Solar photodegradation of dichloroacetic acid and 2,4-dichlorophenol using an enhanced photo-Fenton process

The photo-Fenton process using potassium ferrioxalate as a mediator was investigated for the photodegradation of dichloracetic acid (DCA) and 2,4-dichlorophenol (DCP) in aqueous medium using solar light as source of irradiation. The influence of the solution depth, the light intensity and the effect of stirring the solution during irradiation process were evaluated using DCA as a model compound. A negligible influence of stirring the solution was observed when the concentration of ferrioxalate (FeOx) was 0.8 mM and solution depth was 4.5 or 14 cm. The optimum FeOx concentration determined for solution depths between 4.5 and 14 cm was 0.8 mM considering total organic carbon (TOC) removal during DCA irradiation. The high efficiency of the photo-Fenton process was demonstrated on summer days, when only 10 min of exposition (around noon) were sufficient to completely destroy the organic carbon of a 1.0 mM DCA solution in the presence of 0.8 mM FeOx and 6.0 mM H2O2 using a solution depth of 4.5 cm. It was observed that the photodegradation efficiency increases linearly with the solar light intensity up to values around 15 Wm-2 but this linear relationship does not hold above this value showing a square root dependence. The photodegradation of a solution of DCP/FeOx showed a lower TOC removal rate than that observed for DCA/FeOx, achieving ∼90% after 35 min irradiation under 19 Wm-2, while under this light intensity, the same TOC removal of DCA/FeOx was achieved in only 10 min irradiation. © 2002 Elsevier Science Ltd. All rights reserved.

Photoelectrocatalytic degradation of Remazol Brilliant Orange 3R on titanium dioxide thin-film electrodes

Degradation of reactive dye Remazol Brilliant Orange 3R (RBO) has been performed using photoeletrocatalysis. A biased potential is applied across a titanium dioxide thin-film photoelectrode illuminated by UV light. It is suggested that charges photogenerated at the electrode surface give rise to chlorine generation and powerful oxidants (OH) that causes the dye solution to decolorize. Rate constants calculated from color decay versus time reveal a first-order reaction up to 5.0×10-5 mol l-1 in dye concentration. The best experimental conditions were found to be pH 6.0 and 1.0 mol l-1 NaCl when the photoelectrode was biased at +1V (versus SCE). Almost complete mineralization of the dye content (70% TOC reduction) was achieved in a 3-h period using these conditions. Effects of other electrolytes, dye concentration and applied potentials also have been investigated and are discussed. © 2003 Elsevier Science B.V. All rights reserved.

Behavior of bromide in the photoelectrocatalytic process and bromine generation using nanoporous titanium dioxide thin-film electrodes

In this study, the photoelectrocatalytic behavior of bromide and generation of bromine using TiO2 was investigated in the separate anode and cathode reaction chambers. Our results show that the generation of bromine begins around a flatband potential of -0.34 V vs. standard calomel electrode (SCE) at pH 3.0 under UV illumination and increases with an increase in positive potential, finally reaching a steady-state concentration at 1.0 V vs. SCE. Maximum bromine formation occurs over the range of pH 4-6, decreasing sharply at conditions where the pH > 7. © 2003 Elsevier Ltd. All rights reserved.

Evaluation of the combined solar TiO2/photo-Fenton process using multivariate analysis

The effect of combining the photocatalytic processes using TiO 2 and the photo-Fenton reaction with Fe3+ or ferrioxalate as a source of Fe2+ was investigated in the degradation of 4-chlorophenol (4CP) and dichloroacetic acid (DCA) using solar irradiation. Multivariate analysis was used to evaluate the role of three variables: iron, H2O2 and TiO2 concentrations. The results show that TiO2 plays a minor role when compared to iron and H2O2 in the solar degradation of 4CP and DCA in the studied conditions. However, its presence can improve TOC removal when H2O2 is totally consumed. Iron and peroxide play major roles, especially when Fe(NO3)3 used in the degradation of 4CP. No significant synergistic effect was observed by the addition of TiO 2 in this process. On the other hand, synergistic effects were observed between FeOx and TiO2 and between H 2O2 and TiO2 in the degradation of DCA. © IWA Publishing 2004.

Photoelectrocatalytic production of active chlorine on nanocrystalline titanium dioxide thin-film electrodes

The production of chlorine and hypochlorite is of great economical and technological interest due to their large-scale use in many kinds of commercial applications. Yet, the current processes are not without problems such as inevitable side reactions and the high cost of production. This work reports the photoelectrocatalytic oxidation of chloride ions to free chlorine as it has been investigated by using titanium dioxide (TiO2) and several metal-doped titanium dioxide (M-TiO2) material electrodes. An average concentration of 800 mg L-1 of free chlorine was obtained in an open-air reactor using a TiO2 thin-film electrode biased at +1.0 V (SCE) and illuminated by UV light. The M-doped electrodes have performed poorly compared with the pure TiO2 counterpart. Test solutions containing 0.05 mol L-1 NaCl pH 2.0-4.0 were found to be the best conditions for fast production of free chlorine. A complete investigation of all parameters that influence the global process of chlorine production by the photoelectrocatalytic method such as applied potential, concentration of NaCl, pH solution, and time is presented in detail. In addition, photocurrent vs potential curves and the reaction order are also discussed.

A new firefly luciferase with bimodal spectrum: Identification of structural determinants of spectral pH-sensitivity in firefly luciferases

Fireflies emit flashes in the green-yellow region of the spectrum for the purpose of sexual attraction. The bioluminescence color is determined by the luciferases. It is well known that the in vitro bioluminescence color of firefly luciferases can be shifted toward the red by lower pH and higher temperature; for this reason they are classified as pH-sensitive luciferases. However, the mechanism and structural origin of pH sensitivity in fireflies remains unknown. Here we report the cloning of a new luciferase from the Brazilian twilight active firefly Macrolampis sp2, which displays an unusual bimodal spectrum. The recombinant luciferase displays a sensitive spectrum with the peak at 569 nm and a shoulder in the red region. Comparison of the bioluminescence spectra of Macrolampis, Photinus and Cratomorphus firefly luciferases shows that the distinct colors are determined by the ratio between green and red emitters under luciferase influence. Comparison of Macrolampis luciferase with the highly similar North American Photinus pyralis luciferase (91%) showed few substitutions potentially involved with the higher spectral sensitivity in Macrolampis luciferase. Site-directed mutagenesis showed that the natural substitution E354N determines the appearance of the shoulder in the red region of Macrolampis luciferase bioluminescence spectrum, helping to identify important interactions and residues involved in the pH-sensing mechanism in firefly luciferases. © 2005 American Society for Photobiology.

The influence of the loop between residues 223-235 in beetle luciferase bioluminescence spectra: A solvent gate for the active site of pH-sensitive luciferases

Beetle luciferases emit a wide range of bioluminescence colors, ranging from green to red. Firefly luciferases can shift the spectrum to red in response to pH and temperature changes, whereas click beetle and railroadworm luciferases do not. Despite many studies on firefly luciferases, the origin of pH-sensitivity is far from being understood. Through comparative site-directed mutagenesis and modeling studies, using the pH-sensitive luciferases (Macrolampis and Cratomorphus distinctus fireflies) and the pH-insensitive luciferases (Pyrearinus termitilluminans, Phrixotrix viviani and Phrixotrix hirtus) cloned by our group, here we show that substitutions dramatically affecting bioluminescence colors in both groups of luciferases are clustered in the loop between residues 223-235 (Photinus pyralis sequence). The substitutions at positions 227, 228 and 229 (P. pyralis sequence) cause dramatic redshift and temporal shift in both groups of luciferases, indicating their involvement in labile interactions. Modeling studies showed that the residues Y227 and N229 are buried in the protein core, fixing the loop to other structural elements participating at the bottom of the luciferin binding site. Changes in pH and temperature (in firefly luciferases), as well as point mutations in this loop, may disrupt the interactions of these structural elements exposing the active site and modulating bioluminescence colors. © 2007 The Authors.

Heterogeneous photocatalytic treatment of organic dyes in air and aqueous media

This review focuses on the heterogeneous photocatalytic treatment of organic dyes in air and water. Representative studies spanning approximately three decades are included in this review. These studies have mostly used titanium dioxide (TiO2) as the inorganic semiconductor photocatalyst of choice for decolorizing and decomposing the organic dye to mineralized products. Other semiconductors such as ZnO, CdS, WO3, and Fe2O3 have also been used, albeit to a much smaller extent. The topics covered include historical aspects, dark adsorption of the dye on the semiconductor surface and its role in the subsequent photoreaction, semiconductor preparation details, photoreactor configurations, photooxidation kinetics/mechanisms and comparison with other Advanced Oxidation Processes (e.g., UV/H2O2, ozonation, UV/O3, Fenton and photo-Fenton reactions), visible light-induced dye decomposition by sensitization mechanism, reaction intermediates and toxicity issues, and real-world process scenarios. © 2008 Elsevier B.V. All rights reserved.

Effect of light energy density on conversion degree and hardness of dual-cured resin cement

This study evaluated the effect of different light energy densities on conversion degree (CD) and Knoop hardness number (KHN) of RelyX ARC (RLX) resin cement. After manipulation according to the manufacturer's instructions, RLX was inserted into a rubber mold (0.8 mm X 5 mm) and covered with a Mylar strip. The tip of the lightcuring unit (LCU) was positioned in contact with the Mylar surface. Quartz-tungsten-halogen (QTH) and light-emitting diode (LED) LCUs with light densities of 10, 20 and 30 J/cm2 were used to light-cure the specimens. After light curing, the specimens were stored dry in lightproof containers at 37°C. After 24 hours, the CD was analyzed by FT-Raman and, after an additional 24-hours, samples were submitted to Knoop hardness testing. The data of the CD (%) and KHN were submitted to two-way ANOVA and the Tukey's test (α=0.05). QTH and LED were effective light curing units. For QTH, there were no differences among the light energy densities for CD or KHN. For LED, there was a significant reduction in CD with the light energy density set at 10 J/cm2. KHN was not influenced by the lightcuring unit and by its light energy density. © Operative Dentistry.

Validação de método de análise quantitativa para a triancinolona a partir de complexo ternário por espectrofotometria de UV-Vis

Triamcinolone (TRI), a drug widely used in the treatment of ocular inflammatory diseases, is practically insoluble in water, which limits its use in eye drops. Cyclodextrins (CDs) have been used to increase the solubility or dissolution rate of drugs. The purpose of the present study was to validate a UV-Vis spectrophotometric method for quantitative analysis of TRI in inclusion complexes with beta-cyclodextrin (B-CD) associated with triethanolamine (TEA) (ternary complex). The proposed analytical method was validated with respect to the parameters established by the Brazilian regulatory National Agency of Sanitary Monitoring (ANVISA). The analytical measurements of absorbance were made at 242nm, at room temperature, in a 1-cm path-length cuvette. The precision and accuracy studies were performed at five concentration levels (4, 8, 12, 18 and 20μg.mL -1). The B-CD associated with TEA did not provoke any alteration in the photochemical behavior of TRI. The results for the measured analytical parameters showed the success of the method. The standard curve was linear (r2 > 0.999) in the concentration range from 2 to 24 μg.mL -1. The method achieved good precision levels in the inter-day (relative standard deviation-RSD <3.4%) and reproducibility (RSD <3.8%) tests. The accuracy was about 80% and the pH changes introduced in the robustness study did not reveal any relevant interference at any of the studied concentrations. The experimental results demonstrate a simple, rapid and affordable UV-Vis spectrophotometric method that could be applied to the quantitation of TRI in this ternary complex.

Effect of experimental photopolymerized coatings on the hydrophobicity of a denture base acrylic resin and on Candida albicans adhesion

Objective: This study investigated the effect of experimental photopolymerized coatings, containing zwitterionic or hydrophilic monomers, on the hydrophobicity of a denture base acrylic resin and on Candida albicans adhesion. Methods: Acrylic specimens were prepared with rough and smooth surfaces and were either left untreated (control) or coated with one of the following experimental coatings: 2-hydroxyethyl methacrylate (HE); 3-hydroxypropyl methacrylate (HP); and 2-trimethylammonium ethyl methacrylate chloride (T); and sulfobetaine methacrylate (S). The concentrations of these constituent monomers were 25%, 30% or 35%. Half of the specimens in each group (control and experimentals) were coated with saliva and the other half remained uncoated. The surface free energy of all specimens was measured, regardless of the experimental condition. C. albicans adhesion was evaluated for all specimens, both saliva conditioned and unconditioned. The adhesion test was performed by incubating specimens in C. albicans suspensions (1 × 10 7 cell/mL) at 37 °C for 90 min. The number of adhered yeasts were evaluated by XTT (2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-5-[{phenylamino} carbonyl]-2H-tetrazolium-hydroxide) method. Results: For rough surfaces, coatings S (30 or 35%) and HP (30%) resulted in lower absorbance values compared to control. These coatings exhibited more hydrophilic surfaces than the control group. Roughness increased the adhesion only in the control group, and saliva did not influence the adhesion. The photoelectron spectroscopy analysis (XPS) confirmed the chemical changes of the experimental specimens, particularly for HP and S coatings. Conclusions: S and HP coatings reduced significantly the adhesion of C. albicans to the acrylic resin and could be considered as a potential preventive treatment for denture stomatitis. © 2012 Elsevier Ltd.

Photodynamic inactivation of planktonic cultures and biofilms of Candida albicans mediated by aluminum-chloride-phthalocyanine entrapped in nanoemulsions

New drug delivery systems, such as nanoemulsions (NE), have been developed to allow the use of hydrophobic drugs on the antimicrobial photodynamic therapy. This study evaluated the photodynamic potential of aluminum-chloride- phthalocyanine (ClAlPc) entrapped in cationic and anionic NE to inactivate Candida albicans planktonic cultures and biofilm compared with free ClAlPc. Fungal suspensions were treated with different delivery systems containing ClAlPc and light emitting diode. For planktonic suspensions, colonies were counted and cell metabolism was evaluated by XTT assay. Flow cytometry evaluated cell membrane damage. For biofilms, the metabolic activity was evaluated by XTT and ClAlPc distribution through biofilms was analyzed by confocal laser scanning microscopy (CLSM). Fungal viability was dependent on the delivery system, superficial charge and light dose. Free ClAlPc caused photokilling of the yeast when combined with 100 J cm-2. Cationic NE-ClAlPc reduced significantly both colony counts and cell metabolism (P < 0.05). In addition, cationic NE-ClAlPc and free ClAlPc caused significant damage to the cell membrane (P < 0.05). For the biofilms, cationic NE-ClAlPc reduced cell metabolism by 70%. Anionic NE-ClAlPc did not present antifungal activity. CLSM showed different accumulation on biofilms between the delivery systems. Although NE system showed a lower activity for planktonic culture, cationic NE-ClAlPc showed better results for Candida biofilms. Candida albicans biofilm overview after 30 min of contact with free ClAlPc. This study presents the photodynamic potential of aluminum-chloride-phthalocyanine (ClAlPc) entrapped in cationic and anionic nanoemulsions (NE) to inactivate C. albicans planktonic cultures and biofilm comparing with free ClAlPc. The photodynamic effect was dependent on the delivery system, superficial charge and light dose. Cationic NE-ClAlPc and free ClAlPc caused significant reduction in colony counts, cell metabolism and damage to the cell membrane (P < 0.05). However, only the free ClAlPc was able to cause photokilling of the yeast. The anionic NE-ClAlPc did not present antifungal activity. Although NE system showed a lower activity for planktonic culture, cationic NE-ClAlPc showed better results for Candida biofilms. © 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiology.

First crystal structures of lanthanide-hydrocinnamate complexes: Hydrothermal synthesis and photophysical studies

Five new lanthanide(III) complexes of hydrocinnamic acid (Hcin), [Ln(cin)3(H2O)3]·3Hcin (Ln = Tb(III) (1), Dy(III) (2), Er(III) (3), Eu(III) (4) and Gd(III) (5)) have been synthesized and characterized. The X-ray structures of 1-5 reveal that all compounds are isostructural and that each lanthanide ion is nine-coordinated by oxygen atoms in an overall distorted tricapped trigonal-prismatic geometry. Six oxygen atoms are provided by carboxylate moieties, and the other three by water molecules. The supramolecular architectures of 1-5 show the presence of uncoordinated hydrocinnamic acid molecules which induce the formation of numerous hydrogen bonds. The photophysical properties of these complexes in the solid state at room temperature were studied using diffuse reflectance (DR), fluorescence excitation and emission spectra. An energy level diagram was used to establish the most relevant channels involved in the ligand-to-metal energy transfer, indicating that cin- ligands can act as intramolecular energy donors for Tb(III), Dy(III) and Eu(III) ions. © 2012 Elsevier B.V.

Gas phase photocatalytic bacteria inactivation using metal modified TiO2 catalysts

The present study describes the efficiency of heterogeneous photocatalytic reactor for the inactivation of three air born bacteria, Escherichia coli, Bacillus subtilis and Staphylococcus aureus using metal modified TiO2 photocatalysts and blacklight irradiation. The catalysts were prepared by photodeposition of silver, palladium or iron on commercial TiO2, immobilized on glass plates. X-ray photoelectron spectroscopy analysis was applied to determine the atomic percentage and species of each metal on the TiO2 surface, showing that 85% of silver, 73% of palladium and 45% of iron were present in metallic form on TiO2 surface. The plates were positioned on the inner lateral walls of a chamber through which the contaminated air flow passed for disinfection. Irradiation of bare TiO 2 resulted in 50% inactivation of E. coli while 41% and 35% inactivation of B. subtilis and S. aureus were obtained, respectively. When metal modified TiO2 was applied, the inactivation of B. subtilis was improved to 91% using Pd-TiO2 while of S. aureus was improved to 94% with Fe-TiO2, showing in this case no significant difference when compared to Ag-TiO2 and Pd-TiO2. In contrast, inactivation of E. coli was not significantly increased when metal modified TiO2 was used, ranging from 47% to 57%. © 2012 Elsevier B.V.