Development of a functional assay to detect inhibitors of Plasmodium falciparum glutathione reductase utilizing liquid chromatography–mass spectrometry

Plasmodium falciparum (Pf) like most other organisms, has a sophisticated antioxidant system, part of which includes glutathione reductase (GR). GR works by recycling toxic glutathione disulfide to glutathione, thereby reducing reactive oxygen species and making a form of glutathione (GSH) the parasite can use. Inhibition of this enzyme in Pf impedes parasite growth. In addition, it has been confirmed that PfGR is not identical to human GR. Thus, PfGR is an excellent target for antimalarial drug development. A functional assay utilizing liquid chromatography–mass spectrometry was developed to specifically identify and evaluate inhibitors of PfGR. Using recombinant PfGR enzyme and 1,4‐naphthoquinone (1) as a reference compound and 4‐nitrobenzothiadiazole (2) and methylene blue (3) as additional compounds, we quantified the concentration of GSH produced compared with a control to determine the inhibitory effect of these compounds. Our results coincide with that presented in literature: compounds 1–3 inhibit PfGR with IC₅₀ values of 2.71, 8.38, and 19.23 µm , respectively. Good precision for this assay was exhibited by low values of intraday and interday coefficient of variation (3.1 and 2.4%, respectively). Thus, this assay can be used to screen for other potential inhibitors of PfGR quickly and accurately. Copyright © 2015 John Wiley & Sons, Ltd.     

Predicting Properties of Iron(III) TAML Activators of Peroxides from Their III/IV and IV/V Reduction Potentials or a Lost Battle to Peroxidase

A cyclic voltammetry study of a series of iron(III) TAML activators of peroxides of several generations in acetonitrile as solvent reveals reversible or quasireversible Fe^III/IV and Fe^IV/V anodic transitions, the formal reduction potentials (E°′) for which are observed in the ranges 0.4–1.2 and 1.4–1.6 V, respectively, versus Ag/AgCl. The slope of 0.33 for a linear E°′(IV/V) against E°′(III/IV) plot suggests that the TAML ligand system plays a bigger role in the Fe^III/IV transition, whereas the second electron transfer is to a larger extent an iron-centered phenomenon. The reduction potentials appear to be a convenient tool for analysis of various properties of iron TAML activators in terms of linear free energy relationships (LFERs). The values of E°′(III/IV) and E°′(IV V⁻¹) correlate 1) with the pK_a values of the axial aqua ligand of iron(III) TAMLs with slopes of 0.28 and 0.06 V, respectively; 2) with the Stern–Volmer constants K_SV for the quenching of fluorescence of propranolol, a micropollutant of broad concern; 3) with the calculated ionization potentials of Fe^III and Fe^IV TAMLs; and 4) with rate constants k_I and k_II for the oxidation of the resting iron(III) TAML state by H₂O₂ and reactions of the active forms of TAMLs formed with donors of electrons S, respectively. Interestingly, slopes of log k_II versus E°′(III/IV) plots are lower for fast-to-oxidize S than for slow-to-oxidize S. The log k_I versus E°′(III/IV) plot suggests that the manmade TAML catalyst can never be as reactive toward H₂O₂ as a horseradish peroxidase enzyme.     

Correction to: X-coordinates of Pell equations as sums of two Tribonacci numbers

Periodica Mathematica Hungarica - In this work, we correct an oversight from [1].     

Core carbo-mer of an Extended Tetrathiafulvalene: Redox-Controlled Reversible Conversion to a carbo-Benzenic Dication

carbo-Benzene is an aromatic molecule devised by inserting C₂ units within each C−C bond of the benzene molecule. By integrating the corresponding carbo-quinoid core as bridging unit in a π-extended tetrathiafulvalene (exTTF), it is shown that a carbo-benzene ring can be reversibly formed by electrochemical reduction or oxidation. The so-called carbo-exTTF molecule was thus experimentally prepared and studied by UV–visible absorption spectroscopy and cyclic voltammetry, as well as by X-ray crystallography and by scanning tunneling microscopy (STM) on a surface of highly oriented pyrolytic graphite (HOPG). The molecule and its oxidized and reduced forms were subjected to a computational study at the density functional theory (DFT) level, supporting carbo-aromaticity as a driving force for the formation of the dication, radical cation, and radical anion. By allowing co-planarity of the dithiolylidene rings and carbo-quinoidal core, carbo-exTTFs present a promising new class of redox-active systems.     

Thermodynamics and Kinetics of the Complexation Reaction of Lead by Calix‐DANS4

The thermodynamics and kinetics of the complexation reaction between lead ions and the fluorescent sensor Calix‐DANS4 are determined to optimize the geometry of the microreactor used for the flow‐injection analysis of lead and to tune the working conditions of this microdevice. Under our experimental conditions (pH 3.2, low concentration of Calix‐DANS4) the 1:1 Pb²⁺‐Calix‐DANS4 complex is predominantly formed with a high stability constant (log K_1:1=6.82) and a slow second‐order rate constant (k=9.4×10⁴ L mol^?1 s^?1). Due to this sluggish complexation reaction, the microchannel length must be longer than 130 mm and the flow rate lower than 0.25 mL h^?1 to have an almost complete reaction at the output of the microchannel and a high sensitivity for the heavy metal detection. After determination of the values of the reaction times in our different microdevices, it is possible to simulate the calibration curves for the fluorimetric detection of lead under different conditions. An original method is also presented to determine mixing times in microreactors.     

Characterization of the aerosol produced by infrared femtosecond laser ablation of polyacrylamide gels for the sensitive inductively coupled plasma mass spectrometry detection of selenoproteins

A 2D high repetition rate femtosecond laser ablation strategy (2-mm wide lane) previously developed for the detection of selenoproteins in gel electrophoresis by inductively coupled plasma mass spectrometry was found to increase signal sensitivity by a factor of 40 compared to conventional nanosecond ablation (0.12-mm wide lane) [G. Ballihaut, F. Claverie, C. Pécheyran, S. Mounicou, R. Grimaud and R. Lobinski, Sensitive Detection of Selenoproteins in Gel Electrophoresis by High Repetition Rate Femtosecond Laser Ablation-Inductively Coupled Plasma Mass Spectrometry, Anal. Chem. 79 (2007) 6874–6880]. Such improvement couldn't be explained solely by the difference of amount of material ablated, and then, was attributed to the aerosol properties. In order to validate this hypothesis, the characterization of the aerosol produced by nanosecond and high repetition rate femtosecond laser ablation of polyacrylamide gels was investigated. Our 2D high repetition rate femtosecond laser ablation strategy of 2-mm wide lane was found to produce aerosols of similar particle size distribution compared to nanosecond laser ablation of 0.12-mm wide lane, with 38% mass of particles < 1 µm. However, at high repetition rate, when the ablated surface was reduced, the particle size distribution was shifted toward thinner particle diameter (up to 77% for a 0.12-mm wide lane at 285 µm depth). Meanwhile, scanning electron microscopy was employed to visualize the morphology of the aerosol. In the case of larger ablation, the fine particles ejected from the sample were found to form agglomerates due to higher ablation rate and then higher collision probability. Additionally, investigations of the plasma temperature changes during the ablation demonstrated that the introduction of such amount of polyacrylamide gel particles had very limited impact on the ICP source (ΔT~ 25 ± 5 K). This suggests that the cohesion forces between the thin particles composing these large aggregates were weak enough to have negligible impact on the ICPMS detection.     

Analytical speciation of mercury in fish tissues by reversed phase liquid chromatography-inductively coupled plasma mass spectrometry with Bi as internal standard

In this work, the quantification of two mercury species (Hg²⁺ and CH₃Hg⁺) in fish tissues has been revisited. The originality of our approach relies on the use of Bi³⁺ as internal standard (IS) and on the modification of typical extraction conditions. The IS (125 μl, 1000 μg l⁻¹ Bi³⁺) was added to the aliquot of fresh fish tissue (400-500 mg). A high-speed blender and ultrasound-assisted homogenization/extraction was carried out in the presence of perchloric acid (1.5 ml, 0.6 mol l⁻¹), l-cysteine (500 μl, 0.75 mol l⁻¹) and 500 μl toluene:methanol (1:1). Perchloric acid was used for protein denaturation and precipitation, toluene helped to destroy lipid structures potentially sequestering CH₃Hg⁺, l-cysteine was used to form water-soluble complexes with Bi³⁺, Hg²⁺ and CH₃Hg⁺. The excess of perchloric acid was eliminated by addition of potassium hydroxide (pH 5 with acetic acid). The obtained extract, was diluted with the mobile phase (1:1) and introduced (20 μl) to the reversed phase HPLC-ICP-MS system. The separation was achieved by isocratic elution (2.5 mmol l⁻¹ cysteine, 12.5 mmol l⁻¹ (NH₄)₂HPO₄, 0.05% triethylamine, pH 7.0:methanol (96:4)) at a flow rate 0.6 ml min⁻¹. Column effluent was on-line introduced to ICP-MS for specific detection of ²⁰²Hg, ²⁰⁰Hg and ²⁰⁹Bi. Analytical signal was defined as the ratio between ²⁰²Hg/²⁰⁹Bi peak areas. The detection limits evaluated for Hg²⁺ and CH₃Hg⁺ were 0.8 and 0.7 μg l⁻¹. Recovery of the procedure, calculated as the sum of species concentrations found in the sample with respect to total ICP-MS-determined Hg was 91.9% for king mackerel muscle and 89.5% for red snapper liver. In the standard addition experiments, the recovery results were 98.9% for Hg²⁺ and 100.6% for CH₃Hg⁺. It should be stressed that the use of Bi³⁺ as IS enabled to improve analytical performance by compensating for incomplete extraction and for imprecision of sample handling during relatively non-rigorous protocol.     

Semiparametric Bayesian measurement error modeling

This work presents a Bayesian semiparametric approach for dealing with regression models where the covariate is measured with error. Given that (1) the error normality assumption is very restrictive, and (2) assuming a specific elliptical distribution for errors (Student-t for example), may be somewhat presumptuous; there is need for more flexible methods, in terms of assuming only symmetry of errors (admitting unknown kurtosis). In this sense, the main advantage of this extended Bayesian approach is the possibility of considering generalizations of the elliptical family of models by using Dirichlet process priors in dependent and independent situations. Conditional posterior distributions are implemented, allowing the use of Markov Chain Monte Carlo (MCMC), to generate the posterior distributions. An interesting result shown is that the Dirichlet process prior is not updated in the case of the dependent elliptical model. Furthermore, an analysis of a real data set is reported to illustrate the usefulness of our approach, in dealing with outliers. Finally, semiparametric proposed models and parametric normal model are compared, graphically with the posterior distribution density of the coefficients.     

Higher derivatives estimate for the 3D Navier–Stokes equation

In this article, a nonlinear family of spaces, based on the energy dissipation, is introduced. This family bridges an energy space (containing weak solutions to Navier–Stokes equation) to a critical space (invariant through the canonical scaling of the Navier–Stokes equation). This family is used to get uniform estimates on higher derivatives to solutions to the 3D Navier–Stokes equations. Those estimates are uniform, up to the possible blowing-up time. The proof uses blow-up techniques. Estimates can be obtained by this means thanks to the galilean invariance of the transport part of the equation.