Methyldopa is a catecholamine widely used in the treatment of mild to moderate hypertension whose... more Methyldopa is a catecholamine widely used in the treatment of mild to moderate hypertension whose determination in pharmaceutical formulae is of upmost importance for dose precision. Henceforth, a low-cost carbon paste electrode (CPE) consisting of graphite powder obtained from a crushed pencil stick was herein modified with nanostructured TiO2 (TiO2@CPE) aiming for the detection of methyldopa in pharmaceutical samples. The TiO2-modified graphite powder was characterized by scanning electron microscopy and X-ray diffraction, which demonstrated the oxide nanostructured morphology. Results evidenced that sensitivity was nonetheless increased due to electro-catalytic effects promoted by metal modification, and linear response obtained by differential pulse voltammetry for the determination of methyldopa (pH = 5.0) was between 10–180 μmol/L (Limit of Detection = 1 μmol/L) with the TiO2@CPE sensor. Furthermore, the constructed sensor was successfully applied in the detection of methyldop...
Carvedilol (CRV) is a non-selective blocker of α and β adrenergic receptors, which has been exten... more Carvedilol (CRV) is a non-selective blocker of α and β adrenergic receptors, which has been extensively used for the treatment of hypertension and congestive heart failure. Owing to its poor biopharmaceutical properties, CRV has been incorporated into different types of drug delivery systems and this necessitates the importance of investigating their compatibility and stability. In this sense, we have investigated the applicability of several electroanalytical tools to assess CRV compatibility with lipid excipients. Voltammetric and electrochemical impedance spectroscopy techniques were used to evaluate the redox behavior of CRV and lipid excipients. Results showed that Plurol® isostearic, liquid excipient, and stearic acid presented the greatest anode peak potential variation, and these were considered suitable excipients for CRV formulation. CRV showed the highest stability at room temperature and at 50 °C when mixed with stearic acid (7% w/w). The results also provided evidence t...
This work details the study of the redox behavior of the drugs cyclobenzaprine (CBP), amitriptyli... more This work details the study of the redox behavior of the drugs cyclobenzaprine (CBP), amitriptyline (AMP) and nortriptyline (NOR) through voltammetric methods and computational chemistry. Results obtained in this study show that the amine moiety of each compound is more likely to undergo oxidation at 1a at Ep1a ≈ 0.69, 0.79, 0.93 V (vs. Ag/AgCl/KClsat) for CBP, AMP and NOR, respectively. Moreover, CBP presented a second peak, 2a at Ep2a ≈ 0.98 V (vs. Ag/AgCl/KClsat) at pH 7.0. Furthermore, the electronic structure calculation results corroborate the electrochemical assays regarding the HOMO energies of the lowest energy conformers of each molecule. The mechanism for each anodic process is proposed according to electroanalytical and computational chemistry findings, which show evidence that the methods herein employed may be a valuable alternative to study the redox behavior of structurally similar drugs.
The increasing demand for rare earth elements in green technology, electronic components, petrole... more The increasing demand for rare earth elements in green technology, electronic components, petroleum refining, and agricultural activities has resulted in their scattering and accumulation in the environment. This study determined cerium, lanthanum and praseodymium in environmental water samples with the help of adsorptive differential pulse stripping voltammetry (AdDPSV) and inductive coupled plasma-optical emission spectroscopy (ICP-OES). A comparison of the results of these two analytical techniques was also made. The accuracy and precision of the methods were evaluated by spiking water samples with a known amount of REEs. The detection limit obtained for the stripping analysis was 0.10 μg/L for Ce(III), and 2.10 μg/L for combined La(III) and Pr(III). The spectroscopic method of determination by ICP-OES was applied to the same samples to evaluate the effectiveness of the voltammetry procedure. The ICP-OES detection limit obtained was 2.45, 3.12 and 3.90 μg/L for Ce(III), La(III) a...
The emission of toxic compounds by increasing anthropogenic activities affects human health and t... more The emission of toxic compounds by increasing anthropogenic activities affects human health and the environment. Heavy road traffic and mining activities are the major anthropogenic activities contributing to the presence of metals in the environment. The release of palladium (Pd), platinum (Pt), and rhodium (Rh) into the environment increases the levels of contamination in soils, road sediments, airborne particles, and plants. These Pd, Pt, and Rh in road dusts can be soluble and enter aquatic environment posing a risk to environment and human health. The aim of this study is to determine the levels of Pd, Pt, and Rh with spectroscopy and voltammetric methods. Potential interferences by other metal ions (Na(I), Fe(III), Ni(II), Co(II)) in voltammetric methods have also been investigated in this study. At all the sampling sites very low concentrations of Pd, Pt, and Rh were found at levels that range from 0.48 ± 0.05 to 5.44 ± 0.11 ng/g (dry weight (d.wt)) for Pd(II), with 17.28 ± 3...
The vegetable kingdom is a wide source of a diverse variety of enzymes with broad biotechnologica... more The vegetable kingdom is a wide source of a diverse variety of enzymes with broad biotechnological applications. Among the main classes of plant enzymes, the polyphenol oxidases, which convert phenolic compounds to the related quinones, have been successfully used for biosensor development. The oxidation products from such enzymes can be electrochemically reduced, and the sensing is easily achieved by amperometric transducers. In this work, the polyphenoloxidases were extracted from jurubeba ( L.) fruits, and the extract was used to construct a carbon paste-based biosensor for pharmaceutical analysis and applications. The assay optimization was performed using a 0.1 mM catechol probe, taking into account the amount of enzymatic extract (50 or 200 μL) and the optimum pH (3.0 to 9.0) as well as some electrochemical differential pulse voltammetric (DPV) parameters (e.g., pulse amplitude, pulse range, pulse width, scan rate). Under optimized conditions, the biosensor was evaluated for t...
The atmospheric deposition of mercury (Hg) occurs via several mechanisms, including dry and wet s... more The atmospheric deposition of mercury (Hg) occurs via several mechanisms, including dry and wet scavenging by precipitation events. In an effort to understand the atmospheric cycling and seasonal depositional characteristics of Hg, wet deposition samples were collected for approximately 5 years at 17 selected GMOS monitoring sites located in the Northern and Southern hemispheres in the framework of the Global Mercury Observation System (GMOS) project. Total mercury (THg) exhibited annual and seasonal patterns in Hg wet deposition samples. Interannual differences in total wet deposition are mostly linked with precipitation volume, with the greatest deposition flux occurring in the wettest years. This data set provides a new insight into baseline concentrations of THg concentrations in precipitation worldwide, particularly in regions such as the Southern Hemisphere and tropical areas where wet deposition as well as atmospheric Hg species were not investigated before, opening the way f...
A co-disposal reaction was used wherein fly ash (FA) was reacted with acid mine drainage (AMD), t... more A co-disposal reaction was used wherein fly ash (FA) was reacted with acid mine drainage (AMD), to collect filtrates for zeolite synthesis. Raw fly ash as well as fly ash leached with HCl were subjected to the same alkaline hydrothermal zeolite synthesis conditions, as for the co-disposal filtrates, in order to evaluate the zeolitic material obtained. The Si and Al contents of the fly ash (FA) filtrates were used as precursor species for the alkaline hydrothermal conversion of the fly ash filtrates into zeolites. These filtrates were then analysed by XRF spectrometry for quantitative determination of SiO 2 and Al 2 O 3. The [SiO 2 ]/[Al 2 O 3 ] ratio obtained in the filtrates range from 1.4 to 2.5. The [SiO 2 ]/[Al 2 O 3 ] ratio was used to predict whether the fly ash filtrates could successfully be converted into faujasite zeolitic material by the adopted synthesis procedures. If the [SiO 2 ]/[Al 2 O 3 ] ratio is higher than 1.5 in the co-disposal filtrates, it favours the formation of faujasite. The zeolite synthesis included an alkaline fusion of the co-disposal filtrates, followed by aging for 8 hours and hydrothermal conversion by crystallisation at 100 8C. Different variables were investigated during the synthesis of zeolite to ascertain their influence on the end product. These variables include adding different amounts of deionised water to the FA-related starting material, using different compositions of FA related starting material and different FA:NaOH ratios in fusing the starting material.
Journal of Environmental Science and Health Part B Pesticides Food Contaminants and Agricultural Wastes, Mar 26, 2007
The behavior of an amperometric organic-phase biosensor consisting of a gold electrode modified f... more The behavior of an amperometric organic-phase biosensor consisting of a gold electrode modified first with a mercaptobenzothiazole self-assembled monolayer, followed by electropolymerization of polyaniline in which acetylcholinesterase as enzyme was immobilized, has been developed and evaluated for organophosphorous pesticide detection. The voltammetric results have shown that the formal potential shifts anodically as the Au/MBT/PANI/AChE/PVAc thick-film biosensor responded to acetylthiocholine substrate addition under anaerobic conditions in selected organic solvent media containing 2% v/v 0.05 M phosphate buffer, 0.1 M KCl (pH 7.2) solution. Detection limits in the order of 0.147 ppb for diazinon and 0.172 ppb for fenthion in acetone-saline phosphate buffer solution, and 0.180 ppb for diazinon and 0.194 ppb for fenthion in ethanol-saline phosphate buffer solution has been achieved.
Methyldopa is a catecholamine widely used in the treatment of mild to moderate hypertension whose... more Methyldopa is a catecholamine widely used in the treatment of mild to moderate hypertension whose determination in pharmaceutical formulae is of upmost importance for dose precision. Henceforth, a low-cost carbon paste electrode (CPE) consisting of graphite powder obtained from a crushed pencil stick was herein modified with nanostructured TiO2 (TiO2@CPE) aiming for the detection of methyldopa in pharmaceutical samples. The TiO2-modified graphite powder was characterized by scanning electron microscopy and X-ray diffraction, which demonstrated the oxide nanostructured morphology. Results evidenced that sensitivity was nonetheless increased due to electro-catalytic effects promoted by metal modification, and linear response obtained by differential pulse voltammetry for the determination of methyldopa (pH = 5.0) was between 10–180 μmol/L (Limit of Detection = 1 μmol/L) with the TiO2@CPE sensor. Furthermore, the constructed sensor was successfully applied in the detection of methyldop...
Carvedilol (CRV) is a non-selective blocker of α and β adrenergic receptors, which has been exten... more Carvedilol (CRV) is a non-selective blocker of α and β adrenergic receptors, which has been extensively used for the treatment of hypertension and congestive heart failure. Owing to its poor biopharmaceutical properties, CRV has been incorporated into different types of drug delivery systems and this necessitates the importance of investigating their compatibility and stability. In this sense, we have investigated the applicability of several electroanalytical tools to assess CRV compatibility with lipid excipients. Voltammetric and electrochemical impedance spectroscopy techniques were used to evaluate the redox behavior of CRV and lipid excipients. Results showed that Plurol® isostearic, liquid excipient, and stearic acid presented the greatest anode peak potential variation, and these were considered suitable excipients for CRV formulation. CRV showed the highest stability at room temperature and at 50 °C when mixed with stearic acid (7% w/w). The results also provided evidence t...
This work details the study of the redox behavior of the drugs cyclobenzaprine (CBP), amitriptyli... more This work details the study of the redox behavior of the drugs cyclobenzaprine (CBP), amitriptyline (AMP) and nortriptyline (NOR) through voltammetric methods and computational chemistry. Results obtained in this study show that the amine moiety of each compound is more likely to undergo oxidation at 1a at Ep1a ≈ 0.69, 0.79, 0.93 V (vs. Ag/AgCl/KClsat) for CBP, AMP and NOR, respectively. Moreover, CBP presented a second peak, 2a at Ep2a ≈ 0.98 V (vs. Ag/AgCl/KClsat) at pH 7.0. Furthermore, the electronic structure calculation results corroborate the electrochemical assays regarding the HOMO energies of the lowest energy conformers of each molecule. The mechanism for each anodic process is proposed according to electroanalytical and computational chemistry findings, which show evidence that the methods herein employed may be a valuable alternative to study the redox behavior of structurally similar drugs.
The increasing demand for rare earth elements in green technology, electronic components, petrole... more The increasing demand for rare earth elements in green technology, electronic components, petroleum refining, and agricultural activities has resulted in their scattering and accumulation in the environment. This study determined cerium, lanthanum and praseodymium in environmental water samples with the help of adsorptive differential pulse stripping voltammetry (AdDPSV) and inductive coupled plasma-optical emission spectroscopy (ICP-OES). A comparison of the results of these two analytical techniques was also made. The accuracy and precision of the methods were evaluated by spiking water samples with a known amount of REEs. The detection limit obtained for the stripping analysis was 0.10 μg/L for Ce(III), and 2.10 μg/L for combined La(III) and Pr(III). The spectroscopic method of determination by ICP-OES was applied to the same samples to evaluate the effectiveness of the voltammetry procedure. The ICP-OES detection limit obtained was 2.45, 3.12 and 3.90 μg/L for Ce(III), La(III) a...
The emission of toxic compounds by increasing anthropogenic activities affects human health and t... more The emission of toxic compounds by increasing anthropogenic activities affects human health and the environment. Heavy road traffic and mining activities are the major anthropogenic activities contributing to the presence of metals in the environment. The release of palladium (Pd), platinum (Pt), and rhodium (Rh) into the environment increases the levels of contamination in soils, road sediments, airborne particles, and plants. These Pd, Pt, and Rh in road dusts can be soluble and enter aquatic environment posing a risk to environment and human health. The aim of this study is to determine the levels of Pd, Pt, and Rh with spectroscopy and voltammetric methods. Potential interferences by other metal ions (Na(I), Fe(III), Ni(II), Co(II)) in voltammetric methods have also been investigated in this study. At all the sampling sites very low concentrations of Pd, Pt, and Rh were found at levels that range from 0.48 ± 0.05 to 5.44 ± 0.11 ng/g (dry weight (d.wt)) for Pd(II), with 17.28 ± 3...
The vegetable kingdom is a wide source of a diverse variety of enzymes with broad biotechnologica... more The vegetable kingdom is a wide source of a diverse variety of enzymes with broad biotechnological applications. Among the main classes of plant enzymes, the polyphenol oxidases, which convert phenolic compounds to the related quinones, have been successfully used for biosensor development. The oxidation products from such enzymes can be electrochemically reduced, and the sensing is easily achieved by amperometric transducers. In this work, the polyphenoloxidases were extracted from jurubeba ( L.) fruits, and the extract was used to construct a carbon paste-based biosensor for pharmaceutical analysis and applications. The assay optimization was performed using a 0.1 mM catechol probe, taking into account the amount of enzymatic extract (50 or 200 μL) and the optimum pH (3.0 to 9.0) as well as some electrochemical differential pulse voltammetric (DPV) parameters (e.g., pulse amplitude, pulse range, pulse width, scan rate). Under optimized conditions, the biosensor was evaluated for t...
The atmospheric deposition of mercury (Hg) occurs via several mechanisms, including dry and wet s... more The atmospheric deposition of mercury (Hg) occurs via several mechanisms, including dry and wet scavenging by precipitation events. In an effort to understand the atmospheric cycling and seasonal depositional characteristics of Hg, wet deposition samples were collected for approximately 5 years at 17 selected GMOS monitoring sites located in the Northern and Southern hemispheres in the framework of the Global Mercury Observation System (GMOS) project. Total mercury (THg) exhibited annual and seasonal patterns in Hg wet deposition samples. Interannual differences in total wet deposition are mostly linked with precipitation volume, with the greatest deposition flux occurring in the wettest years. This data set provides a new insight into baseline concentrations of THg concentrations in precipitation worldwide, particularly in regions such as the Southern Hemisphere and tropical areas where wet deposition as well as atmospheric Hg species were not investigated before, opening the way f...
A co-disposal reaction was used wherein fly ash (FA) was reacted with acid mine drainage (AMD), t... more A co-disposal reaction was used wherein fly ash (FA) was reacted with acid mine drainage (AMD), to collect filtrates for zeolite synthesis. Raw fly ash as well as fly ash leached with HCl were subjected to the same alkaline hydrothermal zeolite synthesis conditions, as for the co-disposal filtrates, in order to evaluate the zeolitic material obtained. The Si and Al contents of the fly ash (FA) filtrates were used as precursor species for the alkaline hydrothermal conversion of the fly ash filtrates into zeolites. These filtrates were then analysed by XRF spectrometry for quantitative determination of SiO 2 and Al 2 O 3. The [SiO 2 ]/[Al 2 O 3 ] ratio obtained in the filtrates range from 1.4 to 2.5. The [SiO 2 ]/[Al 2 O 3 ] ratio was used to predict whether the fly ash filtrates could successfully be converted into faujasite zeolitic material by the adopted synthesis procedures. If the [SiO 2 ]/[Al 2 O 3 ] ratio is higher than 1.5 in the co-disposal filtrates, it favours the formation of faujasite. The zeolite synthesis included an alkaline fusion of the co-disposal filtrates, followed by aging for 8 hours and hydrothermal conversion by crystallisation at 100 8C. Different variables were investigated during the synthesis of zeolite to ascertain their influence on the end product. These variables include adding different amounts of deionised water to the FA-related starting material, using different compositions of FA related starting material and different FA:NaOH ratios in fusing the starting material.
Journal of Environmental Science and Health Part B Pesticides Food Contaminants and Agricultural Wastes, Mar 26, 2007
The behavior of an amperometric organic-phase biosensor consisting of a gold electrode modified f... more The behavior of an amperometric organic-phase biosensor consisting of a gold electrode modified first with a mercaptobenzothiazole self-assembled monolayer, followed by electropolymerization of polyaniline in which acetylcholinesterase as enzyme was immobilized, has been developed and evaluated for organophosphorous pesticide detection. The voltammetric results have shown that the formal potential shifts anodically as the Au/MBT/PANI/AChE/PVAc thick-film biosensor responded to acetylthiocholine substrate addition under anaerobic conditions in selected organic solvent media containing 2% v/v 0.05 M phosphate buffer, 0.1 M KCl (pH 7.2) solution. Detection limits in the order of 0.147 ppb for diazinon and 0.172 ppb for fenthion in acetone-saline phosphate buffer solution, and 0.180 ppb for diazinon and 0.194 ppb for fenthion in ethanol-saline phosphate buffer solution has been achieved.
My past, current and future research activities are in the fields of:
1. Development and constru... more My past, current and future research activities are in the fields of:
1. Development and construction of electrochemical sensors for the improved analytical determination of pesticide and metallic compounds.
• Major achievements in this area include the construction and application of different types of biosensors consisting of acetylcholinesterase (AChE) and horseradish peroxidase (HRP) for the detection of organophosphate and carbamate pesticides in water and fruit samples.
• In the field of chemical sensors, the toxic mercury voltammetric sensor has been successfully replaced by alternative transducer surfaces such as a conducting polymer, bismuth, antimony, silver, graphene film and combinations thereof.
2. Determination of the sources, transport pathways and fates of inorganic and organic pollutants in the environment (aquatic ecosystems) and to determine to what extend they impact on water resources and human health.
• In the field of biomonitoring, research activities involved the determination of the fate and pollution levels of various metal ions (Hg, Ni, Cu, Pb, Cd, Pt, Pd and Rh) in surface water, sediment and biota samples. • In the case of organic pollutants, research activities have included the determination of organophosphates (e.g. parathion-methyl, malathion and chlorpyrifos) and carbamates (e.g. carbaryl, carbofuran and methomyl) pesticides in various samples.
3. Investigation of aspects of improving analytical and electrochemical techniques for the quantification of different pollutants in water, sediment and biota samples.
• Major achievements include the construction of electrochemical sensors for better sensitivity and detection limits for inorganic and organic pollutants in environmental samples.
4. Synthesis, characterisation and electrochemical evaluation of (organo)metallic for medicinal purposes, focussing on the evaluation of these compounds for potential use as anti-microbial agents.
• This research focus area is slowly taking shape and will focus on the possible use of ruthenium (Ru) and silver (Ag) complexes as anti-microbial compounds for medicinal or environmental applications.
5. Determination of the environmental occurrence, fate and pathways of benzodiazepine compounds and nanomaterials as emerging pollutants in the aquatic environment, followed by improved voltammetric and spectroscopic analysis of these compounds in environmental samples.
• This work forms part of collaboration between me and Scientists at the Federal University of Goias in Brazil. A laccase biosensor and electrochemical remediation techniques are applied for the analysis of benzodiazepines and its metabolites in sample matrices.
6. Investigation and evaluation (spectroscopic and electrochemical) of synthetic or natural antioxidant compounds for potential use in the bioremediation of emerging contaminants.
• This work is also part of an ongoing collaboration with Scientists in Brazil (Federal University of Goias) and focus on the application of antioxidants in the voltammetric analysis of emerging pharmaceutical compounds in environmental samples.
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Papers by Vernon Somerset
1. Development and construction of electrochemical sensors for the improved analytical determination of pesticide and metallic compounds.
• Major achievements in this area include the construction and application of different types of biosensors consisting of acetylcholinesterase (AChE) and horseradish peroxidase (HRP) for the detection of organophosphate and carbamate pesticides in water and fruit samples.
• In the field of chemical sensors, the toxic mercury voltammetric sensor has been successfully replaced by alternative transducer surfaces such as a conducting polymer, bismuth, antimony, silver, graphene film and combinations thereof.
2. Determination of the sources, transport pathways and fates of inorganic and organic pollutants in the environment (aquatic ecosystems) and to determine to what extend they impact on water resources and human health.
• In the field of biomonitoring, research activities involved the determination of the fate and pollution levels of various metal ions (Hg, Ni, Cu, Pb, Cd, Pt, Pd and Rh) in surface water, sediment and biota samples.
• In the case of organic pollutants, research activities have included the determination of organophosphates (e.g. parathion-methyl, malathion and chlorpyrifos) and carbamates (e.g. carbaryl, carbofuran and methomyl) pesticides in various samples.
3. Investigation of aspects of improving analytical and electrochemical techniques for the quantification of different pollutants in water, sediment and biota samples.
• Major achievements include the construction of electrochemical sensors for better sensitivity and detection limits for inorganic and organic pollutants in environmental samples.
4. Synthesis, characterisation and electrochemical evaluation of (organo)metallic for medicinal purposes, focussing on the evaluation of these compounds for potential use as anti-microbial agents.
• This research focus area is slowly taking shape and will focus on the possible use of ruthenium (Ru) and silver (Ag) complexes as anti-microbial compounds for medicinal or environmental applications.
5. Determination of the environmental occurrence, fate and pathways of benzodiazepine compounds and nanomaterials as emerging pollutants in the aquatic environment, followed by improved voltammetric and spectroscopic analysis of these compounds in environmental samples.
• This work forms part of collaboration between me and Scientists at the Federal University of Goias in Brazil. A laccase biosensor and electrochemical remediation techniques are applied for the analysis of benzodiazepines and its metabolites in sample matrices.
6. Investigation and evaluation (spectroscopic and electrochemical) of synthetic or natural antioxidant compounds for potential use in the bioremediation of emerging contaminants.
• This work is also part of an ongoing collaboration with Scientists in Brazil (Federal University of Goias) and focus on the application of antioxidants in the voltammetric analysis of emerging pharmaceutical compounds in environmental samples.