Apparent Average Molecular Weight Research Articles

Responses of wastewater biofilms to chronic CeO2 nanoparticles exposure: Structural, physicochemical and microbial properties and potential mechanism

With the accelerated application of CeO2 nanoparticles (NPs), wastewater treatment plants will increasingly receive CeO2 NPs, thus inevitably causing CeO2 NPs to encounter microaggregates. Here, we comprehensively elucidate the responses in the structural, physicochemical and microbial properties of wastewater biofilms to chronic exposure (75 days) to different CeO2 NPs concentrations, with a particular emphasis on the protective mechanisms of stratified extracellular polymeric substances (EPSs). Chronic exposure to 0.1 mg/L CeO2 NPs boosted the content and broadened the distribution of α-d-glucopyranose polysaccharides (PS), while the sharply increased production and breadth of β-d-glucopyranose PS, forming a formidable shield, was a response to 10 mg/L CeO2 NPs. After the bacteria were exposed to CeO2 NPs, loosely bound EPSs (LB-EPSs) aggregated into macromolecules (increasing in apparent molecular weight (AMW)) but at a lower abundance, whereas the average AMW in tightly bound EPSs (TB-EPSs) decreased. The acetyl content and (α-helix+3-turn helix)/β-sheet value of TB-EPSs increased to resist CeO2 NPs. Furthermore, long-term exposure to CeO2 NPs decreased cell viability, reduced microbial diversity and shifted the microbial composition. N-acylated-l-homoserine lactone concentrations increased with increased density of Pseudomonas, which was associated with PS-regulated control, thus promoting PS production in EPSs in response to CeO2 NPs. These results expand the understanding of how microaggregates resist environmental stress caused by NPs.

Effect of precipitation time and solvent power on asphaltene characteristics

The kinetics of asphaltene precipitation is studied regarding the characterization of the precipitated material. The association of different components of the crude oil depends on the solvent power of the blend heptane/oil and produces aggregates with a variable composition that change as a function of time. It was found that the precipitate contains a significant amount of maltenes whose relative content decreases as a function of time. In agreement with this behavior, the precipitate becomes more hydrogen deficient. These changes also produced a significant increase in the apparent average molecular weight of the precipitate as measured using size exclusion chromatography. This increase correlated with the amount of asphaltenes in the precipitated material independently of time or heptane/oil ratio. Solubility profile measurements showed that the average characteristics of the asphaltenes found in the precipitate varied as a function of time. As more asphaltene molecules precipitated, the distributions of these molecules changed decreasing its average solubility parameter. Considerable differences in the amount collected at low and high heptane/oil ratios as a function of time were also found. Based on the measurements, a new model was developed that describes the complex aggregation behavior involved in asphaltene precipitation.

분자량 크기별 토양 휴믹산(HA)의 구조적 특성 및 페난트렌 흡착 반응특성 비교

A sample of soil humic acid (HA) was divided by ultrafiltration (UF) into five fractions of different molecular size (UF1: > 300, UF2: 100~300, UF3: 30~100, UF4: 10~30, UF5: 1~10 kilodaltons). Apparent average molecular weight (Mw) of the HA fractions were measured using high performance size exclusion chromatography (HPSEC), and the chemical and structural properties of the five HA fractions were characterized by elemental compositions (H/C, O/C and w ((2O + 3NH)/ C)) and ultraviolet-visible absorption ratios (SUVA, A4/6). The organic carbon normalized-sorption coefficients (Koc) for the binding of phenanthrene to the HA fractions were determined by fluorescence quenching and relationship between the sorption coefficients and structural characteristics of the HA fractions were investigated. The elemental analysis and UV-vis spectral data indicated that the HA fractions with higher molecular weights have grater aliphatic character and lower contents of oxygen, while the HA fractions with lower molecular size have greater aromatic character and molecular polarity that correspond to greater SUVA and internal oxidation values (w). The log Koc values (L/kg C) were gradual increased from 4.45 for UF5 to 4.87 for UF1. The correlation study between the structural descriptors of the HA fractions and log Koc values of phenanthrene show that the magnitude of Koc values positively correlated with and H/C, while negatively correlated with the independent descriptors of the O/C, w, SUVA and A4/6.

Composition and physicochemical properties of Zedo gum exudates from Amygdalus scoparia

Composition and physicochemical properties of three types of Zedo gum exudates from Amygdalus scoparia were investigated. Monosaccharide analysis by GC–MS indicated the occurrence of arabinose and galactose as the main sugars. FTIR spectra showed no differences in functional groups among the samples. Steady shear rheological data and power law parameters revealed that the white gum (W) was the most shear sensitive type and had the highest value of consistency coefficient. The mechanical spectra derived from the strain and frequency sweep measurements indicated a liquid viscoelastic behavior for Zedo gum dispersions. GPC–MALLS revealed that the white sample had the highest apparent average molecular weight (4.74×106Da) and the lowest dispersity (1.045). TG–DTA analysis showed that the character of gum decomposition significantly depended on the gum type and the white sample had the highest thermal stability.

Water-soluble carbohydrate compound from the bodies of Herba Cistanches: Isolation and its scavenging effect on free radical in skin

A polysaccharide was isolated from the Herba Cistanches. This polysaccharides contained glucose, galactose, rhamnose, arabinose and fructose. The native polysaccharide could be fractionated by size exclusion chromatography into one major fraction. The apparent average molecular weight of the purified polysaccharide was estimated to be approximately 385 kDa by size-exclusion HPLC. Furthermore, this polysaccharides still exhibited strong antioxidant activities in aged rats’ skin. Namely, Herba Cistanches polysaccharides inhibited the oxidative modification of lipids, thus protecting cells from injury by the oxidized molecules in aged rats’ skin. The present results were in accordance with previous studies on the mode of the protective effect of the plant extract which showed positively that the protection may possibly be attributed to the combination of more than one biological activities and that the use of antioxidants might be an useful approach in the treatment of some skin aging diseases.

Long term case study of MIEX pre-treatment in drinking water; understanding NOM removal

Removal of natural organic matter (NOM) is a key requirement to improve drinking water quality. This study compared the removal of NOM with, and without, the patented magnetic ion exchange process for removal of dissolved organic carbon (MIEX DOC) as a pre-treatment to microfiltration or conventional coagulation treatment over a 2 year period. A range of techniques were used to characterise the NOM of the raw and treated waters. MIEX pre-treatment produced water with lower concentration of dissolved organic carbon (DOC) and lower specific UV absorbance (SUVA). The processes incorporating MIEX also produced more consistent water quality and were less affected by changes in the concentration and character of the raw water DOC. The very hydrophobic acid fraction (VHA) was the dominant NOM component in the raw water and was best removed by MIEX pre-treatment, regardless of the raw water VHA concentration. MIEX pre-treatment also produced water with lower weight average apparent molecular weight (AMW) and with the greatest reduction in complexity and range of NOM. A strong correlation was found between the VHA content and weight average AMW confirming that the VHA fraction was a major component of the NOM for both the raw water and treated waters.

Compatibility analysis of pectin at different esterification degree from intrinsic viscosity data of diluted ternary solutions

This paper aims to set-up a compatibility criterion for couple of pectins at different degree of methoxylation (DM) based on specific viscosity data, slightly modifying a criterion already proposed in the field of synthetic polymers. Four different commercial pectins were preliminarily characterised by using dilute solution viscosity measurements and molecular weight was calculated from intrinsic viscosity data. Four ternary dilute solutions of pectin at different DM, were also investigated and two compatibility criteria, based on viscosity data, were applied. Data revealed that positive molecular interactions take place when pectins in solution have a different DM (i.e. HM/LM mixtures), whilst an incompatible behaviour was found for similar pectin in solution (i.e. both HM or LM). In addition, in the case of incompatible pairs of pectin, also the apparent average molecular weight of mixed pectin, obtained by measurements carried out on ternary solutions, showed an increase with respect to the additive mixing rule, owing to repulsive forces. On the contrary, owing to attractive forces in case of compatible pectin pairs, the apparent molecular weight is lower than the calculated average.

Components and Antioxidant Activity of the Polysaccharide from Streptomyces virginia H03

A polysaccharide was isolated from the broth of cultured Streptomyces virginia H03 which was treated by ethanol deposition and savage method to remove the protein, and was purified using Sephadex G-150 column chromatography. The components of the polysaccharide were determined by gas chromatography. The purified polysaccharide was made up of mannose, glucose and galactose, in a 2:1:1 proportion. Its average apparent molecular weight was 3.76 x 10(4) Da which was determined by gel permeation chromatography. In addition, several antioxidant assays were adopted to investigate the antioxidant activity of the polysaccharide in vitro. The results indicated that the purified polysaccharide showed significant antioxidant activity against superoxide anion, hydrogen peroxide and 1,1-diphenyl-2-picrylhydrazyl radical, and lipid peroxidation as with standard antioxidants such as vitamin C. Furthermore, the polysaccharide had a better heat stability than vitamin C, which suggested that the polysaccharide might be a potent useful antioxidant.

Relationship between the network morphology and properties of commercial vinyl ester resins

AbstractTwo commercial vinyl ester resins, Derakane 411‐350 (resin D) and Derakane 411‐350 Momentum (resin M), were characterized. Despite the large quantity of publications in the literature about vinyl ester resins, few experimental results have been reported for resin M. The effect of the styrene content on the mechanical properties and morphological structure was studied. An increase in the styrene content produced a network with a low storage modulus in the rubber state and a glass‐transition temperature. The apparent average molecular weight between crosslink points and glass‐transition temperature were slightly higher for resin D than for resin M. The Fourier transform infrared spectra and molecular weight distributions were similar. However, resin M was tougher than resin D, and this may have been due to the closer structure in the fully cured state. Atomic force microscopy was performed for each cured resin and confirmed the difference in the nanostructures. The main reason for the differences in the developed structures was the use of an accelerator, which influenced the final morphology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3895–3903, 2006

Thermosensitive noncovalently bonded block copolymerlike micelles from interpolymer complexes

AbstractInterpolymer complexes between polystyrene‐b‐poly(2‐vinylpyridine), (PS‐P2VP), and poly(methacrylic acid) (PMAA), have been studied in dioxane. Dioxane is a good solvent for PS‐P2VP copolymers but it is a nonsolvent for PMAA at room temperature. In this way noncovalent bonded micelles are formed after mixing the solutions of the polymers at 60 °C and then allowing them to cool at room temperature. Static and dynamic light scattering as well as viscosity measurements have been used to study the dependence of aggregate mass and size as a function of the molar ratio of functional groups in PS‐P2VP/PMAA mixtures, as well as temperature. Plots of apparent average molecular weight and hydrodynamic radius of the aggregates versus amine to carboxyl group ratio show a maximum at a ratio close to one. The size of the aggregates decreases at higher ratios because of the formation of more stable micelles with smaller cores. In all cases rather compact structures were formed, as evidenced by viscometry. The mass of the aggregates was found to decrease by an increase in temperature while hydrodynamic radii were increased. This was attributed to the increase of the thermodynamic quality of the solvent toward PMAA as temperature increases. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6230–6237, 2004

Separation of soluble selenium compounds in different fish species

Sephacryl S-100 was used for systematic studies on soluble selenocompounds in fish. Commonly-eaten species (mackerel, herring, salmon, rainbow trout, eel, cod, plaice, turbot, flounder and dab) were investigated. The mackerel, herring and the flat fish species contained 0.262–0.498 μg Se/g wet weight whereof 23–34% was soluble. Gel chromatography showed that cod, salmon, rainbow trout and eel had most of the soluble selenium (76–88%) in the high-molecular-weight range (>10 kDa). For mackerel and herring, about half of the selenium eluted in the high-molecular-weight range and half in the low-molecular-weight range. All flat fish species contained large amounts of low-molecular-weight selenocompounds with an average apparent molecular weight of 2 kDa. This study shows that there are large differences in selenium distribution among fish species.

Dispersion copolymerization of polyoxyethylene macronomer and styrene 4. Solution properties of polystyrene-graft-polyoxyethylene copolymers

The graft copolymers (polystyrene-graft-polyoxyethylene) (PSt-graft-PEO) were prepared by the radical dispersion copolymerization of methacryloyl (MA)-terminated PEO macromonomer and styrene. By means of size-exclusion chromatography, liquid chromatography at the critical adsorption point, and light scattering, the molecular weight parameters and the solution properties of PSt-graft-PEO were investigated. The apparent average molecular weight and the molecular weight distribution (MWD) of graft copolymers were found to decrease with increasing molecular weight of PEO-MA macromonomer. This decreased molecular weight was attributed to the chain transfer to PEO unit and increased contribution of the solution polymerization. The broad MWD varied with the ratio of the polymerization in the continuous phase and the polymer particles. The number of PEO grafts per PSt backbone decreased with increasing molecular weight of the PSt-graft-PEO copolymer, which was attributed to the intramolecular association of PEO segments. The intrinsic viscosity or the coil size of graft copolymer molecules varied with temperature as a result of the dehydration of PEO segments. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3087–3097, 1999

Depolymerization of the Glutenin Macropolymer During Dough Mixing: I. Changes in Levels, Molecular Weight Distribution, and Overall Composition

ABSTRACTChanges in the amounts, molecular weight distributions, and levels of major groups of subunits in the glutenin macropolymer (GMP) of doughs during mixing were investigated. The GMP (gel protein) is the unreduced fraction of gluten protein that remains as a layer on top of the starch after extraction of SDS‐soluble proteins and centrifugation. Experiments involved doughs prepared from flours derived from one weak and one strong cultivar and lines derived from cv. Olympic that were null for specific high molecular weight glutenin subunits (HMW‐GS). During mixing, the amount of GMP decreased; the major changes occurred before peak mixing time (MT, achievement of peak resistance). In addition, the average apparent molecular weight of GMP (determined by both size‐exclusion HPLC and multilayer gel electrophoresis) decreased during mixing, but in this case, the major changes were seen later in the mixing process, during dough breakdown. Even after extensive mixing, polymers and oligomers were released, not free glutenin subunits. During dough breakdown, the composition of GMP also changed, such that the proportion of HMW‐GS decreased but β‐amylases/D low molecular weight glutenin subunits (LMW‐GS) increased. Changes in the total amounts of other LMW‐GS typically were smaller with a decrease in the proportion of B subunits and an increase in the proportion of C subunits. The major changes in GMP composition were observed after peak MT (peak resistance) occurring earlier and to a greater extent in the weaker dough. Our results suggest that dough breakdown during mixing may be triggered by loss of HMW‐GS, leading to changes in the molecular weight distribution and composition of the disulfide‐bonded GMP.

Structure and mucoadhesion of mussel glue protein in dilute solution.

Purified mussel adhesive protein mefp-1 (Mytilus edulis foot protein 1) has been studied regarding its state of oligomerization and gross conformation in dilute solution. Sedimentation equilibrium in the analytical ultracentrifuge of a dilute solution of protein (0.4 mg/mL) in acetate buffer at pH 4.5 and I = 0.10 M yielded an apparent molecular weight (whole distribution weight average, Mw, app) of 114 000 +/- 5000 via the "M" procedure, a value in almost exact agreement with the monomeric molecular weight obtained by MALDI mass spectrometry. At this low concentration, it is reasonable to assume thermodynamic ideality, i.e., Mw,app approximately Mw. This result, together with plots of point weight average apparent molecular weight versus concentration for three different loading concentrations (0.4, 0.8, 1.0 mg/mL), clearly demonstrates that this protein is essentially monomeric in dilute solution. Sedimentation velocity experiments yielded an estimate of the sedimentation coefficient s020,w = 2.34 +/- 0.17 S, which for M = 110 000 gives a frictional ratio f/f0 = 3.2 +/- 0.3. The interpretation of this, in terms of an extended rather than globular conformation for the structure of mefp-1 in dilute solution, is considered, within plausible limits of molecular hydration, and models for the structure in solution are considered, in light of the thermodynamic nonideality behavior of these molecules and previously published circular dichroism data. The significance of these observations in terms of the bioadhesive properties of mefp-1 is described, and the very strong interaction in dilute solution with a mucin glycoprotein is demonstrated.

Vegetable-oil-based printing ink formulation and degradation

Printing ink vehicles that did not require petroleum components were prepared from modified vegetable oil. The apparent average molecular weight ( M W ) of vehicles made from representative vegetable oils, such as soybean, sunflower, cottonseed, safflower and canola oils were compared by gel permeation chromatography (GPC), and a correlation between viscosity and apparent M W of these vehicles was established. Physical properties of the formulated inks meet or exceed the industry standards for lithographic and letterpress newsprint applications. Elimination of petroleum-based resin and reduced pigment requirements, due to the light vehicle color, should provide a competitively priced alternative to petroleum-based inks. These ink vehicles along with the commercial ones were subjected to biodegradation. Results show that the vegetable-oil vehicles degrade faster and more completely than commercial soy- or mineral-oil-based vehicles. Fermentations were allowed to proceed for 5, 12 and 25 days. Both mono- and mixed cultures of microorganisms, which are commonly found in soil, were used. Greater increase in biodegradation with time was observed for our vehicles than the commercial vehicles. In 25 days, commercial mineral-oil-based vehicles degrade 17–27%, while commercial partial soy-oil-based vehicles degrade 58–68% and our 100% soy-oil-based vehicles degrade 82–92%.

Study of radical methyl methacrylate-methacrylic acid copolymerization in isopropyl alcohol by dynamic laser scattering and 13C-NMR spectroscopy

The copolymerization of methyl methacrylate and methacrylic acid in isopropyl alcohol is studied by kinetic, dynamic laser scattering and 13C-NMR methods. Correlations are established between the dependence of the copolymerization rate, the apparent average molecular weight, the diffusion coefficients and the configurational triad composition on the monomer feed. These correlations and the fact that both copolymerization constants are smaller than unity ( r MMA = 0.63 ± 0.03; r MA = 0.25 ± 0.05) are in good agreement with the assumption that a comonomer complex takes part in the propagation reaction. A new Markov chain method for the estimation of the configurational triad mole fraction which accounts for the complex participation in a macromolecule formation is developed. Qualitative criteria for evidence the participation of the comonomer complex in copolymerization are proposed using experimental and terminal model calculated mole fractions of the compositional triads and diads.

Isolation and partial characterization of a novel β- d-galactan sulfate from the brown seaweed Laminaria angustata var. longissima

The fastest-moving component (LA-5) on electrophoresis was isolated from a sulfated polysaccharide fraction of the brown seaweed Laminaria angustata var. longissima by anion-exchange chromatography, fractional precipitation with ethanol, and gel filtration. LA-5 consisted of galactose, fucose, glucuronic acid and sulfate (100:2:3:74) and had an apparent average molecular weight of 400 000. The results of enzymatic digestion, optical rotation and 13C-NMR suggested that galactose is present predominantly as the β- d-form in LA-5. By IR, 13C-NMR and methylation analyses, LA-5 has been shown to have a backbone of →3)-β- d-galactosyl-(1→6)-β- d-galactosyl-(1→. Most sulfate groups may be attached to position 6 of 3-linked galactosyl residues. This indicates that the polysaccharide is a new type of galactan sulfate different from the well known galactans from red seaweeds and ascidians. This is the first report on the presence of galactan sulfate in the brown seaweeds.

Inhibition of basal and calmodulin-activated Ca2+-pump ATPase by fractionated compound [formula omitted

Compound 4880 (4880), a mixture of polycationic compounds was fractionated using affinity chromatography on calmodulin-Sepharose. Unfractionated 4880 and various fractions were tested for their potential inhibitory effects on ATPase activities of isolated human red blood cell membranes. ATPase activities tested included: Mg2+-ATPase, the Na+/K+-pump ATPase, and the Ca2+-pump ATPase in both its basal (calmodulin-independent) and calmodulin-activated state. Neither 4880 nor its various fractions were very potent or efficacious inhibitors of the Mg2+-ATPase or the Na+/K+-pump ATPase. In agreement with previous reports, 4880 was found to be an inhinitor of the calmodulin-activated Ca2+-pump ATPase. By contrast, we found that unfractionaed, as well as some fractionated, material inhibited both the basal (calmodulin-independent) and calmodulin-activated Ca2+-pump ATPase activity. A fraction designated as Fraction III bound to calmodulin-Sepharose in the presence of Ca2+ and low salt and was eluted in the absence of Ca2+ and 0.15 M NaCl. By gel filtration, Fraction III had an apparent average molecular weight of 2064 (1320 for unfractionated material). Fraction III was the most potent inhibitor of the Ca2+-pump ATPase with IC50 values for the basal and calmodulin-activated forms of the enzyme of 0.6 and 1.2 μg/ml, respectively. Inhibition by Fraction III was cooperative with n apparent values of 2.4 and 5.7, respectively, for the basal and calmodulin-activated forms of the enzyme. Thus, binding of 4880 constituents to calmodulin can not fully account for the observed data. Direct interaction of 4880 constituent(s) with the enzyme and/or the lipid portion of the membrane is suggested.

BAND SPREADING MODELING AND CORRECTION IN SIZE EXCLUSION CHROMATOGRAPHY PART I LINEAR CHROMATOGRAPHY THEORY AND THE PREDICTION OF THE SHAPE OF SINGLE COMPONENT CHROMATOGRAMS

A modified form of Tung's integral equation allows the variance M 2p of the observed polymer chromatogram to be expanded as the sum of the main contribution due to molecular weight distribution plus the band spreading contribution μ2 (the variance of a single component chromatogram being eluted, at the same average elution volume) and a series of correction terms negligible for narrow molecular weight distribution. A model of the chromatographic separation taking into account hydrodynamical and diffusional spreading effects in each of the different columns in the apparatus leads to a Van Deemter's relationship relating μ2 to solvent flowrate. The coupling of the two above quoted relationships was used to exploit experimental measurements of M 2p for anionically polymerized polystyrene samples vs. solvent flowrate in a set of 3 μ-styragel R columns having nominal pores sizes 103, 104 and 105 Å. These measurements, as well as previous work (where methods of treatment of data are discussed) were used to bring information on polymer intraparticle diffusion. Simulation based studies were undertaken in order to arrive at a simplified representation of chromatographic peak shape. Peak skewing in ordinary conditions was shown to be small. This explains that no appreciable error is made when using Hamielec and Ray's original formulae for correcting apparent (band spreading distorted) average molecular weights, although these formulae assume single component peaks to be gaussian, which is not correct.

Covalent cross-linking of the active sites of vesicle-bound cytochrome b5 and NADH-cytochrome b5 reductase.

A water-soluble carbodiimide has been used to promote the formation of amide bonds between carboxyl residues on cytochrome b5 and lysyl residues on cytochrome b5 reductase. The visible and UV absorption spectrum of the purified cross-linked complex was identical with the sum of the spectra of the individual enzymes, and the average apparent molecular weight of the complex, determined by sodium dodecyl sulfate-gel electrophoresis, was within 12% of the sum of the apparent molecular weights of the two monomeric enzymes, indicating that the cross-linked derivative was a dimer containing one molecule each of cytochrome b5 and cytochrome b5 reductase. When reconstituted into phospholipid vesicles, the amphipathic derivative showed substantially reduced Vmax values with the soluble electron acceptors potassium ferricyanide, cytochrome b5 heme peptide and cytochrome c, and with the membrane-bound acceptors amphipathic cytochrome b5 and stearyl-CoA desaturase. The soluble catalytic fragment of the derivative, produced by limited digestion with subtilisin Carlsberg, showed similar decreases in Vmax values with the above soluble acceptors. In contrast, intradimer electron transfer in the soluble fragment, measured by stopped flow spectrophotometry at 2 degrees C was very efficient. Ninety per cent of the cytochrome b5 in the derivative was reduced with a first order rate constant of 51 s-1 upon the addition of NADH; the transfer of electrons from NADH to the reductase FAD prosthetic group, which is known to be the rate-limiting step in the reductase reaction mechanism, proceeded with an apparent rate constant of 57 s-1 under these conditions. These kinetic data show that the enzymes in the complex are cross-linked together at the surfaces involved in protein-protein contacts during electron transfer in an orientation similar to that assumed during electron transfer between the free proteins.