Role of imine isomerization in the stereocontrol of the Staudinger reaction between ketenes and imines

Computational–experimental analysis has allowed determining that the stereochemistry of the Staudinger reaction between ketenes and imines is strongly associated with the nature of the imine, which affects the two steps of the reaction. The first step, namely the nucleophilic attack of the sp2-hybridized nitrogen atom of the imine on the sp-hybridized carbon atom of the ketene, is affected by the energetically accessible in situ isomerization patterns of the imine. The second step consists of a conrotatory electrocyclization of the zwitterionic intermediate formed in the previous step. This latter pericyclic step depends on the inward/outward torquoelectronic effects generated by the substituents of the imine. The impact of these factors on the stereochemistry of this reaction has been analyzed kinetically by numerical methods. The results of these simulations are compatible with the experimental results and support these conclusions

Size and branching effects on the fluorescence of benzylic dendrimers possessing one apigenin fluorophore at the core

Different generations of dendrimers incorporating one fluorescent core of apigenin and three Fréchet benzylic dendrons have been prepared. The chief geometric features of these dendrimers have been obtained by Molecular Dynamics simulations. These computational data suggest that the asphericities of dendrimers belonging to the third and fourth generations are considerably larger than those associated with lower radii of gyration. Fluorescence spectra of high generation dendrimers evolve along time and quantum yields show an appreciable lowering for the fourth generation dendrimer. All these data suggest aggregation phenomena and lower quantum yields for nonspheric dendrimers in solution.Financial support by the Spanish Ministry of Economy and Competitiveness, with the participation of European Union (MINECO, projects CTQ2010-16959/BQU, CTQ2012- 35535 and Consolider-Ingenio CSD2007-00006), from the University of the Basque Country (UPV/EHU, UFI11/22 QOSYC), from the Basque Government (GV/EJ, grant IT-324-07), from the Donostia International Physics Center (DIPC), from the Ministry of Education, Youth and Sports of the Czech Republic (grant MSM6046137305), and Czech Science Foundation (projects 304/10/1951, P503/11/0616) is acknowledged. M. d. B. thanks the CSIC for the JAE-Pre contract funding for her PhD. The authors also thank the SGI/IZO-SGIker UPV/EHU and the DIPC for generous allocation of computational resources.Peer reviewe

Resonance driven regioselective demethylation of berberine. Microwave assisted synthesis of berberrubine and its assessment as fluorescent chemosensor for alkanes

11 figures, 1 table.-- Supplementary information available.Berberrubine has been synthesized by microwave assisted selective demethylation of berberine. The high selectivity observed in this reaction has been explained and justified by means of computational calculations using Density Functional Theory (DFT) and Natural Resonance Theory (NRT). The existence of two resonant structures of berberrubine is the driving force of regioselective demethylation. Berberrubine is a chemosensor of alkanes, and may have practical applications in petrochemical analysis as a ‘mass’ detector because fluorescent response of saturated hydrocarbons does not depend on hydrocarbon chain length. Berberrubine operates via dipole-induced dipole interactions. Likewise, it has two fluorescent forms in acidic and basic media, which correspond to a keto-enol tautomerism. The fluorescent signal for berberrubine and the amplification of berberrubine-alkane signals by heating can be rationalized from the predominance of enol form when berberrubine is adsorbed onto silica gel.This work was supported by the Spanish MINECO, UE-FEDER (projects CTQ2012-35535, CTQ 2012-34774, and CTQ 2008-06751-C02-01/BQU) and the Gobierno Vasco/Eusko Jaurlaritza (Grant IT673-13). A.D-C. and O. L. thanks MICINN for a grant.Peer reviewe

Monocolor chemosensors for Ba2+ tagging experiments

Resumen del póster presentado a la XXXVIII Reunión Bienal de la Real Sociedad Española de Química, celebrada en el Palacio de Congresos de Granada, del 27 de junio al 30 de junio de 2022.The BOLD experiment is focused on the observation of the neutrinoless double β decay of 136Xe to 136Ba2+ through the detection of the daughter cation. For this purpose, different molecular sensors can be developed. These chemosensors can be classified into monocolor (offon) or bicolor (on-on’), depending on the shifts (Δλ) and changes in the intensity (ΔI) observed in their emission spectra. In this context, different off-on radiometric chemosensors have been synthesized in order to understand their photophysics upon interaction with Ba2+ ions in vacuo and in solution. These sensors incorporate two components: a fluorophore and a metal-binding group. The fluorophores are kept as simple as possible, using structures with well-known photophysical properties. On the other hand, N-aza-crown ether derivatives have been used as metal-binding groups. Finally, the effects of disconnecting the abovementioned elements by splitting of components Ar1 and Ar2 (Figure 1: Description of the off-on chemosensors synthesized in this work), will be discussed.Financial support from the Basque Government (IT-1346-19 and IT-1180-19), the Spanish MICINN (PID2019-104772-GB-I00, PID2019-111281-GB-I00, RED2018-102387-T, and RED2018-102471-T), and by the European Commission (ERC-2020-SyG-951281) is gratefully acknowledged.Peer reviewe

New generation of fluorescent bicolour sensors for barium tagging experiments

Resumen del póster presentado a la XXXVIII Reunión Bienal de la Real Sociedad Española de Química, celebrada en el Palacio de Congresos de Granada, del 27 de junio al 30 de junio de 2022.One of the most important questions in particle physics and cosmology consists of demonstrating that the neutrino is a Majorana fermion. Observation of the neutrinoless double β decay of 136Xe to generate the daughter cation 136Ba2+ is the most promising practical way to demonstrate this hypothesis. Within this context, our research group has designed and synthesized the first generation of fluorescent bicolour sensors (FBI-G1), whose emission spectra change upon binding to Ba2+ ions by formation of supramolecular complexes in dry media involving solid-gas interphases. In this presentation, the synthesis of a second generation (G2) of bicolour sensors is reported. These sensors have two essential components, a metal-binding group, and a fluorophore. The latest structure is based on a benzo[a]imidazo[2,1,5-cd]indolizine derivative (Figure 1: Description of generation 1 (left) and generation 2 (right) chemosensors). Finally, preliminary research involving the linkage of our sensors to surfaces such as indium tin oxide glass (ITO), will be discussed.Financial support from the Basque Government (IT-1346-19 and IT-1180-19), the Spanish MICINN (PID2019-104772-GB-I00, PID2019-111281-GB-I00, RED2018-102387-T, and RED2018-102471-T), and by the European Commission (ERC-2020-SyG-951281) is gratefully acknowledged.Peer reviewe

Iridium-based sensor for cations

Resumen del póster presentado a la XXXVIII Reunión Bienal de la Real Sociedad Española de Química, celebrada en el Palacio de Congresos de Granada, del 27 de junio al 30 de junio de 2022.Traditionally, techniques such as inductively coupled plasma mass spectroscopy or gas chromatography have been used for cation detection. However, these methods need long analysis times and sophisticated instrumentation. Simpler and faster methods have been developed these days, such us optical methods (colorimetric and/or fluorescent), which can entail easy visualization, high sensitivity and cheaper instrumentation. Among these, ratiometric (bicolour) fluorescent sensors stand out due to the lower limit of detection. In this area, both organic molecules and metal complexes are being developed as luminescent probes. Indeed, some iridium complexes demonstrated to be selective luminescent sensors for different cations. Different strategies are used to trap or interact with the cation, which permits a rational tuning of the iridium’s emission. In our group, we have been working with iridium complexes for a variety of objectives. In this contribution, an iridium-based sensor for cations will be described including its response to cations in solution and on solid supports.Financial support from the Basque Government (PRE_2020_2_0230, IT-1346-19 and IT-1180-19), the Spanish MICINN (PID2019-104772-GB-I00, PID2019-111281-GB-I00, RED2018-102387-T, and RED2018-102471-T), and by the European Commission (ERC-2020-SyG-951281) is gratefully acknowledged.Peer reviewe

Boosting background suppression in the NEXT experiment through Richardson-Lucy deconvolution

Next-generation neutrinoless double beta decay experiments aim for half-life sensitivities of similar to 10(27) 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 Tl-208 1.6 MeV double escape peak (with Compton events as background), recorded in the NEXT-White demonstrator at the Laboratorio Subterraneo 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 similar to 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.The NEXT Collaboration acknowledges support from the following agencies and institutions: the European Research Council (ERC) under the Advanced Grant 339787-NEXT; the European Union's Framework Programme for Research and Innovation Horizon 2020 (2014-2020) under the Grant Agreements No. 674896, 690575 and 740055; the Ministerio de Economia y Competitividad and the Ministerio de Ciencia, Innovacion y Universidades of Spain under grants FIS2014-53371-C04, RTI2018-095979, the Severo Ochoa Program grants SEV-2014-0398 and CEX2018-000867-S, and the Maria de Maeztu Program MDM-2016-0692; the Generalitat Valenciana under grants PROMETEO/2016/120 and SEJI/2017/011; the Portuguese FCT under project PTDC/FIS-NUC/2525/2014 and under projects UID/04559/2020 to fund the activities of LIBPhys-UC; the U.S. Department of Energy under contracts No. DE-AC02-06CH11357 (Argonne National Laboratory), DE-AC02-07CH11359 (Fermi National Accelerator Laboratory), DE-FG02-13ER42020 (Texas A&M) and DE-SC0019223/DE-SC0019054 (University of Texas at Arlington); the University of Texas at Arlington (U.S.A.); and the Pazy Foundation (Israel) under grants 877040 and 877041. DGD acknowledges Ramon y Cajal program (Spain) under contract number RYC-2015-18820. JM-A acknowledges support from Fundacion Bancaria "la Caixa" (ID 100010434), grant code LCF/BQ/PI19/11690012. AS acknowledges support from the Kreitman School of Advanced Graduate Studies at Ben-Gurion University. Documen

Ba+2 ion trapping using organic submonolayer for ultra-low background neutrinoless double beta detector

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.This material is based upon work supported by the following agencies and institutions: the European Research Council (ERC) under ERC-2020-SyG 951281; the MCIN/AEI/10.13039/501100011033 of Spain and ERDF A way of making Europe under grants PID2020-114252GB-I00, PID2019-107338RB-C63, PID2019-104772GB-I00, PID2019-111281GB-I00, and RTI2018-095979, the Severo Ochoa Program grant CEX2018-000867-S; the Basque Government (GV/EJ) under grants IT-1553-22, IT-1591-22. The NEXT Collaboration acknowledges support from the following agencies and institutions: the European Union’s Framework Programme for Research and Innovation Horizon 2020 (2014-2020) under Grant Agreement No. 957202-HIDDEN; the MCIN/AEI of Spain and ERDF A way of making Europe under grants RTI2018-095979 and PID2021-125475NB, the Severo Ochoa Program grant CEX2018-000867-S and the Ramón y Cajal program grant RYC-2015-18820; the Generalitat Valenciana of Spain under grants PROMETEO/2021/087 and CIDEGENT/2019/049; the Department of Education of the Basque Government of Spain under the predoctoral training program non-doctoral research personnel; the Portuguese FCT under project UID/FIS/04559/2020 to fund the activities of LIBPhys-UC; the Pazy Foundation (Israel) under grants 877040 and 877041; the US Department of Energy under contracts number DE-AC02-06CH11357 (Argonne National Laboratory), DE-AC02-07CH11359 (Fermi National Accelerator Laboratory), DE-FG02-13ER42020 (Texas A&M), DE-SC0019054 (Texas Arlington) and DE-SC0019223 (Texas Arlington); the US National Science Foundation under award number NSF CHE 2004111; the Robert A Welch Foundation under award number Y-2031-20200401. Finally, we are grateful to the Laboratorio Subterráneo de Canfranc for hosting and supporting the NEXT experiment.Peer reviewe