The functionalized covalent organic framework materials play an important role in catalytic application. A convenient tactic is developed to design and synthesize an imine‐linked covalent organic ...frameworks (COFs) material (COF‐PD) with abundant nitrogen atoms, which can provide coordination active site and facilitate the incorporation of COFs with nickel ions. Nickel‐coordinated COF‐PD complex (COF‐PD‐Ni) is prepared and used in ethylene oligomerization. COF‐PD‐Ni displays the highest catalytic activity of 1.98 × 105 g/(mol·Ni·h) in ethylene oligomerization with MAO as co‐catalyst and cyclohexane as solvent. Various reaction parameters including reaction temperature, time, solvent, and the amount of cocatalyst are evaluated in detail, dramatically impacting the catalytic activities as well as the distribution of the products. What is more, the effect of COFs structure on the catalytic performance is also studied, suggesting more coordination sites were more important for high activity.
An imine‐linked covalent organic frameworks (COFs) material (COF‐PD) with abundant nitrogen atoms and large surface area was synthesized to provide coordination active site and facilitate the incorporation of COFs with nickel ions to form nickel‐coordinated COF‐PD complex (COF‐PD‐Ni). The large surface area of COF‐PD‐Ni was far lower than that of COF‐PD before loading nickel because of pore blockage caused by the coordination of Ni2+. COF‐PD‐Ni displayed excellent catalytic activity with a strong preference for the 1‐butene in ethylene oligomerization, which attributed to the faster rate of chain transferring process than the chain propagation because of the confinement effect aroused by pore features of covalent organic frameworks.
Herein a quenched-flow kinetic technique was applied to calculate the rate constants of 1-hexene and 1-octene oligomerization catalyzed by the Cp2ZrCl2 and Cp2HfCl2/MAO catalyst systems, and ...subsequently a mechanism for the higher α-olefin oligomerization reaction was proposed. The oligomerization results showed that Zr-based catalyst in the oligomerization of 1-octene had the highest activity of 17 in comparison to Hfbased one with an activity value of 15 g oligomer/(mmolCat.h)). According to the obtained results, increasing monomer length led to a shift in molecular weight and polydispersity index value (Mw/Mn) to lower values. Furthermore, the microstructure-viscosity relationship was followed by the calculation of branching ratio and short-chain branching percentage. The obtained results revealed that, the oligomers synthesized by the Cp2HfCl2 catalyst had lower short chain branching ratio value and short-chain branching percentages. According to the kinetic results, the initiation rate constant (ki) of Zr-based catalyst was higher than that of Hf-based catalyst, and the order of calculated propagation rate constants was Zr>Hf for both the 1-hexene and 1-octene-based oligomerizations.
LIGAND RECOGNITION BY αβ T CELL RECEPTORS Davis, Mark M; Boniface, J. Jay; Reich, Ziv ...
Annual review of immunology,
04/1998, Volume:
16, Issue:
1
Journal Article
Peer reviewed
While still incomplete, the first data concerning the biochemistry of T cell
receptor-ligand interactions in cell-free systems seem to have
considerable predictive value regarding whether a T cell ...response is strong or
weak or suppressive. This data will help considerably in elucidating the
mechanisms behind T cell responsiveness. Also of great interest are the first
structures of T cell receptor molecules and, particularly, TCR-ligand
complexes. These appear to confirm earlier suggestions of a fixed orientation
for TCR engagement with peptide/MHC and should form the basis for understanding
higher oligomers, evidence for which has also just emerged. We conclude with an
analysis of the highly diverse CDR3 loops found in all antigen receptor
molecules and suggest that such regions form the core of both TCR and antibody
specificity.
Summary
Mast cells (MCs) are innate immune cells that are scattered in tissues throughout the organism being particularly abundant at sites exposed to the environment such as the skin and mucosal ...surfaces. Generally known for their role in IgE‐mediated allergies, they have also important functions in the maintenance of tissue integrity by constantly sensing their microenvironment for signals by inflammatory triggers that can comprise infectious agents, toxins, hormones, alarmins, metabolic states, etc. When triggered their main function is to release a whole set of inflammatory mediators, cytokines, chemokines, and lipid products. This allows them to organize the ensuing innate immune and inflammatory response in tight coordination with resident tissue cells, other rapidly recruited immune effector cells as well as the endocrine and exocrine systems of the body. To complete these tasks, MCs are endowed with a large repertoire of receptors allowing them to respond to multiple stimuli or directly interact with other cells. Here we review some of the receptors expressed on MCs (ie, receptors for Immunoglobulins, pattern recognition receptors, nuclear receptors, receptors for alarmins, and a variety of other receptors) and discuss their functional implication in the immune and inflammatory response focusing on non‐IgE‐mediated activation mechanisms.
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•Highly active nickel pre-catalysts in ethylene oligo-/polymerization.•N-donor ligand effects on ethylene enchainment: oligomers through to polymers.•Influence of multidentate ligand ...frame on the catalytic activity and thermal stability of nickel complex.•Correlation between ligand structure and the degree of branching in the polyethylene.•Using temperature to influence the branching content of the polymer.
Homogeneous nickel catalysts have a considerable track record for mediating ethylene chain growth in the form of oligomerization and more recently polymerization. Within the polymerization arena, high molecular weight materials incorporating various degrees of branching, anywhere from linear to moderately branched through to hyperbranched, highlight the versatility of this type of catalyst. This review focuses on recent progress related to structural modifications made to the pre-catalyst, and in particular to the multidentate Nimine-ligand manifold, and how these changes impact on thermal stability and activity of the catalyst as well as the microstructural properties of the polyethylene and the distribution of the oligomeric fractions. In addition to ongoing process development directed towards commodity-type polyolefinic materials, the emergence of nickel catalysts that can form elastomeric-type materials from a single ethylene feed, without the addition of a high-cost α-olefin such as 1-hexene or 1-octene, offers considerable opportunities for future commercial applications.
Liquid-liquid phase separation plays a key role in the assembly of diverse intracellular structures. However, the biophysical principles by which phase separation can be precisely localized within ...subregions of the cell are still largely unclear, particularly for low-abundance proteins. Here, we introduce an oligomerizing biomimetic system, “Corelets,” and utilize its rapid and quantitative light-controlled tunability to map full intracellular phase diagrams, which dictate the concentrations at which phase separation occurs and the transition mechanism, in a protein sequence dependent manner. Surprisingly, both experiments and simulations show that while intracellular concentrations may be insufficient for global phase separation, sequestering protein ligands to slowly diffusing nucleation centers can move the cell into a different region of the phase diagram, resulting in localized phase separation. This diffusive capture mechanism liberates the cell from the constraints of global protein abundance and is likely exploited to pattern condensates associated with diverse biological processes.
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•Corelets are phase-separating photoinduced oligomers of self-interacting proteins•FUSN Corelets phase diagram with binodal and spinodal regimes mapped in live cells•Mutations reshape phase diagrams allowing quantitative sequence space interrogation•Localized oligomerization drives condensation even at undersaturated concentrations
Probing cellular phase separation with a biomimetic system suggests a mechanism for condensate formation with low abundance molecules.
Neuroinflammation is one of the pathophysiologies of Parkinson's disease (PD). Lewy bodies, the pathological hallmark of PD, emerge as a consequence of α-synuclein aggregation, and neuroinflammation ...is induced concurrently with this aggregation. Imaging and cerebrospinal fluid (CSF) biomarkers that reflect PD pathophysiology have been developed or are under investigation. The IgG index of CSF is a marker of inflammation, and may also reflect the pathophysiology of PD.
We examined if the IgG index reflects the pathophysiology of PD in drug-naïve PD patients.
The subjects were 20 consecutive PD patients who underwent 123I-MIBG scintigraphy for assessment of the heart to mediastinum (H/M) ratio and wash out rate, 123I-Ioflupane SPECT for examination of the specific binding ratio in the striatum, and lumbar puncture before treatment. The CSF IgG index and levels of pathogenic proteins (total α-synuclein, oligomeric α-synuclein, total tau, phosphorylated tau and amyloid Aβ1–42) were determined. The IgG index was compared with the other parameters using Spearman correlation analysis.
The IgG index showed a significant correlation with the H/M ratio in early (r = −0.563, p = 0.010) and delayed (r = −0.466, p = 0.038) images in 123I-MIBG scintigraphy and with the CSF total tau level (r = −0.513, p = 0.021).
Neuroinflammation is involved in PD pathophysiology in some patients, and a higher IgG index indicates the presence of neuroinflammation accompanied by emergence of Lewy bodies.
•We examined if the IgG index reflects the pathophysiology of PD using biomarkers.•IgG index significantly correlated with the H/M ratios of 123I-MIBG scintigraphy.•The IgG index significantly correlated with CSF total tau level.•Neuroinflammation is involved in PD pathophysiology in some patients.•A higher IgG index indicates neuroinflammation linked to Lewy body pathophysiology.
The possibility of using TiO2‐based compositions: individual and sulfated titania, and their composites with carbon nanotubes as catalysts for glycerol oligomerization has been displayed. The effect ...of modification of TiO2 with sulfur and carbon nanotubes on acid‐base and catalytic characteristics in the glycerol conversion was investigated. The activation of glycerol on the catalysts has been studied using attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy. Only the samples based on sulfated titania are active over glycerol transformation, showing up to 58.7 % conversion. This is explained by the presence of strong base sites. Glycerides up to pentaglycerides, both linear and nonlinear structure are formed by glycerol oligomerization over TiO2−S. The addition of nanotubes to the catalyst reduces both the glycerol conversion (up to 10.5 %) and the yield of glycerides. However, the spectrum of the resulting products is significantly narrowed, increasing the selectivity for short‐chain glycerides: the portion of diglycerides reaches 72 %, and triglycerides 21 %. Herewith, glycerides of a linear structure only formed.
Modification of TiO2 with sulfonic groups causes the appearance of catalytic activity with the formation of a wide range of polyglycerides. Fabrication of a composite of sulfated titania with carbon nanotubes limits the spectrum of products with short‐chain linear glycerides. Thus, it gives a promising way to obtain a selective catalyst for the processing of glycerol into short‐chain polyglycerides.
SQSTM1/p62, also known as sequestosome 1 (SQSTM1) or p62, is an intracellular protein induced by stress and functions as an adaptor molecule in diverse cellular processes. Oxidative damage induced by ...overproduction of amyloid-β (Aβ) and the impairment of endogenous antioxidant Nrf2 signaling have been documented in the brains of Alzheimer’s disease (AD) patients. The causes of the inactivation of Nrf2 signaling under Aβ-induced oxidative stress are unclear, and p62 might be involved in this process. In this study, APP/PS1 transgenic mice, Aβ intrahippocampal injection rat model, and SH-SY5Y cells were used to reveal that the alterations in the oligomeric state of p62 participated in the regulation of Nrf2 signaling under Aβ insult. The present in vivo and in vitro studies revealed that short-term treatment of Aβ activated Nrf2 signaling, while long-term Aβ treatment inhibited it through either canonical or noncanonical Nrf2 activation pathway. p62 oligomerization was largely attenuated under long-term Aβ treatment. The reduction of p62 oligomerization weakened p62 sequestration to Keap1, leading to Nrf2 signaling inhibition. Our findings provide a better understanding of p62-mediated modulation on Nrf2 activity and highlight a potential therapeutic target of p62 in AD.
•Chronic oxidative stress induced by Aβ inhibited Nrf2 signaling.•p62-mediated noncanonical pathway was involved in the inhibition of Nrf2 signaling by Aβ.•Reduction of p62 oligomers contributed to Aβ-induced inhibition of Nrf2 signaling.
While the field of organic electronics has developed extensively in recent years, it remains limited by number of materials available. Further expansion requires the innovation of new types of ...π‐conjugated backbones, but suitable candidates are discovered only very rarely. The recent introduction of a new class of conjugated materials, long α‐oligofurans, was therefore greeted with considerable interest. α‐Oligofurans possess many of the properties required to excel in applications as organic electronic materials, can be manufactured from renewable resources, and are expected to be biodegradable. This Minireview provides an account of long oligofurans from the perspectives of their synthesis, molecular properties, chemical reactivity, and use in electronic devices.
Long and short of it: A critical account of a new class of π‐conjugated materials, long oligofurans, from the perspectives of their synthesis, molecular properties, chemical reactivity, and use in electronic devices is presented.
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