Determination of six metals in galician red wines (in northwestern Spain) by capillary electrophoresis

A simple technique is described for the routine simultaneous capillary electrophoretic determination of 6 cations in wine. Separation was achieved on a fused silica capillary column with a UV-Cat-1, alpha-hydroxysobutyric acid and 18-crown-6-ether buffer at pH 4.5 and indirect UV detection at 214 nm. The content of magnesium, sodium, potassium, calcium, manganese, and lithium was determined. The method is quantitative, with recoveries in the 92-102% range, and linear over more than one order of magnitude. The precision is better than 2.5-3.4%. The method is sensible, with detection limits between 0.01 and 0.06 mg/L. Twenty-five red wines with a Certified Brand of Origin from Galicia (north-western Spain) were analyzed by the proposed method. Various wines showed very similar electrophoretic profiles, but significant quantitative differences were observed.     

A Comparative Study of Electrochemical Reduction of 4‐Nitrophenyl Covalently Grafted on Gold and Carbon

4‐Nitrophenyl layers were grafted on gold and glassy carbon surfaces by electrochemical reductive adsorption of the corresponding diazonium salt. Electrochemical conversion efficiencies of 4‐nitrophenyl moieties to 4‐aminophenyl moieties on gold versus on glassy carbon in a protic medium were investigated using X‐ray photoelectron spectroscopy (XPS). In total contrast to all previous comparative studies showing greater electrochemical reactivity of aryl diazonium salt‐derived layers on gold than on glassy carbon, a much lower rate of conversion to 4‐aminophenyl was observed on gold than on glassy carbon by both cyclic voltammetry (CV) and chronoamperometry (CA) methods. The lower electron transfer rate during conversion observed on gold versus glassy carbon was proposed to be due to a mechanism related to the molecular structure rearrangement of 4‐nitrophenyl during the process on glassy carbon. However, whilst complete conversion of 4‐nitrophenyl to 4‐aminophenyl on gold by chronoamperometry was achieved, on glassy carbon complete reduction could not be achieved under the same conditions.     

Structural and functional diversity of glutaredoxins in yeast

Glutaredoxins are defined as thiol disulfide oxidoreductases that reduce disulfide bonds employing reduced glutathione as electron donor. They constitute a complex family of proteins with a diversity of enzymatic and functional properties. Thus, dithiol glutaredoxins are able to reduce disulfide bonds and deglutathionylate mixed disulfides between glutathione and cysteine protein residues. They could act regulating the redox state of sulfhydryl residues of specific proteins, while thioredoxins (another family of thiol disulfide oxidoreductases which employ NADPH as electron donor) would be the general sulfhydryl reductants. Some dithiol glutaredoxins such as human Grx2 form dimers bridged by one iron-sulfur cluster, which acts as a sensor of oxidative stress, therefore regulating the activity of the glutaredoxin. The ability to interact with iron-sulfur clusters as ligands is also characteristic of monothiol glutaredoxins with a CGFS-type active site. These do not display thiol oxidoreductase activity, but have roles in iron homeostasis. The three members of this subfamily in Saccharomyces cerevisiae participate in the synthesis of the iron-sulfur clusters in mitochondria (Grx5), or in signalling the iron status inside the cell for regulation of iron uptake and intracellular iron relocalization (Grx3 and Grx4). Such a role in iron metabolism seems to be evolutionary conserved. Fungal cells also contain membrane-associated glutaredoxins structurally and enzymatically similar to dithiol glutaredoxins, which may act as redox regulators at the early stages of the protein secretory machinery.     

The role of MAPK signal transduction pathways in the response to oxidative stress in the fungal pathogen Candida albicans: implications in virulence

In recent years, Mitogen-Activated Protein Kinase (MAPK) pathways have emerged as major regulators of cellular physiology. In the fungal pathogen Candida albicans, three different MAPK pathways have been characterized in the last years. The HOG pathway is mainly a stress response pathway that is activated in response to osmotic and oxidative stress and also participates regulating other pathways. The SVG pathway (or mediated by the Cek1 MAPK) is involved in cell wall formation under vegetative and filamentous growth, while the Mkc1-mediated pathway is involved in cell wall integrity. Oxidative stress is one of the types of stress that every fungal cell has to face during colonization of the host, where the cell encounters both hypoxia niches (i.e. gut) and high concentrations of reactive oxygen species (upon challenge with immune cells). Two pathways have been shown to be activated in response to oxidative stress: the HOG pathway and the MKC1-mediated pathway while the third, the Cek1 pathway is deactivated. The timing, kinetics, stimuli and functional responses generated upon oxidative stress differ among them; however, they have essential functional consequences that severely influence pathogenesis. MAPK pathways are, therefore, valuable targets to be explored in antifungal research.     

Selective synthesis of mono- and distannylpyridines from chloropyridinols via an SRN1 mechanism

A selective two-step synthesis of either mono- or distannylated pyridines from commercially available pyridinols, involving its conversion to the corresponding diethyl pyridyl phosphates (pyDEP) followed by the reaction with Me₃SnNa in liquid ammonia, is described.The results obtained clearly indicate that the reactions proceed through an unimolecular radical nucleophilic substitution mechanism (S_RN1) with intermediacy of a monosubstitution product.     

UV-MALDI-TOF mass spectrometry analysis of heparin oligosaccharides obtained by nitrous acid controlled degradation and high performance anion exchange chromatography

Nitrous acid degradation of heparin followed by high-performance anion-exchange chromatography (HPAEC) separation and ultraviolet matrix assisted laser desorption/ionization time-of-flight (UV-MALDI-TOF) analysis led to the structural determination of six sulfated oligosaccharides. Three different matrices (α-cyano-4-hydroxycinnamic acid (CHCA), nor-harmane, and dihydroxybenzoic acid (DHB)) have been used, and the complementary results obtained allowed in most cases to assign the position of sulfate groups. Based on the different cleavages produced on the purified oligosaccharides in source during the MS analysis by the use of the different matrices, this approach provides a new tool for structural analysis.     

Feasibility of electron impact and electron capture negative ionisation mass spectrometry for the trace determination of tri- to deca-brominated diphenyl ethers in human samples

The applicability of two different MS ionisation modes (EI and ECNI) for the determination of PBDEs at low-trace levels in small-size (up to 1 mL) human samples was compared. The instrumental precision, expressed as R.S.D., obtained for both ionisation modes was similar and lower than 6% (repeatability) and 12% (intermediate precision) for all congeners investigated, except PBDE 209. The LODs obtained when using the ECNI-MS operation mode (6-507 fg) were lower than those found in EI-MS experiments (9 and 10,909 fg), mainly for those congeners with a high bromination degree, i.e., hepta- to deca-BDEs. The selectivity of the ECNI-MS method proposed in the present work was improved by using two ions of the [M−H_xBr_y]⁻ cluster as both qualifier and quantifier ions. For the final validation of the methods, serum and breast milk samples from two different inter-laboratory exercises were analysed. A good agreement was found between the results obtained using the proposed methods and the results provided by the different inter-laboratory organisations, but only ECNI-MS provided the low-LODs necessary for the quantification of high brominated congeners (mainly, PBDEs 196, 197 and 209) at low concentration levels in small-size human samples. Finally, the ECNI-MS method was applied to real-life samples obtained from the Spanish population and the preliminary results obtained were in the same range as those found in other European and Asian regions and lower than the concentrations reported in USA populations.