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232 results on '"Quintas, Alexandre"'

2. Bar Adsorptive Microextraction Approach for Trace Determination of Local Anesthetics in Urine Matrices.

Author

Pereira, Joana R. P., Rocha, Daniela C., Neng, Nuno R., Maurício, Paulo, Torres, M. Edite, Ahmad, Samir M., and Quintas, Alexandre

Abstract

The present work reports the development, optimization, and validation, of a methodology to determine lidocaine, procaine, tetracaine, and benzocaine in urine matrices. Two extractive preconcentration techniques, solid-phase microextraction (SPME) LC Tips and bar adsorptive microextraction (BAμE), were studied and applied to the four target anesthetics, followed by gas chromatography-mass spectrometry (GC-MS) analysis. Several parameters that could affect microextraction and back-extraction were optimized using two different designs of experiments (Box–Behnken and full-factorial) to maximize extraction efficiency from aqueous media. Under optimized experimental conditions, the BAμE technique showed better performance than SPME LC Tips and was chosen for validation assays and urine sample analysis. In blank urine, the BAµE/GC-MS methodology revealed suitable sensitivity (LOD between 2 and 18 ng/mL), good linearity (r2 ≥ 0.9945) between 0.5 and 30.0 µg/mL and recovery yields of 30.3–97.9%. Good precision (%RSD ≤ 8.8%) and accuracy (bias % between −15.9 and 15.0%) values were achieved. The developed methodology was successfully applied to the target anesthetics analysis of volunteers' urine matrices and proved to be an environmentally friendly alternative to monitor trace levels of local anesthetics in complex matrices compared to other extraction techniques. [ABSTRACT FROM AUTHOR]

Published
2025
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13. Measuring Intracellular Enzyme Concentrations: Assessing the Effect of Oxidative Stress on the Amount of Glyoxalase I

Author

Miranda, Hugo Vicente, Ferreira, Antonio E. N., and Quintas, Alexandre

Abstract

Enzymology is one of the fundamental areas of biochemistry and involves the study of the structure, kinetics, and regulation of enzyme activity. Research in this area is often conducted with purified enzymes and extrapolated to "in vivo" conditions. The specificity constant, k[subscript S], is the ratio between k[subscript cat] (the catalytic constant) and K[subscript m] (Michaelis-Menten constant), and expresses the efficiency of an enzyme as a catalyst. This parameter is usually determined for purified enzymes, and in this work, we propose a classroom experiment for its determination "in situ," in permeabilized yeast cells, based on a method of external enzyme addition, which was previously reported. Under these conditions, which resemble the "in vivo" state, enzyme concentrations and protein interactions are preserved. The students are presented with a novel approach in enzymology, based on the titration methods that allow the measurement of the enzyme amount, and thus the k[subscript cat] and k[subscript S]. The method will also be used to investigate the effect of exposure to oxidative stress conditions on yeast glyoxalase I. (Contains 1 footnote, 2 figures and 1 table.)

Published
2008
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14. GC-MS Silylation Derivative Method to Characterise Black BIC ® Ballpoint 2-Phenoxyethanol Ratio Evaporation Profile—A Contribution to Ink Ageing Estimation.

Author

Leal, Teresa Argente, Ferreira, Carla, Ribeiro, Ana, Ahmad, Samir Marcos, Quintas, Alexandre, and Bernardo, Alexandra

Subjects
GAS chromatography/Mass spectrometry (GC-MS), SILYLATION, INK
Abstract

One of the major challenges in forensic document analysis is estimating the age of ink deposition on a manually written document. The present work aims to develop and optimise a methodology, based on the evaporation of 2-phenoxyethanol (PE) over time, that can contribute to ink age estimation. A black BIC® Crystal Ballpoint Pen was purchased in a commercial area, and ink deposition began in September 2016 over 1095 days. For each ink sample, 20 microdiscs were subjected to n-hexane extraction in the presence of an internal standard (ethyl benzoate) followed by derivatisation with a silylation reagent. A gas chromatography-mass spectrometry (GC/MS) method was optimised for PE-trimethylsilyl (PE-TMS) to characterise the ageing curve. The developed method presented good linearity between 0.5 and 50.0 μg mL−1, as well as limits of detection and quantification of 0.026 and 0.104 μg mL−1, respectively. It was possible to characterise PE-TMS concentration over time, which reveals a two-phase decay behaviour. First, there was a substantial decline between the 1st and the 33rd day of deposition, followed a by a stabilisation of the signal, which allowed to detect the presence of PE-TMS up to 3 years. Two unknown compounds were also present and allowed to identify three dating time frames for the same ink stroke: (i) between time 0 and 33 days, (ii) between time 34 and 109 days, and (iii) more than 109 days. The developed methodology allowed to characterise the behaviour of PE over time and to establish a relative dating of three-time frames. [ABSTRACT FROM AUTHOR]

Published
2023
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18. Erratum to: Glycation potentiates α-synuclein-associated neurodegeneration in synucleinopathies

Author

Miranda, Hugo Vicente, primary, Szegő, Éva M, additional, Oliveira, Luís M A, additional, Breda, Carlo, additional, Darendelioglu, Ekrem, additional, de Oliveira, Rita M, additional, Ferreira, Diana G, additional, Gomes, Marcos A, additional, Rott, Ruth, additional, Oliveira, Márcia, additional, Munari, Francesca, additional, Enguita, Francisco J, additional, Simões, Tânia, additional, Rodrigues, Eva F, additional, Heinrich, Michael, additional, Martins, Ivo C, additional, Zamolo, Irina, additional, Riess, Olaf, additional, Cordeiro, Carlos, additional, Ponces-Freire, Ana, additional, Lashuel, Hilal A, additional, Santos, Nuno C, additional, Lopes, Luisa V, additional, Xiang, Wei, additional, Jovin, Thomas M, additional, Penque, Deborah, additional, Engelender, Simone, additional, Zweckstetter, Markus, additional, Klucken, Jochen, additional, Giorgini, Flaviano, additional, Quintas, Alexandre, additional, and Outeiro, Tiago F, additional

Published
2021
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19. Neuroprotection or neurotoxicity of illicit drugs on Parkinson’s disease

Author

Ferreira, Carla, Almeida, Catarina, Tenreiro, Sandra, Quintas, Alexandre, NOVA Medical School|Faculdade de Ciências Médicas (NMS|FCM), and Centro de Estudos de Doenças Crónicas (CEDOC)

Subjects
Opioids, Parkinson’s Disease, Cocaine, Novel psychoactive substances, Biochemistry, Genetics and Molecular Biology(all), Space and Planetary Science, Amphetamine-type stimulants, Palaeontology, Ecology, Evolution, Behavior and Systematics, Phytocannabinoids
Abstract

Parkinson’s Disease (PD) is currently the most rapid growing neurodegenerative disease and over the past generation, its global burden has more than doubled. The onset of PD can arise due to environmental, sporadic or genetic factors. Nevertheless, most PD cases have an unknown etiology. Chemicals, such as the anthropogenic pollutant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and amphetamine-type stimulants, have been associated with the onset of PD. Conversely, cannabinoids have been associated with the treatment of the symptoms’. PD and medical cannabis is currently under the spotlight, and research to find its benefits on PD is on-going worldwide. However, the described clinical applications and safety of pharmacotherapy with cannabis products are yet to be fully supported by scientific evidence. Furthermore, the novel psychoactive substances are currently a popular alternative to classical drugs of abuse, representing an unknown health hazard for young adults who may develop PD later in their lifetime. This review addresses the neurotoxic and neuroprotective impact of illicit substance consumption in PD, presenting clinical evidence and molecular and cellular mechanisms of this association. This research area is utterly important for contemporary society since illicit drugs’ legalization is under discussion which may have consequences both for the onset of PD and for the treatment of its symptoms. publishersversion published

Published
2020

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