Molecular Weight Characteristics Research Articles

Formation of N-nitrosamines from chlorination and chloramination of molecular weight fractions of natural organic matter

N-Nitrosamines are a class of disinfection by-products (DBPs) that have been reported to be more toxic than the most commonly detected and regulated DBPs. Only a few studies investigating the formation of N-nitrosamines from disinfection of natural waters have been reported, and little is known about the role of natural organic matter (NOM) and the effects of its nature and reactivity on the formation of N-nitrosamines. This study investigated the influence of the molecular weight (MW) characteristics of NOM on the formation of eight species of N-nitrosamines from chlorination and chloramination, and is the first to report on the formation of eight N-nitrosamines from chlorination and chloramination of MW fractions of NOM. Isolated NOM from three different source waters in Western Australia was fractionated into several apparent MW (AMW) fractions using preparative-scale high performance size exclusion chromatography. These AMW fractions of NOM were then treated with chlorine or chloramine, and analysed for eight species of N-nitrosamines. Among these N-nitrosamines, N-nitrosodimethylamine (NDMA) was the most frequently detected. All AMW fractions of NOM produced N-nitrosamines upon chlorination and chloramination. Regardless of AMW characteristics, chloramination demonstrated a higher potential to form N-nitrosamines than chlorination, and a higher frequency of detection of the N-nitrosamines species was also observed in chloramination. The results showed that inorganic nitrogen may play an important role in the formation of N-nitrosamines, while organic nitrogen is not necessarily a good indicator for their formation. Since chlorination has less potential to form N-nitrosamines, chloramination in pre-chlorination mode was recommended to minimise the formation of N-nitrosamines. There was no clear trend in the formation of N-nitrosamines from chlorination of AMW fractions of NOM. However, during chloramination, NOM fractions with AMW <2.5 kDa were found to produce higher concentrations of NDMA and total N-nitrosamines. The precursor materials of N-nitrosamines appeared to be more abundant in the low to medium MW fractions of NOM, which correspond to the fractions that are most difficult to remove using conventional drinking water treatment processes. Alternative or advanced treatment processes that target the removal of low to medium MW NOM including activated carbon adsorption, biofiltration, reverse osmosis, and nanofiltration, can be employed to minimise the formation of N-nitrosamines.

Molecular-weight characteristics and deemulsifying activity of oligourethanes based on alkylene oxide block copolymers and propylene oxide homopolymers prepared in the presence of a double metal cyanide catalyst

The molecular-weight characteristics of Laprol 6003-2B-18, of oligourethanes based on it, and of a new series of propylene oxide homopolymers prepared using a double metal cyanide catalyst were determined. This catalyst allows synthesis of polyethers whose molecular-weight distribution width smoothly varies with the molecular weight. The polyethers were tested for the deemulsifying activity. The tests showed that high-molecular-weight polyethers ensure high degree of dehydration of crude oil emulsions.

Physicochemical characteristics of polyethers prepared using double metal cyanide catalysts

Branched macromolecular polyethers (PEs) based on propylene and ethylene oxides are used as an active base for composites of demulsifiers of oil emulsions. In this work, features of the polymerization of propylene oxide in the presence of double metal cyanide catalysts are studied using the example of PE based on monoethylene glycol and glycerol by varying the molecular weight in the range of 6000–150000. Polymerization is performed in a laboratory reactor at 110–120°C and a catalyst concentration of 50 to 300 ppm. The viscosity, iodine value, and molecular weight characteristics of the PE samples are determined. It is shown that PEs with molecular weights of 6000–40000 have narrow molecular weight distributions (MWDs) and low concentrations of unsaturated impurities. A further increase in the molecular weight of PEs leads to the broadening of MWDs and a polydispersity value of 2.5–3.9, due to the formation of low-molecular weight unsaturated and bifunctional PEs. The results from this work can be employed to developing a process technology for PEs using double metal cyanide catalysts.

Glass transition in thin supported polystyrene films probed by temperature-modulated ellipsometry in vacuum

Glass transition in thin (1-200 nm thick) spin-cast polystyrene films on silicon surfaces is probed by ellipsometry in a controlled vacuum environment. A temperature-modulated modification of the method is used alongside a traditional linear temperature scan. A clear glass transition is detected in films with thicknesses as low as 1-2 nm. The glass transition temperature (T(g)) shows no substantial dependence on thickness for coatings greater than 20 nm. Thinner films demonstrate moderate T(g) depression achieving 18 K for thicknesses 4-7 nm. Less than 4 nm thick samples are excluded from the T(g) comparison due to significant thickness nonuniformity (surface roughness). The transition in 10-20 nm thick films demonstrates excessive broadening. For some samples, the broadened transition is clearly resolved into two separate transitions. The thickness dependence of the glass transition can be well described by a simple 2-layer model. It is also shown that T(g) depression in 5 nm thick films is not sensitive to a wide range of experimental factors including molecular weight characteristics of the polymer, specifications of solvent used for spin casting, substrate composition, and pretreatment of the substrate surface.

Conditions of synthesis and properties of dimethacrylate derivatives containing a fragment of a dimerized fatty acid

A series of dimethacrylate esters of a dimerized fatty acid were prepared. The dependence of their formation rate on the kind of the glycol used was examined. The correlation between the molecular-weight characteristics of the esters and their synthesis conditions is discussed.

Synthesis, post-modification and characterization of linear polystyrene-based supports for interaction with immobilized biocatalysts

A series of linear polystyrene-based supports has been synthesized using conventional or controlled (reversible addition fragmentation chain transfer or nitroxide-mediated) free radical polymerizations, in order to modulate their molecular weight characteristics. Polymer post-modification via esterification of the primary hydroxyl alcohol functionalities, pendant from the polymer backbone, with a mandelic acid derivative introduces efficiently (>85% yield) racemic, enzyme-cleavable moieties. A study of the interactions of these polymeric substrates with immobilized penicillin G acylase, in mixed organic/aqueous buffer solvent systems, results in a modest enantioselectivity (comparable with that of racemic mandelic acid methyl ester), but reveals that the biocatalytically active moieties on the linear polymers can be cleaved with first-order rate kinetics, as observed with small molecules in solution; the reaction rates (which can differ by more than one order of magnitude) are influenced both by the synthetic polymer length and by the polymer structure resulting from the method of polymerization used. Copyright © 2012 Society of Chemical Industry

Influence of Processing Methods on the Structure and Properties of Composite Polymeric Materials

The results of investigating the influence of processing methods on the structure and properties of composite polymeric materials are given. It has been established that the defectiveness of the structure of highly filled composite polymeric materials is closely tied with the inhomogeneity of the molecular weight characteristics of the polymer and with the non-uniformity of distribution of the filler particles in morphological zones of the article, and may be attributed to the difference in the moulding conditions of the material in the mould cross-section.

Glycerine and levulinic acid: Renewable co-substrates for the fermentative synthesis of short-chain poly(hydroxyalkanoate) biopolymers

Glycerine (a biodiesel co-product) and levulinic acid (a pulp and paper co-product) were used as co-substrates for the fermentative synthesis of short-chain polyhydroxyalkanoate (sc-PHA) biopolymers with tunable monomer and molecular weight characteristics. Pseudomonas oleovorans NRRL B-14682 utilized glycerine alone to produce poly(3-hydroxybutyrate) (PHB). When levulinic acid was added to the media at shake-flask scale in concentrations ⩽0.6wt.%, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB/V) copolymers were produced with 3-HV contents ranging from 37 to 97mol%; a glycerine:levulinic acid ratio of 0.2%:0.8% (w/v) resulted in poly(3-hydroxyvalerate) (PHV). Ten-liter batch fermentations using glycerine:levulinic acid ratios of 1%:0, 0.75%:0.25%, 0.5%:0.5% and 0.25%:0.75% (w/v) resulted in PHB, P(73%-3HB-co-27%-3HV), P(30%-3HB-co-70%-3HV) and PHV with increasing number average molecular weights (×103g/mol) of 328, 511, 728 and 1330, respectively, owing to glycerine-based chain termination. These results provide a novel means by which glycerine and levulinic acid can be used collectively to produce an array of distinct sc-PHA biopolymers.

β‐Glucans are involved in immune‐modulation of THP‐1 macrophages

We aimed to examine different immunological aspects of β-glucans derived from different food sources (oat, barley and shiitake) on phorbol myristate acetate (PMA)-differentiated THP-1 macrophages. Commercially purified barley β-glucan (commercial BG) and lentinan were included to compare β-glucans from the same origin but different degree of purity and processing. Chemical composition and molecular weight distribution of β-glucan samples were determined. Inflammation-related gene expression kinetics (IL-1β, IL-8, nuclear factor kappa B [NF-κB] and IL-10) after 3, 6 and 24 h of stimulation with 100 μg/mL β-glucan were investigated. All tested β-glucans mildly upregulated the observed inflammation-related genes with differential gene expression patterns. Similar gene expression kinetics, but different fold induction values, was found for the crude β-glucan extracts and their corresponding commercial forms. Pre-incubation of THP-1 macrophages with β-glucans prior to lipopolysaccharide (LPS) exposure decreased the induction of inflammation-related genes compared to LPS treatment. No production of nitric oxide (NO) and hydrogen peroxide (H₂O₂) was detected in β-glucan stimulated THP-1 macrophages. Phagocytic activity was not different after stimulation by β-glucan samples. Based on these in vitro analyses, it can be concluded that the analysed β-glucans have varying levels of immunomodulating properties, which are likely related to structure, molecular weight and compositional characteristic of β-glucan.

Star-shaped polymers with the fullerene C60 branching center

The anionic methods for the synthesis of homo- and heteroarm (hybrid) star-shaped polymers using fullerene C60 aPre considered. The possibilities of fullerene C60 as an agent of combination of living polymer chains and the procedures of transformation of polymer derivatives of C60 (hexaadducts) into polyfunctional macroinitiators of anionic polymerization of vinyl monomers are shown. The methods for functionalization of polymer fullerene derivatives and their combinations into structures of complex controlled architecture are presented. The structural features and initiating properties of the living polymer fullerene derivatives and their role in the formation of heteroarm star-shaped macromolecules with the controlled number of branches and predetermined molecular weight characteristics of the arms are discussed. The hydrodynamic properties of the star-shaped fullerene-containing polymers are considered. The data on the small-angle neutron scattering study of self-organization of the stars in solutions are presented.

Effect of monomer/nanoclay interaction on the kinetics of atom transfer radical homo- and copolymerization of styrene and methyl acrylate

Atom transfer radical homo- and copolymerization of styrene and methyl acrylate initiated with CCl3-terminated poly(vinyl acetate) macroinitiator were performed at 90°C in the presence of nanoclay (Cloisite 30B). Controlled molecular weight characteristics of the reaction products were confirmed by GPC. It was shown that nanoclay slightly decreased the rate of styrene polymerization, while it significantly enhanced the rate of methyl acrylate polymerization and its copolymerization with styrene. The reactivity ratios of the monomers in the presence and in the absence of nanoclay were calculated (rSt = 1.002 ± 0.044, rMA = 0.161 ± 0.018 by extended Kelen-Tudos method and rSt = 1.001 ± 0.038, rMA = 0.163 ± 0.016 by Mao-Huglin method), confirming that the presence of nanoclay has no influence on monomer reactivity. The enhancement in the homopolymerization rate of methyl acrylate as well as its copolymerization rate with styrene was attributed to nanoclay effect on the dynamic equilibrium between active (macro)radicals and dormant species. Dipole moments of the monomers were successfully used to predict structure of the polymer/clay nanocomposites prepared via in situ polymerization.

Synthesis and Study of Copolymers of Methyl Pheophorbide a and its CuII Complexes with Methyl Methacrylate

We studied radical polymerization in methyl methacrylate solution with methyl pheophorbide a and its copper complex. We have shown the possibility of controlled synthesis of copolymers with controllable molecular weight characteristics when reaction medium parameters are varied. We have established that the composition of copolymers depends on the comonomer content of the original reaction medium, on the yield and influence of the metal in the porphyrin coordination centre on copolymer properties.

Propylene polymerization using supported Ziegler–Natta catalyst systems with mixed donors

AbstractMagnesium dichloride supported titanium catalyst incorporated with varying concentration of ethylbenzoate and diisobutyl phthalate together as internal donor are synthesized. The synthesized catalysts are characterized and compared with respect to composition, phase characteristics, crystallite size, and particle morphology. Performance of catalysts containing mixed donors is compared with the conventional single donor‐based catalysts. The polymerization studies of the catalysts for propylene polymerization show dependence of polymerization kinetics on relative concentration of diisobutyl phthalate and ethylbenzoate. Molecular weight characteristics of polypropylene obtained from these catalysts are studied and correlated with the nature and concentration of donors present in the catalyst. Morphology replication from catalyst precursor to polymer is observed irrespective of the nature of donor being incorporated in the synthesized catalyst. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Efficient catalytic systems based on paramagnetic closo-ruthenacarboranes for the controlled synthesis of polymers

Novel catalytic systems were proposed for controlled radical polymerization of vinyl monomers. These systems are based on the paramagnetic (17-electron) closo-complex, namely, 3,3-(dppb)-3-Cl-closo-3,1,2-RuC2B9H11 (1, dppb is 1,4-bis(diphenylphosphino)butane) and its mono(P-phenylene)- and di(P,P-ortho-phenylene)cycloboronated derivatives, namely, (R = H, n = 10 (2); R = Me, n = 8 (3)) and (4). With the polymerization of methyl methacrylate as an example, the effect of the steric hindrances in complexes 1–4 on the synthesis and molecular-weight characteristics of the resulting polymers was analyzed. In the presence of aliphatic amines, the polymerization rate increases substantially and the catalyst concentration can be lowered without losing control of the process. The structure of 17-electron complex 3 in the solid state and its paramagnetic nature were confirmed by X-ray diffraction and ESR spectroscopy.

Mycoplasma genitalium: A comparative genomics study of metabolic pathways for the identification of drug and vaccine targets

Increasing emergence of antibiotic-resistant pathogenic microorganisms is one of the biggest challenges for biomedical research and drug development. Traditional drug discovery methods are time-consuming, expensive and often yield few drug targets. In contrast, advances in complete genome sequencing, bioinformatics and cheminformatics represent an attractive alternative approach to identify drug targets worthy of experimental follow-up. Mycoplasma genitalium is a human parasitic pathogen that is associated with several sexually transmitted diseases. Recently, emergence of treatment-resistant isolates has been reported, which raises serious concern and a need for identification of additional drug targets. In the present study, a systematic workflow consisting of comparative genomics, metabolic pathways analysis and additional drug prioritizing parameters was defined for the identification of novel drug and vaccine targets that are essential for M. genitalium, but absent in its human host. In silico analyses and manual mining identified 79 proteins of M. genitalium, which showed no similarity to human proteins. Among these, 67 proteins were identified as non-homologous essential proteins that could serve as potential drug and vaccine targets. Subcellular localization, molecular weight, and three-dimensional structural characteristics that could facilitate filtering of attractive drug targets were also calculated for the non-homologous essential proteins. Enzymes from thiamine biosynthesis, protein biosynthesis, and folate biosynthesis were identified as attractive candidates for drug development. Furthermore, druggability of each of the identified drug targets was also evaluated by the DrugBank database. Results from this study could facilitate selection of M. genitalium proteins for entry into drug design and vaccine production pipelines.

Solution and melt viscoelastic properties of controlled microstructure poly(lactide)

A series of controlled microstructure poly(lactide) (PLA) samples were synthesized using a novel chiral dinuclear indium catalyst capable of living polymerization of lactide. PLAs with different ratios of L- to D- monomer ratios of 100:0, 90:10, 75:25, 50:50, and 0:100 were investigated. The relationship between intrinsic viscosity and the absolute molar mass distribution of the samples obtained by light scattering gel permeation chromatography in tetrahydrofuran gives [η] = 0.014 + 0.75 Mw, a scaling law of typical coil dimensions of linear macromolecules in good solvent. The melt rheological study includes determination of zero-shear viscosity and its relationship with the molecular weight, the relaxation spectrum, and its relation with molecular weight characteristics, as well as plateau modulus and other important rheological parameters that are helpful in predicting the linear viscoelasticity of PLA. Emphasis is placed on the uniaxial melt behavior of these polymers. At low temperatures, significant strain hardening is observed, which gradually disappears with an increase in temperature and decrease of Hencky strain rate. The K-BKZ constitutive equation is used to model the experimental data. It is concluded that in spite of their linear structure, PLAs exhibit strain hardening which is not due to strain-induced crystallization, and it is solely due to the dynamics of molecular relaxation.

Investigating the Effect of Extrusion Processing of Polyethylenes on their Molecular Weight and Physicomechanical Characteristics

An investigation was made of the process of extrusion processing of linear low-density polyethylene (LLDPE) (CEB-1 and CEH-1) and high-density polyethylene (HDPE) with the aim of studying the effect of a change in their fractional composition on the properties of articles.

One-step synthesis of alkyd resins in the presence of new sulfonated cation-exchange (nano)catalysts

A method for the one-step synthesis of alkyd resins based on glycerol, phthalic anhydride, and vegetable oils using new sulfonated cation-exchangers and Ti-containing metal-polymer nanocomposites as catalysts has been developed. The film-forming properties, composition, structure and molecular weight characteristics of the synthesized resins have been studied by IR, NMR spectroscopy, and gel chromatography. The possibilities of regulating the molecular-weight distribution of the obtained alkyd resins depending on the nature of the catalyst and the reaction conditions have been revealed.

Design and Synthesis of Monofunctionalized, Water-Soluble Conjugated Polymers for Biosensing and Imaging Applications

Water-soluble conjugated polymers with controlled molecular weight characteristics, absence of ionic groups, high emission quantum yields, and end groups capable of selective reactions of wide scope are desirable for improving their performance in various applications and, in particular, fluorescent biosensor schemes. The synthesis of such a structure is described herein. 2-Bromo-7-iodofluorene with octakis(ethylene glycol) monomethyl ether chains at the 9,9'-positions, i.e., compound 4, was prepared as the reactive premonomer. A high-yielding synthesis of the organometallic initiator (dppe)Ni(Ph)Br (dppe = 1,2-bis(diphenylphosphino)ethane) was designed and implemented, and the resulting product was characterized by single-crystal X-ray diffraction techniques. Polymerization of 4 by (dppe)Ni(Ph)Br can be carried out in less than 30 s, affording excellent control over the average molecular weight and polydispersity of the product. Quenching of the polymerization with [2-(trimethylsilyl)ethynyl]magnesium bromide yields silylacetylene-terminated water-soluble poly(fluorene) with a photoluminescence quantum efficiency of 80%. Desilylation, followed by copper-catalyzed azide-alkyne cycloaddition reaction, yields a straightforward route to introduce a wide range of specific end group functionalities. Biotin was used as an example. The resulting biotinylated conjugated polymer binds to streptavidin and acts as a light-harvesting chromophore to optically amplify the emission of Alexa Fluor-488 chromophores bound onto the streptavidin. Furthermore, the biotin end group makes it possible to bind the polymer onto streptavidin-functionalized cross-linked agarose beads and thereby incorporate a large number of optically active segments.

Analysis of the molecular structure of ethylene hexene-1 copolymers produced over highly active supported Ziegler-Natta catalysts

The mechanical and rheological properties of ethylene α-olefin copolymers are governed by a molecular and supramolecular structure that depends on its molecular weight characteristics, comonomer concentration, and the uniformity of branching distributions for polymer chains with different molecular weights (compositional heterogeneity). Using state-of-the-art methods, we study the parameters of molecular weight distribution, molecular structure, and compositional heterogeneity of ethylene hexene-1 copolymers with different compositions, produced over highly active supported Ti-Mg and V-Mg Ziegler-Natta catalysts, and show the possibility of controlling these parameters to improve the quality of the resulting polymers.