Raman, IR, UV-vis and EPR characterization of two copper dioxolene complexes derived from L-dopa and dopamine.

The anionic complexes [Cu(L(1-))3](1-), L(-)=dopasemiquinone or L-dopasemiquinone, were prepared and characterized. The complexes are stable in aqueous solution showing intense absorption bands at ca. 605 nm for Cu(II)-L-dopasemiquinone and at ca. 595 nm for Cu(II)-dopasemiquinone in the UV-vis spectra, that can be assigned to intraligand transitions. Noradrenaline and adrenaline, under the same reaction conditions, did not yield Cu-complexes, despite the bands in the UV region showing that noradrenaline and adrenaline were oxidized during the process. The complexes display a resonance Raman effect, and the most enhanced bands involve ring modes and particularly the nuCC+nuCO stretching mode at ca. 1384 cm(-1). The free radical nature of the ligands and the oxidation state of the Cu(II) were confirmed by the EPR spectra that display absorptions assigned to organic radicals with g=2.0005 and g=2.0923, and for Cu(II) with g=2.008 and g=2.0897 for L-dopasemiquinone and dopasemiquinone, respectively. The possibility that dopamine and L-dopa can form stable and aqueous-soluble copper complexes at neutral pH, whereas noradrenaline and adrenaline cannot, may be important in understanding how Cu(II)-dopamine crosses the cellular membrane as proposed in the literature to explain the role of copper in Wilson disease.

Reaction of a model siderophore with Ni(II), Co(II) and Zn(II) in aqueous solution: kinetics and spectroscopy.

A spectroscopic study was performed showing that the [Fe(III)(L(2-))(2)](1-) (L(2-)=dopacatecholate) complex reacts with Ni(II), Co(II) and Zn(II) in an aqueous solution containing S(2)O(3)(2-) resulting in the soluble [M(L(1-))(3)](1-) (L(1-)=dopasemiquinone; M=Ni(II), Co(II) or Zn(II) complex species. The Raman and IR spectra of the [CTA][M(L(1-))(3)] complexes, CTA=hexadecyltrimethylammonium cation, in the solid state were obtained. The kinetic constants for the metal substitution reactions were determined at four different temperatures, providing values for DeltaH(not equal), DeltaS(not equal) and DeltaG(not equal). The reactions were slow (k=10(-11) Ms(-1)) and endothermic. The system investigated can be considered as a simplified model to explain some aspects of siderophore chemistry.

Preparation, UV-vis, IR, EPR and resonance Raman study of Fe, Ni, Co and Zn dioxolene complexes.

An UV-vis, Raman, IR and EPR spectroscopic study was performed for the water soluble complexes of Fe(III), Ni(II), Co(II) and Zn(II) coordinated to dioxolene ligands derived from oxidized dopamine. The complexes were obtained and stabilized at neutral pH by the strong reducing agent sodium thiosulfate. Iron(III) stabilizes the ligand in catecholate form as [Fe(III)(Cat)2]1-, Cat=dopacatecholate, and the divalent metals as dopasemiquinone (SQ): [Ni(SQ)3]1-, [Co(SQ)3]1- and [Zn(SQ)3]1-. The resonance Raman spectra of the solid complexes as [CAT][Ni(SQ)3], [CTA][Co(SQ)3] and [CTA][Zn(SQ)3], CTA is the cetyltrimethylammonium, are very similar to the spectra of the complexes in solution, while the Fe(III) complex is a mixture of two iron complexes, with catecholate or dopasemiquinone ligands.

Simultaneous spectrophotometric determination of Hg2+, Pb2+, and Cu2+ by Zn(dmit) using the multivariate calibration method.

This work investigates the applicability of the anionic complex [NBu4]2[Zn(1,3-dithiol-2-tione-4,5-dithiolate)2] on the simultaneous spectrophotometric determination of transition metals. Principal Component Regression was used in the data analysis. This method was used to determine Hg2+, Cu2+ and Pb2+ in water solution, at t = 0, 20 and 60 min of reaction. The root mean square errors (rms) for Hg2+, Cu2+, Pb2+ were 1.92 x 10(-7), 1.89 x 10(-7) and 9.35 x 10(-8) for t = 0 min, 1.79 x 10(-7), 2.1 x 10(-7) and 2.22 x 10(-7) for t = 20 min and 1.22 x 10(-7), 1.31 x 10(-7) and 1.10 x 10(-7) for t = 60 min, respectively. Results showed the viability of the method in determining concentrations of metallic ions in aqueous medium with high spectral overlap. It is an efficient alternative method for exploring the kinetic behavior of multicomponents systems of interest in physicochemical research.

Interpretation of seasonal variation of metals and abiotic properties in a tropical lake using multivariate analysis and MINTEQA2 program.

The hydrological cycle of Lake Ipê and the principal parameters that could affect its abiotic parameters and its metal (Fe, Mn, and Cd) concentrations were investigated. A detailed study of seasonal variations using Principal Components Analysis (PCA) for the most relevant metals (Fe, Mn and Cd) was performed, assisted by the MINTEQA2 geochemical equilibrium program using 15 water abiotic parameters. The abiotic variables and metals in the lake were governed by the hydrological regimen of the Parana River and by the occurrence of occasional flood pulses and rainfall. The occurrence of cadmium is a concern; its presence could be due to industrial or agricultural activities or even to a natural geochemical process.

Comparison of metal analysis in sediments using EDXRF and ICP-OES with the HCl and Tessie extraction methods.

The work presents an investigation on metal availability in sediments during 13 months using the dispersive-energy X-ray fluorescence (EDXRF) and atomic emission spectrometry with induced argon plasma (ICP-OES) techniques and single extraction (0.1moll(-1) HCl) and Tessie's sequential speciation methods. The EDXRF technique could yield essentially the same profile as ICP-OES for the seasonal variation of metals in sediments, but in a more practical way. The sequential extraction procedure (SEP) was more efficient in metal dissolution than single extraction. The Pb, Ni, Al, Cr, and Fe elements were less efficiently extracted with single extraction in relation to sequential extraction. For Co both methodologies were equivalent, but for Cu and Mn the extraction was higher with single extraction. Single extraction does not mobilize Pb, Ni, Al, Cr, and Fe adsorbed on oxides and bound to organic matter. However for Cu and Mn, not only extracted these metals from the four fractions, but it also dissolved part of the fifth fraction (residual). Principal Component Analysis discriminated seasonal variations in the content of several metals, mainly Fe, Co, Ni, and Zn. The mobility of metallic ions in the sediments is conditioned to the seasonal flow of organic and inorganic material coming from the river or by the erosion of adjacent soils.

Clearance of manganese from the rat substantia nigra following intra-nigral microinjections.

Chronic exposure to manganese (Mn) positively correlates with the occurrence of Parkinsonism but little is known about mechanisms of its neurotoxicity. In the present study, we determined the clearance of Mn from rat substantia nigra after its nigral injection and correlated it with the establishment of apomorphine-induced rotational behaviour and loss of striatal tyrosine hydroxylase (TH) immunoreactivity. Our results suggest that Mn is slowly cleared from the substantia nigra, following a first-order kinetics with a t(1/2) of 3 days. Appearance of apomorphine-induced rotational behaviour and loss of TH immunoreactivity within the striatum follows metal clearance were both detected 24 hours after intra-nigral Mn microinjection and maximal 72 hours after injection. The present data suggest that the cellular mechanisms induced by Mn and leading to dopaminergic cell death, occurred shortly after its injection and that the metal concentration needs to reach a threshold value to induce neurotoxic effects. This would indicate that nigral damages are a direct consequence of Mn accumulation.