GPx-Like activity of selenides and selenoxides: experimental evidence for the involvement of hydroxy perhydroxy selenane as the active species

The reaction mechanism of the GPx-like oxidation of PhSH with H(2)O(2) catalyzed by selenoxides proceeds via formation of the hydroxy perhydroxy selenane, which is a stronger oxidizing agent than selenoxide. A hydroxy perhydroxy selenane intermediate was observed by electrospray ionization mass spectrometry and (77)Se NMR spectroscopy in reactions of selenoxide 8 with H(2)O(2).The initial velocity of oxidation of PhSH by H(2)O(2) with selenoxide 8 is 4 orders of magnitude higher than that of 8 without peroxide. Selenoxide 8 is not reduced to selenide 6 by PhSH in the presence of H(2)O(2). While electronic substituent effects have minimal impact on the catalytic performance of selenoxides, chelating groups increase the rate of catalysis.     

31P NMR assessment of the phosvitin-iron complex in mayonnaise

Lipid oxidation is the main reason for the limited shelf life of mayonnaise. One of the main catalysts of this process is iron, which is introduced in its ferric (Fe(III)) form via phosvitin, an egg yolk phosphoprotein rich in phosphoserines. The binding of Fe(III) to phosvitin and its ability to establish a redox couple with Fe(II) is believed to determine the oxidation rate of unsaturated lipids. In this work, a ³¹P NMR based method was developed to quantify loading of phosvitin with Fe(III) and its reductive release. Both features could be quantified in model phosvitin solutions by exploiting the paramagnetic broadening of ³¹P NMR signal of phosphoserine residues by Fe(III). This method was then successfully applied to quantify the phosvitin-Fe(III) loading in mayonnaise water phase by liquid NMR, whereas ³¹P NMR MAS could only provide a qualitative measure. The ³¹P NMR method showed a direct relation between loading of the Fe(III)-phosvitin complex and lipid oxidation.     

Dephosphorylation reactions with deferoxamine, a potential chemical nuclease

We report a detailed kinetic and mechanistic study of the reaction of a widely used therapeutic agent, deferoxamine (DFO), which contains three nucleophilic hydroxamate groups, with the model phosphate diester bis-2,4-dinitrophenylphosphate BDNPP. We clarify the mechanism by detecting important phosphorylated intermediates in the model reaction and show that the mechanism can be extended to the reaction with DNA. The effectiveness of DFO in cleaving DNA was examined over a range of pH in the absence and presence of a biologically available metal (Zn(2+)). The results inform and complement ongoing studies involving DFO, which can act as a powerful nucleophile toward DNA and other targets susceptible to nucleophilic attack.     

Dispersive liquid–liquid microextraction based on solidification of floating organic drop combined with field‐amplified sample injection in capillary electrophoresis for the determination of beta(2)‐agonists in bovine urine

Dispersive liquid–liquid microextraction based on solidification of floating organic drop (DLLME–SFO) was for the first time combined with field‐amplified sample injection (FASI) in CE to determine four β₂‐agonists (cimbuterol, clenbuterol, mabuterol, and mapenterol) in bovine urine. Optimum BGE consisted of 20 mM borate buffer and 0.1 mM SDS. Using salting‐out extraction, β₂‐agonists were extracted into ACN that was then used as the disperser solvent in DLLME–SFO. Optimum DLLME–SFO conditions were: 1.0 mL ACN, 50 μL 1‐undecanol (extraction solvent), total extraction time 1.5 min, no salt addition. Back extraction into an aqueous solution (pH 2.0) facilitated direct injection of β₂‐agonists into CE. Compared to conventional CZE, DLLME–SFO–FASI–CE achieved sensitivity enhancement factors of 41–1046 resulting in LODs in the range of 1.80–37.0 μg L^?1. Linear dynamic ranges of 0.15–10.0 mg L^?1 for cimbuterol and 15–1000 μg L^?1 for the other analytes were obtained with coefficients of determination (R²) ≥ 0.9901 and RSD% ≤5.5 (n = 5). Finally, the applicability of the proposed method was successfully confirmed by determination of the four β₂‐agonists in spiked bovine urine samples and accuracy higher than 96.0% was obtained.     

Photocatalytic Hydrogen Evolution by Oleic Acid‐Capped CdS,CdSe, and CdS0.75Se0.25 Alloy Nanocrystals

Photocatalytic generation of hydrogen by using oleic acid‐capped CdS, CdSe, and CdS_0.75Se_0.25 alloy nanocrystals (quantum dots) has been investigated under visible‐light irradiation by employing Na₂S and Na₂SO₃ as hole scavengers. Highly photostable CdS_0.75Se_0.25 alloy nanocrystals gave the highest hydrogen evolution rate (1466 μmol h^?1 g^?1), which was about three times higher than that of CdS and seven times higher than that of CdSe.     

半胱氨酸在碳钢与硫酸界面的缓蚀行为

Interfacial behavior of cysteine (Cys) between mild steel and sulfuric acid solution as a corrosion inhibitor has been studied with electrochemical AC (alternating current) and DC (direct current) techniques at (25.0±0.1) ℃. The AC impedance results were evaluated using equivalent circuits in which a constant phase element (CPE) has been replaced with double layer capacitance (Cdl) to represent the frequency distribution of experimental data. Changes in impedance parameters (charge transfer resistance and double layer capacitance) indicated that cysteine molecules acted by accumulating at the metal/solution interface. The fractional coverage of the metal surface (θ) was determined using AC impedance results and it was found that the adsorption of cysteine on the mild steel surface followed a Langmuir isothermmodel with a standard free energy of adsorption (⊿G0ads) of -35.1 kJ·mol-1.  To clarify the type of interaction between mild steel surface and cysteine molecules with a molecular orbital approach, electronic properties, such as, the highest occupied molecular orbital (HOMO) energy, the lowest unoccupied molecular orbital (LUMO) energy, and the frontier molecular orbital coefficients have been calculated. Energy gaps for the interaction of mild steel surface and cysteine molecules (ELUMOFe-EHOMOCys and ELUMOCys-EHOMOFe) were used to determine whether cysteine molecules acted as electron donors or electron acceptors when they interacted with the mild steel surface. The local reactivity was evaluated through the condensed Fukui indices. Theoretical calculations were carried out using the density functional theory (DFT) at B3LYP level with the 6-311++G(d,p) basis set for all atoms by Gaussian 03W program.     

1, 1, 1-Trichloropropanone: A Mild,Selective Acetylating Agent

The use of the title compound in the acetylation of primary and secondary amines i s described.     

Interaction of gold nanoparticles with mitochondria

Mitochondrion is one of the most important organelles in cells with several vital responsibilities. The consequence of a deficiency in the function of mitochondrion could result with the wide range of diseases and disorders. In this study, we investigated the feasibility of utilizing surface-enhanced Raman scattering (SERS) to understand the mode of interaction of gold nanoparticles (GNPs) with mitochondria. The living lung cancer cells and the isolated mitochondria from these cells were treated with gold colloidal suspension for SERS experiments. The AFM images of the mitochondria confirmed that the treatment did not cause substantial damage to mitochondria. The localization of GNPs in living cells is investigated with confocal microscopy and found that GNPs form aggregates in the cytosol away from the mitochondria. However, SERS spectra obtained from isolated mitochondria and living cells indicate that GNPs escaped from the endosomes or entered into the living cell through another route may be in contact with mitochondria in a living cell. The findings of this study indicate that SERS can be used for mitochondrial research.