Elementary Steps in Olefin Metathesis: Nickelacyclobutanes via Cycloaddition to Nickel Carbenes.

Olefin metathesis and cyclopropanation, major reactions in the synthetic toolbox, are predominantly catalyzed by platinum-group metals. First-row transition metal alternatives are desirable from the perspective of supply-chain sustainability. Although cyclopropanation by nickel catalysts is well established, limited evidence exists for the chemical feasibility of the cycloaddition step essential for inner-sphere cyclopropanation or olefin metathesis.

Hypershape Recognition: A General Framework for Moment-Based Molecular Similarity.

Due to the widespread use of molecular similarity assessments in drug design, numerous methods for the calculation of similarity scores of organic molecules have been developed. When applied to other types of molecules, such as inorganic and organometallic compounds, these methods face significant challenges. To overcome these challenges, we here introduce Hypershape Recognition (HSR), a versatile framework for moment-based similarity assessment of three-dimensional (3D) chemical representations annotated with atomic features.

Automated de Novo Design of Olefin Metathesis Catalysts: Computational and Experimental Analysis of a Simple Thermodynamic Design Criterion.

Methods for computational de novo design of inorganic molecules have paved the way for automated design of homogeneous catalysts. Such studies have so far relied on correlation-based prediction models as fitness functions (figures of merit), but the soundness of these approaches has yet to be tested by experimental verification of de novo-designed catalysts. Here, a previously developed criterion for the optimization of dative ligands L in ruthenium-based olefin metathesis catalysts RuCl(L)(L')(═CHAr), where Ar is an aryl group and L' is a phosphine ligand dissociating to activate the catalyst, was used in de novo design experiments.

BubbleDrive, a low-volume incubation chamber for acute brain slices.

Acute brain slices are a common and useful preparation in experimental neuroscience. A wide range of incubation chambers for brain slices exists but only a few are designed with very low volumes of the bath solution in mind. Such chambers are necessary when high-cost chemicals are to be added to the solution or when small amounts of substances released by the slice are to be collected for analysis.

Distinct effects of AMPAR subunit depletion on spatial memory.

Pharmacological studies established a role for AMPARs in the mammalian forebrain in spatial memory performance. Here we generated global GluA1/3 double knockout mice () and conditional knockouts lacking GluA1 and GluA3 AMPAR subunits specifically from principal cells across the forebrain (). In both models, loss of GluA1 and GluA3 resulted in reduced hippocampal GluA2 and increased levels of the NMDAR subunit GluN2A.

Increased membrane Ca permeability drives astrocytic Ca dynamics during neuronal stimulation at excitatory synapses.

Astrocytes are intricately involved in the activity of neural circuits; however, their basic physiology of interacting with nearby neurons is not well established. Using two-photon imaging of neurons and astrocytes during higher frequency stimulation of hippocampal CA3-CA1 Schaffer collateral (Scc) excitatory synapses, we could show that increasing levels of released glutamate accelerated local astrocytic Ca elevation. However, blockage of glutamate transporters did not abolish this astrocytic Ca response, suggesting that astrocytic Ca elevation is indirectly associated with an uptake of extracellular glutamate.

Mesomeric Acceleration Counters Slow Initiation of Ruthenium-CAAC Catalysts for Olefin Metathesis (CAAC = Cyclic (Alkyl)(Amino) Carbene).

Ruthenium catalysts bearing cyclic (alkyl)(amino)carbene (CAAC) ligands can attain very high productivities in olefin metathesis, owing to their resistance to unimolecular decomposition. Because the propagating methylidene species RuCl(CAAC)(=CH) is extremely susceptible to bimolecular decomposition, however, turnover numbers in the metathesis of terminal olefins are highly sensitive to catalyst concentration, and hence loadings. Understanding how, why, and how rapidly the CAAC complexes partition between the precatalyst and the active species is thus critical.

Enabling Molecular-Level Computational Description of Redox and Proton-Coupled Electron Transfer Reactions of Samarium Diiodide.

Samarium diiodide (SmI, Kagan's reagent) is a one-electron reductant with applications ranging from organic synthesis to nitrogen fixation. Highly inaccurate relative energies of redox and proton-coupled electron transfer (PCET) reactions of Kagan's reagent are predicted by pure and hybrid density functional approximations (DFAs) when only scalar relativistic effects are accounted for. Calculations including spin-orbit coupling (SOC) show that the SOC-induced differential stabilization of the Sm(III) versus the Sm(II) ground state is little affected by ligands and solvent, and a standard SOC correction derived from atomic energy levels is thus included in the reported relative energies.

Selective Hydrodeoxygenation of Lignin-Derived Phenols to Aromatics Catalyzed by NbO-Supported Iridium.

The dominating catalytic approach to aromatic hydrocarbons from renewables, deoxygenation of phenol-rich depolymerized lignin bio-oils, is hard to achieve: hydrodeoxygenation (HDO) of phenols typically leads to the loss of aromaticity and to non-negligible fractions of cyclohexanones and cyclohexanols. Here, we report a catalyst, niobia-supported iridium nanoparticles (Ir@NbO), which combines full conversion in the HDO of lignin-derived phenols with appreciable and tunable selectivity for aromatics (25-95%) under mild conditions (200-300 °C, 2.5-10 bar of H).

Impaired astrocytic Ca signaling in awake-behaving Alzheimer's disease transgenic mice.

Increased astrocytic Ca signaling has been shown in Alzheimer's disease mouse models, but to date no reports have characterized behaviorally induced astrocytic Ca signaling in such mice. Here, we employ an event-based algorithm to assess astrocytic Ca signals in the neocortex of awake-behaving tg-ArcSwe mice and non-transgenic wildtype littermates while monitoring pupil responses and behavior. We demonstrate an attenuated astrocytic Ca response to locomotion and an uncoupling of pupil responses and astrocytic Ca signaling in 15-month-old plaque-bearing mice.

The Janus face of high trans-effect carbenes in olefin metathesis: gateway to both productivity and decomposition.

Ruthenium-cyclic(alkyl)(amino)carbene (CAAC) catalysts, used at ppm levels, can enable dramatically higher productivities in olefin metathesis than their N-heterocyclic carbene (NHC) predecessors. A key reason is the reduced susceptibility of the metallacyclobutane (MCB) intermediate to decomposition β-H elimination. The factors responsible for promoting or inhibiting β-H elimination are explored density functional theory (DFT) calculations, in metathesis of ethylene or styrene (a representative 1-olefin) by Ru-CAAC and Ru-NHC catalysts.

NEIL1 and NEIL2 DNA glycosylases modulate anxiety and learning in a cooperative manner in mice.

Oxidative DNA damage in the brain has been implicated in neurodegeneration and cognitive decline. DNA glycosylases initiate base excision repair (BER), the main pathway for oxidative DNA base lesion repair. NEIL1 and NEIL3 DNA glycosylases affect cognition in mice, while the role of NEIL2 remains unclear.

Bimolecular Coupling in Olefin Metathesis: Correlating Structure and Decomposition for Leading and Emerging Ruthenium-Carbene Catalysts.

Bimolecular catalyst decomposition is a fundamental, long-standing challenge in olefin metathesis. Emerging ruthenium-cyclic(alkyl)(amino)carbene (CAAC) catalysts, which enable breakthrough advances in productivity and general robustness, are now known to be extraordinarily susceptible to this pathway. The details of the process, however, have hitherto been obscure.

Voltage-independent GluN2A-type NMDA receptor Ca signaling promotes audiogenic seizures, attentional and cognitive deficits in mice.

The NMDA receptor-mediated Ca signaling during simultaneous pre- and postsynaptic activity is critically involved in synaptic plasticity and thus has a key role in the nervous system. In GRIN2-variant patients alterations of this coincidence detection provoked complex clinical phenotypes, ranging from reduced muscle strength to epileptic seizures and intellectual disability. By using our gene-targeted mouse line (Grin2a), we show that voltage-independent glutamate-gated signaling of GluN2A-containing NMDA receptors is associated with NMDAR-dependent audiogenic seizures due to hyperexcitable midbrain circuits.

Challenging Metathesis Catalysts with Nucleophiles and Brønsted Base: Examining the Stability of State-of-the-Art Ruthenium Carbene Catalysts to Attack by Amines.

Critical to advancing the uptake of olefin metathesis in leading contexts, including pharmaceutical manufacturing, is identification of highly active catalysts that resist decomposition. Amines constitute an aggressive challenge to ruthenium metathesis catalysts. Examined here is the impact of 1,8-diazabicyclo[5.

Unsaturated and Benzannulated -Heterocyclic Carbene Complexes of Titanium and Hafnium: Impact on Catalysts Structure and Performance in Copolymerization of Cyclohexene Oxide with CO.

Tridentate, bis-phenolate -heterocyclic carbenes (NHCs) are among the ligands giving the most selective and active group 4-based catalysts for the copolymerization of cyclohexene oxide (CHO) with CO. In particular, ligands based on imidazolidin-2-ylidene (saturated NHC) moieties have given catalysts which exclusively form polycarbonate in moderate-to-high yields even under low CO pressure and at low copolymerization temperatures. Here, to evaluate the influence of the NHC moiety on the molecular structure of the catalyst and its performance in copolymerization, we extend this chemistry by synthesizing and characterizing titanium complexes bearing tridentate bis-phenolate imidazol-2-ylidene (unsaturated NHC) and benzimidazol-2-ylidene (benzannulated NHC) ligands.

Optic Atrophy 1 Controls Human Neuronal Development by Preventing Aberrant Nuclear DNA Methylation.

Optic atrophy 1 (OPA1), a GTPase at the inner mitochondrial membrane involved in regulating mitochondrial fusion, stability, and energy output, is known to be crucial for neural development: Opa1 heterozygous mice show abnormal brain development, and inactivating mutations in OPA1 are linked to human neurological disorders. Here, we used genetically modified human embryonic and patient-derived induced pluripotent stem cells and reveal that OPA1 haploinsufficiency leads to aberrant nuclear DNA methylation and significantly alters the transcriptional circuitry in neural progenitor cells (NPCs). For instance, expression of the forkhead box G1 transcription factor, which is needed for GABAergic neuronal development, is repressed in OPA1+/- NPCs.

Benefit of a hemilabile ligand in deoxygenation of fatty acids to 1-alkenes.

One of the most important tasks for chemistry in our time is to contribute to sustainable chemical production. A green industrial process for linear α-olefins, the arguably most important class of petrochemical intermediates, from renewable resources would be a major contribution to this end. Plant oils are attractive renewable feedstocks for this purpose because their triglycerides can be hydrolyzed to fatty acids that contain valuable long-chain hydrocarbons (C16-C22).

DENOPTIM: Software for Computational Design of Organic and Inorganic Molecules.

A general-purpose software package, termed DE Novo OPTimization of In/organic Molecules (DENOPTIM), for design and virtual screening of functional molecules is described. Molecules of any element and kind, including metastable species and transition states, are handled as chemical objects that go beyond valence-rules representations. Synthetic accessibility of the generated molecules is ensured via detailed control of the kinds of bonds that are allowed to form in the automated molecular building process.

Astroglial endfeet exhibit distinct Ca signals during hypoosmotic conditions.

Astrocytic endfeet cover the brain surface and form a sheath around the cerebral vasculature. An emerging concept is that endfeet control blood-brain water transport and drainage of interstitial fluid and waste along paravascular pathways. Little is known about the signaling mechanisms that regulate endfoot volume and hence the width of these drainage pathways.