Glycosylated flavonoid kaempferitrin: Electroanalytical detection and the proposal of an oxidation mechanism supported by quantum chemical calculations.

In this work, the electrochemical behavior of the glycosylated flavonoid kaempferitrin was studied, and an electroanalytical methodology was developed for its determination in infusions of Bauhinia forficata using a boron-doped diamond electrode (BDD). The electrochemical behavior of the flavonoid was studied by cyclic voltammetry, and two irreversible oxidation peaks at 0.80 and 1.0 V vs Ag/AgCl were observed. The influence of the pH on the voltammograms was examined, and higher sensitivity was found at pH 7.0. The electrochemical process corresponding to peak 1 at 0.80 V is predominantly diffusion-controlled, as the study shows at varying scan rates. An analytical plot was obtained by square wave voltammetry at optimized experimental conditions (frequency = 100 s-1, amplitude = 90 mV, and step potential = 8 mV) in the concentration range from 3.4 µmol L-1 to 58 µmol L-1, with a linearity of 0.99. The limit of detection and limit of quantification values were 1.0 µmol L-1 and 3.4 µmol L-1, respectively. Three samples of Bauhinia forficata infusions (2 g of sample in 100 mL of water) were analyzed, and the KF values found were 5.0 × 10-4 mol L-1, 3.0 × 10-4 mol L-1, and 7.0 × 10-4 mol L-1, with recovery percentages of 98 %, 106 % and 94 %, respectively. Finally, experiments were performed with two other flavonoids (chrysin and apeginin) to compare and propose an electrochemical oxidation mechanism for kaempferitrin, which was supported by quantum chemical calculations.

Universal adhesive: the effect of different simulated pulpal pressure fluids and bonding modes to dentin.

The aim of this study was to evaluate the effect of SPP with either fetal bovine serum (FBS) or deionized water (DW) on the bond strength (µTBS) of a Universal adhesive to dentin, in both etch-and-rinse (ER) and self-etch (SE) modes. The kinematic viscosity (cSt) of FBS and DW was measured at 25 °C ± 0.1 ºC. Seventy-two sound human molars were sectioned and randomly divided into three groups according to the SPP conditions: (1) Control (0 cm H2O), (2) SPP (15 cm H2O) with FBS, (3) SPP (15 cm H2O) with DW. Each group was subdivided (n = 10) based on the bonding modes: ER (37% phosphoric acid + ScothBond Universal Adhesive) or SE (ScothBond Universal Adhesive). Samples were then submitted to µTBS. Data were analyzed by Student's t test, two-way ANOVA and Tukey tests (p < 0.05). The cSt results showed that DW (23.59 ± 0.39) had significantly higher values than FBS (22.33 ± 0.06). With regard to SPP, the control group (36.1 MPa) had significantly higher values of µTBS when compared to the SPP using FBS (31.06 MPa) and SPP with DW (26.55 MPa). According to ANOVA, the bonding modes and the interaction of simulated pulpal pressure (SPP) did not statistically influence the results (p < 0.05). The presence of SPP reduced the bond strength of Universal adhesive to dentin. DW during SPP had significantly reduced bonding values when compared to FBS. Bonding strategies were not affected by SPP when evaluated in a short period of time (24 h).

Pluronic-loaded Silver Nanoparticles/Photosensitizers Nanohybrids: Influence of the Polymer Chain Length on Metal-enhanced Photophysical Properties.

Silver nanoparticles (AgNPs) are incredibly versatile nanostructures that more recently have been exploited to create advanced optoelectronic materials due enhancement of local magnetic field after its irradiation. However, the use of AgNPs as nanoantennas to amplify photophysical properties of close photosensitizer (PS) molecules in photodynamic therapy is still underexplored. The reason for that is the difficulty to control crucial parameters such as silver-PS distance in aqueous solution. In this scenario, here we propose a nanohybrid system where AgNP/PS distance is controlled by a thin layer of different Pluronic copolymers. The controllable distance and aqueous stability of proposed nanohybrids allow a tunable enhancement of fluorescence emission and singlet oxygen generation of some selected PS molecules. A detailed mechanism investigation demonstrated that the observed metal-enhanced photophysics is due to magnetic field enhancement close to AgNP surface (AgNP/PS distance-controlled effect) and the resonant coupling of AgNP hot electrons and HOMO-LUMO energies of the PS (AgNP/PS spectral overlap-controlled effect). These results show that the rational design in engineering new nanohybrid structures allowed photophysical improvement of PS molecules in aqueous solution in a tunable way and point out Pluronic-based AgNP/PS nanohybrids as a smart material for further developments aiming at theranostic applications in photodynamic therapy.

Photochemical and photophysical properties of tetracarboxylic acid phthalocyanines from glycolic and lactic acids in homogeneous and micro heterogeneous media.

Glycolic acid and lactic acid substituted zinc phthalocyanines were studied concerning their photophysical and photochemical properties in eight organic solvents (homogeneous medium) and in aqueous media with the presence of CTAB and PVP 360 surfactants. Solvent effects were investigated according to several physical solvent parameters, including studies that used more than one parameter at a time, such as the ET(30) scale and the Lippet-Mataga equation. Computational studies were realized and was found in good agreement with experimental data indicating J-type dimers' formation through hydrogen bonds, which may not affect the spectroscopic properties. Fluorescence lifetimes were recorded using a time-correlated single-photon counting setup (TCSPC) technique. The direct method (analyzing the phosphorescence decay curves of singlet oxygen at 1270 nm) was employed to study singlet oxygen quantum yields. Phthalocyanine macrocycle with lactic acid substituent showed better solvation arrangement than the glycolic derivative, which can be explained based on the presence of the methyl group bonded to the chain. The water solvation of Pc's in the presence of cationic surfactant (CTAB) and biocompatible polymer PVP 360 increses the importance of this study for appliance in photodynamic therapy (PDT).

Theranostic verteporfin- loaded lipid-polymer liposome for photodynamic applications.

In this study we report a novel theranostic lipid-polymer liposome, obtained from DPPC and the triblock copolymer F127 covalently modified with 5(6)-carboxyfluorescein (CF) for photodynamic applications. Due to the presence of F127, small unilamellar vesicle (SUV) liposomes were synthesized by a simple and fast thin-film hydration method without the need for an extrusion process. The vesicles have around 100 nm, low polydispersity and superb solution stability. The clinically used photosensitizer verteporfin (VP) was entrapped into the vesicles, mostly in monomeric form, with 90% loading efficiency. Stern-Volmer and fluorescence lifetime assays showed heterogeneous distribution of the VP and CF into the vesicles, ensuring the integrity of their individual photophysical properties. The theranostic properties were entirely photoactivatable and can be trigged by a unique wavelength (470 nm). The feasibility of the system was tested against the Glioblastoma multiforme cell line T98G. Cellular uptake by time-resolved fluorescence microscopy showed monomerized VP (monoexponential decay, 6.0 ns) at nucleus level, while CF was detected at the membrane by fluorescence microscopy. The strategy's success was supported by the reduction of 98% in the viability of T98G cells by the photoactivated lipid-polymer liposome with [VP] = 1.0 µmol L-1. Therefore, the novel theranostic liposome is a potential system for use in cancer and ocular disease therapies.

Synthesis of Pluronic-based silver nanoparticles/methylene blue nanohybrids: Influence of the metal shape on photophysical properties.

Nanotechnology development provides new strategies to improve different treatment modalities by integration of multiple molecules in a single multifunctional nanoparticle. In this scenario, we highlight silver nanoparticles (AgNPs) favorable optical properties such as absorption and emission of light in the visible region of the spectrum. This allows its synergic combination with the photosensitizer molecule methylene blue (MB) in order to improve outcomes in photodynamic-based therapies. Therefore, we engineered here a new multifunctional nanostructured system based in the synthesis of pluronic-based AgNP/MB nanohybrids inspired by the concept of supramolecular chemistry. Silver reduction in water and Pluronic F127 aqueous solutions in the presence of hydrogen peroxide as etching agent at several concentrations induced the formation of anisotropic forms of AgNPs. Electronic absorption and TEM studies demonstrated a greater kinetic and morphological control for Pluronic synthetized NPs. The smart design of the proposed nanohybrids favored the enhancement of MB photophysical properties such as fluorescence emission and singlet oxygen production due a synergic action from resonant coupling between AgNP magnetic field and MB molecules. Results also demonstrated that AgNP-MB distance modulation in Pluronic matrix is a relevant parameter in MB photophysical improvement. Finally, since AgNP absorbance spectrum is dependent on AgNP shape, it plays a critical role in the improvement of MB photophysical properties. These results show that the rational design in engineering new multifunctional nanoparticles is essential and point out that Pluronic AgNP/MB nanohybrids as a smart material for further developments aiming photodynamic-based therapies.

Removal of Orange II (OII) dye by simulated solar photoelectro-Fenton and stability of WO2.72/Vulcan XC72 gas diffusion electrode.

The objectives of this study were to determine the viability of removing Orange II (OII) dye by simulated solar photoelectro-Fenton (SSPEF) and to evaluate the stability of a WO2.72/Vulcan XC72 gas diffusion electrode (GDE) and thus determine its best operating parameters. The GDE cathode was combined with a BDD anode for decolorization and mineralization of 350 mL of 0.26 mM OII by anodic oxidation with electrogenerated H2O2 (AO-H2O2), electro-Fenton (EF) and photoelectro-Fenton (PEF) at 100, 150 and 200 mA cm-2 and SSPEF at 150 mA cm-2. The GDE showed successful operation for electrogeneration, good reproducibility and low leaching of W. Decolorization and OII decay were directly proportional to the current density (j). AO-H2O2 had a reduced performance that was only half of the SSPEF, PEF and EF treatments. The mineralization efficiency was in the following order: AO-H2O2 < EF < PEF ≈ SSPEF. This showed that the GDE, BDD anode and light radiation combination was advantageous and indicated that the SSPEF process is promising with both a lower cost than using UV lamps and simulating solar photoelectro-Fenton process. The PEF process with the lowest j (100 mA cm-2) showed the best performance-mineralization current efficiency.

Use of chitosan in the treatment of obesity: evaluation of interaction with vitamin B12.

Is well known that obesity has increased significantly in recent times and therefore many dietary supplements, synthetic or natural, have been proposed in order to prevent and/or to treat obesity or overweight. Chitosan, a polysaccharide with ability to act as a carrier and to absorb fat, has been used for this purpose. However, interactions with other molecules present in the body may also occur and, therefore, the purpose of this study was to evaluate interactions of chitosan with vitamin B12. Spectroscopic properties of vitamin B12 (acid aqueous solution) were monitored in the absence and the presence of chitosan in order to evaluate possible interactions between the two. Results showed that the rigid micro-environment generated by chitosan solution modifies the photophysical properties of vitamin B12. Thus, chitosan is able to eliminate vitamin B12 and, based on this information, some care must be taken during prolonged treatment with chitosan.

pKa determinations of xanthene derivates in aqueous solutions by multivariate analysis applied to UV-Vis spectrophotometric data.

Xanthenes form to an important class of dyes which are widely used. Most of them present three acid-base groups: two phenolic sites and one carboxylic site. Therefore, the pKa determination and the attribution of each group to the corresponding pKa value is a very important feature. Attempts to obtain reliable pKa through the potentiometry titration and the electronic absorption spectrophotometry using the first and second orders derivative failed. Due to the close pKa values allied to strong UV-Vis spectral overlap, multivariate analysis, a powerful chemometric method, is applied in this work. The determination was performed for eosin Y, erythrosin B, and bengal rose B, and also for other synthesized derivatives such as 2-(3,6-dihydroxy-9-acridinyl) benzoic acid, 2,4,5,7-tetranitrofluorescein, eosin methyl ester, and erythrosin methyl ester in water. These last two compounds (esters) permitted to attribute the pKa of the phenolic group, which is not easily recognizable for some investigated dyes. Besides the pKa determination, the chemometry allowed for estimating the electronic spectrum of some prevalent protolytic species and the substituents effects evaluation.

Spectrofluorimetric determination of second critical micellar concentration of SDS and SDS/Brij 30 systems.

Potentially useful stead-state fluorimetric technique was used to determine the critical micellar concentrations (CMC(1) and CMC(2)) for two micellar media, one formed by SDS and the other by SDS/Brij 30. A comparative study based on conductimetric and surfacial tension measurements suggests that the CMC(1) estimated by the fluorimetric method is lower than the value estimated by these other techniques. Equivalent values were observed for SDS micelles without Brij 30 neutral co-surfactant. The use of acridine orange as fluorescent probe permitted to determine both CMC(1) and CMC(2). Based on it an explanation on aspects of micelle formation mechanism is presented, particularly based on a spherical and a rod like structures.

Solvent effects on the photophysics of 3-(benzoxazol-2-yl)-7-(N,N-diethylamino)chromen-2-one.

The photophysics of 3-(benzoxazol-2-yl)-7-(N,N-diethylamino)chromen-2-one was studied in different solvents and in SDS micelles. This compound presents characteristics which include an S(0)---> S(1) ( pi,pi*) transition with a (1)(n,pi*) perturbative component, due to the electronic coupling between the diethylamino group and the coumarin ring, considerable solvatochromism, dual fluorescence and high fluorescence quantum yields in almost all solvents studied. The electronic structure of the S(1) and S(2) excited states permits vibronic coupling between them, making configurational changes of the S(2) excited state possible, leading to the formation of an S(2)(TICT) state. Analysis of the TCSPC data indicates an equilibrium between the S(2)(TICT) and S(1)(LE) states in favour of the former. In protic solvents, the hydrogen bonding between the solvent and the diethylamino moiety results in the formation of an S(2)(HICT) state, making internal conversion an important deactivation process. Quantum mechanical calculations for the isolated molecule show that the diethylamino group in the S(2)(TICT) state is twisted at least 56 degree from the plane of the coumarin ring, with partial electronic decoupling between -NEt(2) and the coumarin ring. This twisting angle must be positively influenced by solute-solvent interactions. [capital Phi](ST) is found to be small, but not negligible. However, Phi (delta) can be considered negligible, an indication that T(1) is a short-lived state. Based on the experimental data and theoretical calculations, the most probable sequence for the first excited states, including the TICT state, is T(1)(n, pi*) < S(2)(TICT) < S(1)(pi,pi*) approximate S(2) (n,pi*).

Preparation of silver nanoprisms using poly(N-vinyl-2-pyrrolidone) as a colloid-stabilizing agent and the effect of silver nanoparticles on the photophysical properties of cationic dyes.

The synthesis of silver nanoprisms in aqueous solution using poly(N-vinyl-2-pyrrolidone) (PVP) with different molecular weights (29, 55 and 1300 kg mol(-1)) as a stabilizing agent is described. Low molecular weight PVP (55 kg mol(-1)) is indicated for the preparation of a stable blue solution containing Ag nanoprisms via extended irradiation of a yellow colloidal solution of nanospheres with polychromatic visible light. The fluorescence properties of some cationic dyes (acridine, 9-aminoacridine, Nile Blue and auramine), free and bound to poly(methacrylic acid), have been studied in the presence of different shaped Ag colloidal particles in solution. Only auramine displays an amplification of the fluorescence signal with increasing colloid concentration, while the fluorescence of the other dyes is quenched by interaction with the polymer-stabilized metal nanoparticles.