Direct electron paramagnetic resonance monitoring of the peptide synthesis coupling reaction in polymeric support

This work demonstrates, for the first time. a time-resolved electron paramagnetic resonance (EPR) monitoring of a chemical reaction occurring in a polymeric structure. The progress of the coupling of a N-alpha-tert-butyloxycarbonyl-2.2.6.6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (Boc-TOAC) spin probe to a model peptide-resin was followed through EPR spectra. Progressive line broadening of EPR peaks was observed, indicative of an increased population of immobilized spin probe molecules attached to the solid support. The time for spectral stabilization of this process coincided with that determined in a previous Coupling study. thereby validating this in situ quantitative monitoring of the reaction. In addition, the influence of polymer swelling degree and solvent viscosity, as well as of the steric hindrance within beads. on the rate of coupling reaction was also addressed. A deeper evaluation of the latter effect was possible by determining unusual polymer parameters such as the average site-site distance and site-concentration within resin beads in each solvent system. (c) 2006 Elsevier Ltd. All rights reserved.

An electrode and use thereof

The application relates to an electrode for use in the electrochemical detection of a target species, wherein the electrode has a planar surface disposed on which are probe molecules that are capable of binding selectively to the target species, wherein the electrode, prior to binding of the probe molecules with the target species, has an electron transfer resistance per area of the electrode of from 10 megaohms cm-2 to 95 megaohms cm-2.

Electrocatalytic activity under oscillatory regime: The electro-oxidation of formic acid on ordered Pt3Sn intermetallic phase

Despite the considerable progress in the understanding of the mechanistic aspects of the oscillatory electro-oxidation of C1 molecules, there are apparently no systematic studies concerning the impact of surface modifiers on the oscillation dynamics. Herein we communicate on the oscillatory electro-oxidation of formic acid on ordered Pt3Sn intermetallic phase, and compare the results with those obtained on a polycrystalline platinum electrode. Overall, the obtained results were very reproducible, robust and allowed a detailed analysis on the correlation between the catalytic activity and the oscillation dynamics. The presence of Sn in the intermetallic electrode promotes drastic effects on the oscillatory dynamics. The decrease in the mean electrode potential and in the oscillation frequency, as well as the pronounced increase in the number oscillations (and also in the oscillation time), was discussed in connection with the substantial catalytic enhancement of the Pt3Sn towards the electro-oxidation of formic acid. The self-organized potential oscillations were used to probe the electrocatalytic activity of the Pt3Sn electrode and compare it with that for polycrystalline Pt. The presence of Sn resulted in a significant decrease (2-11 times, depending on the applied current) of the rate of surface poisoning. © 2012 Elsevier B.V.

A theoretical study on the gas phase reactions of the anions NbO3-, NbO5-, and NbO2(0H)(2)(-) with H2O and O-2

The potential energy surfaces at the singlet (s) and the triplet (t) electronic states associated with the gas-phase ion/molecule reactions of NbO3-, NbO5-, and NbO2(OH)(2)(-) with H2O and O-2 have been investigated by means of DFT calculations at the B3LYP level. An analysis of the results points out that the most favorable reactive channel comprises s-NbO3- reacting with H2O to give an ion-molecule complex s-NbO3(H2O)without a barrier. From this minima, an intramolecular hydrogen transfer takes place between the incoming water molecule and an oxygen atom of the NbO3- fragment to render the most stable minimum, s-NbO2(OH)(2)(-). This oxyhydroxide system reacts with O-2 along a barrierless process to obtain the triplet t-NbO4(OH)(2)(-)-A intermediate, and the crossing point, CP1, between s and t electronic states has been characterized. The next step is the hydrogen-transfer process between the oxygen atom of a hydroxyl group and the one adjacent oxygen atom to render a minimum with the two OH groups near each other, t-NbO4(OH)(2)(-)-B. From this point, the last hydrogen migration takes place, to obtain the product complex, t-NbO5(H2O)(-), that can be connected with the singlet separated products, s-NbO5- and H2O. Therefore, a second crossing point, CP2, has been localized. The nature of the chemical bonding of the key minima (NbO3-, NbO2(OH)(2)(-), NbO4(OH)(2)(-)-B, and NbO5-) in both electronic states of the reaction and an interaction with O-2 has been studied by topological analysis of Becke-Edgecombe electron-localization function (ELF) and atoms-in-molecules (AIM) methodology. The niobium-oxygen interactions are characterized as unshared-electron (ionic) interactions and some oxygen-oxygen interactions as protocovalent bonds.

Rhamnolipids and PHAs: Recent reports on Pseudomonas-derived molecules of increasing industrial interest

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

An ultraviolet photoacoustic spectroscopy study of the interaction between Lys49-phospholipase A(2) and amphiphilic molecules

We have used near ultraviolet photoacoustic spectroscopy (PAS) over the wavelength range 240-320 nm to investigate the complex formed between the homodimeric bothropstoxin-I, a lysine-49-phospholipase A(2) from the venom of Bothrops jararacussu (BthTx-I), with the anionic amphiphile sodium dodecyl sulfate (SDS). At molar ratios > 10, the complex developed a significant light scatter, accompanied by a decrease in the intrinsic tryptophan fluorescence intensity emission (ITFE) of the protein, and an increase in the near UV-PAS signal. Difference PAS spectroscopy at SDS/BthTx-I ratios < 8 were limited to the region 280-290 nm, suggesting initial SDS binding to the tryptophan 77 located at the dimer interface. At SDS/BthTx-I ratios > 10, the intensity between 260 and 320 nm increases demonstrating that the more widespread tyrosine and phenylalanine residues contribute to the SDS/BthTx-I interaction. PAS signal phase changes at wavelengths specific for each aromatic residue suggest that the Trp77 becomes more buried on SDS binding, and that protein structural changes and dehydration may alter the microenvironments of Tyr and Phe residues. These results demonstrate the potential of near UV-PAS for the investigation of membrane proteins/detergent complexes in which light scatter is significant. (c) 2006 Elsevier B.V. All rights reserved.

The effect of sodium chloride on the formation of W/O microemulsions in soy bean oil/surfactant/water systems and the solubilization of small hydrophilic molecules

Partial pseudoternary phase diagrams were constructed for soy bean oil (SBO)/surfactant/NaCl aqueous solution systems, at 25 degrees C, using the anionic sodium bis(2-ethylhexyl) sulfosuccinate (ACT) and zwiterionic phosphatidylcholine (PC) or mixtures of these surfactants. The isotropic single phase of water-in-oil (W/O) microemulsions (MEs) is shown in the phase diagram and their viscosity reported. ME samples containing small amount of surfactant exhibit slightly higher viscosity than pure SBO, and were used in the solubilization of small water soluble molecules. NaCl enhances the area of the ME phase and MEs with different surfactant composition exhibit different induction time as obtained from tests of oxidative stability, and so are the MEs enriched with ascorbic acid, folic acid and FeSO4, with the latter exhibiting lower stability. The so prepared enriched soy bean oil has potential application in food industry since the surfactants are food grade. (C) 2007 Elsevier B.V. All rights reserved.

Hydrothermal syntheses of ETS-10 like vanadosilicates using chiral organic molecules. Part I

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Phase Diagrams of the Aqueous Two-Phase Systems of Poly(ethylene glycol)/Sodium Polyacrylate/Salts

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A fluorescence probe study of gemini surfactants in aqueous solution: a comparison between n-2-n and n-6-n series of the alkanediyl-a,w-bis (dimethylalkylammonium bromides)

Two series of alkanediyl-a,w-bis (dimethylalkylammonium bromide (n-2-n and n-6-n; n=8, 10,12, and 16) have been synthesized and their micelles properties studied in aqueous solution using pyrene, pyrenecarboxaldehyde (PCA) and 1,8 anilinonaphtalene sulfonic acid sodium salt (ANS) as fluorescent probes. The micelles from these surfactants have been characterized on the basis of the information provided by micelle-solubilized fluorescent probes. The obtained results indicated that the surfactant concentration at which a marked decrease in l max parameter of pyrenecarboxaldehyde (PCA) occurs corresponds to the CMC determined by conductimetric measurements. Changes in the emission spectra of ANS and PCA observed in the submicellar range for both surfactants series (n-2-n and n-6-n) were interpreted as formation of pre-aggregates. It was found that the dimeric surfactants with long spacer (s= 6) form more hydrated aggregates when compared with those formed by the n-2-n and CnTAB surfactants series. This was attributed to a more difficult packing of n-6-n surfactant molecules to form micelles.

Electron transfer by singlet excited state of porphyn and electron acceptor affinity in rigid medium: photoacoustic phase angle analysis

A espectroscopia fotoacústica obtém informações sobre amplitude e fase, da resposta de um sistema submetido a excitação por luz. Este artigo apresenta estudos do ângulo de fase no processo de transfereência de elétrons entre octaetilporfirina (OEP) e derivados de quinona ambos dispersos em uma matriz polimérica. Observou-se uma tendência no comportamento da fase para valores menores na região espectral próximo de 620 nm. Enquanto que para comprimentos de onda menores este efeito não foi apresentado. Estas medidas sugerem que a transferência de elétrons para o aceitador ocorreu com a participação do estado singleto excitado da octaetilporfirina.

Photo luminescence: A probe for short, medium and long-range self-organization order in ZrTiO4 oxide

Photoluminescent disordered ZrTiO4 powders were obtained by the polymeric precursor soft-chemical method. This oxide system (ordered and disordered) was characterized by photoluminescence, Raman spectroscopy, X-ray diffraction, differential scanning calorimetry and UV vis absorption experiments. The UV absorption tail formation in the disordered oxides was related to the diminution of optical band gap. In the disordered phase, this oxide displayed broad band photoluminescence caused by change in coordination number of titanium and zirconium with oxygen atoms. The gap decreased from 3.09 eV in crystalline oxide to 2.16 eV in disordered oxide. The crystalline oxide presented an orthorhombic alpha-PbO2-type structure in which Zr4+ and Ti4+ were randomly distributed in octahedral coordination polyhedra with oxygen atoms. The amorphous-crystalline transition occurred at almost 700 degrees C, at which point the photoluminescence vanished. The Raman peak at close to 80-200 cm(-1) indicated the presence of locally ordered Ti-O-n and Zr-O-n polyhedra in disordered photoluminescent oxides. (c) 2006 Elsevier B.V. All rights reserved.

A 4.2 kDa synthetic peptide as a potential probe to evaluate the antibacterial activity of coumarin drugs

The coumarin antibiotics are potent inhibitors of DNA replication whose target is the enzyme DNA gyrase, an ATP-dependent bacterial type II topoisomerase. The coumarin drugs inhibit gyrase action by competitive binding to the ATP-binding site of DNA gyrase B protein. The production of new biologically active products has stimulated additional studies on coumarin-gyrase interactions. In this regard, a 4.2 kDa peptide mimic of DNA gyrase B protein from Escherichia coli has been designed and synthesized. The peptide sequence includes the natural fragment 131-146 (coumarin resistance-determining region) and a segment containing the gyrase-DNA interaction region (positions 753-770). The peptide mimic binds to novobiocin (K-a = 1.4 +/- 0.3 x 10(5) m(-1)), plasmid (K-a = 1.6 +/- 0.5 x 10(6) m(-1)) and ATP (K-a = 1.9 f 0.4 x 10(3) m(-1)), results previously found with the intact B protein. on the other hand, the binding to novobiocin was reduced when a mutation of Arg-136 to Leu-136 was introduced, a change previously found in the DNA gyrase B protein from several coumarin-resistant clinical isolates of Escherichia coLi. In contrast, the binding to plasmid and to ATP was not altered. These results suggest that synthetic peptides designed in a similar way to that described here could be used as mimics of DNA gyrase in studies which seek a better understanding of the ATP, as well as coumarin, binding to the gyrase and also the mechanism of action of this class of antibacterial drugs. Copyright (C) 2004 European Peptide Society and John Wiley Sons, Ltd.

Thermal diffusivity analysis of doped poly(methyl-methacrylate) with electron donor and acceptor molecules

A computer-assisted method for analysing photoacoustic spectra has been developed in the Windows(TM) environment with the use of an easy graphical interface, the computer simulation was carried out with the aim of using the entire expression of the Rosencwaig-Gersho theory, thus permitting multiple applications. The simulation was applied to a system that mimics the electron transfer process in which the concentration of octaethylporphin donor molecules was constant whereas the concentration of duroquinone and 2,3-dichloro-5,6-dicyano-1, l-benzoquinone acceptor molecules varied. The increment of the acceptor concentration influenced the photoacoustic amplitude and phase signals. In the phase signal a significant shift to smaller values was observed, denoting a faster heat generation. The analysis of the photoacoustic signal enabled the determination of the thermal diffusivity, the result obtained through the simulation was about (7 +/- 1) x 10(-7) m(2) s(-1) indicating that changes in the photoacoustic phase signals were due to the electron transfer process rather than changes in the thermal properties of the sample.

Eu3+ as a spectroscopic probe in phosphors based on spherical fine particle gadolinium compounds

This work reports on the luminescence spectroscopy sensitivity in the determination of the phase purity in gadolinium compounds using Eu3+ as a probe. Cubic Gd2O3 and hexagonal Gd2O2S doped with Eu3+ spherical fine particles were obtained from doped gadolinium basic carbonates with morphological control and were also characterized by IR and XRD. Doped samples present Eu3+ characteristic transitions, with specific energy positions related to each phase. Emission and excitation spectra patterns were established for oxide and oxysulfide compounds, then oxysulfate and oxide impurities generated during oxysulfide preparation were monitored. From emission spectra some experimental intensity parameters were also calculated. All spectroscopic results reflect the presence or not of impurities in all compounds. (C) 2001 Elsevier B.V. Ltd. All rights reserved.