A novel photoelectrochemical sensor was developed for determination of tert-butyl-hydroquinone (T... more A novel photoelectrochemical sensor was developed for determination of tert-butyl-hydroquinone (TBHQ) in edible vegetable oils, based on CdSe/ZnS core-shell quantum dots sensitized with lithium tetracyanoethylenide (LiTCNE). The CdSe/ZnS/LiTCNE photoelectrochemical sensor presented a TBHQ photocurrent about 13-fold higher and a charge transfer resistance 62-fold lower than observed for a CdSe/ZnS sensor. The photoelectrochemical sensor showed selectivity to TBHQ, with a high photocurrent for this antioxidant compared to the photocurrent responses for other phenolic antioxidants. The CdSe/ZnS/LiTCNE photoelectrochemical sensor presented a linear range from 0.6 to 250μmolL(-1), sensitivity of 0.012μALμmol(-1), and a limit of detection of 0.21μmolL(-1) for TBHQ, under optimized experimental conditions. The sensor was successfully employed in the analysis of edible oil samples, with recoveries of between 98.25% and 99.83% achieved.
This work describes a DFT level theoretical quantum study using the B3LYP functional with the Lan... more This work describes a DFT level theoretical quantum study using the B3LYP functional with the Lanl2TZ(f)/6-31G* basis set to calculate parameters including the bond distances and angles, electronic configurations, interaction energies, and vibrational frequencies of FeTClTAA (iron-tetrachloro-tetraaza[14]annulene), FeTOHTAA (iron-tetrahydroxy-tetraaza[14]annulene), FeTOCH3TAA (iron- tetramethoxy-tetraaza[14]annulene), FeTNH2TAA (iron-tetraamino-tetraaza[14]annulene), and FeTNO2TAA (iron-tetranitro-tetraaza[14]annulene) complexes, as well as their different spin multiplicities. The calculations showed that the complexes were most stable in the triplet spin state (S = 1), while, after interaction with carbon monoxide, the singlet state was most stable. The reactivity of the complexes was evaluated using HOMO-LUMO gap calculations. Parameter correlations were performed in order to identify the best complex for back bonding (3d xzFe → 2p xC and 3d yzFe → 2p zC) with carbon monoxide, and...
Theoretical chemistry calculations using the Density Functional Theory (DFT) were carried out to ... more Theoretical chemistry calculations using the Density Functional Theory (DFT) were carried out to understand the interaction between oxygen (O2) and MnN4 type manganese-based complexes during the formation of MnN4-O2 adducts. In order to understand how this interaction is affected by different macrocyclic ligands, O2 was bonded to manganese-porphyrin (MnP), manganese-octamethylporphyrin (MnOMP), manganese-tetraaza[14]annulene (MnTAA), manganese-dibenzo [b,i] [1, 4, 8, 11]-tetraaza [14] annulene (MnDBTAA), manganese-2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene ([(tim)Mn](2+)), and manganese-2,3,9,10-tetraphenyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene ([(ph-tim)Mn](2+)). The binding and activation of the oxygen molecule was facilitated by an increasing trend in the O-O bond lengths and a decreasing one in the O-O vibrational frequency, with preference for the O2 side-on interaction among MnN4 macrocycles. The catalytic activities of the MnN4 complexe...
Batch injection analysis (BIA) with amperometric detection, using a pyrolytic graphite electrode ... more Batch injection analysis (BIA) with amperometric detection, using a pyrolytic graphite electrode modified with cobalt phthalocyanine (PG/CoPc), was employed for determination of α-lipoic acid (ALA) in pharmaceutical product and in synthetic urine samples. The proposed BIA method is based on the application of a potential of +0.9V vs. Ag/AgCl, KCl sat, enabling quantification of ALA over a concentration range from 1.3×10(-6) to 1.0×10(-4)molL(-1), with a detection limit of 1.5×10(-8)molL(-1). A sampling rate of 180 injections per hour was attained and measurements of the reproducibility of successive injections (100µmolL(-1) ALA on the same electrode) showed a RSD of 2.11% for 40 successive injections. The new sensor was utilised for ALA quantification in a dietary pharmaceutical supplement and in synthetic urine and the results obtained for both samples were compared with parallel analysis using high performance liquid chromatography (HPLC), the method recommended by the United States Pharmacopeia. The results obtained were similar (at a 95% confidence level) and in the case of the synthetic urine sample (prepared with a known amount of ALA) the recovery was situated between 98.0% and 102.6%.
A new and simple electroanalytical method was developed for determination of Cu(II) by derivative... more A new and simple electroanalytical method was developed for determination of Cu(II) by derivative potentiometric stripping analysis (dPSA). The method employed a basal plane pyrolytic graphite (BPPG) electrode modified with 4-[10,15,20-tris(4-sulfophenyl)-21,22-dihydroporphyrin-5-yl] benzenesulfonic acid (H2 TSPP) adsorbed onto multi-walled carbon nanotubes (MWCNT). The modified electrode showed excellent stability and was able to detect Cu(II) at nanomolar levels. The electrochemical method is based on simultaneous preconcentration/reduction of Cu(II) ions on the H2 TSPP/MWCNT/BPPG electrode at -0.25 V vs. Ag/AgCl(sat) in 0.1 mol/L phosphate buffer solution (pH 7.0), during 240 s, followed by subsequent chemical stripping. The analytical signal showed a linear response for Cu(II) concentrations in the range 5 to 1600 nmol/L (R = 0.9998), with a detection limit of 1.0 nmol/L. The sensor was successfully applied for Cu(II) determination in gasoline samples, and the results were in ag...
Luminescence : the journal of biological and chemical luminescence, Jan 2, 2015
This paper describes a new technique for the determination of captopril in pharmaceutical formula... more This paper describes a new technique for the determination of captopril in pharmaceutical formulations, implemented by employing multicommuted flow analysis. The analytical procedure was based on the reaction between hypochlorite and captopril. The remaining hypochlorite oxidized luminol that generated electromagnetic radiation detected using a homemade luminometer. To the best of our knowledge, this is the first time that this reaction has been exploited for the determination of captopril in pharmaceutical products, offering a clean analytical procedure with minimal reagent usage. The effectiveness of the proposed procedure was confirmed by analyzing a set of pharmaceutical formulations. Application of the paired t-test showed that there was no significant difference between the data sets at a 95% confidence level. The useful features of the new analytical procedure included a linear response for captopril concentrations in the range 20.0-150.0 µmol/L (r = 0.997), a limit of detect...
ABSTRACT This paper describes the feasibility of using direct current electrical resistivity meas... more ABSTRACT This paper describes the feasibility of using direct current electrical resistivity measurements to evaluate AISI 304 austenitic stainless steel sensitization. ASTM A262 - Practice A and double loop electrochemical potentiodynamic reactivation (DL-EPR) tests were performed to assess the degree of sensitization (DoS) qualitatively and quantitatively, and electrical resistivity (ER) was measured by the four-point direct-current potential drop method. The results indicate that the DoS increases rapidly while the ER decreases gradually in response to increasing sensitization. Thereafter, the two parameters tend to remain approximately constant. This behavior may be due to the rapid increase in the volume fraction of M23C6 precipitates over a sensitization time of 4 to 6 hours, thereafter remaining relatively constant. The ER results, which were corroborated by other techniques used in this study, confirm the promising potential of this property to monitor the sensitization phenomenon in AISI 304 steel.
Journal of the Chemical Society, Chemical Communications, 1987
ABSTRACT Reductive dimerization of tricarbonyl(1-methoxycarbonylcyclohexadienyl)iron hexafluoroph... more ABSTRACT Reductive dimerization of tricarbonyl(1-methoxycarbonylcyclohexadienyl)iron hexafluorophosphate proceeds in a regioselective manner using either zinc dust or electrochemical techniques, cyclic voltammetry experiments providing evidence for a one-electron transfer process involving free radical intermediates; the first example of intramolecular cross coupling of the free radical with an alkene moiety is reported.
ABSTRACT In this work voltammetric techniques were explored for quantification of α-Lipoic acid (... more ABSTRACT In this work voltammetric techniques were explored for quantification of α-Lipoic acid (ALA) using a pyrolytic graphite electrode modified with cobalt phthalocyanine. Cyclic voltammograms recorded in phosphate buffer solution containing 1×10−3 mol L−1 of ALA presented an oxidation peak located at +0.8 V vs. SCE. The modification of the electrode produced a 100 mV shift of the onset oxidation potential to less positive value and a substantial increase in the ALA oxidation current. Among the voltammetric techniques explored, differential pulse voltammetry showed the best performance for quantifications of the analyte in low concentrations. Limits of detection and quantification of ALA obtained corresponds to 3.4×10−9 mol L−1 and 1.2×10−8 mol L−1, respectively.
ABSTRACT The present article describes a DFT study of dibenzotetraaza[14]annulene complexed with ... more ABSTRACT The present article describes a DFT study of dibenzotetraaza[14]annulene complexed with first row transition metals (MII(DBTAA)), employing calculations made using the B3LYP hybrid functional with the Lanl2DZ/6-31G∗ basis set. The parameters considered were bond distances and angles, electron configurations, interaction energies, vibrational frequencies, and frontier molecular orbitals (HOMO and LUMO). The calculations indicated that the key to complexes of the metals Ti, and Cr was the high spin state, while for Mn and Fe it was the intermediate spin state and for Co, Ni, Cu, and Zn it was the low spin state. The M-N distance (d(M-N)) and vibrational frequency showed inversely proportional behavior as a function of the atomic number of the metal. The Ni(DBTAA) complex showed the smallest d(M-N) and highest vibrational frequency, indicating greater compaction of the ligand on nickel. The interaction energy and the gap (HOMO-LUMO) were also calculated in order to estimate the stability and reactivity of the complexes. The stability increased with the atomic number of the central metal, in agreement with the Irving-Williams series, with Ni(DBTAA) being the most stable, and Ti(DBTAA) and Mn(DBTAA) being the most reactive of the complexes investigated.
This work describes the highly sensitive detection of organophosphorus pesticides employing the c... more This work describes the highly sensitive detection of organophosphorus pesticides employing the cobalt(II) 4,4,4,4-tetrasulfo-phthalocyanine (CoTSPc) macrocycle complex, carbon nanotubes (CNT), and 1-methyl-3-octylimidazolium tetrafluoroborate (OMIM[BF4]). The technique is based on enzyme acetylcholinesterase (AChE) inhibition. The composite was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and amperometry. The AChE was immobilized on the composite electrode surface by cross-linking with glutaraldehyde and chitosan. The synergistic action of the CoTSPc/CNT/OMIM[BF4] composite showed excellent electrocatalytic activity, with a low applied potential for the amperometric detection of thiocholine (TCh) at 0.0 V vs. Ag/AgCl. The calculated catalytic rate constant, kcat, was 3.67 × 10(3) mol(-1) L s(-1). Under the optimum conditions, the inhibition rates of these pesticides were proportional to their concentrations in the ranges of 1.0 pmol L(-1) to 1.0 nmol L(-1) (fenitrothion), 2.0 pmol L(-1) to 8.0 nmol L(-1) (dichlorvos), and 16 pmol L(-1) to 5.0 nmol L(-1) (malathion).
Microcystins (MCs) are cyclic hepatotoxic heptapeptides produced by certain strains of freshwater... more Microcystins (MCs) are cyclic hepatotoxic heptapeptides produced by certain strains of freshwater cyanobacteria toxic for humans and animals. The electrochemical behaviour of microcystin-LR (MC-LR) at a glassy carbon electrode (GCE) was investigated using cyclic voltammetry (CV), square wave voltammetry (SWV) and differential pulse voltammetry (DPV). The oxidation of MC-LR is a diffusion-controlled irreversible and pH-independent process that occurs with the transfer of only one electron and does not involve the formation of any electroactive oxidation product. Upon incubation in different pH electrolytes, homogeneous degradation of MC-LR in solution was electrochemically detected by the appearance of a new oxidation peak at a lower potential. The electrochemical behaviour of chemically degraded MC-LR is an irreversible, pH-dependent process, and involves the formation of two redox products that undergo reversible oxidation. The formation of degradation products of MC-LR was confirmed by HPLC with UV detection at room temperature. Experiments were also carried out in solutions containing constituent MC-LR amino acids, which enabled the understanding of the MC-LR electron transfer reaction and degradation. An oxidation mechanism for MC-LR is proposed.
A novel photoelectrochemical sensor was developed for determination of tert-butyl-hydroquinone (T... more A novel photoelectrochemical sensor was developed for determination of tert-butyl-hydroquinone (TBHQ) in edible vegetable oils, based on CdSe/ZnS core-shell quantum dots sensitized with lithium tetracyanoethylenide (LiTCNE). The CdSe/ZnS/LiTCNE photoelectrochemical sensor presented a TBHQ photocurrent about 13-fold higher and a charge transfer resistance 62-fold lower than observed for a CdSe/ZnS sensor. The photoelectrochemical sensor showed selectivity to TBHQ, with a high photocurrent for this antioxidant compared to the photocurrent responses for other phenolic antioxidants. The CdSe/ZnS/LiTCNE photoelectrochemical sensor presented a linear range from 0.6 to 250μmolL(-1), sensitivity of 0.012μALμmol(-1), and a limit of detection of 0.21μmolL(-1) for TBHQ, under optimized experimental conditions. The sensor was successfully employed in the analysis of edible oil samples, with recoveries of between 98.25% and 99.83% achieved.
This work describes a DFT level theoretical quantum study using the B3LYP functional with the Lan... more This work describes a DFT level theoretical quantum study using the B3LYP functional with the Lanl2TZ(f)/6-31G* basis set to calculate parameters including the bond distances and angles, electronic configurations, interaction energies, and vibrational frequencies of FeTClTAA (iron-tetrachloro-tetraaza[14]annulene), FeTOHTAA (iron-tetrahydroxy-tetraaza[14]annulene), FeTOCH3TAA (iron- tetramethoxy-tetraaza[14]annulene), FeTNH2TAA (iron-tetraamino-tetraaza[14]annulene), and FeTNO2TAA (iron-tetranitro-tetraaza[14]annulene) complexes, as well as their different spin multiplicities. The calculations showed that the complexes were most stable in the triplet spin state (S = 1), while, after interaction with carbon monoxide, the singlet state was most stable. The reactivity of the complexes was evaluated using HOMO-LUMO gap calculations. Parameter correlations were performed in order to identify the best complex for back bonding (3d xzFe → 2p xC and 3d yzFe → 2p zC) with carbon monoxide, and...
Theoretical chemistry calculations using the Density Functional Theory (DFT) were carried out to ... more Theoretical chemistry calculations using the Density Functional Theory (DFT) were carried out to understand the interaction between oxygen (O2) and MnN4 type manganese-based complexes during the formation of MnN4-O2 adducts. In order to understand how this interaction is affected by different macrocyclic ligands, O2 was bonded to manganese-porphyrin (MnP), manganese-octamethylporphyrin (MnOMP), manganese-tetraaza[14]annulene (MnTAA), manganese-dibenzo [b,i] [1, 4, 8, 11]-tetraaza [14] annulene (MnDBTAA), manganese-2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene ([(tim)Mn](2+)), and manganese-2,3,9,10-tetraphenyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene ([(ph-tim)Mn](2+)). The binding and activation of the oxygen molecule was facilitated by an increasing trend in the O-O bond lengths and a decreasing one in the O-O vibrational frequency, with preference for the O2 side-on interaction among MnN4 macrocycles. The catalytic activities of the MnN4 complexe...
Batch injection analysis (BIA) with amperometric detection, using a pyrolytic graphite electrode ... more Batch injection analysis (BIA) with amperometric detection, using a pyrolytic graphite electrode modified with cobalt phthalocyanine (PG/CoPc), was employed for determination of α-lipoic acid (ALA) in pharmaceutical product and in synthetic urine samples. The proposed BIA method is based on the application of a potential of +0.9V vs. Ag/AgCl, KCl sat, enabling quantification of ALA over a concentration range from 1.3×10(-6) to 1.0×10(-4)molL(-1), with a detection limit of 1.5×10(-8)molL(-1). A sampling rate of 180 injections per hour was attained and measurements of the reproducibility of successive injections (100µmolL(-1) ALA on the same electrode) showed a RSD of 2.11% for 40 successive injections. The new sensor was utilised for ALA quantification in a dietary pharmaceutical supplement and in synthetic urine and the results obtained for both samples were compared with parallel analysis using high performance liquid chromatography (HPLC), the method recommended by the United States Pharmacopeia. The results obtained were similar (at a 95% confidence level) and in the case of the synthetic urine sample (prepared with a known amount of ALA) the recovery was situated between 98.0% and 102.6%.
A new and simple electroanalytical method was developed for determination of Cu(II) by derivative... more A new and simple electroanalytical method was developed for determination of Cu(II) by derivative potentiometric stripping analysis (dPSA). The method employed a basal plane pyrolytic graphite (BPPG) electrode modified with 4-[10,15,20-tris(4-sulfophenyl)-21,22-dihydroporphyrin-5-yl] benzenesulfonic acid (H2 TSPP) adsorbed onto multi-walled carbon nanotubes (MWCNT). The modified electrode showed excellent stability and was able to detect Cu(II) at nanomolar levels. The electrochemical method is based on simultaneous preconcentration/reduction of Cu(II) ions on the H2 TSPP/MWCNT/BPPG electrode at -0.25 V vs. Ag/AgCl(sat) in 0.1 mol/L phosphate buffer solution (pH 7.0), during 240 s, followed by subsequent chemical stripping. The analytical signal showed a linear response for Cu(II) concentrations in the range 5 to 1600 nmol/L (R = 0.9998), with a detection limit of 1.0 nmol/L. The sensor was successfully applied for Cu(II) determination in gasoline samples, and the results were in ag...
Luminescence : the journal of biological and chemical luminescence, Jan 2, 2015
This paper describes a new technique for the determination of captopril in pharmaceutical formula... more This paper describes a new technique for the determination of captopril in pharmaceutical formulations, implemented by employing multicommuted flow analysis. The analytical procedure was based on the reaction between hypochlorite and captopril. The remaining hypochlorite oxidized luminol that generated electromagnetic radiation detected using a homemade luminometer. To the best of our knowledge, this is the first time that this reaction has been exploited for the determination of captopril in pharmaceutical products, offering a clean analytical procedure with minimal reagent usage. The effectiveness of the proposed procedure was confirmed by analyzing a set of pharmaceutical formulations. Application of the paired t-test showed that there was no significant difference between the data sets at a 95% confidence level. The useful features of the new analytical procedure included a linear response for captopril concentrations in the range 20.0-150.0 µmol/L (r = 0.997), a limit of detect...
ABSTRACT This paper describes the feasibility of using direct current electrical resistivity meas... more ABSTRACT This paper describes the feasibility of using direct current electrical resistivity measurements to evaluate AISI 304 austenitic stainless steel sensitization. ASTM A262 - Practice A and double loop electrochemical potentiodynamic reactivation (DL-EPR) tests were performed to assess the degree of sensitization (DoS) qualitatively and quantitatively, and electrical resistivity (ER) was measured by the four-point direct-current potential drop method. The results indicate that the DoS increases rapidly while the ER decreases gradually in response to increasing sensitization. Thereafter, the two parameters tend to remain approximately constant. This behavior may be due to the rapid increase in the volume fraction of M23C6 precipitates over a sensitization time of 4 to 6 hours, thereafter remaining relatively constant. The ER results, which were corroborated by other techniques used in this study, confirm the promising potential of this property to monitor the sensitization phenomenon in AISI 304 steel.
Journal of the Chemical Society, Chemical Communications, 1987
ABSTRACT Reductive dimerization of tricarbonyl(1-methoxycarbonylcyclohexadienyl)iron hexafluoroph... more ABSTRACT Reductive dimerization of tricarbonyl(1-methoxycarbonylcyclohexadienyl)iron hexafluorophosphate proceeds in a regioselective manner using either zinc dust or electrochemical techniques, cyclic voltammetry experiments providing evidence for a one-electron transfer process involving free radical intermediates; the first example of intramolecular cross coupling of the free radical with an alkene moiety is reported.
ABSTRACT In this work voltammetric techniques were explored for quantification of α-Lipoic acid (... more ABSTRACT In this work voltammetric techniques were explored for quantification of α-Lipoic acid (ALA) using a pyrolytic graphite electrode modified with cobalt phthalocyanine. Cyclic voltammograms recorded in phosphate buffer solution containing 1×10−3 mol L−1 of ALA presented an oxidation peak located at +0.8 V vs. SCE. The modification of the electrode produced a 100 mV shift of the onset oxidation potential to less positive value and a substantial increase in the ALA oxidation current. Among the voltammetric techniques explored, differential pulse voltammetry showed the best performance for quantifications of the analyte in low concentrations. Limits of detection and quantification of ALA obtained corresponds to 3.4×10−9 mol L−1 and 1.2×10−8 mol L−1, respectively.
ABSTRACT The present article describes a DFT study of dibenzotetraaza[14]annulene complexed with ... more ABSTRACT The present article describes a DFT study of dibenzotetraaza[14]annulene complexed with first row transition metals (MII(DBTAA)), employing calculations made using the B3LYP hybrid functional with the Lanl2DZ/6-31G∗ basis set. The parameters considered were bond distances and angles, electron configurations, interaction energies, vibrational frequencies, and frontier molecular orbitals (HOMO and LUMO). The calculations indicated that the key to complexes of the metals Ti, and Cr was the high spin state, while for Mn and Fe it was the intermediate spin state and for Co, Ni, Cu, and Zn it was the low spin state. The M-N distance (d(M-N)) and vibrational frequency showed inversely proportional behavior as a function of the atomic number of the metal. The Ni(DBTAA) complex showed the smallest d(M-N) and highest vibrational frequency, indicating greater compaction of the ligand on nickel. The interaction energy and the gap (HOMO-LUMO) were also calculated in order to estimate the stability and reactivity of the complexes. The stability increased with the atomic number of the central metal, in agreement with the Irving-Williams series, with Ni(DBTAA) being the most stable, and Ti(DBTAA) and Mn(DBTAA) being the most reactive of the complexes investigated.
This work describes the highly sensitive detection of organophosphorus pesticides employing the c... more This work describes the highly sensitive detection of organophosphorus pesticides employing the cobalt(II) 4,4,4,4-tetrasulfo-phthalocyanine (CoTSPc) macrocycle complex, carbon nanotubes (CNT), and 1-methyl-3-octylimidazolium tetrafluoroborate (OMIM[BF4]). The technique is based on enzyme acetylcholinesterase (AChE) inhibition. The composite was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and amperometry. The AChE was immobilized on the composite electrode surface by cross-linking with glutaraldehyde and chitosan. The synergistic action of the CoTSPc/CNT/OMIM[BF4] composite showed excellent electrocatalytic activity, with a low applied potential for the amperometric detection of thiocholine (TCh) at 0.0 V vs. Ag/AgCl. The calculated catalytic rate constant, kcat, was 3.67 × 10(3) mol(-1) L s(-1). Under the optimum conditions, the inhibition rates of these pesticides were proportional to their concentrations in the ranges of 1.0 pmol L(-1) to 1.0 nmol L(-1) (fenitrothion), 2.0 pmol L(-1) to 8.0 nmol L(-1) (dichlorvos), and 16 pmol L(-1) to 5.0 nmol L(-1) (malathion).
Microcystins (MCs) are cyclic hepatotoxic heptapeptides produced by certain strains of freshwater... more Microcystins (MCs) are cyclic hepatotoxic heptapeptides produced by certain strains of freshwater cyanobacteria toxic for humans and animals. The electrochemical behaviour of microcystin-LR (MC-LR) at a glassy carbon electrode (GCE) was investigated using cyclic voltammetry (CV), square wave voltammetry (SWV) and differential pulse voltammetry (DPV). The oxidation of MC-LR is a diffusion-controlled irreversible and pH-independent process that occurs with the transfer of only one electron and does not involve the formation of any electroactive oxidation product. Upon incubation in different pH electrolytes, homogeneous degradation of MC-LR in solution was electrochemically detected by the appearance of a new oxidation peak at a lower potential. The electrochemical behaviour of chemically degraded MC-LR is an irreversible, pH-dependent process, and involves the formation of two redox products that undergo reversible oxidation. The formation of degradation products of MC-LR was confirmed by HPLC with UV detection at room temperature. Experiments were also carried out in solutions containing constituent MC-LR amino acids, which enabled the understanding of the MC-LR electron transfer reaction and degradation. An oxidation mechanism for MC-LR is proposed.
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