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排序方式: 共有1243条查询结果,搜索用时 15 毫秒
941.
Piedade JA Fernandes IR Oliveira-Brett AM 《Bioelectrochemistry (Amsterdam, Netherlands)》2002,56(1-2):81-83
Adriamycin, a cancerostatic anthracycline antibiotic, causes considerable death of tumour cells, together with the induction of breaks in DNA single and double strands. The interaction of this compound with DNA was investigated using an electrochemical DNA-biosensor. Adriamycin intercalation in DNA disrupts the double helix and the detection of guanine and 8-oxoguanine could mimic one possible mechanism for the in vivo adriamycin drug action. 相似文献
942.
Different multidimensional chromatographic techniques were used to study wine aroma pattern changes during malolactic fermentation (MLF). Ethyl lactate enantiomeric ratios were determined using on-line multidimensional gas chromatography. The values found agree with a spontaneous MLF. Off-line multidimensional HPLC/GC was used to deconvolute and enrich the sample and ease enantioselective chromatography. Chiral compound enantiomeric ratio changes during MLF were monitored. Evaluation of enantiomeric ratio changes during MLF has never been studied. (R,R), (S,S) and meso-butane-2,3-diol and pentane-2,4-diol (reported in wines for the first time) were submitted to untrained sensory panel tests. All stereoisomers revealed different sensory notes; pentane-2,4-diol showed an aromatic impact. 相似文献
943.
Roberto S. Fernandes Gaspar González Elizabete F. Lucas 《Colloid and polymer science》2005,283(4):375-382
Oil-in-water emulsions are usually formed during oil production and treatment. Before being discarded, such dispersions should be treated. In order to improve the oil–water separation process using physical processes (decantation, flotation, centrifugation, etc.) the particle size of the disperse phase should be increased. This may be achieved through flocculation, which consists in the agglomeration of various particles or drops, using, as flocculating agents, high molecular weight hydrophilic macromolecules. A few studies have been carried out on the flocculation of finely divided oil drops in brine with the aid of generally ionic polyelectrolytes. This work shows the results obtained using nonionic polymers as flocculants. Commercial samples of poly(ethylene oxide-b-propylene oxide) and poly(vinyl alcohol) were evaluated through flocculation–flotation tests as well as the drop size distribution. The performance of such additives as flocculants for oil–water dispersions is related to their structure, composition, molecular weight and hydrophilic–lipophilic balance. The composition of the produced water is also an important parameter when choosing the features of the flocculant additive. 相似文献
944.
M. J. B. Souza A. O. S. Silva J. M. F. B. Aquino V. J. Fernandes Jr. A. S. Araújo 《Journal of Thermal Analysis and Calorimetry》2004,75(2):693-698
The siliceous MCM-41 molecular sieve was synthesized starting from a hydrogel with the following molar composition: 4.58SiO2:0.437Na2O:1CTMABr:200H2O. The cetyltetramethylammonium bromide (CTMABr) was used as structure template. A kinetic study of template removal after
the syntheses was performed by Vyazovkin model-free kinetic method obtaining apparent activation energy of 166±8.2 kJ mol-1.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
945.
Susete Fernandes Francisco Lemos Richard J. Maldanis James C.W. Chien Maria M. Marques 《Journal of organometallic chemistry》2005,690(4):895-909
The nickel complexes {bis[N,N′-di(2-t-butylphenyl)imino]acenaphthene} dibromonickel (1-NiBr2) and {bis[N,N′-di(2-phenylphenyl)imino]acenaphthene} dibromonickel (2-NiBr2) were studied in homo-, co- and terpolymerization of ethylene and propylene with polar monomers and the results compared to those previously obtained with another catalyst precursor [bis(N,N′-dimesitylimino)acenaphthene] dibromonickel (3-NiBr2). In order to understand the effect of the ligand in the activity and rate of comonomer incorporation some theoretical studies, using both a semi-empirical molecular orbital method and a density-functional theory model, were performed. Good agreement was found between the computed parameters and the experimental results for the order of homo-polymerization, the differences in polymer molecular weight distribution, and, in some cases, the incorporation of functionalized copolymers in the case of copolymerization, and also on the inhibition effects caused by these copolymers. 相似文献
946.
Januário AH Lourenço MV Domézio LA Pietro RC Castilho MS Tomazela DM da Silva MF Vieira PC Fernandes JB França Sde C 《Chemical & pharmaceutical bulletin》2005,53(7):740-742
Crude extracts of callus and roots of Dipteryx odorata were analyzed by HPLC to detect and quantify isoflavone contents. Based on spectroscopic and X-ray crystallography data the structures of two isoflavones were elucidated as 7-hydroxy-4',6-dimethoxyisoflavone and 3',7-dihydroxy-4',6-dimethoxyisoflavone. The production of dry biomass of 7-hydroxy-4',6-dimethoxyisoflavone in cultured callus was 4.12 mg/g, approximately eleven fold higher than the amount accumulated in roots of D. odorata wild-growing plants. The 7-hydroxy-4',6-dimethoxyisoflavone was effective against glyceraldehyde-3-phosphate dehydrogenase from Trypanosoma cruzi. This is the first report on those bioactive isoflavones accumulated in callus of D. odorata. 相似文献
947.
Nataly A. Santos Marileide L. A. Tavares R. Rosenhaim F. C. Silva V. J. Fernandes Jr Iêda M. G. Santos A. G. Souza 《Journal of Thermal Analysis and Calorimetry》2007,87(3):649-652
The growing petroleum deficit
requires the development of alternative fuel sources. Biodiesel is a good
alternative, as it is a biodegradable and renewable product, which obeys the
carbon cycle. In this work, the biodiesel from babassu was synthesized using
the methanol route, and characterized by physico-chemical analyses in order
to make able the investigated biodiesel to fulfill with its properties the
requirements of Brazilian National Agency for Petroleum, Natural Gas and Biofuel
(ANP). Besides gas chromatography, IR spectroscopy experiments and thermoanalytical
measurements in air and in nitrogen were done to determine the main thermal
decomposition processes and calorimetric events. The evaporation temperature
of babassu biodiesel was similar in both atmospheres, started around 52 in
air and around 60°C in nitrogen. 相似文献
948.
Ernesto Schulz Lang Ramo Marceli Fernandes Jr Clvis Peppe Robert Alan Burrow Ezequiel M. Vzquez‐Lpez 《无机化学与普通化学杂志》2003,629(2):215-218
The reaction of diphenylditelluride with pyridine, 2‐bromopyridine or 2‐bromopyridine/tetraamminedichlorocobalt(III) chloride in 12 M hydrochloric acid afforded the tetrachlorophenyltellurate(IV) compounds [C5NH6][PhTeCl4] ( 1 ), [2‐Br‐C5NH5] [PhTeCl4] ( 2 ), and [{2‐Br‐C5NH5}{Co(NH3)4Cl2}] [PhTeCl4]2 ( 3 ). They were all characterized structurally by single crystal X‐ray diffraction. In all structures, the arrangement about the tellurium atoms is square pyramidal. The [PhTeCl4]— anions in 1 and 2 form trimeric and dimeric units, respectively, through Te···Cl secondary bonding. Compound 3 shows an unusual face‐to‐face packing of the [PhTeCl4]—anions with hydrogen bonding to the bromopyridium cation. 相似文献
949.
In this work, the thermotropic liquid crystal MBBA (N-(4-methoxybenzilidene)-4-butylaniline), entrapped on hydrogels, based on cross-linked polyacrylamide (PAAm), was studied. The liquid crystalline phases of system were characterized by polarized optical microscopy (POM), refractive index, optical transmittance, scanning electron microscopy (SEM) and water loss. It was verified the presence of birefringence on hydrogel + liquid crystal. The dynamic of formation of such birefringence finished 40 days after the hydrogel synthesis. The effective birefringence Δn, i.e., the difference on refractive index of polyacrylamide hydrogel to refractive index of hydrogel + liquid crystal (Δn1) and the difference on refractive index of liquid crystal (MBBA) to refractive index of hydrogel + liquid crystal (Δn2) are dependent of content of acrylamide (AAm) and MBBA on hydrogel. The increase on Δn1 and Δn2 with the polyacrylamide content on hydrogel was attributed to decreasing of the mobility liquid crystal inside the hydrogel. Also, an increase on MBBA concentration in the polymeric matrix provides a reduction in the values of optical transmittance in the system. The morphology observed by SEM shows that hydrogel + liquid crystal is more compact that PAAm hydrogels. The presence of MBBA causes an increase in hydrophobicity. The water loss speed is favored by the increase in the amount of MBBA present in the hydrogels. 相似文献
950.