Madalena Areias - Academia.edu (original) (raw)
Papers by Madalena Areias
Green Chemistry, May 4, 2011
ABSTRACT Mixtures of carbonyl compounds and allylhalides, adsorbed on a graphite powder cathode, ... more ABSTRACT Mixtures of carbonyl compounds and allylhalides, adsorbed on a graphite powder cathode, were reduced under aqueous anolyte to give high yields of homoallylic alcohols. Catalytic amounts of silver or tetrabutylammonium tetrafluoroborate improved the yields significantly. Inexpensive allyl chloride gave superior results when compared to allyl bromide.
The Analyst, 2016
The electrochemical determination of cysteine is investigated by adsorptive stripping voltammetri... more The electrochemical determination of cysteine is investigated by adsorptive stripping voltammetric detection of a copper-cysteine complex compound using a bare glassy carbon electrode. In acidic 0.1 M KNO3 solution (pH 4), the electrochemical oxidation of this complex compound generates a characteristic anodic peak ca. -0.17 V vs. a standard mercury/mercurous sulphate reference electrode. The voltammetric response is highly reproducible within 2.1% error (n = 3). A linear dynamic range is obtained for a cysteine concentration of 1.0 μM to 10.0 μM. The sensitivity of 0.18 ± 0.006 μA μM(-1) and the limit of detection of 0.03 μM (n = 3) make our methodology highly applicable for practical applications. Successful determination of cysteine concentration in the presence of glutathione has also been demonstrated by the sequential determination of the concentrations of total thiol and the tripeptide alone.
The Analyst, 2016
A simple, sensitive, and rapid detection of glutathione by cyclic voltammetry using a bare glassy... more A simple, sensitive, and rapid detection of glutathione by cyclic voltammetry using a bare glassy carbon electrode is reported in which glutathione forms a 1 : 1 complex compound with copper(ii) ions. This complex compound is adsorbed onto the electrode surface and undergoes electrochemical oxidation at a characteristic oxidation potential of ca. -0.20 V vs. the standard mercury/mercurous sulphate reference electrode, which is used to detect the glutathione concentration. The linear dynamic range is obtained for a glutathione concentration from 1 μM to 12.5 μM, and the sensitivity is found to be 0.1 ± 0.002 μA μM(-1). A low limit of detection (n = 3) of 0.14 μM and a precision of 1.8% are achieved using a simple, unmodified electrode. The robustness of the present methodology is demonstrated by the successful quantitative analysis of glutathione in the presence of cysteine.
Electrochimica Acta, 2015
ABSTRACT Benzyl chloride reduction was studied in a powder macroelectrode (PME) made of silver, g... more ABSTRACT Benzyl chloride reduction was studied in a powder macroelectrode (PME) made of silver, graphite or silver/graphite mixtures (1:3, 1:1 and 3:1) in absence of solvent, or using a very low amount of DMF as solvent (PhCH2Cl/DMF 3:1). A 0.1 mol L−1 KCl aqueous solution was used as anolyte. A competitive hydrogenation and dimerization process was observed, affording the respective toluene and bibenzyl products. The well-known electrocatalytic effect of silver on reduction of the CCl bond was confirmed by a significant positive shift of the benzyl chloride reduction potential in comparison with pure graphite powder. The products distribution was analysed after linear sweep voltammetries at low scan rate (0.1 mV s−1), indicating high yields of bibenzyl produced on Ag/graphite-PME. Pure graphite-PME was not selective towards dimer formation. The best results for bibenzyl production occurred at more positive potentials, in the presence of silver. A small amount of solvent (DMF) play an important role on the electrode surface desorption and diffusion of intermediary species.
Proceedings of the 15th Brazilian Meeting on Organic Synthesis Proceedings, 2013
Proceedings of the 14th Brazilian Meeting on Organic Synthesis Proceedings, 2013
RSC Advances, 2013
ABSTRACT A green electrochemical heterocoupling procedure has been developed. Prenyl halides and ... more ABSTRACT A green electrochemical heterocoupling procedure has been developed. Prenyl halides and benzaldehyde adsorbed on a graphite powder cathode were reduced in a cavity cell using aqueous anolyte, providing isomer mixtures of prenylated alcohols. High α-regioselectivity was observed using graphite with 3% TBABF4, while high γ-regioselectivity was obtained using 2% silver-doped graphite.
Proceedings of the 14th Brazilian Meeting on Organic Synthesis Proceedings, 2013
Green Chemistry, 2011
ABSTRACT Mixtures of carbonyl compounds and allylhalides, adsorbed on a graphite powder cathode, ... more ABSTRACT Mixtures of carbonyl compounds and allylhalides, adsorbed on a graphite powder cathode, were reduced under aqueous anolyte to give high yields of homoallylic alcohols. Catalytic amounts of silver or tetrabutylammonium tetrafluoroborate improved the yields significantly. Inexpensive allyl chloride gave superior results when compared to allyl bromide.
Electrochimica Acta, 2014
ABSTRACT Six alpha-haloesters and eighteen carbonyl compounds were submitted to electrochemical c... more ABSTRACT Six alpha-haloesters and eighteen carbonyl compounds were submitted to electrochemical coupling on a graphite powder cathode using aqueous anolyte free of organic solvents. Preparative yields of coupling products could be obtained with ethyl 2-bromoisobutyrate and aromatic aldehydes. Ethyl 2-bromopropionate was much less efficient. Extensive variation of applied potential, electrolyte composition, stoichiometry, catalyst, leaving halogen and activating substituents on the carbonyl compound led to the conclusion that the reaction mechanism in most cases proceeds via a radical intermediate generated from the halide reduction. Ethyl chloroacetate produced only trace amounts of coupling product, most probably by a carbanionic mechanism.
Electrochimica Acta, 2013
Six ␣-haloketones adsorbed on a graphite powder cathode were reduced in the presence of benzaldeh... more Six ␣-haloketones adsorbed on a graphite powder cathode were reduced in the presence of benzaldehyde using undivided cell, inert anode and aqueous electrolyte. High yields of aldol coupling product were obtained from 2-chloropinacolone in the presence of catalytic amounts of silver. For the corresponding bromo compound, the reaction was much less satisfactory. Chloroacetone gave moderate yields of the ␣,-unsaturated coupling product. 2-Chlorobutanone produced two main products in low yield: the expected aldol and the corresponding 1,3-diketone. With 2-bromopropiophenone and 2-bromoisobutyrophenone no coupling with benzaldehyde was observed but only reductive dehalogenation. The results can be interpreted in terms of a carbanionic intermediate generated by a two-electron transfer.
Talanta, 2005
A highly selective, fast and stable biosensor for determination of glucose in soluble coffee has ... more A highly selective, fast and stable biosensor for determination of glucose in soluble coffee has been developed. The biosensor electrode consist of a thin film of ferric hexacyanoferrate (Prussian Blue or PB) electrodeposited on the glassy carbon electrode (GCE) (to provide a catalytic surface for the detection of hydrogen peroxide) glucose oxidase immobilized on top of the electrode and a Nafion ® polymer layer. The stability of the PB film and the biosensor was evaluated by injecting standard-solution (50 M H 2 O 2 and 0.5 mM glucose) during 4 h in a flow-injection system with the electrodes polarized at −50 mV versus Ag/AgCl. The system is able to handle about 60 samples per hour and is very stable and suitable for industrial control. Determination of glucose in the range 2.5 and 15% (w/v) in phosphate buffer with precision (r.s.d. < 1.5%) has been achieved and is in agreement with the conventional procedures. Linear calibration in the range of 0.15 and 2.50 mM with detection limits of ca. 0.03 mM has been obtained. The morphology of the enzyme glucose oxidase on the modified electrode has been analyzed by scanning electron microscopy (SEM) measurements.
Journal of Electroanalytical Chemistry, 2004
An electrochemical method, aimed at the hydrogenation of organic substrates, was developed, using... more An electrochemical method, aimed at the hydrogenation of organic substrates, was developed, using a nickel sacrificial anode. The electrochemical system included an iron cathode with deposited nickel and presented good electrochemical efficiency. Some different parameters such as co-solvent, current density, supporting electrolyte and pH were studied to obtain the maximum efficiency for the process. An elevated cell voltage was observed (2.3 V) when 0.2 M NH 4 Ac was used as supporting electrolyte, whereas in NH 4 Cl experiments could be carried out at a low potential (1.3 V). Electrocatalytic hydrogenation (ECH) of organic substrates showed that non-conjugated olefins (cyclohexene and geraniol) were not reactive, while conjugated substrates (2-cycloexen-1-one, benzaldehyde, acetophenone, styrene, trans-trans-2,4-hexadien-1-ol, 1,3-cyclohexadiene, citral and linalool) showed good reactivity and selectivity in some cases. A direct correlation was observed between the electrochemical efficiency, substrate concentration and current density.
Journal of The Chilean Chemical Society, 2009
A suitable flow-injection method for the analysis of commercial solutions of hydrogen peroxide is... more A suitable flow-injection method for the analysis of commercial solutions of hydrogen peroxide is described. A Nafion-coated glassy carbon electrode, modified by deposition of copper hexacyanoferrate (CuCHF), is employed as an amperometric sensor. The method allows the analysis of 45 samples per hour, with peroxide concentrations in the range of 1.25 -10.0 mM, with relative standard deviations smaller than 1%.
Electrochimica Acta, 2010
Benzyl halides adsorbed on a cathode made of pure or silver-doped graphite powder were reduced in... more Benzyl halides adsorbed on a cathode made of pure or silver-doped graphite powder were reduced in an undivided cell using an aqueous electrolyte and an inert anode, in the absence or presence of benzaldehyde. The product ratio is influenced by the applied potential, the leaving halide group and presence/absence of silver electrocatalyst. The highest yield of bibenzyl was obtained from the electrolysis of benzyl bromide on silver-doped graphite at a constant potential equal to −1.0 V vs Ag/AgCl (sat. KCl). Benzyl chloride is less prone to dimerization, but undergoes efficient carbonyl addition to benzaldehyde, especially in the presence of silver. The results can be interpreted as a competition of radical and anionic processes.
Journal of Electroanalytical Chemistry, 2003
... Indeed, when we used a 0.1 M NH 4 Cl solution in methanol+water (1:5), a trace amount of 0.1%... more ... Indeed, when we used a 0.1 M NH 4 Cl solution in methanol+water (1:5), a trace amount of 0.1% of ethyl 2,2-dimethyl-3-hydroxy-3-phenylpropionate (5) could be detected (Table 1, entry 1), but all attempts to improve this result in the undivided cell were unsuccessful, except ...
Green Chemistry, May 4, 2011
ABSTRACT Mixtures of carbonyl compounds and allylhalides, adsorbed on a graphite powder cathode, ... more ABSTRACT Mixtures of carbonyl compounds and allylhalides, adsorbed on a graphite powder cathode, were reduced under aqueous anolyte to give high yields of homoallylic alcohols. Catalytic amounts of silver or tetrabutylammonium tetrafluoroborate improved the yields significantly. Inexpensive allyl chloride gave superior results when compared to allyl bromide.
The Analyst, 2016
The electrochemical determination of cysteine is investigated by adsorptive stripping voltammetri... more The electrochemical determination of cysteine is investigated by adsorptive stripping voltammetric detection of a copper-cysteine complex compound using a bare glassy carbon electrode. In acidic 0.1 M KNO3 solution (pH 4), the electrochemical oxidation of this complex compound generates a characteristic anodic peak ca. -0.17 V vs. a standard mercury/mercurous sulphate reference electrode. The voltammetric response is highly reproducible within 2.1% error (n = 3). A linear dynamic range is obtained for a cysteine concentration of 1.0 μM to 10.0 μM. The sensitivity of 0.18 ± 0.006 μA μM(-1) and the limit of detection of 0.03 μM (n = 3) make our methodology highly applicable for practical applications. Successful determination of cysteine concentration in the presence of glutathione has also been demonstrated by the sequential determination of the concentrations of total thiol and the tripeptide alone.
The Analyst, 2016
A simple, sensitive, and rapid detection of glutathione by cyclic voltammetry using a bare glassy... more A simple, sensitive, and rapid detection of glutathione by cyclic voltammetry using a bare glassy carbon electrode is reported in which glutathione forms a 1 : 1 complex compound with copper(ii) ions. This complex compound is adsorbed onto the electrode surface and undergoes electrochemical oxidation at a characteristic oxidation potential of ca. -0.20 V vs. the standard mercury/mercurous sulphate reference electrode, which is used to detect the glutathione concentration. The linear dynamic range is obtained for a glutathione concentration from 1 μM to 12.5 μM, and the sensitivity is found to be 0.1 ± 0.002 μA μM(-1). A low limit of detection (n = 3) of 0.14 μM and a precision of 1.8% are achieved using a simple, unmodified electrode. The robustness of the present methodology is demonstrated by the successful quantitative analysis of glutathione in the presence of cysteine.
Electrochimica Acta, 2015
ABSTRACT Benzyl chloride reduction was studied in a powder macroelectrode (PME) made of silver, g... more ABSTRACT Benzyl chloride reduction was studied in a powder macroelectrode (PME) made of silver, graphite or silver/graphite mixtures (1:3, 1:1 and 3:1) in absence of solvent, or using a very low amount of DMF as solvent (PhCH2Cl/DMF 3:1). A 0.1 mol L−1 KCl aqueous solution was used as anolyte. A competitive hydrogenation and dimerization process was observed, affording the respective toluene and bibenzyl products. The well-known electrocatalytic effect of silver on reduction of the CCl bond was confirmed by a significant positive shift of the benzyl chloride reduction potential in comparison with pure graphite powder. The products distribution was analysed after linear sweep voltammetries at low scan rate (0.1 mV s−1), indicating high yields of bibenzyl produced on Ag/graphite-PME. Pure graphite-PME was not selective towards dimer formation. The best results for bibenzyl production occurred at more positive potentials, in the presence of silver. A small amount of solvent (DMF) play an important role on the electrode surface desorption and diffusion of intermediary species.
Proceedings of the 15th Brazilian Meeting on Organic Synthesis Proceedings, 2013
Proceedings of the 14th Brazilian Meeting on Organic Synthesis Proceedings, 2013
RSC Advances, 2013
ABSTRACT A green electrochemical heterocoupling procedure has been developed. Prenyl halides and ... more ABSTRACT A green electrochemical heterocoupling procedure has been developed. Prenyl halides and benzaldehyde adsorbed on a graphite powder cathode were reduced in a cavity cell using aqueous anolyte, providing isomer mixtures of prenylated alcohols. High α-regioselectivity was observed using graphite with 3% TBABF4, while high γ-regioselectivity was obtained using 2% silver-doped graphite.
Proceedings of the 14th Brazilian Meeting on Organic Synthesis Proceedings, 2013
Green Chemistry, 2011
ABSTRACT Mixtures of carbonyl compounds and allylhalides, adsorbed on a graphite powder cathode, ... more ABSTRACT Mixtures of carbonyl compounds and allylhalides, adsorbed on a graphite powder cathode, were reduced under aqueous anolyte to give high yields of homoallylic alcohols. Catalytic amounts of silver or tetrabutylammonium tetrafluoroborate improved the yields significantly. Inexpensive allyl chloride gave superior results when compared to allyl bromide.
Electrochimica Acta, 2014
ABSTRACT Six alpha-haloesters and eighteen carbonyl compounds were submitted to electrochemical c... more ABSTRACT Six alpha-haloesters and eighteen carbonyl compounds were submitted to electrochemical coupling on a graphite powder cathode using aqueous anolyte free of organic solvents. Preparative yields of coupling products could be obtained with ethyl 2-bromoisobutyrate and aromatic aldehydes. Ethyl 2-bromopropionate was much less efficient. Extensive variation of applied potential, electrolyte composition, stoichiometry, catalyst, leaving halogen and activating substituents on the carbonyl compound led to the conclusion that the reaction mechanism in most cases proceeds via a radical intermediate generated from the halide reduction. Ethyl chloroacetate produced only trace amounts of coupling product, most probably by a carbanionic mechanism.
Electrochimica Acta, 2013
Six ␣-haloketones adsorbed on a graphite powder cathode were reduced in the presence of benzaldeh... more Six ␣-haloketones adsorbed on a graphite powder cathode were reduced in the presence of benzaldehyde using undivided cell, inert anode and aqueous electrolyte. High yields of aldol coupling product were obtained from 2-chloropinacolone in the presence of catalytic amounts of silver. For the corresponding bromo compound, the reaction was much less satisfactory. Chloroacetone gave moderate yields of the ␣,-unsaturated coupling product. 2-Chlorobutanone produced two main products in low yield: the expected aldol and the corresponding 1,3-diketone. With 2-bromopropiophenone and 2-bromoisobutyrophenone no coupling with benzaldehyde was observed but only reductive dehalogenation. The results can be interpreted in terms of a carbanionic intermediate generated by a two-electron transfer.
Talanta, 2005
A highly selective, fast and stable biosensor for determination of glucose in soluble coffee has ... more A highly selective, fast and stable biosensor for determination of glucose in soluble coffee has been developed. The biosensor electrode consist of a thin film of ferric hexacyanoferrate (Prussian Blue or PB) electrodeposited on the glassy carbon electrode (GCE) (to provide a catalytic surface for the detection of hydrogen peroxide) glucose oxidase immobilized on top of the electrode and a Nafion ® polymer layer. The stability of the PB film and the biosensor was evaluated by injecting standard-solution (50 M H 2 O 2 and 0.5 mM glucose) during 4 h in a flow-injection system with the electrodes polarized at −50 mV versus Ag/AgCl. The system is able to handle about 60 samples per hour and is very stable and suitable for industrial control. Determination of glucose in the range 2.5 and 15% (w/v) in phosphate buffer with precision (r.s.d. < 1.5%) has been achieved and is in agreement with the conventional procedures. Linear calibration in the range of 0.15 and 2.50 mM with detection limits of ca. 0.03 mM has been obtained. The morphology of the enzyme glucose oxidase on the modified electrode has been analyzed by scanning electron microscopy (SEM) measurements.
Journal of Electroanalytical Chemistry, 2004
An electrochemical method, aimed at the hydrogenation of organic substrates, was developed, using... more An electrochemical method, aimed at the hydrogenation of organic substrates, was developed, using a nickel sacrificial anode. The electrochemical system included an iron cathode with deposited nickel and presented good electrochemical efficiency. Some different parameters such as co-solvent, current density, supporting electrolyte and pH were studied to obtain the maximum efficiency for the process. An elevated cell voltage was observed (2.3 V) when 0.2 M NH 4 Ac was used as supporting electrolyte, whereas in NH 4 Cl experiments could be carried out at a low potential (1.3 V). Electrocatalytic hydrogenation (ECH) of organic substrates showed that non-conjugated olefins (cyclohexene and geraniol) were not reactive, while conjugated substrates (2-cycloexen-1-one, benzaldehyde, acetophenone, styrene, trans-trans-2,4-hexadien-1-ol, 1,3-cyclohexadiene, citral and linalool) showed good reactivity and selectivity in some cases. A direct correlation was observed between the electrochemical efficiency, substrate concentration and current density.
Journal of The Chilean Chemical Society, 2009
A suitable flow-injection method for the analysis of commercial solutions of hydrogen peroxide is... more A suitable flow-injection method for the analysis of commercial solutions of hydrogen peroxide is described. A Nafion-coated glassy carbon electrode, modified by deposition of copper hexacyanoferrate (CuCHF), is employed as an amperometric sensor. The method allows the analysis of 45 samples per hour, with peroxide concentrations in the range of 1.25 -10.0 mM, with relative standard deviations smaller than 1%.
Electrochimica Acta, 2010
Benzyl halides adsorbed on a cathode made of pure or silver-doped graphite powder were reduced in... more Benzyl halides adsorbed on a cathode made of pure or silver-doped graphite powder were reduced in an undivided cell using an aqueous electrolyte and an inert anode, in the absence or presence of benzaldehyde. The product ratio is influenced by the applied potential, the leaving halide group and presence/absence of silver electrocatalyst. The highest yield of bibenzyl was obtained from the electrolysis of benzyl bromide on silver-doped graphite at a constant potential equal to −1.0 V vs Ag/AgCl (sat. KCl). Benzyl chloride is less prone to dimerization, but undergoes efficient carbonyl addition to benzaldehyde, especially in the presence of silver. The results can be interpreted as a competition of radical and anionic processes.
Journal of Electroanalytical Chemistry, 2003
... Indeed, when we used a 0.1 M NH 4 Cl solution in methanol+water (1:5), a trace amount of 0.1%... more ... Indeed, when we used a 0.1 M NH 4 Cl solution in methanol+water (1:5), a trace amount of 0.1% of ethyl 2,2-dimethyl-3-hydroxy-3-phenylpropionate (5) could be detected (Table 1, entry 1), but all attempts to improve this result in the undivided cell were unsuccessful, except ...