Sensing of 2,4-dichlorophenoxyacetic acid by surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) spectra of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) was obtained by employing a bi-layer gold substrate, assembled by the reduction of Au(III) over gold-seeded nanoparticles immobilized on functionalized glass substrates. The SERS signal was linear with the logarithm of the solution concentrations between 1.0 x 10(-7) mol L(-1) and 1.0 x 10(-3) mol L(-1), indicating that the bi-layer gold substrate affords a significant dynamic range for SERS, providing an excellent analytical response within this concentration range, and revealing the high sensitivity of the gold surface towards such analyte. In addition, using the same gold substrate, a similar calibration curve was obtained for crystal-violet (CV), and it was possible to identify the concentration limit corresponding to the transition from the average SERS to the nonlinear SERS response. (C) 2010 Elsevier B.V. All rights reserved.

The role of HBF(4) in electro-catalysis: Arsenic contamination and anion adsorption

We present in this work a comprehensive investigation of the role played by dissolved tetrafluoroboric acid on the electrochemical response of a polycrystalline platinum electrode in acidic media. HBF(4) from two different suppliers was employed and characterized in terms of the amount of arsenic contamination by Inductively Coupled Plasma-Optical Emission Spectroscopy. The effect of different amounts of HBF(4) on the voltammetric profile of the Pt vertical bar HClO(4)(aq) interface was investigated by means of electrochemical quartz crystal nanobalance (EQCN). Despite the comparable cyclic voltammograms, the presence of arsenic in one of the two HBF(4) used resulted in dramatic variations in the mass change profile, which evidences the deposition/dissolution of arsenic prior to the surface oxidation. For the arsenic-free HBF(4), its effect on the mass change profile was mainly associated to anion adsorption. The impact of dissolved HBF(4) on the electro-oxidation of formic acid was rationalized in terms of two contributions: current enhancement at low potentials due to the arsenic-assisted formic acid electro-oxidation and inhibition at high potentials due to anion adsorption. (C) 2011 Elsevier B.V. All rights reserved.

Differential kinase requirement for enhancement of Fc gamma R-mediated phagocytosis in alveolar macrophages by leukotriene B(4) vs. D(4)

In alveolar macrophages, leukotriene (IT) B(4) and cysteinyl LTs (LTC(4), LTD(4) and LTE(4)) both enhance Fc gamma receptor (Fc gamma R)-mediated phagocytosis. In the present study we investigated the role of specific PKC isoforms (PKC-alpha and -delta), the MAP kinases p38 and ERK 1/2, and PI3K in mediating the potentiation of Fc gamma R-mediated phagocytosis induced by addition of leukotrienes to the AMs. It was found that exogenously added LTB(4) and LTD(4) both enhanced PKC-delta and -alpha phosphorylation during Fc gamma R engagement. Studies with isoform-selective inhibitors indicated that exogenous LTB(4) effects were dependent on both PKC-alpha and -delta, while LTD(4) effects were exclusively due to PKC-delta activation. Although both exogenous LTB(4) and LTD(4) enhanced p38 and ERK 1/2 activation, LTB(4) required only ERK 1/2, while LTD(4) required only p38 activation. Activation by both LTs was dependent on PI3K activation. Effects of endogenous LTs on kinase activation were also investigated using selective LT receptor antagonists. Endogenous LTB(4) contributed to Fc gamma R-mediated activation of PKC-alpha, ERK 1/2 and PI3K, while endogenous cysLTs contributes to activation of PKC-delta, p38 and PI3K. Taken together, our data show that the capacities of LTB(4) and LTD(4) to enhance Fc gamma R-mediated phagocytosis reflect their differential activation of specific kinase programs. (C) 2008 Elsevier Ltd. All rights reserved.

Regulation of Na(+)/H(+) exchanger NHE3 by glucagon-like peptide 1 receptor agonist exendin-4 in renal proximal tubule cells

Carraro-Lacroix LR, Malnic G, Girardi AC. Regulation of Na(+)/H(+) exchanger NHE3 by glucagon-like peptide 1 receptor agonist exendin-4 in renal proximal tubule cells. Am J Physiol Renal Physiol 297: F1647-F1655, 2009. First published September 23, 2009; doi:10.1152/ajprenal.00082.2009.-The gut incretin hormone glucagon-like peptide 1 (GLP-1) is released in response to ingested nutrients and enhances insulin secretion. In addition to its insulinotropic properties, GLP-1 has been shown to have natriuretic actions paralleled by a diminished proton secretion. We therefore studied the role of the GLP-1 receptor agonist exendin-4 in modulating the activity of Na(+)/H(+) exchanger NHE3 in LLC-PK(1) cells. We found that NHE3-mediated Na(+)-dependent intracellular pH (pH(i)) recovery decreased similar to 50% after 30-min treatment with 1 nM exendin-4. Pharmacological inhibitors and cAMP analogs that selectively activate protein kinase A (PKA) or the exchange protein directly activated by cAMP (EPAC) demonstrated that regulation of NHE3 activity by exendin-4 requires activation of both cAMP downstream effectors. This conclusion was based on the following observations: 1) the PKA antagonist H-89 completely prevented the effect of the PKA activator but only partially blocked the exendin-4-induced NHE3 inhibition; 2) the MEK1/2 inhibitor U-0126 abolished the effect of the EPAC activator but only diminished the exendin-4-induced NHE3 inhibition; 3) combination of H-89 and U-0126 fully prevented the effect of exendin-4 on NHE3; 4) no additive effect in the inhibition of NHE3 activity was observed when exendin-4, PKA, and EPAC activators were used together. Mechanistically, the inhibitory effect of exendin-4 on pHi recovery was associated with an increase of NHE3 phosphorylation. Conversely, this inhibition took place without changes in the surface expression of the transporter. We conclude that GLP-1 receptor agonists modulate sodium homeostasis in the kidney, most likely by affecting NHE3 activity.

Synthesis optimization, structural evolution and optical properties of Y(0.9)Er(0.1)Al(3)(BO(3))(4) nanopowders obtained by soft chemistry methods

This paper describes the structural evolution of Y(0.9)Er(0.1)Al(3)(BO(3))(4) nanopowders using two soft chemistry routes, the sol-gel and the polymeric precursor methods. Differential scanning calorimetry, differential thermal analyses, thermogravimetric analyses, X-ray diffraction, Fourier-transform infrared, and Raman spectroscopy techniques have been used to study the chemical reactions between 700 and 1200 degrees C temperature range. From both methods the Y(0.9)Er(0.1)Al(3)(BO(3))(4) (Er:YAB) solid solution was obtained almost pure when the powdered samples were heat treated at 1150 degrees C. Based on the results, a schematic phase formation diagram of Er:YAB crystalline solid solution was proposed for powders from each method. The Er:YAB solid solution could be optimized by adding a small amount of boron oxide in excess to the Er:YAB nominal composition. The nanoparticles are obtained around 210 nm. Photoluminescence emission spectrum of the Er:YAB nanocrystalline powders was measured on the infrared region and the Stark components of the (4)I(13/2) and (4)I(15/2) levels were determined. Finally, for the first time the Raman spectrum of Y(0.9)Er(0.1)Al(3)(BO(3))(4) crystalline phase is also presented. (C) 2008 Elsevier Masson SAS. All rights reserved.

1,4-Dioxane enhances properties and biocompatibility of polyanionic collagen for tissue engineering applications

Polyanionic collagen obtained from bovine pericardial tissue submitted to alkaline hydrolysis is an acellular matrix with strong potential in tissue engineering. However, increasing the carboxyl content reduces fibril formation and thermal stability compared to the native tissues. In the present work, we propose a chemical protocol based on the association of alkaline hydrolysis with 1,4-dioxane treatment to either attenuate or revert the drastic structural modifications promoted by alkaline treatments. For the characterization of the polyanionic membranes treated with 1,4-dioxane, we found that (1) scanning electron microscopy (SEM) shows a stronger reorientation and aggregation of collagen microfibrils; (2) histological evaluation reveals recovering of the alignment of collagen fibers and reassociation with elastic fibers; (3) differential scanning calorimetry (DSC) shows an increase in thermal stability; and (4) in biocompatibility assays there is a normal attachment, morphology and proliferation associated with high survival of the mouse fibroblast cell line NIH3T3 in reconstituted membranes, which behave as native membranes. Our conclusions reinforce the ability of 1,4-dioxane to enhance the properties of negatively charged polyanionic collagen associated with its potential use as biomaterials for grafting, cationic drug- or cell-delivery systems and for the coating of cardiovascular devices.

Optimization of performances of gelatin/LiBF(4)-based polymer electrolytes by plasticizing effects

Gelatin is a cheap and abundant natural product with very good biodegradation properties and can be used to obtain acetic acid or LiClO(4)-based gel polymer electrolytes (GPEs) with high ionic conductivity and good stability. This article presents results of GPEs obtained by the plasticization of gelatin and addition of LiBF(4), where the optimization of the system was achieved by using a factorial design type 22 with two variables: glycerol and LiBF(4). From this analysis it was stated that the effect of glycerol as a plasticizer on the ionic conductivity results is much more important than the effect obtained by varying the lithium salt content or the effect of the interaction of both variables. Also all the samples were characterized by X-ray diffraction measurements, UV-vis-NIR spectroscopy and scanning electron microscopy (SEM) and impedance spectroscopy. The ionic conductivity results of all analyzed samples as a function of temperature obey predominantly an Arrhenius relationship and the samples are stable up to 160 degrees C. Good conductivity results combined with transparency and good adhesion to the electrodes have shown that gelatin-based GPEs are very promising materials to be used as solid electrolytes in electrochromic devices. (C) 2009 Elsevier Ltd. All rights reserved.