A simplified spectrophotometric method for routine analysis of saccharin in commercial noncaloric sweeteners

A simple, rapid, and sensitive spectrophotometric method for routine analysis of saccharin in commercial noncaloric sweeteners is proposed. This method is based on the reaction of saccharin with tetrachloro-p-benzoquinone (p-chloranil) accelerated by hydrogen peroxide and conducted in an ethanol:acetone (4:1) medium, producing a violet-red compound (γ max = 550 nm). Beer's law is obeyed in a concentration range of 2.05 × 10 -4 to 3.00 × 10 -3 M with an excellent correlation coefficient (r = 0.9998). The detection limit was 1.55 × 10 -5 M, and the effect of interferences on the spectrophotometric measurements was evaluated. The proposed procedure was applied successfully to the determination of saccharin in noncaloric sweeteners. Recoveries were within 99.2-104.3% with standard deviations ranging from to 0.5-1.6%. Results of the proposed method compare very favorably with those given by the high-performance liquid chromatography method recommended by the Food and Drug Administration.

Antimicrobial endodontic compounds do not modulate alkylation-induced genotoxicity and oxidative stress in vitro

Objective: To investigate if formocresol, paramonochlorophenol, or calcium hydroxide modulate the genotoxic effects induced by the oxidatively damaging agent hydrogen peroxide (H 2O 2) or the alkylating agent methyl methanesulfonate (MMS) in vitro by using single cell gel (comet) assay. Study design: Chinese hamster ovary (CHO) cells in culture were exposed directly to formocresol, paramonochlorophenol, or calcium hydroxide (adjusted to 100 μg/mL) for 1 hour at 37°C. Subsequently the cultures were incubated with increasing concentrations (0-10 μmol/L) of MMS in phosphate-buffered solution (PBS) for 15 minutes at 37°C or of H 2O 2 at increasing concentrations (0-100 μmol/L) in distilled water for 5 minutes on ice. The negative control cells were treated with PBS for 1 hour at 37°C. The parameter from the comet assay (tail moment) was assessed by the Kruskal-Wallis nonparametric test followed by a post hoc analysis (Dunn test). Results: Clear concentration-related effects were observed for the genotoxin-exposed CHO cells. Increase of MMS-induced DNA damage was not significantly altered by the presence of the compounds tested. Similarly, no significant changes were observed when hydrogen peroxide was used with the endodontic compounds evaluated. Conclusion: Formocresol, paramonochlorophenol, and calcium hydroxide are not able to modulate alkylation-induced genotoxicity or oxidative DNA damage as depicted by the single cell gel (comet) assay. © 2006 Mosby, Inc. All rights reserved.

Simultaneous determination of Cd and Pb in antibiotics used in sugar-cane fermentation process by GFAAS

A method has been developed for the simultaneous determination of Cd and Pb in antibiotics used in sugar-cane fermentation by GFAAS. The integrated platform of transversely heated graphite atomizer was treated with tungsten to form a coating of tungsten carbide. Six samples of commercial solid antibiotics were analyzed by injecting 20 μL of digested samples into the pretreated graphite platform with co-injection of 5 μL of 1000 mg L-1 Pd as chemical modifier. Samples were mineralized in a closed-vessel microwave-assisted acid-digestion system using nitric acid plus hydrogen peroxide. The pyrolysis and atomization temperatures of the heating program of the atomizer were selected as 600°C and 2200°C, respectively. The calculated characteristic mass for Cd and Pb was 1.6 pg and 42 pg, respectively. Limits of detection (LOD) based on integrated absorbance were 0.02 μg L -1 Cd and 0.7 μg L-1 Pb and the relative standard deviations (n = 10) for Cd and Pb were 5.7% and 8.0%, respectively. The recoveries of Cd and Pb added to the digested samples varied from 91% to 125% (Cd) and 80% to 112% (Pb).

Kinetic study of the plastoquinone pool availability correlated with H2O2 release in seawater and antioxidant responses in the red alga Kappaphycus alvarezii exposed to single or combined high light, chilling and chemical stresses

Under biotic/abiotic stresses, the red alga Kappaphycus alvarezii reportedly releases massive amounts of H2O2 into the surrounding seawater. As an essential redox signal, the role of chloroplast-originated H2O2 in the orchestration of overall antioxidant responses in algal species has thus been questioned. This work purported to study the kinetic decay profiles of the redox-sensitive plastoquinone pool correlated to H2O2 release in seawater, parameters of oxidative lesions and antioxidant enzyme activities in the red alga Kappaphycus alvarezii under the single or combined effects of high light, low temperature, and sub-lethal doses of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), which are inhibitors of the thylakoid electron transport system. Within 24 h, high light and chilling stresses distinctly affected the availability of the PQ pool for photosynthesis, following Gaussian and exponential kinetic profiles, respectively, whereas combined stimuli were mostly reflected in exponential decays. No significant correlation was found in a comparison of the PQ pool levels after 24 h with either catalase (CAT) or ascorbate peroxidase (APX) activities, although the H2O2 concentration in seawater (R = 0.673), total superoxide dismutase activity (R = 0.689), and particularly indexes of protein (R = 0.869) and lipid oxidation (R = 0.864), were moderately correlated. These data suggest that the release of H2O2 from plastids into seawater possibly impaired efficient and immediate responses of pivotal H2O2-scavenging activities of CAT and APX in the red alga K. alvarezii, culminating in short-term exacerbated levels of protein and lipid oxidation. These facts provided a molecular basis for the recognized limited resistance of the red alga K. alvarezii under unfavorable conditions, especially under chilling stress. © 2006 Elsevier B.V. All rights reserved.

Micropropagação de babosa (Aloe vera L.)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Microhardness and fluoride release of restorative materials in different storage media

This study evaluated the surface microhardness and fluoride release of 5 restorative materials - Ketac-Fil Plus, Vitremer, Fuji II LC, Freedom and Fluorofil - in two storage media: distilled/deionized water and a pH-cycling (pH 4.6). Twelve specimens of each material, were fabricated and the initial surface microhardness (ISM) was determined in a Shimadzu HMV-2000 microhardness tester (static load Knoop). The specimens were submitted to 6- or 18-h cycles in the tested media. The solutions were refreshed at the end of each cycle. All solutions were stored for further analysis. After 15-day storage, the final surface microhardness (FSM) and fluoride release were measured. Fluoride dose was measured with a fluoride-specific electrode (Orion 9609-BN) and digital ion analyzer (Orion 720 A). The variables ISM, FSM and fluoride release were analyzed statistically by analysis of variance and Tukey's test (p<0.05). There was significant difference in FSM between the storage media for Vitremer (pH 4.6 = 40.2 ± 1.5; water = 42.6 ± 1.4), Ketac-Fil Plus (pH 4.6 = 73.4 ± 2.7; water = 58.2 ± 1.3) and Fluorofil (pH 4.6 = 44.3 ± 1.8; water = 38.4 ± 1.0). Ketac-Fil Plus (9.9 ± 18.0) and Fluorofil (4.4 ± 1.3) presented higher fluoride release in water, whereas Vitremer (7.4 ± 7.1), Fuji II LC (5.7 ± 4.7) and Freedom (2.1 ± 1.7) had higher fluoride release at pH 4.6. Microhardness and fluoride release of the tested restorative materials varied according to the storage medium.

Modulatory effect of Byrsonima basiloba extracts on the mutagenicity of certain direct and indirect-acting mutagens in Salmonella typhimurium assays

Byrsonima basiloba A. Juss. species is a native arboreal type from the Brazilian cerrado (tropical American savanna), and the local population uses it to treat diseases, such as diarrhea and gastric ulcer. It belongs to the Malpighiaceae family, and it is commonly known as murici. Considering the popular use of B. basiloba derivatives and the lack of pharmacological potential studies regarding this vegetal species, the mutagenic and antimutagenic effect of methanol (MeOH) and chloroform extracts were evaluated by the Ames test, using strains TA97a, TA98, TA100, and TA102 of Salmonella typhimurium. No mutagenic activity was observed in any of the extracts. To evaluate the antimutagenic potential, direct and indirect mutagenic agents were used: 4 nitro-o-phenylenediamine, sodium azide, mitomycin C, aflatoxin B1, benzo[a]pyrene, and hydrogen peroxide. Both the extracts evaluated showed antimutagenic activity, but the highest value of inhibition level (89%) was obtained with the MeOH extract and strain TA100 in the presence of aflatoxin B1. Phytochemical analysis of the extracts revealed the presence of n-alkanes, lupeol, ursolic and oleanolic acid, (+)-catechin, quercetin-3-O-α-L-arabinopyranoside, gallic acid, methyl gallate, amentoflavone, quercetin, quercetin-3-O-(2″-O-galloyl)-β-D- galactopyranoside, and quercetin-3-O-(2″-O-galloyl)-α-L- arabinopyranoside. © 2008 Mary Ann Liebert, Inc.

Determinação de fármacos diuréticos em associação por cromatografia em camada delgada e espectrofotometria

A rapid, sensitive and reliable thin-layer chromatography/spectrophotometry screening procedure was developed for quantitative determination of diuretics associated in pharmaceutical dosage forms. The chromatographic method employed microcrystalline cellulose and butanol : acetic acid : water (4:1:1) or amilic alcohol : ammonium hydroxide 25% (9:1) as mobile phases and detection by U.V. light. The drugs were extracted using a simple procedure and were quantified by U.V. spectrophotometry. Results varied from 97.5 to 102.5% and are similar to those obtained by conventional methods. This method of quantification of diuretics is promising for quality control of drugs.

The Mycobacterium tuberculosis Rv2540c DNA sequence encodes a bifunctional chorismate synthase

Background. The emergence of multi- and extensively-drug resistant Mycobacterium tuberculosis strains has created an urgent need for new agents to treat tuberculosis (TB). The enzymes of shikimate pathway are attractive targets to the development of antitubercular agents because it is essential for M. tuberculosis and is absent from humans. Chorismate synthase (CS) is the seventh enzyme of this route and catalyzes the NADH- and FMN-dependent synthesis of chorismate, a precursor of aromatic amino acids, naphthoquinones, menaquinones, and mycobactins. Although the M. tuberculosis Rv2540c (aroF) sequence has been annotated to encode a chorismate synthase, there has been no report on its correct assignment and functional characterization of its protein product. Results. In the present work, we describe DNA amplification of aroF-encoded CS from M. tuberculosis (MtCS), molecular cloning, protein expression, and purification to homogeneity. N-terminal amino acid sequencing, mass spectrometry and gel filtration chromatography were employed to determine identity, subunit molecular weight and oligomeric state in solution of homogeneous recombinant MtCS. The bifunctionality of MtCS was determined by measurements of both chorismate synthase and NADH:FMN oxidoreductase activities. The flavin reductase activity was characterized, showing the existence of a complex between FMN ox and MtCS. FMNox and NADH equilibrium binding was measured. Primary deuterium, solvent and multiple kinetic isotope effects are described and suggest distinct steps for hydride and proton transfers, with the former being more rate-limiting. Conclusion. This is the first report showing that a bacterial CS is bifunctional. Primary deuterium kinetic isotope effects show that C4-proS hydrogen is being transferred during the reduction of FMNox by NADH and that hydride transfer contributes significantly to the rate-limiting step of FMN reduction reaction. Solvent kinetic isotope effects and proton inventory results indicate that proton transfer from solvent partially limits the rate of FMN reduction and that a single proton transfer gives rise to the observed solvent isotope effect. Multiple isotope effects suggest a stepwise mechanism for the reduction of FMNox. The results on enzyme kinetics described here provide evidence for the mode of action of MtCS and should thus pave the way for the rational design of antitubercular agents. © 2008 Ely et al; licensee BioMed Central Ltd.

Evaluating the bonding of two adhesive systems to enamel submitted to whitening dentifrices.

The aim of this study was to evaluate by micro-shear bond strength test, the bond strength of composite resin restoration to enamel submitted to whitening dentifrices. Forty bovine teeth were embedded in polystyrene resin and polished. The specimens were randomly divided into eight groups (n=5), according to the dentifrice (carbamide peroxide, hydrogen peroxide and conventional dentifrice) and the adhesive system (Prime & Bond 2.1 and Adper Single Bond 2). Dentifrice was applied for 15 minutes a day, for 21 days. Thirty minutes after the last exposure to dentifrice, the samples were submitted to a bonding procedure with the respective adhesive system. After that, four buttons of resin were bonded in each sample using transparent cylindrical molds. After 24 hours, the teeth were submitted to the micro-shear bond strength test and subsequent analysis of the fracture mode. Data were submitted to analysis of variance and Fisher's PLSD test (alpha = 0.05). The micro-shear bond strength showed no difference between adhesives systems but a significant reduction was found between the control and carbamide groups (p = 0.0145) and the control and hydrogen groups (p = 0.0370). The evaluation of the failures modes showed that adhesive failures were predominant. Cohesive failures were predominant in group IV The use of dentifrice with peroxides can decrease bonding strength in enamel.

pH-changes during intracoronal bleaching: An in vivo study

Objectives: This study aimed to measure pH changes during 14 days intracoronal bleaching with hydrogen peroxide/sodium perborate and carbamide peroxide/sodium perborate. Materials and methods: Twenty patients presenting endodontically treated central maxillary incisors with color alterations were divided in two groups (n = 10): Group CP + SP: 37% carbamide peroxide + sodium perborate paste; Group HP + SP: 30% hydrogen peroxide + sodium perborate paste. The pH values were measured using a digital microprocessor at different times: Baseline, 2, 7 and 14 days. Data were analyzed with two-way ANOVA followed by Tukey's test (α = 0.05). Results: ANOVA showed p < 0.00 which indicated significant difference between the groups. The mean values (± sd) and the results of the Tukey's test were: HP + SP/14 days-7.98 (±0.58)a; HP + SP/7 days-8.59 (±0.18)b; HP + SP/2 days-8.83 (±0.32)bc; HP + SP/Baseline-8.83 (±0.01)bc; CP + SP/Baseline-8.89 (±0.01)bc; CP + SP/14 days-9.11 (±0.58)cd; CP + SP/7 days-9.54 (±0.16)de; CP + SP/2 days-9.66 (±0.08) de. The group HP + SP resulted in significantly lower pH values compared with group CP + SP. Conclusion: It can be concluded that both associations showed alkaline pH values; however, there was significant reduction in the pH values of the 30% hydrogen peroxide associated with sodium perborate after 14 days. Clinical Significance: The association of hydrogen peroxide and carbamide peroxide with sodium perborate paste presented alkaline characteristics during the 14-day evaluated period. Thus, regarding pH changes, both associations can be considered safe as intracoronal bleaching agents.

Micropatterned nanocomposite hydrogels for biosensing applications

This paper describes the use of Au nanoparticle (NP)-containing hydrogel microstructures in the development of electrochemical enzyme-based biosensors. To fabricate biosensors, AuNPs were conjugated with glucose oxidase (GOX) or horseradish peroxidase (HRP) molecules and were dispersed in the prepolymer solution of poly(ethylene glycol) diacrylate (PEG-DA). Vinylferrocene (VF) was also added into the prepolymer solution in order to lower operating potential of the biosensor and to prevent oxidation of interfering substances. The prepolymer solution was photolithographically patterned in alignment with an array of Au electrodes fabricated on glass. As a result, electrode arrays became functionalized with AuNP/GOX- or AuNP/HRP-carrying hydrogel microstructures. Performance of the biosensors was characterized by impedance spectroscopy, chronoapmerometry and cyclic voltammetry. Impedance measurements revealed that inclusion of Au nanoparticles improved conductivity of PEG hydrogel by a factor of 5. Importantly, biosensors based on AuNP-GOX complex exhibited high sensitivity to glucose (100μAmM -1cm -2) in the linear range from 0.1 to 10mM. The detection limit was estimated to be 3.7×10- 7M at a signal-to-noise ratio of 3. Biosensors with immobilized AuNP/HPR had a linear response from 0.5 to 5.0μM of hydrogen peroxide with sensitivity of 1.4mAmM -1cm -2. The method for fabricating nanoparticle-carrying hydrogel microstructures described in this paper should be widely applicable in the development of robust and sensitive electrochemical biosensors. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Adhesion between fiber post and root dentin: evaluation of post surface conditioning for bond strength improvement.

The aim of this paper was to evaluate two surface conditioning methods associated with the application of adhesive on the post surface for improving the bond to resin cement. Sixty single-rooted bovine teeth were sectioned at 16 mm in length, prepared (9 mm depth), embedded in a PVC cylinder using acrylic resin, and allocated into 3 groups (N.=20) according to post surface treatment: cleaning with ethanol (control group); etching with hydrogen peroxide; etching with hydrofluoric acid. Ten posts for each group were silanized and other 10 posts were silanized and received an adhesive agent. The posts were cemented with self-adhesive resin cement (RelyX U100 resin cement). All teeth were sectioned perpendicularly to the long axis (2 mm thickness per slice), submitted to push out bond strength testing and the type of failure was recorded. The obtained data were submitted to two-way ANOVA and Turkey's test, with the level of significance set at 5%. Neither the hydrofluoric acid or hydrogen peroxide post surface treatment, nor the adhesive application, had an influence on bond strength values. The main type of failure was adhesive between cement and dentin. Etching and the application of an adhesive on the post surface did not presented a significant influence on the bond strength results for the fiber post resin cement-root dentin assembly. The cement appears to adhere very well to the fiber post surface rather than the dentin surface.

Growth and morphology of eumelanin thin films - A future bioelectronic material?

We present a study on the thin film morphology and the optical properties of eumelanin resulting from different synthesis routes: the oxidation of tyrosine with hydrogen peroxide, the auto-oxidation of dihydroxyphenylanaline in water and its auto-oxidation in dimethyl sulfoxid. Atomic Force Microscopy images indicate that the presence of holes and particles depends on the eumelanin synthesis route and the substrate employed. Smooth films with very few defects could be obtained with eumelanin synthesized in dimethyl sulfoxide deposited on glass substrates. Our study shows that all eumelanin preparations are comparable in terms of thin film morphology on the submicrometer scale and UV-visible transmission properties. ©The Electrochemical Society.

Antioxidant and cytotoxic studies for kaempferol, quercetin and isoquercitrin

The aim of the present study was to investigate a cytotoxic oxidative cell stress related and the antioxidant profile of kaempferol, quercetin, and isoquercitrin. The flavonol compounds were able to act as scavengers of superoxide anion (but not hydrogen peroxide), hypochlorous acid, chloramine and nitric oxide. Although flavonoids are widely described as antioxidants and this activity is generally related to beneficial effects on human health, here we show important cytotoxic actions of three well known flavonoids. They were able to promote hemolysis which one was exacerbated on the presence of hypochlorous acid but not by AAPH radical. Therefore, despite they expected scavenger action over free radicals an oxidants, these compounds could be very lesive to living organisms by acting over erythrocytes and maybe other cellular types.