The mechanism of boron-to-nickel transmetalation, the key step of the nickel-catalyzed Suzuki-Miyaura (SM) coupling, was examined both experimentally and theoretically. Dinuclear μ -hydroxo-bridged complexes formed by reaction of trans[ArNi(PR3)2X] with hydroxide are not directly involved in transmetalation, but they rather act as a resting state for the catalyst. The base/boronic acid ratio is the crucial parameter, as it modulates the extent of formation of these dinuclear species and thus tunes the catalytic activity. These findings explain some limitations encountered in practical applications of nickel-catalyzed S-M couplings and suggest how to tailor the experimental conditions in order to overcome these difficulties.
Pour plus d’information, consultez le communiqué de presse associé à cet article : Rationaliser une catalyse au nickel entre théorie et expérience !
References:
Taming Nickel-Catalyzed Suzuki-Miyaura Coupling: A Mechanistic Focus on Boron-to-Nickel Transmetalation
Pierre-Adrien Payard, Luca Alessandro Perego, Ilaria Ciofini, and Laurence Grimaud*
ACS Catal. 2018, 8, 4812−4823
DOI: 10.1021/acscatal.8b00933
Arnaud GAUTIER, Maître de Conférence au Pôle Chimie Biophysique du Département de Chimie de l’ENS, a été nominé « membre junior » à l’Institut Universitaire de France (IUF).
L’IUF a pour mission de favoriser le développement de la recherche de haut niveau dans les universités et de renforcer l’interdisciplinarité. Créé par le décret du 26 août 1991, sous la forme d’un service du ministère de l’Enseignement supérieur et de la Recherche, il vient de fêter ses 20 ans.
Les enseignants-chercheurs qui y sont nommés sont distingués pour l’excellence de leur activité scientifique, attestée par leur rayonnement international.
The synthesis and characterisation of a novel Reversibly Photoswitchable Chelator (RPC) of calcium ions, designed as a stepping stone towards producing pulses of calcium concentration in an aqueous environment, is reported. This RPC is constituted of a photochromic diarylethene core connected on one side to a BAPTA (1,2-bis(2-aminophenoxy)ethane-N,N,N’,N’-tetraacetic acid) calcium chelator and, on the other side, to an electron-withdrawing group. The operation principle consists in photoswitching on and off an intramolecular charge transfer between one nitrogen atom of the BAPTA moiety and the electron-withdrawing group, thereby modulating the chelating affinity of BAPTA for calcium ions. Solubility of the compound in a partially aqueous solvent was achieved by grafting a short PEG (polyethylene glycol) tail to the electron-withdrawing group. A reduction of the affinity for calcium ions upon photoswitching by a factor of 3–4, in the hundred nM range of dissociation constant, is reported and constitutes a proof of concept of this type of RPC.
References:
A photochromic calcium chelator is reported to reversibly reduce its affinity for calcium upon photoswitching in aqueous media.
Nadia Dozova,Guillaume Pousse, Bogdan Barnych, Jean-Maurice Mallet, Janine Cossy, Bernard Valeur, Pascal Plaza
J. Photochem., 2018, 360, 181
DOI:10.1016/j.jphotochem.2018.04.029
La Médaille Lavoisier, qui commémore l’œuvre d’Antoine-Laurent Lavoisier, est attribuée en reconnaissance de services éminents rendus aux sciences de la chimie.
Le 11 avril dernier, le Conseil d’administration a décidé à l’unanimité de décerner la Médaille Lavoisier au professeur Christian Amatore, directeur de recherche de classe exceptionnelle au CNRS (département de chimie de l’ENS), membre de l’Académie des sciences (où il est délégué à l’Éducation et à la Formation depuis 2011), pour l’ensemble de ses remarquables réalisations scientifiques, tout particulièrement pour ses travaux pionniers tant théoriques qu’expérimentaux en électrochimie moléculaire et analytique ayant conduit au développement des ultra-microélectrodes et de leurs applications.
Three rhodamine derivatives exhibiting electrofluorochromic properties were investigated by cyclic voltammetry and UVeVis/fluorescence spectroelectrochemistry. Rhodamine 101 (Rh101, compound 1) was used as a reference model. In compound 2, the carboxylate anion of Rh101 was replaced by an alkyne moiety to allow further functionalization. The compound 3 was prepared from 2 by conversion of the alkyne to a triazole group bearing an alkyl chain with an alcohol function. These three rhodamine derivatives exhibited similar electrochemical behaviors. Their mono-electronic reductions produced the corresponding radical species which were stable on the time-scale of cyclic voltammetry. Additional reduction of electrogenerated radicals produced unstable anions which underwent subsequent chemical reaction, most likely protonation. Based on cyclic voltammetry investigations, absorption and fluorescence spectroelectrochemistry were then performed on compounds 1, 2, 3 and their parent reduced radicals 1a, 2a, 3a. UVeVis spectroelectrochemistry, combined with TD-DFT calculation, confirmed the formation of radicals upon mono-electronic reduction of starting rhodamines. Fluorescence spectroelectrochemistry showed that, contrary to their parent molecules, electrogenerated radicals were non-fluorescent. Electrochemical fluorescence extinction was successfully achieved with all studied compounds. Moreover, compound 1 underwent on/off switching between fluorescent and nonfluorescent states repeatedly. Also, recovery of fluorescence in compound 3 was observed, which open interesting opportunities for the development of versatile rhodamine-based probes.
Pour plus d’information,consultez le communiqué de presse associé à cet article :
L’électrofluorochromisme : quand l’électrochimie rencontre la fluorescence !
References:
Electrochemical switching fluorescence emission in rhodamine derivatives
Martina Cízkova, Laurent Cattiaux, Jean-Maurice Mallet, Eric Labbé, Olivier Buriez
Electrochimica Acta 260 (2018) 589-597
doi : 10.1016/j.electacta.2017.12.104
Christian AMATORE have been elected as Corresponding Member of the Brazilian Academy of Sciences.
High-purity cardiomyocytes (CMs) derived from human induced pluripotent stem cells (hiPSCs) are promising for drug development and myocardial regeneration. However, most hiPSC-derived CMs morphologically and functionally resemble immature rather than adult CMs, which could hamper their application. Here, we obtained high-quality cardiac tissue-like constructs (CTLCs) by cultivating hiPSC-CMs on low-thickness aligned nanofibers made of biodegradable poly(D,L-lactic-co-glycolic acid) polymer. We show that multilayered and elongated CMs could be organized at high density along aligned nanofibers in a simple one-step seeding process, resulting in upregulated cardiac biomarkers and enhanced cardiac functions. When used for drug assessment, CTLCs were much more robust than the 2D conventional control.We also demonstrated the potential of CTLCs for modeling engraftments in vitro and treating myocardial infarction in vivo. Thus, we established a handy framework for cardiac tissue engineering, which holds high potential for pharmaceutical and clinical applications.
Pour plus d’information, consultez le communiqué de presse associé à cet article :
Réparer le cœur après un infarctus à l’aide de cellules souches !
References:
Human Pluripotent Stem Cell-Derived Cardiac Tissue-like Constructs for Repairing the Infarcted Myocardium
Junjun Li, Itsunari Minami, Motoko Shiozaki, Leqian Yu, Shin Yajima, Shigeru Miyagawa, Yuji Shiba, Nobuhiro Morone, Satsuki Fukushima, Momoko Yoshioka, Sisi Li, Jing Qiao, Xin Li, Lin Wang, Hidetoshi Kotera, Norio Nakatsuji, Yoshiki Sawa, Yong Chen, and Li Liu
Stem Cell Reports, 2017, 9, 1546–1559
DOI : 10.1016/j.stemcr.2017.09.007
We present speed out-of-phase imaging after optical modulation (OPIOM), which exploits reversible photoswitchable fluorophores as fluorescent labels and combines optimized periodic illumination with phase-sensitive detection to specifically retrieve the label signal. Speed OPIOM can extract the fluorescence emission from a targeted label in the presence of spectrally interfering fluorophores and autofluorescence. Up to four fluorescent proteins exhibiting a similar green fluorescence have been distinguished in cells either sequentially or in parallel. Speed OPIOM is compatible with imaging biological processes in real time in live cells. Finally speed OPIOM is not limited to microscopy but is relevant for remote imaging as well, in particular, under ambient light. Thus, speed OPIOM has proved to enable fast and quantitative live microscopic and remote-multiplexed fluorescence imaging of biological samples while filtering out noise, interfering fluorophores, as well as ambient light.
Pour plus d’information, consultez le communiqué de presse associé à cet article :
Au-delà des frontières de la bioimagerie !
References:
Resonant out-of-phase fluorescence microscopy and remote imaging overcome spectral limitations
Jérôme Quérard, Ruikang Zhang, Zsolt Kelemen, Marie-Aude Plamont, Xiaojiang Xie, Raja Chouket, Insa Roemgens, Yulia Korepina, Samantha Albright, Eliane Ipendey, Michel Volovitch, Hanna L. Sladitschek, Pierre Neveu, Lionel Gissot, Arnaud Gautier, Jean-Denis Faure, Vincent Croquette, Thomas Le Saux & Ludovic Jullien
Nature Communications 8, 969 (2017)
DOI: 10.1038/s41467-017-00847-3
Describing the dynamics of nuclei in molecules requires a potential energy surface, which is traditionally provided by the Born-Oppenheimer or adiabatic approximation. However, we also need to assign masses to the nuclei. There, the Born-Oppenheimer picture does not account for the inertia of the electrons, and only bare nuclear masses are considered. Nowadays, experimental accuracy challenges the theoretical predictions of rotational and vibrational spectra and requires the participation of electrons in the internal motion of the molecule. More than 80 years after the original work of Born and Oppenheimer, this issue has still not been solved, in general. Here, we present a theoretical and numerical framework to address this problem in a general and rigorous way. Starting from the exact factorization of the electron-nuclear wave function, we include electronic effects beyond the Born-Oppenheimer regime in a perturbative way via positiondependent corrections to the bare nuclear masses.
Consultez le communiqué associé à cet article : Corriger l’approximation de Born-Oppenheimer !
References:
On the Mass of Atoms in Molecules: Beyond the Born-Oppenheimer Approximation
Arne Scherrer, Federica Agostini, Daniel Sebastiani, E. K. U. Gross & Rodolphe Vuilleumier
PHYSICAL REVIEW X 25 août 2017
DOI: 10.1103/PhysRevX.7.031035
Anne BOUTIN a reçu, jeudi 31 août 2017, les insignes de Chevalier de la Légion d’Honneur par Gilberte CHAMBAUD, chimiste, Professeur émérite à l’Université Paris-Est Marne la Vallée.
Directrice du Département de Chimie de l’ENS, Anne BOUTIN est une spécialiste de la thermodynamique moléculaire. Elle développe et utilise des outils de simulation ainsi que des approches théoriques, pour étudier divers phénomènes touchant à la structure, la dynamique, la thermodynamique et la réactivité, de phases condensées, le plus souvent de fluides moléculaires confinés.
