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171.
Pinho e Melo TM Soares MI Gonsalves AM Paixão JA Beja AM Silva MR 《The Journal of organic chemistry》2005,70(17):6629-6638
1-Azafulvenium methides, generated from pyrrolo[1,2-c]thiazole-2,2-dioxides' thermal extrusion of sulfur dioxide, led to the synthesis of functionalized pyrroles. The intramolecular trapping of these transient 8pi 1,7-dipoles in pericyclic reactions, namely sigmatropic [1,8]H shifts and 1,7-electrocyclization, allowed the synthesis of N-vinylpyrroles and C-vinylpyrroles which, under flash vacuum pyrolysis conditions, are converted into 5-oxo-5H-pyrrolizines or 4-oxo-1,4-dihydro-1-aza-benzo[f]azulenes, respectively. These heterocycles can also be obtained directly from FVP of pyrrolo[1,2-c]thiazole 2,2-dioxides. The synthesis and X-ray structure of a new 6-oxocyclopenta[b]pyrrole derivative is also reported. 相似文献
172.
Preto MA Melo A Maia HL Mavromoustakos T Ramos MJ 《The journal of physical chemistry. B》2005,109(37):17743-17751
Angiotensin II (Ang II) is an octapeptidic hormone, which plays an important role in the mechanisms of blood pressure control. In this work, extensive molecular dynamics (MD) simulations have been carried out on this peptide, both in aqueous and in dimethyl sulfoxide (DMSO) environments. Experimentally proposed models for the structure of angiotensin II in both environments are not consensual and the results obtained have provided some further insight about the structural properties of this hormone. In these simulations, the N-terminus of Ang II in the aqueous environment has been associated with a considerable larger flexibility than the correspondent C-terminus, but this was not found in the case of the DMSO environment. This is consistent with the assumption that the biological activity of Ang II is associated with its C-terminal residues embedded in a hydrophobic environment of its AT1 receptor. Other features detected in DMSO environment were an H(His6 imidazole)-O(Phe8 carboxylate) hydrogen bond and a salt-bridge structure involving the Asp1 and Arg2 side chains. An additional important conformational feature is the spatial proximity between Tyr4 and His6 in both water and DMSO environments. This molecular feature may trigger the interest for the synthetic chemists to apply rational design for the synthesis of novel AT1 antagonists. 相似文献
173.
A. H. Parente E. T. A. Marques W. M. Azevedo F. B. Diniz E. H. M. Melo J. L. Lima Filho 《Applied biochemistry and biotechnology》1992,37(3):267-273
A biosensor for glucose utilizing kinetics of glucose oxidase (EC 1.1.3.4.) was developed. The enzyme was immobilized on polyaniline
by covalent bonding, using glutaraldehyde as a bifunctional agent. The system showed a linear response up to 2.2 mM of glucose
with a response time of 2.5–4.0 min. In addition, the immobilized enzyme had a higher activity between pH 6.5 and 7.5. The
system retained 50% of its activity after 30 d of daily use. The optical absorption spectra of the polyaniline/glucose oxidase
electrode after glucose had been added to the buffer solution showed that the absorption band around 800 nm had changed considerably
when glucose was allowed to react with the electrode. This optical variation makes polyaniline a very promising polymer for
use as a support in optical sensor for clinical application. 相似文献
174.
Daniela Pinheiro Marta Pineiro Adelino M. Galvo J. Srgio Seixas de Melo 《Chemical science》2021,12(1):303
Using green chemistry procedures the synthesis of N-alkyl (NCnInd) and N,N′-dialkyl (N,N′CnInd) indigo derivatives, with n = 1–3, 6, 8, 12 and 18, was undertaken, leading to compounds with blueish to greenish colors in solution. The effect of the alkyl chain length on the spectral (including color) and photophysical properties of the compounds was explored. This was done with solvents of different viscosities and polarities (dielectric constants). From time-resolved fluorescence and femtosecond-transient absorption (fs-TA) for the NCnInd derivatives with n = 1 and 2, the decays are, in methylcyclohexane (MCH) and n-dodecane, single-exponential, while in 2-methyltetrahydrofuran (2MeTHF) they are bi-exponential. The excited state proton transfer (ESPT) is ultrafast (<1 ps) for NC1,2Ind in MCH and n-dodecane, supported by time-dependent density functional theory (TDDFT) calculations, thus showing that both the chain length and solvent influence the ESPT process. For N,N′CnInd, from time-resolved experiments, and with the exception of the shortest member of the series, N,N′C1Ind, two conformers are found to be present in the excited state.Using green chemistry procedures the synthesis of N- and N,N′-alkyl indigo derivatives was undertaken and the effect of the alkyl chain length on the spectral (including color) and photophysical properties of the compounds explored. 相似文献
175.
L. M. Q. C. Julião A. M. G. F. Azeredo M. S. Santos D. R. Melo B. M. Dantas J. L. Lipsztein 《Journal of Radioanalytical and Nuclear Chemistry》1994,177(1):121-126
This study is a comparison between bioassay data of thorium-exposed workers from two different facilities. The first of these facilities is a monazite sand extraction plant. Isotopic equilibrium between232Th and228Th was not observed in excreta samples of these workers. The second facility is a gas mantle factory. An isotopic equilibrium between232Th and228Th was observed in excreta samples. Whole body counter measurements have indicated a very low intake of thorium through inhalation. As the concentration of thorium in feces was very high we concluded that the main pathway of entrance of the nuclide was ingestion, mainly via contamination through dirty hands.The comparison between the bioassay results of workers from the two facilities shows that the lack of Th isotopic equilibrium observed in the excretion from the workers at the monazite sand plant possibly occurred due to an additional Th intake by ingestion of contaminated fresh food. This is presumably because228Ra is more efficiently taken up from the soil by plants, in comparison to228Th or232Th, and subsequently,228Th grows in from its immediate parent,228Ra. 相似文献
176.
Costa T Miguel MG Lindman B Schillén K Lima JC Seixas de Melo J 《The journal of physical chemistry. B》2005,109(8):3243-3251
The solution properties of two water-soluble polymers, poly(acrylic acid) (PAA), covalently labeled with the fluorescent hydrophobic dye naphthalene (Np), have been investigated in water:organic solvent mixtures. The naphthalene chromophores have been randomly attached, onto the polymer, with two different degrees of labeling. Fluorescence measurements (steady-state and time-resolved) have been used to follow the photophysical behavior of the polymers and consequently report on the self-association of the polymers in the mixed organic (methanol or dioxane):aqueous solutions. The emission spectra of the high-labeled Np PAA reveal the presence of monomer and excimer bands whereas with the low-labeled polymer only monomer emission is observed. The excitation spectra collected at the monomer and excimer emission bands show significant differences, depending on the water content of the mixture, which indicate the simultaneous presence of preformed and dynamic dimers as routes to excimer formation. The time-resolved data decay profiles of the high-labeled polymer in the mixtures were always triple exponential whereas in pure methanol and dioxane they follow biexponential laws. The data in the mixtures are consistent with two types of monomers and one excimer. Both monomers are able to give rise to excimer in the excited state, one type involving the movement of long distant Np chromophores and the other involving a local reorientation of adjacent Np chromophores. These correspond to different decay times: (1) a long which corresponds to the long distant approach of non-neighboring Np chromophores forming an excimer and (2) a short corresponding to the fast adjustment of two neighboring Np chromophores in order to have the adequate parallel geometry. An additional decay time corresponding to the excimer decay was found to be present at all wavelengths. All the decay times were dependent on the water content of the mixture. An estimation of the two excimer forming rate constants values is made for the mixed media considered in this work. On the whole, using both steady-state and time-resolved fluorescence parameters, and by comparing data for a polymer with a small number of hydrophobes with a more highly modified one, it is possible in great detail to demonstrate how association is controlled by solvent quality for the hydrophobes and by the distance between hydrophobes. 相似文献
177.
M. D. B. Barroso T. A. A Melo S. Prasad R. M. Gomes I. C. E. S. G. Lima A. G. Souza S. J. G. Lima 《Journal of Thermal Analysis and Calorimetry》2004,75(2):655-660
The crystallization behavior of Co75-xFexGe15B10 (x=3.0, 4.6 and 6.0) amorphous alloys was monitored by differential thermal analysis and thermo-mechanical analysis. The crystallization
process of the melt spun ribbons was interrupted at 450, 525, 650, 800 and 900°C and their microstructures were investigated
by X-ray diffractometry. It was observed that the crystallization occurs in a sequential mode attributed to the formation
of different types of precipitates. It was shown that the crystallization products change as a function of Fe content. After
full crystallization, GeFe, Co3B, FeGe2 and Co2Ge compounds were found as well as a Co rich solid solution.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
178.
Scheila F. Braga Louraine C. de Melo P.M.V.B. Barone 《Journal of Molecular Structure》2004,710(1-3):51-59
Ellipticine [5,11-dimethyl-6H-pyrido[4,3]carbazole] is a planar organic compound isolated from the plant extract of Ochrosia elliptica, with a high degree of antitumor and cytotoxic activity. Ellipticine and its derivatives have different modes of action, which may include intercalation or covalent binding to DNA and interference with the activity of topoisomerase II. In the present work we studied the electronic, geometrical and spectroscopic properties of 31 ellipticine derivatives and analogue compounds, using the semiempirical methods Parametric Method 3 and Zerner's Intermediate Neglect of Differential Overlap. The Zero Differential Overlap semiempirical Molecular Electrostatic Potential (MEP) was also calculated in order to interpret the electronic structure of the molecules. For the biologically tested ellipticines and olivacines we have observed a rule based on the dipole moment values and a selective distribution of active sites (coming from the MEP calculations) that can be used to identify the active molecules. These results provide a pattern which can be used to select potentially active molecules from the untested group of molecules and to design new ellipticine derivatives with improved antitumor activity. 相似文献
179.
Garrido Pedrosa A. M. Câmara M. S. C. Borges F. M. M. de Souza H. K. S. Scatena Jr H. Melo D. M. A. Zinner L. B. 《Journal of Thermal Analysis and Calorimetry》2003,73(3):895-902
Complexes of rare earth trifluoroacetates (TFA) with 4-methylmorpholine-N-oxide (MMNO) of composition Ln(TFA)3·3MMNO (Ln=Eu, Dy, Ho, Er, Yb and Y) were synthesized and characterized by elemental analysis data, complexometric titration with EDTA,
IR absorption spectra, thermogravimetric analyses and differential scanning calorimetry (DSC) in N2 atmosphere. Infrared spectroscopy data revealed that the MMNO molecules are bound to the central ion through the oxygen of
NO groups. These data suggest that the trifluoracetate groups are also coordinated. Thermogravimetric curves indicate that
the decomposition of MMNO begins at approximately 350 K and results in Ln2O3 residue at around 1170 K. A theoretical kinetic study was carried out using a QBASIC program with the TG input data for the
Dy complex.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
180.
J. J. LaBrecque L. Melo P. R. Cordoves F. Urbani 《Journal of Radioanalytical and Nuclear Chemistry》2004,261(2):343-347
A simple and rapid technique is presented to determine the relative counts of 214Bi in surface soils to locate active fault traces of the El Pilar Fault in the state of Sucre, Venezuela. The method employes a portable differential gamma-ray spectrometer on site with 300 seconds of measuring time. Three transects across the El Pilar fault of very different geological aspects were studied. One of the advantages of this technique in respect to determining 222Rn in soil-gas is that no soil-gas probes are required to be inserted in the soil and it is not necessary to know the appropriate depth. Finally, it has been suggested that measurements of 1000 seconds would be preferred rather than 300 seconds for future studies even though this would limit the number of measurements to about 20 per day.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献