Wagner José Barreto

A RAMAN AND UV-VIS STUDY OF CATECHOLAMINES OXIDIZED WITH MN(III)

Abstract A UV-Vis and Raman spectroscopy study of three aminochromes generated through Mn 3+ oxidation of the dopamine, l -dopa and adrenaline molecules at physiological pH was performed. The UV-Vis spectra of the catecholamines oxidized using Mn 3+ in buffer solution at pH 7.2 show a band at ca. 300 nm, formed by two transitions at 280 nm and 300 nm assigned to an L a and L b transition respectively, and other at ca. 470 nm assigned to an n – π * transition localized in the carbonyl group. This assignment is suggested by the UV-Vis and Raman spectra of ortho -aminoquinone generated by MnO 2 oxidation of a dopamine aqueous acidic solution. The resonance Raman spectra of the three chromes at buffer pH 7.2 show a very similar feature and the most intense bands are observed in the spectral range 1100–1800 cm −1 . The band around 1680 cm −1 for the three compounds is assigned to a ν (CO) stretching vibration, 1630 cm −1 to the ν (CC) ring mode, two bands at 1423, 1439 cm −1 ; 1427, 1438 cm −1 and 1456, 1475 cm −1 are assigned to a ν (CN + ) vibration, for aminochrome, dopachrome and adrenochrome, respectively. The excitation profiles for the most intense bands for aminochrome and adrenochrome were obtained. The band assigned to the ν (CN + ) present a red shift with respect to the visible band peak, however the band in adrenochrome at 1475 cm −1 shows a profile similar to ν (CO) and ν (CC) modes that reflects the methyl group effect on mixing this mode more effectively with the ν (CC) ring mode.

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 Tessies 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.

Adsorption of the diazo dye Direct Red 23 onto a zinc oxide surface: A spectroscopic study

The adsorption of the diazo dye Direct Red 23 onto a zinc oxide surface at 30 degrees C in the dark was investigated. The color reduction was monitored by spectrophotometry at 503 nm. The FTIR and Raman spectra of the Direct Red 23 adsorption as a function of ZnO concentration were registered. From the PM3 semi-empirical calculations of the atomic charge density and dipole moment of the Direct Red 23 molecule, it was demonstrated that the azo dye molecule may be adsorbed onto the ZnO surface through molecule geometry modifications, enhancing the interfacial area causing a variation in the bonding frequencies.

Citric acid as multifunctional agent in blowing films of starch/PBAT

Citric acid was used as a compatibilizer in the production of starch and PBAT films plasticized with glycerol and processed by blow extrusion. Films produced were characterized by WVP, mechanical properties, FT-IR-ATR and SEM. WPV ranged from 3.71 to 12.73×10-11 g m-1 s-1 Pa-1, while tensile strength and elongation at break ranged from 1.81 to 7.15 MPa and from 8.61 to 23.63%, respectively. Increasing the citric acid concentration improved WVP and slightly decreased film resistance and elongation. The films micrographs revealed a more homogeneous material with the addition of citric acid. However, the infrared spectra revealed little about cross-linking esterification reaction

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.

Spectrophotometric method for the simultaneous determination of proteins and amino acids with p-benzoquinone

Abstract A spectrophotometric method for the simultaneous determination of proteins and total amino acids in mixtures is described, based on the observation that the products of the reaction between p -benzoquinone (PBQ) and proteins show an absorbance band at about 350 nm, whereas for most of the essential amino acids the absorbance band is at about 440 nm. Beers law was obeyed by the products of the reaction between PBQ and 1:1 or 2:1 (w/w) mixtures of proteins and amino acids for a wide range of concentrations. The products of the reaction were stable for 2 h at either 5 or 30°C; shifts of the wavelength of maximum absorbance were not observed for up to 48 h after starting the reaction. The molar and specific absorptivities for several amino acids and proteins, respectively, were determined. The detection limit observed with the PBQ method was compared with those obtained with other methods. A recovery of about 100% was observed for both BSA and total amino acids when the PBQ method was applied to an amino acid-protein mixture resembling cerebrospinal fluid.

Adsorption of caffeic acid on titanium dioxide: A spectroscopic study

Caffeic acid is an ortho-phenol found in vegetable tissues presenting important properties such as carcinogenesis inhibitor, anti-oxidant, anti-viral, anti-inflammatory and anti-rheumatic actions. It was observed that caffeic acid was not degraded in daylight during the adsorption on TiO(2) at pH 4.8. The adsorption fit very well to a Brunauer-Emmett-Teller isotherm equation with a monolayer coverage of 68.15 mg(CA)g(-1)(TiO2 and saturation coverage of 195.4 mg(CA)g(-1)(TiO2). A strong adsorption of caffeic acid was verified on TiO(2) for the dry solid obtained from the mixture. The Raman and IR spectroscopies revealed that the adsorption should occur through the interaction of the diphenol oxygens with contribution of CC double bond of the acrylic group, however, the carboxylic acid group did not have participation in the adsorption.

A new method for total protein determination.

Abstract A new method for total protein determination was developed and applied to samples of skin milk powder. The method is based on the products of the reaction between p-benzoquinone and protein (casein), which show a charge-transfer band at 350 nm. The effects of concentration, reaction time, and pH were studied. The results were compared with those obtained with the Kjeldahl and Lowry methods; the standard deviations observed with the proposed method and with Lowrys method are of the same order of magnitude.

Interruption of the MnO2 oxidative process on dopamine and l-dopa by the action of S2O32−

The oxidation effects of Mn2+, Mn3+ or MnO2 on dopamine can be studied in vitro and, therefore, this offers a model of the auto-oxidation process that appears naturally in neurons causing Parkinsons disease. The use of MnO, as an oxidizer in aqueous solution at pH 7 causes the oxidation of catecholamines (L-dopa, dopamine, noradrenaline and adrenaline) to melanin. However, this work shows that, in water at pH 6-7, the oxidation of catecholamines by MnO2 in the presence of sodium thiosulphate (Na2S2O3) occurs by other mechanisms. For dopamine and L-dopa, MLCT complexes were formed with bands at 312, 350 (sh), 554 (sh) nm, and an intense band at 597 nm (epsilon approximately/= 4 x 10(3) M(-1) cm(-1)) and at ca. 336, 557 (sh) nm, and an intense band at 597 nm (epsilon approximately 6 x 10(3) M(-1) cm(-1)), respectively. The latter transitions were assigned to d(pi)-->pi*-SQ. Noradrenaline and adrenaline do not form this blue complex in solution, but generate soluble oxidized compounds. The resonance Raman spectra of these complexes in solution showed bands at 950, 1006, 1258, 1378, 1508 and 1603 cm(-1) for the complex derivation of L-dopa and at 948, 1010, 1255, 1373, 1510 and 1603 cm(-1) for the dopamine-derived compound. The most intense Raman band at ca. 1378 cm(-1) was assigned to C-O stretching with major C1-C2 characteristics and indicated that dopamine and L-dopa do not occur complexed with manganese in the catecholate or quinone form, but suggests an intermediate compound such as an anionic o-semiquinone (SQ-), forming a complex such as [Mn(II)(SQ-)3]-. All enhanced Raman frequencies are characteristic of the benzenic ring without the participation of the aminic nitrogen. A mechanism is proposed for the formation of the dopamine and L-dopa complexes and a computational simulation was performed to support it.

Iron oxide and pyrocatechol: a spectroscopy study of the reaction products

The reaction of 1,2-dihydroxy-benzene (pyrocatechol) (C6H6O2) with iron oxide (Fe2O3) and sodium thiosulfate (Na2S2O3) in aqueous medium (pH 7) was investigated. Pyrocatechol suffers autoxidation and coordinates with Fe3+ in solution. The presence of S2O32- in solution was fundamental to generate and stabilize the pyrocatechol oxidation products as o-semiquinones. This compound was isolated and its structure characterized using FT-IR, EPR and UV-Vis Spectroscopy as [CTA][Fe(SQ)2(Cat)]. A thermal mass loss mechanism was proposed based on Thermogravimetric Analysis (TG) to support the structural characterization.