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981.
Guilherme Rocha Pereira 《Tetrahedron letters》2010,51(7):1022-651
A bis-malonate C60 derivative bearing terminal alkyne groups prepared by the Bingel reaction has been used as a building block under copper-catalyzed azide-alkyne cycloaddition conditions to produce a series of new fullerene glycoconjugate derivatives. 相似文献
982.
The preparation by means of different synthetic paths of a series of bis-BINOL and bis-H8BINOL ligands is described. The ligands consist of two BINOL or H8BINOL fragments, joined by diverse linkages through the oxygen at the 2′-position of the arylic fragments. These ligands were applied to the Ti(OiPr)4 catalyzed asymmetric alkylation of benzaldehyde with Et2Zn. The performance of these catalysts is very sensitive to the nature of the ether linkage. The ligand with a propylene link shows better enantioselectivity (ca. 70%) than those with two or four carbon atoms joining the BINOL fragments. Furthermore, using the propylene link, but replacing (R)-BINOL by (R)-H8BINOL, a significant improvement in the stereoselectivity of the catalysts was achieved (ca. 80% ee in (R)-1-phenylpropan-1-ol). A cooperative effect was observed between the chirality at the BINOL fragment and that of a (S,S)-4,5-bis(methylene)-2,2-dimethyl-1,3-dioxolane link, derived from tartaric acid. When this chiral link combines with two (S)-BINOL fragments, the alkylation of benzaldehyde in toluene produces 70% ee of (S)-1-phenylpropan-1-ol, while the (R)-BINOL derivative ligand with the same link, in identical conditions, yields only 40% ee of the (R)-alcohol. 相似文献
983.
Barbara van Asch Raquel Pinheiro Rui Pereira Cíntia Alves Vânia Pereira Filipe Pereira Leonor Gusmão António Amorim 《Electrophoresis》2010,31(2):303-308
This study reports the methodology used to search, select and characterize STR loci on the canine X chromosome using publicly available genome resources and following the current guidelines for human and non‐human forensic testing. After several rounds of selection, 12 X‐STR markers were optimized for simultaneous co‐amplification in a single PCR, and genetic profiles were determined in a sample of 103 unrelated dogs. Mendelian inheritance was verified and mutation rates were assessed using family groups. Alleles that varied in size were sequenced to create a standardized nomenclature proposal based on the number of repeats. All loci conformed to Hardy–Weinberg expectations. The resulting panel showed high forensic efficiency, presenting high values of power of discrimination (in males and females) and mean exclusion chance, both in trios involving female offspring and in duos composed of dam and male offspring. Its use may complement the information obtained by autosomal STR analysis and contribute to the resolution of complex cases of kinship in dogs. The presented methodology for the de novo construction of an STR multiplex may also provide a helpful framework for analogous work in other animal species. As an increasing number of reference genomes become available, convenient tools for individual identification and parentage testing based on STR loci selected from autosomes or sex chromosomes' sequences may be created following this strategy. 相似文献
984.
Gomes I Di RE Pereira PM Pereira IA Saraiva LM Penadés S Franco R 《Langmuir : the ACS journal of surfaces and colloids》2006,22(24):9809-9811
A modified silver electrode was prepared by the self-assembly of a thiol-derivatized neoglycoconjugate, forming a 2D surface with maltose functionality. This self-assembled-monolayer-modified electrode was utilized for adsorption and spectroelectrochemical studies of tetraheme-containing type II cytochrome c3. The glycosylated surface allowed for the determination of the hemes' redox potentials and demonstrated enhanced spectroelectrochemical performance, in comparison to the widely used self-assembled monolayer of 11-mercapto-undecanoic acid. 相似文献
985.
Gulaboski R Mirćeski V Pereira CM Cordeiro MN Silva AF Quentel F L'Her M Lovrić M 《Langmuir : the ACS journal of surfaces and colloids》2006,22(7):3404-3412
The kinetics of the transfer of a series of hydrophilic monovalent anions across the water/nitrobenzene (W/NB) interface has been studied by means of thin organic film-modified electrodes in combination with electrochemical impedance spectroscopy and square-wave voltammetry. The studied ions are Cl-, Br-, I-, ClO4-, NO3-, SCN-, and CH3COO-. The electrode assembly comprises a graphite electrode (GE) covered with a thin NB film containing a neutral strongly hydrophobic redox probe (decamethylferrocene or lutetium bis(tetra-tert-butylphthalocyaninato)) and an organic supporting electrolyte. The modified electrode is immersed in an aqueous solution containing a supporting electrolyte and transferring ions, and used in a conventional three-electrode configuration. Upon oxidation of the redox probe, the overall electrochemical process proceeds as an electron-ion charge-transfer reaction coupling the electron transfer at the GE/NB interface and compensates ion transfer across the W/NB interface. The rate of the ion transfer across the W/NB interface is the limiting step in the kinetics of the overall coupled electron-ion transfer reaction. Moreover, the transferring ion that is initially present in the aqueous phase only at a concentration lower than the redox probe, controls the mass transfer regime in the overall reaction. A rate equation describing the kinetics of the ion transfer that is valid for the conditions at thin organic film-modified electrodes is derived. Kinetic data measured with two electrochemical techniques are in very good agreement. 相似文献
986.
We present an extensive analysis of cavity statistics in the interior of three different proteins, in liquid n-hexane, and in water performed using molecular-dynamics simulations. The heterogeneity of packing density over atomic length scales in different parts of proteins is evident in the wide range of values observed for the average cavity size, the probability of cavity formation, and the corresponding free energy of hard-sphere insertion. More interestingly, however, the distribution of cavity sizes observed at various points in the protein interior is surprisingly homogeneous in width. That width is significantly smaller than that measured for similar distributions in liquid n-hexane or water, indicating that protein interior is much less flexible than liquid hexane. The width of the cavity size distribution correlates well with the experimental isothermal compressibility data for liquids and proteins. An analysis of cavity statistics thus provides an efficient method to quantify local properties, such as packing, stiffness, or compressibility in heterogeneous condensed media. 相似文献
987.
Caimi G Perucchi A Degiorgi L Ott HR Pereira VM Neto AH Bianchi AD Fisk Z 《Physical review letters》2006,96(1):016403
Substituting Eu by Ca in ferromagnetic EuB6 leads to a percolation limited magnetic ordering. We present and discuss magneto-optical data of the Eu(1-x)Ca(x)B6 series, based on measurements of the reflectivity R(omega) from the far infrared up to the ultraviolet, as a function of temperature and magnetic field. Via the Kramers-Kronig transformation of R(omega) we extract the complete absorption spectra of samples with different values of x. The change of the spectral weight in the Drude component by increasing the magnetic field agrees with a scenario based on the double-exchange model, and suggests a crossover from a ferromagnetic metal to a ferromagnetic Anderson insulator upon increasing Ca content at low temperatures. 相似文献
988.
Martins MA Pereira CM Cunico W Moura S Rosa FA Peres RL Machado P Zanatta N Bonacorso HG 《Ultrasonics sonochemistry》2006,13(4):364-370
A convenient method for the preparation of 5-hydroxy-5-trihalo-4,5-dihydroisoxazoles and beta-enamino trihalomethyl ketones, from the reaction of 1,1,1-trihalo-4-alkoxy-3-alken-2-ones with hydroxylamine and anilines, respectively, using water as solvent and under ultrasound irradiation is reported. 相似文献
989.
Fluorochromic dyes derived from 9-aminoacridinium containing a vinylene function with electron withdrawing groups such as diethyl [(acridinium-9-ylamino)methylene]malonate (I), ethyl [(acridinium-9-ylamino)methylene]cyanoacetate (II), [(acridinium-9-ylamino)methylene]malononitrile (III), are prepared and studied in their monoprotonated form. Absorption spectra of the new dyes are red shifted compared to that of the precursor dye. The observed dual fluorescence and multiexponential decay are ascribed to normal emission from the acridinium chromophore in addition to excited-state intramolecular charge transfer (ESICT) process. However, biexponential decay character is observed only for the dicyano derivative (compound III), whereas for the two other systems, more complex kinetics and a three-component decay is recovered. The analysis of the fluorescence decays in different solvents for the first two compounds reveals two short-lived components in the range of 160-350 ps and 1.1-3.0 ns, related to formation and decay of the ESICT state, plus a third one with decay time of about 9 ns, which is ascribed to the normal emission from the acridinium chromophore as an enol tautomer or as an intramolecular H-bond conformer (closed form tautomer). For the dicyano derivative, in which the absence of carbonyl group precludes the H-bond interaction, the biexponential fitting reveals a slightly fast formation rate of the ESICT state with values on the order of 10(10) s(-1), whereas its decay time is between 0.6 and 3.2 ns, depending on the solvent used. 相似文献
990.
Recently there has been a lot of effort to model extremes of spatially dependent data. These efforts seem to be divided into
two distinct groups: the study of max-stable processes, together with the development of statistical models within this framework;
the use of more pragmatic, flexible models using Bayesian hierarchical models (BHM) and simulation based inference techniques.
Each modeling strategy has its strong and weak points. While max-stable models capture the local behavior of spatial extremes
correctly, hierarchical models based on the conditional independence assumption, lack the asymptotic arguments the max-stable
models enjoy. On the other hand, they are very flexible in allowing the introduction of physical plausibility into the model.
When the objective of the data analysis is to estimate return levels or kriging of extreme values in space, capturing the
correct dependence structure between the extremes is crucial and max-stable processes are better suited for these purposes.
However when the primary interest is to explain the sources of variation in extreme events Bayesian hierarchical modeling
is a very flexible tool due to the ease with which random effects are incorporated in the model. In this paper we model a
data set on Portuguese wildfires to show the flexibility of BHM in incorporating spatial dependencies acting at different
resolutions. 相似文献