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991.
Juan M. González Alejandro J. Müller Miguel F. Torres A. Eduardo Sáez 《Rheologica Acta》2005,44(4):396-405
The rheological behavior of hydrophobically modified hydroxyethyl cellulose (HMHEC) and xanthan gum solutions has been characterized in simple shear flow, opposed-jets flow, and flow through porous media. Both polymers exhibit shear thinning in simple shear flow and apparent shear thinning in flow through porous media. Analysis of the results shows there is a direct correspondence between shear viscosities determined in simple shear experiments and apparent viscosities in porous media flow at relatively low shear rates. At high shear rates the extensional component of the flow in porous media appreciably increases the apparent viscosity over the simple shear values. This increase is shown to correlate with results obtained in opposed-jets experiments, and is attributed to formation of transient entanglements. 相似文献
992.
Alejandro C. Olivieri 《Solid state nuclear magnetic resonance》1998,11(3-4):181-187
It is shown how to calculate random errors in chemical shift tensor components and in the Euler angles which fix the orientation of the σ tensor in the molecular frame, as obtained from spinning sideband analysis of MAS NMR spectra of powdered solids, when heteronuclear dipolar coupling interactions occur in a two spin system. The procedure was applied to experimental data corresponding to the chemical shift tensor of a carbon-13 bonded to a phosphorus-31 nucleus. Clues are given concerning the experimental variables to be set in order to obtain the desired accuracy in the orientation angles. 相似文献
993.
Alejandro G. HernánVincent Guillot Alexander KuvshinovJeremy D. Kilburn 《Tetrahedron letters》2003,44(47):8601-8603
Polymer-supported dibutyltin chloride and dimethyltin chloride resins were synthesised and used in Maleczka's catalytic Stille reaction. 相似文献
994.
995.
Quintana M Montellano A del Rio Castillo AE Van Tendeloo G Bittencourt C Prato M 《Chemical communications (Cambridge, England)》2011,47(33):9330-9332
Graphene sheets have been functionalized with a PAMAM dendron, finding that graphene can be efficiently functionalized all over the surface, or only at the edges, depending on the reactions used in the functionalization process. 相似文献
996.
Castro L Dommergue A Renard A Ferrari C Ramirez-Solis A Maron L 《Physical chemistry chemical physics : PCCP》2011,13(37):16772-16779
The determination of the solvation shell of Hg(II)-containing molecules and especially the interaction between Hg(II) and water molecules is the first requirement to understand the transmembrane passage of Hg into the cell. We report a systematic DFT study by stepwise solvation of HgCl(2) including up to 24 water molecules. In order to include pH and salinity effects, the solvation patterns of HgClOH, Hg(OH)(2) and HgCl(3)(-) were also studied using 24 water molecules. In all cases the hydrogen bond network is crucial to allow orbital-driven interactions between Hg(II) and the water molecules. DFT Born-Oppenheimer molecular dynamics simulations starting from the stable HgCl(2)-(H(2)O)(24) structure revealed that an HgCl(2)-(H(2)O)(3) trigonal bipyramid effective solute appears and then the remaining 21 water molecules build a complete first solvation shell, in the form of a water-clathrate. In the HgCl(2), HgClOH, Hg(OH)(2)-(H(2)O)(24) optimized structures Hg also directly interacts with 3 water molecules from an orbital point of view (three Hg-O donor-acceptor type bonds). All the other interactions are through hydrogen bonding. The cluster-derived solvation energies of HgCl(2), HgClOH and Hg(OH)(2) are estimated to be -34.4, -40.1 and -47.2 kcal mol(-1), respectively. 相似文献
997.
Roukala J Maldonado AF Vaara J Aucar GA Lantto P 《Physical chemistry chemical physics : PCCP》2011,13(47):21016-21025
The leading-order perturbation theory approach to relativistic effects on the nuclear magnetic shielding provides an economic method for obtaining the chemical shifts in heavy-element containing systems. The method features detailed analysis potential in terms of the different physical mechanisms affecting the shielding tensors of heavy nuclei. The perturbative nature, however, results in an increasing error with increasingly heavy elements in the system. In this work, we investigate the performance of the Breit-Pauli perturbation theory (BPPT) against fully relativistic four-component theory in computing the nuclear shielding constants as well as the chemical shifts with respect to corresponding atomic ions of group-12 metals, M = Zn, Cd, and Hg, in dimethyl M(CH(3))(2) and aqueous M(H(2)O)(6)(2+) complexes. It is shown that five out of the total of sixteen BPPT correction terms are responsible for most of the relativistic corrections for the chemical shift of studied metals. The relativity is important already for Cd and BPPT is proven to work well up to Hg for the chemical shift, as calibrated with the fully relativistic method. 相似文献
998.
999.
García Velázquez D González Orive A Hernández Creus A Luque R Gutiérrez Ravelo A 《Organic & biomolecular chemistry》2011,9(19):6524-6527
Novel C(3)-symmetrical heteroaromatic hexaazatrinaphthylene (HATNA) gelators symmetrically end-substituted with pendant aromatic and aliphatic amines were synthesized. Some of these π-conjugated structures induce self-assembly, forming fibers able to gelate solvents of different polarity at low wt% as demonstrated by spectroscopic and microscopic techniques. 相似文献
1000.
Jacobo-Salcedo Mdel R Alonso-Castro AJ Salazar-Olivo LA Carranza-Alvarez C González-Espíndola LA Domínguez F Maciel-Torres SP García-Lujan C González-Martínez Mdel R Gómez-Sánchez M Estrada-Castillón E Zapata-Bustos R Medellin-Milán P García-Carrancá A 《Natural product communications》2011,6(12):1925-1928
The antimicrobial effects of the Mexican medicinal plants Guazuma ulmifolia, Justicia spicigera, Opuntia joconostle, O. leucotricha, Parkinsonia aculeata, Phoradendron longifolium, P. serotinum, Psittacanthus calyculatus, Tecoma stans and Teucrium cubense were tested against several human multi-drug resistant pathogens, including three Gram (+) and five Gram (-) bacterial species and three fungal species using the disk-diffusion assay. The cytotoxicity of plant extracts on human cancer cell lines and human normal non-cancerous cells was also evaluated using the MTT assay. Phoradendron longifolium, Teucrium cubense, Opuntia joconostle, Tecoma stans and Guazuma ulmifolia showed potent antimicrobial effects against at least one multidrug-resistant microorganism (inhibition zone > 15 mm). Only Justicia spicigera and Phoradendron serotinum extracts exerted active cytotoxic effects on human breast cancer cells (IC50 < or = 30 microg/mL). The results showed that Guazuma ulmifolia produced potent antimicrobial effects against Candida albicans and Acinetobacter lwoffii, whereas Justicia spicigera and Phoradendron serotinum exerted the highest toxic effects on MCF-7 and HeLa, respectively, which are human cancer cell lines. These three plant species may be important sources of antimicrobial and cytotoxic agents. 相似文献