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Cyclization of Citronellal to Isopulegol Catalyzed by Temperature-Stable Aluminum Complexes with Tripodal Tris(silanolate) Ligands
No full text(−)-Isopulegol is a key intermediate in the industrial routes to (−)-menthol. New aluminum catalysts are now presented for the diastereoselective transformation of citronellal to isopulegol, which carry tridentate tris(silanolate) ligands connected by a central arene ring. Such ligands are readily available on a multigram scale; the derived complexes can be regarded as soluble molecular proxies for Lewis-acidic aluminum sites on a silica surface with the additional advantage of being tunable. Thus, proper choice of the substituents on the silicon linkers allows an appropriate binding site to be crafted in order to confer high chemo- and diastereoselectivity onto the carbonyl-ene type cyclization reaction without compromising reactivity. Moreover, the chelate structure together with a certain rigidity of the ligand backbone imparts excellent stability onto the complexes even at 100 °C under reaction conditions; this makes the separation of product and catalyst by distillation possible as illustrated by a cycling experiment in which no loss of activity or selectivity was noticed over five runs. This thermal and chemical robustness, in combination with a stable performance, distinguishes the new complexes from the standard catalysts described in the literature carrying monodentate phenolate or silanolate ligands
Fetal dehydroepiandrosterone from hair samples at birth predicts language development
Get PDFObjectiveSex hormones testosterone and estradiol have been related to children’s language development. Expanding the focus on dehydroepiandrosterone (DHEA), which has not yet been considered as a biological marker of language ability, may provide novel insights, as emerging evidence suggests that fetal DHEA plays a critical role in the organization of the neonatal brain, potentially shaping later language development. The present study investigated whether fetal DHEA, compared to fetal testosterone, is associated with infant language development.Design and methodsDHEA and testosterone concentrations were measured in newborn hair strands (n = 63) collected two weeks after birth, capturing fetal long-term hormone secretions during the third trimester of pregnancy. At six months of age, children's language abilities were assessed using the German version of the Bayley Scales of Infant Development.ResultsMultiple linear regression analysis revealed fetal DHEA levels to be significantly associated with language abilities at six months of age in boys only, with lower DHEA levels corresponding to higher language scores. Control analyses assessing general cognitive abilities showed no association of fetal DHEA levels with infant cognitive function. Testosterone levels were not associated with language.ConclusionsThe current study identifies fetal DHEA levels extracted from newborn hair samples as a potential biological factor influencing infant language development in boys
Mechanochemically Synthesized Transition Metal Carbide Fillers for Coating Metallic Bipolar Plates in Proton Exchange Membrane Fuel Cells
No full textMetal bipolar plates, especially stainless steel 316 L bipolar plates, are of commercial interest due to their mechanical stability and low manufacturing cost, but they require a protective coating on their surface to improve their electrical conductivity as well as their corrosion performance. Herein, transition metal carbides (TiC, Cr3C2, NbC, VC, Mo2C, and TaC) are synthesized by a mechanochemical synthesis route, incorporated as electrically conductive fillers into a polyurethane-based binder matrix, and are applied to stainless steel plates by the wet paint technique. For comparison, a commercially available graphite, the standard filler for coated metal bipolar plates, and a commercially available Cr3C2 are used as fillers in coatings. All protective films show good adhesion to the metal substrate and a homogeneous filler-binder distribution. Contact resistance measurements indicate that, among all the coatings, those with mechanochemically synthesized Cr3C2 and Mo2C have the best conductivity performance, well below 10 mOhm cm2. From potentiodynamic and potentiostatic polarization tests, the Cr3C2- containing coating has superior corrosion behavior, while the Mo2C coating is unable to protect the metal from corrosion. Based on these results, Cr3C2-coated stainless steel is an attractive candidate for bipolar plates in proton exchange membrane fuel cells
Calcium homeostasis role in preserving sperm function and metabolic activity during liquid storage of pig semen
No full textFrom age two, children use pronouns to predict who will speak next in conversation
Get PDFChildren’s exposure to language is shaped by interactional needs in conversation. Prior research has largely focused on how such language influences word learning and long-term lexical knowledge. However, the effects of interactional language are likely to go far beyond word learning. Earlier studies showed that in conversation, from around age 2;6 children who are watching a conversation are more likely to spontaneously switch their gaze to an upcoming responder when they hear a question compared to when they hear a non-question. However, what information drives these predictions remains unclear. Tracking the eye gaze behavior of Dutch children (1–4-year-olds) and adults, the purpose of this research was to examine whether participant’s predictions are driven by individually informative linguistic cues, comparing two cues associated with interrogatives: one lexical cue (subject pronoun) and one canonically associated prosodic cue (utterance-final intonation). We find that from age children 2;0 make more and earlier anticipations of an upcoming addressee response when hearing the early lexical cue (you vs. I subject pronouns), but we have no evidence that their predictions are changed by the later prosodic cue. Further, we investigated how cue use depends on linguistic context by comparing semantically meaningful (Study 1) and non-meaningful (Study 2) context. Only in meaningful contexts did participants show a pronoun advantage in predicting conversational structure. This suggests that using these cues relies on broader linguistic context. The findings take us a step closer to understanding how linguistic and interactional skills become intertwined in development
Input-independent and Krawtchouk-parameter-independent parallel model order reduction based on Krawtchouk moments and block DFT for two-dimensional discrete-time systems
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Adaptation of Moreau–Yosida regularization to the modulus of convexity
Get PDFWe study a generalization of Moreau–Yosida regularization that is adapted to the geometry of Banach spaces where the dual space is uniformly convex with modulus of convexity of power type. Important properties for regularized convex functions are given, in particular strong monotonicity of the subdifferential of their convex conjugate and Hölder-continuity of their gradient