Ther oom temperature radical cycloetherification/arylation cascade of allenols andd iazonium salts hasb een accomplished via ac ombination of gold and photoredox catalysis to provide 2,3,4-trisubstituted-2,5-dihydrofurans.T he functionalized oxacycle formation sequence is chemo-andr egioselective for the cycloetherification and for the position that bears the aryl moiety after the cross-coupling. Mechanistici nvestigationsr evealed that this transforma-tion proceeds through an initial oxidation of gold(I) to ap henyl gold(III) complex, which,u pon coordination to the allene,c atalyzes its cyclization and leads to the coupling product after ar eductive elimination regenerating Au(I).Scheme 5. Gold-photoredox-cocatalyzed reaction of allenols 5a-e with aryldiazonium salts 2.C ontrolled synthesis of oxaspirooxindoles 6aa-6ee.Scheme6.Gold-photoredox-cocatalyzed reaction of allenols 7 with aryldiazonium salts 2.C ontrolled synthesis of oxaspiro-b-lactams 8.Scheme9.Alternative mechanistice xplanation for the goldphotoredox-cocatalyzed preparation of oxacycles 3, 6, 8,a nd 10 from allenols 1, 5, 7,and 9 and diazonium salts 2.Scheme 10. Oxidationo ft he original Au(I) complex by addition of aP hr adical and single electron transfer from Ru(bipy) 3 . [3] Theb arrier for the reductive eliminationoni ntermediate VI is low (2.2 kcal mol À1 )a nd explains the presence of the aryl-phospine couplingproduct amongt he reaction products.
Next-generation neutrinoless double beta decay experiments aim for half-life sensitivities of ∼ 1027 yr, requiring suppressing backgrounds to < 1 count/tonne/yr. For this, any extra background rejection handle, beyond excellent energy resolution and the use of extremely radiopure materials, is of utmost importance. The NEXT experiment exploits differences in the spatial ionization patterns of double beta decay and single-electron events to discriminate signal from background. While the former display two Bragg peak dense ionization regions at the opposite ends of the track, the latter typically have only one such feature. Thus, comparing the energies at the track extremes provides an additional rejection tool. The unique combination of the topology-based background discrimination and excellent energy resolution (1% FWHM at the Q-value of the decay) is the distinguishing feature of NEXT. Previous studies demonstrated a topological background rejection factor of ∼ 5 when reconstructing electron-positron pairs in the 208Tl 1.6 MeV double escape peak (with Compton events as background), recorded in the NEXT-White demonstrator at the Laboratorio Subterráneo de Canfranc, with 72% signal efficiency. This was recently improved through the use of a deep convolutional neural network to yield a background rejection factor of ∼ 10 with 65% signal efficiency. Here, we present a new reconstruction method, based on the Richardson-Lucy deconvolution algorithm, which allows reversing the blurring induced by electron diffusion and electroluminescence light production in the NEXT TPC. The new method yields highly refined 3D images of reconstructed events, and, as a result, significantly improves the topological background discrimination. When applied to real-data 1.6 MeV e−e+ pairs, it leads to a background rejection factor of 27 at 57% signal efficiency.
If neutrinos are their own antiparticles the otherwise-forbidden nuclear reaction known as neutrinoless double beta decay can occur. The very long lifetime expected for these exceptional events makes its detection a daunting task. In order to conduct an almost background-free experiment, the NEXT collaboration is investigating novel synthetic molecular sensors that may capture the Ba dication produced in the decay of certain Xe isotopes in a high-pressure gas experiment. The use of such molecular detectors immobilized on surfaces must be explored in the ultra-dry environment of a xenon gas chamber. Here, using a combination of highly sensitive surface science techniques in ultra-high vacuum, we demonstrate the possibility of employing the so-called Fluorescent Bicolor Indicator as the molecular component of the sensor. We unravel the ion capture process for these molecular indicators immobilized on a surface and explain the origin of the emission fluorescence shift associated to the ion trapping.
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