Elemental concentration in the cortex and hippocampus of Wistar rats by X-ray total reflection fluorescence with synchrotron radiation

Summary The study of trace element levels is of great importance due to their relevance in agingand several neurodegenerative diseases. This work compares the elemental concentrations in different postnatal ages and between the temporal cortex, entorhinal cortex and hippocampus from Wistar rats, using X-ray total reflection fluorescence with synchrotron radiation. Ten elements were determined in brain samples: Ti, Cr, Mn, Fe, Cu, Zn, (at trace level) and P, S, Cl and K (at major levels). The elements that increased with aging in cortical areas were: S, K, Fe, Cu and Zn. Ca and Zn levels decreased with advancing age in the hippocampus. In addition to this, Ti, Mn and Fe levels were more conspicuous in the entorhinal cortex.     

Preconcentration of heavy metals ions from aqueous solutions by means of cellulose phosphate: an application in water analysis

Cellulose phosphate (CELLPHOS) was studied as a collector for analytical preconcentration of traces of Cd(II), Cr(III), Cu(II) and Ni(II) from aqueous sample solution. It has been proved that using chromatographic columns packed with CELLPHOS for preconcentration and 1.0 mol 1(-1) HCl for elution the adsorbed analytes are quantitatively enriched. An enrichment factor of 20 (100 ml sample, 5 ml concentrate) was achieved by this separation procedure, which was applied to a series of water analyses (river, sea, bog water).     

Catalytic cathodic stripping voltammetry of oxidized glutathione at a hanging mercury drop electrode in the presence of nickel ion

Oxidized glutathione (GSSG) can be determined after previous accumulation on the HMDE at E > -0.2 V (vs. the Ag AgCl reference electrode). GSH is formed during the accumulation, possibly by a mercury-ion-assisted hydrolytic disproportionation of GSSG. In the subsequent cathodic scan GSH is released and catalyses the reduction of nickel ion, giving a peak located at -0.6 V. This enables the determination of GSSG by differential-pulse cathodic stripping voltammetry at pH 7.0 in the phosphate acetate or MOPS buffer containing 0.5-1.0 mM Ni(II). The detection limit is 10 nM. The calibration graph is linear even in the presence of small amounts of human serum albumin, HSA. However, HSA increases the detection limit (20 nM for 3 x 10(-4)% HSA). Acetyl-cysteine in small excess or Cu(II) present as reagent impurity do not interfere. Glutathione, cysteine and similar compounds, which accumulate as mercury salts and form stable nickel complexes, will interfere. The method is put forward as a novel alternative stripping voltammetric method to those involving accumulation and determination as mercury or copper salts and complexes, in the knowledge that it may have advantages in particular analytical situations. In particular the method discriminates against compounds which accumulate as mercury salts but which do not form stable nickel complexes.     

Analysis of beers from Brazil with synchrotron radiation total reflection X-ray fluorescence

Summary In this study the concentrations of P, S, Cl, K, Ca, Mn, Fe, Zn and Br in twenty-nine brands of national and international beers were determined by synchrotron radiation total reflection X-ray fluorescence analysis (SR-TXRF). The results were compared with the limits established by the Brazilian legislation and the nutritional values established by National Agricultural Library (NAL, USA). The measurements were performed at the X-Ray Fluorescence Beamline at Brazilian National Synchrotron Light Laboratory, in Campinas, S?o Paulo, Brazil, using a polychromatic beam for excitation. A small volume of 5 ml of beers containing an internal standard used to correct geometry effects was analyzed without pretreatment. The measuring time was 100 seconds and the detection limits obtained varied from 1 mg ^. l^-1 for Mn and Fe to 15 mg ^. l^-1 for P.     

NO Release from trans-[Ru(NH3)4L(NO)]3+ Complexes Upon Reduction (L = 1-Methylimidazole or Benzoimidazole)

The synthesis, characterization and reactivity of trans-[Ru(NH₃)₄(L)NO](PF₆)₃(L = benzoimidazole or 1-methylimidazole in trans position to NO) are presented. ¹H-n.m.r. spectroscopy data indicate that the benzoimidazole and 1-methylimidazole ligands are coordinated to Ru^II through carbon and nitrogen, respectively. The nitrosyl stretching frequencies [(NO) > 1900 cm^–1] suggest that the coordinated nitrosyl has substantial NO⁺ character. The complexes undergo a single-electron reduction (E ⁰–0.245 versus NHE), which involves the coordinated nitrosyl. Dissociation of NO in the reduced species is facilitated by the 1-methylimidazole ligand, which is not observed for the benzoimidazole species. The complex with 1-methylimidazole does not suffer hydroxide attack on the NO⁺, at least at pH values lower than 11.     

Solid-phase fluorescence spectroscopy for the determination of acetylsalicylic acid in powdered pharmaceutical samples

A rapid, simple and rugged procedure without requiring any prior sample treatment was developed for the determination of acetylsalicylic acid (ASA) in tablets formulations by solid-phase fluorescence spectroscopy. The method was carried out on powdered samples, consisting of an active substance dispersed in lactose, maize starch, talc and magnesium stearate. Previous knowledge of the sample bulk composition is needed for proper application of the method. Wavelengths for maximum excitation and emission were 288 and 318 nm, respectively, and the fluorescence intensity was linear with ASA concentration within the 50-170 mg g⁻¹ range. Detection and quantification limits were 2.2 and 7.3 mg g⁻¹, and the analytical frequency was 200 h⁻¹. For a typical sample, the relative standard deviation of results was estimated as 2.3% (n = 10). Accuracy was assessed by comparing the analytical results obtained with the proposed method with those related to a reference method recommended by British Pharmacopoeia: no differences between the methods were found at the 95% confidence level.     

31P{1H}-n.m.r. as a tool for identification of ruthenium isomers containing PPh3 or 1,4-bis(diphenylphosphino)butane ligands. X-ray structures of the cis-{RuCl2(PPh3)2 [4,4′-(-X)2-2,2′-bipy]} complexes [X=-H, -Me, -SMe and (-Cl, -Me)]

A series of cis-{RuCl₂(PPh₃)₂[4,4-(X)₂-2,2-bipy]} [cis-chlorines; X=-H, -Me, -SMe, and (-Cl,-Me)] complexes have had their structures determined by single crystal X-ray diffraction. The geometry of these complexes, also determined in CH₂Cl₂ solution by ³¹P{¹H}-n.m.r. spectroscopy, showed that the chemical shifts for the phosphorus atoms are slightly dependent on the pKa of the 4,4-(-X)₂-2,2-bipy ligands.     

Titanium as a chemical modifier for the determination of cobalt in marine sediments

The determination of cobalt in marine sediments by electrothermal atomic absorption spectrometry was studied using no modifier and magnesium and titanium as modifiers. Titanium is one of the major sediment constituents, which widely affects the cobalt determination and it was studied as a chemical modifier since it was the only concomitant that increased the cobalt signal in the concentration range usually found in sediments. The performance of Mg and Ti as chemical modifiers was compared relative to maximum pyrolysis and atomization temperatures, linear calibration range, sensitivity and matrix effects. The pyrolysis curves showed that the analyte could be stabilized up to 1400 °C when either Ti or Mg(NO₃)₂ was present, while only 1000 °C could be used in the absence of a modifier. The optimum atomization temperature was 2500 °C in all cases. Analytical curves were compared using no modifier, 5 μg Ti and 100 μg Mg(NO₃)₂ as modifiers, and the linear range found was up to approximately 4 ng Co whether a modifier was used or not. With Ti as a chemical modifier, analytical curves for cobalt in aqueous solution and in a synthetic matrix resulted in the same sensitivity (m₀=55 pg), whereas the use of Mg led to characteristic mass values of 59 and 72 pg in aqueous solution and in a synthetic matrix, respectively, showing some matrix effect. The detection limits (3σ, n=10) were 0.4 μg g⁻¹ using no modifier and 0.3 μg g⁻¹ with Ti as a modifier in the original matrix. A reference estuarine sediment NIST 1646 with a non-certified content of 10.5 μg g⁻¹ Co was analyzed and the found value of 10.9±2.4 μg g⁻¹, (n=3), using Ti as chemical modifier and calibration against aqueous standards, was in good agreement with the recommended value.     

EPR spectroscopy on irradiated nickel tetracyanide in NaCl host lattice: mechanism for the simultaneous formation of reduced and oxidized species

The kinetics of oxidized and reduced Ni²⁺ complexes produced by X-ray irradiation on single crystals of NaCl doped with [Ni(CN)₄]²⁻ is studied by Electron Paramagnetic Resonance at room temperature. The interdependent generation of these two complexes is attributed to migration of the charge compensating vacancy from the reduced to the oxidized complex in a reversible reaction. At higher X-ray doses, there is a predominant formation of the reduced complex.     

Mechanism for basic hydrolysis of N-nitrosoguanidines in aqueous solution

A kinetic study was carried out on the hydrolysis of two N-nitrosoguanidines, 1-nitroso-1-methyl-3-tolylsulfonylguanidine (TSGNO) and 1-nitroso-1-methyl-3-benzoylguanidine (BCGNO). We observed an absence of buffer catalysis using H(2)PO(4)(-)/HPO(4)(2)(-), H(3)BO(3)/H(2)BO(3)(-), and HCO(3)(-)/CO(3)(2)(-) regulators and a complex dependency of the rate constant on the pH. We discovered the existence of three simultaneous reaction paths: spontaneous decomposition of the neutral form of the N-nitrosoguanidine, decomposition of the monoanion, and decomposition through the form of the dianion. The analysis of the kinetic data has allowed us to obtain the acidity constant for the formation of the monoanion of the N-nitrosoguanidine, with values of p = 11.5. The reaction rate for the process through the monoanion, k(2), decreases as the acidity increases. The application of the principle of nonperfect synchronization shows that the basicity and reactivity do not correlate when there exists a possibility of stabilization of the negative charge by resonance. This behavior is consistent with the mechanism E1cB whereby the stabler the negative charge, the slower the elimination reaction. When dealing with the case of the elimination through the neutral form we observe that the reaction rate increases together with the capacity of stabilization of the positive charge on the nitrogen atom adjacent to the imino group. For the reaction through the dianion we used a maximum value of k(3) = 10(10) s(-)(1) to estimate the value of p for the formation of the dianion of the N-nitrosoguanidine, obtaining values of p < 24.