RESUMO
A bathochromic shift for both Soret and Q bands in the polyCo(III)PP were indicative of Co(III) oxidation state in film. The presence of an isosbestic point indicates a chemical equilibrium between polyCo(III)PP (band I) in polyCo(III)PP with water as axial neutral ligand (band II). Concentration levels of iodide of 10(-1) M showed irreversible broadening of Soret band with a maximum shift from 400 nm to 380 nm attributed to film reduction. The thiocyanate anion shows a remarkable effect on polyCo(III)PP spectra. The degree of configuration interaction for Q and B transitions is nearly constant in air and water for Ni(II)PP, Cu(II)PP and Zn(II)PP films. The poly[Co(III)-protoporphyrin IX] showed strong deviation from the pattern. This result indicates that the Co atom does not present a planar conformation in polyCo(III)PP which is consistent with the less packed structure of this film. The apparent diffusion coefficients (D') were calculated for electroactive species using the polyNi(II)PP chemically modified electrode, with an experiment short enough to avoid preconcentration. D' was compared with D (diffusion coefficient), obtained with the bare working electrode. Apparent diffusion coefficients (D') changed regularly with molecular volume indicating certain molecular sieving effect.
Assuntos
Cobalto/química , Polímeros/química , Porfirinas/química , Ânions/química , Eletrólitos , Ligantes , Estrutura Molecular , Oxirredução , Análise EspectralRESUMO
Liquid chromatography with electrochemical detector (LC-ED), using a chemically modified electrode coated with a metalloporphyrin film, is reported for determination of bisphenol A (BPA) migration from polycarbonate baby bottles. The extraction process of the samples was performed according to regulations of the Southern Common Market (MERCOSUR), where certain food-simulating liquids [(A) distilled water, (B) acetic acid 3% V/V in distilled water, and (C) ethanol 15% V/V in distilled water] are defined along with controlled time and temperature conditions. The baseline obtained using the naked electrode showed a considerable drift which increased the detection limit. This effect was suppressed with the chemically modified electrode. A linear range up to 450 ppb along with a detection limit of 20 ppb for the amperometric detection technique was observed. The procedure described herein allowed lowering the detection limit of the method to 0.2 ppb. The value found for BPA in the food-simulating liquid is 1.2 ppb, which is below the tolerance limit for specific migration (4.8 ppm).
Assuntos
Alimentação com Mamadeira , Estrogênios não Esteroides/análise , Fenóis/análise , Polímeros , Compostos Benzidrílicos , Alimentação com Mamadeira/instrumentação , Cromatografia Líquida de Alta Pressão/métodos , Eletroquímica/métodos , Humanos , Indicadores e Reagentes , Lactente , MetaloporfirinasRESUMO
The apoenzymes of horseradish and wheat germ peroxidases were reconstituted with synthetic hemins that differ from natural heme in the substitution pattern of side chains. Both enzymes show dual peroxidase and oxygenase activity, being the latter the oxidation of porphobilinogen in the presence of oxygen and a reducing agent. The oxygenase activity was almost unaffected in both enzymes reconstituted with synthetic hemes, while peroxidase activities were inhibited to different extents. According to the pattern of activity inhibition it was concluded that there is low flexibility of both apoproteins in the regions of the acid side chain contact which could be a general features of peroxidases.