Herein, we report a nickel–1,2-bis(dicyclohexylphosphino)ethane (dcype) complex for the catalytic Buchwald–Hartwig amination of aryl thioethers. The protocol shows broad applicability with a ...variety of different functional groups tolerated under the catalytic conditions. Extensive organometallic and kinetic studies support a nickel(0)–nickel(II) pathway for this transformation and revealed the oxidative addition complex as the resting state of the catalytic cycle. All the isolated intermediates have proven to be catalytically and kinetically competent catalysts for this transformation. The fleeting transmetalation intermediate has been successfully synthesized through an alternative synthetic organometallic pathway at lower temperature, allowing for in situ NMR study of the C–N bond reductive elimination step. This study addresses key factors governing the mechanism of the nickel-catalyzed Buchwald–Hartwig amination process, thus improving the understanding of this important class of reactions.
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IJS, KILJ, NUK, PNG, UL, UM
We introduce a photoresist based on methacrylate copolymers bearing photochromic spirothiopyran moieties as side groups that can crosslink via supramolecular interaction between the chromophores. ...Upon two-photon excitation, the resist is capable of generating freestanding three-dimensional structures and offers an inhibition channel, which allows for stimulated-emission depletion-inspired laser lithography. Reversible inhibition, linewidth narrowing, and resolution enhancement are demonstrated.
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IJS, KILJ, NUK, PNG, UL, UM
Animal research indicates that a combination of physical activity and sensory enrichment has the largest and the only sustaining effect on adult neuroplasticity. Dancing has been suggested as a human ...homologue to this combined intervention as it poses demands on both physical and cognitive functions. For the present exploratory study, we designed an especially challenging dance program in which our elderly participants constantly had to learn novel and increasingly difficult choreographies. This six-month-long program was compared to conventional fitness training matched for intensity. An extensive pre/post-assessment was performed on the 38 participants (63-80 y), covering general cognition, attention, memory, postural and cardio-respiratory performance, neurotrophic factors and-most crucially-structural MRI using an exploratory analysis. For analysis of MRI data, a new method of voxel-based morphometry (VBM) designed specifically for pairwise longitudinal group comparisons was employed. Both interventions increased physical fitness to the same extent. Pronounced differences were seen in the effects on brain volumes: Dancing compared to conventional fitness activity led to larger volume increases in more brain areas, including the cingulate cortex, insula, corpus callosum and sensorimotor cortex. Only dancing was associated with an increase in plasma BDNF levels. Regarding cognition, both groups improved in attention and spatial memory, but no significant group differences emerged. The latter finding may indicate that cognitive benefits may develop later and after structural brain changes have taken place. The present results recommend our challenging dance program as an effective measure to counteract detrimental effects of aging on the brain.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In general, it is well recognized that both acute physical exercises and regular physical training influence brain plasticity and cognitive functions positively. However, growing evidence shows that ...the same physical exercises induce very heterogeneous outcomes across individuals. In an attempt to better understand this interindividual heterogeneity in response to acute and regular physical exercising, most research, so far, has focused on non-modifiable factors such as sex and different genotypes, while relatively little attention has been paid to exercise prescription as a modifiable factor. With an adapted exercise prescription, dosage can be made comparable across individuals, a procedure that is necessary to better understand the dose–response relationship in exercise–cognition research. This improved understanding of dose–response relationships could help to design more efficient physical training approaches against, for instance, cognitive decline.
Functional group metathesis is an emerging field in organic chemistry with promising synthetic applications. However, no complete mechanistic studies of these reactions have been reported to date, ...particularly regarding the nature of the key functional group transfer mechanism. Unraveling the mechanism of these transformations would not only allow for their further improvement but would also lead to the design of novel reactions. Herein, we describe our detailed mechanistic studies of the nickel-catalyzed functional group metathesis reaction between aryl methyl sulfides and aryl nitriles, combining experimental and computational results. These studies did not support a mechanism proceeding through reversible migratory insertion of the nitrile into a Ni–Ar bond and provided strong support for an alternative mechanism involving a key transmetalation step between two independently generated oxidative addition complexes. Extensive kinetic analysis, including rate law determination and Eyring analysis, indicated the oxidative addition complex of aryl nitrile as the resting state of the catalytic reaction. Depending on the concentration of aryl methyl sulfide, either the reductive elimination of aryl nitrile or the oxidative addition into the C(sp2)–S bond of aryl methyl sulfide is the turnover-limiting step of the reaction. NMR studies, including an unusual 31P–2H HMBC experiment using deuterium-labeled complexes, unambiguously demonstrated that the sulfide and cyanide groups exchange during the transmetalation step, rather than the two aryl moieties. In addition, Eyring and Hammett analyses of the transmetalation between two Ni(II) complexes revealed that this central step proceeds via an associative mechanism. Organometallic studies involving the synthesis, isolation, and characterization of all putative intermediates and possible deactivation complexes have further shed light on the reaction mechanism, including the identification of a key deactivation pathway, which has led to an improved catalytic protocol.
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The past 20 years have seen an extensive implementation of nickel in homogeneous catalysis through the development of unique reactivity not easily achievable by using noble transition metals. Many ...catalytic cycles propose Ni(I) complexes as potential reactive intermediates, yet the scarcity of nickel(I) precursors and the lack of a general, non-ligand-specific protocol for their synthesis have hampered progress in this field of research. This has in turn also limited the access to novel, well-defined Ni(I) species for the development of new catalytic reactions. Herein, we report a simple, general route to access a wide variety of Ni(I)–phenolate complexes via an unusual example of an olefinic Ni(I) complex, Ni(COD)(OPh*) (COD = 1,5-cyclooctadiene, OPh* = O( t Bu)3C6H2). This route has proven to be highly efficient for several coordination numbers and ligand classes enabling access to the following complexes: Ni(IPr)(OPh*) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), Ni(dcype)(OPh*) (dcype = 1,2-bis(dicyclohexylphosphino)ethane), Ni(dppe)(OPh*) (dppe = 1,2-bis(diphenylphosphino)ethane), and Ni(terpy)(OPh*) (terpy = 2,2′:6′,2″-terpyridine). Moreover, reacting Ni(dcype)(OPh*) with trimethylsilyl triflate has led to the isolation of a unique example of a cationic binuclear Ni(I)–arene complex. All these complexes have been characterized by single-crystal X-ray, DFT, and EPR analyses, thus providing crucial experimental and theoretical information about their coordination environment and confirming a d9 electronic structure for all complexes involved. Overall, this new synthetic approach offers exciting opportunities for the discovery of new stoichiometric and catalytic reactivity as well as the mechanistic elucidation of Ni-based catalytic cycles.
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In order to contribute to the appropriate tissues during development, cells need to know their position within the embryo. This positional information is conveyed by gradients of signaling molecules, ...termed morphogens, that are produced in specific regions of the embryo and induce concentration-dependent responses in target tissues. Positional information is remarkably robust, and embryos often develop with the correct proportions even if large parts of the embryo are removed. In this Review, we discuss classical embryological experiments and modern quantitative analyses that have led to mechanistic insights into how morphogen gradients adapt, scale and properly pattern differently sized domains. We analyze these experimental findings in the context of mathematical models and synthesize general principles that apply to multiple systems across species and developmental stages.
3D printing is a powerful emerging technology for the tailored fabrication of advanced functional materials. This Review summarizes the state‐of‐the art with regard to 3D laser micro‐ and ...nanoprinting and explores the chemical challenges limiting its full exploitation: from the development of advanced functional materials for applications in cell biology and electronics to the chemical barriers that need to be overcome to enable fast writing velocities with resolution below the diffraction limit. We further explore chemical means to enable direct laser writing of multiple materials in one resist by highly wavelength selective (λ‐orthogonal) photochemical processes. Finally, chemical processes to construct adaptive 3D written structures that are able to respond to external stimuli, such as light, heat, pH value, or specific molecules, are highlighted, and advanced concepts for degradable scaffolds are explored.
It's all in print: Recent progress in micro‐ and nanoprinting by 3D laser lithography is highlighted and the critical chemical challenges identified. These include the design of functional photoresists for the generation of multifunctional nanostructures as well as the ability to write disparate material properties from one resist with different colors of light and the ability to conduct subdiffraction 3D lithography.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Phosphine-stabilized monovalent nickel complexes play an important role in catalysis, either as catalytically active species or as decomposition products. Most routes to access these complexes are ...highly ligand specific or rely on strong reducing agents. Our group recently disclosed a path to access nickel(I)–phenolate complexes from bis(1,5-cyclooctadiene)nickel(0) (Ni(cod)2). Herein, we demonstrate this protocol’s broad applicability by ligating a wide range of mono- and bidentate phosphine ligands. We further show the versatility of the phenolate fragment as a precursor to nickel(I)–alkyl or aryl species, which are relevant to Ni catalysis or synthetically useful nickel(I)–chloride and hydride complexes. We also demonstrate that the chloride complex can be synthesized in a one-pot procedure starting from Ni(cod)2 in good yield, making this protocol a valuable alternative to current procedures. Single-crystal X-ray diffraction, IR, and EPR (or NMR) spectroscopy were employed to characterize all of the synthesized nickel complexes.
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IJS, KILJ, NUK, PNG, UL, UM
In this study, we investigated the cost-effectiveness of four alternatives: Liquified Natural Gas (LNG), methanol, green hydrogen, and green ammonia, for the case of top 20 most frequently calling ...ships to Irish ports in 2019, through the Net Present Value (NPV) methodology, incorporating the benefits incurred through saved external, carbon tax and conventional fuel costs. LNG had the highest NPV (€6,166 million), followed by methanol (€1,705 million) and green hydrogen (€319 million). Green ammonia utilisation (as a hydrogen carrier) looks inviable due to higher operational costs, resulting from its excessive consumption (i.e., losses) during the cracking and purifying processes and its lower net calorific value. Green hydrogen remains the best option to meet future decarbonisation targets, although, a further reduction in its current fuel price (by 60%) or a significant increment in the proposed carbon tax rate (by 275%) will be required to improve its cost-competitiveness over LNG and methanol.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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