Browsing by Author "Garrido, E. Manuela"
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- An Electrochemical Outlook on Tamoxifen Biotransformation: Current and Future ProspectsPublication . Garrido, Jorge; Garrido, E. Manuela; Oliveira-Brett, Ana Maria; Borges, FernandaTamoxifen is a nonsteroidal antiestrogen that is currently and widely used in the treatment of breast cancer in all of its stages, in adjuvant therapy as a long-term suppressant of tumor recurrence and also as a chemopreventive agent in women that are in high risk of developing this type of estrogen-dependent cancer. From a toxicological and (bio)analytical point of view the knowledge of the metabolic pathways of a drug is found to be extremely important. So, in the present work the most important tamoxifen biotransformation steps were reviewed in the light of recent pharmacological data. This overview also includes the current controversy concerning tamoxifen DNA-damaging (genotoxic) versus non-genotoxic mechanisms. A special focus will be given to the putative application of electrochemical methods as a modern and reliable analytical tool for determination of tamoxifen and its metabolites. Moreover, the potential of DNA electrochemical sensors for detection of structural damage to DNA as a basis for toxicity screening is highlighted. Future prospects looking for the importance of developing new analytical methodologies are also discussed.
- Carbon nanotube β-cyclodextrin-modified electrode for quantification of cocaine in seized street samplesPublication . Garrido, Jorge; Borges, F.; Brett, C. M. A.; Garrido, E. ManuelaDetection and quantification of cocaine is a key tool in fields such as police apprehensions and the fight against drug trafficking. Thus, a simple, fast and inexpensive electroanalytical methodology for the determination of cocaine in seized street samples has been developed, employing linear sweep voltammetry. The method is based on the use of a glassy carbon (GC) electrode modified by a combination of multi-walled carbon nanotubes (MWCNT) with β- cyclodextrin (β-CD) incorporated in a polyaniline film. The proposed method shows high reproducibility, repeatability and specificity. Under optimal conditions, the β-CD/ MWCNT-modified GC electrode gives a detection limit of 1.02 μM cocaine. The results obtained are in good agreement with those obtained by the high-performance liquid chromatography reference method. The new methodology proposed has excellent potential as the basis of a portable analytical sensor for on-site screening of cocaine in seized street samples.
- Design of an Emulgel for Psoriasis Focused on Patient PreferencesPublication . Oliveira, Rita Sanches; da Silva, Diva Ferraz; Mota, Sandra; Garrido, Jorge; Garrido, E. Manuela; Lobo, José Manuel Sousa; Almeida, Isabel FilipaAdherence to topical treatments is low and is known to be influenced by the vehicle properties. Betamethasone dipropionate (BD) is an anti-inflammatory steroid, used in psoriasis treatment in the form of an ointment, cream, or solution. The aim of this work was to develop a new vehicle for BD, focusing on the preferences of patients with psoriasis as a strategy to improve treatment adherence. Two vehicles with an aqueous external phase were explored: an emulgel and a hydrogel based on a cyclodextrin inclusion complex used to improve the aqueous solubility of BD. Since BD solubilization was not fully achieved in the hydrogel, only the emulgel was selected for further characterization. This new vehicle (emulgel) is characterized by its white, shiny appearance and good spreading properties. In comparison with petrolatum, a lower residue, higher evaporation rate, lower stickiness, and reduced ability to stain polyester fabric were observed. This vehicle also showed shear thinning behavior. The impact of this new vehicle on adherence to topical treatments should be further confirmed in clinical settings.
- Development of electrochemical methods for determination of tramadol - analytical application to pharmaceutical dosage formsPublication . Garrido, E. Manuela; Garrido, Jorge; Borges, F.; Delerue-Matos, CristinaA square-wave voltammetric (SWV) method and a flow injection analysis system with amperometric detection were developed for the determination of tramadol hydrochloride. The SWV method enables the determination of tramadol over the concentration range of 15-75 µM with a detection limit of 2.2 µM. Tramadol could be determined in concentrations between 9 and 50 µM at a sampling rate of 90 h-1, with a detection limit of 1.7 µM using the flow injection system. The electrochemical methods developed were successfully applied to the determination of tramadol in pharmaceutical dosage forms, without any pre-treatment of the samples. Recovery trials were performed to assess the accuracy of the results; the values were between 97 and 102% for both methods.
- Effects of Chlorophenoxy Herbicides and Their Main Transformation Products on DNA Damage and Acetylcholinesterase ActivityPublication . Benfeito, Sofia; Silva, Tiago; Garrido, Jorge; Andrade, Paula B.; Sottomayor, M. J.; Borges, Fernanda; Garrido, E. ManuelaPersistent pesticide transformation products (TPs) are increasingly being detected among different environmental compartments, including groundwater and surface water. However, there is no sufficient experimental data on their toxicological potential to assess the risk associated with TPs, even if their occurrence is known. In this study, the interaction of chlorophenoxy herbicides (MCPA, mecoprop, 2,4-D and dichlorprop) and their main transformation products with calf thymus DNA by UV-visible absorption spectroscopy has been assessed. Additionally, the toxicity of the chlorophenoxy herbicides and TPs was also assessed evaluating the inhibition of acetylcholinesterase activity. On the basis of the results found, it seems that AChE is not the main target of chlorophenoxy herbicides and their TPs. However, the results found showed that the transformation products displayed a higher inhibitory activity when compared with the parent herbicides. The results obtained in the DNA interaction studies showed, in general, a slight effect on the stability of the double helix. However, the data found for 4-chloro-2-methyl-6-nitrophenol suggest that this transformation product can interact with DNA through a noncovalent mode.
- Electroanalytical determination of oxadiazon and characterization of its base-catalyzed ring-opening productsPublication . Garrido, E. Manuela; Lima, J. L. F. C.; Delerue-Matos, Cristina; Borges, F.; Oliveira-Brett, A. M.The electrochemical behavior of the hydrolysis products of oxadiazon was studied by cyclic and square-wave voltammetry using a glassy carbon electrode. Maximum currents were obtained at pH 12.8 in an aqueous electrolyte solution containing 30% ethanol and the current did not decrease with time showing that there was little adsorption of the reaction products on the electrode surface. The hydrolysis products of oxadiazon were identi®ed, after isolation and puri®cation, as 1-trimethylacetyl-2-(2,4-dichloro-5-isopropoxyphenyl)-2-ethoxycarbonylhydrazine (Oxa1) and 1-trimethylacetyl-2-(2,4-dichloro-5-isopropoxyphenyl) hydrazine (Oxa2) with redox potentials 0.6Vand 70.1V (vs. Ag=AgCl), respectively. Based on the electrochemical behavior of 1-trimethylacetyl-2-(2,4-dichloro-5-isopropoxyphenyl) hydrazine (Oxa2) a simple electroanalytical procedure was developed for the determination of oxadiazon in commercial products used in the treatment of rice crops in Portugal that contain oxadiazon as the active ingredient. The detection limit was 161074 M, the mean content and relative standard deviation obtained for seven samples of two different commercial products by the electrochemical method were 28.4 0.8% (Ronstar) and 1.9 0.2% (Ronstar GR), and the recoveries were 100.3 5.4% and 101.1 5.3 %, respectively.
- Electroanalytical study of the pesticide asulamPublication . Nouws, Henri P. A.; Delerue-Matos, Cristina; Lima, J. L. F. C.; Garrido, E. Manuela; Vincke, Pieter; Maes, Noel A.The electrochemical behaviour of the herbicide Asulam was studied by cyclic and square wave voltammetry. Asulam may be irreversibly oxidised at a glassy carbon electrode. Maximum currents were obtained at pH=1.9 in aqueous electrolyte solution. Based on the electrochemical behaviour of Asulam, two analytical methodologies were developed for its determination in water samples, using square wave voltammetry (SWV) and flow injection analysis (FIA) coupled with an amperometric detector. Limits of detection of 7.1x10-6 mol L-1 and 1.2x10-8 mol L-1 for SWV and FIA respectively, were achieved. Repeatability was calculated by assessing the relative standard deviation (%) for 10 consecutive determinations of one sample. The found values were 2.1% for SWV and 5.0% for FIA. Validation of the results provided by SWV and FIA methodologies was performed by comparison with results from an HPLC-DAD technique. Good relative deviations were found (<5%). Recovery trials were performed to assess the accuracy of the results and the obtained values were between 84% and 107% for both methods.
- Electrochemical and spectroscopic studies of the oxidation mechanism of the herbicide propanilPublication . Garrido, E. Manuela; Lima, J. L. F. C.; Delerue-Matos, Cristina; Borges, F.; Silva, A. M. S.; Piedade, J. A. P.; Oliveira-Brett, A. M.Electrochemical oxidation of propanil in deuterated solutions was studied by cyclic, differential pulse, and square wave voltammetry using a glassy carbon microelectrode. The oxidation of propanil in deuterated acid solutions occurs at the nitrogen atom of the amide at a potential of +1.15 V vs Ag/ AgCl. It was also found that, under the experimental conditions used, protonation at the oxygen atom of propanil occurs, leading to the appearance of another species in solution which oxidizes at +0.60 V. The anodic peak found at +0.79 V vs Ag/AgCl in deuterated basic solutions is related to the presence of an anionic species in which a negative charge is on the nitrogen atom. The electrochemical data were confirmed by the identification of all the species formed in acidic and basic deuterated solutions by means of NMR spectroscopy. The results are supported by electrochemical and spectroscopic studies of acetanilide in deuterated solutions.
- Electrochemical determination of the herbicide bentazone using a carbon nanotube b-Cyclodextrin modified electrodePublication . Rahemi, V.; Garrido, Jorge; Borges, Fernanda; Oliveira-Brett, A. M.; Garrido, E. ManuelaAn electrochemical sensor has been developed for the determination of the herbicide bentazone, based on a GC electrode modified by a combination of multiwalled carbon nanotubes (MWCNT) with b-cyclodextrin (b-CD) incorporated in a polyaniline film. The results indicate that the b-CD/MWCNT modified GC electrode exhibits efficient electrocatalytic oxidation of bentazone with high sensitivity and stability. A cyclic voltammetric method to determine bentazone in phosphate buffer solution at pH 6.0, was developed, without any previous extraction, clean-up, or derivatization steps, in the range of 10–80 mmolL 1, with a detection limit of 1.6 mmolL 1 in water. The results were compared with those obtained by an established HPLC technique. No statistically significant differences being found between both methods.
- Electrochemical methods in pesticides controlPublication . Garrido, E. Manuela; Delerue-Matos, Cristina; Lima, J. L. F. C.; Oliveira-Brett, A. M.The state of the art of voltammetric and amperometric methods used in the study and determination of pesticides in crops, food, phytopharmaceutical products, and environmental samples is reviewed. The main structural groups of pesticides, i.e., triazines, organophosphates, organochlorides, nitrocompounds, carbamates, thiocarbamates, sulfonylureas, and bipyridinium compounds are considered with some degradation products. The advantages, drawbacks, and trends in the development of voltammetric and amperometric methods for study and determination of pesticides in these samples are discussed.
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