Laura T. Okano

Photolysis of ferric ions in the presence of sulfate or chloride ions: implications for the photo-Fenton process

The photo-Fenton process (Fe(2+)/Fe(3+), H(2)O(2), UV light) is one of the most efficient and advanced oxidation processes for the mineralization of the organic pollutants of industrial effluents and wastewater. The overall rate of the photo-Fenton process is controlled by the rate of the photolytic step that converts Fe(3+) back to Fe(2+). In this paper, the effect of sulfate or chloride ions on the net yield of Fe(2+) during the photolysis of Fe(3+) has been investigated in aqueous solution at pH 3.0 and 1.0 in the absence of hydrogen peroxide. A kinetic model based on the principal reactions that occur in the system fits the data for formation of Fe(2+) satisfactorily. Both experimental data and model prediction show that the availability of Fe(2+) produced by photolysis of Fe(3+) is inhibited much more in the presence of sulfate ion than in the presence of chloride ion as a function of the irradiation time at pH 3.0.

Stereoselective determination of midodrine and desglymidodrine in culture medium: application to a biotransformation study employing endophytic fungi.

A CE method was developed and validated for the stereoselective determination of midodrine and desglymidodrine in Czapek culture medium to be applied to a stereoselective biotransformation study employing endophytic fungi. The electrophoretic analyses were performed using an uncoated fused‐silica capillary and 70 mmol/L sodium acetate buffer solution (pH 5.0) containing 30 mmol/L heptakis (2, 3, 6‐tri‐O‐methyl)‐β‐CD as running electrolyte. The applied voltage and temperature used were 15 kV and 15°C, respectively. The UV detector was set at 200 nm. The sample preparation was carried out by liquid–liquid extraction using ethyl acetate as extractor solvent. The method was linear over the concentration range of 0.1–12 μg/mL for each enantiomer of midodrine and desglymidodrine (r≥0.9975). Within‐day and between‐day precision and accuracy evaluated by RSDs and relative errors, respectively, were lower than 15% for all analytes. The method proved to be robust by a fractional factorial design evaluation. The validated method was used to assess the midodrine biotransformation to desglymidodrine by the fungus Phomopsis sp. (TD2), which biotransformed 1.1% of (−)‐midodrine to (−)‐desglymidodrine and 6.1% of (+)‐midodrine to (+)‐desglymidodrine.

Determining Counterion Exchange Selectivities at Micelle Surfaces from Fluorescence Decay Measurements

A method for determining counterion exchange selectivities at the surface of ionic micelles from time‐resolved fluorescence quenching measurements is developed. This method is employed to determine selectivity coefficients for thiosulfate/chloride exchange at the surface of cati‐onic hexadecyltrimethylammonium chloride micelles (KTS/CI, = 1.1 ± 0.4) and for copper (II)/sodium exchange at the surface of anionic sodium dodecyl sulfate micelles (KCu/Na= 1.3 ± 0.3). In both cases, the selectivity coefficients are found to be independent of detergent and added salt concentration.

In vitro metabolism of grandisin, a lignan with anti-chagasic activity.

Tetrahydrofuran lignans represent a well-known group of phenolic compounds capable of acting as antiparasitic agents. In the search for new medicines for the treatment of Chagas disease, one promising compound is grandisin which has shown significant activity on trypomastigote forms of Trypanosoma cruzi. In this work, the in vitro metabolism of grandisin was studied in the pig cecum model and by biomimetic phase I reactions, aiming at an ensuing a preclinical pharmacokinetic investigation. Although grandisin exhibited no metabolization by the pig microbiota, one putative metabolite was formed in a biomimetic model using Jacobsen catalyst. The putative metabolite was tested against T. cruzi revealing loss of activity in comparison to grandisin.

Safety, osseointegration, and bone ingrowth analysis of PMMA‐based porous cement on animal metaphyseal bone defect model

Bone defects created after curettage of benign bone tumors are customarily filled with solid poly(methyl methacrylate) (PMMA) or other bone substitutes. In this study, we depicted a porous PMMA-based cement (produced by mixing sodium bicarbonate and citric acid) and evaluated the prospect of its clinic application. Cement samples were characterized by high-performance liquid chromatography (HPLC) coupled to mass spectrometry and its cytotoxicity evaluated in fibroblast cultures. Implantation in rabbits allowed the histologic analysis of bone, kidneys, and liver for toxicity and coagulation tests, and MRI images for hemostasis evaluation. Osseointegration was analyzed through radiography, microtomography (micro-CT), SEM, and histology of sheep specimens. Rabbit specimens were analyzed 1, 4, and 7 days after implantation of porous or solid bone cement in 6.0 mm femoral defects. Sheep specimens were analyzed 3 and 6 months after implantation or not of porous or solid cement in 15.0 mm subchondral tibial defects. The production process did not release any detectable toxic substance but slightly reduced fibroblast proliferation in vitro. Until 7 days after surgery, no local or systemic alterations could be detected in histology, or hematoma formation in histology or MRI. Sheep implants showed 6 mm linear ingrowth from the bone-cement interface and 20% bone ingrowth considering the whole defect area. Radiography, micro-CT, SEM, and histology confirmed these findings. We conclude that our porous PMMA-based cement is an attractive alternative treatment for bone defect filling that combines osseointegration and early weight bearing.

Study of the Mode of Inclusion for 7-Hydroxyflavone in β-Cyclodextrin Complexes

This paper aimed to study the mode of inclusion for 7-hydroxyflavone (7HF) in β-cyclodextrin (β-CD) complex in basic (pH 12) and acid (pH 4.5) media. The thermodynamic parameters of the complexation of 7HF with β-CD were evaluated by means of steady-state fluorescence and solubility measurements at several temperatures. The 7HF–β-CD inclusion complex was spontaneously formed at 1:1 stoichiometry in both basic and acid media. The high number of hydrogen bonds formed between the host and the guest molecules favored complexation in the basic medium, with a ground-state equilibrium constant (K) of 990 ± 130 mol −1 L, at 25 o C. The quantum-mechanics calculations showed that complexation of 7HF (neutral or anionic form) with β-CD occurred mainly via the phenyl group of the flavonoid. This result agreed with the induced circular dichroism signal of 7HF complexed with β-CD.

Synthesis and stereochemical assignment of methyl 3-(3-hydroxyphenoxy) acrylate via cis-trans photoisomerization

3-(3-Hidroxi-fenoxi)acrilato de metila (2), um novo e importante material de partida para inumeras reacoes e um precursor potencial do produto natural 3-(3-hidroxi-fenoxi)-2-propenal (1), foi sintetizado a partir de resorcinol e propiolato de metila. A configuracao trans da dupla ligacao presente no composto 2 foi confirmada atraves de uma reacao de fotoisomerizacao.

EFFECT OF ANIONIC AND NONIONIC WATER-IN-OIL MICROEMULSIONS ON ACID-BASE EQUILIBRIA OF HYDROPHILIC INDICATORS

ApparentpKavalues (hereafter writtenpK) for the hydrophilic, negatively-charged indicators 2-hydroxy-5-bromo sodium benzenesulphonate (HBBS), 2-hydroxy-5-nitro sodium benzenesulphonate (HNBS), and 2-(5,7-dinitro-8-hydroxy) sodium naphthalenesulphonate (napthol yellow, NY) in the presence of water-in-heptane microemulsions of bis(2-ethylhexyl) sodium sulphosuccinate (AOT, anionic) and polyoxyethylene (4) dodecyl ether (Brij-30, nonionic) were determined spectrophotometrically. The variables studied were the type of buffer (borate, imidazole, nicotinamide, phosphate, and piperidine) and the ratios [water]/[surfactant] and [buffer]/[surfactant]. Partition experiments between water and heptane and UV-VIS spectra of the indicators in aqueous buffer in the presence of anionic and nonionic aqueous and reversed micelles showed that these indicators are confined within the second hydration shell of the microemulsion, i.e., are not adsorbed at the water-in-oil (W/O) interface. Buffer-independentpK values were obtained after the initial pHs of the solubilized buffer solutions were corrected for the ion exchange with counter-ion of the surfactant (AOT) and for the lower polarity of the micelle-solubilized water (Brij-30 and AOT). The micelle-inducedpK shifts were in the range 1.66–2.08 units for HBBS/AOT, 1.17–2.14 units for HNBS/AOT, 0.73–1.31 units for NY/AOT, 1.06–1.40 units for HNBS/Brij-30, and 0.12–0.33 units for NY/Brij-30. The observed pK shifts are explained as due to the effect of two factors, i.e., the lower polarity of the micelle-solubilized water (relative to bulk water, AOT, and Brij-30) and electrostatic perturbation of the ― → ― ― equilibria by the negatively charged surfactant. The smaller micellar effect on thepK of NY was attributed to the extensive electron delocalization in its conjugate base.