Navegando por Autor "REBELO, Monaliza Maia"

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Antioxidant capacity and biological activity of essential oil and methanol extract of Conobea scoparioides (Cham. & Schltdl.) Benth
(2009) REBELO, Monaliza Maia; SILVA, Joyce Kelly do Rosário da; ANDRADE, Eloisa Helena de Aguiar; MAIA, José Guilherme Soares
The essential oils of the sub-aquatic plant Conobea scoparioides (fresh and dried previously) showed yields of 3.4 and 3.3%, respectively. The main identified constituents were thymol methyl ether (39.6 and 47.7%), thymol (40.0 and 26.4%), α-phellandrene (12.1 and 14.3%) and p-cymene (1.5 and 1.7%), totalizing more than 90% of the oils. The DPPH radical scavenging activity (EC50) of the oils and extract was 46.7 ± 3.6 µg mL-1 in the fresh plant (CsO-f), 56.1 ± 2.4 µg mL-1 in the dried plant (CsO-d), and 23.0 ± 2.2 µg mL -1 in the methanol extract. The extract (CsE-d)value is comparable to BHT (19.8 ± 0.5 µg mL-1) used as antioxidant standard. The mean value of the oils is twice smaller but equally important as antioxidant agent. The mean amount of Total Phenolics (TP, 124.6 ± 8.7 mg GAE per g) and the Trolox Equivalent (TEAC, 144.1 ± 4.9 mg TE per g) of the methanol extract confirmed the significant antioxidant activity of C. scoparioides. Similarly, in the brine shrimp bioassay (Artemia salina) the mean value of the lethal concentration for the oils (CL50, 7.7 ± 0.3 µg mL-1) was ten times higher than the methanol extract (CL50, 77.6 ± 7.1 µg mL-1) showing important biological activity.
Acesso aberto (Open Access)
Antioxidant capacity and biological activity of essential oil and methanol extract of Hyptis crenata Pohl ex Benth
(2009-03) REBELO, Monaliza Maia; SILVA, Joyce Kelly do Rosário da; ANDRADE, Eloisa Helena de Aguiar; MAIA, José Guilherme Soares
The essential oils of fresh and dried leaves and fine stems of Hyptis crenata furnished the following yields: 1.4% and 0.9%. The main volatile constituents were α-pinene (22.0%; 19.5%), 1,8-cineole (17.6%; 23.2%), β-pinene (17.0%; 13.8%), camphor (4.7%; 11.6%), limonene (5.4%; 4.4%) and γ-terpinene (3.5%; 2.4%), totalizing more than 70% in the oils. The DPPH radical scavenging activity (EC50, 16.7 + 0.4 µg/mL) of the methanol extract was comparable to BHT (19.8 ± 0.5 µg/mL) showing a significant antioxidant activity. The oils showed low activities. The amount of total phenolics (TP, 373.0 + 15.9 mg GAE/g) and trolox equivalent (TEAC, 226.8 + 0.5 mg TE/g) confirmed the antioxidant activity of the methanol extract that can be attributed to the presence of polar phenolic compounds. In the brine shrimp bioassay the lethal concentrations (LC50) for the oil and methanol extract were 6.7 + 0.2 µg/mL and 13.0 + 3.7 µg/mL, respectively, providing important evidence of their biological activities.
Acesso aberto (Open Access)
Hidróxidos duplos lamelares à base de escória de alto forno
(2012) REBELO, Monaliza Maia; CUNHA, Márcia Valéria Porto de Oliveira; CORRÊA, José Augusto Martins
Hydrotalcite like compounds (HT) were prepared by co-precipitation (Mg/Al = 3.5), using an acid solution with blast furnace slag and MgCl2.6H2O and aqueous solutions of NaOH. The following synthesis variables were investigated: temperature (30 and 45 ºC) and pH (9 and 12). Depending of the temperature two systems were observed: Mg-Al-CO3 (T = 30 ºC); Mg-Al-Cl-CO3 (T = 45 ºC). An increase in the pH of synthesis and Mg2+ concentration produced HTs well-crystallized and with greater values of all cell parameters. The study showed the potentiality of BFS in the synthesis of well-crystallized LDHs without the presence of other crystalline phases.
Acesso aberto (Open Access)
Hidróxidos duplos lamelares e sílica gel à base de escória de alto forno, com ênfase na aplicação do HDL na catálise do óleo essencial de Conobea scoparioides da região Amazônica
(Universidade Federal do Pará, 2012-12-03) REBELO, Monaliza Maia; CORRÊA, José Augusto Martins; http://lattes.cnpq.br/6527800269860568
Lamellar double hydroxides (LDHs) and silica gel were obtained from the residue steel blast furnace (SBF) from the municipality of Maraba-PA. The SBF when digested in HCl resulted in two phases. The soluble phase (solution SBF) was used to synthesize the LDHs, while the solid phase is characterized by different techniques. The LDHs were synthesized by coprecipitation with increasing pH by mixing an aqueous NaOH solution with SBF and MgCl2.6H2O, establishing a theoretical molar ratio Mg/Al = 3.5. The variables investigated were the synthesis temperature (30 to 45 °C) and pH (9 and 12). The HDLs showed a hydrotalcite like structure. The LDHs synthesized at 30 °C showed characteristics of the system Mg-Al-CO3 while synthesized at 45 °C were belonging to the system Mg-Al-CO3-Cl. The pH values directly influenced the crystal structure of LDHs. The LDHs synthesized at higher pH values shown greater degree of structural ordering and highest values of the unit cell parameters a and c and basal spacing d (003), besides having higher Mg content. The resulting solid phase from the acid digestion of SBF, silica-coded EAF, showed amorphous character, typical of amorphous silica. The EAF-silica showed similar properties as those of commercial high purity silica, with a 99.65%-weight of SiO2, moisture free. It showed a high specific surface area (282 m2/g), high affinity for physio-sorbed water (12,27%) and high amount of water content (6.18%). It has extremely fine particle sizes, forming agglomerates of varying sizes, some of them smaller than 1 μm with morphology typical of porous material. The particles of EAF-silica exhibited unimodal size distribution and good uniformity with a mean diameter D50 equal to 7,0 μm. With the intent to find an application for LDHs based SBF, the EAF hydrotalcite-HDL-4 belonging to the system Mg-Al-CO3-Cl, with a molar ratio Mg/ Al: 3.2 and porous morphology was evaluated as a catalyst in the conversion between the major constituents of the essential oil of C. scoparioides, an aromatic herb from the Amazon region known as “pataqueira”. The EAF-4-HDL showed a strong influence on the conversion of α-phellandrene, ρ-cymene, methyl ether of thymol and thymol, with high selectivity to the formation of thymol. The EAF-HDL-4 in contact with the oil sample in EtOH showed no significant catalytic activity. However, in the samples of the oil in EtOH: water showed a decreasing trend in the percentage of α-phellandrene, ρ-cymene and thymol methyl ether, with increasing water content, while the percentage of thymol has been increased. It was found that, in the samples analyzed after contact with the EAF-HDL-4, the percentage of thymol was above those in the respective control samples, with values increased between 2.69% to 86.75%. Based on these data, we suggest that the conversion between the major constituents was favored by water and catalyzed by EAF-HDL-4. We propose that both the α-phellandrene and ρ-cymene and thymol methyl ether were converted to thymol, increasing it percentage in the essential oil of C. scoparioides that was 41.62% and after contact with the HDL went up to a percentage of 95.02% thymol.
Acesso aberto (Open Access)
Sílica gel obtida de escória de alto forno: Marabá, Pará
(Universidade Federal do Pará, 2015-09) REBELO, Monaliza Maia; NASCIMENTO, Lidiane Diniz do; CORRÊA, José Augusto Martins
Silica gel with similar properties to commercial silica was obtained from blast furnace slag (EAF) using digestion with hydrochloric acid. The EAF-silica was obtained and characterized by different techniques. The results showed that the EAF-silica obtained was amorphous, with 99.7% purity and specific area 282 m2/g. It presented high hydrophilic character (12.27%), with constitution water of ~ 6.18%, which was confirmed by mass loss in thermogravimetric analysis. The EAF-silica particles had micrometric sizes (< 1 µm) with aggregates, unimodal size distribution and D50 7.0 µm.