerenerotaxanes were quenched by electron transfer to the fullerene in benzonitrile, resulting in charge separated states with oxidized copper and reduced fullerene moieties, (Fc)(2)-[Cu(phen)(2)](2+)-C(60)(•-). Even though electron transfer from Fc to the oxidized copper complex is predicted to be exergonic by 0.16 to 0.20 eV, no unequivocal evidence in support of such a process was obtained. The conclusion that Fc plays no role in the photoinduced processes in our systems rests on the lack of enhancement of the lifetime of the charge separated state, as measured by decay of C(60)(•-) at ∼1000 nm, since one-electron oxidized Fc is very difficult to detect spectroscopically in the 500-800 nm spectral region.
Langmuir, 2007
The molecular organization of a mixed film, containing a water-soluble tetracationic porphyrin (T... more The molecular organization of a mixed film, containing a water-soluble tetracationic porphyrin (TMPyP) and a p-tert-butyl calix[8]arene octacarboxylic acid derivative (C8A), at the air-water interface and on a solid support (LB film), has been investigated. Although the TMPyP aggregation was not detected at the air-water interface, TMPyP J-aggregates have been found in the LB films (Y-type). Unlike tetraanionic porphyrins, for example TSPP, the TMPyP J-aggregates are not induced by a zwitterion formation. The TMPyP J-aggregation is a result of a "double comb" configuration, where porphyrins from opposite layers are interwoven in a linear infinite J-aggregate. Our results confirm that TMPyP molecules tend to self-aggregate strongly, provided the electrostatic repulsions of their peripheral groups are cancelled by the anionic groups of the C8A matrix.
Journal of the American Chemical Society, 2010
A new class of [2]catenanes containing zinc(II)-porphyrin (ZnP) and/or [60]fullerene (C(60)) as a... more A new class of [2]catenanes containing zinc(II)-porphyrin (ZnP) and/or [60]fullerene (C(60)) as appended groups has been prepared. A complete description of the convergent synthetic approach based on Cu(I) template methodology and "click" 1,3-dipolar cycloaddition chemistry is described. This new electron donor-acceptor catenane family has been subjected to extensive spectroscopic, computational, electrochemical and photophysical studies. (1)H NMR spectroscopy and computational analysis have revealed that the ZnP-C(60)-[2]catenane adopts an extended conformation with the chromophores as far as possible from each other. A detailed photophysical investigation has revealed that upon irradiation the ZnP singlet excited state initially transfers energy to the (phenanthroline)(2)-Cu(I) complex core, producing a metal-to-ligand charge transfer (MLCT) excited state, which in turn transfers an electron to the C(60) group, generating the ZnP-[Cu(phen)(2)](2+)-C(60)(*-) charge-separated state. A further charge shift from the [Cu(phen)(2)](2+) complex to the ZnP subunit, competitive with decay to the ground state, leads to the isoenergetic long distance ZnP(*+)-[Cu(phen)(2)](+)-C(60)(*-) charge-separated radical pair state, which slowly decays back to the ground state on the microsecond time scale. The slow rate of back-electron transfer indicates that in this interlocked system, as in previously studied covalently linked ZnP-C(60) hybrid materials, this process occurs in the Marcus-inverted region.
Journal of Materials Chemistry, 2008
A novel pseudospherical fluorinated iridium(III) derivative, Ir-dye/PF 6 , [Ir(F 2 -ppy) 2 (bpy)]... more A novel pseudospherical fluorinated iridium(III) derivative, Ir-dye/PF 6 , [Ir(F 2 -ppy) 2 (bpy)]PF 6 (F 2 -ppy ¼ 2-(2,4-difluoro)phenylpyridine, bpy ¼ 2,2 0 -bipyridine), has been organized by using a lipid matrix, DMPA (dimyristoyl-phosphatidic acid), in several molar ratios at the air-water interface. The molecular organization of both components and the degree of miscibility in the different mixed films have been inferred by surface techniques such as p-A isotherms, ellipsometry, reflection spectroscopy, Brewster angle microscopy (BAM), and IR spectroscopy for the LB films, additionally the results have been discussed according to the additivity rule. The equimolecular Ir-dye/DMPA mixture leads to a totally miscible, stable and homogeneous monolayer. Any surplus of DMPA with respect to the 1 : 1 ratio segregates under compression while forming domains. By varying the surface concentration of DMPA in the mixture we demonstrate that the Ir-dye can be confined to certain regions of the 2D patterned structure formed at the air-water interface. The fraction of surface containing the photofunctional complex can be controlled by both the fraction of lipid in the initial co-spread mixture and the surface pressure applied to the film. Finally, the additivity rule has been applied, for the first time to our knowledge, to simulate the ellipsotherms of mixed monolayers.
Journal of Colloid and Interface Science, 2007
In this work, organized mixed monolayers containing a cationic water-insoluble iridium(III) compl... more In this work, organized mixed monolayers containing a cationic water-insoluble iridium(III) complex, Ir-dye, [Ir(ppy) 2 (tmphen)]PF 6 , (tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline, and ppy = 2-phenylpyridine), and an anionic lipid matrix, DMPA, dimyristoyl-phosphatidic acid, with different molar proportions, were formed by the co-spreading method at the air-water interface. The presence of the dye at the interface, as well as the molecular organization of the mixed films, is deduced from surface techniques such as π -A isotherms, Brewster angle microscopy (BAM) and reflection spectroscopy. The results obtained remark the formation of an equimolar mixed film, Ir-dye/DMPA = 1:1. BAM images reveal a whole homogeneous monolayer, with gradually increasing reflectivity along the compression process up to reaching the collapse of this equimolecular monolayer at π ≈ 37 mN m −1 . Increasing the molar ratio of DMPA in the mixture, the excess of lipid molecules organizes themselves forming dark flower-like domains of pure DMPA at high surface pressures, coexisting with the mixed Ir-dye/DMPA = 1:1 monolayer. On the other hand, unstable mixed monolayers are obtained by using an initial dye surface concentration higher than the equimolecular one. These mixed Langmuir monolayers have been successfully transferred onto solid substrates by the LB (Langmuir-Blodgett) technique.
Biophysical Journal, 2014
proteins consistent with single-particle tracking data. For system (2), we perform drug-trial exp... more proteins consistent with single-particle tracking data. For system (2), we perform drug-trial experiments on living COS-7 cells to show that kICS can quantify the degree to which the drugs will affect kinetic binding/unbinding rates. By labeling the glycolipid membrane receptor GM1 with a fluorescent cholera toxin B-subunit, we show that cytoskeleton perturbations with the drug cytochalasin D result in significant changes (k u = 0.013 5 0.004 s À1 to 0.08 5 0.02 s À1 ) to the undocking rate of GM1 to the actin cytoskeleton. With these two proof-of-concept experiments, we pave the way to using kICS as an efficient and reliable method to elucidate kinetic binding rates and transport dynamics parameters for studies in biomembranes.