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111.
Ronaldo S. Nunes Gilbert Bannach José M. Luiz Flávio J. Caires Claudio T. Carvalho Massao Ionashiro 《Journal of Thermal Analysis and Calorimetry》2011,106(2):525-529
Solid-state compounds of general formula Ln2L3·nH2O, where L represents 1,4-bis(3-carboxy-3-oxo-prop-1-enyl)benzene and Ln = La, Ce, Pr, Nd, Sm, were synthesized. Complexometric
titrations with EDTA, thermogravimetry (TG), differential thermal analysis (DTA), differential scanning calorimetry (DSC),
X-ray powder diffractometry, elemental analysis and infrared spectroscopy have been employed to characterize and to study
the thermal behavior of these compounds in dynamic air atmosphere. The results led to information about the composition, dehydration,
crystallinity, and thermal decomposition of the synthesized compounds. 相似文献
112.
Luiz K. C. de Souza Juliana J. R. Pardauil José R. Zamian Geraldo N. da Rocha Filho Carlos E. F. da Costa 《Journal of Thermal Analysis and Calorimetry》2011,106(2):355-361
Al-modified MCM-41, La-modified MCM-41, and Ce-modified MCM-41 mesoporous materials were prepared with different molar ratios
(Si/M = 10; 25; 50; 100 and 200) at room temperature. The materials were characterized using XRD, BET–BJH, and TG–DTA. The
XRD showed four peaks, due to the ordered hexagonal array of parallel silica tubes, which could be indexed as (100), (110),
(200), and (210), assuming a hexagonal unit cell. The surface area decreased as the concentration of the metal incorporated
in the material increased. The thermal stability of the materials was around 650 °C. The CeO2 phase made the mass transfer process more difficult, hindering Hofmann degradation and favoring oxidation. 相似文献
113.
Ana Rita de Mello Costa Flávia Silva Marquiafável Mirela Mara de Oliveira Lima Leite Vaz Bruno Alves Rocha Paula Carolina Pires Bueno Pedro Luiz M. Amaral Hernane da Silva Barud Andresa Ap. Berreta-Silva 《Journal of Thermal Analysis and Calorimetry》2011,104(1):273-278
Quercetin is a flavonoid very well studied and has already entered clinical trials emerging as prospective anticancer drug candidate. In addition, quercetin has being reported to its free-radical scavenging activity and suggests potential uses for the prevention and treatment of pathologies as atherosclerosis, chronic inflammation, and others. However, quercetin is sparingly soluble in water, which may be responsible for its limited absorption upon oral administration. The solid dispersion of quercetin with polyvinylpyrrolidone Kollidon® 25 (PVP K25) suggests an interesting way to increase quercetin solubility, antioxidant activity, and consequently bioavailability. Then, the purpose of this study was to prepare solid dispersions of quercetin with PVP K25 and evaluate their thermal characterization, antioxidant activity and quercetin improvement solubility. For this purpose, quercetin-PVP K25 solutions were dried and quercetin-PVP K25 solids were obtained. The formation of quercetin-PVP K25 solid dispersion was evaluated by solubility studies, powder X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), thermogravimetry (TG), and antioxidant activity. It was observed that PVP K25 was able to provide quercetin clear aqueous solutions and that quercetin solubility was increased in a PVP K25 concentration dependent manner, improving solubility even 436-fold the pure quercetin. The results obtained with XRD, FT-IR, DSC, and TG demonstrated possible quercetin-PVP K25 solid dispersion formation. Besides, the antioxidant activity of the quercetin-PVP K25 solid dispersions dissolved in aqueous solution and pure quercetin dissolved in methanol showed IC50 value of 0.61 ± 0.03 and 1.00 ± 0.02 μg/mL, respectively, demonstrating that the solid dispersions presented a significant increase in antioxidant activity (P < 0.05). Putting results together, it was possible to conclude there was the formation of quercetin-PVP K25 solid dispersion. 相似文献
114.
Medeiros MR Prado LA Fernandes VC Figueiredo SS Coppede J Martins J Fiori GM Martinez-Rossi NM Beleboni RO Contini SH Pereira PS Fachin AL 《Natural product communications》2011,6(2):193-196
Tabernaemontana catharinensis root bark ethanol extract, EB2 fraction and the MMV alkaloid (12-methoxy-4-methylvoachalotine) were evaluated for their antimicrobial activities. T. catharinensis ethanol extract was effective against both strains of the dermatophyte Trichophyton rubrum at concentrations of 2.5 mg/mL (wild strain) and 1.25 mg/mL (mutant strain), while the EB2 fraction and MMV alkaloid showed a strong antifungal activity against wild and mutant strains with MIC values of <0.02 and 0.16 mg/mL, respectively. The EB2 fraction showed a strong antibacterial activity against ATCC strains of S. aureus, S. epidermidis, E. coli and P. aeruginosa with MICs from <0.02 to 0.04 mg/mL, as well as against resistant clinical isolates species of Enterococcus sp, Klebsiella oxytoca, Citrobacter, K. pneumoniae, P. mirabilis, S. aureus, S. epidermidis, E. coli and P. aeruginosa with MIC values ranging from 0.04 to 0.08 mg/mL. The MMV alkaloid presented a MIC of 0.16 mg/mL against the strains of S. aureus and E. coli ATCC. For the resistant clinical isolates Enterococcus sp, Citrobacter, S. aureus, S. epidermidis, E. coli and P. aeruginosa the MIC of MMV ranged from 0.08 to 0.31 mg/mL. The chromatography analysis of the EB2 fraction revealed the presence of indole alkaloids, including MMV, possibly responsible for the observed antimicrobial activity. 相似文献
115.
Lago JH Carvalho LA Ferreira MJ Romoff P Zanin JL Soares MG Fávero OA 《Natural product communications》2011,6(2):243-245
The essential oils from leaves and stem barks of Drimys brasiliensis Miers (Winteraceae), collected in July and December 2008, were analyzed by GC/FID and GC/MS. The stem bark oils were composed mainly of monoterpenes (July, 45 +/- 3%; December, 92 +/- 4%), while the oils from leaves showed the predominance of sesquiterpenes (July, 47 +/- 1%; December, 55 +/- 1%). The variation in the relative amount of constituents could be associated, at least in part, to several microclimatic parameters such as precipitation, temperature and/or phenological state, which were different for each collection of D. brasiliensis. 相似文献
116.
A rank-three condition for invariant (1, 2)-symplectic almost Hermitian structures on flag manifolds
Nir Cohen Caio J.C. Negreiros Luiz A.B. San Martin 《Bulletin of the Brazilian Mathematical Society》2002,33(1):49-73
This paper considers invariant (1, 2)-symplectic almost Hermitian structures on the maximal flag manifod associated to a
complex semi-simple Lie group G. The concept of cone-free invariant almost complex structure is introduced. It involves the rank-three subgroups of G, and generalizes the cone-free property for tournaments related to 𝕊l (n,ℂ) case. It is proved that the cone-free property is necessary for an invariant almost-complex structure to take part in
an invariant (1, 2)-symplectic almost Hermitian structure. It is also sufficient if the Lie group is not B
l , l ≥ 3, G
2 or F
4. For B
l and F
4 a close condition turns out to be sufficient.
Received: 28 October 2001 相似文献
117.
Antonio Luiz P. S. Campos Adaildo Gomes d''Assunção Marcos A. Barbosa de Melo 《International Journal of Infrared and Millimeter Waves》2002,23(1):123-133
The analysis of periodic structures on anisotropic substrates is presented for incident millimeter waves. Frequency selective surface structures composed by a periodic array of conducting crossed dipoles on anisotropic layers are analyzed. A full-wave analysis for the problem of scattering is performed. The formulation uses the moment method in combination with the immitance approach, in the Fourier domain, to determine the scattering parameters of the considered structures. A set of entire-domain type basis functions is used in the expansion for the unknown induced current. This analysis is computationally efficient, and its accuracy is verified by the agreement between results obtained in this work and those available in the literature, for particular cases. 相似文献
118.
Rodrigo Lambert Oréfice Wander Luiz Vasconcelos 《Journal of Sol-Gel Science and Technology》1997,9(3):239-249
The capacity of the sol-gel process of producing highly pure, homogeneous alumina-silica based materials had been demonstrated
in the last few years. However, a full understanding on the mechanisms associated to sol formation and sol to gel transition
has not yet been achieved and is required for the development of a new generation of nano-structurally tailored materials
that will significantly enhance the technological importance of the sol-gel process. In this work, tetraethyl orthosilicate
(TEOS) and aluminum isopropoxide were used to prepare materials within the entire silica-alumina system. Process parameters,
such as gelation time, were correlated to variables of the initial stage of the process, such as pH, temperature of hydrolysis
and water/alkoxide ratio. The obtained gels were dried at 105°C and subsequently heat treated at 500 and 1100°C for 3 hours.
X-ray diffraction and infrared spectroscopy were used to characterize the materials and phase transformations. Structural
information obtained from phase characterization and phase transformations was correlated to the effects of the process variables
on sol formation and gelation, providing insights related to the mechanisms involved. The influence of temperature of aluminum
isopropoxide hydrolysis on peptization and gelation of the mixtures was noted. The different behavior of mixtures hydrolyzed
at low and high temperatures was suggested to be caused by different mechanisms of surface charge formation on the structurally
different aluminum hydroxides. Monophasic and diphasic mullite xerogels were produced by changing temperature of aluminum
isopropoxide hydrolysis, and led to formation of mullite and Al−Si spinel phases respectively, when treated at 1100°C. 相似文献
119.
We consider two analogues of associativity for ternary algebras: total and partial associativity. Using the corresponding ternary associators, we define ternary analogues of alternative and assosymmetric algebras. On any ternary algebra the alternating sum [a, b, c] = abc − acb − bac + bca + cab − cba (the ternary analogue of the Lie bracket) defines a structure of an anticommutative ternary algebra. We determine the polynomial identities of degree ?7 satisfied by this operation in totally and partially associative, alternative, and assosymmetric ternary algebras. These identities define varieties of ternary algebras which can be regarded as ternary analogues of Lie and Malcev algebras. Our methods involve computational linear algebra based on the representation theory of the symmetric group. 相似文献
120.
A method for the microdetermination of copper in air pollution investigations, using a dithiooxamide crayon and the ring-oven technique is presented. The limit of detection for the method is 0.04 μg, and the quantitative determination is applicable in the range of 0.05 to 0.5 μg of copper. The method is free from interferences that might be of significance in the study of air samples. 相似文献