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- ItemAldehydes and ketones influence reactivity and selectivity in nickel-catalysed Suzuki-Miyaura reactions(Cambridge : RSC, 2020) Cooper, Alasdair K.; Leonard, David K.; Bajo, Sonia; Burton, Paul M.; Nelson, David J.The energetically-favorable coordination of aldehydes and ketones-but not esters or amides-to Ni0 during Suzuki-Miyaura reactions can lead either to exquisite selectivity and enhanced reactivity, or to inhibition of the reaction. Aryl halides where the C-X bond is connected to the same π-system as an aldehyde or ketone undergo unexpectedly rapid oxidative addition to [Ni(COD)(dppf)] (1), and are selectively cross-coupled during competition reactions. When aldehydes and ketones are present in the form of exogenous additives, the cross-coupling reaction is inhibited to an extent that depends on the strength of the coordination of the pendant carbonyl group to Ni0. This work advances our understanding of how common functional groups interact with Ni0 catalysts and how these interactions affect workhorse catalytic reactions in academia and industry. This journal is © The Royal Society of Chemistry.
- ItemMechanical performance and corrosion behaviour of Zr-based bulk metallic glass produced by selective laser melting(Amsterdam : Elsevier B.V., 2020) Deng, L.; Gebert, A.; Zhang, L.; Chen, H.Y.; Gu, D.D.; Kühn, U.; Zimmermann, M.; Kosiba, K.; Pauly, S.Nearly fully dense, glassy Zr52.5Cu17.9Ni14.6Al10Ti5 bulk specimens were fabricated by selective laser melting (SLM) and their behaviour during compressive loading, during wear testing and in a corrosive medium was investigated. Their performance was compared with as-cast material of the same composition. The additively manufactured samples exhibit a yield strength around 1700 MPa combined with a plastic strain of about 0.5% after yielding despite the residual porosity of 1.3%, which is distributed uniformly in the samples. The propagation of shear bands in the bulk metallic glass prepared by SLM was studied. The specific wear rate and the worn surfaces demonstrated that similar wear mechanisms are active in the SLM and the as-cast samples. Hence, manufacturing the glass in layers does not adversely affect the wear properties. The same holds for the corrosion tests, which were carried out in 0.01 M Na2SO4 and 0.1 M NaCl electrolyte. The anodic polarization curves of SLM samples and as-cast samples revealed a similar corrosion behaviour. However, the SLM samples have a slightly reduced susceptibility to pitting corrosion and exhibit an improved surface healing ability, which might be attributed to an improved homogeneity of the additively manufactured glass.
- ItemKinetic Control over Self-Assembly of Semiconductor Nanoplatelets(Washington, DC : American Chemical Society, 2020) Momper, R.; Zhang, H.; Chen, S.; Halim, H.; Johannes, E.; Yordanov, S.; Braga, D.; Blülle, B.; Doblas, D.; Kraus, T.; Kraus, T.; Bonn, M.; Wang, H.I.; Riedinger, A.Semiconductor nanoplatelets exhibit spectrally pure, directional fluorescence. To make polarized light emission accessible and the charge transport effective, nanoplatelets have to be collectively oriented in the solid state. We discovered that the collective nanoplatelets orientation in monolayers can be controlled kinetically by exploiting the solvent evaporation rate in self-assembly at liquid interfaces. Our method avoids insulating additives such as surfactants, making it ideally suited for optoelectronics. The monolayer films with controlled nanoplatelets orientation (edge-up or face-down) exhibit long-range ordering of transition dipole moments and macroscopically polarized light emission. Furthermore, we unveil that the substantial in-plane electronic coupling between nanoplatelets enables charge transport through a single nanoplatelets monolayer, with an efficiency that strongly depends on the orientation of the nanoplatelets. The ability to kinetically control the assembly of nanoplatelets into ordered monolayers with tunable optical and electronic properties paves the way for new applications in optoelectronic devices.
- ItemEffects of natamycin and Lactobacillus buchneri on the fermentative process and aerobic stability of maize silage(Warszawa : Omnitech Press, 2020) Pinto, S.; Warth, J.F.G.; Novinski, C.O.; Schmidt, P.The present study was aimed to evaluate the reduction in fermentative losses and the improvement of aerobic stability of maize silage treated with Lactobacillus buchneri bacteria, antifungal natamycin and a combination of L. buchneri and natamycin. The study was completely randomized using four treatments with four replicates (silo) each. The treatments were as follows: C - control (forage without additives), NA - forage with low dose of natamycin (8 g/t) addition, LB - forage inoculated with low dose of L. buchneri (5 × 104 cfu/g) and NLB - forage treated with both natamycin (8 g/t) and L. buchneri (5 × 104 cfu/g). The losses of dry matter (DM) and gas, effluent production, chemical composition, yeast count and aerobic stability were calculated for all treatments. During fermentation, NLB produced more propionic and lactic acids and caused less DM and gas losses than other treatments (P < 0.01). The positive effect of NLB on yeast inhibition improved the aerobic stability of maize silage (P < 0.05). Thus, the combination of low doses of natamycin and heterolactic bacteria L. buchneri can reduce fermentative losses and improve the aerobic stability of maize silage after exposure to air. © 2020 Polish Academy of Science. All rights reserved.