M M Correia dos Santos

New University of Lisbon, Caparica, Distrito de Setubal, Portugal

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Publications (29)62.55 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The activation mechanism of Pseudomonas stutzeri cytochrome c peroxidase (CCP) was probed through the mediated electrochemical catalysis by its physiological electron donor, P. stutzeri cytochrome c-551. A comparative study was carried out, by performing assays with the enzyme in the resting oxidized state as well as in the mixed-valence activated form, using cyclic voltammetry and a pyrolytic graphite membrane electrode. In the presence of both the enzyme and hydrogen peroxide, the peak-like signal of cytochrome c-551 is converted into a sigmoidal wave form characteristic of an E(r)C'(i) catalytic mechanism. An intermolecular electron transfer rate constant of (4 ± 1) × 10(5) M(-1) s(-1) was estimated for both forms of the enzyme, as well as a similar Michaelis-Menten constant. These results show that neither the intermolecular electron transfer nor the catalytic activity is kinetically controlled by the activation mechanism of CCP in the case of the P. stutzeri enzyme. Direct enzyme catalysis using protein film voltammetry was unsuccessful for the analysis of the activation mechanism, since P. stutzeri CCP undergoes an undesirable interaction with the pyrolytic graphite surface. This interaction, previously reported for the Paracoccus pantotrophus CCP, induces the formation of a non-native conformation state of the electron-transferring haem, which has a redox potential 200 mV lower than that of the native state and maintains peroxidatic activity.
    European Journal of Biochemistry 05/2011; 16(6):881-8. · 3.42 Impact Factor
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    ABSTRACT: The determination of fluoride ions in water samples is accomplished by using a tubular flow through detector constructed by drilling a channel through a commercially available LaF(3) crystal electrode in such a way that the original contacts of the non-modified unit are maintained. Its performance when incorporated in both FIA and SIA systems was evaluated and the results show that the tubular unit retains the characteristics of the non-modified electrode. In SIA conditions an extended linear range of response and lower detection limit were achieved when compared with the electrode performance in FIA conditions. These aspects together with the additional advantage of low sample and reagent consumptions in SIA when compared to FIA, makes the incorporation of the proposed tubular ISE in a SIA system the preferred approach for on line determination and monitoring of fluoride content in natural water samples.
    Talanta 07/2008; 76(1):107-10. · 3.50 Impact Factor
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    ABSTRACT: A comparative study of direct and mediated electrochemistry of metalloproteins in bulk and membrane-entrapped solutions is presented. This work reports the first electrochemical study of the electron transfer between a bacterial cytochrome c peroxidase and horse heart cytochrome c. The mediated catalysis of the peroxidase was analysed both using the membrane electrode configuration and with all proteins in solution. An apparent Michaelis constant of 66 +/- 4 and 42 +/- 5 microM was determined at pH 7.0 and 0 M NaCl for membrane and bulk solutions, respectively. The data revealed that maximum activity occurs at 50 mM NaCl, pH 7.0, with intermolecular rate constants of (4.4 +/- 0.5) x 10(6) and (1.0 +/- 0.5) x 10(6) M(-1) s(-1) for membrane-entrapped and bulk solutions, respectively. The influence of parameters such as pH or ionic strength on the mediated catalytic activity was analysed using this approach, drawing attention to the fact that careful analysis of the results is needed to ensure that no artefacts are introduced by the use of the membrane configuration and/or promoters, and therefore the dependence truly reflects the influence of these parameters on the (mediated) catalysis. From the pH dependence, a pK of 7.5 was estimated for the mediated enzymatic catalysis.
    JBIC Journal of Biological Inorganic Chemistry 07/2008; 13(5):779-87. · 3.35 Impact Factor
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    ABSTRACT: This work reports the direct electrochemistry of Paracoccus pantotrophus pseudoazurin and the mediated catalysis of cytochrome c peroxidase from the same organism. The voltammetric behaviour was examined at a gold membrane electrode, and the studies were performed in the presence of calcium to enable the peroxidase activation. A formal reduction potential, E (0)', of 230 +/- 5 mV was determined for pseudoazurin at pH 7.0. Its voltammetric signal presented a pH dependence, defined by pK values of 6.5 and 10.5 in the oxidised state and 7.2 in the reduced state, and was constant up to 1 M NaCl. This small copper protein was shown to be competent as an electron donor to cytochrome c peroxidase and the kinetics of intermolecular electron transfer was analysed. A second-order rate constant of 1.4 +/- 0.2 x 10(5) M(-1) s(-1) was determined at 0 M NaCl. This parameter has a maximum at 0.3 M NaCl and is pH-independent between pH 5 and 9.
    JBIC Journal of Biological Inorganic Chemistry 07/2007; 12(5):691-8. · 3.35 Impact Factor
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    ABSTRACT: Desulfovibrio vulgaris Hildenborough cytochrome c(3) contains four hemes in a low-spin state with bis-histidinyl coordination. High-spin forms of cytochrome c(3) can be generated by protonation of the axial ligands in order to probe spin equilibrium (low-spin/high-spin). The spin alterations occurring at acid pH, the associated changes in redox potentials, as well as the reactivity towards external ligands were followed by the conjunction of square wave voltammetry and UV-visible, CD, NMR and EPR spectroscopies. These processes may be used for modelling the action of enzymes that use spin equilibrium to promote enzyme activity and reactivity towards small molecules.
    Journal of Inorganic Biochemistry 01/2007; 100(12):2009-16. · 3.20 Impact Factor
  • M. A. Trancoso, M. M. Correia Dos Santos, M. L. Simões Gonçalves
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    ABSTRACT: The adsorption of lead by a non-contaminated loamy sand soil (Guarda, Portugal) was studied by voltammetric titrations using differential pulse polarography for pH values of 6.0, 6.8 and 7.2 and I of 0.5, 0.1 and 0.01 mol L−1. After lead or soil additions, residual lead in solution was measured in the presence of the soil particles after an equilibration period, thus with minimum sample manipulation. The characteristics of the surface groups were studied by acid base potentiometric titrations. Lead retention by the soil is influenced both by pH and ionic strength of the medium. From the voltammetric data surface constants and total available binding groups have been estimated according to a complex surface model for the different experimental conditions and the results interpreted in terms of the surface characteristics of the soil and the support medium. Surface binding capacities in the range 1 to 70 mmol Pb kg−1 were found depending on the pH and the ionic strength. The behavior found is in agreement with what is known in soil chemistry thus supporting the conclusion that voltammetric methods are quite appropriate for determining the extent of interaction between metal ions and soils.
    Electroanalysis 05/2004; 16(12):1024 - 1032. · 2.82 Impact Factor
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    ABSTRACT: In this article, a flow system developed for the amperometric determination of a great variety of pharmaceuticals that are known to lead the rapid poisoning of the working electrode surface is described. The referred system was made up of two parallel flow channels that shared the voltammetric detector of tubular configuration, whose movement in the manifold followed the concept of multi-site location of detector. In this way, after each measurement, the conditioning of the working electrode was possible through the passage by its surface of a regeneration solution without implying the alteration of the carrier that flowed in the analytical channel of the manifold. The methodology proposed was evaluated through the determination of two drugs belonging to two distinct therapeutic groups: an antihypertensive (diltiazem) and a non-steroid anti-inflammatory (nimesulide). The results obtained after evaluation of various pharmaceutical formulations on the Portuguese market were in the case of diltiazem compared with those supplied by the reference US Pharmacopoeia XXIV method, with no statistically significant differences having been observed for a confidence interval of 95%. In the case of nimesulide, since no official reference method exists, a series of recovery experiments were proceeded with and a mean value of 101.1% with a R.S.D. of 0.7% was obtained.
    Journal of Pharmaceutical and Biomedical Analysis 12/2003; 33(4):571-80. · 2.95 Impact Factor
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    ABSTRACT: Membrane electrodes (ME) were constructed using gold, glassy carbon and pyrolytic graphite supports and a dialysis membrane, and used to study the electrochemical behavior of small size electron transfer proteins: monohemic cytochrome c522 from Pseudomonas nautica and cytochrome c533 as well as rubredoxin from Desulfovibrio vulgaris. Different electrochemical techniques were used including cyclic voltammetry (CV), square wave voltammetry (SW) and differential pulse voltammetry (DP). A direct electrochemical response was obtained in all cases except with rubredoxin where a facilitator was added to the protein solution entrapped between the membrane and the electrode surface. Formal potentials and heterogeneous charge transfer rate constants were determined from the voltammetric data. The influence of the ionic strength and the pH of the medium on the electrochemical response at the ME were analyzed. The benefits from the use of the ME in protein electrochemistry and its role in modulating the redox behavior are analyzed. A critical comparison is presented with data obtained at non-MEs. Finally, the interactions that must be established between the proteins and the electrode surfaces are discussed, thereby modeling molecular interactions that occur in biological systems.
    Journal of Electroanalytical Chemistry 01/2003; · 2.58 Impact Factor
  • M M Correia Dos Santos, Vila Famila, M L Simões Gonçalves
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    ABSTRACT: Direct square-wave voltammetry (SWV) and square-wave cathodic stripping voltammetry (SWCSV) at hanging mercury drop electrodes have been developed for determination of the psychoactive 1,4-benzodiazepine compounds clonazepam, bromazepam, midazolam, diazepam, medazepam, and flurazepam over a wide range of concentrations. Analysis was performed with better precision, lower detection limits, and much more rapidly than by previously reported voltammetric techniques. The applicability of both procedures is discussed. The methods were applied to the analysis of commercially available tablets with minimum sample manipulation. The accuracy of the results was accessed by comparison with those obtained by use of the methods described in official pharmacopoeias. A critical comparison with those procedures is also presented.
    Analytical and Bioanalytical Chemistry 12/2002; 374(6):1074-81. · 3.66 Impact Factor
  • M M Correia dos Santos, Vila Famila, M L Simões Gonçalves
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    ABSTRACT: Copper complexation by the 1,4-benzodiazepines medazepam, diazepam, flurazepam, nitrazepam, and clonazepam was investigated using differential pulse polarography and cyclic voltammetry at a mercury electrode in 0.10 M KNO3 and pH 7.0 +/- 0.1. Because the 1,4-benzodiazepines are easily reduced at a mercury electrode through the two-electron reduction of the 4,5-azomethine functional group, copper reduction, as well as that of the ligands, was analyzed under varying experimental conditions. In most situations adsorption phenomena occurred and their influence on voltammetric signals had to be carefully analyzed. The voltammetric behavior was then interpreted in terms of complex formation. The results showed that all benzodiazepines can act as ligands toward copper(II) ions, forming 1:1 and 1:2 complexes with similar stabilities. The stoichiometric acidity constants of the benzodiazepines under study were also determined by potentiometric titration in water-ethanol medium and 0.10 M KNO3 and then extrapolated to 0% concentration of ethanol.
    Analytical Biochemistry 05/2002; 303(2):111-9. · 2.58 Impact Factor
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    ABSTRACT: The electrochemical behaviour of rubredoxin from Desulfovibrio vulgaris is analysed in 0.1 M KCl at pH 7.6±0.1 (10 mM Tris buffer) using gold disk electrodes (r=12.5 μm and r=0.08 cm) in the presence of Mg2+ and/or neomycin, and revisited using a carbon electrode (r=0.15 cm) in the presence of Mg2+ and further analysed in solutions with neomycin with and without Mg2+. The results show that, depending on the modifier and its concentration, the electrode surface may have different densities of electroactive sites and so different mass transport processes may take place, thus accounting for the shape of the voltammograms. Values for ks, D and E°′ determined under all conditions agreed with each other within experimental error, no matter what the size or material of the electrode or the modifier used.
    Journal of Electroanalytical Chemistry 01/2001; 501:173-179. · 2.58 Impact Factor
  • M. M. Correia dos Santos, V. Famila, M. L. Simões Gonçalves
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    ABSTRACT: Complexation of copper ions with the 1,4-benzodiazepines bromazepam, midazolam and chlordiazepoxide is investigated using voltammetric methods, mainly differential pulse polarography in KNO3 0.10 M and pH 7.0±0.1. Additional evidence of the complexation of copper was obtained by an UV-spectrophotometric study. Reduction of the metal ion as well as that of the ligands followed and the voltammetric behavior was interpreted in terms of complex formation. Stability constants have been determined for the experimental conditions used and the values were compared with those from the spectrophotometric study. The results show that copper(II) complexation is favored by the presence of chelating groups other than the azomethine group common to all the 1,4-benzodiazepines. It is also apparent that in some circumstances copper in the +1 oxidation state may be stabilized by complex formation. This result could only be inferred from the voltammetric data since in the presence of appropriate ligands the copper(I) oxidation state is produced electrochemically at the electrode/solution interface. The processes studied may help in understanding some of the features of the binding mechanisms between copper ion and the 1,4-benzodiazepine derivatives.
    Electroanalysis 02/2000; 12(3):216 - 222. · 2.82 Impact Factor
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    ABSTRACT: The determination of fluoride ions in water samples was accomplished by using a gradient flow titration. A standard commercial combined electrode is used in a cell configuration that combines the gradient chamber and the electrode in a single unit. The methodology developed gives results with a relative standard deviation of about 3%. The average recoveries after spiking natural samples with fluoride are in the range 100-102%. The method was used successful in determining the fluoride concentration in water samples.
    Talanta 02/2000; 50(6):1245-52. · 3.50 Impact Factor
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    M C Rollemberg, M L Gonçalves, M M Correia dos Santos, M J Botelho
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    ABSTRACT: From voltammetric titration curves of living Chlorella marina cells with cadmium ion, at constant pH, the surface binding capacity of the alga was determined and interpreted in terms of average conditional equilibrium constants and of differential equilibrium function. Since the alga can live in estuaries, the influence of ionic strength and competition of alkaline and alkaline earth cations has been considered. Cadmium complexation with dead algae killed by heat or using formaldehyde has also been studied for comparison.
    Bioelectrochemistry and Bioenergetics 03/1999; 48(1):61-8.
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    ABSTRACT: The aim of this work is to use microelectrodes as a current approach for the study of unmediated electrochemistry of redox proteins. An electrochemical study of monohemic cytochromes c552 from Pseudomonas nautica 617, cytochrome c553 from Desulfovibrio vulgaris and horse heart cytochrome c is presented at inlaid disk microelectrodes of platinum, gold and carbon. Different electrochemical techniques were used such as linear scan, differential pulse and square wave voltammetry. The electrochemical response was also analysed at conventional size (macro) electrodes for comparison. In all situations a promoter was used. The electrochemical behaviour was evaluated in terms of kinetics of the electrode processes and the formal potentials determined. Diffusion coefficients were also calculated from the voltammetric data. A critical comparison of the results obtained is carried out and the advantages of microelectrodes for electrochemical studies of metalloproteins are pointed out.
    Journal of Electroanalytical Chemistry 01/1999; 464(1):76-84. · 2.58 Impact Factor
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    ABSTRACT: The interaction of divalent metal ions such as copper ions with basic constituents of nucleic acids may help to gain an insight into the mechanisms with DNA itself. In this work the complexation of copper by pyrimidine bases and their nucleosides, namely cytosine and cytidine, is analysed at the ionic strength of 0.10 M and in the pH range 3.5–6.5, using anodic stripping voltammetry with the hanging mercury drop electrode. In the presence of cytosine and cytidine, stabilisation of copper(I) oxidation state occurs due to complex formation, and so copper(II) redox reaction proceeds in two one-electron steps. From the peak potential shifts with increasing ligand concentration, the stoichiometry and formation constants of the complexes with copper(II) and copper(I) have been determined. The values obtained were analysed in terms of ligand structure.
    Bioelectrochemistry and Bioenergetics. 01/1998;
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    ABSTRACT: An approach for speciation of iron (as Fe(II) and Fe(III)) based on integration of retention of the Fe(III)-SCN complex with detection using a conventional spectrophotometer is proposed here. The device (namely, a flow-cell packed with an exchange resin) has been coupled to a flow-injection manifold with inner-coupled injection valves which enables discrimination between Fe(III) and Fe(II) taking advantage of a redox minicolumn housed in the loop of one of the valves. The method thus proposed has good selectivity with a determination limit of 80 μgl−1 and affords a determination range of 80–500 μgl−1 for Fe(II) plus Fe(III). Application to synthetic and real samples containing both the oxidation states of iron lead to average recoveries of 103% and 101% for Fe(II) and total iron (Fe(II)+Fe(III)), respectively, thus showing the usefulness of the overall approach.
    Analytica Chimica Acta 05/1997; · 4.39 Impact Factor
  • M.M.Correia dos Santos, C.M.L.Freire Lopes, M.L.Simões Gonçalves
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    ABSTRACT: Anodic stripping voltammetry with a hanging mercury drop electrode has been used to investigate the interaction of cooper with the purines adenine, hypoxanthine, xanthine and purine nucleosides adenosine, guanosine and inosine at an ionic strength of 0.1 M in KNO3 and in the pH range 3.5–5.5. In all cases stabilisation of copper(I) occurs suggesting that the oxidation of copper(0) in the presence of excess ligand proceeds in two one-electron steps.Adsorption onto the electrode has been analysed and conditions where this is negligible were chosen for complexation studies. From the shift of the peak potential corresponding to Cu(0)/Cu(I) oxidation with increasing ligand concentration the stoichiometry of the complexes and their formation constants have been determined. The values obtained are discussed in terms of the ligand structure.
    Bioelectrochemistry and Bioenergetics 01/1996;
  • M. M. Correia dos Santos, M. L. Simões Gonçalves, J. C. Romão
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    ABSTRACT: The use of square wave voltammetry (SWV) at a hanging mercury drop electrode to study a chemical reaction preceding a reversible electron transfer (CE mechanism) is reported. Two cases were analysed: cadmium(II) + nitrilotriacetic acid and the cadmium(II) + aspartic acid systems. In both situations the homogeneous reaction in buffered solutions and in the presence of an excess of ligand was considered to be first order.Experimental data were analysed in terms of theory of SWV for kinetic systems. Rate constants of dissociation of the complexes of cadmium with nitrilotriacetic acid and aspartic acid were determined using a numerical procedure based on a one variable fit. The results obtained are in good agreement with published values where other techniques have been used, in particular cyclic voltammetry.
    Journal of Electroanalytical Chemistry 01/1996; 413(1):97-103. · 2.58 Impact Factor
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    ABSTRACT: The use of rapid gradient flow-injection titration for the determination of equilibrium constants in solution, previously used in pK measurements of monobasic and multibasic weak acids is extended to the more demanding case of metal complexation. Formation constants for the complexes ML and ML2 of Cd2+ with glycine have been determined by that technique using potentiometric detection with a glass electrode. Under optimum conditions formation constants in good agreement with batch and literature values are obtained in several minutes.
    Analytica Chimica Acta 02/1995; 302(1):97–102. · 4.39 Impact Factor

Publication Stats

91 Citations
62.55 Total Impact Points

Institutions

  • 2007–2011
    • New University of Lisbon
      • Faculty of Sciences and Technology
      Caparica, Distrito de Setubal, Portugal
  • 1983–2011
    • Instituto Técnico y Cultural
      Santa Clara de Portugal, Michoacán, Mexico
  • 2002–2007
    • Instituto Superior de Contabilidade e Administração de Lisboa
      Lisboa, Lisbon, Portugal
  • 2003
    • University of Porto
      • Faculdade de Farmácia
      Porto, Distrito do Porto, Portugal