Eliane D'Elia

Chloroperoxidase mediated oxidation of chlorinated phenols using electrogenerated hydrogen peroxide

Chloroperoxidase (CPO) from Caldariomyces fumago catalyses the oxidation of several chlorinated phenols (CP) commonly found in industrial waste waters in the presence of hydrogen peroxide. This study compares the direct addition of hydrogen peroxide (DA) with its continuous electrogeneration (EG) during the enzymatic oxidation of CP. Reaction mixtures were studied containing chemically modified CPO, hydrogen peroxide and the phenolic substrates: phenol (P), 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP), in 100 mM sodium-potassium phosphate buffer pH 6.0, at 25oC. Results were compared in terms of residual phenol concentration (oxidation efficiency), precipitate formation (removal) and residual enzyme activity (stability). With the electrochemical system evaluated at -620 mVSCE, and continuous aeration the maximum H2O2 concentration of 1.2 mM was obtained. Under this conditions and after 4 hrs using EG, no phenol or 4-CP were detected, and 97%, 93% and 88% of 2,4-DCP, 2,4,6-TCP and PCP were degraded, respectively. The use of EG improves enzyme half-life time in comparison to the results obtained by DA

Aqueous extracts of mango and orange peel as green inhibitors for carbon steel in hydrochloric acid solution

In this paper, aqueous extracts of mango and orange peels were shown to be good corrosion inhibitors for carbon steel in a 1 mol L - 1 HCl solution. The inhibition efficiency increased as the extract concentration increased over a concentration range of 200-600 mg L - 1, varying from 79 to 96% (mango) and 84 to 91% (orange) using Tafel plots and from 69 to 94% (mango) and 76 to 90% (orange) using electrochemical impedance. In the presence of 400 mg L - 1 of mango and orange peel extracts, the weight loss measurements showed an increase in the inhibition efficiency with immersion time, where the best results after 24 h of immersion were 97% and 95%, respectively. The adsorption of the extract components on the surface of the carbon steel follows the Langmuir adsorption isotherm. With the extraction procedure used in this work, it can be surmised that it is likely that the more polar heterosides in the extracts are responsible for the corrosion inhibition of carbon steel in an acid solution.

Statistic evaluation of cysteine and allyl alcohol as additives for Cu-Zn coatings from citrate baths

In the present work, cysteine and allyl alcohol were added to citrate baths as additives to Cu-Zn coatings on steel substrates. In order to verify the effects of the deposition parameters (current density, mechanical stirring speed, and additives) on the coating composition, electrochemical behavior, morphology, and microstructure properties of Cu-Zn coatings, the electrodeposition of the alloy was carried out using an experimental composite design 23, in which these parameters were considered the entry variables and the measured properties were the response variables. The confidence level was 95% and the results were shown as response surface diagrams. It was possible to verify that the current density affected the zinc content in the coating, while the coating produced from cysteine-contained bath presented the worse anticorrosive performance. In a general way, it was possible to observe that the studied parameters affected the morphology, grain size, and the electrochemical behavior of these coatings, although only a few response variables were statistically influenced by them.

The inhibitory action of Bauhinia purpurea extracts on the corrosion of carbon steel in sulfuric acid medium

The inhibitory effect of Bauhinia purpurea (Fabaceae) extract was studied in the corrosion of carbon steel in 1.0 mol∙L-1 sulfuric acid solution. This plant was collected from the Brazilian rainforest. The carbon steel protection was observed by varying the extract concentration from 50 to 500 mg∙L-1. Polarization curves revealed that this extract acted as an adsorption inhibitor decreasing both anodic and cathodic density currents. Weight loss measurements showed that the extract remains stable for at least 72 hours. The adsorption process of this extract obeyed the Langmuir adsorption isotherm. Lastly, Arrhenius plot suggested the physical adsorption of the extract.

Flow injection analysis with amperometric detection for morpholine determination in corrosion inhibitors

In this study, an electrochemical method is proposed using flow injection analysis and amperometric detection with screen-printed carbon electrodes for morpholine determination to monitor the quality of morpholine-based commercial inhibitors and the residual concentration of inhibitors that control internal corrosion in oil industry pipelines. The amperometric method resulted in a strong linear correlation coefficient (r = 0.9941) with a linear response over a concentration range of 20-120 mg L-1, a limit of detection of 10 mg L-1 and a limit of quantification of 30 mg L-1. In addition, the method has been shown to be precise, linear and homoscedastic. The recovery for the amperometric method was 100 ± 6%, and the recovery for the real condensate sample was 99 ± 2%. Thus, the proposed method is promising for analysing morpholine-based commercial inhibitors in oil industry pipelines with simple and low-cost methodologies compared with ion chromatography techniques.

Simple enzymatic methods for glycerol analysis in commercial beverages

Two enzymatic methods using amperometric and colorimetric detection based on two coupled activities (glyceroquinase and glycerol-3-phosphate oxidase) were compared for the glycerol content determination. The enzymatic conversion of glycerol consumes oxygen, which is measured amperometrically in a Clark-type electrode and correlated with the glycerol concentration. In addition to the enzymatic-colorimetric method, there is a third enzymatic reaction that can be used to form a coloured compound; this method involves the addition of peroxidase, 4-chlorophenol and 4-aminoantipyrine. The enzymatic methods studied showed good linearity in the range of 4 to 60 μmol L−1 glycerol with a detection limit of 1 μmol L−1. Studies of glycerol recovery in fortified sugar cane liquor showed a recovery of 98 ± 2% for the enzymatic-amperometric method and of 96 ± 1% for the enzymatic-colorimetric method. These two methods were applied to the determination of glycerol in beverages and good correlations were found between these methods.

DETERMINAÇÃO DE GLICEROL LIVRE E TOTAL EM AMOSTRAS DE BIODIESEL POR MÉTODO ENZIMÁTICO COM DETECÇÃO COLORIMÉTRICA

A method based on enzymatic activities was developed using three enzymes (glycerokinase, glycerol-3-phosphate oxidase and peroxidase) and colorimetric detection for the determination of glycerol in biodiesel. The enzymatic conversion of glycerol produces H2O2 that is eliminated by the action of peroxidase, an oxygen acceptor and 4- aminoantipirine, producing water and a colored compound, which was analyzed. This method showed good linear correlation coefficient (r = 0.9937) in the concentration range of 4.95 x 10-5 to 3.96 x 10-4% (w/w) and had experimental limits of detection and quantitation of 7.10 x 10-6 and 2.10 x 10-5% (w/w), respectively.

On the applicability of SiO2/Al2O3/Nb2O5 and SiO2/Al2O3/TiO2 as a biocompatible platform for chloroperoxidase

In the present work, two mixed oxides, namely, SiO2/Al2O3/Nb2O5 and SiO2/Al2O3/TiO2 (designated as SiAlNb and SiAlTi, respectively), obtained using the sol–gel method were used to immobilize chloroperoxidase. Hydrogen peroxide was quantified using potassium hexacyanoferrate(II) as a redox-mediator and amperometric measurements at 0.0 V vs. Ag/AgCl/Cl− (3 M). The SiAlTi biosensor presented higher sensitivity than the SiAlNb biosensor, however, the first one did not present a good response regarding time. The developed biosensor using the SiAlNb mixed oxide provided good signal levels, good linearity, good stability (retaining approximately 70% of its original response after 6 weeks of usage), a low detection limit (3 μM), good sensitivity, a suitable working range (from 4 to 19 μM), fast response and good repeatability. The recovery of the amperometric method for the detection of hydrogen peroxide in synthetic samples was approximately 100 ± 2%, and for Listerine® Whitening Pre-Brush Rinse samples fortified with 1, 2 and 3% (v/v) of hydrogen peroxide, it was 100 ± 3%.

A comparison of amperometric and spectrophotometric methods for the iodide concentration measurement: a tracer in produced water from offshore oil reservoirs

with limits of detection and of quantification of 1 and 3 mg L -1 , respectively. Both methods showed to be accurate, linear, homoscedastic and their recoveries were 101 ± 2 and 100 ± 3%, respectively, while the recoveries for produced reservoir water samples (fortified with iodide) were 97 ± 7 and 100 ± 3%, respectively. High amounts of sulfate interfere in the spectrophotometric method. Both methods are promising, simple and inexpensive alternatives to ion chromatography for the detection of iodide tracer in produced water reservoir samples.

Electrogeneration of hydrogen peroxide applied to the peroxide-mediated oxidation of (R)-limonene in organic media

Horse radish peroxidase (HRP) from Armoracia rusticana catalyses the oxidation of ( R )-limonene into the oxidized derivatives carveol and carvone. This study compares the direct addition (DA) of hydrogen peroxide with its continuous electrogeneration (EG) during the enzymatic oxidation of ( R )-limonene. Reaction mixtures containing HRP, ( R )-limonene as substrate, and hydrogen peroxide, added directly or electrogenerated, in 100 mM sodium-potassium phosphate buffer pH 7.0, at 25oC were studied. Two electrochemical systems for the hydrogen peroxide electrogeneration were evaluated, both containing as auxiliary electrode (AE) a platinum wire and saturated calomel electrode (SCE) as reference. Reticulated vitreous carbon foam (RVCF) and an electrolytic copper web (CW) were evaluated as working electrodes (WE). Results were compared in terms of hydrogen peroxide electrogeneration, ( R )-limonene residual concentration or conversion and product selectivity. Best results in terms of maximum H 2 O 2 concentration (1.2 mM) were obtained using the CW electrode at -620 mV SCE , and continuous aeration. Use of the EG system under optimized conditions, which included the use of acetone (30% v/v) as a cosolvent in a 3 hrs enzymatic reaction, lead to a 45% conversion of ( R )-limonene into carveol and carvone (2:1). In comparison to the results obtained with DA, the use of EG also improved the half-life of the enzyme.