High active and selective 1–3 chromium catalysts based on the corresponding Ph2PN(cyclopentyl)P (NR2)2‐type L1–L3 ligands (L1: R = methyl, L2: R = ethyl, L3: R = isopropyl) have been explored for ...selective ethylene tri‐/tetramerization. We found that the ligand substituents and the experimental conditions considerably influenced the catalytic performance of 1–3 based catalysts. Combining a higher ethylene pressure can elevate the selectivity of 1‐octene (67.98%) of precatalyst 1 with high catalytic activity (9.3 × 106 g/molCr h). Furthermore, precatalysts 2–3 efficiently offer selective ethylene trimerization and afforded 97.76% 1‐hexene selectivity with 5.8 × 106 g/(molCr h) catalytic activity (in case precatalyst 3). A relatively low catalyst mass, high Al/Cr molar ratio, and high ethylene pressure display excellent catalytic activity and selectivity for ethylene oligomerization.
The chromium 1–3 complexes of the corresponding Ph2PN(cyclopentyl)P (NR2)2‐type L1–L3 ligands (L1: R = methyl, L2: R = ethyl, L3: R = isopropyl) when activated with MMAO‐3A cocatalyst afforded efficient catalysts for selective ethylene tri‐/tetramerization. The distribution of products showed that these systems have a significant impact on their catalytic performance in ethylene oligomerization. Precatalyst 1 exhibited 67.98% selectivity toward 1‐octene, whereas precatalysts 2–3 afforded 97.76% high selectivity 1‐hexene selectivity with significantly high catalytic activity.
The ability to control the molecular structure (e.g., degree of branching) of iso-olefins produced from oligomerizing light olefins is a valuable tool for tuning the final compositions of hydrocarbon ...fuels and targeting specific fuel properties. In this study, we demonstrated that the degree of branching of iso-olefins obtained from butene oligomerization can be controlled by tuning process conditions (i.e., temperature, weight hourly space velocity WHSV, nature of butene feedstock) and by choosing the proper catalyst (i.e., Amberlyst-36 vs. Y/ZSM-22). We produced three types of iso-olefin mixtures: 1) a methyl-heptenes rich (74 wt%) mixture,2) dimethyl-hexenes rich (80–96 wt%) mixtures, and 3) highly branched (i.e., ≥3 methyl substitutions) iso-olefins rich (>50 wt%) mixtures. While dimethyl-hexenes are preferentially formed at lower temperatures (60–100 °C) and WHSV (i.e., 2 hr−1), methyl-heptenes are favorably produced at higher temperatures (>100 °C) and WHSVs (i.e., 7 hr−1) over Amberlyst-36. The use of either 1-butene or 2-butene as feedstock resulted in liquid products with similar branching because facile intramolecular isomerization occurs prior to oligomerization. The use of isobutylene feedstock forms a more branched olefin product. For each type of iso-olefins mixture, we determined fuel properties including research octane number (RON), motor octane number (MON), and octane sensitivity (S), which is the difference between RON and MON. We found that not only RON and MON but also S values increased with the degree of branching of these complex mixtures of iso-olefins. The highest RON of 99.7 and S value of 9.3 were obtained for a mixture of highly branched iso-olefins.
The coronavirus disease 2019 (COVID‐19) pandemic has rapidly transformed the whole world and forced us to look through comorbid diseases and risk factors from a different perspective. COVID‐19 shows ...some inherent risk factors like cardiovascular comorbidities independent from age, gender, and geographic location. One of the most peculiar features of the COVID‐19 pandemic is that severe acute respiratory syndrome coronavirus 2 respiratory infections disproportionately impact patients with hypertension, diabetes, and other cardiovascular comorbidities rather than those with allergic respiratory diseases and immune‐compromised conditions. Migraine is a complex neuro‐vasculo‐inflammatory disorder that is also packed frequently with certain medical conditions including vascular disorders, hypertension, allergic diseases such as asthma and systemic inflammatory disorders. Accordingly, 2 different questions arise during the pandemic: (1) Do share comorbidities of cardiovascular diseases and hypertension increase the risk of symptomatic COVID‐19 for migraine patients? (2) Do comorbid allergic and atopic diseases, including asthma act as opposite influencers alongside with female gender? This paper focuses on the co‐existence of comorbidities of COVID‐19, in comparison with migraine, based on a wide clinical dataset and available reports. Discussed mechanisms include potential strategic roles of angiotensin‐converting enzyme 2, angiotensin‐II, and nucleotide oligomerization domain‐like receptor family, pyrin domain containing 3 inflammasome, playing remarkable parts in the pathogenesis of COVID‐19 and migraine. There are also some clues about the importance of endothelial and pericyte dysfunction and neuroinflammation in COVID‐19 infection, related to complications and survival of the patients. The large epidemiological studies as well as basic research, focusing on migraine patients with COVID‐19 will clarify these vital questions during the upcoming periods.
Light and temperature in plants are perceived by a common receptor, phytochrome B (phyB). How phyB distinguishes these signals remains elusive. Here, we report that phyB spontaneously undergoes phase ...separation to assemble liquid-like droplets. This capacity is driven by its C terminus through self-association, whereas the intrinsically disordered N-terminal extension (NTE) functions as a biophysical modulator of phase separation. Light exposure triggers a conformational change to subsequently alter phyB condensate assembly, while temperature sensation is directly mediated by the NTE to modulate the phase behavior of phyB droplets. Multiple signaling components are selectively incorporated into phyB droplets to form concentrated microreactors, allowing switch-like control of phyB signaling activity through phase transitions. Therefore, light and temperature cues are separately read out by phyB via allosteric changes and spontaneous phase separation, respectively. We provide a conceptual framework showing how the distinct but highly correlated physical signals are interpreted and sorted by one receptor.
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•Photo-activated phyB proteins undergo LLPS to form liquid droplets•C terminus and NTE are, respectively, the driving force and modifier of phyB LLPS•PhyB selectively recruits its interacting transcription factors into droplets•The NTE directly senses thermal signals to modify phyB phase behaviors
Light and temperature are correlated but independent signals. Chen et al. uncover that phyB photobodies are formed through phase separation and function as tunable thermosensors. Light induces conformational changes to subsequently alter phyB photobody formation, while temperature signals are directly sensed by the condensates through the N-terminal extension of phyB.
Many examples exist for the chromium catalyzed selective ethylene oligomerization in which the influence of ligands is essential for the formation of products. Regarding the tri‐ and tetramerization ...to 1‐hexene or 1‐octene mostly PNP ligands are responsible for the tetra‐ and some of such modified ligands for the trimerization. A very special case in these reactions are PNPN−H ligands, showing in most cases highly selective trimerization of ethylene to 1‐hexene. In this review all existing published information about these PNPN−H ligands is accumulated and compared to some other related PNP, PNPN and NPNPN ligands in the chromium catalyzed selective ethylene oligomerization with respect to the switch from tetra‐ to trimerization and back by different substituent pattern of PNP ligand. Mechanistic information and arguments are collected to explain the switch from tetra‐ to trimerization and back by substitution of functional groups in classical PNP to PNPN−H ligands as a result of mono‐ and dinuclear catalytic species.
From tetra‐ to trimerization and back: PNP ligands are responsible for the selective tetra‐ and as modified ligands for the trimerization of ethylene. The very special PNPN−H ligands are highly selective for the formation of 1‐hexene, compared to other similar PNP, PNPN and NPNPN ligands. In this minireview all published information about these PNPN−H ligands are summarized and compared to some other similar ligands. Mechanistic information are collected to explain the switch from tetra‐ to trimerization and back by substituents.
Recently, Power-to-Liquids (PtL) and Power-to-Gas (PtG) technologies have been regarded as promising pathways for renewable energy storage and CO2 mitigation. Herein, we newly proposed two PtL/PtG ...hybrid processes (Cases A and B) by integrating the Fe-based Fischer-Tropsch (F-T) synthesis and olefin oligomerization, to further enhance the production of value-added liquid hydrocarbons. The process modelling and case study were implemented to evaluate their process performances by using Aspen Plus. In addition, the effects of different feeding conditions (i.e., CO/CO2 feeding) and process configurations (i.e., F-T synthesis only or two-stage reactor) were also comparatively analyzed. It is found that both Cases A and B are efficient technologies for converting CO2 into value-added hydrocarbons, and Case A is found to be more beneficial in the aspects of the carbon and thermal efficiencies, and net CO2 reduction. While, Case B is competitive in producing high-value liquid hydrocarbons. Moreover, the options of CO2 feeding and two-stage reactor are more preferable than the options of CO feeding and F-T synthesis only, and both Cases A and B are more competitive in the aspects of syncrude production, thermal efficiency, and CO2 reduction, as compared to the Base cases 1–3.
•Two PtL/PtG hybrid process options are proposed for CO2 transformation.•F-T synthesis and olefin oligomerization are integrated in the proposed PtL/PtG processes.•A comparative analysis of the present and previous PtL/PtG processes are conducted.•The present PtL/PtG processes are technically more competitive than the previous ones.
For over 40 years following the polyolefin catalyst discoveries of Hogan and Banks (Phillips) and Ziegler (Max Planck Institute), chemists traversed the periodic table searching for new transition ...metal and lanthanide-based olefin polymerization systems. Remarkably, none of these “hits” employed iron, that is, until three groups independently reported iron catalysts for olefin polymerization in the late 1990’s. The history surrounding the discovery of these catalysts was only the beginning of their uniqueness, as the ensuing years have proven these systems remarkable in several regards. Of primary importance are the pyridine-bis(imine) ligands (herein referred to as PDI), which produced iron catalysts that are among the world’s most active for ethylene polymerization, demonstrated “staying power” despite over 15 years of ligand improvement efforts, and generated highly active polymerization systems with cobalt, chromium, and vanadium. Although many ligands have been employed in iron-catalyzed polymerization, the PDI family has thus far provided the most information about iron’s capabilities and tendencies. For example, iron systems tend to be highly selective for ethylene over higher olefins, making them strong candidates for producing highly crystalline polyethylene, or highly linear α-olefins. Iron PDI polymerizes propylene with 2,1-regiochemistry via a predominantly isotactic, chain end control mechanism. Because the first insertion proceeds via 1,2-regiochemistry, iron (and cobalt) PDI systems can be tailored to make highly linear dimers of α-olefins by “head-to-head” coupling, resulting from a switch in regiochemistry after the first insertion. Finally, PDI ligands, while not being surpassed in activity, have inspired the development of related ligand families and complexes, such as pendant donor diimines (PDD), which are also highly efficient at producing linear α-olefins. This Account will detail a variety of oligomerization and polymerization results achieved with PDI and PDD catalysts. Our studies on ligand modification are discussed, but numerous ligands have been synthesized by others. Computational approaches, identification of catalyst active sites, noninnocent ligand studies, commercialization efforts, and other outstanding research are only briefly mentioned, at most. The reader is directed to review articles where appropriate, in order to address the cursory treatment of these areas.
Oligomeric acceptors are expected to combine the advantages of both highly developed small molecular and polymeric acceptors. However, organic solar cells (OSCs) based on oligomers lag far behind due ...to their slow development and low diversity. Here, three oligomeric acceptors were produced through oligomerization of small molecules. The dimer dBTICγ‐EH achieved the best power conversion efficiencies (PCEs) of 14.48 % in bulk heterojunction devices and possessed a T80 (80 % of the initial PCE) lifetime of 1020 h under illumination, which were far better than that of small molecular and polymeric acceptors. More excitingly, it showed PCEs of 16.06 % in quasi‐planar heterojunction (Q‐PHJ) devices which is the highest value OSCs using oligomeric acceptors to date. These results suggest that oligomerization of small molecules is a promising strategy to achieve OSCs with optimized performance between the high efficiency and durable stability, and offer oligomeric materials a bright future in commercial applications.
Three oligomeric acceptors were synthesized in this work. Investigations revealed that oligomer acceptor‐based devices showed much better photovoltaic performance and light‐soaking stability than small molecules and polymers. dBTICγ‐EH, a dimer, showed a power conversion efficiency (PCE) of 16.06 % in Q‐PHJ devices with superior device stability, which is the highest value among the reported oligomeric acceptors to date.
Peroxiredoxins are central to cellular redox homeostasis and signaling. They serve as peroxide scavengers, sensors, signal transducers, and chaperones, depending on conditions and context. Typical ...2-Cys peroxiredoxins are known to switch between different oligomeric states, depending on redox state, pH, posttranslational modifications, and other factors. Quaternary states and their changes are closely connected to peroxiredoxin activity and function but so far have been studied, almost exclusively, outside the context of the living cell. Here we introduce the use of homo-FRET (Förster resonance energy transfer between identical fluorophores) fluorescence polarization to monitor dynamic changes in peroxiredoxin quaternary structure inside the crowded environment of living cells. Using the approach, we confirm peroxide- and thioredoxin-related quaternary transitions to take place in cellulo and observe that the relationship between dimer–decamer transitions and intersubunit disulfide bond formation is more complex than previously thought. Furthermore, we demonstrate the use of the approach to compare different peroxiredoxin isoforms and to identify mutations and small molecules affecting the oligomeric state inside cells. Mutagenesis experiments reveal that the dimer–decamer equilibrium is delicately balanced and can be shifted by single-atom structural changes. We show how to use this insight to improve the design of peroxiredoxinbased redox biosensors.
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