Loading...
7 results
Search Results
Now showing 1 - 7 of 7
- Kinetics of photodegradation of the fungicide fenarimol in natural waters and in various salt solutions: salinity effects and mechanistic considerationsPublication . Mateus, Maria da Conceição; Silva, Abílio M. da; Burrows, Hugh D.The rate of photodegradation of the Fungicide fenarimol (alpha-(2-chlorophenyl)-alpha-(4-chlorophenyl)-5-pyrimidine-methanol) by solar radiation has been studied in natural waters with different salinities. Photodegradation rates and quantum yields are found to decrease with increasing salinity. To explain this behaviour, experiments were pei formed with different salt solutions (NaCl, NaBr, BaCl2 and ZnCl2) using both solar irradiation and a photoreactor (lambda(excit) 313 nm). As with natural waters, marked effects of added salt were observed on the photolysis rater which decreased significantly from 0.67 h(-1) in the absence of salt to 0.11 h(-1) in the presence of BaCl2. In photoreactor studies, the observed order of quenching was BaCl2 > ZnCl2 and NaBr > NaCl. In contrast, neither the triplet state quencher sorbic acid nor oxygen had any effect on the photolysis, supporting the idea that photodegradation goes by the lowest excited singlet state of fenarimol. To understand the origin of the effect of added salts, fluorescence quenching studies have been performed with various halide and nonhalide salts and the respective quenching constants determined. With NaCl and NaBr, the ratio of fluorescence quenching constants is identical to the ratio of reciprocal quantum yields for photodegradation of fenarimol, indicating a common mechanism. The correlation of fluorescence quenching rates with halide ion oxidation potentials strongly suggests that this involves an electron transfer mechanism. It is suggested that the effect may be used to stabilise the fungicide towards photodegradation. (C) 2000 Elsevier Science Ltd. All rights reserved.
- TiO2:(Fe, S) Thin Films Prepared from Complex Precursors by CVD, Physical Chemical Properties, and PhotocatalysisPublication . Bessergenev, V.; Mateus, Maria da Conceição; Vasconcelos, D. A.; Mariano, José; do Rego, A. M. Botelho; Lange, R.; Burkel, E.The TiO2 thin films were prepared using Ti(dpm)(2)(OPri)(2) and Ti(OPri)(4) (dpm = 2,2,6,6-tetramethylheptane-3,5-dione, Pr-i = isopropyl) as the precursors. The volatile compounds Fe[(C2H5)(2)NCS2](3) and [(CH3)C](2)S-2 were used to prepare doped TiO2 films. The synthesis was done in vacuum or in the presence of Ar and O-2. The pressure in the CVD chamber was varied between 1.2 x 10(-4) mbar and 0.1 mbar, with the system working either in the molecular beam or gas flow regime. Physical, chemical, and photocatalytic properties of the (Fe, S)-doped TiO2 films were studied. Those TiO2:(Fe, S) films prepared from the Ti(OPri)(4) precursor show increased photocatalytic activities, very close to those of Degussa P25 powder in UV region.
- Structure, anti-Phytophthora and anti-tumor activities of a nortriterpenoid from the rhizome of Phlomis purpurea (Lamiaceae)Publication . Mateus, Maria Da Conceição; Neves, Dina; Dacunha, Bruno; Laczko, Endre; Maia, Cristiana; Teixeira, Rúben; Cravador, AlfredoTo investigate bioactive compounds potentially involved in the biotic interactions exhibited by Phlomis purpurea (Lamiaceae) in rhizospheres infested with Phytophthora cinnamomi, the plant rhizome was chemically analysed. The nortriterpenoid (175)-2 alpha,3 alpha,11 alpha,23,24-pentahydroxy-19(18 -> 17)-abeo-28-norolean-12-en-18-one, was isolated and its structure was elucidated by comprehensive spectroscopic analysis, chiefly using 2D NMR experiments, and X-ray analysis. It was shown to be exuded by roots and to exhibit anti-Phytophthora and antitumor activities. (C) 2016 Published by Elsevier Ltd.
- Impact of fifteen combinations of the main components of rosemary, lavender and citrus essential oils on in vitro biological activitiesPublication . Kharraf, Sara El; EL-GUENDOUZ, Soukaina; Farah, Abdellah; Mateus, Maria Da Conceição; Hadrami, El Mestafa El; Miguel, Maria GracaSince ancient times, essential oils or their volatiles have been used in food, health and aromatherapy. Essen-tial oils are complex mixtures constituted by dozens of compounds, which makes it difficult to attribute their biological properties to this or that compound or compound combinations. Moreover, the quantification of the volatiles is generally made through their relative percentage abundances. In the present study, the major volatiles isolated from Rosmarinus officinalis, Lavandula angustifolia, and Citrus aurantium essential oils extracted by simultaneous hydrodistillation-steam distillation were quantified through the external standard calibration method. Fifteen volatile mixtures were made using individual volatiles identified in the essential oils (EOs) to better find their role in the biological activities (antioxidant, anti-glucosidase, anti-inflammatory, anti-tyrosinase and anti-acetylcholinesterase activities). For almost mixtures assayed, the in vitro biological activities were generally poorer than those obtained for crude EOs, with the exception of the inhibitory effect on the a-glucosidase activity. In this case, 1,8-cineole and a-terpineol seem to have a positive role in inhibit-ing a-glucosidase activity, in contrast to camphor and borneol, which had the opposite action. Therefore there was a possible antagonist effect of both camphor and borneol in the volatile mixtures assayed on inhibiting the a-glucosidase activity. This approach also permitted us to conclude that there were several other factors not determined in the present work that were responsible for the activities found in the EOs,(c) 2023 SAAB. Published by Elsevier B.V. All rights reserved.
- Solution and surface photochemistry of fenarimol: a comparative studyPublication . Silva, José P. da; Mateus, Maria Da Conceição; Silva, Abílio M. da; Ferreira, Luís F. Vieira; Burrows, Hugh D.The photochemistry of the pesticide fenarimol was studied in methanol and on a cellulose surface. The ground state absorption and fluorescence spectra are similar in solution and at the solid/gas interface. Room temperature phosphorescence emission was observed in cellulose. Transient absorption of fenarimol and of its chromophoric units, chlorobenzene and pyrimidine, showed a common absorption band centered at 320 nm in methanol. An absorption band above 350 nm was observed only for fenarimol and was assigned to a recombination intermediate. On cellulose the transient absorption is broader and extends up to 600 nm. The main photodegradation pathway in methanol involves the homolytic cleavage of the bond to the pyrimidyl ring, followed by a fast in-cage recombination of the initially formed pyrimidine and ketyl radicals. On cellulose surfaces, dechlorination is also one of the important photodegradation pathways. (c) 2006 Elsevier B.V. All rights reserved.
- O "menu químico" das plantas: uma abordagem ao ensino da química no ensino secundárioPublication . Rio, Carolina; Mateus, Maria Da ConceiçãoO papel da interdisciplinaridade na sedimentação de conceitos básicos e estruturantes para o desenvolvimento da aprendizagem em química pode ser implementado através de pequenos projetos que implicam a realização de procedimentos laboratoriais repetitivos conducentes ao desenvolvimento da memória de longo prazo, bem como criativos e de interligação de conceitos. O projeto aqui apresentado é uma proposta de trabalho para implementação nas escolas de ensino secundário, em atividades paralelas à sala de aula. Tendo como objeto de estudo os sistemas biológicos, é proposta a monitorização de diversos parâmetros químicos, necessários ao desenvolvimento de espécies hortícolas selecionadas, com o objetivo de dinamizar a aprendizagem de um conjunto significativo de conceitos químicos incorporados nos programas curriculares dos 10.º, 11.º e 12.º anos do ensino secundário.
- Photocatalytic reactor, CVD technology of its preparation and water purification from pharmaceutical drugs and agricultural pesticidesPublication . Bessergenev, V.; Mateus, Maria da Conceição; Morgado, I. M.; Hantusch, M.; Burkel, E.A tubular photocatalytic reactor of the immersion type for water purification from organic pollutants has been developed. Few important principles were used in the construction of the reactor, namely, a symmetrical and uniform light distribution with direct incidence of UV irradiation on the photocatalyst surface, a highly active mixing of contaminated water as a result of an air bubbling flux, that simultaneously supplying oxygen that is necessary for a photocatalytic reaction. The implemented highly active thin film photocatalyst was prepared by the Chemical Vapor Deposition (CVD) technology using titanium(isopropoxide) (TTIP) as a precursor. The factor K = Surface/Volume of this reactor is about 255 m(-1). Together with an effective mixing, it creates excellent contacts between the contaminants and the photocatalyst which is very favorable for water purification. The efficiency of this reactor was proven by the decomposition of some pharmaceutical drugs (Ibuprofen, Acetylsalicylic acid, Sulphanilamide, Paracetamol, Caffeine) and of some pesticides (Dimethoate, Azoxystrobin, Iprodione, Propizamid, Isoproturon, Fenarimol). The relation between the kinetic constants of photocatalysis and of photolysis is K-photcat/K-photolysis = 2 divided by 18. These results demonstrate the feasibility of the developed photoreactor for the degradation of recalcitrant organic pollutants, such as pharmaceuticals and pesticides in water. (C) 2016 Elsevier B.V. All rights reserved.