Determination of beta-carboline alkaloids in foods and beverages by high-performance liquid chromatography with electrochemical detection at a glassy carbon electrode modified with carbon nanotubes

Simple and sensitive methods for the separation and quantification of β-carboline alkaloids in foods and beverages by HPLC with electrochemical detection at carbon nanotubes-modified glassy carbon electrodes (CNTs-GCE) are reported. Electrode modification with multi-wall CNTs produced an improved amperometric response to β-carbolines, in spite of the working medium consisting of methanol:acetonitrile: 0.05 mol L⁻¹ Na₂HPO₄ solution of pH 9.0 (20:20:60). On the contrary to that observed at a bare GCE, a good repeatability of the amperometric measurements carried out at +900 mV versus Ag/AgCl (R.S.D. of 3.2% for i_p, n = 20) was achieved at the CNTs-GCE. Using an Ultrabase C₁₈ column and isocratic elution with the above mentioned mobile phase, a complete resolution of the chromatographic peaks for harmalol, harmaline, norharmane, harmane and harmine, was achieved. Calibration graphs over the 0.25-100 μM range with detection limits ranging between 4 and 19 ng mL⁻¹, were obtained. The HPLC-ED at CNTs-GCE method was applied to the analysis of beer, coffee and cheese samples, spiked with β-carbolines at concentration levels corresponding to those may be found in the respective samples. The steps involved in sample treatment, such as extraction and clean-up, were optimized for each type of sample. Recoveries ranging between 92 and 102% for beer, 92 and 101% for coffee, and 88 and 100% for cheese, at sub-μg mL⁻¹ or g⁻¹ analytes concentration levels were achieved.     

Alkoxy-substituted difluoroboron benzoylmethanes for photonics applications: a photophysical and spectroscopic study

Two series of novel boron difluoride adducts (BDFs), namely [BF(2)(OO(R(n)))] (type I) and [BF(2)(OO(2R(n)))] (type II) (R = C(6)H(4)OC(n)H(2n+1); n = 10-18), containing β-diketonate ligands bearing 4-alkoxyphenyl substituents in position 1 or in positions 1,3 of the β-diketonate core, respectively, have been prepared. All of them display a strong interaction between the ligand and the BF(2) group, as deduced from the IR spectroscopic data, and strong blue-violet emission (λ(em)(max) from 400 to 440 nm), with fluorescence quantum yields from 0.69 to 0.84 (type I) and 0.48 to 0.66 (type II) and fluorescence lifetimes of 1.7 and 2.2 ns in diluted dichloromethane solution, respectively. The photophysical properties of I and II series of dyes are independent of the solvent polarity and the chain length of the alkoxyphenyl substituent(s). Moreover, they exhibit high photostability even under intense laser light. Contradicting previous interpretations, our detailed photophysical and spectroscopic study rules out excimer formation even in highly concentrated solution or in the solid state, demonstrating the resistance of these dyes to self-aggregation. All those features pave the way to the application of such fluorophores in OLEDs, solid dye lasers, chemical sensors and two-photon biological labels, to name a few.     

Electron ionization mass spectral studies of bridgehead-substituted norbornan-2-ones: camphor derivatives

The electron ionization (EI) mass spectra of a series of bridgehead-substituted 3,3-dimethylnorbornan-2-ones, derived from natural (1R)-(+)-camphor, have been studied and their cleavage mechanisms rationalized on the basis of the substituent shifts as well as on the identification of relevant peaks through accurate mass measurements and collision-induced dissociation (CID) tandem mass spectrometric experiments. The fragmentation patterns are very dependent on both the structural nature and the electronic properties of the bridgehead substituent. The driving force for the main fragmentation pathways are competitive cleavages of the C(1)-C(2) and C(2)-C(3) bonds directed by the bridgehead substituent and either the gem-dimethyl or carbonyl groups. These cleavages lead to distonic ions in which the charge is preferentially located either at the C(1), C(2) or C(3) positions depending on the electronic character and structural nature of the bridgehead substituent. This charge distribution determines the subsequent rearrangements and fragmentations.     

Anacardium occidentale Bark Lectin: Purification, Immobilization as an Affinity Model and Influence in the Uptake of Technetium-99M by Rat Adipocytes

Lectins, proteins that recognize carbohydrates, have been immobilized on inert supports and used in the screening or purification of glycoproteins. Anacardium occidentale bark infusion has been used as a hypoglycemic agent in Brazil. The toxicity of natural products may be evaluated determining their capability to alter the biodistribution of technetium-99M (^99mTc). This work reports the isolation and characterization of a lectin from A. occidentale bark (AnocBL), its evaluation as an affinity support for glycoprotein isolation and lectin effect on the uptake of ^99mTc by rat adipocytes. AnocBL was isolated from 80?% ammonium sulphate supernatant by affinity chromatography on fetuin?Cagarose. SDS?CPAGE showed a single protein band of 47?kDa. The monossacharide l-arabinose and the glycoproteins fetuin, asialofetuin, ovomucoid, casein, thyroglobulin, peroxidase, fetal bovine serum and IgG inhibited the activity. The lectin activity was stable until 70?°C and at a pH range of 3.0?C7.5. AnocBL?CSepharose column bound fetuin indicating that the lectin matrix may be used to obtain glycoconjugates of biotechnological interest. In vitro assay revealed that glucose and insulin increase ^99mTc uptake by rat adipocytes. AnocBL decreases ^99mTc uptake, and this effect was not detected in the presence of glucose. Fetuin inhibited AnocBL effect in all insulin concentrations.     

1,2-disubstituted ferrocenyl carbohydrate chloroquine conjugates as potential antimalarial agents

This work presents a new family of organometallic antimalarial compounds consisting of ferrocene bearing a chloroquine-derived moiety as well as a 1,2;3,5-diisopropylidene glucofuranose moiety at a cyclopentadienyl scaffold in a 1,2-substitution pattern. The synthetic route proceeds via a stereoselective functionalization of ferrocene carboxaldehyde to the 1,2-disubstituted conjugates. After complete characterization of these new, trifunctional conjugates, they were examined for their cytotoxicity in two cancerous cell lines (MDA-MB-435S and Caco2) and one non-cancerous cell line (MCF-10A), showing that increased cytotoxicity can be observed for the chloroquine ferrocenyl conjugates compared to their carbohydrate-substituted precursors. The antiplasmodial activity of the conjugates in a chloroquine-sensitive strain of Plasmodium falciparum (D10) and a chloroquine-resistant strain (Dd2) was determined. Monosubstituted conjugates 13, 14 and 15 exhibit decreasing activity with increasing alkyl chain length between the ferrocene and quinoline moiety, bifunctional conjugates 16, 17, 18 show constant activity, performing better than chloroquine in the Dd2 strain.     

Electropolymerized network of polyamidoamine dendron-coated gold nanoparticles as novel nanostructured electrode surface for biosensor construction

Polyfuntionalized gold nanoparticles were prepared by using 2-mercaptoethanesulfonic acid, p-aminothiophenol and cysteamine core polyamidoamine G-4 dendron as capping ligands. The nanoparticles were electropolymerized on a Au electrode surface through the formation of a bisaniline-cross-linked network. The enzyme tyrosinase was further crosslinked on this nanostructured matrix. The enzyme electrode, poised at -100 mV, was used for the amperometric quantification of cathecol. The biosensor showed a linear response from 50 nM to 10 μM cathecol, with a low detection limit of 20 nM and a sensitivity of 1.94 A M(-1) cm(2). The electrode retained 96% and 67% of its initial activity after 16 and 30 days of storage at 4 °C under dry conditions.     

Jet multiplicity distributions: medium dependence in MLLA

We study the medium dependence of the multiplicity distributions in the modified leading logarithmic approximation. We focus in the enhancement in the number of branchings as the partons travel trough a dense medium created in a heavy-ion collision. We study the effect of a higher number of splittings in some jet observables by introducing the medium as a constant (f _med) in the splitting functions. Having as our ansatz for the quark and gluon jets mean multiplicities 〈n _G 〉=e ^{γ y} and 〈n _Q 〉=r ⁻¹e ^{γ y} , we study in an analytic approach the dependence with the medium (f _med) of the anomalous dimension (γ), the multiplicity ratio (r), and so the mean multiplicities. We also obtain the higher-order moments of the multiplicity distribution, what allows us to study its dispersion.     

Inulin-containing biomass for ethanol production

The use of stalks instead of tubers as a source of carbohydrates for ethanol production has been investigated. The inulin present in the stalks of Jerusalem artichoke was extracted with water and the effect of solid-liquid ratio, temperature, and acid addition was studied and optimized in order to attain a high-fructose fermentable extract. The maximum extraction efficiency (corresponding to 35 g/L) of soluble sugars was obtained at 1/6 solidliquid ratio. Fermentations of hydrolyzed extracts by baker's yeast and direct fermentation by an inulinease activity yeast were also performed and the potential to use this feedstock for bioethanol production assessed. The results show that the carbohydrates derived from Jerusalem artichoke stalks can be converted efficiently to ethanol by acidic hydrolysis followed by fermentation with Saccharomyces cerevisiae or by direct fermentation of inulin using Kluyveromyces marxianus strains. In this last case about 30 h to complete fermentation was required in comparison with 8–9 h obtained in experiments with S. cerevisiae growth on acid extracted juices.     

Properties of two polymerisable surfactants aqueous solutions: dodecylethylmethacrylatedimethylammonium bromide and hexadecylethylmethacrylatedimethylammonium bromide. II. Partial molar volume and micelle hydration

The partial molar volume and hydration number of two micellised polymerisable surfactants (dodecylethylmethacrylatedimethylammonium bromide (C₁₂PS) and hexadecylethylmethacrylatedimethylammonium bromide (C₁₆PS)) were determined. Results support marginally the annular conformation of the polar head group (N⁺(CH₃)₂-CH₂-CH₂-O-CO-C(CH₃)(=CH₂)) proposed in the literature.