Metallcarboxylate und auf N4-Liganden basierende Komplexe als Katalysatoren für die Kupplung von Epoxiden mit Kohlenstoffdioxid

In der vorliegenden Arbeit wurden zwei unterschiedliche Ligandensysteme und deren Metallkomplexe als potentielle, homogene Katalysatoren für die Kupplung von Epoxiden mit Kohlenstoffdioxid (CO2) zu den entsprechenden organischen Carbonaten getestet. Dabei stand die selektive Umsetzung zu cyclischen Carbonaten oder zu aliphatischen Polycarbonaten im Fokus. Das große Interesse für diese Kupplungsreaktion beruht auf der Möglichkeit CO2 als Synthesebaustein zu benutzen und eine zukünftige kommerzielle Nutzung dieser Kupplungsprodukte voranzutreiben. Als Ausgangspunkt der Synthese des ersten Komplexsystems fungierten Variationen des N,N-Bis(2-pyridincarboxamid)-1,2-benzen-Liganden (N4-bpb-Ligand). Durch Umsetzung dieser N4-Liganden mit einerseits Übergangsmetallacetat- bzw. Übergangsmetallhalogenid-Precursoren und den entsprechenden Tetraalkylammonium-Salzen und andererseits mit Diethylaluminiumchlorid, sowie Diethylzink, gelang es 21 ionische, oktaedrische Cobalt-, Eisen-, Chrom(bpb)-Komplexe und acht neutrale Aluminium- bzw. Zink(bpb)-Komplexe zu synthetisieren und teilweise ihre Struktur mittels Röntgenstrukturanalyse genau zu beschreiben. Das zweite Komplexsystem besteht aus der basischen Variante der Metallacetate von Chrom, Eisen und Mangan, welche eine außergewöhnliche, dreikernige, 3 oxo verbrückte, ionische Struktur besitzt, sowie dem zweikernigen Dichrom tetraacetat-dihydrat-Komplex. Diese Verbindungen konnten erfolgreich durch Umsetzung geeigneter Metallprecursoren mit Eisessig bzw. Natriumacetat synthetisiert werden. Zur Überprüfung ihres Katalysatorpotentials für die Kupplungsreaktion erfolgten systematische Katalysetests beider Komplexsysteme mit den Standardtestsubstraten Propylen- und Cyclohexenoxid. Des Weiteren wurde für einige aktive Katalysatoren ein breiteres Screening mit anderen, kommerziell erhältlichen Epoxiden durchgeführt. Ihre Testung zeigte, dass sich durch die Wahl des Katalysators selektiv aliphatische Polycarbonate oder cyclische Carbonate darstellen lassen. Die Cobalt(bpb)bromid- und Eisen(bpb)chlorid-Komplexe eignen sich ohne Zusatz eines Cokatalysators zur quantitativen Synthese von Propylencarbonat. Im Gegensatz dazu benötigen die Zink- bzw. Aluminium(bpb)-Komplexe den Zusatz eines ionischen Cokatalysators wie Tetrabutylammoniumiodid um eine quantitative Umsetzung zu erreichen. Hervorzuheben sind die Zink(bpb)-Komplexe, die auch unter milden Reaktionsbedingungen (60°C, 2 bar CO2-Druck) Propylencarbonat bilden. Zur Gewinnung von reinem Polycyclohexencarbonat sind die Cobalt(bpb)acetat- und Cobalt(bpb)chlorid-Komplexe zu bevorzugen. Aliphatische Poly-ether-carbonate aus Propylenoxid konnten stattdessen nur mit den basischen Metallacetaten hergestellt werden. Eine weitere wichtige Erkenntnis ist, dass zum Beispiel im Falle der Cobalt(bpb)chlorid-Komplexe eine Modifikation des N4-Liganden-Gerüstes mit einem elektronenziehenden Substituenten am ortho Phenylen-Linker (Einbau einer Nitro-gruppe) zu einer deutlichen Steigerung der Ausbeute an Propylencarbonat von 42 auf 86 % führt. Weiterhin gelang es aus den Erkenntnissen der Katalysatortestung, teilweise unterstützt durch kinetische Messungen mittels in situ FT-IR-Spektroskopie, für die verschiedenen neuen Katalysatortypen in dieser Arbeit jeweils Postulate über den Reaktionsmechanismus aufzustellen

A Consensus on Second Stage Analyses in Ecological Inference Models

Statistic

Principal investigator in a box: Version 1.2 documentation

Principal Investigator (PI) in a box is a computer system designed to help optimize the scientific results of experiments that are performed in space. The system will assist the astronaut experimenters in the collection and analysis of experimental data, recognition and pursuit of 'interesting' results, optimal use of the time allocated to the experiment, and troubleshooting of the experiment apparatus. This document discusses the problems that motivate development of 'PI-in-a-box', and presents a high- level system overview and a detailed description of each of the modules that comprise the current version of the system

When are the Patients Satisfied with Their Outcome? Correlation of PROMIS Values with Patient Acceptable Symptom State (PASS) Scores in Foot and Ankle Patients

Introduction/Purpose: PROMIS values are being adopted due to ease of use and influence on clinical decision making. Studies support the use of PROMIS physical function (PF), pain interference (PI), and Depression (D) for pre-surgical decision making. Patient Acceptable Symptom State (PASS) is a validated outcome measure commonly used in other areas of medicine and surgery that captures when patient’s symptoms reach a daily acceptable level. Knowing what PROMIS scores are associated with a patient’s PASS(Yes)/(No) rating would further enhance the use of PROMIS scales. The purpose of this study: 1) association of PROMIS scales with a PASS rating, 2) threshold values of PROMIS PF, PI, D associated with PASS rating, and 3) whether PROMIS, and patient demographics are predictive of a PASS rating

Clinical Utilization of Patient Reported Outcome (PROMIS) Scores for Surgical Reconstruction of Posterior Tibialis Tendon Dysfunction

Introduction/Purpose: Previous studies have demonstrated that preoperative Patient Reported Outcome Instrumentation System (PROMIS) scores effectively predict improvement in foot and ankle surgery. Adult acquired flatfoot deformity (AAFD) and Posterior Tibialis Tendon Dysfunction (PTTD) are a common surgical problem, but it is unclear if the specific thresholds for the physical function (PF), pain interference (PI) and depression published previously for all foot and ankle surgeries apply to a specific diagnosis. Furthermore, the interplay of PROMIS scores and clinical variables has not been evaluated. The purpose of this study was: 1) to investigate the change in PROMIS scales and radiographic measurements from pre- to postoperative follow up in AAFD/PTTD patients, 2) to determine if preoperative PROMIS scales predict post-surgical improvement, 3) to determine if demographic, clinical variables combined with pre-operative PROMIS scales predict post-surgical improvement

A longer vernal window: The role of winter coldness and snowpack in driving spring thresholds and lags

Climate change is altering the timing and duration of the vernal window, a period that marks the end of winter and the start of the growing season when rapid transitions in ecosystem energy, water, nutrient, and carbon dynamics take place. Research on this period typically captures only a portion of the ecosystem in transition and focuses largely on the dates by which the system wakes up. Previous work has not addressed lags between transitions that represent delays in energy, water, nutrient, and carbon flows. The objectives of this study were to establish the sequence of physical and biogeochemical transitions and lags during the vernal window period and to understand how climate change may alter them. We synthesized observations from a statewide sensor network in New Hampshire, USA, that concurrently monitored climate, snow, soils, and streams over a three-year period and supplemented these observations with climate reanalysis data, snow data assimilation model output, and satellite spectral data. We found that some of the transitions that occurred within the vernal window were sequential, with air temperatures warming prior to snow melt, which preceded forest canopy closure. Other transitions were simultaneous with one another and had zero-length lags, such as snowpack disappearance, rapid soil warming, and peak stream discharge. We modeled lags as a function of both winter coldness and snow depth, both of which are expected to decline with climate change. Warmer winters with less snow resulted in longer lags and a more protracted vernal window. This lengthening of individual lags and of the entire vernal window carries important consequences for the thermodynamics and biogeochemistry of ecosystems, both during the winter-to-spring transition and throughout the rest of the year

Complete Momentum Balance in Ionization of H₂ by 75-keV-Proton Impact for Varying Projectile Coherence

We report on a kinematically complete experiment on ionization of H2 by proton impact. While a significant impact of the projectile coherence properties on the scattering-angle dependence of double-differential cross sections (DDCSs), reported earlier, is confirmed by the present data, only weak coherence effects are found in the electron and recoil-ion momentum dependence of the DDCSs. This suggests that the phase angle in the interference term is determined primarily by the projectile momentum transfer rather than by the recoil-ion momentum. We therefore cannot rule out the possibility that the interference observed in our data is not primarily due to a two-center effect

Fully Differential Study of Interference Effects in the Ionization of H₂ by Proton Impact

We have measured fully differential cross sections for ionization of H2 by 75-keV proton impact. The coherence length of the projectile beam was varied by changing the distance between a collimating slit and the target. By comparing the cross sections measured for large and small coherence lengths pronounced interference effects could be identified in the data. A surprising result is that the phase angle in the interference term is primarily determined by the momentum transfer and only to a lesser extent by the recoil-ion momentum

Integration of IEEE C37.118 and publish/subscribe communication

IEEE C37.118 is the current standard for synchrophasor measurements in power systems. It defines the measurement method and communication protocols for the entities in a synchrophasor network. The standard offers two different modes for client-server communication, but cannot be used unchanged over publish/subscribe communication architectures, whose major advantage is simplified and incremental integration of new applications. This work reviews the communication part of IEEE C37.118, and provides an adapter-based solution to easily connect and integrate entities in a synchrophasor network over a publish/subscribe communication architecture. The proposed adapters offer standard-compliant communication between the synchrophasor measurement network entities to facilitate the exchange of measurement data