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821.
Leonardo Rossi Cristián Huck-Iriart María Ana Castro 《Journal of Coordination Chemistry》2017,70(21):3633-3649
The reaction of dirhodium tetrakis(3,4,5-trialkoxy)benzoates Rh2(B3OCn)4 (n = 10, 14, and 18) with three different dinitrogenated axial ligands (Lax), namely tetrazine (tz), phenazine (phz), and 4,4′-bipyridine (bpy), gave rise to three homologous series of mesogenic coordination polymers, [Rh2(B3OCn)4]Lax. All of them exhibited thermotropic columnar mesophases that were of the hexagonal type for tz and phz and rectangular for bpy. The lighter n = 10 homologs of the three series are liquid crystals (LC) at room temperature. Their mesomorphic properties have been compared with those of the previously studied Lax = pyrazine series. Models for the supramolecular organization of the three polymeric series in their Col LC phases are proposed on the basis of their structural parameters, as measured by XRD and SAXS. The differences are interpreted in terms of different coordination features of the axial ligands. 相似文献
822.
Jesus Jeronimo Castro 《Discrete and Computational Geometry》2007,37(3):409-417
Let
be a family of convex figures in the plane. We say that
has property T if there exists a line intersecting every member of
. Also, the family
has property T(k) if every k-membered subfamily of
has property T. Let B be the unit disc centered at the origin. In this paper we prove that if a finite family
of translates of B has property T(4) then the family
, where
, has property T. We also give some results concerning families of translates of the unit disc which has either property T(3)
or property T(5). 相似文献
823.
Lílian Aguiar-Ricz Roberto Oliveira Dantas Hilton Ricz Ingrid Gielow Rui C.M. Mamede Gleici Castro Perdon 《Journal of voice》2007,21(2):248-256
BACKGROUND: After total laryngectomy, the interruption of the upper digestive tube and the section of the cricopharyngeal segment alter the high-pressure zone of the pharyngoesophageal transition, which will not only start to have a digestive function, but also be stimulated to take on the production of voice and speech. The pressure observed in the cricopharyngeal segment seems to act as a critical factor for the development of esophageal sound production, and manometry is the procedure capable of quantifying the pressure observed in this region. OBJECTIVE: The objective of the current study was to assess the upper esophageal sphincter pressure in laryngectomized patients who are either successful or unsuccessful esophageal speakers, both at rest and during esophageal phonation, using manometry. METHODS: Twenty laryngectomized persons aged 32 to 83 years (mean, 44.2 years) were submitted to evaluation by a speech pathologist and divided into two groups, ie, successful esophageal speakers (N=12) and unsuccessful esophageal speakers (N=8), according to a scale validated by Wepman et al (1953). The upper esophageal sphincter (UES) pressure was assessed by manometry both at rest and during the following voice emissions in Portuguese: the vowel "a," the monosyllable "pa," and the sentence "papai papou pipoca." The amplitude, the duration of the pressure wave, and the area under the curve were measured. RESULTS: At rest, the mean UES pressure was 11.83 mm Hg for successful esophageal speakers and 9.92 mm Hg for unsuccessful esophageal speakers, with no significant difference between groups; the mean for the two groups as a whole was 11.06 mm Hg. During the voice and speech sequence tests, no significant difference was observed when the emissions in Portuguese of "a," "pa," and the sentence were analyzed separately. CONCLUSION: As the pressure observed at rest did not differ between the successful esophageal speakers and the unsuccessful esophageal speakers, and the amplitude, the duration of the pressure wave, and the area under the amplitude x duration curve were also equal for both groups, we conclude that the cricopharyngeal segment pressure is not a preponderant factor for the acquisition of esophageal voice and speech. 相似文献
824.
Lysosomes of trypanosomatid protozoa are poorly known. In this work we have cytochemically detected the lysosomal enzyme aryl sulphatase in the trypanosomatids Trypanosoma cruzi and Crithidia fasciculata, by using p-nitrocatecholsulphate as substrate. Positive reaction was located exclusively inside membrane-bound cytoplasmic vesicles distributed throughout the cell body. Electron-dense reaction was either dispersed homogeneously through the vesicular matrix or located at the vesicle periphery, apposed to the membrane, with fine granular deposits occasionally found at the vesicular matrix. Trypomastigote and epimastigote forms of T. cruzi lacked electron-dense deposits at the plasma membrane, thus indicating that aryl sulphatase was not secreted to the environment. Furthermore, no positive reaction was detected in epimastigote reservosomes, which are organelles considered as pre-lysosomal compartments. Thus, our data show that reservosomes and lysosomes are organelles that can be distinguished by the cytochemical localization of aryl sulphatase in T. cruzi epimastigotes and trypomastigotes. Positive reaction in cytoplasmic vesicles of C. fasciculata choanomastigotes confirmed the specificity of the reaction for lysosomes in other trypanosomatid species. 相似文献
825.
Castro M Garcia R Warrender SJ Slawin AM Wright PA Cox PA Fecant A Mellot-Draznieks C Bats N 《Chemical communications (Cambridge, England)》2007,(33):3470-3472
A 'co-templating' strategy supported by molecular modelling has been used to prepare, for the first time, silicoaluminophosphates with the SAV and KFI framework topologies, each of which has a three-dimensionally connected pore system with high specific volume. 相似文献
826.
Sancho MI Jubert AH Blanco SE Ferretti FH Castro EA 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,68(2):387-393
The influence of temperature and solvent effects on the stability of the complex formed by two molecules of 1,2-dihydroxybenzene and one molecule of AlCl3 were experimentally and theoretically studied, by means of UV spectroscopic methods and Density Functional Theory methods. The changes of the stability constant with the temperature were analyzed using the van't Hoff equation, while the variations with the permittivity of the reaction medium were explained with an equation proposed by us. The experimental and theoretical data obtained allowed proving that the increase in the hydrogen-bond donor ability of the solvents favors a higher thermodynamic stability of the reactants with respect to the complex and, therefore a decrease in the corresponding stability constant. The non-planar structure proposed for the 2:1 ligand-metal complex is coherent with the small batochromic shift experimentally observed. In the complex molecule, the planes containing the phenyl rings are tilted by approximately 89 degrees with each other. It was concluded that the complexation reaction is an endothermic process in which the solvent-solute interactions play an essential role. 相似文献
827.
Neves P Leite A Rangel M de Castro B Gameiro P 《Analytical and bioanalytical chemistry》2007,387(4):1543-1552
Partition coefficients of moxifloxacin in liposomes of dimyristoyl-L-α-phosphatidylcholine or dimyristoyl-L-α-phosphatidylglycerol and water were determined by spectrophotometry and fluorimetry. The K
p values obtained were larger than those reported for most of the other fluoroquinolones, a consequence of the structural changes
observed in the molecule of moxifloxacin, which in turn change its acid/base properties. Introduction of a methoxy group at
position 8 and a diazabicyclonyl ring at position 7 in the basic fluoroquinolone structure alters the charge distribution
at the physiological pH of 7.4, and these changes seem to be responsible for its improved antibacterial potency and broader
spectrum of activity. Location studies have also been performed using fluorescence and electron paramagnetic resonance (EPR)
spectroscopies. The results show that moxifloxacin must be located near the phospholipid headgroups, similar to other fluoroquinolones,
but contributions from a hydrophobic component were also detected. These results suggest that the enhanced activity of this
drug may be related to a more facilitated entrance into the bacterial cell, perhaps including a mediator step involving electrostatic
interaction with a hydrophobic component; this step then controls the extent or orientation of insertion and improves the
electrostatic interaction. 相似文献
828.
Pérez-Serradilla JA Luque de Castro MD 《Analytical and bioanalytical chemistry》2007,389(5):1541-1547
Sorbent material packed in a PTFE laboratory-made flow cell located in the specimen holder of an energy-dispersive X-ray fluorescence
(EDXRF) detector has been used for in situ solid-phase extraction (SPE) preconcentration–detection of metals. The flow cell
was connected to a single-channel flow-injection (FI) manifold (for full automation of the steps and proper development of
the method) by two PTFE tubes of 0.5-mm inner diameter introduced into the spectrometer specimen holder by a small orifice
without distortion or modification of the instrument. The optical window open in the PTFE flow cell was adjusted to the X-ray
irradiation zone of the spectrometer and fixed to it. The approach was tested by using both Pb and Cd aqueous solutions and
a Dowex 50 cation-exchange resin as a sorbent, and flushing the sample through the flow cell for EDXRF measurements after
removal of the sample matrix. The limits of detection and the limits of quantification (LOQs) thus obtained were 0.15 and
0.5 μg for Pb and 0.3 and 0.8 μg for Cd, respectively, values that allow the approach to be used for the analysis of drinking
water by injecting a 100-mL sample into the FI manifold, taking into account the EC drinking water directives. The linear
dynamic ranges are between the LOQ and 600 μg for both analytes. The method was validated by the standard addition method
using tap-water samples. In addition, the integrated SPE–EDXRF approach enables the study of the variables influencing the
sorption step–namely the effects of the volume of sample flushed through the column, concentrations of the analytes in the
sample, breakthrough volume of the resin, elution profiles, sample pH and retention and elution flow rates–in an automatic,
cheap, fast and precise way. 相似文献
829.
Ultrasound in analytical chemistry 总被引:1,自引:0,他引:1
Ultrasound is a type of energy which can help analytical chemists in almost all their laboratory tasks, from cleaning to detection.
A generic view of the different steps which can be assisted by ultrasound is given here. These steps include preliminary operations
usually not considered in most analytical methods (e.g. cleaning, degassing, and atomization), sample preparation being the
main area of application. In sample preparation ultrasound is used to assist solid-sample treatment (e.g. digestion, leaching,
slurry formation) and liquid-sample preparation (e.g. liquid–liquid extraction, emulsification, homogenization) or to promote
heterogeneous sample treatment (e.g. filtration, aggregation, dissolution of solids, crystallization, precipitation, defoaming,
degassing). Detection techniques based on use of ultrasonic radiation, the principles on which they are based, responses,
and the quantities measured are also discussed. 相似文献
830.
Eduardo A Castro 《Chemistry Central journal》2007,1(1):1-5