Mixture Of Oligomers Research Articles

Pelletization of Immobilized Amine Carbon Dioxide Sorbents with Fly Ash and Poly(vinyl chloride)

AbstractA combination of coal fly ash (FA) and a polymer binder, namely, poly(vinyl chloride) (PVC), was used to pelletize immobilized amine CO2 sorbents. The pelletization of mixtures of FA and 50 wt % tetraethylenepentamine (TEPA) or ethylenimine oligomer mixture (Mw=423)/silica (EI423‐S) with PVC created a rigid PVC/FA/sorbent network. The strength of the network was attributed, in part, to the hydrogen bonding of PVC with the hydroxy and amine groups of the FA and sorbent (infrared spectroscopy). Increasing the PVC molecular weight or FA content enhanced the pellet strength and reduced CO2 capture. The optimum pellet, FA/EI423‐S (20/80)_PVC62 [10 wt % PVC62 (Mw=62 000), 17 wt % FA], captured 1.33 mmol g−1 and exhibited a crush strength of 1.42 MPa. The reaction between PVC and amines produced ammonium ions (−NH3+/−NH2+), which reduced the CO2 captured by the pellet during stability testing. This issue was partially resolved by replacing PVC62 with p‐phenylenediamine‐modified PVC62, which also enhanced the pellet CO2 capture to 1.5 mmol g−1.

Pinus massoniana Bark Extract: Structure-Activity Relationship and Biomedical Potentials.

Proanthocyanidins (PAs) belong to the condensed tannin subfamily of natural flavonoids. Recent studies have shown that the main bioactive compounds of Pinus massoniana bark extract (PMBE) are PAs, especially the proanthocyanidins B series, which play important roles in cell cycle arrest, apoptosis induction and migration inhibition of cancer cells in vivo and in vitro. PA-Bs are mixtures of oligomers and polymers composed of flavan-3-ol, and the relationship between their structure and corresponding biomedical potentials is summarized in this paper. The hydroxyl at certain positions or the linkage between different carbon atoms of different rings determines or affects their anti-oxidant and free radical scavenging bioactivities. The degree of polymerization and the water solubility of the reaction system also influence their biomedical potential. Taken together, PMBE has a promising future in clinical drug development as a candidate anticancer drug and as a food additive to prevent tumorigenesis. We hope this review will encourage interested researchers to conduct further preclinical and clinical studies to evaluate the anticancer activities of PMBE, its active constituents and their derivatives.

Recycling of poly(ethylene terephthalate) – A review focusing on chemical methods

Recycling of poly(ethylene terephthalate) (PET) is of crucial importance, since worldwide amounts of PETwaste increase rapidly due to its widespread applications. Hence, several methods have been developed, like energetic, material, thermo-mechanical and chemical recycling of PET. Most frequently, PET-waste is incinerated for energy recovery, used as additive in concrete composites or glycolysed to yield mixtures of monomers and undefined oligomers. While energetic and thermo-mechanical recycling entail downcycling of the material, chemical recycling requires considerable amounts of chemicals and demanding processing steps entailing toxic and ecological issues. This review provides a thorough survey of PET-recycling including energetic, material, thermo-mechanical and chemical methods. It focuses on chemical methods describing important reaction parameters and yields of obtained reaction products. While most methods yield monomers, only a few yield undefined low molecular weight oligomers for impaired applications (dispersants or plasticizers). Further, the present work presents an alternative chemical recycling method of PET in comparison to existing chemical methods.

Powering tyrosol antioxidant capacity and osteogenic activity by biocatalytic polymerization

Oxidative polymerization of tyrosol afforded a mixture of oligomers (OligoTyr) which proved to be more active than tyrosol as antioxidant and as stimulator of alkaline phosphatase (ALP) activity when loaded into polylactic acid (PLA) scaffolds.

Gene expression and molecular characterization of a chaperone protein HtpG from Bacillus licheniformis

Heat shock protein 90 (Hsp90/HtpG) is a highly abundant and ubiquitous ATP-dependent molecular chaperone consisting of three flexibly linked regions, an N-terminal nucleotide-binding domain, middle domain, and a C-terminal domain. Here the putative htpG gene of Bacillus licheniformis was cloned and heterologously expressed in Escherichia coli M15 cells. Native-gel electrophoresis, size exclusion chromatography, and cross-linking analysis revealed that the recombinant protein probably exists as a mixture of monomer, dimer and other oligomers in solution. The optimal conditions for the ATPase activity of B. licheniformis HtpG (BlHtpG) were 45°C and pH 7.0 in the presence of 0.5mM Mg2+ ions. The molecular architecture of this protein was stable at higher temperatures with a transition point (Tm) of 45°C at neutral pH, whereas the Tm value was reduced to 40.8°C at pH 10.5. Acrylamide quenching experiment further indicated that the dynamic quenching constant (Ksv) of BlHtpG became larger at higher pH values. BlHtpG also experienced a significant change in the protein conformation upon the addition of ATP and organic solvents. Collectively, our experiment data may provide insights into the molecular properties of BlHtpG and identify the alteration of protein structure to forfeit the ATPase activity at alkaline conditions.

Probing the binding of procyanidin B3 to trypsin and pepsin: A multi-technique approach

Proanthocyanidins are a mixture of monomers, oligomers, and polymers of flavan-3-ols that are widely distributed in the plant kingdom. One of the most widely studied proanthocyanidins is procyanidin B3. In this study, the binding of procyanidin B3 to trypsin and pepsin was investigated using spectrofluorimetry, equilibrium microdialysis, circular dichroism (CD) spectroscopy and molecular modeling. Fluorescence experiments indicate procyanidin B3 quenches the fluorescence of trypsin/pepsin through a static process. Thermodynamic analysis reveals that procyanidin B3 binds to trypsin/pepsin is synergistically driven by enthalpy and entropy, and the major driving forces are hydrophobic, hydrogen bonding, and electrostatic interactions. Procyanidin B3 binds trypsin in a more firmly way than pepsin, and one molecule of procyanidin B3 combines with one molecule of trypsin/pepsin. The binding parameters obtained from equilibrium microdialysis are consistent with the results obtained from fluorescence spectroscopy. Synchronous fluorescence spectroscopy and CD spectroscopy show that procyanidin B3 may induce microenvironmental and conformational changes of trypsin and pepsin. Molecular modeling displays the specific binding site of procyanidin B3 on trypsin and pepsin. The study provides an accurate and full basic data for clarifying the binding mechanisms of procyanidin B3 with trypsin and pepsin and is helpful for understanding its biological activity in vivo.

Evans Enolates: Solution Structures of Lithiated Oxazolidinone-Derived Enolates.

The results of a combination of (6)Li and (13)C NMR spectroscopic and computational studies of oxazolidinone-based lithium enolates-Evans enolates-in tetrahydrofuran (THF) solution revealed a mixture of dimers, tetramers, and oligomers (possibly ladders). The distribution depended on the structure of the oxazolidinone auxiliary, substituent on the enolate, and THF concentration (in THF/toluene mixtures). The unsolvated tetrameric form contained a D(2d)-symmetric core structure, whereas the dimers were determined experimentally and computationally to be trisolvates with several isomeric forms.

NMR method for accurate quantification of polysorbate 80 copolymer composition.

(13)C NMR spectroscopic integration employing short relaxation delays and a 30° pulse width was evaluated as a quantitative tool for analyzing the components of polysorbate 80. (13)C NMR analysis revealed that commercial polysorbate 80 formulations are a complex oligomeric mixture of sorbitan polyethoxylate esters and other intermediates, such as isosorbide polyethoxylate esters and poly(ethylene glycol) (PEG) esters. This novel approach facilitates the quantification of the component ratios. In this study, the ratios of the three major oligomers in polysorbate 80 were measured and the PEG series was found to be the major component of commercial polysorbate 80. The degree of polymerization of -CH2CH2O- groups and the ratio of free to bonded -CH2CH2O- end groups, which correlate with the hydrophilic/hydrophobic nature of the polymer, were analyzed, and were suggested to be key factors for assessing the likelihood of adverse biological reactions to polysorbate 80. The (13)C NMR data suggest that the feed ratio of raw materials and reaction conditions in the production of polysorbate 80 are not well controlled. Our results demonstrate that (13)C NMR is a universal, powerful tool for polysorbate analysis. Such analysis is crucial for the synthesis of a high-quality product, and is difficult to obtain by other methods.

Preparation, structure and properties of hybrid materials based on geopolymers and polysiloxanes

Abstract New hybrid materials with no phase separation up to nanometric level were obtained by performing the in situ co-reticulation of an aluminosilicate source (metakaolin), a mixture of dialkylsiloxane oligomers with different degrees of polymerization and an alkaline solution. As supported by SEM and NMR analyses, these hybrid materials are characterized by a highly interpenetrated structure due to the chemical similarity between the components, resulting in excellent physical and mechanical properties compared to neat geopolymers. These promising results represent a further step in developing alternative “low-carbon” binders (as also geopolymers) with improved engineering properties in the concrete technology. The enhanced mechanical properties, along with the high fire resistance, also suggest their utilization for structural applications as heat insulating and heat-resistant panels for the construction industry, and in the production of heat-resistant protective coatings or adhesives for technologically advanced uses.

Thin and ordered hydrogel films deposited through electrospinning technique; a simple and efficient support for organic bilayers

Thermal behavior of Dipalmitoylphosphatidylcholine (DPPC) bilayers deposited over hydrogel fibers was examined. Thus, membrane stability, water absorption–release, phase transitions and phase transition temperatures were studied through different methods during heating cycles. Hydrogel films were realized using an oligomer mixture (HEMA–PEGDA575/photo-initiator) with adequate viscosity. Then, the fibers were deposited over silicon wafers (hydrophilic substrate) through electrospinning technique using four different voltages: 15, 20, 25 and 30kV. The films were then exposed to UV light, favoring polymer chain crosslinking and interactions between hydrogel and substrate. For samples deposited at 20 and 25kV, hierarchical wrinkle folds were observed at surface level, their arrangement distribution depends directly on thickness and associated point defects. DPPC bilayers were then placed over hydrogel scaffold using Langmuir–Blodgett technique. Field emission scanning electron microscopy (FE-SEM) analysis were used to investigate sample surface, micrographies show homogeneous layer formation with chain polymer order/disorder related to applied voltage during hydrogel deposition process, among other parameters. According to the results obtained, it is possible to conclude that the oligomer deposited at 20kV produce thin homogenous films (~40nm) with enhanced ability to absorb water and release it in a controlled way during heating cycles. These scaffold properties confer to DPPC membrane thermal stability, which allow an easy detection of phase(s) and phase transitions. Thermal behavior was also studied via Atomic Force Microscopy (roughness analysis). Contact angle measurements corroborate system wettability, supporting the theory that hydrogel thin films act as DPPC membrane enhancers for thermal stability against external stimuli.

Dynamics-based selective 2D (1)H/(1)H chemical shift correlation spectroscopy under ultrafast MAS conditions.

Dynamics plays important roles in determining the physical, chemical, and functional properties of a variety of chemical and biological materials. However, a material (such as a polymer) generally has mobile and rigid regions in order to have high strength and toughness at the same time. Therefore, it is difficult to measure the role of mobile phase without being affected by the rigid components. Herein, we propose a highly sensitive solid-state NMR approach that utilizes a dipolar-coupling based filter (composed of 12 equally spaced 90° RF pulses) to selectively measure the correlation of (1)H chemical shifts from the mobile regions of a material. It is interesting to find that the rotor-synchronized dipolar filter strength decreases with increasing inter-pulse delay between the 90° pulses, whereas the dipolar filter strength increases with increasing inter-pulse delay under static conditions. In this study, we also demonstrate the unique advantages of proton-detection under ultrafast magic-angle-spinning conditions to enhance the spectral resolution and sensitivity for studies on small molecules as well as multi-phase polymers. Our results further demonstrate the use of finite-pulse radio-frequency driven recoupling pulse sequence to efficiently recouple weak proton-proton dipolar couplings in the dynamic regions of a molecule and to facilitate the fast acquisition of (1)H/(1)H correlation spectrum compared to the traditional 2D NOESY (Nuclear Overhauser effect spectroscopy) experiment. We believe that the proposed approach is beneficial to study mobile components in multi-phase systems, such as block copolymers, polymer blends, nanocomposites, heterogeneous amyloid mixture of oligomers and fibers, and other materials.

Urea Dependent (15)N NMR-Relaxation Studies on PfP2 Multimers Reveal that the C-Terminal Behaves like an Independent Intrinsically Disordered Peptide.

Intrinsically disordered proteins or such domains in globular proteins are believed to be playing important roles in protein functions by virtue of their ability to adapt themselves to requirements of different binding partners and thereby accord high specificity to the interaction. Eukaryotic ribosomal stalk is made up of a supramolecular assembly of P0, P1 and P2 proteins. In Plasmodium falciparum, homo-oligomers of P2 are also seen which seem to be involved in many non-ribosomal functions of the protein in the parasite, and in all of these the protein interacts with different interactors. Here we show by extensive (15)N NMR relaxation studies that the C-terminal stretch of about 45 residues of the protein always remains as a flexible disordered domain, regardless of the state of association of the protein. The relaxation behaviors and the derived rotational correlation times for this portion of the protein are essentially the same in the presence of different concentrations of urea which produce different mixtures of PfP2 oligomers in rapid exchange, whereas the rest of the protein shows substantial variations with urea concentration in the relaxation behaviors. In other words, the C-terminal domain behaves as if it were an independent intrinsically disordered peptide. This would augment the notion that the C-terminal domain of PfP2 would be acting as a scavenger for different interactors depending upon the different functions of the protein inside the parasite.

Oligomerization of Two Membrane Proteins Critical for Bacterial Mating

Bacterial mating allows for the transfer of DNA through a DNA translocation channel. These large, multi‐protein complexes can be found in many bacteria and are known as Type IV secretion systems (T4SSs). Our work focuses on the T4SS of the integrative and conjugative element ICEBs1 found in the Gram‐positive bacterium Bacillus subtilis. Two crucial components of the ICEBs1 T4SS are ConE and ConB. ConE is a VirB4‐like peripheral membrane ATPase, likely providing the energy necessary to pump DNA though the cell membrane. ConB is a VirB8‐like integral membrane protein that recruits ConE to the membrane. Our objective was to purify ConB and to characterize its oligomerization state and potential interactions with ConE in vitro using blue native polyacrylamide gel electrophoresis (BN‐PAGE). We found that purified full‐length His6‐ConB is a mixture of oligomers, forming tetramers up to dodecamers. Truncated His6‐ConB lacking its N‐terminal transmembrane segment is monomeric. Confirming a prior study, we found that purified His6‐ConE and MBP‐His6‐ConE form dimers and a mixture of higher order oligomers. No interactions were detected between any of our purified ConE and ConB proteins using BN‐PAGE. Our results on ConB and ConE multimerization are consistent with previous findings on homologous T4SS proteins. We propose that VirB8‐like proteins function as dodecamers and VirB4‐like proteins function as hexamers in assembled T4SSs in vivo. ConB and ConE likely must interact with the membrane and/or other components of the T4SS to achieve the fully oligomerized state.

Synthesis of Aliphatic Polyesters via Ring‐Opening Polymerization of Macrocyclic Oligoesters

SummaryTo synthesize high molecular weight aliphatic polyesters, ring‐opening polymerization (ROP) of macrocyclic oligoesters made from several dicarboxylic acids and diols was investigated. Macrocyclic oligoesters used for the ROP were synthesized in ca. 50% yield via polycondensation of dicarboxylic acids (small excess) and diols under dilute condition in toluene, followed by washing with aq. NaHCO3 to remove linear oligomers. The obtained products were the mixtures of macrocyclic oligoesters with various ring size (dimer to heptamer). The polymerization of the macrocyclic oligoesters made from succinic acid and 1,4‐butanediol using rare earth catalysts such as Nd(BH3)(thf)3 and Nd(OiPr)3 was found to give high molecular weight polymers in good yields. Cyclic dimer of butylene succinate ((BS)2) was isolated from the mixture of the cyclic oligomers by column chromatography, and was similarly polymerized by the rare earth catalysts. Bulk polymerization of (BS)2 by Nd(BH3)(thf)3 yielded poly(butylene succinate) with Mn up to 38 000. Cyclic oligomers of trimethylene oxalate were not polymerized under the similar conditions applied in this study.

Atomistic Simulations of Coating of Silver Nanoparticles with Poly(vinylpyrrolidone) Oligomers: Effect of Oligomer Chain Length

Silver nanoparticles (AgNPs) possess unique physicochemical properties, which are different from those of matter of the same chemical composition on a larger scale. These features open up the opportunity for their use in many promising chemical and biomedical applications. In this study we have developed an atomistic model for molecular dynamics (MD) simulations of AgNP coated by poly(N-vinyl-2-pyrrolidone) (PVP) oligomers. We focus on identifying the relative length of PVP oligomers, enabling effective protecting of a crystalline silver core of 4.5 nm diameter from water contacts. Three different PVP-coated AgNP systems have been compared: (i) a nanoparticle coated by a mixture of short-chain PVP oligomers of the varying size and (ii,iii) the silver core wrapped by a single, long-chain PVP polymer with the number of monomers equal to 816 and 1440, respectively. We have validated the MD models of the PVP–AgNPs using a series of MD simulations reproducing adsorption, wrapping, and coating of PVP around a silver core either as short PVP oligomers or as a single-chain, long polymer of a varying length. Our simulations predict that the saturated coating of PVP around the silver core of the given diameter can occur when the polymer chain length approaches 2600–2800 units.

Abiotic ligation of DNA oligomers templated by their liquid crystal ordering.

It has been observed that concentrated solutions of short DNA oligomers develop liquid crystal ordering as the result of a hierarchically structured supramolecular self-assembly. In mixtures of oligomers with various degree of complementarity, liquid crystal microdomains are formed via the selective aggregation of those oligomers that have a sufficient degree of duplexing and propensity for physical polymerization. Here we show that such domains act as fluid and permeable microreactors in which the order-stabilized molecular contacts between duplex terminals serve as physical templates for their chemical ligation. In the presence of abiotic condensing agents, liquid crystal ordering markedly enhances ligation efficacy, thereby enhancing its own phase stability. The coupling between order-templated ligation and selectivity provided by supramolecular ordering enables an autocatalytic cycle favouring the growth of DNA chains, up to biologically relevant lengths, from few-base long oligomers. This finding suggests a novel scenario for the abiotic origin of nucleic acids.

Well‐Controlled Synthesis of Poly (phenylene sulfide) (PPS) Starting from Cyclic Oligomers

SummaryThe mixture of cyclic PPS oligomers (c‐PPS) with more than 99% of purity, less than 15 ppm of metal content and more than 4 of repeating units was prepared by the nucleophilic substitution reaction between dichlorobenzene (DCB) and sodium sulfide (Na2S) in relatively dilute solution. Melt polymerization of the c‐PPS in the absence of initiator at high temperature resulted in P(c‐PPS) having high molecular weight, relatively narrow molecular weight distribution and extremely low weight loss at high temperature. Results from MALDI‐TOF‐MS, GPC and in‐situ ESR analysis of the polymerization intermediates suggested that the polymerization of c‐PPS proceeded by a sulfide exchanging polymerization. In addition, the sulfide exchanging polymerization of c‐PPS in the presence of bis(4‐substituted phenyl) sulfides (BPS‐X) such as bis(4‐aminopheny) sulfide (BPS‐NH2), bis(4‐carboxyphenyl) sulfide (BPS‐COOH), and bis(4‐chlorophenyl) sulfide (BPS‐Cl) produced end‐group modified and ring‐opened P(c‐PPS)s. Comparison of polymerization rate in the presence of BPS‐X suggested that the BPS‐X acted as both initiator and chain transfer agent, and the sulfide exchanging polymerization was accelerated by the addition of BPS‐NH2 and BPS‐COOH due to the activation of sulfide linkage through the substitution effect.

Differential Effects of Cell-derived Amyloid-beta Monomers and Dimers on Spontaneous Neuronal Network Activity

Introduction Growing evidence suggests that soluble amyloid-beta (Abeta) peptides play a pivotal role in Alzheimer’s disease(AD) pathogenesis by mediating synaptotoxic effects particularly at early disease stages. Objectives/ Aims We quantified the effects of different order Abeta assemblies on spontaneous firing dynamics ofneuronal networks cultured on multielectrode arrays ('neurochips”) as a read-out. We used naturally secreted, stable and conformationally highly homogenous Abeta monomers, dimers, and a mixture of different low-noligomers, derived from permanently transfected cell lines. Results Abeta dimers promoted a dose-dependent suppression of overall activity and network synchrony and altered the burst structure already in the low picomolar dose range. By contrast, Abeta monomers exhibited no effect on overall activity, but only a slight effect on burst structure and a moderate effect on network synchrony. A yet different response pattern was seen for a mixture of various low-n Abeta oligomers. Thus, multiparametric assessment of electrical activity changes on neurochips revealed characteristic signatures of the network response for the different Abeta assemblies. Since alterations of Network function likely occur in initial disease stages, these results confirm the pivotal role of Abeta dimers in early AD pathogenesis. Conclusions Neurochip recordings of toxic dimeric Abeta species may serve as a valuable diagnostic read-out in early AD and may also be applicable for future testing of drugs, antibodies, or small molecules aiming at Abeta dimers.

In vitro antitumor activity of heterochitooligosaccharides (a review)

This review presents an analysis of the literature data over the last decade in order to reveal the relationship between the structure and composition of chitin/chitosan oligomers and their antitumor activity. Oligosaccharides consisting of N-acetylglucosamine and/or glucosamine units connected to each other by β-1,4-O-glycoside bond are generally called chitooligosaccharides. Homochitooligosaccharides are the oligomers of N-acetylglucosamine (AGA) or glucosamine (GA). Heterooligosaccharides are a mixture of various oligomers differing in the degree of polymerization (DP), acetylation (DA), or deacetylation (DD), as well as in the location of N-acetyl residues in the oligomer chain. Heterochitooligomers with a polymerization degree of no more than 10 are usually water soluble. The solubility of chitooligosaccharides with a DP of more than 10 depends on the DA and pH of a solution. The pharmaceutical and food industries, as well as scientists engaged in basic research, are interested in the use of heterochitooligosaccharides. This is explained by their unique properties, such as good water solubility; minimal toxicity; biocompatibility; the ability to penetrate cell membranes, resulting in a high degree of absorption (unlike chitin and chitosan); and their biological activity. Therefore, in the last decade, researchers have focused their attention on studying the relationship of the structure of oligosaccharides and their specific activity, such as antitumor, antimicrobial, antioxidant, immunemodulatory, and other activities. This is shown by the number of publications, which has doubled compared to the number in 2001.

Synthesis and bioactivity of MSH4 oligomers prepared by an A2 + B2 strategy

Oligomers incorporating the tetrapeptide MSH4, the minimum active sequence of melanocyte stimulating hormone, were synthesized by an A2+B2 strategy involving microwave-assisted copper-catalyzed azide-alkyne cycloaddition. A2 contained an MSH4 core while B2 contained a (Pro-Gly)3 spacer. Soluble mixtures containing compounds with up to eight MSH4 units were obtained from oligomerizations at high monomer concentrations. The avidities of several oligomeric mixtures were evaluated by means of a competitive binding assay using HEK293 cells engineered to overexpress the melanocortin 4 receptor. When based on total MSH4 concentrations, avidities were only minimally enhanced compared with a monovalent control. The lack of variation in the effect of ligands on probe binding is consistent with high off rates for MSH4 in both monovalent and oligomeric constructs relative to that of the competing probe.