1,720,999 research outputs found
Synthsis, coordination properties, and analytical applications of mixed-donor macrocycles containing the 1,10-phenanthroline sub-unit
No full textThe coordination properties towards different metal ions of a new class of mixed N/S-, and N/S/O-donor macrocycles
containing the 1,10-phenanthroline sub-unit in the cyclic framework are reviewed. The conformational constraints imposed by the
heteroaromatic fragment onto the aliphatic portion of the ring determine the coordination mode of these ligands which can
stabilise low-valent Ni+, Pd+, Pt+, and Rh+ metal complexes. Structural and thermodynamic aspects of the coordination chemistry
of these ligands are considered together with possible applications as building blocks in the synthesis of multi-centred systems,
and as template in the construction of extended polyiodide networks. However, solution studies demonstrate the inability of these
ligands to work as selective and specific fluorescent chemosensors for heavy transition and post-transition metal ions and the
formation constants evaluated for the formation of 1:1 complexes with Pb2+, Cd2+, Hg2+, Cu2+, and Ag+ in acetonitrile are of the
same order of magnitude. Nevertheless, some of these macrocyles are extremely effective to recognise Cu2+ or Ag+ over the other
metal ions in transport processes, and have been successfully used as neutral ionophore in the construction of PVC-based ionselective
electrodes and supported liquid membranes for analytical detection and separation, respectively, of these metal ions
A supported liquid membrane system for simultaneous separation of silver(I) and mercury(II) from dilute feed solutions
No full textAn innovative application of supported liquid membranes (SLMs) to the selective simultaneous separation of Ag+ and Hg2+ ions from a dilute
feed by employing a two-membrane–three-compartment cell is introduced. Two micro-porous PP supported membrane loaded with a mixed
N/O/S-donor macrocycle aza-thioether crown containing the 1,10-phenanthroline sub-unit (PhenS2O) and tetrathia-12-crown-4 (TT12C4) were
used for selective transport of silver and mercury ions, respectively. The PhenS2O-loaded membrane was placed between the first and the second
compartments, whereas the TT12C4-loaded membrane was placed between the second and the third compartments of the transport cell. The use of
this cell assembly, under optimized experimental conditions, made it possible to transport Ag+ and Hg2+ ions simultaneously from a 1.0×10−3M
picric acid feed solution containing these two species and several other interfering ions into the two corresponding strip compartments of the
transport cell. Sodium thiosulfate (0.04 M) and EDTA disodium salt (0.025 M) were used as stripping agents for Ag+ and Hg2+ ions, respectively
A new PVC-membrane based ion-selective electrode for perchlorate
No full textThe use of the recently synthesized pyridine-containing thia-aza macrocycle
2,8-dithia-5-aza-2,6-pyridinophane as an anion receptor in a PVC-membrane based ionselective
electrode was studied. The sensor showed selectivity towards perchlorate
anions with a linear working range of 2.1×10-7 to 1.3×10-1 M. The characteristic
response of the membrane-based perchlorate-selective electrode and the selectivity
coefficients towards common diverse ions using dibuthyl phthalate (DBP) as plasticizer
were also determined. The proposed electrode showed a near-Nernstian slope with
detection limit of 2.0×10-7 M (20 ppb) and was used successfully to determine the
perchlorate concentration in drinking water
An efficient and selective flourescent chemical sensor based on 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane as a new fluoroionophore for determination of iron(III) ions. A novel probe for iron speciation
No full textA novel fluorescent chemical sensor for the highly sensitive and selective determination of Fe3+ ions in
aqueous solutions is prepared. The iron sensing system was prepared by incorporating 5-(8-hydroxy-
2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L) as a neutral Fe3+-selective fluoroionophore
in the plasticized PVC membrane containing sodium tetraphenylborate as a liphophilic anionic additive.
The response of the sensor is based on the strong fluorescence quenching of L by Fe3+ ions. At pH 5.5,
the proposed sensor displays a calibration curve over a wide concentration range from 6.0×10−4 to
1.0×10−7 M, with a relatively fast response time of less than 2 min. In addition to a high stability and
reproducibility, the sensor shows a unique selectivity toward Fe3+ ion with respect to common coexisting
cations. The proposed fluorescence optode was applied to the determination of iron(III) content of straw
of rice, spinach and different water samples. The fluorescent sensor was also used as a novel probe for
Fe3+/Fe2+ speciation in aqueous solution
A selective optode membrane for silver ion based on fluorescence quenching of the dansylamidopropyl pendant arm derivative of 1-aza-4,7,10- trithiacyclododecane ([12]aneNS3)
No full textA highly sensitive and selective flourimetric optode membrane for the determination of trace amounts of Ag + ions was prepared. The plasticized PVC-membrane incorporating potassium tetrakis(p-chlorophenyl)borate and 1-(dansylamidopropyl)-1-aza-4,7,10-trithiacyclododecane (L), as a highly fluorescent chromoionophore, displays a calibration response for Ag + ions over a wide concentration range of 5.0 × 10 -7 to 1.7 × 10 -2 M. It has a response time of <40 s. In addition to its high stability, reproducibility and relatively long working lifetime, the optical sensor revealed good selectivity for silver ion over several common diverse ions
Proton NMR study of the stoichiometry, stability and thermodynamics of complexation of Ag+ ion with octathia-24-crown-8 in binary dimethylsulfoxide-nitrobenzene mixtures
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Development of a novel flow injection liquid-liquid microextraction method for on-line separation, preconcentration and fluorimeteric determination of zinc(II) using 5-(8-hydroxy-2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane as a sensitive and selective fluorescent chemosensor
No full textdetermination was developed for the determination of traces of the Zn2+ ion using 5-(8-hydroxy-
2-quinolinylmethyl)-2,8-dithia-5-aza-2,6-pyridinophane (L) as a sensitive and selective fluorimetric
sensor, with lambdaex = 373nmand lambdaem = 530 nm, and hexanol as the extracting organic solvent. In the designed
FIA system, the phase separation takes place via gravitation forces in the absence of any segmenter.
The influence of pH and ionic strength of the solution, amount of ligand, nature of counter ion, volume
of organic solvent, extraction time and coil length was investigated. Under optimized experimental
conditions, the calibration curve found to be liner over a concentration range of 0.025–4.53 micro gmL−1
(R2 = 0.9951) with a limit of detection of 2.3 ngmL−1. The enrichment factor was 45 and relative standard
deviation for 7 replicate determinations was 2.43%. The method is very fast and uses low levels of organic
solvents. The proposed method was applied successfully to the determination of zinc(II) in human hair,
human serum and two inorganic sludge samples
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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