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61.
The problem of classifying finite projective planes
of order n with an automorphism group G and a point orbit
on which G acts two-transitively is investigated in considerable detail, under the assumption that
has length at last n. Combining old and new results a rather satisfying classification is obtained, even though some cases for orbit lengths n and n + 1 remain unsolved. 相似文献
62.
63.
Vitor Alves S da Silva Aymara da Silva Santos Tiago Luiz Ferreira Lúcia Codognoto Eliana Maíra Agostini Valle 《Electroanalysis》2020,32(7):1582-1589
Pesticides are organic molecules used in the control of various pests in different crops. These molecules show functional groups that can interact with metal ions, forming new species with different properties. These new compounds have been attracting attention because they can become a new environmental problem. In this work the interaction of copper and zinc metal ions with Thiram pesticide was studied using electrochemical techniques. Studies in ultrapure water showed the formation of Zn?Thiram complex with reduction potential at ?1.330 V; Cu?Thiram complex showed a cathodic peak at 0.020 V. Thiram causes a different effect on the two metal ions studied. It was observed that the ligand stabilizes more the Cu(II) than Zn(II). Both systems proved to be quasi‐reversible, controlled by the adsorption of the species on the electrode surface. The formation constants of the complexes were calculated to be 2.1×105 for Zn?Thiram and 1.5×1019 for Cu?Thiram. In the samples from Billings dam, the Zn‐complex showed reduction potential at ?1.403 V; Cu‐complex exhibited a reduction peak at 0.012 V. Although there are interferers in river waters, the interaction of these metals with the pesticide showed high affinity, being possible to detect them in natural samples. The Cu(II) complex showed to be more stable in natural matrices when compared to the Zn(II) complex. The sensitivity for thiram electroanalytical determination decreases in the presence of Zn(II) and Cu(II). 相似文献
64.
Ana Luiza Ribeiro de Souza Tatiana Andreani Fernando M. Nunes Douglas Lopes Cassimiro Adélia Emília de Almeida Clóvis Augusto Ribeiro Victor Hugo Vitorino Sarmento Maria Palmira Daflon Gremião Amélia M. Silva Eliana B. Souto 《Journal of Thermal Analysis and Calorimetry》2012,108(1):353-360
Praziquantel (PZQ) is the drug of choice for oral treatment of schistosomiasis and other fluke infections that affect humans.
Its low oral bioavailability demands the development of innovative strategies to overcome the first pass metabolism. In this
article, solid lipid nanoparticles loaded with PZQ (PZQ-SLN) were prepared by a modified oil-in-water microemulsion method
selecting stearic acid as lipid phase after solubility screening studies. The mean particle size (Z-Ave) and zeta potential
(ZP) were 500 nm and −34.0 mV, respectively. Morphology and shape of PZQ-SLN were analysed by scanning electron microscopy
revealing the presence of spherical particles with smooth surface. Differential scanning calorimetry suggested that SLN comprised
a less ordered arrangement of crystals and the drug was molecularly dispersed in the lipid matrix. No supercooled melts were
detected. The entrapment efficiency (EE) and loading capacity of PZQ, determined by high performance liquid chromatography,
were 99.06 ± 0.3 and 17.48 ± 0.05, respectively. Effective incorporation of PZQ into the particles was confirmed by small
angle X-ray scattering revealing the presence of a lipid lamellar structure. Stability parameters of PZQ-SLN stored at room
temperature (25 °C) and at 4 °C were checked by analysing Z-Ave, ZP and the EE for a period of 60 days. Results showed a relatively
long-term physical stability after storage at 4 °C, without drug expulsion. 相似文献
65.
Alexandre Félix FragaEdson de Almeida Filho Eliana Cristina da Silva RigoAnselmo Ortega Boschi 《Applied Surface Science》2011,257(9):3888-3892
Chitosan, which is a non-toxic, biodegradable and biocompatible biopolymer, has been widely researched for several applications in the field of biomaterials. Calcium phosphate ceramics stand out among the so-called bioceramics for their absence of local or systemic toxicity, their non-response to foreign bodies or inflammations, and their apparent ability to bond to the host tissue. Hydroxyapatite (HA) is one of the most important bioceramics because it is the main component of the mineral phase of bone. The aim of this work was to produce chitosan membranes coated with hydroxyapatite using the modified biomimetic method. Membranes were synthesized from a solution containing 2% of chitosan in acetic acid (weight/volume) via the solvent evaporation method. Specimens were immersed in a sodium silicate solution and then in a 1.5 SBF (simulated body fluid) solution. The crystallinity of the HA formed over the membranes was correlated to the use of the nucleation agent (the sodium silicate solution itself). Coated membranes were characterized by means of scanning electron microscopy - SEM, X-ray diffraction - XRD, and Fourier transform infrared spectroscopy - FTIR. The results indicate a homogeneous coating covering the entire surface of the membrane and the production of a semi-crystalline hydroxyapatite layer similar to the mineral phase of human bone. 相似文献
66.
67.
68.
Catia Contado Eleonora Vighi Alessandro Dalpiaz Eliana Leo 《Analytical and bioanalytical chemistry》2013,405(2-3):703-711
Poly(lactic-co-glycolic acid) particles in the 200–400-nm size range were formulated through nanoprecipitation and solvent evaporation methods. Different concentrations of the polymer and stabilizer (Pluronic® F 68) were tested in order to identify the best conditions for making poly(lactic-co-glycolic acid) particles of suitable size, stable in time, and to be used as carriers for brain-targeting drugs. The particles with the best characteristics for delivery system design were those formulated by nanoprecipitation with an organic/water phase ratio of 2:30, a polymer concentration of 25 mg/mL, and a surfactant concentration of 0.83 mg/mL; their surface charge was reasonably negative (approximately -27 mV) and the average size of the almost monodisperse population was roughly 250 nm. Particle characterization was obtained through ζ-potential measurements, scanning electron microscope observations, and particle size distribution determinations; the latter achieved by both photon-correlation spectroscopy and sedimentation field flow fractionation. Sedimentation field flow fractionation, which is considered more reliable than photon-correlation spectroscopy in describing the possible particle size distribution modifications, was used to investigate the effects of 3 months of storage at 4 °C had on the lyophilized particles. Figure
Particle size ditribution from the SdFFF and the PCS techniques 相似文献
69.
Costa FS de Araújo Júnior CA Silva Ede J Bara MT Lima EM Valadares MC Marreto RN 《Ultrasonics sonochemistry》2011,18(5):1002-1007
Pothomorphe umbellata (L.) Miq. is a Brazilian shrub with therapeutic and economic applications. There are some reports on the technological development of P. umbellata preparations; however, there are no studies on the influence of non-conventional extraction procedures on the quality of P. umbellata extracts. The aim of this study was to evaluate the effects of the ultrasound-assisted extraction (UE) parameters upon the extraction yield (EY%) of 4-nerolidylcatechol (4-NC) and the antioxidant activity of P. umbellata extracts using a factorial design and response surface methodology. Extracts obtained by UE and percolation were compared, and the photostability of 4-NC was evaluated via the exposure of UVA and visible light to the samples. The most influential variables observed for the UE were the ethanol-to-water and drug-to-solvent ratios. UE improved the extraction kinetics of 4-NC from plant material and improved the antioxidant activity of the extracts. Some of the ultrasound extracts showed an antioxidant activity that was not proportional to their 4-NC concentration, which suggests the presence of other active antioxidant compounds in these P. umbellata extracts. There was no significant difference in the photostability of 4-NC between the percolated and ultrasound extracts. Surprisingly, the isolated 4-NC material was significantly more stable when exposed to UVA-visible light compared to 4-NC in the plant extracts. 相似文献
70.
Luana B. S. Nascimento Marcos V. Leal‐Costa Marcela A. S. Coutinho Nattacha dos S. Moreira Celso L. S. Lage Nancy dos S. Barbi Sônia S. Costa Eliana S. Tavares 《Photochemistry and photobiology》2013,89(2):391-399
Antioxidant compounds protect plants against oxidative stress caused by environmental conditions. Different light qualities, such as UV‐A radiation and blue light, have shown positive effects on the production of phenols in plants. Kalanchoe pinnata (Lamarck) Persoon (Crassulaceae) is used for treating wounds and inflammations. Some of these beneficial effects are attributed to the antioxidant activity of plant components. We investigated the effects of blue light and UV‐A radiation supplementation on the total phenol content, antioxidant activity and chromatographic profile of aqueous extracts from leaves of K. pinnata. Monoclonal plants were grown under white light, white plus blue light and white plus UV‐A radiation. Supplemental blue light improved the antioxidant activity and changed the phenolic profile of the extracts. Analysis by HPLC of supplemental blue‐light plant extracts revealed a higher proportion of the major flavonoid quercetin 3‐O‐α‐l ‐arabinopyranosyl (1→2) α‐l ‐rhamnopyranoside, as well as the presence of a wide variety of other phenolic substances. These findings may explain the higher antioxidant activity observed for this extract. Blue light is proposed as a supplemental light source in the cultivation of K. pinnata, to improve its antioxidant activity. 相似文献