Large Differences In Molecular Weight Research Articles

Improvement effect of different modifiers on storage stability of high content SBS modified asphalt

High content Styrene-butadiene-styrene (SBS) modified asphalt binder is commonly used for permeable pavements attribute to reasonable adhesion ability, deformation resistance and toughness. However, due to the large difference in molecular weight between styrene-butadiene-styrene block copolymer and asphalt, the compatibility between SBS and asphalt has always been a key issue restricting its development. To improve the compatibility of high content SBS modified asphalt, the preparation process of high content SBS modified asphalt (shear time, temperature, rate, modifier content) was investigated by orthogonal experimental design method. The effects of modifiers (polyphosphoric acid, montmorillonite, and sulfur) on the physical properties and compatibility of high content SBS modified asphalt were investigated by physical property tests, storage stability tests and dynamic shear rheology tests. The results shows that all three additives have improved the storage stability of high content SBS-modified asphalt, among which, nano montmorillonite has the best comprehensive improvement effect. In addition, the preparation process of high content SBS modified asphalt will also affect its physical properties and compatibility. When the content of MMT and SBS is 2% and 8% respectively, the shear temperature is 170 °C, the shear rate is 4000 rpm, and the shear time is 150 min, the high and low temperature performance of high content SBS modified asphalt is good and the compatibility is the best.

Enhancing the hydrophilicity and biofoulant removal ability of a PVDF ultrafiltration membrane via π-π interactions as measured by AFM

Antibiotics are commonly used as inhibitors to terminate protein formation in the biotechnology and pharmaceutical industries; however, due to the large difference in molecular weight between antibiotics and proteins, it is hard to remove them simultaneously through ultrafiltration or nanofiltration. In this work, a novel membrane with nanoscale pores and anti-protein adsorption was developed to reject antibiotics and reduce protein adhesion. Amphiphiles consisting of hydrophobic and hydrophilic moieties were synthesized from a poly(styrene-alt-maleic anhydride) (SMA) copolymer with a 2-hydroxyethyl acrylate (HEA) monomer to enhance the hydrophilicity of polyvinylidene difluoride (PVDF) membranes. A series of SMAs with different polystyrene molar ratios (maleic acid/styrene (m/s) = 1:1, 1:2 and 1:3) was synthesized in this study, and the bonding force between the amphiphiles and PVDF, namely, π-π interactions between styrene molecules and the C–F bonds of PVDF, was evaluated. The π-π interaction between the amphiphiles and the PVDF membrane was determined via atomic force microscopy (AFM) repulsive force measurements for the first time in this work. The repulsive force increased significantly from -5.9 ± 1.0 nN to −18.3 ± 0.8 nN as the m/s ratio increased to 1:3, indicating that the π-π interaction was enhanced as the proportion of polystyrene in the SMA-HEA copolymer increased, resulting in tight attachment. Furthermore, the amphiphile-modified membrane demonstrated better hydrophilicity than the pristine PVDF membrane, and the water contact angle (WCA) decreased considerably from 104° (PVDF) to 55° (m/s = 1:2, P2000-600). The pure water flux recovery rate of P2000-600 improved by approximately 10%, and antibiotic rejections of 92.8%, 99.9% and 97.1% for tetracycline (TC), chloramphenicol (CL) and erythromycin (EM), respectively, were observed during the 7-h filtration process, indicating that P2000-600 can effectively remove antibiotics from water. In addition, P2000-600 also displayed good restriction of bovine serum albumin (BSA) adsorption at 28.4 ± 8.1 μg/cm2 under static adsorption processes and BSA rejection of nearly 90% during the three-cycle filtration.

Permeability of a Fluid Lipid Bilayer to Short-Chain Alcohols from First Principles.

Computational prediction of membrane permeability to small molecules requires accurate description of both the thermodynamics and kinetics underlying translocation across the lipid bilayer. In this contribution, well-converged, microsecond-long free-energy calculations are combined with a recently developed subdiffusive kinetics framework to describe the membrane permeation of a homologous series of short-tail alcohols, from methanol to 1-butanol, with unprecedented fidelity to the underlying molecular models. While the free-energy profiles exhibit barriers for passage through the center of the bilayer in all cases, the height of these barriers decreases with the length of the aliphatic chain of the alcohol, in quantitative agreement with experimentally determined differential solvation free energies in water and oil. A unique aspect of the subdiffusive model employed herein, which was developed in a previous article, is the determination of a position-dependent fractional order which quantifies the degree to which the motion of the alcohol deviates from classical diffusion along the thickness of the membrane. In the aqueous medium far from the bilayer, this quantity approaches 1.0, the asymptotic limit for purely classical diffusion, whereas it dips below 0.75 near the center of the membrane irrespective of the permeant. Remarkably, the fractional diffusivity near the center of membrane, where its influence on the permeability is the greatest, is similar among the four permeants despite the large difference in molecular weight and lipophilicity between methanol and 1-butanol. The relative permeabilities, which are estimated from the free-energy and fractional diffusivity profiles, are therefore determined predominantly by differences in the former rather than the latter. The predicted relative permeabilities are highly correlated with existing experimental results, albeit they do not agree quantitatively with them. On the other hand, quite unexpectedly, the reported experimental values for the short-tail alcohols are nearly three orders of magnitude lower than the available experimental measurement for water. Plausible explanations for this apparent disagreement between theory and experiment are considered in detail.

Topology and Shape Control for Assemblies of Block Copolymer Blends in Solution

We study binary blends of asymmetric diblock copolymers (AB/AC) in selective solvents with a mesoscale model. We investigate the morphological transitions induced by the concentration of the AC block copolymer and the difference in molecular weight between the AB and AC copolymers, when segments B and C exhibit hydrogen-bonding interactions. To the best of our knowledge, this is the first work modeling mixtures of block copolymers with large differences in molecular weight. The coassembly mechanism localizes the AC molecules at the interface of A and B domains and induces the swelling of the B-rich domains. The coil size of the large molecular weight block copolymer depends only on the concentration of the short block copolymer (AC or AB), regardless of the B–C interactions. However, the B–C interactions control the morphological transitions that occur in these blends.

Effect of polyols on the molecular organization and thermodynamic properties of low water content gelatin oligomers

We use Positron Annihilation Lifetime Spectroscopy (PALS) in conjunction with calorimetric measurements to investigate the effects of two polyols (sorbitol and glycerol) and water on the molecular packing and thermodynamic state of low water content gelatin matrices. Our calorimetric measurements show that water, sorbitol and glycerol all reduce the glass transition and dissociation/denaturation temperatures of the gelatin matrices. Glycerol has a more pronounced effect on the thermodynamic state of the matrices compared to sorbitol, while both polyols alter the molecular organization and water sorption behaviour in a similar way, despite the large differences in molecular weight. Our PALS measurements show that over the concentration ranges studied, both sorbitol and glycerol act as packing enhancers, causing similar reductions in the average hole size, vh, of the gelatin matrices. Finally, we observe complex changes in vh as a function of increasing level of hydration, showing two apparent regimes related to the state of water molecules in the gelatin matrices.

Novel chitosan-based pH-sensitive and disintegrable polyelectrolyte nanogels

A novel approach to design pH-sensitive and disintegrable polyelectrolyte nanogels composed of citraconic-based N-(carboxyacyl) chitosan (polyanion) and quaternary chitosan (polycation) was reported. Firstly, the hydrolysis of citraconic-modified chitosan was monitored using fluorescamine assay and it could selectively dissociate in acidic media (e.g., pH ∼5.0) due to the isomerization during the addition of citraconic anhydride to chitosan. Secondly, the self-assembly behaviors of different polyelectrolyte pairs between citraconic-based chitosan and quaternary chitosan were investigated via colloidal titration assay. It was indicated that the difference in molecular weight (MW) of opposite charged polyelectrolytes played an important role on the formation of polyelectrolyte nanogels. Results showed that polyelectrolyte nanogels (ca. 300nm in size) only formed when polyanion and polycation had a very large difference in MW. The pH-sensitive behavior of polyelectrolyte nanogels was comprehensively investigated by dynamic light scattering (DLS) and transmission electron microscope (TEM). The incorporation of charge-conversional citraconic-based chitosan into polyelectrolyte complexes has provided an effective approach to prepare polyelectrolyte nanogels which were very stable at neutral pH but disintegrated quickly in acidic media.

Characterization of organic matter in beef feedyard manure by ultraviolet-visible and fourier transform infrared spectroscopies.

Manure from beef cattle feedyards is a valuable source of nutrients and assists with maintaining soil quality. However, humification and decomposition processes occurring during feedyard manure's on-farm life cycle influence the forms, concentrations, and availability of carbon (C) and nutrients such as nitrogen (N) and phosphorus (P). Improved understanding of manure organic matter (OM) chemistry will provide better estimates of potential fertilizer value of manure from different feedyard sources (e.g., manure accumulated in pens, stockpiled manure after pen scraping) and in settling basin and retention pond sediments. This will also assist with identifying factors related to nutrient loss and environmental degradation via volatilization of ammonia and nitrous oxide and nitrate leaching. We used Fourier-transform infrared (FTIR) and ultraviolet-visible (UV-vis) spectroscopies to characterize structural and functional properties of OM and water-extractable OM (WEOM) from different sources (surface manure, manure pack, settling basin, retention pond) on a typical commercial beef feedyard in the Texas Panhandle. Results showed that as beef manure completes its on-farm life cycle, concentrations of dissolved organic C and N decrease up to 98 and 95%, respectively. The UV-vis analysis of WEOM indicated large differences in molecular weight, lignin content, and proportion of humified OM between manures from different sources. The FTIR spectra of OM and WEOM indicate preferential decomposition of fats, lipids, and proteins over aromatic polysaccharides such as lignin. Further work is warranted to evaluate how application of feedyard manure from different sources influences soil metabolic functioning and fertility.

Distribution Characterization with Fluorescence Cumulant Analysis

Fluorescence correlation spectroscopy (FCS) is a powerful tool for biophysical research, capable of monitoring concentrations and molecular interactions on a femtoliter scale. However, it is difficult in practice to resolve multiple molecular species using FCS unless there is a large difference in molecular weight. Several techniques have been developed to combat this problem, including photon counting histograms (PCH), fluorescence intensity distribution analysis (FIDA), and fluorescence cumulant analysis (FCA). These are capable of resolving multiple components on the basis of differences in molecular brightness, but have typically focused on studying samples with a small number of species. Fluorescence cumulant analysis can be extended to determine the parameters of brightness distributions containing many components, yielding a set of simple algebraic relations between the factorial cumulants of a measured fluorescence intensity series and the moments of the brightness distribution. Using PCH in conjunction with FCA, the best-fit distribution may be distinguished from several candidate models. We present simulations and experiments testing the applicability of this analysis. This technique may be useful in studies where the molecules of interest form a variety of multimers or aggregates.

Enrichment and separation of acidic and basic proteins using the centrifugal ultrafiltration followed by nanoparticle‐filled capillary electrophoresis

This report describes a method for enrichment and separation of acidic and basic proteins using the centrifugal ultrafiltration followed by nanoparticle-filled capillary electrophoresis. To improve stacking and separation efficiencies of proteins, the separation buffer containing 1.6% poly(diallyldimethylammonium chloride) was added with gold nanoparticles (AuNP), poly(ethylene oxide), cetyltrimethylammonium bromide, and poly(vinyl alcohol). As a result, the use of AuNP as additives exhibited better efficiency in separation, stacking, and analysis time. Even for large-volume samples (110 nL), the separation efficiencies of acidic and basic proteins remained greater than 10(4) and 10(5) plates/m, respectively. To further enhance detection sensitivity, protein samples were enriched using the centrifugal ultrafiltration, followed by our proposed stacking method. The detection sensitivity was improved up to 314-fold compared to normal hydrodynamic injection. Additionally, the limits of detection at a signal-to-noise of 3 for most proteins were down to nanomolar range. We have validated the application of our method by means of analyses of 50 nM lysozyme in saliva samples. The proposed method was also successfully applied to the analyses of egg-white proteins, which have large differences in molecular weight and pI.

Structural characterisation of novel lichen heteroglycans by NMR spectroscopy and methylation analysis

Two galactofuranomannans, Ths-4 and Ths-5, were isolated from the lichen, Thamnolia vermicularis var. subuliformis, using ethanol fractionation and anion-exchange and size-exclusion chromatography. The average molecular weights of Ths-4 and Ths-5 were estimated to be 19 and 200 kDa, respectively. Structural characterisation of Ths-4, Ths-5 and their partially hydrolysed derivatives was performed by methanolysis and methylation analysis. The intact and partially hydrolysed Ths-4 was further analysed using NMR spectroscopy (1D, COSY, NOESY, TOCSY, HSQC and HMBC). According to the data obtained, the heteroglycans Ths-4 and Ths-5 have similar structures, but have large differences in molecular weight. The structure is composed of 3-O-linked and 5-O-linked galactofuranosyl chains linked to a mannan core. The mannan core consists of a main chain of α-(1→6)-linked mannopyranosyl residues, substituted at O-2 with either a single α-mannopyranosyl unit or an α-Man p-(1→2)-α-Man p-(1→2)-α-Man p group in the ratio of approximately 1:3, respectively. The polysaccharides have idealised repeating blocks as is shown.

Fundamental Studies of Acid-Breakable Resins for Chemical-Amplification Positive Resist Matrices.

We have investigated acid-breakable (AB) resins for chemical-amplification positive resists. The AB resin was synthesized by a co-condensation reaction between an alkali-soluble polyphenol (4, 4′-[1-[4-[1-(4-Hydroxyphenyl)-1-methylethyl]phenyl]-ethylidene]bis phenol) and an aromatic multi-functional (tri-functional) vinylether compound. The AB resin did not dissolve in an aqueous base developer (TMAH: 2.38%), and it had a good margin for the polyphenol/vinylether feed ratio. Even for AB resins, with large differences in molecular weight, the AB-resin-based resist exhibited almost the same exposure characteristics. We also examined the relationship between the inhomogeneous distribution of the acid generator and the film structure of the AB-resin-based resist.

Small angle neutron scattering investigation of transesterification in Poly(ethylene terephthalate)-poly(Butylene terephthalate) mixtures

The transesterification reaction between polyethylene terephthalate and polybutylene terephthalate (PBT) was investigated by small-angle neutron scattering. For this purpose deuterio polyethylene terephthalate (dPET) was synthesised and fractionated to produce three samples whose molecular weight ranged from circa 14 000 g mol −1 to 63 400 g mol −1. Mixtures of these two polymers containing 10% of the deuterio polymer were transesterified to varying extents by heating for known times at different temperatures. The apparent molecular weight of the deuterio polymer decreases as the extent of reaction increases and this is observed in the small-angle scattering data. From these data second order rate constants were obtained, the values are somewhat larger than those obtained for main-chain mesomorphic polyesters but of the same order of magnitude for transesterification in polyethylene terephthalate alone. No influence of the large difference in molecular weight of the dPET on the rate constants was observed. The activation energy obtained from these data was 61±7 kJ mol −1, a value which is less than half that reported for other polyester transesterifications. The reaction appears to be dominated by the scission of the PBT component of the mixture.

Recovery and reuse of the molecular chaperone GroEL for in vitro protein refolding.

The chaperones GroEL and GroES from Escherichia coli are known to improve in vitro protein refolding yields. We show that, for the molecular chaperone-assisted refolding of hen egg white lysozyme, GroES is not an essential requirement and that activity is recovered with GroEL and ATP alone. The refolding yields of lysozyme in the presence of GroEL are much greater than those obtained by dilution because of a reduction in protein aggregation. On the basis of the large difference in molecular weight between the GroEL complex (MW 840 000) and lysozyme (MW 14 600), we have demonstrated that using an ultrafiltration membrane (MW 30 000) GroEL may be easily retained after refolding while lysozyme passes freely into the permeate. The chaperonin recovered from the refolding solution was then reused several times for further refolding experiments. The effectiveness of GroEL-assisted refolding was found to decrease with reuse, and this has been attributed to a reduction in the GroEL:lysozyme molar ratio.

Molecular weight dependency in the uptake of fractionated [3H]heparin in isolated rat Kupffer cells.

The uptake of low molecular weight fractionated [3H]heparin (LMWFH, 10000 Da) was compared with that of high molecular weight fractionated [3H]heparin (HMWFH, 23000 Da) in isolated rat Kupffer cells. Several heparin analogs, including HMWFH and ligands of scavenger receptors, inhibited both the surface binding and internalization of LMWFH, suggesting the involvement of scavenger receptors in the uptake of LMWFH in isolated rat Kupffer cells as well as HMWFH, in spite of a large difference in molecular weight. Metabolic inhibitors (2,4-dinitrophenol and rotenone), receptor-mediated and adsorptive endocytosis of polypeptides (phenylarsine oxide) and phagocytosis inhibitors (cytochalasine B and colchicine) did not inhibit the internalization of LMWFH. These results suggest that the scavenger receptor-mediated uptake of LMWFH is ATP-independent and different from receptor-mediated and adsorptive endocytosis of polypeptides and phagocytosis, in agreement with our previous results for HMWFH. The equilibrium binding of LMWFH to Kupffer cells was concentration-dependent with the dissociation constant (Kd) of 50 nM and maximum binding capacity (Bmax) of 2.3 pmol/10(6) cells. The dissociation constant of LMWFH was an order of magnitude larger than that of HMWFH (5.7 nM), suggesting a decrease in binding affinity to scavenger receptors with a decrease in the molecular weight of fractionated heparin. It was also shown that LMWFH is internalized by scavenger receptors according to first-order kinetics with an apparent internalization rate constant (Kint,app) of 0.0053 min-1, which is about half that for HMWFH (0.0118 min-1). Molecular weight thus appears to be one of dominant factors determining the uptake of fractionated heparin by scavenger receptors in Kupffer cells, and may partly explain the reported lower hepatic uptake of low molecular weight heparin than that of unfractionated heparin.

Intermolecular electrostatic interactions and their effect on flux and protein deposition during protein filtration.

Although membrane filtration is used extensively to process protein solutions containing a variety of electrolytes, there is currently little fundamental understanding of the effect of the solution environment (and in particular, the solution pH) on the filtrate flux in these systems. We have obtained data for the flux and sieving coefficients during the batch (stirred cell) filtration of solutions of bovine serum albumin, immunoglobulins, hemoglobin, ribonuclease A, and lysozyme through 0.16-micron microfiltration membranes at different pH values. The flux declined significantly for all five proteins due to the formation of a protein deposit on the upper surface of the membrane. The quasi-steady ultrafiltrate fluxes at the individual protein isoelectric pH's were essentially identical, despite the large differences in molecular weight and physicochemical characteristics of these proteins. The flux increased at pH's away from the isoelectric point, with the data well-correlated with the protein surface charge density. These results were explained in terms of a simple physical model in which the protein deposit continues to grow, and thus the flux continues to decline, until the drag force on the proteins associated with the filtrate flow is no longer able to overcome the intermolecular repulsive interactions between the proteins in the bulk solution and those in the protein deposit on the surface of the membrane.

Sodium dodecyl sulfate activation of a plant polyphenoloxidase. Effect of sodium dodecyl sulfate on enzymatic and physical characteristics of purified broad bean polyphenoloxidase.

Latent broad bean polyphenoloxidase was purified and shown to be activated by sodium dodecyl sulfate (SDS). Further characterization of the enzyme was carried out in the presence and absence of SDS. Activation of the enzyme increased in a sigmoidal manner with increasing SDS concentrations up to a maximum of 1.75 mM. The presence of SDS eliminated a low pH optimum induced by acid shocking. Increased thermolability of the enzyme was observed in the presence of SDS as well as an increased binding of [14C]dihydroxy-phenylalanine. Size exclusion chromatography on high performance liquid chromatography showed that the size and apparent molecular mass of the enzyme were slightly altered in the presence (48 kDa) versus absence (47 kDa) of SDS. Although the estimations were larger than those obtained by size exclusion techniques, no large differences in molecular weight were observed after sedimentation equilibrium of the enzyme in the presence (53.9 kDa) and absence (52.3 kDa) of SDS. Relative electrophoretic mobility and intrinsic fluorescence of tyrosine and tryptophan residues increased in a complex fashion as the SDS concentration was increased. Plateau regions in these latter experiments corresponded to concentrations of SDS needed for activation. The ability of SDS to activate the enzyme alters both its enzymatic and physical characteristics and suggests that a limited conformational change, due to binding of small amounts of SDS, may induce or initiate the activation of latent enzyme.

Flow of cerebral interstitial fluid as indicated by the removal of extracellular markers from rat caudate nucleus

Bulk flow of interstitial fluid (ISF) in brain was studied by following the intracerebral distribution of horseradish peroxidase (HRP) injected into the caudate nucleus of rats. Using this technique, channels of ISF flow are outlined as the extracellular pathways of protein distribution away from the injection site. Anionic isoenzymes of HRP were separated from Sigma's Type II HRP using ion-exchange chromatography. Anionic isoenzymes proved superior as markers of ISF flow, presumably because there is less cellular uptake and surface adsorption of anionic protein. Analysis of the distribution of protein 4–8 hr after injection suggests that ISF flows from narrow intercellular clefts of the neuropil along a system of extracellular pathways including perivascular and periventricular areas and between fiber tracts. From this system ISF appears to drain into cerebrospinal fluid (CSF) and possibly also into fenestrated vessels within the brain. Quantitative aspects of fluid drainage from brain were investigated by measuring the rate and route of efllux from brain of radiolabelled extracellular markers: [ 3 H]polyethylene glycol (PEG: 4000 daltons) and [ 14 C]dextran (70 000 daltons). In nine control rats, the amount of isotope remaining in brain 4 hr after injection into the caudate nucleus, as percent of the injected dose (mean± S.E.M. ), was 55·8±6·3 for PEG and 63·1±6·6 for dextran. Similarity in the rates of dextran and PEG removal from brain, despite large differences in molecular weight, is consistent with removal from brain by bulk flow of ISF. A maximum of 20% of the isotope cleared from brain could be recovered from CSF, in agreement with anatomical evidence that CSF may not be the sole route of ISF removal from brain.

Ultrasonic relaxation in gaseous sulphur hexafluoride and tungsten hexafluoride

A pulse technique has been used to measure vibrational relaxation times in sulphur and tungsten hexafluorides. Despite the large differences in molecular weight, the relative relaxation times are as predicited by the general theory of vibration–translation energy transfer. There is no evidence that vibration–rotation transfer is important, or that the unusual mass of the central atom causes unforeseen effects. On the other hand, the vibrational relaxation is more efficient than predicted by a priori calculation (using quantities derived from low-energy collisional phenomena) as is frequently found for polyatomic molecules.