Synthesis and application of a functionalized resin in on-line system for copper preconcentration and determination in foods by flame atomic absorption spectrometry

An on-line system for preconcentration and determination of copper at μg l⁻¹ level by flame atomic absorption spectrometry (FAAS) is proposed. Amberlite XAD-2 functionalized with 3,4-dihydroxybenzoic acid packed in a minicolumn was used as sorbent. Copper(II) ions were sorbed in the minicolumn, from which it could be eluted by hydrochloric acid solution directly to the nebulizer-burner system of the FAAS. Eluent solution was carried by water at a flow rate of 5.00 ml min⁻¹. Signals were measured as peak height by using an instrument software. Achieved sampling rate was 27 samples per hour. Analytical parameters were evaluated and the results demonstrated that copper can be determined, with acetate buffer to adjust the sample pH at 6.0, preconcentration time of 120 s and a sample flow rate of 6.50 ml min⁻¹. The desorption was carried out with 30 μl of a 1.0 mol l⁻¹ hydrochloric acid solution. An enrichment factor of 33 in 13.00 ml of sample (120 s preconcentration time) was achieved by using the time-based technique. The detection limit (DL) (3 s) was 0.27 μg l⁻¹ and the precision (assessed as the relative standard deviation) reached values of 5.7-1.1% in copper solutions of 5.00 to 50.00 μg l⁻¹ concentration, respectively. The accuracy of procedure was confirmed by copper determination in certified reference materials. Recoveries of spike additions (1.0 or 2.0 μg g⁻¹) to food samples were quantitative (90.0-110.0%). These results proved also that the procedure is not affected by matrix interference and can be applied satisfactorily for copper determination in rice flour and starch samples.     

An on-line cloud point extraction system for flame atomic absorption spectrometric determination of trace manganese in food samples

The development of an on-line preconcentration system with cloud point extraction for the determination of manganese is described. The system was used to determine manganese levels in food samples using flame atomic absorption spectrometry (FAAS). All steps of the cloud point extraction procedure were performed on-line, from the mixing of reagents to detection. The manganese ions are complexed in a mixture of the reagent 2-[2′-(6-methyl-benzothiazolylazo)]-4-bromophenol (Me-BTABr) and Triton X-114. The components are retained on a minicolumn and then desorbed with eluent acid to subsequent detection of manganese by FAAS. Under the optimized conditions, the method presented a detection limit of 0.7 μg L^− 1 and an enrichment factor of 17 to a volume of 3000 μL. The sampling frequency was 30 h^− 1. The accuracy of the method was tested by evaluating the amount of Mn in certified reference materials (apple leaves NIST 1515 and spinach leaves NIST 1570a). The proposed procedure was applied to food samples (shrimp powder, flaxseed flour, wheat flour, soy flour and oat), and the results agreed with those obtained by the determination of Mn in foods by atomic absorption spectrometry with electrothermal atomization (ETAAS).     

Two-dimensional difference gel electrophoresis applied for analytical proteomics: fundamentals and applications to the study of plant proteomics

The present review reports the principles, fundamentals and some applications of two-dimensional difference gel electrophoresis for analytical proteomics based on plant proteome analysis, also emphasizing some advantages of 2-D DIGE over 2-D PAGE techniques. Some fluorescent protein labeling reagents, methods of protein labeling, models of 2-D DIGE experiments, and some limitations of this technique are presented and discussed in terms of 2-D DIGE plant proteomes. Finally, some practical applications of this technique are pointed out, emphasizing its potentialities in plant proteomics.     

Physical and chemical characterization insulin-loaded chitosan-TPP nanoparticles

The purpose of this study was to develop and characterize insulin nanoparticles systems using chitosan. Insulin-loaded nanoparticles were prepared by ionic gelation of chitosan with tripolyphosphate anions (TPP). The interactions between insulin and chitosan were evaluated by differential scanning calorimetry (DSC), thermogravimetry/derivative thermogravimetry (TG/DTG), and Fourier-transform infrared (FTIR) spectroscopy. Besides, particle size distribution, polydispersity index (PDI), zeta potential, and association efficiency (AE%) of the nanoparticles were evaluated. In general, inert nanoparticles and insulin-loaded nanoparticles showed an average size of 260.56 nm (PDI 0.502) and 312.80 nm (PDI 0.481), respectively. Both nanoparticles showed positive charge, but after insulin incorporation the zeta potential was reduced, evidencing its incorporation. Nanoparticles obtained also showed AE% around 70%, measured by high-performance liquid chromatography (HPLC). The results of FTIR, DSC, and TG/DTG corroborated the data presented suggesting that insulin was successfully encapsulated. However, drug incorporation seems to be related not only to electrostatic interactions, but also to physical process and/or adsorption phenomena.     

New insights on proteomics of transgenic soybean seeds: evaluation of differential expressions of enzymes and proteins

This work reports the evaluation of differentially expressed enzymes and proteins from transgenic and nontransgenic soybean seeds. Analysis of malondialdehyde, ascorbate peroxidase (EC 1.11.1.11), glutathione reductase (EC 1.6.4.2), and catalase (EC 1.11.1.6) revealed higher levels (29.8, 30.6, 71.4, and 35.3%, respectively) in transgenic seeds than in nontransgenic seeds. Separation of soybean seed proteins was done by two-dimensional polyacrylamide gel electrophoresis, and 192 proteins were identified by matrix-assisted laser desorption/ionization (MALDI) quadrupole time-of-flight (QTOF) mass spectrometry (MS) and electrospray ionization (ESI) QTOF MS. Additionally, the enzyme CP4 EPSPS, involved in the genetic modification, was identified by enzymatic digestions using either trypsin or chymotrypsin and ESI-QTOF MS/MS for identification. From the proteins identified, actin fragment, cytosolic glutamine synthetase, glycinin subunit G1, and glycine-rich RNA-binding protein were shown to be differentially expressed after analysis using the two-dimensional difference gel electrophoresis technique, and applying a regulator factor of 1.5 or greater.     

Synthesis,spectroscopic characterization and X-ray crystallographic studies of trans-[PtCl2(PEt3)(PySOR)] complexes,where PySOR = (2-methylsulphinyl)-pyridine and (2-n-propylsulphinyl)pyridine

Alkylsulphinylpyridine ligands containing three potential donor centres: N, S and O atoms and two complexes of general formula trans-[PtCl₂(PEt₃)PySOR)] (R = Me and ⁿ Pr) were prepared and characterized by elemental analysis, i.r. spectroscopy, ¹H- and ³¹P-n.m.r. and X-ray crystallography. The ambidentate ligands act in both situations as monodentate ligands, bonded to the metal exclusively through the nitrogen atom. The crystal structures revealed the occurrence of discrete molecules and, in both complexes, the Pt atoms are coordinated in square planar arrangements by two chloride ions, in a trans configuration, by the pyridine nitrogen atom, and by the phosphine P atom. The oxygen atoms do not take part in the complexation scheme.     

Photoluminescent BaMoO4 nanopowders prepared by complex polymerization method (CPM)

The BaMoO₄ nanopowders were prepared by the Complex Polymerization Method (CPM). The structure properties of the BaMoO₄ powders were characterized by FTIR transmittance spectra, X-ray diffraction (XRD), Raman spectra, photoluminescence spectra (PL) and high-resolution scanning electron microscopy (HR-SEM). The XRD, FTIR and Raman data showed that BaMoO₄ at 300 °C was disordered. At 400 °C and higher temperature, BaMoO₄ crystalline scheelite-type phases could be identified, without the presence of additional phases, according to the XRD, FTIR and Raman data. The calculated average crystallite sizes, calculated by XRD, around 40 nm, showed the tendency to increase with the temperature. The crystallite sizes, obtained by HR-SEM, were around of 40-50 nm. The sample that presented the highest intensity of the red emission band was the one heat treated at 400 °C for 2 h, and the sample that displayed the highest intensity of the green emission band was the one heat treated at 700 °C for 2 h. The CPM was shown to be a low cost route for the production of BaMoO₄ nanopowders, with the advantages of lower temperature, smaller time and reduced cost. The optical properties observed for BaMoO₄ nanopowders suggested that this material is a highly promising candidate for photoluminescent applications.     

Methylmercury determination using a hyphenated high performance liquid chromatography ultraviolet cold vapor multipath atomic absorption spectrometry system

The present work investigates the use of a multipath cell atomic absorption mercury detector for mercury speciation analysis in a hyphenated high performance liquid chromatography assembly. The multipath absorption cell multiplies the optical path while energy losses are compensated by a very intense primary source. Zeeman-effect background correction compensates for non-specific absorption. For the separation step, the mobile phase consisted in a 0.010% m/v mercaptoethanol solution in 5% methanol (pH = 5), a C₁₈ column was used as stationary phase, and post column treatment was performed by UV irradiation (60 °C, 13 W). The eluate was then merged with 3 mol L^− 1 HCl, reduction was performed by a NaBH₄ solution, and the Hg vapor formed was separated at the gas–liquid separator and carried through a desiccant membrane to the detector. The detector was easily attached to the system, since an external gas flow to the gas–liquid separator was provided. A multivariate approach was used to optimize the procedure and peak area was used for measurement. Instrumental limits of detection of 0.05 µg L^− 1 were obtained for ionic (Hg²⁺) and HgCH₃⁺, for an injection volume of 200 µL. The multipath atomic absorption spectrometer proved to be a competitive mercury detector in hyphenated systems in relation to the most commonly used atomic fluorescence and inductively coupled plasma mass spectrometric detectors. Preliminary application studies were performed for the determination of methyl mercury in sediments.     

Adsorption of methane in activated carbons obtained from coconut shells using H3PO4 chemical activation

Activated carbon samples from coconut shells (Brazilian coconut species “Coco da Baía”) were prepared by chemical activation with phosphoric acid as the activating agent. Samples were characterized by nitrogen adsorption isotherms at 77 K. Some samples were randomly chosen in order to perform methane adsorption experiments under pressures between 1 and 60 bar at 303 K. A close relationship between surface area, micropore volume and methane adsorption capacity for carbons prepared from the same starting material was observed. The highest methane storage capacity in the tested samples was found to be 95 v/v at 303 K and 35 bar, which is comparable to results obtained for commercial samples indicated for this application. A moderate concentration of phosphoric acid (around 35%) seems to favor high surface areas, micropore volumes and, hence, gas storage capacity. The inclusion of an acid wash step before carbonization and the use of inert gas flow during carbonization also seem to enhance the development of porosity. This result suggests that activated carbons prepared from “Coco da Baía” by chemical activation with phosphoric acid have potential to be used as a storage media for natural gas.     

Purification, Characterization, and Preliminary X-Ray Diffraction Analysis of a Lactose-Specific Lectin from Cymbosema roseum Seeds

The unique carbohydrate-binding property of lectins makes them invaluable tools in biomedical research. Here, we report the purification, partial primary structure, carbohydrate affinity characterization, crystallization, and preliminary X-ray diffraction analysis of a lactose-specific lectin from Cymbosema roseum seeds (CRLII). Isolation and purification of CRLII was performed by a single step using a Sepharose-4B-lactose affinity chromatography column. The carbohydrate affinity characterization was carried using assays for hemagglutination activity and inhibition. CRLII showed hemagglutinating activity toward rabbit erythrocytes. O-glycoproteins from mucine mucopolysaccharides showed the most potent inhibition capacity at a minimum concentration of 1.2 microg mL(-1). Protein sequencing by mass spectrometry was obtained by the digestion of CRLII with trypsin, Glu-C, and AspN. CRLII partial protein sequence exhibits 46% similarity with the ConA-like alpha chain precursor. Suitable protein crystals were obtained with the hanging-drop vapor-diffusion method with 8% ethylene glycol, 0.1 M Tris-HCl pH 8.5, and 11% PEG 8,000. The monoclinic crystals belong to space group P2(1) with unit cell parameters a = 49.4, b = 89.6, and c = 100.8 A.