Photophysics and reductive quenching reactivity of gadusol in solution

The photostability and photophysics of gadusol in aqueous solution has been studied. The photodecomposition quantum yields (ca. 4 × 10-2 and 1 × 10-4 at acidic and neutral pH, respectively) confirm the high photostability of the metabolite, independently of the presence of oxygen, under physiological conditions. The nature of the electronic transition of gadusol has been assigned as π → π* on the basis of the solvatochromic shifts of the UV absorption spectrum and the time-dependent density functional theory calculation of the vertical transition energies. The results from the photoacoustic calorimetry point to the rapid non-radiative decay as the dominant relaxation pathway of the excited species at pH 7, which is consistent with the proposed UV-sunscreening role of the molecule in the early atmosphere. Laser flash photolysis experiments probed that the ground state of the enolate form (gadusolate) undergoes electron transfer reactions with some triplet sensitizers in water or methanol solution. A rate constant of 2 × 108 M-1 s-1 has been determined for the quenching of rose bengal triplet state in water at pH 7. This reductive quenching reactivity may be considered as one of the underlying mechanisms that support the antioxidant capacity of gadusol in biological environments. © The Royal Society of Chemistry and Owner Societies 2011.Fil: Arbeloa, Ernesto Maximiliano. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Química; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Bertolotti, Sonia Graciela. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Churio, Maria Sandra. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Físicas de Mar del Plata. Grupo de Investigación del Departamento de Química de la Unmdp | Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Físicas de Mar del Plata. Grupo de Investigación del Departamento de Química de la Unmdp; Argentin

A photophysical and spectroelectrochemical study on N-phenyl-carbazoles and their oxidized species

A series of N-phenyl-carbazole derivatives namely TCz (N-tolyl-carbazol), TCz-TCz (a 3,3´-linked dimer), and CzPh-CH2-PhCz (a methylene-bridged N-phenyl-carbazole), have been synthesized and studied by means of absorption and fluorescence spectra, DFT calculations, cyclic voltammetry and spectroelectrochemistry. It is concluded that the methylene bridge in CzPh-CH2-PhCz isolates the two TCz units, whereas TCz-TCz allows extending the electronic coupling along both carbazoles. Moreover, the phosphorescence spectrum of TCz-TCz showed a high energy triplet state (2.76 eV). It was observed that oxidation of CzPh-CH2-PhCz generates an electrochromic polymer containing TCz-TCz dimer units separated by methylene bridges. Oxidized TCz-TCz subunit was analyzed by EPR spectroscopy, and found to be a Class III mixed valence ion in Robin and Day classification. All results suggest that these molecules might be suitable as selective probes in fluorescence sensing or as host materials in electroluminescent devices.Fil: Ramirez, Cristina Lujan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Biodiversidad y Biotecnología; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Química; ArgentinaFil: Mangione, Maria Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; ArgentinaFil: Bertolotti, Sonia Graciela. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Arbeloa, Ernesto Maximiliano. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Parise, Alejandro Ruben. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Biodiversidad y Biotecnología; Argentin

Sensitized photo-oxidation of gadusol species mediated by singlet oxygen

Gadusols are efficient nature UV sunscreens with antioxidant capacity. The kinetics of the quenching reactionsof singlet oxygen O2(1Δg) by gadusol species was evaluated in aqueous solution as well as in the presenceof direct charged micelles. Time-resolved phosphorescence detection of O2(1Δg) indicated that gadusolate, themain species under biological pH, is a more efficient quencher than the enol form with a rate constant of ca.1.3 × 108 L mol−1 s−1. The deactivation proceeds via a collisional mechanism with clear dominance of chemicalpathways, according to the rates of gadusol and oxygen consumptions, and typical photooxidation quantumyields of ca. 7%. The relative contributions of the chemical and physical quenching steps were not affected bythe presence of anionic or cationic micelles emulating simple pseudo-biological environments. The products ofthe photo-oxidative quenching support a type II mechanism initiated by the addition of O2(1Δg) to the C-C doublebond of gadusolate. These results point to the relevance of considering the role of sacrifice antioxidant along withthe UV-screening function for gadusol, particularly in the context of potential biotechnological applications ofthis natural molecule.Fil: Orallo, Dalila Elisabet. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Físicas de Mar del Plata. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Físicas de Mar del Plata; Argentina. Departamento de Química y Bioquímica; ArgentinaFil: Lores, Nayla Jimena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Arbeloa, Ernesto Maximiliano. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; ArgentinaFil: Bertolotti, Sonia Graciela. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; ArgentinaFil: Churio, María Sandra. Departamento de Química y Bioquímica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Físicas de Mar del Plata. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Físicas de Mar del Plata; Argentin

Quenching of the triplet state of safranine-O by aliphatic amines in AOT reverse micelles studied by transient absorption spectroscopy

The photophysics of Safranine-O (3,6-diamino-2,7-dimethyl-5 phenyl phenazinium chloride) (SfH+Cl-) was investigated in reverse micelles (RMs) of AOT  (sodium bis(2-ethylhexyl) sulfosuccinate) with special emphasis on the triplet state processes. The excited singlet state properties were measured by absorption and fluorescence spectroscopy. Steady state anisotropy was also measured as a function of the water content. All the measurements indicate that the dye is localized in the interface, sensing a medium of polarity similar to EtOH:water (3:1) mixtures. The triplet is formed in its monoprotonated form, independently of the pH of the water used to prepare the RMs. The  maximum of the T-T absorption spectrum in RMs confirms this conclusion. The triplet lifetime is much longer in AOT RMs than in homogeneous organic solvents. The intersystem crossing quantum yields are similar to those in organic solvents. A remarkable difference is observed in the quenching by aliphatic amines, while the quenching by the hydrophobic tributylamine is similar to that in methanol, the hydro-soluble triethanolamine is one order of magnitude more effective in RMs than in homogeneous solution. In the latter case  the quenching process is interpreted by a very fast intramicellar quenching, the overall kinetics being controlled by the exchange of amine molecules between RMs. Semireduced dye is formed in the quenching process in RMs in the di-protonated state with a comparable quantum yield to the monoprotonated state formed in homogeneous solvents. The results point to the advantage of the reverse micellar system for the generation of active radicals for the initiation of vinyl polymerization, since a much lower concentration of amine can be employed with similar quantum yields.Fil: Porcal, Gabriela Valeria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; ArgentinaFil: Chesta, Carlos Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; ArgentinaFil: Biasutti, Maria Alicia. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Bertolotti, Sonia Graciela. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Previtali, Carlos Mario. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Química; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentin

Diketopyrrolopyrrole-fullerene C60 architectures as highly efficient heavy atom-free photosensitizers: Synthesis, photophysical properties and photodynamic activity

Chromophore-fullerene C60 hybrids possess interesting properties that enable them to act as heavy atom-free photosensitizers and reactive oxygen species (ROS) producers. Here, two new diketopyrrolopyrrole-C60 conjugates were efficiently synthesized and characterized. The conjugates show broadband absorption in the visible spectral region, in which diketopyrrolopyrrole dyes act as light-harvesting antenna with very high capacity to populate excited triplet states. Furthermore, the ability of diketopyrrolopyrrole-C60 systems to generate singlet molecular oxygen was explored for the first time in solvents of different polarities. The experimental results show that these architectures exhibit very high production rates of this ROS. In addition, a preliminary study on Staphylococcus aureus cell suspensions indicates that both conjugates exhibit phototoxicity after irradiation with green LED light. Thus, the data obtained provide evidence that these diketopyrrolopyrrole-C60 architectures act as potential heavy atom-free photosensitizers in photodynamic inactivation of microorganisms and other singlet oxygen-mediated applications.Fil: Agazzi, Maximiliano Luis. Universidad Nacional de Río Cuarto. Instituto para el Desarrollo Agroindustrial y de la Salud. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto para el Desarrollo Agroindustrial y de la Salud; ArgentinaFil: Almodovar, Vitor A. S.. Universidade de Aveiro; PortugalFil: Gsponer, Natalia Soledad. Universidad Nacional de Río Cuarto. Instituto para el Desarrollo Agroindustrial y de la Salud. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto para el Desarrollo Agroindustrial y de la Salud; ArgentinaFil: Bertolotti, Sonia Graciela. Universidad Nacional de Río Cuarto. Instituto para el Desarrollo Agroindustrial y de la Salud. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto para el Desarrollo Agroindustrial y de la Salud; ArgentinaFil: Tomé, Augusto C.. Universidade de Aveiro; PortugalFil: Durantini, Edgardo Néstor. Universidad Nacional de Río Cuarto. Instituto para el Desarrollo Agroindustrial y de la Salud. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto para el Desarrollo Agroindustrial y de la Salud; Argentin

Photophysics and photochemistry of porphyrin core PAMAM dendrimers. Excited states interaction with quinones

Quenching of excited states of the meso-substituted tetraphenyl porphyrins with PAMAM branches, and one with PAMAM generation 1 peripherally-modified with thiazole groups by p-benzoquinones, were studied in DMF solution. Fluorescence lifetime measurements evidence a static component in the quenching process. The dynamic quenching rate constants were close to the diffusional limit except for the case of duroquinone. Apparent association constants of the porphyrin compounds with the quinones were determined by comparison of static and dynamic measurements of fluorescence quenching. The ground state interaction is very weak with the exception of tetrachlorobenzoquinone. The triplet state decay kinetics and the transient absorption spectra in the presence of the quinones were determined by laser flash photolysis. Triplet quenching rate constants were lower than those of singlet quenching. An electron transfer mechanism was proposed to explain the results. The long-time transient absorption spectra were assigned to the radical cation of the dyes. Relative radical yields were determined and a dependence on the side chains and the quencher was observed.Fil: Militello, María Paula. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Arbeloa, Ernesto Maximiliano. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Hernández Ramírez, Raquel E.. Tecnológico de Estudios Superiores de Coacalco; MéxicoFil: Lijanova, Irina Victorovna. Instituto Politécnico Nacional; MéxicoFil: Montejano, Hernan Alfredo. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Previtali, Carlos Mario. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; ArgentinaFil: Bertolotti, Sonia Graciela. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; Argentin

Correction to “Effect of Silver Nanoparticles on the Photophysics of Riboflavin: Consequences on the ROS Generation”

The corrected Figure 2: Comparison of transient spectra obtained in pump–probe experiments (λexc = 400 nm): (a) EADS of Pec.AgNP suspensions; (b) EADS of the Rf solution without Pec.AgNP; (c) EADS of the Rf solution in the presence of 1.8 μM Ag; (d) DADS corresponding to the EADS shown in (c).Este documento es una errata de "Effect of Silver Nanoparticles on the Photophysics of Riboflavin: Consequences on the ROS Generation" (ver documento relacionado).Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

A kinetic study on the photodynamic properties of the xanthene dye merbromin (mercurochrome) and its aggregates with amino acids in aqueous solution

The photophysical properties and the photobleaching of the xanthene dye merbromin(MR), as well as the production and quenching of singlet molecular oxygen, O₂(¹∆g), were investigated in aqueous solutions, in comparison with the xanthene dyes eosine (Eos) and rose bengal (RB). MR photobleaches in the absence of O₂ in a process involving the solvent (H₂O or alcohols). No participation of O₂ or O₂(¹∆g) could be established in the presence of O₂, although O₂ Is consumed. In aqueous and alcoholic solutions, MR forms ground state charge transfer (CT) complexes with biologically relevant electron donor amino acids, such as histidine, thyptophan, and other indolic derivatives. These complexes are formed with relatively high association constants (3 x 10³ - 5 x 10³) and are mainly responsible for the photobleaching of MR and the amino acids in these solutions by a mechanism involving O₂(¹∆g) generated probably by an excited state of the CT complex. MR generates O₂(¹∆g) with a relatively high yield (Φ ∆= 0.23 ± 0.04) and quenches O₂(¹∆g) only physically with = (2.3 ± 0.05) 108 M⁻¹ s⁻¹. This process does not affect the photosensitizing ability of MR under the low concentrations needed for its action. Non-donor compounds like the amino acid methionine and linoleic acid methyl ester are photodegraded by a Type II mechanism without implication of a dye CT complex.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Mass spectrometric study of the photooxidation of the ophthalmic drugs timolol and pindolol

A mass spectrometric study of the photooxidation products of the ophthalmic drugs pindolol (1-[1H-indol-4-yloxyl]-3-[isopropylamino]-2-propanol) and timolol (S-[-]-1-[t-butylamino]-3-[(4-morpholino-1,2,5-thiadiazol-3-yl)oxyl]-2-propanol) in water has been performed by LC-MS. Based on these data and the assumption that photooxidation mainly occurs through singlet molecular oxygen attack, a possible reaction mechanism is proposed. The mechanistic pathways involve singlet oxygen attack to the pindolol indole ring and oxidation of the pindolol isopropyl or timolol terbutyl methyl groups.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasLaboratorio de Estudio de Compuestos Orgánico

Kinetic study of the oxidation of phenolic derivatives of α,α,α-trifluorotoluene by singlet molecular oxygen [O₂(¹Δg)] and hydrogen phosphate radicals

The oxidation kinetics and mechanism of the phenolic derivatives of α,α,α-trifluorotoluene, 2-trifluoromethylphenol, 3-trifluoromethylphenol (3-TFMP), 4-trifluoromethylphenol and 3,5-bis(trifluoromethyl)phenol, mediated by singlet molecular oxygen, O2(¹Δg), and hydrogen phosphate radicals were studied, employing time-resolved O2(¹Δg) phosphorescence detection, polarographic determination of dissolved oxygen and flash photolysis. All the substrates are highly photo-oxidizable through a O2(¹Δg)-mediated mechanism. The phenols show overall quenching constants for O2(¹Δg) of the order of 106 M⁻¹ s⁻¹ in D2O, while the values for the phenoxide ions in water range from 1.2 × 10⁸ to 3.6 × 10⁸ M⁻¹ s⁻¹. The effects of the pH and polarity of the medium on the kinetics of the photo-oxidative process suggest a charge-transfer mechanism. 2-Trifluoromethyl-1,4-benzoquinone is suspected to be the main photo-oxidation product for the substrate 3-TFMP. The absolute rate constants for the reactions of HPO4•− with the substrates range from 4 × 10⁸ to 1 × 10⁹ M⁻¹ s⁻¹. The 3-trifluoromethylphenoxyl radical was observed as the organic intermediate formed after reaction of 3-TFMP with HPO₄•⁻, yielding 2,2’-bis(fluorohydroxymethyl)biphenyl-4,4’-diol as the end product. The observed results indicate that singlet molecular oxygen and hydrogen phosphate radicals not only react at different rates with the phenols of α,α,α-trifluorotoluene, but the reactions also proceed through different reaction channels.Instituto de Investigaciones Fisicoquímicas Teóricas y AplicadasLaboratorio de Estudio de Compuestos Orgánico