Molecular Weight Samples Research Articles

Insights on influence of polymer molecular weight on gas sorption, transport and plasticization in glassy 6FDA-DAM polyimide membranes

It is well-known that spinning of defect-free asymmetric polyimide hollow fibers is promoted by using high polymer molecular weight. On the other hand, effects of polymer molecular weight on microstructure and separation performance of dense film 6FDA-based polyimide membranes relevant to sheath layers of composite membranes are less well-explored. In this work, gas sorption, diffusion and permeation of CO2, N2 and CH4 for 6FDA-DAM dense films are considered for 45 kDa and 176 kDa weight average molecular weights. Such molecular weights are relevant for practical hollow fiber spinning of membranes. Earlier results for polystyrene samples show similar trends in dual mode sorption model results like those noted here for the 6FDA-DAM polyimide case; however, effects on permeation like those considered here were not addressed for the polystyrene case. Here we also address actual pure and mixed gas CO2 and CH4 permeation and show higher free volumes, higher gas permeability but lower 50:50 CO2/CH4 selectivity associated with the higher molecular weight sample. Analysis using the self-consistent dual-mode sorption and transport models help understand the observed trends. Our results suggest denser packing of polymer segments exists in the Henry's law environment of the low molecular weight sample. Moreover, the higher polymer segmental packing in the Henry's law environment suppresses CO2 plasticization with a dual-mode microstructure controlling separation performance and plasticization behavior for this important member of the 6FDA polyimide family. We show evidence of effects of charge transfer complexes as possible main features in these trends. These dense film results help guide future work on dense sheath layers on composite hollow fiber membranes.

Waterborne 2-component polyurethane coatings based on acrylic polyols with secondary alcohols

We report the effects of increasing the molecular weight of a secondary alcohol-based polyol in a two-component waterborne polyurethane (2 K-WB-PUR) formulation. The system consists of an acrylic polyol latex and a water-dispersible polyisocyanate (hmPIC, Basonat HW1000 from BASF). The polyols investigated incorporated hydroxypropyl methacrylate as a comonomer to introduce the secondary –OH groups, in contrast to typical polyols which have primary -OH groups. Three molecular weights of this polyol were prepared (Mn ≈ 5100, Ð = 2.4; 10,300, Ð = 2.7; or 12,900 g/mol, Ð = 3.6) with a uniform Tg (∼20 °C) and hydrodynamic diameter (dh) ≈ 120 nm. The polyol and polyisocyanate were mixed with a molar NCO:OH ratio of 1.3:1. The particle size of the mixed dispersion was monitored by dynamic light scattering. The 5 K sample remained stable in dispersion over 7 days whereas the higher molecular weight formulations flocculated after 1 day. Fourier Transform Infrared (FTIR) measurements revealed that all NCO groups were consumed within 15–23 h for all dispersed samples. Fluorescence resonance energy transfer (FRET) experiments were carried out on samples in the dispersed state as well as on films formed from these dispersions. Very little molecular level mixing was observed in the dispersed phase for the samples. In the films, a large extent of mixing was observed in the 5 K sample whereas the extents of mixing for the higher molecular weight samples were reduced. The FTIR measurements recorded as the films formed showed that the NCO consumption in the 5 K film (t1/2 = 56 h) was comparable to an analogous 2 K-WB-PUR formulation based on a 5 K primary alcohol from a previous study. Surprisingly, the NCO consumption in the higher molecular weight samples was faster (t1/2 = 31, 32 h). We found that the composition of the resulting films formed from higher molecular weight polyols contained a greater relative ratio of polyurea to polyurethane.

Investigation of the Effectiveness of Photo Deprotection of Polypeptides in Solution and within the Core of Miniemulsion-Derived Nanoparticles.

Homopolymerization of ortho-nitrobenzyl (oNB)-protected l-cysteine and l-glutamic acid was systematically studied in different solvents and at different monomer to initiator ratios, revealing the best reaction control in dimethylformamide (DMF) across a range of degrees of polymerization. In the subsequent ultraviolet (UV)-cleavage studies, it was found that quantitative deprotection upon UV exposure at 365 nm was not achievable for either of the homopolypeptides as confirmed by 1H NMR and UV/visible (UV/vis) analyses. While the poly(oNB-l-cysteine) deprotected more readily with no effect of the polypeptide molecular weight, lower molecular weight poly(oNB-l-glutamate) reached maximum deprotection faster than high molecular weight samples. This was further confirmed by the pH changes of the solution. When incorporated into the core of miniemulsion-derived nanoparticles, both oNB-protected copolypeptides were successfully deprotected as evident from a color change and a pH change in the case of poly(oNB-l-glutamate). However, the removal of the deprotection byproduct nitrosobenzaldehyde proved unsuccessful, which indicates a diffusion barrier caused by the nanoparticle's surfactant. The study provides insights and guidelines for the UV deprotection of polypeptides and demonstrates the ability to selectively UV-deprotect polypeptides in the confined space of a nanoparticle dispersion.

Single-Ion Mass Spectrometry for Heterogeneous and High Molecular Weight Samples.

In charge detection mass spectrometry (CD-MS) the mass of each individual ion is determined from the measurement of its mass to charge ratio (m/z) and charge. Performing this measurement for thousands of ions allows mass distributions to be measured for heterogeneous and high mass samples that cannot be analyzed by conventional mass spectrometry (MS). CD-MS opens the door to accurate mass measurements for samples into the giga-Dalton regime, vastly expanding the reach of MS and allowing mass distributions to be determined for viruses, gene therapies, and vaccines. Following the success of CD-MS, single-ion mass measurements have recently been performed on an Orbitrap. CD-MS and Orbitrap individual ion mass spectrometry (I2MS) are described. Illustrative examples are provided, and the prospects for higher resolution measurements discussed. In the case of CD-MS, computer simulations indicate that much higher resolving powers are within reach. The ability to perform high-resolution CD-MS analysis of heterogeneous samples will be enabling and disruptive in top-down MS as high-resolution m/z and accurate charge measurements will allow very complex m/z spectra to be unraveled.

Secretome processing for proteomics: A methods comparison.

The cancer cell secretome comprises a treasure-trove for biomarkers since it reflects cross-talk between tumor cells and their surrounding environment with high detectability in biofluids. In this study, we evaluated six secretome sample processing workflows coupled to single-shot mass spectrometry: (1) Protein concentration by ultrafiltration with a molecular weight cut-off (MWCO) filter and sample preparation through in-gel digestion (IGD); (2) Acetone protein precipitation coupled to IGD; (3) MWCO filter-based protein concentration followed by to in-solution digestion (ISD); (4) Acetone protein precipitation coupled to ISD; (5) Direct ISD; (6) Secretome lyophilization and ISD. To this end, we assessed workflow triplicates in terms of total number of protein identifications, unique identifications, reproducibility of protein identification and quantification and detectability of small proteins with important functions in cancer biology such as cytokines, chemokines, and growth factors. Our findings revealed that acetone protein precipitation coupled to ISD outperformed the other methods in terms of the number of identified proteins (2246) and method reproducibility (correlation coefficient between replicates (r=0.94, CV=19%). Overall, especially small proteins such as those from the classes mentioned above were better identified using ISD workflows. Concluding, herein we report that secretome protein precipitation coupled to ISD is the method of choice for high-throughput secretome proteomics via single shot nanoLC-MS/MS.

Optical single molecule characterisation of natural and synthetic polymers through nanopores.

Nanopore techniques are now widely used to sequence DNA, RNA and even oligopeptide molecules at the base pair level by measuring the ionic current. In order to build a more versatile characterisation system, optical methods for the detection of a single molecule translocating through a nanopore have been developed, achieving very promising results. In this work, we developed a series of tools to interpret the optical signals in terms of the physical behaviour of various types of natural and synthetic polymers, with high throughput. We show that the measurement of the characteristic time of a translocation event gives access to the apparent molecular weight of an object, and allows us to quantify the concentration ratio of two DNA samples of different molecular weights in solution. Using the same tools for smaller synthetic polymers, we were able to obtain information about their molecular weight distribution depending on the synthesis method.

Synthesis, Morphology, and Crystallization Kinetics of Polyheptalactone (PHL).

Aliphatic polyesters are widely studied due to their excellent properties and low-cost production and also because, in many cases, they are biodegradable and/or recyclable. Therefore, expanding the range of available aliphatic polyesters is highly desirable. This paper reports the synthesis, morphology, and crystallization kinetics of a scarcely studied polyester, polyheptalactone (PHL). First, we synthesized the η-heptalactone monomer by the Baeyer-Villiger oxidation of cycloheptanone before several polyheptalactones of different molecular weights (in the range between 2 and 12 kDa), and low dispersities were prepared by ring-opening polymerization (ROP). The influence of molecular weight on primary nucleation rate, spherulitic growth rate, and overall crystallization rate was studied for the first time. All of these rates increased with PHL molecular weight, and they approached a plateau for the highest molecular weight samples employed here. Single crystals of PHLs were prepared for the first time, and hexagonal-shaped flat single crystals were obtained. The study of the crystallization and morphology of PHL revealed strong similarities with PCL, making PHLs very promising materials, considering their potential biodegradable character.

Upregulation of tight junction-related proteins by hyaluronic acid in human HaCaT keratinocytes

Hyaluronic acid (HA) is a natural polysaccharide widely used in dermatology; however, HA effects on the expression of proteins related to skin barrier function and their dependence on the HA molecular weight are still limited. In this study, we treated immortalized human keratinocytes with HA samples of low and high molecular weights (LMW-HA, <100 kDa and HMW-HA, >500 kDa, respectively) and analyzed the expression of tight junction-forming proteins. Both LMW-HA and HMW-HA significantly increased the expression of claudin-3 and claudin-4, whereas HMW-HA also upregulated junctional adhesion molecule JAM-1. These results indicate that HA could improve the skin barrier function by inducing the expression of tight junction-related genes in keratinocytes and that the effect could depend on the molecular weight of HA fragments.

Biodegradation Studies of Polyhydroxybutyrate and Polyhydroxybutyrate-co-Polyhydroxyvalerate Films in Soil.

Due to increased environmental pressures, significant research has focused on finding suitable biodegradable plastics to replace ubiquitous petrochemical-derived polymers. Polyhydroxyalkanoates (PHAs) are a class of polymers that can be synthesized by microorganisms and are biodegradable, making them suitable candidates. The present study looks at the degradation properties of two PHA polymers: polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-polyhydroxyvalerate (PHBV; 8 wt.% valerate), in two different soil conditions: soil fully saturated with water (100% relative humidity, RH) and soil with 40% RH. The degradation was evaluated by observing the changes in appearance, chemical signatures, mechanical properties, and molecular weight of samples. Both PHB and PHBV were degraded completely after two weeks in 100% RH soil conditions and showed significant reductions in mechanical properties after just three days. The samples in 40% RH soil, however, showed minimal changes in mechanical properties, melting temperatures/crystallinity, and molecular weight over six weeks. By observing the degradation behavior for different soil conditions, these results can pave the way for identifying situations where the current use of plastics can be replaced with biodegradable alternatives.

Composite based on PLA with improved shape stability under high-temperature conditions

Composite materials based on PLA have been studied in depth for many applications, including food packaging. This manuscript describes extensive research conducted on a biodegradable polymer (PLA), inorganic filler (CaCO3), and polyester-based plasticizer (PEP, based on a copolymer of low-molecular-weight PLA and PEG) prepared under semi-industrial conditions, as applicable for the packaging of hot food. The properties of the composite were achieved by post-processing annealing, notably its thermal stability, thereby permitting contact of the material with hot food. The manner of processing was deemed suitable for deployment at an industrial scale, moreover, the thermal stability of the final product endured, evidencing its applicability for such packaging. Change in the morphology of the structure of the composite material depended on the composition and annealing process, as detailed herein. The effect of the post-production thermal annealing on the molecular weight of samples was studied using the gel permeation chromatography. The thermal properties of the composites were investigated by differential scanning calorimetry, dynamic mechanical analysis, and thermogravimetric analysis. The crystallinity was assessed using X-ray diffraction technique, while mechanical behavior was tested in relation to the given tensile properties, shape stability at high temperature, and permeability by the transmission rates of gas/water vapor.

Investigation of density, viscosity and derived thermodynamic properties of CO2-free and CO2-loaded poly(ethylene imine) aqueous systems at different temperatures and 0.1 MPa

In this work, the density and viscosity for poly(ethylene imine) (PEI1800/10000) aqueous systems with and without CO2 over PEI concentrations (wt% = 5, 10, 15, 20, 30) are measured at temperatures from (293.15 to 333.15) K and 0.1 MPa. Based on the experimental data, the thermal expansion coefficient (αp), viscosity activation energy (Eη) and CO2 diffusion coefficient (DCO2) are calculated. The results show that the density and viscosity increase as the PEI concentration and CO2 loading increase. The higher molecular weight samples also give higher density and viscosity. The high viscosity further results in the large activation energy and low CO2 diffusion coefficient. All the experimental results are discussed from the perspective of intermolecular interactions which are further verified by the reaction mechanism and FT-IR spectra.

Emulsification characteristics of soy hull polysaccharides obtained by membrane separation

Membrane separation technology was used to separate and purify the microwave-assisted oxalic acid extraction of soy hull polysaccharides (MOSP) in order to obtain samples of different molecular weights. The emulsification characteristics of the MOSP were investigated including protein adsorption, polysaccharide adsorption, interfacial tension, emulsion index, and particle size; optical microscopy and Phenom electron microscopy were used to elucidate the emulsion structures. In addition, Fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), and high-performance gel-filtration chromatography (HPGFC) were used to study the differences in the components and structures of MOSP in different molecular weights. The molecular weight had several important effects on the emulsifying properties of MOSP. The adsorption capacities of the emulsion droplets containing low molecular weight MOSP (L-MOSP), middle molecular weight MOSP (M-MOSP), and high molecular weight MOSP (H-MOSP) were relatively low, and those of H-MOSP were slightly higher than those of L-MOSP. With extended storage time, the particle sizes of the emulsions rich in L-MOSP, M-MOSP, and H-MOSP increased. L-MOSP, M-MOSP, and H-MOSP were mainly composed of furans. The conformation of the molecular chain was spherical. The emulsions formed with H-MOSP were the most stable.

The absolute heat capacity of polymer grafted nanoparticles using fast scanning calorimetry*

AbstractThe absolute heat capacity of a matrix‐free polystyrene grafted silica nanocomposite system is investigated using ultrafast Flash differential scanning calorimetry (Flash DSC) and compared to results for a neat polystyrene sample of similar molecular weight. The heat capacity of the polymer in the nanocomposite is 8% lower than that of the neat polystyrene. In addition, the step change in heat capacity at the glass transition Tg is 15% lower, indicating a 2 nm‐thick immobile layer of polymer around the nanoparticles. There is neither an increase in the nanocomposite heat capacity towards that of the neat material nor any additional ∆Cp steps, indicating that the glassy layer around the nanoparticles remains immobile up to 300°C. In addition to the analysis of the absolute heat capacity, the dynamic temperature gradient in the Flash DSC sample increases linearly with increasing rate of measurement, whereas the noise in the heat capacity data increases linearly with the reciprocal of the scanning rate; the optimum rate for measurements lies between 300 and 1000 K/s for the samples studied here and will depend on the sample thickness.

Organizing Nanoparticles in Semicrystalline Polymers by Modifying Particle Diffusivity.

We have previously shown that semicrystalline polymers can be reinforced by adding nanoparticles (NPs) and then ordering them into specific motifs using the crystallization process. A key result we have found is that when the spherulite growth rate is slowed below a critical value, then, NPs can order into the amorphous interlamellar regions of the semicrystalline structure. The effects of spherulite growth rate in this context have previously been examined, and here we focus on the role of NP diffusivity. We achieve this goal by changing the poly(ethylene oxide) (PEO) molecular weight as a route to altering the matrix viscosity. In particular, four molecular weights of PEO were employed ranging from 5.4-46 kDa. Each sample was loaded with 10 vol % of bare 14 nm diameter silica NPs. After initially studying spherulite growth rates, experiments were designed to fix the spherulite growth rate across sample molecular weights to study particle ordering, induced by polymer crystallization. We find that, at the fastest growth rate studied (12 μm/s), the lowest molecular weight sample showed the highest order, presumably due to enhanced particle mobility. However, as the spherulite growth rate is slowed, the maximum ordering behavior is observed at intermediate molecular weights. The trend observed at slow growth rates is explained by the large-scale segregation of NPs (presumably into the grain boundaries, i.e., the interspherulitic regions); evidence for this is the observed transition of spherulite growth to diffusion-control at slow growth rates in the lowest molecular weight PEO sample studied.

Kinetics of alkaline delignification of hemp and determination of lignin content by thermogravimetry

Raw hemp (Cannabis sativa L.) was subjected to alkaline delignification with the application of NaOH ranging from [0.125M] to [1M] for times from 5 to 480 min. Lignin contents of the original and delignified samples were determined. The samples were subjected to thermogravimetric analysis (TGA) under a N2 atmosphere with temperatures ramped from 25 to 600 °C at 10 °C min-1. Lignosulfonates samples of low, medium and high molecular weight were subjected to the same TGA and showed that lignin decomposed over the entire temperature range. The contributions of lignin to the mass loss during thermal decomposition of hemp and kinetics of lignin content and the most relevant TGA results were determined. Regression models estimating the lignin content of the fibers based on TGA results were formulated. These models allow for the prediction of mean lignin content within ± 0.1% (based on dry weight of pulp) in the central range of the experimental field.

Terahertz immunosensing assisted by functionalized Au NPs based on all-dielectric metasurface

Terahertz (THz) sensors have attracted significant attention in the biological field due to their non-destructive and harmless interaction with biochemical samples, but how to achieve efficiently specific sensing for the small molecular weight samples is still challenging. In this work, we incorporated an all-dielectric metasurface with the functionalized gold nanoparticles (Au NPs) to realize an immunosensing of the target biomolecule at nanomole-level concentration. These Au NPs are modified by the Anti-HA tag antibody, which realizes the specific immunobinding of the human influenza hemagglutinin tag protein (HA antigen). By comparing with and without the functionalized Au NPs, the experimental results show that this sensor can quantitatively detect the concentration of HA antigen, and its sensitivity can be greatly improved by the functionalized Au NPs. The maximum sensitivity can be achieved to 2.96 GHz∙ml/nmol, which is 2.66 times higher than that without the Au NPs, and the highest detection accuracy reaches 1.05 nmol/ml. Furthermore, by comparing three other nonspecific proteins, only the HA antigen can be sensitively distinguished, which proves the specificity of this sensing method. Our results illustrate a reliable platform for THz immunosensing applications, and it is expected that the proposed sensing strategy opens new avenues for developing high-efficient, low-cost, and real-time THz all-dielectric sensors for biomolecular detection.

Archaeal Viruses: Production of Virus Particles and Vesicle-like Viruses and Purification Using Asymmetrical Flow Field-Flow Fractionation.

Asymmetrical flow field-flow fractionation (AF4) is a separation method based on hydrodynamic size of the sample components. It can separate a broad size range of components (~103 to 109Da; particle diameter from ~1nm to ~1μm), but is especially well suited for high molecular weight samples such as virus-sized particles and extracellular vesicles. Separation takes place in an open channel where the flows control sample elution. Separation does not involve stationary phase, allowing gentle separation and good recoveries. The method is compatible with a wide variety of buffers. Coupling to various analytical detectors enables rapid assays on the molecular weight and size and their distribution, degradation, and aggregation of the sample components giving information on the sample quality. In addition to being an advanced analytical method, AF4 can be used in a semipreparative mode for purification. Here, we summarize archaeal virus production methods and virus purification by AF4 and provide examples on the steps that need optimization for obtaining good separation with the focus on halophilic archaeal viruses. Importantly, AF4 method is suitable for a variety of viruses and extracellular vesicles regardless of their host organism.

Thermal Properties of Poly(Methyl Methacrylate) Samples of Different Molecular Weights Impregnated with Single-Walled Carbon Nanotubes in Supercritical Carbon Dioxide

Thermal Properties of Poly(Methyl Methacrylate) Samples of Different Molecular Weights Impregnated with Single-Walled Carbon Nanotubes in Supercritical Carbon Dioxide

A Greener Enzymatic Oligoesterification of Biobased Renewable Synthons

Polyesters of xylitol and succinic acid were prepared yielding from 70 to 75% by enzymecatalyzed esterification using a molar mass from 1:1 to 2:5 at 120 and 140 °C employing from 1 to 10% m/m of enzyme. Control over branching degree was achieved by tuning the reaction conditions (temperature, time, comonomer ratio, enzyme content). This one-step process from renewable starting materials avoids protection-deprotection techniques, as well as the use of toxic solvents by introducing limonene as solvent for polyesterification for the first time. All materials were structurally characterized by infrared (IR) and nuclear magnetic resonance (NMR)spectroscopy, their thermal properties were studied by differential scanning calorimetry (DSC)and thermogravimetric analysis (TGA), and the molecular weight of samples were obtained by gel-permeation chromatography (GPC).

The effect of long-term natural aging on the iPB-1 structure and the II – I phase transformation rate

The long-term natural aging of isotactic polybutene-1 samples of different molecular weight has shown that the transformation rate from the initial phase II to the stable phase I significantly decreased after natural aging, ranging from 0 to 17 years. It was found that the total crystallinity decreased with aging time and a small amount of phase II remained untransformed for at least 17 years. The transformation rate of a lower molecular weight sample, DP 0400, was higher than the PB 0110 sample, even after repeated polymer melting of aged samples and their new melt crystallization. The major phenomenon of the iPB-1 aging is the change in a ratio of methyl/methylene functional groups; possibly because of a side chain splitting that reduces the geometric regularity of the molecular chain and consecutively slows down the proceeding phase transformation.