3,132 research outputs found
Hydrogen Atom Transfer (HAT): A Versatile Strategy for Substrate Activation in Photocatalyzed Organic Synthesis
No full textThe adoption of hydrogen atom transfer (HAT) in a photocatalytic approach, in which an excited catalyst is responsible for substrate activation, offers unique opportunities in organic synthesis, enabling the straightforward activation of R–H (R = C, Si, S) bonds in desired reagents. Either a direct strategy, based on the intrinsic reactivity of a limited number of photocatalysts in the excited state, or an indirect one, in which a photocatalytic cycle is used for the generation of a thermal hydrogen abstractor, can be exploited. This microreview summarizes the most recent advances (mainly from the last two years) in this rapidly developing area of research, collecting the selected examples according to the nature of the species promoting the HAT process. From the synthetic point of view, this area has led to the development of a plethora of strategies for C–C, C–Si, C–N, C–S, and C–halogen (particularly, fluorine) bond formation, as well as for oxidation reactions
Alkoxy radicals generation: facile photocatalytic reduction of N-alkoxyazinium or azolium salts
No full textThe generation of alkoxy radicals from N-alkoxyazinium or azolium salts, occurring via the facile mono-electronic photocatalytic reduction of the starting compounds, has been recently reported. The photogenerated radicals can be in turn exploited for synthetic applications. These include the possibility to promote inter- or intramolecular hydrogen atom transfer processes to generate P- or C-centered radicals, and the direct addition onto unsaturated derivatives for the construction of C–O bonds
Decatungstate as Direct Hydrogen Atom Transfer Photocatalyst for SOMOphilic Alkynylation
No full textA versatile approach for the alkynylation of a variety of aliphatic hydrogen donors, including alkanes, is reported. We used tetrabutylammonium decatungstate as photocatalyst to generate organoradicals from C–H/Si–H bonds via hydrogen atom transfer. The latter intermediates underwent SOMOphilic alkynylation by methanesulfonyl alkynes to afford internal alkynes upon loss of a sulfonyl radical. The effect of different radicofugal groups on the reaction outcome was evaluated and rationalized via a combined experimental and computational approach
Morphology-based measurement of activation time in human atrial fibrillation
No full textThe measurement of the activation time is crucial to allow the correct automatic analysis and classification of intracardiac electrograms recorded in the human atria during atrial fibrillation (AF). This study proposes a method which accounts for the morphology of bipolar signals. After ventricular artifact removal and activation wave recognition, the fiducial point of the activation wave was set at its local barycentre (LB). The method was tested on a set of 30 AF bipolar recordings of increasing complexity class; its performance was compared with that of the traditional methods of maximum peak (MP) or maximum slope (MS) estimation, taking the manual measurements performed by an expert cardiologist as a reference. While for signals with low complexity the agreement with manual analysis was high for all automatic methods, in presence of disorganized AF characterized by complex morphology LB estimation resulted more reliable than MP or MS calculation
Quantitative assessment of regularity and synchronization of intracardiac recordings during human atrial fibrillation
No full textThis study proposes the morphology-based evaluation of the regularity (R) and the synchronization (S) of intraatrial electrograms acquired during atrial fibrillation (AF). R is defined as the degree of repetitiveness over time of the shapes of the activation waves detected in single atrial recordings. S accounts for the simultaneous presence of morphologically similar activation waves in two atrial electrograms, and for the dispersion of the propagation delays between the two sites. Both R and S resulted unitary for normal sinus rhythm and decreased significantly moving from atrial flutter (R=0.93, S=0.88) to AF of increasing complexity class (type I AF: R=0.75, S=0.66; type II AF: R=0.32, S=0.27; type III AF: R=0.19, S=0.01). During paroxysmal AF, the proposed indexes allowed to locate atrial regions with high degree of organization and other areas with more complex patterns of electrical activation
Flow field inside a leading edge cooling channel with turbulence promoters in rotating conditions
No full textThe present work deepens the analysis of the flow field inside a triangular equilateral channel with turbulence promoters,
perpendicular to the radial direction, on both leading and trailing sides, under rotation and both isothermal and
nonisothermal conditions (i.e. with centrifugal buoyancy forces). Simulations have been performed at constant
Re1⁄410,000, Ro1⁄40–0.2–0.6, and Bo1⁄40–0.08–0.7, the latter corresponding to 80C temperature difference between
fluid and walls. These conditions match those of the particle image velocimetry measurements, used for comparison
against predictions. After proper validation, the numerical modeling helped with the assessment of the flow field evolution
along the radial extension of the cooling channel. It has been possible to determine the path of the coolant
throughout the channel and localize where the heat transfer would have been enhanced/decreased by secondary flow
structures, with respect to the stationary case. Furthermore, a rather Bo-independency of the flow field in this kind of
geometry has been confirmed. The analysis presented in this paper finds support from the thermal data available from the
open literature, which is rich of thermal analysis indeed, but lacks a detailed description of internal flow fields
An assessment of the impact of possible CAP reform scenarios on Romanian agriculture
No full textUsing a simplified model, with key-variable the prices of two different possible scenarios of CAP reform after 2013 (moderate and radical), this paper present a comparison between the price effects of implementation of each reform scenario at 2015 horizon on Romanian agriculture. This short analysis shows that, under the presented hypotheses, the net welfare effect, due to the price changes, for the selected products, is positive in both reform scenarios, yet greater in the case of the radical reform. Integrated in the large context of Romanian development, it seems that the influence of CAP reform upon agriculture and rural areas will be most likely a gradual one: an interpenetration between the two scenarios is foreseeable, starting with the moderate reform that will dominate the period around 2013, the reform measures acquiring a more radical character afterwards.CAP reform, Romania, welfare effects, Agricultural and Food Policy,
Vinylpyridines as Building Blocks for the Photocatalyzed Synthesis of Alkylpyridines
No full textThis is the final peer-reviewed manuscript accepted for publication in Chemistry - A European Journal
Citation of the published version is: Chem. Eur. J. 2017, 23, 6527-653
A tan for molecules: photocatalyzed synthesis with direct sunlight
No full textPhotocatalytic processes applied to organic synthesis have known an impressive development over the last decade. The reactions
are now routinely carried out upon irradiation with artificial light sources. However, several research groups have profited
of direct sunlight to trigger such processes, in turn boosting the sustainability character of the devised synthetic protocols.
This contribution gathers recent examples in the area, showcasing the possibility to fully exploit the different wavelength
ranges of solar light, with particular regards to both ultraviolet and visible regions. On the other hand, near-infrared light, the
main component of solar light, has not been exploited so far, albeit a handful of examples exploiting artificial near-infrared
irradiation have been recently reported and development in this direction is expected soon
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