Analysis of sulfated peptides from the skin secretion of the Pachymedusa dacnicolor frog using IMAC-Ga enrichment and high-resolution mass spectrometry

Immobilized metal ion affinity chromatography (IMAC) has been widely used for the enrichment of phosphopeptides, whereas no report exists describing the use of IMAC columns for the enrichment of sulfopeptides. In this study, we used IMAC-Ga microcolumns for the enrichment of sulfopeptides from a complex mixture of peptides, extracted from skin secretions of the Pachymedusa dacnicolor frog. The enriched fraction obtained by IMAC-Ga was analyzed by liquid chromatograpy/electrospray ionization mass spectrometry (LC/ESI-MS) in an Orbitrap XL and by matrix-assisted laser desorption/ionization time-of-flight time-of-flight (MALDI-TOF/TOF) in an ABI 4800 instrument. From this fraction, different sulfated and non-sulfated peptides belonging to the caerulin and bradykinin families were structurally characterized. Other interesting negatively charged groups, such as phosphate adducts of dermaseptins and pyridoxal phosphate attached to a protease inhibitor, were also characterized. Unexpectedly, some dermaseptin antimicrobial peptides were also enriched by IMAC-Ga and a Sauvatine-like peptide was also fully sequenced. Furthermore, neutral loss of sulfated peptides and their fragmentation patterns in the gas phase were also compared using collision-induced dissociation (CID) and high-energy collision dissociation (HCD). Our present study provides evidence that IMAC-Ga enrichment is a fast, useful and promising method for high-throughput analysis of sulfated-peptides, since high-resolution mass spectrometers can be used for this purpose.     

Fast determination of thyroid stimulating hormone in human blood serum without chemical preprocessing by using infrared spectroscopy and least squares support vector machines

The least squares support vector machines (LS-SVM) was used to model infrared spectral data for TSH hormone secreted by thyroid, which regulates the basal metabolic rate. This model was used for direct estimation of the content of TSH in blood serum samples, and the results were comparable with those obtained with the conventional analytical method based on chemoluminescence methodology. Excellent agreement was observed between the conventional method and the newly developed calibration model based in analysis of spectral data with LS-SVM. The latter has clear advantages, because it is fast and requires no reagent once the measurements were done directly in the serum by using a simple mid-infrared spectrometer in the ATR mode. An important advantage observed in this calibration method based on LS-SVM is the remarkable capacity to avoid overfitting in the model-building step, that is, the developed method is highly robust.     

Combination of cysteine- and oligomerization domain-mediated protein immobilization on a surface plasmon resonance (SPR) gold chip surface

Here we report an effective method for protein immobilization on a surface plasmon resonance (SPR) gold chip, describing the combination of cysteine- and oligomerization domain-mediated immobilization of enhanced green fluorescent protein (EGFP) as a model protein for the purpose of orientation-controlled surface density packing. In order to facilitate the oligomerization of EGFP, the dimeric and trimeric constructs derived from GCN4- leucine zipper domain were chosen for multimeric EGFP assembly. For orientation-controlled immobilization of the protein, EGFP modified with cysteine residues showing excellent orientation on a gold chip was used as a starting protein, as previously reported in our earlier study (Anal. Chem., 2007, 79, 2680-2687). Constructs of EGFP with oligomerization domains were genetically engineered, and corresponding fusion proteins were purified, applied to a gold chip, and then analyzed under SPR. The immobilized EGFP density on a gold chip increased according to the states of protein oligomerization, as dimeric and trimeric EGFPs displayed better adsorption capability than monomeric and dimeric forms, respectively. Fluorescence measurement corroborated the SPR results. Taken together, our findings indicated that the combination of cysteine- and oligomerization domain-mediated immobilization of protein could be used in SPR biosensor applications, allowing for an excellent orientation and high surface density simultaneously.     

Innovative synthetical and structural features of new aryltellurenyl iodides

The syntheses and the structural characterization of the compounds [(mes)₂Te–Te(I)mes], (PyH)[mesTeI₃(I₃)] (mes = mesityl = 2,4,6-trimethylphenyl; Py = pyridine), (PyH)₃[dmephTeI₂(I₂)]₂(I₃) (dmeph = 2,6-dimethylphenyl), (PyH)₂[RTeI₄]₂·(CH₃)CO(CH₃)·C₆H₅CH₃ (R = p-tert-butylphenyl) and (PyH)₂[PhTeI₄]₂ (Ph = phenyl) are presented. Some earlier analog preparations are compared and the influence of ortho substituents in the aryl group on the oxidation state of tellurium is discussed, as well as the observed conditions for the formation of poly-iodides chains.     

A simple and green analytical method for determination of glyphosate in commercial formulations and water by diffuse reflectance spectroscopy

This article describes a simple, inexpensive, and environmentally friendly method for the monitoring of glyphosate using diffuse reflectance spectroscopy. The proposed method is based on reflectance measurements of the colored compound produced from the spot test reaction between glyphosate and p-dimethylaminocinnamaldehyde (p-DAC) in acid medium, using a filter paper as solid support. Experimental designs were used to optimize the analytical conditions. All reflectance measurements were carried out at 495 nm. Under optimal conditions, the glyphosate calibration graphs obtained by plotting the optical density of the reflectance signal (AR) against the concentration were linear in the range 50-500 μg mL(-1), with a correlation coefficient of 0.9987. The limit of detection (LOD) for glyphosate was 7.28 μg mL(-1). The technique was successfully applied to the direct determination of glyphosate in commercial formulations, as well as in water samples (river water, pure water and mineral drinking water) after a previous clean-up or pre-concentration step. Recoveries were in the ranges 93.2-102.6% and 91.3-102.9% for the commercial formulations and water samples, respectively.     

Structural properties of PbTiO3 and PbZrxTi1−xO3: A quantum‐chemical study

We investigate the structural and electronic properties of pure and Zr‐doped PbTiO₃ crystals. The nature of atomic relaxation around the Zr impurity is studied through quantum‐chemical simulations based on the Hartree–Fock theory and a periodic large unit cell model adopted within the so‐called intermediate neglect of differential overlap approximation. The most stable defect configurations are predicted for different impurity concentrations. The results obtained are compared with those from other theoretical studies and a number of experimental measurements carried out on this technologically important perovskite‐type crystal. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Thiophene‐cored 2,2‐bis(methylol)propionic acid dendrimers for optical‐power‐limiting applications

The synthesis and characterization of dendron‐coated 2,5‐bis(phenylethynyl)thiophene chromophores are described. The dendrimers were grown divergently on the arylthiophene core with the versatile anhydride of 2,2‐bis(methylol)propionic acid. The arylthiophene core was synthesized with Sonogashira coupling reactions. Structurally well‐defined dendrimers up to the fourth generation were grown, as confirmed by size exclusion chromatography, NMR, and matrix‐assisted laser desorption/ionization time‐of‐flight analysis. The different dendritic substitution did not influence the absorption spectra of the compounds in or near the visible region. Solutions of arylthiophenes had good transparency at wavelengths greater than 400 nm. The dendritic thiophenes exhibited an optical‐power limit at the laser wavelength of 532 nm. However, the magnitude of the optical‐power limit of these compounds was slightly lower than that of a nondendritic arylthiophene with n‐pentyl substituents. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1177–1187, 2005     

Solid-state characterization of spray-dried ice cream mixes

The main physicochemical properties of spray-dried ice cream mixes (i.e. surface composition, wettability, flowability and microstructure) were analyzed. Emulsions contained 19-44% milk fat on a dry basis and included mixes with no added emulsifier and/or sucrose. The time necessary for complete wetting of the powders correlated with the amount of surface free-fat measured by means of solvent extraction. Non-micellar casein (sodium caseinate) showed to be a better co-encapsulant than micellar casein (skim milk) as demonstrated by surface fat coverage measured by electron spectroscopy for chemical analysis (ESCA). Emulsifiers influenced the fat surface composition of the powders by reducing the amount of surface protein due to their lower interfacial tension. Surface fat caused an initial overestimation of the particle size of the powders due to fat-related caking. Powders showed no flow before and after surface fat extraction which was attributed to fat-related caking and very small particle size (<80 microm), respectively.