Absolute Molecular Weight Research Articles

Exopolysaccharide production by a unicellular freshwater cyanobacterium Cyanothece sp. isolated from a rice field in Vietnam

A unicellular cyanobacterium that produces a large amount of exopolysaccharide (EPS) was isolated from a rice field in Phu Tho Province, Vietnam. Morphological characteristics and phylogenetic analysis using a partial sequence of the 16S rRNA gene revealed that the isolate was closely related to the genus Cyanothece. The isolate, named Cyanothece sp. Viet Nam 01, grew at a wide range of temperatures (25–40 °C), but was not viable below 20 °C. The isolate had an ability of aerobic nitrogen fixation. The EPS was purified using NaOH extraction and ethanol precipitation, and the absolute molecular weight was estimated to be 4.5 × 104 kDa. The pattern of the Fourier transform infrared spectrum indicated that the EPS had carbonyl and sulfate groups, as well as the typical functional groups of sugars. The uronic acid and sulfur contents were 23 and 8.4 mol% per total monosaccharide, respectively. The EPS constituent monosaccharides were rhamnose, glucose, galactose, xylose, mannose, fucose, arabinose, ribose, and unknown sugar, with molar compositions of 38.6:13.8:4.8:4.8:2.4:3.5:2.0:0.6:6.5, respectively.

Synthesis, characterization and properties of TAP-6FDA hyperbranched polyimides with different branching degrees

A series of hyperbranched polyimides were successfully synthesized by condensation polymerization of A2-type dianhydride monomer 2,2-bis(3,4-dicarboxylphenyl) hexafluoropropane dianhydride (6FDA) and B′B2-type triamine monomer 2,4,6-triaminopyrimidine (TAP). Polymers with different branching degrees (DB) and terminated groups were obtained by changing the monomer addition order and the monomer molar ratio. Fourier transform infrared spectroscopy and 1H NMR were used to verify the structure of the prepared polyimides, which indicated that the amino group still existed in all the products. The DB of the polymers indicated by 1H NMR increased from 30% to 79% with the molar ratio of TAP:6FDA decreasing from 1:1 to 1:2. The absolute molecular weights were measured by size-exclusion chromatography with multi-angle laser light-scattering detection, which suggested that the highest molecular weight would be obtained when the molar ratio of amino groups:anhydride groups of the monomers was 3:3.2. With the DB increasing, the d-spacing values indicated by wide angle X-ray diffraction increased from 5.15 Å to 5.68 Å and the UV − visible spectra of the polymers exhibited decreasing cut-off wavelengths. The 5% weight loss temperature in nitrogen increased with decreasing content of TAP monomer, and the glass transition temperatures of the obtained polyimides decreased from 282 °C to 258 °C with increasing DB. © 2013 Society of Chemical Industry

Polymer Characterization by Static Laser Light Scattering

Low angle laser light scattering (LALLS) and multi-angle laser light scattering (MALLS) methods have become valuable, if not indispensable, tools for the chemist and biochemist, since they can be used to determine the absolute molecular weight and size of molecules in solution. When linked to a gel permeation chromatography system, they become even more powerful tools, providing information on molecular weight averages and their distributions (polydispersity). LALLS has essenttially been superseded by the development of on-line MALLS and size-exclusion chromatography (SEC)/MALLS systems, which have facilitated the greater application of light scattering theory in structure elucidation. For example, the determination of root mean square radii, molecular conformation and structure, branching ratios etc., are now readily achievable. This paper reviews the “theoretical backbone” of light scattering methods and the technology available for use in this particular aspect of macromolecular characterisation. Particular emphasis is placed on the use of SEC/MALLS and SEC/LALLS for the molecular weight elucidation of polysaccharides (such as carrageenans, starch, hyaluronic acid and dextrans), proteins, and the examination of branching in large macromolecular structures

Quality evaluation of lentinan injection produced in China

Lentinan is a β-(1→6) branched β-(1→3)-glucan derived from Lentinula edodes mushroom. It has been developed as an adjuvant to cancer chemotherapy and clinically used in Japan and China. Up to date, six lentinan injections or powders for injection produced by individual manufacturers were widely used in clinic in China. Since antitumor effect of lentinan is highly related to its structure, conformation and molecular weight, quality evaluation of lentinan injection produced in China is crucial to ensure its efficacy, which has never been performed. In this study, absolute molecular weights and their distributions of lentinan in multiple batches of injections from different manufacturers in China were firstly determined through a high performance size exclusive chromatography (HPSEC) combined with multiple angle light scattering detection (MALSD) and refractive index detection (RID). Enzymatic (β-1,3-d-glucanase) digestion characters and triple helical conformation of lentinan were also investigated. The results showed that quality consistency of lentinan injections from different manufacturers in China was poor, which should be greatly improved to ensure their safety and efficacy.

Precise Synthesis and Characterization of Tadpole-Shaped Polystyrenes with High Purity

Tadpole-shaped polystyrenes (PS) were successfully synthesized anionically by coupling reaction between ring polystyrene with two functional groups and living linear polystyrenes. Crude coupling product was confirmed to include unreacted linear tail polymer and tadpole polymer having one tail (single-tail tadpole polymer) and two tails (twin-tail tadpole polymer) by SEC analysis. In order to isolate the tadpole polymers, interaction chromatography (IC) was conducted to remove the linear polymer from the crude product; subsequently, two kinds of tadpole polymers were carefully separated by SEC fractionation. It has been found by SEC-MALS that the absolute molecular weights of the two fractionated products agree well with the sums of the component ring and linear chains, which prove two tadpole polymers, i.e., single-tail and twin-tail, were obtained as designed. It was confirmed that the two tadpole polymers have high molecular weight (58k for ring and 67k for a tail), narrow molecular weight distribution (Mw/Mn = 1.01), and high purity over 99% by rigorous HPLC analyses.

Nucleophilic thiol-Michael chemistry and hyperbranched (co)polymers: synthesis and ring-opening metathesis (co)polymerization of novel difunctional exo-7-oxanorbornenes with in situ inimer formation

Nucleophile-initiated thiol-Michael chemistry was employed to prepare a series of mono- and di-functional exo-7-oxanorbornenes from the reaction between mono- or dithiols with 2-((3aR,7aS)-1,3-dioxo-3a,4,7,7a-tetrahydro-1H-4,7-epoxyisoindol-2(3H)-yl)ethyl acrylate. Homopolymerization of the difunctional species, bis(2-((3aR,7aS)-1,3-dioxo-3a,4,7,7a-tetrahydro-1H-4,7-epoxyisoindol-2(3H)-yl)ethyl)-3,3′-((1,4-phenylenebis(methylene))bis (sulfanediyl))dipropanoate (M1), with Grubbs' first generation catalyst, RuCl2(PCy3)2CHPh, yields a hyperbranched polymer with up to 90% of polymerizable CC bonds consumed as judged by 1H NMR spectroscopy. SEC analysis is consistent with the formation of a hyperbranched structure with an absolute weight average molecular weight (Mw), as measured by static light scattering in CH2Cl2, determined to be 381 000. Bis(2-((3aR,7aS)-1,3-dioxo-3a,4,7,7a-tetrahydro-1H-4,7-epoxyisoindol-2(3H)-yl)ethyl)-3,3′-((thiobis(ethane-2,1-diyl))bis (sulfanediyl))dipropanoate (M2) could not be polymerized with the Grubbs' 1st generation catalyst but rapidly polymerized with 50% conversion of monomeric CC bonds with the Grubbs' 3rd generation species. Bis(2-((3aR,7aS)-1,3-dioxo-3a,4,7,7a-tetrahydro-1H-4,7-epoxyisoindol-2(3H)-yl)ethyl)-7,10-dioxa-4,13-dithiahexadecane-1,16-dioate (M3), in a similar fashion to M1, could be readily homopolymerized to high conversion with the 1st generation species giving organosoluble material. The statistical copolymerization of M1 or M3 with a series of monofunctional monomers containing pyrrole, fluoro, POSS and fluorene functionality is demonstrated. Copolymers of variable composition are readily prepared with the Grubbs' 1st generation catalyst with, in general, CC bond conversions in excess of 90%. Finally, the preparation of novel linear-hyperbranched AB diblock copolymers is demonstrated via the sequential polymerization of a monofunctional sugar derivative, (2S,3S,4S,5R,6R)-6-((3-(2-((3aR,7aS)-1,3-dioxo-3a,4,7,7a-tetrahydro-1H-4,7-epoxyisoindol-2(3H)-yl)ethoxy)-3-oxopropyl)thio) tetrahydro-2H-pyran-2,3,4,5-tetrayl tetraacetate (M8) which yields a well-defined linear homopolymer, as judged by SEC, followed by chain extension with the difunctional substrate M3.

Phosphonium ionenes from well-defined step-growth polymerization: thermal and melt rheological properties

Step-growth polymerization of ditertiary phosphines with dibromoalkanes enabled the synthesis of novel phosphonium ionenes. In situ FTIR spectroscopy monitored the increase in absorbance as a function of time at 1116 cm−1, which corresponded to the polymeric P+–Ph stretch. Aqueous size-exclusion chromatography (SEC) provided absolute molecular weights and confirmed expected molecular weight growth for difunctional, step-growth polymerization. Phosphonium ionenes exhibited improved thermal and base stability compared to ammonium ionenes, which was attributed to the propensity of the ammonium cation towards Hofmann elimination. Melt rheology examined phosphonium ionene viscous flow and the influence of charge density on melt viscosity as a function of shear rate and temperature. Time–temperature superposition (TTS) resulted in both master curves and pseudomaster curves depending on phosphonium ionene composition. Two primary relaxations occurred: (1) onset of long-range segmental motion at Tg, and (2) relaxation attributed to electrostatic interactions. Higher charge densities shifted these two relaxations to longer time scales and increased flow activation energies. Phosphonium ionenes also readily bound pDNA effectively (± ratios of 1), and base stability suggested applications in energy generation.

Amphiphilic poly(alkylthiophene) block copolymers prepared via externally initiated GRIM and click coupling

Block copolymers with a poly(3-alkylthiophene) (P3AT) polymer block can self-organize into periodic, crystalline nanostructures that may be useful for organic electronic applications. However, reliable synthetic methods for the preparation of P3AT block copolymers are lacking. Here, we demonstrate a general method for the synthesis of P3AT rod-coil block copolymers via click-coupling of alkynyl-P3AT. Alkynyl-P3ATs are prepared via externally initiated Grignard metathesis polymerization (GRIM) using a modified nickel catalyst followed by end-group modification. The resulting alkynyl-P3ATs have improved stability and solubility compared with those previously reported. P3ATs are subsequently coupled to an azide-functionalized poly(ethylene glycol) through copper-catalyzed azide–alkyne click coupling, resulting in P3AT-b-PEG block copolymers. The advantages of this synthetic procedure are the improved stability of the alkynyl-P3AT macroreagent, the capability to synthesize high molecular weight P3AT polymer blocks, and facile determination of P3AT absolute molecular weight through 1H NMR analysis. This synthetic method is applied to prepare a series of P3AT-b-PEG block copolymers, with poly(3-hexyl thiophene) (P3HT), poly(3-dodecylthiophene) (P3DDT), and poly(3-(2′-ethyl)hexylthiophene) (P3EHT) polymer blocks. The resulting P3AT block copolymers are dispersed in water to form micelles with crystalline, hydrophobic cores. Absorbance measurements show that crystallization of P3DDT and P3EHT blocks is suppressed in micellar cores due to nanoscale confinement of the P3AT blocks.

An enhanced host–guest electro‐optical polymer system using poly(norbornene‐dicarboximides) via ROMP

AbstractHigh glass transition temperature poly(N‐cyclohexyl‐5‐norbornene‐2,3‐dicarboximide)s (NDI)s prepared by ring opening metathesis polymerization yielded polymers with a narrow polydispersity and well‐controlled molecular weight materials when using the Grubbs first generation initiator. Polymers produced using the Grubbs second generation initiator could not be controlled easily. By initiator selection it was also possible to synthesize polymers with either 98 or 52% trans microstructures. These materials were employed as electro‐optic (EO) polymer hosts for high molecular hyperpolarizability (β) phenyl vinylene thiophene vinylene bridge chromophores. This chromophore was modified by the incorporation of a tert‐butyldiphenylsilane group. The addition was able to further increase its EO coefficient (r33) to reach 93 pm/V in a trans rich poly(NDI) produced by the Grubbs first generation initiator, compared to a benchmark chromophore / polymer combination. We investigated in detail the relationship between polymer microstructure and their absolute molecular weight on forming the best host–guest with the high β chromophore. Our results indicate that by utilizing a very simple host–guest system a high r33 can be realized. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Now for my next trick: Absolute Molecular Weights by Column Calibration

Now for my next trick: Absolute Molecular Weights by Column Calibration

Now for my trick: Absolute Molecular Weights by Column Calibration

Now for my trick: Absolute Molecular Weights by Column Calibration

Determination of absolute molecular weight of sodium lignosulfonates (NaLS) by laser light scattering (LLS)

Abstract The problems related to the determination of the absolute molecular weight (M w) of sodium lignosulfonate (NaLS) are the focus of the present work. Four narrow-dispersed NaLS fractions were collected by filtration, ultrafiltration, and gel permeation chromatography (GPC), and their M w measured by laser light scattering (LLS Mw ) was compared with that obtained by GPC (GPC Mw ). The LLS Mw values were much larger than GPC Mw , and this M w difference increased with increasing M w of NaLS. This finding confirms the known polyelectrolyte and aggregation effects of NaLS. The deviation is also partly due to the conformation differences between the GPC standard (sodium polystyrene sulfonate) and the NaLS molecules. The effects of polyelectrolytes and NaLS aggregates could be inhibited by adding enough NaCl salt in the NaLS solution and filtering the NaLS/NaCl solution through a syringe filter. As a result, the slow mode in dynamic LLS measurement disappeared. By this approach, the absolute LLS Mw values were only slightly larger than that determined by GPC due to the conformation differences between the GPC standard and the NaLS molecules.

Determination of Mark-Houwink Parameters and Absolute Molecular Weight of Medium-Chain-Length Poly(3-Hydroxyalkanoates)

Absolute molecular weight distributions were determined for different medium-chain-length poly(3-hydroxyalkanoates) (MCL PHAs) with predominantly 3-hydroxyoctanoate (PHO), 3-hydroxynonanoate (PHN) or 3-hydroxydodecanoate content. This is the first study to estimate the Mark-Houwink constants of these polymers in the commonly employed GPC carrier solvent tetrahydrofuran (THF). The absolute molecular weight averages were determined via triple-detector size exclusion chromatography and combined with analyses using various detectors. Unlike with the short-chain-length poly(3-hydroxybutyrate), PHB, uncorrected polystyrene calibration in THF provided a good estimate (within 10 %) of absolute MW values for these MCL PHAs, irrespective of side chain length. Weight-average MW values ranged from 172,000 Da for PHO to 18,200 for PHN with 30 mol% 3-hydroxyheptanoate, and dispersities of all samples were close to two. Melt viscosity data suggested an entanglement molecular weight around 8 × 104 Da, significantly higher than most polymers.

Detailed characterization of hyaluronan using aqueous size exclusion chromatography with triple detection and multiangle light scattering detection

Hyaluronan (HA) has attracted great interest and attention from ophthalmic surgical and eye care companies owing to its unique properties. A more complete understanding of HA biopolymers has, therefore, become increasingly critical as thorough characterization of raw materials helps promote product quality and process control. Often, such detailed information requires the use of a combination of analytical techniques. In this study, we compared size exclusion chromatography (SEC) with online multiangle light scattering (SEC-MALS) and SEC with triple detection (SEC-TD) experiments for HA analysis. Three lots of commercially available eye drop grade HA were characterized by SEC-MALS and SEC-TD. The absolute molecular weight averages, molecular weight distribution, radius of gyration, and solution conformation of the three HA lots were determined and compared by the two techniques. In addition, the intrinsic viscosity and intrinsic viscosity distribution were measured by SEC-TD.

Molecular Weight Distributions of Polymer Solutions: Combination of Field Flow Fractionation (FFF) and Analytical Ultracentrifugation (AUC)

Molecular weight, distribution, as well as other molecular characteristics are important drivers in determining the potential behaviors and hence applications of polymeric materials. Out of different methods available for the determination of molecular weight and its distribution, field flow fractionation (FFF) provides absolute molecular weight values and accurate molecular weight distributions. Analytical ultracentrifugation (AUC), on the other hand, relies on the exact density of the polymer materials in solution to determine the accurate molecular weight and its distribution and in the absence of knowledge of exact density, AUC is less accurate than the FFF method. However, combination of the two methods can be achieved to gain insights into the other molecular characteristics of swollen polymer chains. One such example is the determination of the exact density of the swollen polymer chains by the incorporation of the molecular weight information from FFF into AUC analysis. Based on the comparison of the optimized polymer chain density with the bulk density, it was observed that the polyacrylic acid and polyacrylamide chains were swollen in the range of 27 to 29%. Moreover, the FFF and AUC can also complement each other in enhancing the range of characterization possible with the two methods when used separately.

Propagation Rate Coefficients for Homogeneous Phase VDF-HFP Copolymerization in Supercritical CO2

For the first time, propagation rate coefficients, k(p,COPO) , for the copolymerizations of vinylidene fluoride and hexafluoropropene have been determined. The kinetic data was determined via pulsed-laser polymerization in conjunction with polymer analysis via size-exclusion chromatography, the PLP-SEC technique. The experiments were carried out in homogeneous phase with supercritical CO(2) as solvent for temperatures ranging from 45 to 90 °C. Absolute polymer molecular weights were calculated on the basis of experimentally determined Mark-Houwink constants. The Arrhenius parameters of k(p,COPO) vary significantly compared with ethene, which is explained by the high electronegativity of fluorine and less intra- and intermolecular interactions between the partially fluorinated macroradicals.

Evidence for Complex Molecular Architectures for Solvent-Extracted Lignins.

Lignin, an abundant, naturally occurring biopolymer, is often considered "waste" and used as a simple fuel source in the paper-making process. However, lignin has emerged as a promising renewable resource for engineering materials, such as carbon fibers. Unfortunately, the molecular architecture of lignin (in vivo and extracted) is still elusive, with numerous conflicting reports in the literature, and knowledge of this structure is extremely important, not only for materials technologies, but also for production of biofuels such as cellulosic ethanol due to biomass recalcitrance. As such, the molecular structures of solvent-extracted (sulfur-free) lignins, which have been modified using various acyl chlorides, have been probed using small-angle X-ray (SAXS) and neutron (SANS) scattering in tetrahydrofuran (THF) solution along with hydrodynamic characterization using dilute solution viscometry and gel permeation chromatography (GPC) in THF. Mass spectrometry shows an absolute molecular weight ≈18-30 kDa (≈80-140 monomers), while GPC shows a relative molecular weight ∼3 kDa. A linear styrene oligomer (2.5 kDa) was also analyzed in THF using SANS. Results clearly show that lignin molecular architectures are somewhat rigid and complex, ranging from nanogels to hyperbranched macromolecules, not linear oligomers or physical assemblies of oligomers, which is consistent with previously proposed delignification (extraction) mechanisms. Future characterization using the methods discussed here can be used to guide extraction processes as well as genetic engineering technologies to convert lignin into value added materials with the potential for high positive impact on global sustainability.

Asymmetric Mode of Ca2+-S100A4 Interaction with Nonmuscle Myosin IIA Generates Nanomolar Affinity Required for Filament Remodeling

SummaryFilament assembly of nonmuscle myosin IIA (NMIIA) is selectively regulated by the small Ca2+-binding protein, S100A4, which causes enhanced cell migration and metastasis in certain cancers. Our NMR structure shows that an S100A4 dimer binds to a single myosin heavy chain in an asymmetrical configuration. NMIIA in the complex forms a continuous helix that stretches across the surface of S100A4 and engages the Ca2+-dependent binding sites of each subunit in the dimer. Synergy between these sites leads to a very tight association (KD ∼1 nM) that is unique in the S100 family. Single-residue mutations that remove this synergy weaken binding and ameliorate the effects of S100A4 on NMIIA filament assembly and cell spreading in A431 human epithelial carcinoma cells. We propose a model for NMIIA filament disassembly by S100A4 in which initial binding to the unstructured NMIIA tail initiates unzipping of the coiled coil and disruption of filament packing.

Structure function differentiation of truncated hemolysin A using multi‐angle light scattering

In this study, the role of molecular organization was investigated as related to hemolysin A (HpmA265) template‐assisted behavior. Previous studies have shown that full‐length HpmA can be activated through interaction with purified HpmA265 in template‐assisted fashion. HpmA265 was analyzed via template‐assisted hemolysis, circular‐dichroism, size‐exclusion chromatography and multi‐angle light scattering (SEC‐MALS) before and after tryptic digestion. The results from these investigations were utilized to determine the absolute molecular weight of the template‐assisted active species. The pre‐tryptic digestion data reported a heterogeneous mixture of HpmA265 monomer and dimer. Quantitative hemolytic assays have determined the monomer to be the molecularly active species. Subsequent tryptic digestion, followed by SEC‐MALS, generated a homogenous dimeric species with enhanced template‐assisted behavior and thermal stability. From these data, a new model for template‐assisted activity has been developed where exposed, homogenous, and monomeric on‐edge beta‐strands of HpmA265 facilitate the activation of full‐length HpmA. These findings are significant and may apply to other beta‐helix protein dependent disease states like Alzheimer's, Parkinson's and transmittable prion disorders. National Science Foundation Grant (MCB0744754) and (MCB1050435) supported the work.

Molecular dissection of hemolysin A template‐assisted activity

In this study, the role of molecular organization was investigated as related to hemolysin A (HpmA265) template‐assisted behavior. Previous studies have shown that full‐length HpmA can be activated through interaction with purified HpmA265 in template‐assisted fashion. HpmA265 was analyzed via template‐assisted hemolysis, circular‐dichroism, size‐exclusion chromatography and multi‐angle light scattering (SEC‐MALS) before and after tryptic digestion. The results from these investigations were utilized to determine the absolute molecular weight of the template‐assisted active species. The pre‐tryptic digestion data reported a heterogeneous mixture of HpmA265 monomer and dimer. Quantitative hemolytic assays have determined the monomer to be the molecularly active species. Subsequent tryptic digestion, followed by SEC‐MALS, generated a homogenous dimeric species with enhanced template‐assisted behavior and thermal stability. From these data, a new model for template‐assisted activity has been developed where exposed, homogenous, and monomeric on‐edge beta‐strands of HpmA265 facilitate the activation of full‐length HpmA. These findings are significant and may apply to other beta‐helix protein dependent disease states like Alzheimer's Parkinson's and transmittable prion disorders. National Science Foundation Grant (MCB0744754) and (MCB1050435) supported the work.