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Substrate channeling is a widespread mechanism in metabolic pathways to avoid decomposition of unstable intermediates, competing reactions, and to accelerate catalytic turnover. During the biosynthesis of light-harvesting phycobilins in cyanobacteria, two members of the ferredoxin-dependent bilin reductases are involved in the reduction of the open-chain tetrapyrrole biliverdin IXα to the pink pigment phycoerythrobilin. The first reaction is catalyzed by 15,16-dihydrobiliverdin:ferredoxin oxidoreductase and produces the unstable intermediate 15,16-dihydrobiliverdin (DHBV). This intermediate is subsequently converted by phycoerythrobilin:ferredoxin oxidoreductase to the final product phycoerythrobilin. Although substrate channeling has been postulated already a decade ago, detailed experimental evidence was missing. Using a new on-column assay employing immobilized enzyme in combination with UV-Vis and fluorescence spectroscopy revealed that both enzymes transiently interact and that transfer of the intermediate is facilitated by a significantly higher binding affinity of DHBV toward phycoerythrobilin:ferredoxin oxidoreductase. Concluding from the presented data, the intermediate DHBV is transferred via proximity channeling.
Ein Bioraffineriekonzept für (Bier-)Treber wird vorgeschlagen, bei dem im Gegensatz zu bestehenden Konzepten wasserlösliche Komponenten durch Pressen abgetrennt und als Grundlage für eine Milchsäurefermentation mit Lactobacillus delbrueckii subsp. lactis verwendet werden. Die verbleibenden strukturellen Kohlenhydrate des Treberrückstandes werden durch hydrothermale und enzymatische Vorbehandlung in fermentierbare Zucker überführt. Es entstehen deutlich weniger Nebenprodukte, die das Wachstum von Mikroorganismen inhibieren können, als bei der Nutzung von nicht abgepresstem Treber.
In order to discuss the kinds of reasoning a visualization supports and the conclusions that can be drawn within the analysiscontext, a theoretical framework is needed that enables a formal treatment of the reasoning process. Such a model needs toencompass three stages of the visualization pipeline: encoding, decoding and interpretation. The encoding details how dataare transformed into a visualization and what can be seen in the visualization. The decoding explains how humans constructgraphical contexts inside the depicted visualization and how they interpret them assigning meaning to displayed structuresaccording to a formal reasoning strategy. In the presented model, we adapt and combine theories for the different steps intoa unified formal framework such that the analysis process is modelled as an assignment of meaning to displayed structuresaccording to a formal reasoning strategy. Additionally, we propose the ConceptGraph, a combined graph-based representationof the finite-state transducers resulting from the three stages, that can be used to formalize and understand the reasoning process.We apply the new model to several visualization types and investigate reasoning strategies for various tasks.
A novel method for the highly stereoselective synthesis of tetrahydropyrans is reported. This domino reaction is based on a twofold addition of enamides to aldehydes followed by a subsequent cyclization and furnishes fully substituted tetrahydropyrans in high yields. Three new σ-bonds and five continuous stereogenic centers are formed in this one-pot process with a remarkable degree of diastereoselectivity. In most cases, the formation of only one out of 16 possible diastereomers is observed. Two different stereoisomers can be accessed in a controlled fashion starting either from an E- or a Z-configured enamide.
Covering edges in networks
(2019)
In this paper we consider the covering problem on a networkG=(V,E)withedgedemands. The task is to cover a subsetJ⊆Eof the edges with a minimum numberof facilities within a predefined coverage radius. We focus on both the nodal andthe absolute version of this problem. In the latter, facilities may be placed every-where in the network. While there already exist polynomial time algorithms to solvethe problem on trees, we establish a finite dominating set (i.e., a finite subset ofpoints provably containing an optimal solution) for the absolute version in generalgraphs. Complexity and approximability results are given and a greedy strategy isproved to be a (1+ln(|J|))-approximate algorithm. Finally, the different approachesare compared in a computational study.
This contribution presents a novel approach to investigate entrainment in distillation and absorption columns. An image-based probe allows precise droplet detection at various radial and axial positions above trays. Validations achieve an aver-age error of 6.4 % (monospheres 9.2–114.4mm) and 3 % (monodisperse droplet stream up to 19 m s–1and 74.5mm).Experiments in a DN 450 cold flow test rig show an increasing (decreasing) share of larger droplets with higher gas (liq-uid) loads. Locally measured droplet sizes depend on probe position as well as tray design and enable an extrapolation tointegral entrainment rates.
The use of digital media in adult education is very heterogene-ous. To date, there are no empirical studies that have examined the possibility that media-related differences in media usage of adult educators could be in part due to differential media pedagogical attitudes of adult educators. Moreover, there is a lack of empirical evidence to support the understanding of what factors modulate differences in media pedagogical com-petencies of adult educators. In order to examine different the-oretical potentialities, in the present study, an online survey of adult educators (n = 626) was conducted to investigate the attitudes of adult educators in Germany toward their use of digital media. The results of the study indicate that there are influencing factors such as educational level or employment context on attitudes toward digital media.
Organic solutions of lithium bis(fluorosulfonyl)imide (LiFSI) are promising electrolytes for Li-ion batteries. Information on the diffusion coefficients of the species in these solutions is needed for battery design. Therefore, the self-diffusion coefficients in such solutions were studied experimentally with the pulsed-field gradient nuclear magnetic resonance technique. The self-diffusion coefficients of the ions Li+ and FSI− as well as those of the solvents were measured for LiFSI solutions in pure dimethyl carbonate and ethylene carbonate as well as in mixtures of these solvents at 298 K and ambient pressure. Despite the Li+ ion being the smallest species in the solution, its self-diffusion coefficient is the lowest as a result of its strong coordination with the solvent molecules.
The production of nylon-6.6 is one of the largest scale syntheses in industrial chemistry. The standard procedure is based on an energy consuming low-level conversion of cyclohexane to yield adipic acid in two steps that is converted to nylon-6.6 in a separate step. Therefore, there is a strong intent to optimize the synthetic route in an economic and ecologic matter. In this work, we present a one-pot oxygenation of cyclohexane with hydrogen peroxide and a µ4-oxido-copper cluster catalyst to yield dicarboxylic acids with adipic acid as the main product.
This paper provides experimental results on investigations for the validation of photo-grammetric strain measurements of ultra-high-performance concrete (UHPC)-prismssubjected to static and cyclic bending-tensile stress. For this purpose, 4 static and5 cyclic test series were performed. Damage progresses during loading are monitoredby means of a digital image correlation (DIC) system and a clip gauge. The control ofthe DIC by trigger lists and the measurement noise as a function of the measurementrate are examined. All static tests were performed force controlled with the same test-ingspeedandthesamemeasuringrateofDICandclipgauge.Allcyclictestswereperformed with the same upper and lower stress levels but with different loading rates.During the static tests, the DIC can be used to make accurate strain measurementsbefore UHPC failure. In the cyclic tests, the measurement noise of the DICdecreases with an increasing measuring rate. The tests performed confirm the con-trol of the DIC by trigger lists for cyclic tests on UHPC-prisms and show that themeasurement noise is negligible in static and cyclic tests.