Molar Mass Range Research Articles

Investigation of interfacial properties of aqueous two-phase systems by density gradient theory: Dedicated to Prof. Sabine Enders on her 50th birthday and in honor of her previous scientific impact

In this work the interfacial properties of aqueous two-phase systems (ATPS) consisting of an aqueous solution of polyethylene glycol (PEG) and dextran with different molar masses were investigated. To calculate the interfacial properties the density gradient theory was combined with the lattice cluster theory and the Wertheim association theory. With help of this thermodynamic model the liquid–liquid equilibria of the investigated ATPS were calculated in a molar mass range of PEG from 4000 to 20,000g/mol and of dextran from 10,000 to 500,000g/mol; whereas the thermodynamic model was fitted to the phase equilibrium in several selected ATPS. Phase equilibria in all other systems were predicted in a good accordance with experimental data.On the basis of the modelled phase equilibria the interfacial tension was calculated by the density gradient theory in an excellent agreement with experimental data. Moreover, the concentration profile of the phase forming components across the interface was calculated and it could be seen that there is no accumulation of any component in the interface and that the length of interfacial region depends on PEG molar mass.

Analysis of therapeutic proteins and peptides using multiangle light scattering coupled to ultra high performance liquid chromatography.

Analysis of the physical properties of biotherapeutic proteins is crucial throughout all the stages of their lifecycle. Herein, we used size-exclusion ultra high performance liquid chromatography coupled to multiangle light scattering and refractive index detection systems to determine the molar mass, mass-average molar mass, molar-mass dispersity and hydrodynamic radius of two monoclonal antibodies (rituximab and trastuzumab), a fusion protein (etanercept), and a synthetic copolymer (glatiramer acetate) employed as models. A customized instrument configuration was set to diminish band-broadening effects and enhance sensitivity throughout detectors. The customized configuration showed a performance improvement with respect to the high-performance liquid chromatography standard configuration, as observed by a 3 h column conditioning and a higher resolution analysis in 20 min. Analysis of the two monoclonal antibodies showed averaged values of 148.0 kDa for mass-average molar mass and 5.4 nm for hydrodynamic radius, whereas for etanercept these values were 124.2 kDa and 6.9 nm, respectively. Molar-mass dispersity was 1.000 on average for these proteins. Regarding glatiramer acetate, a molar mass range from 3 to 45 kDa and a molar-mass dispersity of 1.304 were consistent with its intrinsic peptide diversity, and its mass-average molar mass was 10.4 kDa. Overall, this method demonstrated an accurate determination of molar mass, overcoming the difficulties of size-exclusion chromatography.

In vitro study of partially hydrolyzed poly(2-ethyl-2-oxazolines) as materials for biomedical applications.

Polymers based on 2-oxazoline, such as poly(2-ethyl-2-oxazolines) (PETOx), are considered to be a type of 'pseudopeptide' with the ability to form novel biomaterials. The hydrolysis of PETOx was carried out to evaluate its use in biomedical applications. In the present work, PETOx samples with a range of molar masses were prepared by living cationic polymerization. Hydrolysis was carried out at time intervals ranging from 15 to 180 min to prepare copolymers with different amounts of ethylene imine units. (1)H NMR spectroscopy was used to identify the structure of the hydrolyzed polymers. The dependence of in vitro cell viability on the degree of hydrolysis was determined using three different model cell lines, namely, mouse embryonic 3T3 fibroblasts, pancreatic βTC3 cells, and mouse lymphoid macrophages P388.D1. It was demonstrated that increasing the degree of hydrolysis decreased cell viability for all cell types. Fibroblast cells displayed the highest tolerance; additionally, the effect of polymer size showed no observable significance. Macrophage cells, immune system representatives, displayed the highest sensitivity to contact with hydrolyzed PETOx. The effect of polymer hydrolysis, polymer concentration and the incubation time on cell viability was experimentally observed. Confocal laser-scanning microscopy provided evidence of cellular uptake of pyrene-labeled (co)polymers.

Separation of parent homopolymers from poly(ethylene oxide) and polystyrene-based block copolymers by liquid chromatography under limiting conditions of desorption – 1. Determination of the suitable molar mass range and optimization of chromatographic conditions

We studied molar mass limits for the LC LCD separation of parent polystyrene (PS) and poly(ethylene oxide) (PEO) homopolymers from PEO/PS based block copolymers and we identified optimized chromatographic conditions. Time delays between barriers and sample injections were 0–2–3′10. Eluent was composed of dimethylformamide (DMF) 40wt.% and 1-chlorobutane (CLB) 60wt.%; Barrier 1 (B1), which retained block copolymer, was composed of 100wt.% CLB and Barrier 2 (B2), which retained PEO, was a mixture of DMF and CLB, which proportions were adjusted to studied block copolymers. With B2 composed of DMF 23wt.% and CLB 77wt.%, we obtained successful separation of PS23K-b-PEO35K-b-PS23K (56.5wt.% of PS, the subscripts indicate the molar mass in kgmol−1 of each polymer part in the block copolymer) from its parent homopolymers. With B2 adjusted to DMF 30wt.% and CLB 70wt.%, PS2.3K-b-PEO3.1K (42.6wt.% of PS) was also efficiently separated from its parent homopolymers.

Polysaccharide characterization by hollow-fiber flow field-flow fractionation with on-line multi-angle static light scattering and differential refractometry

Accurate characterization of the molar mass and size of polysaccharides is an ongoing challenge, oftentimes due to architectural diversity but also to the broad molar mass (M) range over which a single polysaccharide can exist and to the ultra-high M of many polysaccharides. Because of the latter, many of these biomacromolecules experience on-column, flow-induced degradation during analysis by size-exclusion and, even, hydrodynamic chromatography (SEC and HDC, respectively). The necessity for gentler fractionation methods has, to date, been addressed employing asymmetric flow field-flow fractionation (AF4). Here, we introduce the coupling of hollow-fiber flow field-flow fractionation (HF5) to multi-angle static light scattering (MALS) and differential refractometry (DRI) detection for the analysis of polysaccharides. In HF5, less stresses are placed on the macromolecules during separation than in SEC or HDC, and HF5 can offer a higher sensitivity, with less propensity for system overloading and analyte aggregation, than generally found in AF4. The coupling to MALS and DRI affords the determination of absolute, calibration-curve-independent molar mass averages and dispersities. Results from the present HF5/MALS/DRI experiments with dextrans, pullulans, and larch arabinogalactan were augmented with hydrodynamic radius (RH) measurements from off-line quasi-elastic light scattering (QELS) and by RH distribution calculations and fractogram simulations obtained via a finite element analysis implementation of field-flow fractionation theory by commercially available software. As part of this study, we have investigated analyte recovery in HF5 and also possible reasons for discrepancies between calculated and simulated results vis-à-vis experimentally determined data.

Characterization of the global structure of low methoxyl pectin in solution

Low methoxyl citrus pectin (LMP) and amidated low methoxyl pectin (LMAP) were characterized by high performance size exclusion chromatography (HPSEC) with online light scattering (LS), intrinsic viscosity (ηw), differential refractive index (dRI) and ultra-violet (UV) detection, by amino acid analysis (AAA) and by atomic force microscopy (AFM). HPSEC revealed the following: the weight average molar mass (Mw), ranged 103–288 × 103 Da, (ηw), ranged 2.69–4.27 dL/g, radius of gyration (Rgz), was 28.6–49.5 nm and hydrated radius (Rhzv), was 26.3–41.8 nm. The presence of phenylalanine and tyrosine residues as shown by the UV absorbance at 278 nm in the high molar mass range is indicative of protein or fragments associated with LMP derived from citrus fruit. The ρ value (Rgz/Rhzv) as a function of molar mass indicated that high molar mass pectin was more compact in shape than intermediate molar mass pectin. AFM images in this study and earlier studies indicate that high methoxyl pectin (HMP) and LMP form network structures in aqueous solution. Unlike HMP networks, LMP networks do not dissociate when dissolved in water at concentrations that are less than 6.6 μg/mL. Furthermore, AFM images, Mw and ηw values for LMP and LMAP indicate that little or no added sugar is bound.

Molar mass and temperature dependence of the thermodiffusion of polyethylene oxide in water/ethanol mixtures.

In this work, we study the molar mass dependence of the thermodiffusion of polyethylene oxide at different temperatures in ethanol, water/ethanol mixture (c(water) = 0.7), and water in a molar mass range up to M(w) = 180,000 g/mol. Due to the low solubility of polyethylene oxide oligomers in ethanol the measurements are limited up to M(w) = 2200 g/mol. The specific water/ethanol concentration 0.7 has been chosen, because at this weight fraction the thermal diffusion coefficient, D(T), of water/ethanol vanishes so that the system can be treated as a pseudo binary mixture. The addition of ethanol will degrade the solvent quality, so that we expect a change of the interaction energies between polymer and solvent. The analysis of the experimental data within a theoretical model shows the need of a refined model, which takes specific interactions into account.

Decomposition and combustion studies of phosphine oxide containing aromatic polyethers

A comparative study of the decomposition and combustion behavior of systematically varied linear polyether analogs is reported. Properties of aromatic polyethers of bisphenol A/or 4,4′-dihydroxy biphenyl with bis(4-fluorophenyl) derivatives with phosphorus, –CF3 and methoxy –OCH3 constituents were systematically evaluated. All polyethers were synthesized by nucleophilic aromatic polycondensation. The polymers obtained covered a wide range of weight average molar masses (40,000–125,000 g/mol) as determined by size exclusion chromatography with multi-angle light scattering detection. FTIR and NMR spectroscopy revealed formation of the desired polymer structure of the linear polyarylene ethers. All polymers were easily soluble in common organic solvents, thus enabling processing from solution. Film casting from dichloromethane solution yielded transparent, free standing films with high mechanical stability (tensile strengths up to 63 MPa, E-moduli up to 2.5 GPa and elongations at break up to 35%). The thermal decomposition under nitrogen was accessed by thermogravimetry (TGA) and TGA combined with infrared spectroscopy, while the combustion was examined by pyrolysis combustion flow calorimetry (PCFC). The fire behavior was examined for one polymer (P3) by limiting oxygen index that revealed that the phosphine oxide moieties have a measurable influence on flame retardancy compared to the PSU control.

Fine tuning of lithographic masks through thin films of PS-b-PMMA with different molar mass by rapid thermal processing.

The self-assembly of asymmetric polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymer based nanoporous thin films over a broad range of molar mass (Mn) between 39 kg·mol(-1) and 205 kg·mol(-1) is obtained by means of a simple thermal treatment. In the case of standard thermal treatments, the self-assembly process of block copolymers is hindered at small Mn by thermodynamic limitations and by a large kinetic barrier at high Mn. We demonstrate that a fine tuning of the annealing parameters, performed by a Rapid Thermal Processing (RTP) machine, permits us to overcome those limitations. Cylindrical features are obtained by varying Mn and properly changing the corresponding annealing temperature, while keeping constant the annealing time (900 s), the film thickness (∼30 nm), and the PS fraction (∼0.7). The morphology, the characteristic dimensions (i.e., the pore diameter d and the pore-to-pore distance L0), and the order parameter (i.e., the lattice correlation length ξ) of the samples are analyzed by scanning electron microscopy and grazing-incidence small-angle X-ray scattering, obtaining values of d ranging between 12 and 30 nm and L0 ranging between 24 and 73 nm. The dependence of L0 as a 0.67 power law of the number of segments places these systems inside the strong segregation limit regime. The experimental results evidence the capability to tailor the self-assembly processes of block copolymers over a wide range of molecular weights by a simple thermal process, fully compatible with the stringent constraints of lithographic applications and industrial manufacturing.

Strong Linear Polyelectrolytes in Solutions of Extreme Concentrations of One–One Valent Salt. Hydrodynamic Study

Two series of highly charged linear aliphatic polymers—sodium polystyrene-4-sulfonate and random copolymer of N-methyl-N-vinylacetamide and N-methyl-N-vinylamine hydrochloride—were studied in water solution without added salts and in solutions containing up to 5 M NaCl. Intrinsic viscosity in salt-free solutions was estimated by a method proposed earlier [Pavlov et al. Russ. J. Appl. Chem. 2006, 79, 1407–1412]. Molecular characteristics were obtained in 0.2 M NaCl. The polyelectrolytes were studied in more than 10-fold range of molar mass. Qualitatively, the conformational status of the polyelectrolyte chains in different ionic strength was defined with the Kuhn–Mark–Houwink–Sakurada plots normalized by the value of linear chain density. In salt-free solution both polyelectrolytes could be attributed to extra rigid chains with the statistical segment length of 650 nm for sodium polystyrene-4-sulfonate and 100 nm for copolymer chains. Such statistical segment lengths are provided by short-range electrostatic intrachain interactions and are comparable with the Debye screening length. At extremely high NaCl concentration polyelectrolyte chains became discriminated by their degree of hydrophobicity. Chains of hydrophobic nature are compacted up to preglobular state, whereas the chains of the hydrophilic nature stay in the conformation of swelling coils at the highest concentration of NaCl.

Frontiers in Polymer Chemistry

The article shows how the initial concept of Staudinger on linear macromolecules was expanded topologically by increasing the cross-section diameter of polymer chains and by introducing sheet polymers with planar rather than the commonly known linear repeat units. The two concrete projects addressed are the synthesis of dendronized and of two-dimensional polymers. It is explained how these novel macromolecules were achieved and which obstacles had to be overcome but also where these frontiers in polymer chemistry might lead to new insights in polymer science in general and novel applications in particular. The article also provides insights into analytical issues because both target macromolecules are in an extraordinarily high molar mass range and contrast/sensitivity issues can turn rather serious in particular for the two-dimensional polymers.

Peptide diversity in the venom of the social wasp Polybia paulista (Hymenoptera): A comparison of the intra- and inter-colony compositions

The venoms of the social wasps evolved to be used as defensive tools to protect the colonies of these insects against the attacks of predators. Previous studies estimated the presence of a dozen peptide components in the venoms of each species of these insects, which altogether comprise up to 70% of the weight of freeze-dried venoms. In the present study, an optimized experimental protocol is reported that utilizes liquid chromatography coupled to electrospray ionization mass spectrometry for the detection of peptides in the venom of the social wasp Polybia paulista; peptide profiles for both intra- and inter-colonial comparisons were obtained using this protocol. The results of our study revealed a surprisingly high level of intra- and inter-colonial variability for the same wasp species. We detected 78–108 different peptides in the venom of different colonies of P. paulista in the molar mass range from 400 to 3000Da; among those, only 36 and 44 common peptides were observed in the inter- and intra-colony comparisons, respectively.

Metathetic degradation of trans-1,4-polyisoprene with ruthenium catalysts

Abstract Degradation study of trans-1,4-polyisoprene (trans-1,4-PI), that can be produced by the nature, was performed using first and second generation Grubbs and Hoveyda–Grubbs catalysts with olefins (ethylene or 1-octene) as transfer agents in toluene at 60 °C. While first generation Grubbs catalyst afforded low degradation, highlighting the presence of catalyst decomposition and/or inter-chain cross-metathesis reactions, an almost complete metathetic degradation could be reached using the second generation Grubbs catalyst in few minutes. Nevertheless, the synthesis of well-defined polyisoprenes with a targeted molar mass revealed to be difficult with Grubbs catalysts. On the contrary, Hoveyda–Grubbs catalysts were found to be more efficient to control the degradation of trans-1,4-PI. Indeed, regioselective degradation afforded pure trans-1,4-PI with a range of molar mass from 50 000 g/mol to 10 000 g/mol. However, polyisoprenes of lower molar masses (Mn

Rapid and Systematic Access to Quasi‐Diblock Copolymer Libraries Covering a Comprehensive Composition Range by Sequential RAFT Polymerization in an Automated Synthesizer

A versatile, cost-effective approach to the rapid, fully unattended preparation of systematic quasi-diblock copolymer libraries via sequential RAFT polymerization in an automated synthesizer is reported. The procedure is demonstrated with the synthesis of a 23 member library of low dispersity poly(butyl methacrylate)-quasiblock-poly(methyl methacrylate) covering a wide (fivefold) range of molar mass for the second block in a one-pot, sequential, RAFT polymerization.

Modelling of biodiesel fuel droplet heating and evaporation

Biodiesel fuel droplet heating and evaporation is investigated using the previously developed models, taking into account temperature gradient, recirculation, and species diffusion within droplets. The analysis is focused on four types of biodiesel fuels: Palm Methyl Ester, Hemp Methyl Esters, Rapeseed oil Methyl Ester, and Soybean oil Methyl Ester. These fuels contain up to 15 various methyl esters and possibly small amounts of unspecified additives, which are treated as methyl esters with some average characteristics. Calculations are performed using two approaches: (1) taking into account the contribution of all components of biodiesel fuels (up to 16); and (2) assuming that these fuels can be treated as a one component fuel with averaged transport and thermodynamic coefficients. It is pointed out that for all types of biodiesel fuel the predictions of the multi-component and single component models are rather close (the droplet evaporation times predicted by these models differ by less than about 5.5%). This difference is much smaller than observed in the case of Diesel and gasoline fuel droplets, and is related to the fact that in the case of Diesel and gasoline fuel droplets the contribution of components in a wide range of molar masses and enthalpies of evaporation needs to be taken into account, while in the case of biodiesel fuels the main contribution comes from the components in a narrow range of molar masses, boiling temperatures and enthalpies of evaporation. As in the case of Diesel and gasoline fuel droplets, the multi-component model predicts higher droplet surface temperature and longer evaporation times than the single component model.

Size-Exclusion Chromatography of Asphaltenes: An Experimental Comparison of Commonly Used Approaches

Asphaltenes, the heaviest and most polar fraction of crude oil, are responsible for the clogging of oil pipelines and of underground reservoir rocks. Asphaltenes are defined as a solubility class (toluene- or benzene-soluble, n-alkane insoluble), and a consensus is still lacking on the molar mass (M) averages, distribution, and range of these materials. Size-exclusion chromatography (SEC) is among the most widely employed methods for characterizing the M averages and distributions of both natural and synthetic polymers and, as such, has seen widespread application in the study of asphaltenes. SEC analysis of asphaltenes presents a number of challenges, however, some inherent to all low-M materials and some unique to these particular analytes. Here, we have experimentally compared several of the most commonly used approaches to SEC of asphaltenes, in hope of both demonstrating the influence of experimental conditions upon the results obtained as well as to determine optimal conditions of analysis. In the end, while the former goal was met, the latter one remains an open challenge in the field.

Pearl-necklace complexes of flexible polyanions with neutral–cationic diblock copolymers

We study the complexation of very asymmetric diblock copolymers (consisting of a cationic block of 12 lysines connected to a 400 amino acid long hydrophilic polypeptide block with a net charge that is nearly zero) with oppositely charged sodium poly(acrylic acid) (NaPAA) with a range of molar masses between 2 and 1300 kg mol−1. For shorter Na-PAA chains, spherical complex coacervate micelles are formed, but for long Na-PAA chains, with molar masses in excess of 250 kg mol−1, atomic force microscopy indicates the presence of pearl-necklace structures. Complexes most likely consist of only a single NaPAA chain, complexed to multiple diblocks. Hence, the size of the complexes can be fully controlled via the NaPAA molar mass. The occurrence of pearl-necklace complexes at higher NaPAA molar masses is attributed to the packing frustration that arises due to the small size of the cationic block of the diblock copolymers.

Determining Hildebrand Solubility Parameter by Ultraviolet Spectroscopy and Microcalorimetry

The solubility parameter (δ) of a molecule is extremely important, since that new molecules are frequently developed to be applied in liquid systems. In this work, we looked for simple and reliable alternative techniques to determine δ of low and high molecular weight molecules. Pyrene, phenanthrene and naphthalene had their δ determined by microcalorimetry (µDSC), ultraviolet (UV) and calorimetry (DSC). UV results were similar to those obtained by DSC and to those cited in the literature. Polystyrene and sulfonated polystyrene samples had their δ determined by UV, µDSC and intrinsic viscosity ([η]). The [η] results were similar to those obtained by UV. UV procedure was relatively simple, easy operation and reliable for determining δ of molecules in a wide range of molar mass, can be used when developing new molecules. The µDSC procedure still requires some adjustments to become more accurate than [η] procedure.

Opposites attract: influence of the molar mass of branched poly(ethylene imine) on biophysical characteristics of siRNA-based polyplexese

Polymer-based carriers, in particular polycations, represent an interesting alternative to viral vectors, as they form so-called polyplexes with nucleic acids by entropic driven, electrostatic interactions. In this study, we investigate in detail polyplexes based on small interfering RNA (siRNA), the delivery of which into eukaryotic cells represents an attractive route for treating genetic diseases by inhibition of harmful gene expression. Although plasmid DNA (pDNA) based polyplexes are well characterized, we show that not all knowledge can be adopted from pDNA, as siRNA is around 250 times smaller and shows a higher rigidity. The used polymer component is the polycation branched poly(ethylene imine) (B-PEI) of a high range of molar masses (0.6, 1.8, 10, 25 kDa), which are further analyzed by potentiometric titration and cytotoxicity tests. The formation, size, and net-charge of the polyplexes are examined at different ratios of nitrogen of the different polymers and phosphates of the RNA (N/P). Moreover, the stability of siRNA polyplexes against heparin and time was investigated. The obtained physicochemical parameters were then correlated to the cellular internalization of polyplexes. A strong dependency of the molar mass on the polyplex characteristics of the used B-PEI was found. Thereby, high molar mass B-PEI ≥ 10 kDa forms smaller polyplexes of around 50 nm radius with zeta potentials > 25 mV, increased long-term stability, and enhanced cellular uptake compared to low molar mass ones. To gain deeper insight into the differences and characteristics of siRNA based polyplexes, the characterization by analytical and preparative ultracentrifugation (AUC, PUC) is applied on siRNA polyplexes for the first time and referred to conventional characterization methods such as DLS. AUC was also used to identify non-complexed PEI in the polyplex solutions. A virtual N/P of 1.3 for siRNA was measured, independent of the used molar masses of B-PEI. Additionally, differences in cellular uptakes of siRNA and pDNA based polyplexes were found. The results of this study will help to understand the properties of siRNA-based polyplexes and could lead to more efficient polymer design.

Separation of polymeric galactoglucomannans from hot-water extract of spruce wood

Two methods for separation of polymeric galactoglucomannans (GGMs) from a hot-water extract of spruce wood, i.e., membrane filtration and precipitation in ethanol–water, were compared. Filtration through a series of membranes with different pore sizes separated GGMs of different molar masses, from polymers to oligomers. Only polysaccharides were precipitated in ethanol–water. With the optimal water content of 5–15%, the precipitated amount was about 6% on wood basis. The average molar mass of the precipitated polysaccharides was 10–12kDa with a molar mass range of 4–20kDa. GGMs comprised about 80% of the precipitated hemicelluloses. Other precipitated polysaccharides were mainly arabinoglucuronoxylans and pectins (rhamnogalacturonans). Analysis of a lignin-free, ethanol-precipitated GGM preparation by 13C NMR spectroscopy verified that it was structurally almost identical with a GGM-rich ethanol precipitate obtained from spruce wood by extraction at much milder conditions, 90°C for 60min.