Reductive Al-B σ-Bond Formation in Alumaboranes: Facile Scission of Polar Multiple Bonds.

We present facile access to an alumaborane species with electron precise Al-B σ-bond. The reductive rearrangement of 1-(AlI2 ), 8-(BMes2 ) naphthalene (Mes=2,4,6-Me3 C6 H2 ) affords the alumaborane species cyclo-(1,8-C10 H6 )-[1-Al(Mes)(OEt2 )-8-B(Mes)] with a covalent Al-B σ-bond. The Al-B σ-bond performs the reductive scission of multiple bonds: S=C(NiPrCMe)2 affords the naphthalene bridged motif B-S-Al(NHC), NHC=N-heterocyclic carbene, while O=CPh2 is deoxygenated to afford an B-O-Al bridged species with incorporation of the remaining ≡CPh2 fragment into the naphthalene scaffold. The reaction with isonitrile Xyl-N≡C (Xyl=2,6-Me2 C6 H4 ) proceeds via a proposed (amino boryl) carbene species; which adds a second equivalent of isonitrile to ultimately form the Al-N-B bridged species cyclo-(1,8-C10 H6 )-[1-Al(Mes)-N(Xyl)-8-B{C(Mes)=C-N-Xyl}] with complete scission of the C≡N triple bond. The latter reaction is supported with isolated intermediates and by DFT calculations.

Predictive Catalysis in Olefin Metathesis with Ru-based Catalysts with Annulated C60 Fullerenes in the N-heterocyclic Carbenes.

Predictive catalysis must be the tool that does not replace experiments, but acts as a selective agent, so that synthetic strategies of maximum profitability are used in the laboratory in a surgical way. Here, nanotechnology has been used in olefin metathesis from homogeneous Ru-NHC catalysts, specifically annulating a C60 fullerene to the NHC ligand. Based on results with the C60 in the backbone, a sterile change with respect to the catalysis of the metal center, an attempt has been made to bring C60 closer to the metal, by attaching it to one of the two C-N bonds of the imidazole group of the SIMes (1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) ligand (reference NHC ligand of the 2nd generation Grubbs catalysts) to increase the steric pressure of C60 in the first sphere of reactivity of the metal. The DFT calculated thermodynamics and the kinetics of SIMes-derived systems show that they are efficient catalysts for olefin metathesis.

Assessment of ventricular repolarization instability in terms of T-wave alternans induced by head-down bed-rest immobilization.

OBJECTIVE: To assess the effects of different durations of simulated microgravity exposure on ventricular repolarization (VR) in terms of T-wave alternans (TWA) as well as to test whether an increase in VR heterogeneity could be detected once normal gravity was restored. APPROACH: A total of 63 healthy volunteers were recruited in several head-down bed-rest (HDBR) experiments in the context of the European Space Agency bed-rest strategy. TWA is evaluated during the night period using ambulatory ECG recordings, before, during and after long- (60 d), mid- (21 d) and short- (5 d) duration HDBR by the long-term averaging technique. MAIN RESULTS: 5-21 d of exposure to simulated microgravity by means of the HDBR model do not lead to a significant increase of cardiac electrical instability in healthy myocardial substrates up to the point of eliciting TWA on the surface ECG. However, TWA indices increased after long-term HDBR exposure, once normal gravity was re-established, indicative of incipient electrical instability on VR at the conclusion of 60 d of HDBR. SIGNIFICANCE: The results of this work underline the importance of focusing future research on immediate effects after long-term microgravity exposure, both simulated by HDBR or from space mission scenarios, once partial gravity conditions are re-established. A deeper insight in the understanding of human body reactions in these scenarios results crucial in the design of future long-duration spaceflight missions, to mitigate any potential risk that can limit astronaut's performance.