Hadronic corrections to QCD sum rules and light quark masses

A parametrization of theJ ^p =0^? hadronic continuum, in the framework of Extended PCAC, is discussed with emphasis on finite-width effects and on the constraints imposed by the correct threshold behavior of the pion spectral function. As an application light quark masses are calculated using both Hilbert and Laplace transform QCD sum rules. The results for the runing quark masses are: \((\bar m_u + \bar m_d )|_{1 Gev} = 16 \pm 2 MeV,(\bar m_u + \bar m_s )|_{1 Gev} = 199 \pm 27 MeV\) , and a ratio \(R \equiv 2(\bar m_u + \bar m_s )/(\bar m_u + \bar m_d )_{1 Gev} = 25 \pm 4\) .     

Photoprotective properties of a hydrophilic extract of the fern Polypodium leucotomos on human skin cells

The effect of a hydrophilic extract of the fern Polypodium leucotomos (PLE) has been investigated in terms of photoprotection against UV-induced cell damage. PLE efficiently preserved human fibroblast survival and restored their proliferative capability when the cells were exposed to UVA light. This effect was specific and dose-dependent. Photoprotection was not restricted to fibroblasts, as demonstrated by its effect on survival and proliferation of the human keratinocyte cell line HaCat. Finally, treatment of the cells with PLE prevented UV-induced morphological changes in human fibroblasts, namely disorganisation of F-actin-based cytoskeletal structures, coalescence of the tubulin cytoskeleton and mislocalization of adhesion molecules such as cadherins and integrins. Our in vitro results demonstrate the photoprotective effect of PLE on human cells and support its use in the preventive treatment of sunburning and skin pathologies associated with UV-mediated damage.     

Voltammetric analysis of iron oxide pigments

Eighteen earthy and four pure synthetic pigments containing alpha-Fe2O3 (hematite), alpha-FeOOH (goethite) and poorly crystalline Fe and Mn oxide species were analyzed by voltammetry of microparticles. Three natural samples were subjected to an interlaboratory test to evaluate the reproducibility of the voltammetric peak potentials and peak shapes. The results confirmed that linear-sweep voltammetry is able to distinguish between poorly crystalline, ferrihydrite-like oxides and well-crystalline hematite and goethite and to detect XRD-amorphous Mn(III,IV) oxides via the peak occurrence. Voltammetry is further able to distinguish between pigments containing well-crystalline goethite (according to its structural features) and hematite (according to its particle size). The microsamples of primers from two baroque paintings were also analyzed by XRD and voltammetry and shown to be analogous to common clayey ochres.     

Adsorption of differently charged forms of horseradish peroxidase on metal electrodes of different nature: effect of surface charges

The adsorption and bioelectrocatalytical activity in the reaction of H(2)O(2) reduction of two forms of horseradish peroxidase (HRP) offering different surface charges at pH 6.0 were studied on gold and silver electrodes. Positively charged HRP was assessed at pH 6.0 for the case of native HRP (isoenzyme C, pI=8.8), and negatively charged HRP for the case of native HRP exposed to previous oxidation of carbohydrate residues and further introduction of sulfonate groups (pI=5.0). Under oxidative pretreatment, the gold electrode surface was considered to be negatively charged. Data on the direct immobilisation of HRPs on the bare gold surfaces were estimated with quartz crystal microbalance and data on bioelectrocatalytical activity of peroxidases on gold and silver electrodes were obtained in the course of direct and mediated amperometric detection of H(2)O(2). The presented results demonstrate that the surface charges of both the enzyme and the electrode play a dominant role in the immobilisation and, thereby, in the efficiency of the bioelectrocatalytical processes.     

Compounds of molybdenum(VI) with aspartic acid: A spectrophotometric and potentiometric study of the formation and interconversion equilibria in aqueous solution

Summary Addition of Na₂MoO₄ to an excess of aspartic acid (AspH₂) can produce any of four different complexes depending on the pH, namely [MoO₃(Asp)]^2–, [Mo₂O₅(Asp)₂]^2–, [Mo₂O₄(OH)(Asp)₂]^– and [Mo₂O₄(Asp)₂]. The ranges of formation of these species with pH, the number of equivalents of acid necessary for their formation, and their stoichiometries, condensation degrees and stability constants, have been calculated by potentiometric and spectrophotometric techniques. The aspartic acid acts as a tridentate ligand in all cases.     

Tandem enyne metathesis-Diels-Alder reaction for construction of natural product frameworks

Enynes connected through aromatic rings are used as substrates for metathesis reactions. The reactivity of three ruthenium carbene complexes is compared. The resulting 1,3-dienes are suitable precursors of polycyclic structures via a Diels-Alder process. Some domino RCM-Diels-Alder reactions are performed, suggesting a possible beneficial effect of the ruthenium catalyst in the cycloaddition process. Other examples require Lewis acid cocatalyst. When applied to aromatic ynamines or enamines, a new synthesis of vinylindoles is achieved. Monitorization of several metathesis reactions with NMR shows the different behavior for ruthenium catalysts. New carbenic species are detected in some reactions with an important dependence on the solvent used.     

H‐Point Standard Addition Method Applied to Voltammetry of Microparticles. Quantitation of Dyes in Pictorial Samples

A solid‐state electrochemical application of the H‐point standard addition method (HPSAM) for quantifying two electroactive compounds, A, B, that produce strongly overlapped voltammetric peaks is described. It is based on peak current measurement in square‐wave voltammograms recorded for solid samples containing a reference compound R, upon additions of a A‐ (or B‐) containing standard compound. The method allows to the determination of the mass fraction of A and B by applying the H‐point standard addition method to solid state voltammetry. The quotients between the currents measured at two selected potentials and the peak current of R vary linearly with the mass ratio of the added standard and the reference compound, thus providing an electrochemical method for determining the content of A and B in the sample avoiding matrix effects. The method is applied to the simultaneous determination of alizarin and purpurin in madder pigments and pictorial specimens using morin as a reference material.     

Catechol releases iron(III) from ferritin by direct chelation without iron(II) production

It has been traditionally considered that catechols release iron from ferritin by reduction to iron(II), which diffuses through the ferritin channels into the intracellular milieu where it participates in the Fenton reaction, producing highly toxic hydroxyl radicals. However, in the present work we have proved that the mechanism of the release of iron from ferritin by catechol does not take place by iron(II) reduction but by direct iron(III) chelation and therefore without iron(II) production. A possible extension of these findings to other catechols is discussed on the basis of the stability with respect to the internal redox reaction of the iron(III)-catechol complexes.