Measurement Of Molecular Weight Distribution Research Articles

Insight into Antioxidant Activity and Peptide Profile of Jinhua Ham Broth Peptides at Different Cooking Times.

This present study aimed to investigate the effects of various cooking times (1 h, 1.5 h, 2 h, 2.5 h, named as JHBP-1, JHBP-1.5, JHBP-2, JHBP-2.5) on the antioxidant activity and peptide profile of Jinhua ham broth peptides (JHBP). The peptides extracted from uncooked ham were used as an uncooked group with the name of JHBP-0. The results revealed that the antioxidant efficacy in the four cooked groups changed dramatically compared to JHBP-0. After cooking, the DPPH radical scavenging activity, hydroxyl radical scavenging activity and superoxide anion radical scavenging activity decreased, except for the Fe2+ chelation and ABTS+ scavenging capacity which increased significantly. However, the cooked groups still showed a strong antioxidant capacity. In particular, the superoxide anion radical scavenging ability and the Fe2+ chelation action were significantly stronger compared to glutathione (GSH) and butylated hydroxytoluene (BHT) (p < 0.05). JHBP-1.5 also displayed stronger antioxidant capacity than the other three cooked groups, and its secondary structure and mass distribution changed significantly after cooking, specifically with an increased proportion of helix and <1 kDa peptides. Moreover, the constitution of free amino acids (FAAs) and the types of peptides released in the broth increased significantly with a longer cooking time. In total, 1306 (JHBP-0), 1352 (JHBP-1), 1431 (JHBP-1.5), 1500 (JHBP-2), and 1556 (JHBP-2.5) peptide sequences were detected using LC-MC/MC. The proportion of <1 kDa peptides also gradually increased as the cooking time extended, which is consistent with the molecular weight distribution measurements.

The dough-strengthening and spore-sterilizing effects of mannosylerythritol lipid-A in frozen dough and its application in bread making

Biosurfactants have been put into applications in breadmaking industry, while the effects of mannosylerythritol lipid-A (MEL-A) on gluten network of frozen dough, bread quality and microbial spoilage were firstly investigated in this study. Rheology and differential scanning calorimetry (DSC) analysis showed that MEL-A significantly improved the rheological properties of frozen dough and reduced the content of frozen water. Further experiments showed that MEL-A promoted the formation of aggregates by interacting with gluten protein, and strengthened the gluten network through molecular weight distribution measurement and microstructure observation, effectively avoiding the destruction of ice crystals. A series of bread assessments illustrated MEL-A improved the loaf volume, gas retention ability and textural property. In addition, MEL-A (1.5%) killed 99.97% of the vegetative cells of Bacillus cereus and 75.54% of the spores, and at the same time had a slight inactivation effect on yeast. These results indicate that MEL-A has broad application prospects in the baking industry and the storage stage of flour products.

Optimization of the heterogeneous electro-Fenton process assisted by scrap zero-valent iron for treating textile wastewater: Assessment of toxicity and biodegradability

In this work, the heterogeneous electro-Fenton process assisted by scrap zero-valent iron (SZVI) and with graphite electrodes (as anode and cathode) is studied as an alternative way to treat wastewater from a textile plant located in Medellín, Colombia. The effects of the initial pH, SZVI load, and current density in the SZVI-assisted electro-oxidation process (EO/SZVI) are analyzed and optimized using multivariable regression models generated using the Box–Behnken experimental design and convex nonlinear optimization. The EO/SZVI process leads to maximum reductions of approximately 100%, 67%, and 59% in color, chemical oxygen demand (COD), total organic carbon (TOC), respectively, under the optimal operating conditions of pH of 3.5. Further, it leads to an SZVI concentration of 0.6 g/L, and a current density of 20 mA/cm2 during 30 min of electrolysis. The post-process pollutants are characterized further using molecular weight distribution measurements, ultraviolet–visible spectroscopy, high-performance liquid chromatography, biodegradability, and toxicity. The results show that the treated effluent is polluted mostly by carboxylic acids of low molecular weight. A remarkable enhancement of the biodegradability of the effluent is evidenced by an increase in the BOD5/COD ratio (biodegradability index) from 0.15 to 0.54. Although the EO/SZVI process does not improve the toxicity (as measured by the mortality of Artemia salina), the latter is reduced subsequently from 100% to 20% through adsorption using activated carbon (AC). The findings of this study indicate that the EO/SZVI process is an effective and promising alternative for treating textile wastewater.

Using scrap zero valent iron to replace dissolved iron in the Fenton process for textile wastewater treatment: Optimization and assessment of toxicity and biodegradability

A Fenton like advanced oxidation process (AOP) employing scrap zerovalent iron (SZVI) and hydrogen peroxide (H2O2) was studied for industrial textile wastewater treatment from a textile manufacturing plant located at Medellín, Colombia (South America). The wastewater effluent studied contains a mixture of organic compounds resistant to conventional treatments. The effect of initial pH and SZVI concentration and H2O2 concentration were studied by a response surface methodology (RSM) Box-Behnken design of experiment (BBD). The combined SZVI/H2O2 process led to reductions of 95% color, 76% of chemical oxygen demand (COD) and 71% of total organic carbon (TOC) at optimal operating conditions of pH = 3, SZVI = 2000 mg/L and [H2O2] = 24.5 mM. Molecular weight distribution measurement (MWD), ultraviolet–visible (UV–Vis) spectroscopy, HPLC, biodegradability and toxicity were used to characterize the pollutants after the treatment process finding that the resulting effluent was polluted mostly by low molecular weight carboxylic acids. A remarkable biodegradability enhancement of the effluent was evidenced by a BOD5/COD ratio increase from 0.22 to 0.4; also, the SZVI/H2O2 process successfully reduced the toxicity from 60% to 20% of dead A. Salina crustaceans.

Synovial fluid microrheology to identify potential candidates for viscosupplementation

Purpose: Hyaluronic acid (HA) is a large, hydrophilic glycosaminoglycan that functions as the primary viscous lubricant in synovial fluid. Studies suggest that HA can be decreased, increased, or unchanged in concentration and/or molecular weight (MW) distribution in osteoarthritis (OA). Although HA viscosupplementation can be used to treat OA-related pain, it is difficult to predict which patients will respond best to HA supplementation. One potential explanation for the variable clinical response to HA is the presence of distinct OA phenotypes, some of which may benefit from HA supplementation whereas others may not. Here, we first asked whether HA concentration and MW distribution were altered in naturally occurring equine carpal osteoarthritis as a model for naturally occurring OA in humans. Multiple particle-tracking microrheology (MPTM) was performed to determine whether viscosity correlated with HA concentration and/or molecular weight. Methods: All protocols were approved by the university IACUC. Synovial fluid sampling: Synovial fluid samples were obtained from healthy research horses and clinical cases with carpal OA (n=87; 25 healthy and 62 OA joints). HA ELISA: Synovial fluid HA concentrations were quantified for all samples using both a sandwich ELISA (HA DuoSet ELISA, R&D Systems) and a competitive ELISA (HA ELISA, Echelon Biosciences). HA agarose gel electrophoresis: PBS-diluted and proteinase K-digested SF samples were run on 0.5% agarose gels, stained with 0.005% Stains-All and de-stained with 10% ethanol. Densitometric scans of stained gels were used to detect relative HA molecular weight distribution into four categories: >6.1MDa, 6.1-3.1MDa, 3.1-1.5MDa and <1.5MDa. Microrheology: Synovial fluid viscosity was measured using MPTM (n=24; 12 healthy and 12 OA joints). 15μl of synovial fluid was loaded with 0.5 nm yellow-green fluorescent beads and imaged on a custom epifluorescence microscope with a high-speed EMCCD detector. Statistical analysis: Data was log-transformation to achieve normality, and t-tests were used to compare healthy and OA groups. Pearson product-moment correlation coefficients were calculated. Results: Full cohort (n=87): Synovial fluid HA concentrations varied substantially between individual animals (range: 0.04 to 0.9 mg/mL, R&D Systems; 0.14 to 2.74 mg/mL, Echelon Biosciences), but did not differ between healthy and OA joints (median: 0.35 and 0.29 mg/mL, R&D Systems; 0.70 and 0.70 mg/mL, Echelon Biosciences, Fig. 1A). The proportion of high MW (>3.1MDa) to low MW (<3.1MDa) HA was significantly decreased in OA samples (median: 87% and 66%, p=0.009, Fig. 1B). MPTM cohort (n=24): Synovial fluid HA concentrations did not differ between healthy and OA joints. There was a trend for decreased synovial fluid viscosity in OA joints (median: 60 cP, IQR: 34-106) as compared to healthy joints (median: 120 cP, IQR: 68-263, p=0.07, Fig. 2A). HA concentration and viscosity were highly correlated (r=0.75, p<0.001, Fig. 2B). Conclusions: HA concentrations did not differ between healthy and OA joints due to significant inter-individual variability, suggesting that HA viscosupplementation may not be indicated in all OA cases. However, the trend for decreased synovial fluid viscosity in OA joints indicates that MPTM may be a more sensitive assay for detecting pathological changes in synovial fluid compared to measurements of HA total concentration or molecular weight distribution. HA concentration was a better predictor of synovial fluid viscosity than MW distribution. An inherent limitation of HA measurements is that neither HA ELISAs nor gel electrophoresis are able to measure the lowest MW HA isoforms. Multiple particle-tracking microrheology (MPTM) may hold potential promise as a method to identify joints that would be most likely to benefit from HA viscosupplementation. Additional work is needed to assess the rheologic and tribologic behavior of HA-deficient synovial fluid following HA supplementation.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Polymer extrudate-swell: From monodisperse melts to polydispersity and flow-induced reduction in monomer friction

This paper describes finite-element simulations and associated experimental studies of extrudate swell for near-monodisperse and polydisperse polystyrenes. The tube-model based Rolie-Poly constitutive model, when extended to include a reduction of monomeric friction at high extension rates, makes much-improved predictions of extrudate swell at high Weissenberg number. This is especially significant for near-monodisperse polymers where rheological features are unchanged by the effects of polydispersity. Extension of this molecular rheology scheme to a polydisperse constitutive model addresses extrusion experiments on polydisperse polystyrenes inside a multipass rheometer, accounting for experimental data up to Rouse Weissenberg numbers of 50. We, therefore, show that from a measurement of polymer molecular weight distribution, it is possible to predict extrudate swell over a broad range of processing conditions for polydisperse polymers and realistic extrusion processes. Small changes in the capillary length to diameter ratio have little effect on extrudate swell in this range of Weissenberg number. This is because the capillary residence time is sufficiently long for a steady state to be reached within the polymer stretch relaxation time, which controls the most decisive physics responsible for extrudate swell.

Conversion of calibration curves for accurate estimation of molecular weight averages and distributions of polyether polyols by conventional size exclusion chromatography

Accurate measurement of molecular weight averages (M¯n,M¯w,M¯z) and molecular weight distributions (MWD) of polyether polyols by conventional SEC (size exclusion chromatography) is not as straightforward as it would appear. Conventional calibration with polystyrene (PS) standards can only provide PS apparent molecular weights which do not provide accurate estimates of polyol molecular weights. Using polyethylene oxide/polyethylene glycol (PEO/PEG) for molecular weight calibration could improve the accuracy, but the retention behavior of PEO/PEG is not stable in THF-based (tetrahydrofuran) SEC systems. In this work, two approaches for calibration curve conversion with narrow PS and polyol molecular weight standards were developed. Equations to convert PS-apparent molecular weight to polyol-apparent molecular weight were developed using both a rigorous mathematical analysis and graphical plot regression method. The conversion equations obtained by the two approaches were in good agreement. Factors influencing the conversion equation were investigated. It was concluded that the separation conditions such as column batch and operating temperature did not have significant impact on the conversion coefficients and a universal conversion equation could be obtained. With this conversion equation, more accurate estimates of molecular weight averages and MWDs for polyether polyols can be achieved from conventional PS-THF SEC calibration. Moreover, no additional experimentation is required to convert historical PS equivalent data to reasonably accurate molecular weight results.

Single‐ and two‐step procedures of AGET emulsion ATRP of methyl methacrylate in a well‐mixed batch reactor

ABSTRACTThis study investigates the atom transfer radical emulsion polymerization of methyl methacrylate in a 2 L well‐mixed stirred batch reactor using activators generated by electron transfer as the initiation technique. The polymerization was carried out with ethyl‐2‐bromoisobutyrate as the initiator, copper bromide with 4,4′‐di‐5‐nonyl‐2,2′‐bipyridine as the catalyst system, Brij 98 as the surfactant, and ascorbic acid as the reducing agent. The reaction was carried out at constant temperature in the range of 50 to 70 °C under a blanket of nitrogen to minimize the presence of air in the system. Polymerizations were carried out according to single‐step and two‐step procedures. The coagulation was found to be a major problem, especially at high monomer conversion. However, adding more surfactant and lowering the reaction temperature weakened the effect of the coagulation but at the expense of the low monomer conversion. Measurement of molecular weight distribution and Đ using gel permeation show that the two‐step techniques produced polymers with living features of atom transfer radical emulsion polymerization much better than those in the single‐step procedure. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45308.

Combined BAC and MIEX pre-treatment of secondary wastewater effluent to reduce fouling of nanofiltration membranes

Biological activated carbon (BAC) and magnetic ion exchange resin (MIEX) were used to pre-treat secondary wastewater effluent (SWWE) and assessed for their capacity to reduce fouling of a nanofiltration membrane. BAC pre-treated water facilitated a lower but a steady flux while MIEX treated water resulted in a higher but a rapidly declining flux. Their combined use increased average flux from 58 to 89%. MIEX combined with BAC, in that order, was superior in reducing membrane fouling. Measurement of average Stokes radius (m) and apparent molecular weight distribution of dissolved organic matter (DOM), by nuclear magnetic resonance (NMR) and liquid chromatography organic carbon detection (LC-OCD), respectively, revealed that the microbial activity of BAC changed the nature of organic matter, probably by increasing the size of DOM molecules. BAC generally decreased the lower apparent molecular weight (LMW) fraction of dissolved organic carbon (DOC). Hence, the removal of LMW DOC and an increase of average Stokes radius (m) of DOM appeared to be important in facilitating a longer steady flux. Specifically, the combined MIEX/BAC pre-treatments appeared to target and reduce the foulants in SWWE that are largely responsible for the reduction of flux in nanofiltration membranes.

Rheological measurement of molecular weight distribution of polymers

Abstract This paper has described a method to obtain the molecular weight distribution (MWD) of polymeric materials from their rheological data. The method has been developed for linear polymers with log normal molecular weight distribution. The rheological data required to obtain the molecular weight distribution are the shear storage modulus,G' (ω) , and shear loss modulus,G" (ω) , extending from the terminal zone to the plateau region. For determining the molecular weight average, the method uses the relationship between stress moduli and relaxation spectrums, with the equation that connects dynamic rheological data with molecular weight distribution, and so it is not necessary to achieve the relaxation spectrums and the molecular weight distribution is obtained directly from dynamic shear experiments and it is one of the main advantageous of the proposed method. Comparison of calculated and experimental data obtained by GPC for five polypropylene samples produced in different conditions show that model can correctly predict molecular weight distribution for these types of polymers.

Rheological measurement of molecular weight distribution of polymers

Rheological measurement of molecular weight distribution of polymers

Rheological measurement of molecular weight distribution of polymers

Rheological measurement of molecular weight distribution of polymers

Filterability of Block Copolymer Solutions used for Directed Self Assembly Lithography

In order to study the filterability of block copolymer solutions (BCP) with 2 nm to 20 nm rated lithography process filters, the determination of hydrodynamic diameter by dynamic light scattering (DLS), block copolymer concentration determination using UV-Vis spectroscopy and molecular weight distribution measurement using gel permeation chromatography (GPC) were conducted. Hydrodynamic diameters by DLS were sufficiently small and this indicates filtration is feasible. And consistency of BCP concentration by UV-Vis spectroscopy and molecular weight distribution by GPC confirmed that HDPE 5, 2 nm rated filters and Nylon 6,6 20, 10 nm rated filters provided desired filtration without sacrificing critical performance of BCP solution. Based on the results, these filters are recommended for defect reduction in DSAL process which provides 1X nm patterns.

Derivatization-free gel permeation chromatography elucidates enzymatic cellulose hydrolysis

BackgroundThe analysis of cellulose molecular weight distributions by gel permeation chromatography (GPC) is a powerful tool to obtain detailed information on enzymatic cellulose hydrolysis, supporting the development of economically viable biorefinery processes. Unfortunately, due to work and time consuming sample preparation, the measurement of cellulose molecular weight distributions has a limited applicability until now.ResultsIn this work we present a new method to analyze cellulose molecular weight distributions that does not require any prior cellulose swelling, activation, or derivatization. The cellulose samples were directly dissolved in dimethylformamide (DMF) containing 10-20% (v/v) 1-ethyl-3-methylimidazolium acetate (EMIM Ac) for 60 minutes, thereby reducing the sample preparation time from several days to a few hours. The samples were filtrated 0.2 μm to avoid column blocking, separated at 0.5 mL/min using hydrophilic separation media and were detected using differential refractive index/multi angle laser light scattering (dRI/MALLS). The applicability of this method was evaluated for the three cellulose types Avicel, α-cellulose and Sigmacell. Afterwards, this method was used to measure the changes in molecular weight distributions during the enzymatic hydrolysis of the different untreated and ionic liquid pretreated cellulose substrates. The molecular weight distributions showed a stronger shift to smaller molecular weights during enzymatic hydrolysis using a commercial cellulase preparation for cellulose with lower crystallinity. This was even more pronounced for ionic liquid-pretreated cellulose.ConclusionsIn conclusion, this strongly simplified GPC method for cellulose molecular weight distribution allowed for the first time to demonstrate the influence of cellulose properties and pretreatment on the mode of enzymatic hydrolysis.

Polymer Molecular Weight Analysis by 1H NMR Spectroscopy

The measurement and analysis of molecular weight and molecular weight distribution remain matters of fundamental importance for the characterization and physical properties of polymers. Gel permeation chromatography (GPC) is the most routinely used method for the molecular weight determination of polymers whereas matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a fast-emerging absolute, and therefore accurate, technique. Although NMR spectroscopy is one of the most powerful tools available for polymer microstructure characterization, among others, its utility in the molecular weight analysis of polymers is somewhat underappreciated. It is a reliable and more readily available teaching tool in comparison to other known techniques, such as GPC and MALDI-TOF MS, for the molecular weight determination of polymers. Demonstrated herein are the simplicity, reproducibility, and convenience of 1H NMR spectroscopy in the analysis of polymer number-average molecular weig...

Destination of organic pollutants during electrochemical oxidation of biologically-pretreated dye wastewater using boron-doped diamond anode

Electrochemical oxidation of biologically-pretreated dye wastewater was performed in a boron-doped diamond (BDD) anode system. After electrolysis of 12 h, the COD was decreased from 532 to 99 mg L −1 (<100 mg L −1, the National Discharge Standard of China). More importantly, the destination of organic pollutants during electrochemical oxidation process was carefully investigated by molecular weight distribution measurement, resin fractionation, ultraviolet-visible spectroscopy, HPLC and GC–MS analysis, and toxicity test. As results, most organic pollutants were completely removed by electrochemical oxidation and the rest was primarily degraded to simpler compounds (e.g., carboxylic acids and short-chain alkanes) with less toxicity, which demonstrated that electrochemical oxidation of biologically-pretreated dye wastewater with BDD anode was very effective and safe. Especially, the performance of BDD anode system in degradation of large molecular organics such as humic substances makes it very promising in practical applications as an advanced treatment of biologically-pretreated wastewaters.

Effects of coagulation on submerged ultrafiltration membrane fouling caused by particles and natural organic matter (NOM)

Natural organic matter (NOM) and particles in source water are responsible for the majority of ultrafiltration (UF) membrane fouling that occurs during drinking water treatment. This study was conducted to (1) understand the UF membrane fouling phenomena caused by NOM and turbidity-causing particles and (2) investigate the effect of coagulation pretreatment on the alleviation of membrane fouling. In this study, kaolinite and humic acid (HA) were used to simulate the particles and NOM present in source water. The results revealed that the particles contributed to reversible fouling due to cake layer formation on the membrane surface, but that could be effectively reduced by increasing the frequency of physical backwashing. The results of the molecular weight (MW) distribution measurements, resin fractionation, SEM and FTIR analyses showed that HA primarily contributed to irreversible fouling. Taken together, the results of this study imply that the particles and NOM compounds present in source water may have different fouling behavior, and that particles may mitigate the irreversible fouling caused by HA. The addition of coagulant can lead to a higher rate of removal of large-sized hydrophobic compounds. Coagulation pretreatment can improve membrane performance and postpone membrane fouling development effectively, as well as retard the implementation of membrane chemical cleaning.

Effect of autohydrolysis of Eucalyptus globulus wood on lignin structure. Part 2: Influence of autohydrolysis intensity

Abstract Three different levels of autohydrolysis intensity, expressed as the prehydrolysis (P)-factor, were applied to Eucalyptus globulus wood at a liquor/wood ratio of 5:1. Lignin fractions were isolated from the wood residue as milled wood lignin (MWL), from the hydrolysate by centrifugation (insoluble fraction) and by ethyl acetate extraction (soluble fraction), and from the reactor wall as precipitate. With increasing autohydrolysis duration, a decrease in the content of aliphatic hydroxyl groups and of β-O-4 structures was detected in all lignin fractions, whereas the content of phenolic hydroxyl groups increased in the same order. MWL isolated from wood residue after autohydrolysis at the highest P-factor contained only half the β-O-4 structures contained in native lignin. Molecular weight distribution measurements revealed that fragmentation reactions dominated over condensation reactions in all lignin samples investigated. However, low-molecular-weight lignin dissolved in autohydrolysate exhibited extremely high reactivity towards acid-catalysed condensation reaction, which inevitably leads to the formation of sticky precipitates during storage at elevated temperature under the acid conditions prevailing.

Ozonation for the Degradation of Organic Compounds from Nuclear Laundry Water

In this study, the efficiency of ozone to degrade organic compounds of nuclear laundry water was studied at different pH and temperatures and at elevated temperature with hydrogen peroxide. The degradation of non-ionic surfactant and other organic compounds was analyzed by COD, TOC, BOD and molecular weight distribution measurements. Zeta potential measurements were also performed in order to interpret the obtained results. The most favorable degradation conditions were at pH 7 with 43%, 34% and 61% reductions of COD, TOC and BOD, respectively.

Understanding the impacts of moisture and thermal ageing on transformer's insulation by dielectric response and molecular weight measurements

Properties of oil and paper in a transformer degrade primarily due to thermal ageing and moisture ingress. Dielectric diagnostic tests, such as Recovery Voltage (RV), and Polarizations and Depolarization Current (PDC) measurement are currently being explored as potential tools for insulation condition assessment. A modern chemical analysis tool for paper molecular weight (MW) measurement, Gel Permeation Chromatography (GPC) or the more accurately described Size Exclusion Chromatography (SEC) promises to be useful in assessing ageing condition. However, the issue of separately assessing the impacts of ageing and moisture on oil and paper has been a key issue for many years. In the current research project, a series of experiments have been performed under controlled laboratory conditions with preset moisture content, and at controlled high temperature ageing. Whereas RV and PDC measurement results were found to be more sensitive to the moisture content of the oil and paper insulation, the MW distribution measurement by SEC provided a trend of insulation thermal ageing. This paper first provides a brief description of RVM, PDC and SEC procedures followed by a description of the experimental techniques adopted. Results are then analysed with the view of separately understanding the impacts of thermal ageing and moisture on the condition of oil and paper insulation in a transformer.