Distribution Of Oligomers Research Articles

Elongation of Model Prebiotic Proto-Peptides by Continuous Monomer Feeding

Mixtures of amino acids with hydroxy acids allow for the formation of peptide bonds in a plausible prebiotic scenario via ester bond formation followed by ester–amide exchange. Here, we investigate the ability of the ester-mediated reaction pathway to form even longer polymers with peptide backbones based on the specific details of the reaction protocol. Fresh monomers were fed to the polymer/monomer mixture periodically by an automated “day–night machine” that was designed to simulate wet–dry cycles that would have been common on the prebiotic Earth. Quantitative analysis of peptide bond formation in the complex oligomer mixture was enabled by a simple hydrolysis treatment. In the ester-mediated peptide elongation process, new monomers add to one end of the chain step-by-step without termination. The feed composition (hydroxy acids and/or amino acids) was found to determine the final oligomer distribution. Production of longer oligomers enriched in peptide bonds was more efficient when only amino acids w...

Impact of an integrated process of hot pressurised liquid extraction–macroporous resin purification over the polyphenols, hydroxymethylfurfural and reducing sugars content of Vitis vinifera ‘Carménère’ pomace extracts

SummaryThermal degradation and generation of objectionable compounds such as hydroxymethylfurfural have been observed in hot pressurised water extraction of polyphenols. Addition of small amounts of ethanol can reduce process temperatures and retain extraction efficiencies. However, ethanol may reduce the recovery of polyphenols in the subsequent purification stage. The overall effect of increasing amounts of ethanol (0–15%) and reduced temperatures (90, 75, 60 °C) in the extraction stage, as well as increasing amounts of ethanol in the desorption eluent (60–80%) were analysed in a combined hot pressurised liquid extraction–resin purification grape pomace polyphenols process for the first time. Without decreasing the polyphenols recovery (~24 mg GAE g−1), ethanol addition (15%) reduced the extraction temperature (from 130 to 90 °C) which not only decreased the reducing sugar extraction (~25%) but also avoided the hydroxymethylfurfural generation in the extraction stage. Additionally, the combined hot pressurised liquid extraction–resin purification process preserved the proanthocyanidin oligomeric distribution and was selective to polyphenols. The operating conditions found for the combined process, efficiently produced purified polyphenols extracts (11 mg GAE g−1), free of hydroxymethylfurfural and reducing sugars.

Structural and functional effects of manipulating the degree of methylesterification in a model homogalacturonan with a pseudo-random fungal pectin methylesterase followed by a processive methylesterase

We explored the possibility of controlling charge distribution in the homogalacturonan regions of pectin to produce a population of demethylesterified molecules with desirable functional properties by utilizing consecutive treatments with pectin methylesterases (PME) having different modes of action. A fungal PME from Aspergillus aculeatus (Aa-PME), with a pseudo-random mode of action, was used to demethylesterify a extremely high methylesterified HG (DM 94%, average degree of polymerization 246) by reducing the degree of methylesterification (DM) from 94% to either 70% or 80%. A second demethylesterification step, to 50% DM, was performed using a processive PME from Carica papaya (CpL-PME). Introduced demethylesterified blocks were released either by exhaustive or limited endo polygalacturonase (EPG) digestion. Degree of blockiness (DB), absolute degree of blockiness (DBabs), average demethylesterified block size (BS¯) and number of average sized demethylesterified blocks per molecule (BN¯) were estimated. BS¯ and BN¯ as well as DB/DBabs differed depending on the initial DM reduction by AaPME, the number of activity units of CpLPME used and the reaction pH (P < 0.05). Consecutive demethylesterification of HG by AaPME to 80% DM and then by CpLPME to 50% DM at pH 4.5 produced significantly longer oligomer blocks compared to Aa-PME demethylesterification to 70% DM followed by CpL-PME to 50% DM at pH 7.0. Limited EPG digestion released nearly intact demethylesterified blocks and the released oligomers were coupled with in silico modeling. Resulting oligomer distribution corresponded to the in silico mode of action representing contiguous demethylesterification of 10 GalA residues rather than that of random or complete block-wise demethylesterification. Calcium-mediated gels of the modified HGs displayed G′ higher than G″ values and both moduli differed significantly according to the amount of CpLPME applied even though their final DMs were identical. These results suggest the possibility of controlling BS¯ and engineering a population of demethylesterified pectin molecules with specified demethylesterified BS¯ and functional properties.

Spatiotemporal Analysis of K-Ras Plasma Membrane Interactions Reveals Multiple High Order Homo-oligomeric Complexes.

Self-assembly of plasma membrane-associated Ras GTPases has major implications to the regulation of cell signaling. However, the structural basis of homo-oligomerization and the fractional distribution of oligomeric states remained undetermined. We have addressed these issues by deciphering the distribution of dimers and higher-order oligomers of K-Ras4B, the most frequently mutated Ras isoform in human cancers. We focused on the constitutively active G12V K-Ras and two of its variants, K101E and K101C/E107C, which respectively destabilize and stabilize oligomers. Using raster image correlation spectroscopy and number and brightness analysis combined with fluorescence recovery after photobleaching, fluorescence correlation spectroscopy and electron microscopy in live cells, we show that G12V K-Ras exists as a mixture of monomers, dimers and larger oligomers, while the K101E mutant is predominantly monomeric and K101C/E107C is dominated by oligomers. This observation demonstrates the ability of K-Ras to exist in multiple oligomeric states whose population can be altered by interfacial mutations. Using molecular modeling and simulations we further show that K-Ras uses two partially overlapping interfaces to form compositionally and topologically diverse oligomers. Our results thus provide the first detailed insight into the multiplicity, structure, and membrane organization of K-Ras homomers.

Role of Cell-Penetrating Peptides in Intracellular Delivery of Peptide Nucleic Acids Targeting Hepadnaviral Replication.

Peptide nucleic acids (PNAs) are potentially attractive antisense agents against hepatitis B virus (HBV), although poor cellular uptake limits their therapeutic application. In the duck HBV (DHBV) model, we evaluated different cell-penetrating peptides (CPPs) for delivery to hepatocytes of a PNA-targeting hepadnaviral encapsidation signal (ε). This anti-ε PNA exhibited sequence-specific inhibition of DHBV RT in a cell-free system. Investigation of the best in vivo route of delivery of PNA conjugated to (D-Arg)8 (P1) showed that intraperitoneal injection to ducklings was ineffective, whereas intravenously (i.v.) injected fluorescein-P1-PNA reached the hepatocytes. Treatment of virus carriers with i.v.-administered P1-PNA resulted in a decrease in viral DNA compared to untreated controls. Surprisingly, a similar inhibition of viral replication was observed in vivo as well as in vitro in primary hepatocyte cultures for a control 2 nt mismatched PNA conjugated to P1. By contrast, the same PNA coupled to (D-Lys)4 (P2) inhibited DHBV replication in a sequence-specific manner. Interestingly, only P1, but not P2, displayed anti-DHBV activity in the absence of PNA cargo. Hence, we provide new evidence that CPP-PNA conjugates inhibit DHBV replication following low-dose administration. Importantly, our results demonstrate the key role of CPPs used as vehicles in antiviral specificity of CPP-PNA conjugates.

Molecular size is important for the safety and selective inhibition of intrinsic factor Xase for fucosylated chondroitin sulfate

Fucosylated chondroitin sulfate from sea cucumber Isostichopus badionotus (FCS-Ib) showed potent anticoagulant activities without selectivity. The present study focused on developing safe FCS-Ib oligomers showing selective inhibition of intrinsic factor Xase (anti-FXase) prepared through partial N-deacetylation–deaminative cleavage. The N-deacetylation degree was regulated by reaction time, controlling the resulting oligomer distribution. Structure analysis confirmed the selectivity of degradation, and 12 high purity fractions with trisaccharide-repeating units were separated. In vitro anticoagulant assays indicated a decrease in molecular weight (Mw) dramatically reduced activated partial thromboplastin time (APTT), thrombin time (TT), AT-dependent anti-FIIa and anti-FXa activities, while the oligomers retained potent anti-FXase activity until they fell below 3kDa. Meanwhile, human FXII activation and platelet aggregation were markedly reduced with decreasing Mw and were moderate when under 12.0kDa. Thus, fragments of 3–12.0kDa should be safe and effective as selective inhibitors of intrinsic tenase complex for application as clinical anticoagulants.

Cycloheptyl‐fused NNO‐ligands as electronically modifiable supports for M(II) (M = Co, Fe) chloride precatalysts; probing performance in ethylene oligo‐/polymerization

ABSTRACTThe N,N,O‐cobalt(II), [2,3‐{C4H8C(NAr)}:5,6‐{C4H8C(O)}C5HN]CoCl2 (Ar = 2,6‐(CHPh2)2‐4‐MeC6H2 Co1, 2,6‐(CHPh2)2‐4‐EtC6H2 Co2, 2,6‐(CHPh2)2‐4‐ClC6H2 Co3, 2,6‐(CHPh2)2‐4‐FC6H2 Co4) and N,N,O‐iron(II) complexes, [2,3‐{C4H8C(NAr)}:5,6‐{C4H8C(O)}C5HN]FeCl2 (Ar = 2,6‐(CHPh2)2‐4‐MeC6H2 Fe1, 2,6‐(CHPh2)2‐4‐EtC6H2 Fe2, 2,6‐(CHPh2)2‐4‐ClC6H2 Fe3, 2,6‐(CHPh2)2‐4‐FC6H2 Fe4), each containing one sterically enhanced but electronically modifiable N‐2,6‐dibenzhydryl‐4‐R2‐phenyl group, have been prepared by a one‐pot template approach using α,α′‐dioxo‐2,3:5,6‐bis(pentamethylene)pyridine, the corresponding aniline along with the respective cobalt or iron salt in acetic acid. Distorted square pyramidal geometries are a feature of the molecular structures of Co1–Co4. Upon activation with MAO or MMAO, Co1–Co4 show good activities (up to 2.2 × 105 g mol−1(Co) h−1) affording short chain oligomers (C4–C30) with good α‐olefin selectivity. By contrast, Fe1–Fe4, in the presence of MMAO, displayed moderate activities (up 10.9 × 104 g(PE) mol−1(Fe) h−1) for ethylene polymerization forming low‐molecular‐weight linear polymers (up to 13.0 kg mol−1) incorporating saturated n‐propyl and i‐butyl chain ends. For both cobalt and iron, the precatalysts incorporating the more electron withdrawing 4‐R2‐substituents [Cl (Co3/Fe3), F (Co4/Fe4)] deliver the best catalytic activities, while with cobalt, these types of substituents additionally broaden the oligomeric distribution. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3980–3989

Elucidation of insulin assembly at acidic and neutral pH: Characterization of low molecular weight oligomers.

Deficiency in insulin secretion and function that characterize type 2 diabetes often requires administration of extraneous insulin, leading to injection-site amyloidosis. Insulin aggregation at neutral pH is not well understood. Although oligomer formation is believed to play an important role, insulin oligomers have not been fully characterized yet. Here, we elucidate similarities and differences between in vitro insulin aggregation at acidic and neutral pH for a range of insulin concentrations (2.5-100 μM) by using kinetic thioflavin T fluorescence, circular dichroism, atomic force and electron microscopy imaging. Importantly, we characterize the size distribution of insulin oligomers at different assembly stages by the application of covalent cross-linking and gel electrophoresis. Our results show that at the earliest assembly stage, oligomers comprise up to 40% and 70% of soluble insulin at acidic and neutral pH, respectively. While the highest oligomer order increases with insulin concentration at acidic pH, the opposite tendency is observed at neutral pH, where oligomers up to heptamers are formed in 10 μM insulin. These findings suggest that oligomers may be on- and off-pathway assemblies for insulin at acidic and neutral pH, respectively. Agitation, which is required to induce insulin aggregation at neutral pH, is shown to increase fibril formation rate and fibrillar mass both by an order of magnitude. Insulin incubated under agitated conditions at neutral pH rapidly aggregates into large micrometer-sized aggregates, which may be of physiological relevance and provides insight into injection-site amyloidosis and toxic pulmonary aggregates induced by administration of extraneous insulin.

Iron, cobalt and nickel complexes bearing hyperbranched iminopyridyl ligands: Synthesis, characterization and evaluation as ethylene oligomerization catalysts

A series of hyperbranched iminopyridyl ligands [ethylenediamine as terminal groups (L1), 1,4-butanediamine as terminal groups (L2), 1,6-hexamethylenediamine as terminal groups (L3)] were prepared. Ligands L1-L3 were reacted with MCl2·nH2O (M=Fe, Co, Ni) to form three types of complexes (C1-C5). Both L1-L3 and C1-C5 were fully characterized by FT-IR, 1H NMR, UV and ESI-MS. The nickel complexes exhibited better catalytic properties than iron and cobalt complexes for ethylene oligomerization. On activation with methylaluminoxane (MAO), the nickel complex C1 exhibited moderate catalytic activities up to 1.56×106gmol−1h−1 for ethylene oligomerization and the oligomers showed Schulz-Flory distribution. However, on activation with EtAlCl2, the nickel complex C1 exhibited higher catalytic activity up to 8.94×106gmol−1h−1 for ethylene oligomerization, but the products were mainly alkylated-toluenes. The influence of the solvent and reaction parameters such as reaction temperature, ethylene pressure and Al/Ni molar ratio on the catalytic behavior of the nickel complex C1 was also investigated. Moreover, in comparison with the catalytic activity and the distribution of oligomers obtained with related hyperbranched salicylaldimine nickel complex and other non-hyperbranched iminopyridyl nickel complexes, the catalytic activity and the content of low carbon number olefins (C4 and C6) obtained in this work possessed relatively higher.

Analysis of PEG oligomers in black gel inks: Discrimination and ink dating

Carbon-based black gel inks are common samples in forensic practice of questioned document examination in China, but there are few analytical methods for this type of ink. In this study, a liquid chromatography–.high resolution mass spectrometry (LC–HRMS) method was established for the analysis of PEG oligomers in carbon-based black gel ink entries. The coupled instruments achieve both the identification and quantification of PEG oligomers in ink entries with reproducible results. Twenty carbon-based black gel inks, whose Raman spectra appeared identical, were analyzed using the LC–HRMS method. As a result, the twenty gel inks were classified into four groups according to the distribution of PEG oligomers. Artificially aging of PEG 400 and a gel ink showed that as PEG degraded, the relative amounts of low molecular weight PEG oligomers increased, while those of high molecular weight decreased. The degradation of PEG oligomers in a naturally aged gel ink was consistent with those in the artificially aged samples, but occurred more slowly. This study not only provided a new method for discriminating carbon-based black gel ink entries, but also offered a new approach for studying the relative ink dating of carbon-based black gel ink entries.

Glycerol oligomerization in continuous flow reactor

Abstract The first synthesis of polyglycerol in continuous flow reactor in presence of potassium carbonate as homogeneous catalyst was reported varying different parameters: temperature, flow and residence time. The different regioisomers of glycerol dimers and glycerol trimmers have been characterized and the distribution of the different oligomers has been quantified. Further investigations in a cyclic mode, combined with short path distillation, afforded a mixture of predefined glycerol oligomers with a distribution: glycerol dimer (20 wt%), glycerol trimer (21 wt%), glycerol tetramer (16 wt%) and glycerol pentamer (11 wt%).

Mass spectrometric characterization of oligomeric phosphaalkenes

Oligomeric phosphaalkenes are readily characterized using electrospray ionization mass spectrometry (ESI-MS). The high affinity of phosphines for silver ions permits the detection of the unadulterated polymer as [M + xAg]x+ions (x = 2–3). When the oligomers are oxidized using H2O2, the resulting phosphine oxide polymer may be treated with sodium ions to produce [M + xNa]x+ions (x = 2–3). Both methods predict a similar distribution of oligomers: Mnvalues of 3450 ± 100 Da and a PDI of 1.09 ± 0.01 cover both analyses. This distribution represents oligomers of the general formula Me(PMesCPh2)nH from n = 4–20, maximizing at ∼n = 10.

Synthesis and application of bidentate nickel complexes bearing hyperbranched salicylaldimine ligands in ethylene oligomerization

Three bidentate salicylaldimine nickel complexes containing different long-chain alkyl groups in their ligand backbone were synthesized in good yield. All the bidentate salicylaldimine ligands and their nickel complexes were fully characterized by FT-IR, 1H NMR, UV spectroscopies, and mass spectrometry. Three bidentate nickel complexes were evaluated as catalyst precursors in ethylene oligomerization. Upon activation with methylaluminoxane (MAO), the catalytic activity was 5.75 × 105 g/(mol Ni·h) and the oligomers were mainly butenes (52.10%) and octenes (32.63%) for bidentate nickel complex with 1-tetradecyl as core in the ligand backbone (R14-complex) using toluene as solvent. However, bidentate nickel complex with 1-octadecyl as core in the ligand backbone (R18-complex) produced mainly octenes (59.38%) and C10 + olefins (29.01%) and the catalytic activity was 2.23 × 105 g/(mol Ni·h). After activation with ethylaluminum sesquichloride (EASC) in toluene, three nickel complexes yielded mainly C10 + products which contained Friedel-Craft alkylated-toluene, and their catalytic activities were above 1.5 × 106 g/(mol Ni·h). For the bidentate salicylaldimine nickel catalysts with hyperbranched molecules as ligand backbones, the solvent and the reaction conditions had a large effect on catalytic activity as well as oligomerization distribution except the structure of the catalyst and the co-catalyst.

Atomic Force Microscopy Thermally-Assisted Microsampling with Atmospheric Pressure Temperature Ramped Thermal Desorption/Ionization-Mass Spectrometry Analysis.

The use of atomic force microscopy controlled nanothermal analysis probes for reproducible spatially resolved thermally assisted sampling of micrometer-sized areas (ca. 11 × 17 μm wide × 2.4 μm deep) from relatively low number-average molecular weight (Mn < 3000) polydisperse thin films of poly(2-vinylpyridine) (P2VP) is presented. Following sampling, the nanothermal analysis probes were moved up from the surface and the probe temperature ramped to liberate the sampled materials into the gas phase for atmospheric pressure chemical ionization and mass spectrometric analysis. The procedure and mechanism for material pickup, the sampling reproducibility and sampling size are discussed, and the oligomer distribution information available from slow temperature ramps versus ballistic temperature jumps is presented. For the Mn = 970 P2VP, the Mn and polydispersity index determined from the mass spectrometric data were in line with both the label values from the sample supplier and the value calculated from the simple infusion of a solution of polymer into the commercial atmospheric pressure chemical ionization source on this mass spectrometer. With a P2VP sample of higher Mn (Mn = 2070 and 2970), intact oligomers were still observed (as high as m/z 2793 corresponding to the 26-mer), but a significant abundance of thermolysis products were also observed. In addition, the capability for confident identification of the individual oligomers by slowly ramping the probe temperature and collecting data-dependent tandem mass spectra was also demonstrated. The material type limits to the current sampling and analysis approach as well as possible improvements in nanothermal analysis probe design to enable smaller area sampling and to enable controlled temperature ramps beyond the present upper limit of about 415 °C are also discussed.

Augmentation of Interactions between Dimers Stabilizes Higher Order Oligomers of Membrane-Bound K-Ras: A Single Molecule Perspective

Ras proteins are small GTPases that control cell growth, differentiation and proliferation. They primarily reside on the inner leaflet of the plasma membrane and are crucial anticancer drug targets. The structural organization of Ras proteins on the plasma membrane has attracted major interest in recent years. Computational work by our group predicted three interfaces that are variously involved in the oligomerization of K-Ras, the most frequently mutated isoform of Ras proteins. In the current study, we examined a charge reversal K-Ras mutant K101E and a double cysteine mutant K101C/E107C that represent constructs with predicted weak and strong potential for oligomerization, respectively relative to the oncogenic G12V control (WT). We used fluorescence recovery after photobleaching (FRAP), fluorescence correlation spectroscopy (FCS) and image correlation spectroscopy (ICS) to monitor the distribution of dimers and higher-order oligomers of these proteins. Our data show that the distribution of monomers, dimers and higher-order oligomers is such that the K101E mutant is mostly monomeric, K-Ras G12V exists as both dimer and higher-order oligomer whereas the percentage of dimers and larger oligomers is much greater in K101C/E107C, consistent with our prediction and data from signaling assays. These results establish that K101 and E107 play a key role in K-Ras oligomerization and establish the co-existence of diverse K-Ras oligomeric states.

Regulation of Bace1 Mrna Expression in Alzheimer'S Disease by Green Tea Catechins and Black Tea Theaflavins

Every 67 seconds, someone in America develops Alzheimer's disease (AD). Among the top 10 causes of death, AD is the only disease that cannot be cured, treated, or prevented. The amyloid cascade hypothesis states that amyloid-β (Aβ) protein follows a nucleation-dependent pathway to form aggregates that induce nerve damage and deterioration. Aβ monomers originate from the proteolytic cleavage of the amyloid precursor protein (APP) via sequential β-secretase-1 (BACE1) and γ-secretase cleavage. In vitro models show that the presence of Aβ leads to an upregulation of BACE1 mRNA expression, resulting in a feed-forward mechanism for the amyloidogenic cleavage of APP. Epidemiological studies have correlated diets high in green tea catechins and black tea theaflavins with a reduced incidence of AD.Previous studies in our lab demonstrated the varying inhibitory capabilities of catechins (epicatechin, epigallocatechin, epigallocatechin gallate) and theaflavins (theaflavin, theaflavin monogallate) towards Aβ oligomerization, the most toxic Aβ aggregate. This study further characterized these changes in oligomer formation as well as the antioxidant capabilities of these compounds and subsequently utilized SH-SY5Y neuroblastoma cells to determine whether catechins and theaflavins could reduce Aβ-induced upregulation of BACE1 mRNA expression. While catechins had little effect on oligomerization, theaflavins altered both the size distribution and conformation of oligomers. When SH-SY5Y cells were treated with oligomers made in the presence of compounds, epicatechin and epigallocatechin reduced BACE1 expression relative to treatment with native Aβ oligomers. When SH-SY5Y cells were treated instead with native oligomers and antioxidant-capable concentrations of compounds, both epicatechin and theaflavin reduced Aβ-induced BACE1 expression. These results indicate that the antioxidant characteristic of catechins and theaflavins may be more essential in down regulating BACE1 mRNA expression than their capability to inhibit Aβ oligomerization.

Mapping Ceacam 1-4L's Nanoscale Spatial Distribution, Structure, Dynamics, and Association with Lipid Ordered Domains by Super-Resolution Microscopy

Super-resolution microscopy has provided novel quantitative insights into the nanoscale spatial distribution of membrane proteins, including the observation that some systems form micro- and nano-sized clusters. However, details of the protein's self-association state (monomer / dimer / oligomer) within the different cluster types are often missing. Since it has been shown that a protein's oligomeric form might be a crucial determinant of its function, it is important to have a technique capable of measuring both spatial distribution and association state. To that end, we have applied a correlated dSTORM/homo-FRET approach to characterize CEACAM 1-4L, the progenitor isoform of the carcinoembryonic antigen-related cellular adhesion molecule (CEACAMs) family. CEACAMs are cell surface glycoproteins involved in homo- and hetero-philic intercellular interactions that control cellular growth, differentiation, tumourigenesis, inflammation and infection. While CEACAM1-4L is known to exist as a monomer or oligomer with the former being hypothesized to be involved in activatory intercellular interactions, the basis for its spatial distribution and association state as a function of distribution remain poorly understood. Our correlated approach involved live cell homo-FRET studies of eYFP-CEACAM1-4L in HeLa cells followed by fixed cell dSTORM imaging performed using nanobody labeling with Alexa Fluor 647 (AF647) conjugated to an anti-eYFP single domain antibody. Cluster analysis of the dSTORM datasets using Voronoi tessellation revealed that the CEACAM1-4L nanoclusters were preferentially comprised of monomeric CEACAM1-4L while microclusters contained a heterogeneous distribution of CEACAM1-4L monomers and oligomers. To further characterize these clusters, super-resolution imaging using Alexa-647 labelled cholera toxin was performed to examine the co-localization of lipid ordered domains, which are known to drive membrane protein lateral distribution and clustering, with CEACAM1-4L. Finally, live-cell single particle tracking (SPT) of CEACAM1-4L was performed to investigate the putative confined, obstructed, free diffusion, and directed motion dynamics of CEACAM1-4L.

Selective Ethylene Oligomerization with Chromium-Based Metal–Organic Framework MIL-100 Evacuated under Different Temperatures

MIL-100(Cr) was synthesized and evacuated under different temperatures to generate a series of heterogeneous catalysts for ethylene oligomerization. These catalysts showed moderate catalytic activities for ethylene oligomerization but high selectivities to low carbon olefins C6, C8, and C10. Moreover, the oligomer distribution was different depending on the evacuation temperature. The XPS results showed the reduction of some CrIII active sites in the MIL-100(Cr) structure to CrII active sites, which made the catalysts show polymerization activities. The MIL-100(Cr)-250 catalyst evacuated at 250 °C exhibited the highest oligomerization and polymerization activities up to 9.27 × 105 g/(molCr·h) and 0.99 × 105 g/(molCr·h) respectively. The oligomerization selectivity to low carbon olefins C6, C8, and C10 was about 99%. The byproduct polymer from MIL-100(Cr)-250 belonged to linear polyethylene with ultrahigh molecular weight and broad molecular weight distributions. This work demonstrated that MOFs containing...

Ethylene oligomerization in metal-organic frameworks bearing nickel(ii) 2,2'-bipyridine complexes.

The metal-organic frameworks Zr6O4(OH)4(bpydc)6 (1; bpydc2- = 2,2'-bipyridine-5,5'-dicarboxylate) and Zr6O4(OH)4(bpydc)0.84(bpdc)5.16 (2; bpdc2- = biphenyl-4,4'-dicarboxylate) were readily metalated with Ni(DME)Br2 (DME = dimethoxyethane) to produce the corresponding metalated frameworks 1(NiBr2)6 and 2(NiBr2)0.84. Both nickel(ii)-containing frameworks catalyze the oligomerization of ethylene in the presence of Et2AlCl. In these systems, the pore environment around the active nickel sites significantly influences their selectivity for formation of oligomers over polymer. Specifically, the single-crystal structure of 1(NiBr2)5.64 reveals that surrounding metal-linker complexes enforce a steric environment on each nickel site that causes polymer formation to become favorable. Minimizing this steric congestion by isolating the nickel(ii) bipyridine complexes in the mixed-linker framework 2(NiBr2)0.84 markedly improves both the catalytic activity and selectivity for oligomers. Furthermore, both frameworks give product mixtures that are enriched in shorter olefins (C4-10), leading to deviations from the expected Schulz-Flory distribution of oligomers. Although these deviations indicate possible pore confinement effects on selectivity, control experiments using the nickel-treated biphenyl framework Zr6O4(OH)4(bpdc)6(NiBr2)0.14 (3(NiBr2)0.14) reveal that they likely arise at least in part from the presence of nickel species that are not ligated by bipyridine within 1(NiBr2)5.64 and 2(NiBr2)0.84.

Equilibrium condition and stabilization kinetics of lactic acid oligomers in aqueous solutions

Lactic acid is one of the most important compounds in the field of bio‐renewable chemicals. Lactic acid is present in nature but can also be produced by chemical synthesis or by fermentation of biomass. It can be used as raw material for the production of biodegradable and environmentally friendly polymers or copolymers, such as poly lactic acid (PLA).In this work, the equilibrium distribution of monomer and low molecular weight oligomers of lactic acid in aqueous solutions at different overall concentrations of lactic acid (from 0.09 g/g to 0.94 g/g) and temperatures (423 K and 453 K), was investigated.In addition, a kinetic study of monomer and oligomer esterification reactions, of a lactic acid aqueous solution at about 0.09 g/g, was carried out at 423, 433, 443, and 453 K. The values of the kinetic constants were successfully correlated through Arrhenius’ law.