921 research outputs found
Electrochemical catalytic cyclization reactions using environmentally friendly methodologies
The electrochemical intramolecular cyclisation of bromoalkoxylated derivatives 1 was carried out using Ni(II) complexes as the
catalysts in ethanol solutions by constant-current electrolysis in one-compartment cell in the absence of sacrificial anodes as an
environmentally friendly system. The reduction of the substrates proceeds via one-electron cleavage of the carbon–bromine bond to
form radical-type intermediates that undergo cyclisation to afford cyclic ethers in moderate to good yields.Fundação para a Ciência e a Tecnologia (FCT
Indirect electrochemical cyclisation of bromoalkoxylated derivatives using environmentally friendly methodologies
The electrochemical intramolecular cyclization of bromoalkoxylated derivatives 1 using Ni(II) complex as mediator of electron transfer was carried out in ethanol by constant-current electrolysis in one-compartment cell in the absence of sacrificial anodes as an environmentally friendly systems.
It is demonstrated that the electroreduction reaction of bromoalkoxylated derivatives was catalyzed by the electrogenerated Ni(I) complexes. Only cyclization to the five-membered-ring esters was obtained in moderate to good yields as the main products. Functionalyzed tetrahydrofurans are important intermediates in the synthesis of natural products such as lignans.
A mechanistic scheme is proposed to explain the results obtained by means of cyclic voltammetry and constant-current electrolysis.Fundação para a Ciência e a Tecnologia (FCT
Mid Campanian-Lower Maastrichtian magnetostratigraphy of the James Ross Basin, Antarctica: Chronostratigraphical implications
The James Ross Basin, in the northern Antarctic Peninsula, exposes which is probably the world thickest and most complete Late Cretaceous sedimentary succession of southern high latitudes. Despite its very good exposures and varied and abundant fossil fauna, precise chronological determination of its infill is still lacking. We report results from a magnetostratigraphic study on shelfal sedimentary rocks of the Marambio Group, southeastern James Ross Basin, Antarctica. The succession studied covers a ~1,200 m-thick stratigraphic interval within the Hamilton Point, Sanctuary Cliffs and Karlsen Cliffs Members of the Snow Hill Island Formation, the Haslum Crag Formation, and the lower López de Bertodano Formation. The basic chronological reference framework is given by ammonite assemblages, which indicate a Late Campanian – Early Maastrichtian age for the studied units. Magnetostratigraphic samples were obtained from five partial sections located on James Ross and Snow Hill islands, the results from which agree partially with this previous biostratigraphical framework. Seven geomagnetic polarity reversals are identified in this work, allowing to identify the Chron C32/C33 boundary in Ammonite Assemblage 8-1, confirming the Late Campanian age of the Hamilton Point Member. However, the identification of the Chron C32/C31 boundary in Ammonite Assemblage 8-2 assigns the base of the Sanctuary Cliffs Member to the early Maastrichtian, which differs from the Late Campanian age previously assigned by ammonite biostratigraphy. This magnetostratigraphy spans ~14 Ma of sedimentary succession and together with previous partial magnetostratigraphies on Early-Mid Campanian and Middle Maastrichtian to Danian columns permits a complete and continuous record of the Late Cretaceous distal deposits of the James Ross Basin. This provides the required chronological resolution to solve the intra-basin and global correlation problems of the Late Cretaceous in the Southern Hemisphere in general and in the Weddellian province in particular, given by endemism and diachronic extinctions on invertebrate fossils, including ammonites. The new chronostratigraphic scheme allowed us to calculate sediment accumulation rates for almost the entire Late Cretaceous infill of the distal James Ross Basin (the Marambio Group), showing a monotonous accumulation for more than 8 Myr during the upper Campanian and a dramatic increase during the early Maastrichtian, controlled by tectonic and/or eustatic causes.Fil: Milanese, Florencia Nidia. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Olivero, Eduardo Bernardo. Universidad Nacional de Tierra del Fuego; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro Austral de Investigaciones CientÃficas; ArgentinaFil: Raffi, MarÃa Eugenia. Universidad Nacional de Tierra del Fuego; Argentina. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro Austral de Investigaciones CientÃficas; ArgentinaFil: Franceschinis, Pablo Reinaldo. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Gallo, Leandro César. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Skinner, Steven M.. California State University; Estados UnidosFil: Mitchell, Ross N.. California Institute of Technology; Estados UnidosFil: Kirschvink, Joseph L.. California Institute of Technology; Estados Unidos. Tokyo Institute of Technology; JapónFil: Rapalini, Augusto Ernesto. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentin
Direct experimental observation of nonclassicality in ensembles of single photon emitters
In this work we experimentally demonstrate for the first time a recently
proposed criterion adressed to detect nonclassical behavior in the fluorescence
emission of ensembles of single-photon emitters. In particular, we apply the
method to study clusters of NV centres in diamond observed via
single-photon-sensitive confocal microscopy. Theoretical considerations on the
behavior of the parameter at any arbitrary order in presence of poissonian
noise are presented and, finally, the opportunity of detecting manifold
coincidences is discussed
All-carbon multi-electrode array for real-time in vitro measurements of oxidizable neurotransmitters
We report on the ion beam fabrication of all-carbon multi electrode arrays
(MEAs) based on 16 graphitic micro-channels embedded in single-crystal diamond
(SCD) substrates. The fabricated SCD-MEAs are systematically employed for the
in vitro simultaneous amperometric detection of the secretory activity from
populations of chromaffin cells, demonstrating a new sensing approach with
respect to standard techniques. The biochemical stability and biocompatibility
of the SCD-based device combined with the parallel recording of
multi-electrodes array allow: i) a significant time saving in data collection
during drug screening and/or pharmacological tests over a large number of
cells, ii) the possibility of comparing altered cell functionality among cell
populations, and iii) the repeatition of acquisition runs over many cycles with
a fully non-toxic and chemically robust bio-sensitive substrate.Comment: 24 pages, 5 figure
A modified technique of orthotopic transplant of the kidney in rabbits
In this study kidneys were harvested from bred-for-research cats weighing 4 to 5 kg. General principles of donor bilateral nephrectomy en bloc with aorta, vena cava, renal vessels, and ureters were followed. After the harvest the grafts were placed in lactated Ringer slush. A cuff was prepared on the renal vein over a 10 French plastic tube. The aorta was divided and left in connection with the renal artery at each side. Twenty female checkered Flemish giant rabbits weighing 4.0-6.0 kg served as recipients. After premedication with 40 mg/kg of ketamine, anesthesia was maintained with repeated doses (every 10-15 min) of a 0.1-mL mixture of 5 parts ketamine and 1 part acepromazine diluted 50% in a normal saline. Arterial pressure, CVP, blood gases, and temperature were monitored. Through a limited midline incision a native left nephrectomy was performed. The venous anastomosis was performed with a cuff technique without clamping the vena cava (which causes severe hemodynamic instability); the anastomotic time was 2-3 min. The arterial anastomosis was performed with an end-to-side aorta-to-aorta anastomosis; the anastomotic time was 5 to 7 min. There were no episodes of venous or arterial thrombosis. The donor procedure took approximately 40 min, and the backtable preparation of the graft an additional 45 to 60 min. Preparation of the recipient for the anastomosis took 15 min and the anastomotic time (warm ischemia) was 13 +/- 5 min. In this model suitable for xenograft research the duration of the surgery in the recipient has been greatly reduced because of (1) the previous backtable preparation of the graft, and (2) the cuff technique used for venous anastomosis. The present anesthesia regimen and careful hemodynamic monitoring were also important in the success of this model
Reactions radicalaires dans des milieux protiques et aprotiques : comparaisons entre les cyclisations reductives electrochimiques catalysees par des complexes du nickel
The electrochemical reductive cyclisation of unsaturated organic halides in the presence of Ni(II) complexes as catalysts was
examined in aprotic solvents such as DMF and in protic solvents such as ethanol, butanol or ethanolewater mixtures. The presence
of the alcohol media enhanced the rate of recycling of the catalytic species.La cyclisation réductive électrochimique d’halogénures insaturés en présence de complexes de Ni(II) comme catalyseurs a été examinée dans des solvants comme le DMF et dans des solvants protiques comme l’éthanol, le butanol ou des mélanges éthanol-eau. La présence du milieu alcoolique augmente la vitesse du recyclage des espèces catalytiques.Fundação para a Ciência e a Tecnologia (FCT
Single-photon-emitting optical centers in diamond fabricated upon Sn implantation
The fabrication of luminescent defects in single-crystal diamond upon Sn
implantation and annealing is reported. The relevant spectral features of the
optical centers (emission peaks at 593.5 nm, 620.3 nm, 630.7 nm and 646.7 nm)
are attributed to Sn-related defects through the correlation of their
photoluminescence (PL) intensity with the implantation fluence. Single
Sn-related defects were identified and characterized through the acquisition of
their second-order auto-correlation emission functions, by means of
Hanbury-Brown-Twiss interferometry. The investigation of their single-photon
emission regime as a function of excitation laser power revealed that
Sn-related defects are based on three-level systems with a 6 ns radiative decay
lifetime. In a fraction of the studied centers, the observation of a blinking
PL emission is indicative of the existence of a dark state. Furthermore,
absorption dependence from the polarization of the excitation radiation with
about 45 percent contrast was measured. This work shed light on the existence
of a new optical center associated with a group-IV impurity in diamond, with
similar photo-physical properties to the already well-known Si-V and Ge-V
emitters, thus providing results of interest from both the fundamental and
applicative points of view.Comment: 10 pages, 4 figure
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