High Degree Of Polydispersity Research Articles

Morphological analysis of polydisperse nanoplatelets using SAXS

Two-dimensional materials like graphene and boron nitride find applications in numerous innovations thanks to their high specific surface area and unusual electrical, thermal and optical properties. These materials are often produced via liquid-phase exfoliation, yielding nanoplatelets with a high degree of polydispersity. Unfortunately, methods for the characterization of both lateral dimension and thickness for dispersed polydisperse nanoplatelets are still lacking. In this work, a fast and quantitative method for the characterization of polydisperse nanoplatelets in dispersion is proposed using the example of graphene nanoplatelets (GNPs). The method is benchmarked using well-defined gibbsite nanoplatelets. Synchrotron small-angle X-ray scattering (SAXS) is used to probe the structure of the platelets over a wide range of length scales. The SAXS data are fitted with a polydisperse form factor for discs, which yields size distributions in both thickness and diameter. Benchmarking the procedure with the gibbsite model system shows excellent agreement between the SAXS results and previous transmission electron microscopy and atomic force microscopy data. The method is also successfully applied to GNPs from 1–60 layers in thickness and 20–2000 nm in diameter. We believe that this work brings reliable quantitative in situ characterization, for instance during preparation, of nanoplatelet dispersions within reach.

Self-aggregating properties of inulin in a dilute solution

The creation of functional food products based on inulin-containing vegetable raw materials can provide the population with functional diabetic nutrition. In this regard, investigation of the technological parameters of obtaining inulin from Jerusalem artichoke tubers (Helianthus tuberosus L.) and determination of its quantitative characteristics seem highly relevant. This study aims to determine the qualitative characteristics of inulin obtained from Jerusalem artichoke tubers by both flash extraction and conventional methods. Jerusalem artichoke inulin samples were obtained by the flash extraction method at a high temperature of 105 °C during both shorter and longer periods of time and by the conventional method at a temperature of 75 °C in a neutral medium. The hydrodynamic properties and molecular weight of the samples demonstrated the self-aggregating properties of this biopolymer. Inulin obtained by the flash extraction method consists of two fractions: low-molecular weight inulin and high-molecular weight aggregate represented by a polysaccharide complex. These aggregates can be formed both by inter- and intramolecular interactions of various inulin fractions in the solution. As expected, their isolation using conventional methods appeared impossible: the method of concentration yielded a number of subfractions on the UV membrane and a large amount of aggregated water-insoluble microgel. At the same time, inulin obtained by the conventional method consists of one fraction, although having a high degree of polydispersity. In order to obtain high-quality inulin intended for nutritional and prophylactic purposes, it is preferable to use the flash extraction method over short periods of time.

Effect of Synthesis Temperature on Size, Structure, and Volume Phase Transition of Polysaccharide Microgels

High-molecular-weight polysaccharide microgels were synthesized at a range of temperatures above the polymer lower critical solution temperature (LCST) (ΔT = 0.6–18.1 °C), and ΔT was found to strongly influence the structure, dynamics, and volume phase transition temperature of the resulting particles. Static and dynamic light scattering studies and mean field theory analysis of the microgels below and above volume phase transition revealed several distinct regimes. At small ΔT, lower density, larger, and more polydisperse microgels that deswell by a factor 10 in volume were synthesized. At intermediate ΔT = 5–8 °C, the formed microgels were the smallest, densest, and most monodisperse below the transition, but exhibited deswelling only by a factor of 5 above the transition. Synthesis at high ΔT led to the formation of nonuniform microgels with small density, a high degree of polydispersity, and in some cases the apparent presence of the un-cross-linked polymer. Furthermore, the volume phase transition temperature dropped significantly as ΔT increased. This work suggests that synthesis temperature can be used to tune the size, deswelling capacity, and volume phase transition temperature of the polymeric microgels.

Novel site-specific PEGylated L-asparaginase.

L-asparaginase (ASNase) from Escherichia coli is currently used in some countries in its PEGylated form (ONCASPAR, pegaspargase) to treat acute lymphoblastic leukemia (ALL). PEGylation refers to the covalent attachment of poly(ethylene) glycol to the protein drug and it not only reduces the immune system activation but also decreases degradation by plasmatic proteases. However, pegaspargase is randomly PEGylated and, consequently, with a high degree of polydispersity in its final formulation. In this work we developed a site-specific N-terminus PEGylation protocol for ASNase. The monoPEG-ASNase was purified by anionic followed by size exclusion chromatography to a final purity of 99%. The highest yield of monoPEG-ASNase of 42% was obtained by the protein reaction with methoxy polyethylene glycol-carboxymethyl N-hydroxysuccinimidyl ester (10kDa) in 100 mM PBS at pH 7.5 and PEG:ASNase ratio of 25:1. The monoPEG-ASNase was found to maintain enzymatic stability for more days than ASNase, also was resistant to the plasma proteases like asparaginyl endopeptidase and cathepsin B. Additionally, monoPEG-ASNase was found to be potent against leukemic cell lines (MOLT-4 and REH) in vitro like polyPEG-ASNase. monoPEG-ASNase demonstrates its potential as a novel option for ALL treatment, being an inventive novelty that maintains the benefits of the current enzyme and solves challenges.

Percolation of binary disk systems: Modeling and theory.

The dispersion and connectivity of particles with a high degree of polydispersity is relevant to problems involving composite material properties and reaction decomposition prediction and has been the subject of much study in the literature. This work utilizes Monte Carlo models to predict percolation thresholds for a two-dimensional systems containing disks of two different radii. Monte Carlo simulations and spanning probability are used to extend prior models into regions of higher polydispersity than those previously considered. A correlation to predict the percolation threshold for binary disk systems is proposed based on the extended dataset presented in this work and compared to previously published correlations. A set of boundary conditions necessary for a good fit is presented, and a condition for maximizing percolation threshold for binary disk systems is suggested.

Studies of reaction products of hydrolytic lignin with nitric acid

The properties of the reaction products of hydrolytic lignin with nitric acid in water—dioxane medium were studied. The products are a mixture of nitrogen-containing oligomeric compounds with high degree of polydispersity.

A comprehensive structural evaluation of humic substances using several fluorescence techniques before and after ozonation. Part I: Structural characterization of humic substances

The main objective of this work (Part I) is to conduct a comprehensive structural characterization of humic substances, using all the current fluorescence techniques: emission scan fluorescence (ESF), synchronous fluorescence spectroscopy (SFS), total luminescence spectroscopy (TLS or EEM) through the use of both 2-D contour maps and 3-D plots, fluorescence index and the λ0.5 parameter. Four humic substances were studied in this work: three of them were provided by the International Humic Substances Society (Suwannee River Fulvic Acid Standard, Suwannee River Humic Acid Standard and Nordic Reservoir Fulvic Acid Reference) and the other one was a commercial humic acid widely used as a surrogate for aquatic humic substances in various studies (Aldrich Humic Acid: ALHA). The EEM spectra for the three natural aquatic substances were quite similar, showing two main peaks of maximum fluorescence intensity: one located in the ultraviolet region and centered at around Ex/Em values of 230/437nm (peak A) and another one in the visible region, centered at around 335/460nm (peak C); however, the EEM spectrum of ALHA is completely different to those of natural aquatic humic substances, presenting four poorly resolved main peaks with a high degree of spectral overlap, located at 260/462, 300/479, 365/483 and 450/524nm. The synchronous spectra at Δλ=18 and 44nm (especially at Δλ=18nm) allowed the identification of a protein-like peak at λsyn around 290nm, which was not detected in the EEM spectra; as it happened with EEM spectra, the synchronous spectra of ALHA are quite different from those of the aquatic humic substances, presenting a higher number of bands that suggest greater structural complexity and a higher degree of polydispersity. Good correlations were achieved between 13C NMR aromaticity and both fluorescence index and λ0.5 parameter. The different spectra presented by ALHA compared to those shown by the natural aquatic humic substances for all the fluorescence techniques studied suggest an important structural difference between them, which cast doubt on the use of commercial humic acids as surrogates for natural humic substances.

Single Molecule Surface-Enhanced Raman Spectroscopy without Nanogaps

We provide conclusive proof of single molecule (SM) detection by surface-enhanced Raman spectroscopy (SERS) for discrete Ag triangular nanopyramids prepared via nanosphere lithography (NSL). While the observation of SMSERS has been well-demonstrated using various chemically synthesized nanoparticle substrates, they have a high degree of polydispersity in shape, size, and aggregation state resulting in an interest to develop more reproducible and uniform nanoparticles. Here triangular-based nanopyramids were characterized by scanning electron microscopy to confirm their geometry and interparticle spacing. Then the isotopologue approach with Rhodamine 6G was used to conclusively prove SM sensitivity for the individual nanoparticles. NSL’s straightforward, simple fabrication procedure produces large active arrays. Furthermore, the tunable localized surface plasmon resonance makes NSL prepared substrates effective for the detection of resonant molecules by SMSERS.

Effects of visible and UV light on the characteristics and properties of crude oil-in-water (O/W) emulsions

The effects of visible and UV light on the characteristics and properties of Prudhoe Bay (PB) and South Louisiana (SL) emulsions were investigated to better understand the role of sunlight on the fate of spilled crude oils that form emulsions with a dispersant in the aquatic environment. Before irradiation, crude oil emulsions showed the presence of dispersed crude oil micelles in a continuous water phase and crude oil components floating on the surface. The crude oil micelles decreased in size with irradiation, but emulsions retained their high degree of polydispersity. UV irradiation reduced the stability of emulsions more effectively than visible light. The reduction of micelles size caused the viscosity of emulsions to increase and melting point to decrease. Further, irradiation increased acid concentrations and induced ion formation which lowered the pH and increased the conductivity of emulsions, respectively. Ni and Fe in PB emulsions were extracted from crude oil with UV irradiation, which may provide an efficient process for metal removal. The emulsions were stable toward freeze/thaw cycles and their melting temperatures generally decreased with irradiation. Evidence of ˙OH production existed when emulsions were exposed to UV but not to visible light. The presence of H(2)O(2) enhanced the photodegradation of crude oil. Overall, the changes in emulsion properties were attributed to direct photodegradation and photooxidation of crude oil components.

Effect of polydispersity and soft interactions on the nematic versus smectic phase stability in platelet suspensions

We theoretically discuss, using density-functional theory, the phase stability of nematic and smectic ordering in a suspension of platelets of the same thickness but with a high polydispersity in diameter, and study the influence of polydispersity on this stability. The platelets are assumed to interact like hard objects, but additional soft attractive and repulsive interactions, meant to represent the effect of depletion interactions due to the addition of nonabsorbing polymer, or of screened Coulomb interactions between charged platelets in an aqueous solvent, respectively, are also considered. The aspect (diameter-to-thickness) ratio is taken to be very high, in order to model solutions of mineral platelets recently explored experimentally. In this regime a high degree of orientational ordering occurs; therefore, the model platelets can be taken as completely parallel and are amenable to analysis via a fundamental-measure theory. Our focus is on the nematic versus smectic phase interplay, since a high degree of polydispersity in diameter suppresses the formation of the columnar phase. When interactions are purely hard, the theory predicts a continuous nematic-to-smectic transition, regardless of the degree of diameter polydispersity. However, polydispersity enhances the stability of the smectic phase against the nematic phase. Predictions for the case where an additional soft interaction is added are obtained using mean-field perturbation theory. In the case of the one-component fluid, the transition remains continuous for repulsive forces, and the smectic phase becomes more stable as the range of the interaction is decreased. The opposite behavior with respect to the range is observed for attractive forces, and in fact the transition becomes of first order below a tricritical point. Also, for attractive interactions, nematic demixing appears, with an associated critical point. When platelet polydispersity is introduced the tricritical temperature shifts to very high values.

Rheology of a dispersion of low-molar-mass liquid crystal droplets in polydimethylsiloxane

We describe the linear viscoelastic response of dispersions of droplets of two biphenylcarbonitriles that exhibit both isotropic and liquid crystalline phases, 4′-pentyl-4-biphenylcarbonitrile (5CB) and 4′-octyl-4-biphenylcarbonitrile (8CB), in polydimethylsiloxane (PDMS). The Palierne emulsion model agrees well with the storage modulus data for 8CB in both isotropic and nematic phases, but the model overpredicts the magnitude of the interfacial relaxation in the 5CB dispersion, where the volume fraction of the dispersed phase required to fit the data is substantially smaller than the actual value. Similarly, the interfacial tension of 5CB against PDMS deduced from the Palierne fit shows much less temperature dependence than values measured with pendant drop tensiometry. The 8CB droplets are small, with a narrow size distribution, while the 5CB droplets are considerably larger and have a high degree of polydispersity. The basic mechanics of the Palierne theory appear to be applicable to nematic liquids, at least under conditions where the entropic elasticity is weak relative to the interfacial stress; the data suggest, however, that the theory is not applicable to smectic systems, and it needs to be used with considerable care with large droplets accompanied by a large degree of polydispersity.

Effect of water-soluble cross-linker on the growth and properties of ethyl acrylate-methacrylic acid emulsion opolymer particles

Model ethyl acrylate–methacrylic acid copolymer latices and latices of particles cross-linked by copolymerizing small amounts of water-soluble N,N′-methylenebisacrylamide were prepared by nonseeded semicontinuous emulsion copolymerization. Dynamic and static light scattering measurements indicated a slightly higher degree of polydispersity in the case of cross-linked particles, especially in the initial stages of polymerization. The hydrodynamic volume of the alkalinized particles controlling the viscosity properties of the dispersions decreased with the time of polymerization and in the case of cross-linked copolymer almost reached a constant value at about 1 h. The different character of the particle structure was confirmed by differences in particle disintegration after alkali addition or in the presence of methanol.

Polydispersity and heterogeneity of squid cranial cartilage proteoglycans as assessed by immunochemical methods and electron microscopy

The three populations of squid cranial cartilage proteoglycans, D1D1A, D1D1B and D1D2 appeared to have a high degree of polydispersity. Gel electrophoresis and immunoblotting analysis showed that polydispersity was mainly due to the variable size of chondroitin sulphate E chains. This was further ascertained after rotary shadowing electron microscopy of proteoglycan core proteins and glycosaminoglycan side chains and statistical analysis of the sizes measured for both components. Enzymic treatment of the proteoglycan core proteins produced different peptides from each population, suggesting that the observed heterogeneity of the proteoglycans is due to their core proteins. Antibodies were raised in rabbits against all proteoglycans and enzyme-linked immunosorbent analysis of proteoglycan core proteins revealed that the proteoglycans, even heterogeneous, shared many common epitopes. Part of the common proteoglycan epitopes were found to be located in chondroitin sulphate E chains. Heterogeneity of squid proteoglycans was also investigated by studying their interactions with collagen and it was found that only the two populations of high molecular mass, D1D1A and D1D2, were able to interact with only collagen type I, the latter stronger than the former.

Production process and service of quartz steel-casting refractories. Part 1. Features of the process

Conditions for manufacturing quartz refractories with a prolonged service life are formulated. The most important technological factor consists in preparation of limitingly concentrated suspensions of molten quartz (12–13% moisture content) with a high degree of polydispersity for slip casting or centrifugal shaping. A method for shaping articles based on ceramic castable mixtures that makes it possible to reduce the porosity of shaped semifinished products to 7–12% is suggested. The dynamics of the growth of the production of quartz refractories at the Pervouralskii Dinas Plant is described. The output has been increased fourfold during the last four years.

High-Resolution Studies of Hyaluronic Acid Mixtures through Capillary Gel Electrophoresis

Hyaluronic acid is a negatively charged polysaccharide with a high degree of polydispersity that makes the separation of its oligomers extremely difficult. Through the use of columns filled with a highly viscous polyacrylamide matrix, the unit resolution of hyaluronate oligomers could be achieved, up to at least 80 kDa of mass, through capillary electrophoresis. As analytical application examples, the fractions of enzymatically or ultrasonically degraded hyaluronates were monitored through this method. Because of the very high resolving power, peaks additional to the regular oligomers can be observed that are assumed to be conformers of this regular, unbranched biopolymer.

Human Mucin Genes MUC2, MUC3,MUC4, MUC5AC, MUC5B, andMUC6 Express Stable and Extremely Large mRNAs and Exhibit a Variable Length Polymorphism: AN IMPROVED METHOD TO ANALYZE LARGE mRNAs

Of the nine mucin genes that have been characterized, only MUC1 and MUC7 have been fully sequenced, and their transcripts can be detected as distinct bands of predicted size by Northern blot analysis. In contrast, the RNA patterns observed for each of the other MUC genes have usually shown a very high degree of polydispersity. This polydispersity has been believed to be one of the typical features of the mucin mRNAs, but until now, its origin has remained unexplained. In the work described in the present paper, we investigated two possible kinds of explanation for this phenomenon: namely that the extensive polydispersity results from a biological mechanism or that it is artifactual in origin. The data obtained, as a result of improving the purification and blotting methods, allowed us to show that in all of the tissues analyzed, each of the genes, MUC2-6, expresses mRNAs that are stable and are of an unusually large size to be found in eukaryotes (14-24 kilobases). Moreover, allelic variations in length of these mucin transcripts were observed. We demonstrate that these variations are directly related to the variable number of tandem repeat polymorphisms seen at the DNA level.

Isolation, structural determination, and calcium-binding properties of the major glycoprotein present in Bufo japonicus japonicus egg jelly.

Although the previous studies showed that the jelly coat is essential in anuran fertilization under natural conditions, identification and structural studies of the macromolecules that play functional roles have remained to be elucidated. In the present study we isolated acidic glycoproteins (JGP) from the solubilized egg jelly of Bufo japonicus japonicus, and showed that they were the major non-dialyzable macromolecular components of the jelly coat. JGP was a typical mucin-type glycoprotein, and it showed high degree of polydispersity in molecular masses ranging over 100-4000 kDa, but both amino acid and carbohydrate compositions were practically identical among fractions, suggesting that JGP was composed of a repeating glycoprotein unit. Four types of short O-glycan chains were isolated from JGP by reductive beta-elimination and their structures were determined as: Gal beta 1-->3[NeuAc alpha 2-->6]GalNAcol (= N-acetylgalactosaminitol), Fuc alpha 1-->2Gal beta 1-->3 [NeuAc alpha 2-->6]GalNAcol, Fuc alpha 1-->2Gal beta 1-->3[GlcNAc beta 1-->6]GalNAcol, and Fuc alpha 1-->2Gal beta 1-->3-GalNAcol. These carbohydrate units (about 80% of the mass of JGP) were linked to nearly all the serine and threonine residues which accounted for 55% of total amino acid residues. The Ca(2+)-binding property of JGP was studied by equilibrium dialysis. The high Ca(2+)-binding capacity of JGP was abolished by its desialylation of JGP and was highly dependent on the JGP concentration. When the low JGP concentrations as in the hydrated Bufo jelly were used, a 50% increment of both n (the number of binding sites) and Kd (the dissociation constant of JGP-Ca2+) values was observed. This property of JGP is suited to retaining Ca2+ and keeping its concentration at that just necessary for fertilizing sperm.

Polydispersions radiation envelope: Influence of particle size and assumed distribution function

The influence of polydispersity, particle size and of assumed distribution on angular dependence of theMie intensity functions in systems with relative refractive indexm = 1.10 was studied theoretically. Two distribution functions were used; Stevenson-Heller-Wallach (SHWD) and logarithmic distribution of negative order (NOLD). It was found, that for highly polydisperse systems the functional dependences obtain also undulative character. By means of NOLD the angular shift of extremes on the curves studied with increasing polydispersity was not observed. The application of this distribution in comparison with SHWD shows more structured angular scattering patterns with increasing particle size and this fact can also be employed in modelling and in distribution analysis of dispersion with higher degree of polydispersity.

Characteristics of Lipase-Rich Fractions of Milk Protein

Lipase-rich fractions of skimmilk, frozen-thawed skimmilk and a water extract of rennet-casein, were obtained by Sephadex gel filtration. Three similar fractions were obtained from all materials. Protein predominated in the fast-moving fraction and lipase activity concentrated in the two slow-moving components. Slow components showed 10–200 fold greater activity than the starting material, with the slowest moving component being the highest. Slower moving components from frozen-thawed skimmilk and from the water extract of rennet casein were 5–10 times higher in specific activity than comparable skimmilk fractions.Two slow-moving components from the three materials contained sulfur and carbohydrate in all fractions. Molecular weights were less than 10,000. Variations in 200/280 mu absorption UV ratios suggested differences in molecular structure.The second extract from the rennet casein showed a complex composition containing amino sugars, neuraminic acid, glucose or galactose, and an unknown ninhydrin positive component.Lipase activity was unaffected by pressure ultrafiltration but decreased by freeze drying. Polyacrylamide electrophoresis revealed the freeze-dried fractions had a relatively high degree of protein homogeneity, whereas, in the ultrafiltrated fractions the protein had aggregated with a high degree of polydispersity and heterogeneity.

Osmometric study of the degradation of fluorine-containing polymers

IN STUDIES of the influence of various chemical, physicochemica], and mechanical processes on the properties of polymers, it is frequently necessary to obtain information on the degradation of the polymer and the change in its polydispersity. The most widely used method [1] of determining the change in the molecular weight and polydispersity of a polymer due to degradation is the measurement of its intrinsic viscosity in dilute solutions. This method, however, only permits an estimation of the over-all change in the molecular weight of the polymer and does not enable the amount of low-molecular-weight fraction (molecular weights from 25,000 to 20,000) in the polymer formed by degradation to be determined or to be separated from the bulk of the polymer. These problems can be solved by using the osmometric method, which is widely employed at the present time to determine the molecular weights of polymers. In determining the molecular weight of a polymer having a high degree of polydispersity, the low-molecularweight fraction of the polymer may pass through the membrane; of course, this fact is reflected in the value of the number-average molecular weight and is negative. However, the diffusion of the low-molecular-weight fraction through the membrane may be used to obtain information on the increase in the content of low-molecular-weight fractions as a result of various influences on the polymer. We have used this circumstance in an investigation of the thermal-oxidative degradation of the fluorine-containing polymer Ftorlon.