Uniform Molecular Weight Research Articles

Molecular growth from coal-based asphaltenes to spinnable pitch

The chemical composition of spinnable pitch determined the performance of resultant carbon fiber. Three spinnable pitches were prepared from asphaltenes by a modified air-blowing method and their component and structural differences were comparatively investigated using MALDI-TOF and Q-TOF MS. The three spinnable pitches had insignificant changes in elemental compositions, while the molecular species and their relative content varied significantly, and the molecular weight growth of spinnable pitches was consistent with the 24/50 rule of aromatic annelation. Dominant compounds in the molecular weight range of 250–600 Da showed a clear growth tendency via alternate additions of C4H2 and C2, and species of larger molecular weight grew mainly in conjunction with C2. As an excellent precursor for pitch-based carbon fiber, spinnable pitch derived from asphaltenes should have a uniform molecular weight distribution and high number-average molecular weight (1672.6 Da), good thermal stability, high polycondensation degree and aromatic hydrocarbons with the short or few chains in its light fraction. This work systematically analyzed spinnable pitch composition and shed light on the controllable synthesis of pitch-based carbon fiber.

Efficient separation of acetylated cellulose from eucalyptus and its enhancement on the mechanical strength of polylactic acid

A simplified and green strategy was provided for the synthesis of cellulose acetate. Cellulose acetate (CA) was isolated from the directly acetylated eucalyptus powder after hydrothermal treatment to selectively remove hemicellulose without delignification. The conversion rate of cellulose (90.75%) and the yield of the acetylated product (61.34%) were greatly improved by hydrothermal treatment, while the re-condensation of lignin during hydrothermal treatment made no adverse difference. The characterization results verified that the acetylated product was cellulose acetate with uniform molecular weight, good thermal stability and semi-crystalline structure. Moreover, CA was used to reinforce polylactic acid (PLA) films prepared by solvent casting. The PLA-CA composite with 5 wt% CA showed an increase of 80.63% in tensile strength and 59.51% in Young's modulus, and their density decreased from 1.2427 g/cm3 to 1.0028 g/cm3. The lightweight and excellent mechanical properties promote the application potential of biodegradable composites to replace petroleum-based plastics.

Characterization and Antioxidant Activity of Released Exopolysaccharide from Potential Probiotic Leuconostoc mesenteroides LM187.

A released exopolysaccharide (rEPS)-producing strain (LM187) with good acid resistance, bile salt resistance, and cholesterol-lowering properties was isolated from Sichuan paocai and identified as Leuconostoc mesenteroides subsp. mesenteroides. The purified rEPS, designated as rEPS414, had a uniform molecular weight of 7.757 × 105 Da. Analysis of the monosaccharide composition revealed that the molecule was mainly composed of glucose. The Fourier transform-infrared spectrum showed that rEPS414 contained both α-type and β-type glycosidic bonds. 1H and 13C nuclear magnetic resonance spectra analysis showed that the purified rEPS contained arabinose, galactose, and rhamnose, but less uronic acid. Scanning electron microscopy demonstrated that the exopolysaccharide displayed a large number of scattered, fluffy, porous cellular network flake structures. In addition, rEPS414 exhibited strong in vitro antioxidant activity. These results showed that strain LM187 and its rEPS are promising probiotics with broad prospects in industry.

A synergistic hydrothermal-deep eutectic solvent (DES) pretreatment for rapid fractionation and targeted valorization of hemicelluloses and cellulose from poplar wood

A synergistic pretreatment that realizing effective fractionation and targeted valorization can guarantee the implementability to future biorefinery scenario. In the present study, a stepwise approach using hydrothermal and deep eutectic solvents (DES) pretreatment was developed to preferentially dissociate hemicelluloses and further remove lignin from poplar, while retaining a cellulose-rich substrate that can be easily digested via enzymatic saccharification to obtain glucose. Results showed that the hydrothermal filtrate is mainly composed of xylooligosaccharide (XOS), monosaccharides, byproducts, and xylan-type hemicelluloses, which have homogenous structures and uniform molecular weights distribution as well as excellent antioxidant activity. Subsequent DES pretreatment further removed the lignin barriers, leading to a remarkable increase in the saccharification efficiency from 15.72% to 96.33% under optimum conditions for enzymatic hydrolysis. In short, the integrated pretreatment is effective for dissociating and chemical conversion of poplar wood, which was reasonable to promote the frontier of highly available biorefinery.

Purification Process of Poly Methyl Methacrylate Products Made with Suspension Polymerization Techniques

Poly Methyl Methacrylate (PMMA) is a commodity polymer produced from Methyl Methacrylate (MMA) monomer. This applied in various industries such as automotive and in the manufacture of artificial bones. Suspension polymerization techniques are able to produce polymer powders in micron size, uniform molecular weight and desired particle size distribution. This research was initiated by conducting polymerization process by heating Polyvinyl Alcohol (PVA, dispersant)/aqua dest (H2O) mixture accompanied by nitrogen gas purging and stirring, then MMA and Benzoyl Peroxide (BPO, initiator) was added. The results of the polymerization process produce PMMA products in the form of powders which are suspected to still contain MMA, BPO, and PVA so that the washing process is required for PMMA products. Therefore, PMMA products resulting from the polymerization process are washed with water solvent with stirring, then the results of washing PMMA products are filtered and dried. The results of final PMMA products in the form of white powder which are then analyzed using Fourier Transform Infrared Spectroscopy (FTIR) analysis showed that product there is still a residual MMA. Scanning Electron Microscopy (SEM) analysis which results produce spheres of varying size and average particle size of 64.45 µm. Particle Size Analyzer result presents the average size of 62.05 µm.

Study on physicochemical properties and antioxidant activity of polysaccharides from Desmodesmus armatus

Physicochemical properties and antioxidant activities of Desmodesmus armatus polysaccharides (DAP) were studied. They were extracted by microwave-assisted constant temperature extraction and purification by DEAE-cellulose 52. Four eluents of water (DAP1), 0.25mol/L NaCl (DAP2), 0.5mol/L NaCl (DAP3), and 1.0mol/L NaCl (DAP4) were collected. Four polysaccharides fractions were analyzed, and they were all composed of mannose, rhamnose, glucuronic acid, galacturonic acid, arabinose, and fucose. Gel Permeation Chromatography (GPC) analysis showed that the four polysaccharides fractions have a uniform molecular weight distribution. Scanning electron microscope showed that DAP1 had a dense structure and a smooth but uneven surface, while DAP2, DAP3, and DAP4 were amorphous solids in sheets. Oxidation in vitro experiments showed that DAP2 and DAP3 had scavenging effects on ABTS, DPPH, and hydroxyl radicals. PRACTICAL APPLICATIONS: In the determination of the antioxidant activity, it was found that the antioxidative activity of the polysaccharide of Desmodesmus armatus measured was significantly stronger than the crude polysaccharide of other microalgae. After the polysaccharide was purified, two polysaccharide fractions (DAP2 and DAP3) of Desmodesmus armatus were found to have strong scavenging ability to ABTS, DPPH, and hydroxyl radicals. They can be regarded as a new type of antioxidant, and the differences in the physicochemical properties between the parts can provide a preliminary explanation for the differences in antioxidant activity. But the connection between them needs further analysis. The Desmodesmus armatus used in the experiment is easy to cultivate and easy to obtain, which greatly increases its applicability. This research opens up new possibilities for the development of antioxidants and provides favorable evidence for the use of Desmodesmus armatus in food and feed.

Purification, Preliminary Structural Characterization, and In Vitro Inhibitory Effect on Digestive Enzymes by β-Glucan from Qingke (Tibetan Hulless Barley)

Background and Objective. Qingke (Tibetan hulless barley, Hordeum vulgare L.) contains a high content of β-glucan among all the cereal varieties. Although β-glucan has multiple physiological functions, the physiological function of qingke β-glucan was few studied. In this study, the β-glucan was isolated, purified, determined the structural characterization, and measured the inhibitory activity to enzymes correlating blood sugar and lipid. Methods. β-Glucan was isolated from enzymatic aqueous extract of qingke by using deproteinization, decolorization, DEAE-52 column chromatography, and sepharose CL-4B agarose gel column chromatography. The structure of the β-glucan was determined using FT-IR and 13C-NMR spectra analysis, and molecular mass by use of HPSEC-dRI-LS. The kinematic viscosity was measured. The inhibitory effects of this β-glucan on four enzymes were investigated. Results. This β-glucan had a uniform molecular weight of 201,000 Da with β-(1⟶4) as the main chain and β-(1⟶3) as a side chain. The β-glucan presented a relatively strong inhibitory activity on α-glucosidase, moderate inhibition on invertase, and a weak inhibition on α-amylase, whereas it did not inhibit lipase. Conclusion. The study indicates that the enzymatic β-glucan from qingke has the potential as natural auxiliary hypoglycemic additives in functional medicine or foods.

Extraction, characterization and antioxidant activity evaluation of polysaccharides from Smilacina japonica

Three polysaccharides of uniform molecular weight designated as SJP1-1, SJP2-1, and SJP3-1 from Smilacina japonica were studied in this paper. Respectively, their specific optical rotations were −45°, −75°, and −35°, their polysaccharide contents were 89.22%, 93.05%, and 59.83%, their relative average molecular weights were 1.87 × 105 Da, 1.04 × 105 Da, and 1.36 × 104 Da. Three polysaccharides were all composed mainly of the three monosaccharides mannose, glucose, and galactose, which together in SJP1–1, SJP2–1, and SJP3–1 respectively made up 96.34%, 98.23%, and 91.67% of the total polysaccharide. The polysaccharide structure was maintained mostly by β-glucose (1 → 3), β-glucose (1 → 4), α-mannose (1 → 3), and α-galactose (1 → 4) glycosidic linkages. Scanning electron microscopy showed that SJP1–1, SJP2–1, and SJP3–1 were smooth uniform microspheres with diameters of 10–20 μm that combined to form both uniformly dispersed particles and blocky structures. Finally, antioxidant assay showed that these polysaccharides all had a strong ability to scavenge ·OH and DPPH· radicals, with the effects of purified polysaccharides being greater than those of crude polysaccharides. This first report on the properties of these polysaccharides provides a basis for further studies to shed light on the medical properties of Smilacina japonica.

Researches on the Internal Molecular Weight Uniformity of Chitosan Biomaterials

Uniform molecular weight (Mw) chitosan (CS) is highly demanded in medical biomaterial industry. This present article described heterogeneous degradation of CS in aqueous HCl/ethanol solution, in which progress uniform Mw CS was successfully prepared. The Mw distribution of CS was measured by gel permeation chromatography (GPC) analysis. Moreover, the structure and properties of degraded CS were characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy ( 1 H NMR), X-ray diffraction (XRD) and thermogravimetric (TG) analysis. In addition, the biocompatibility of degraded CS was also assessed by hemolysis rate (HR) measurement. The Mw of CS dramatically decreased from 246 KDa to 76 kDa at the initial 30 min, and stabilized at 18 kDa after 24 h. GPC analysis results showed that the degraded CS molecular become homogenization. FT-IR and 1H NMR analysis confirmed the basic structure of CS molecular backbone was not destroyed during this progress. Besides, the water solubility of CS was not significantly influenced by this reaction. Moreover, the XRD analysis revealed that crystallinity of degraded CS increased from 70.32% to 99.25% with time. The TG analysis showed improved thermal stability of degraded CS. HR measurement demonstrated the degraded CS possessed excellent biocompatibility. This simple and efficient heterogeneous degradation would open up a new route to produce uniform Mw CS.

Optimizing the property of cross-linked carbazole-based polymer for efficient hole transport in bulk-heterojunction photovoltaic device

Thin films made of cross-linked carbazole pendants of poly(ethylmethacrylate) deposited on indium tin oxide (ITO) was assessed for potential use as hole transport layer (HTL) in a fabricated photovoltaic cell configuration (ITO/PCDTBT/PCBM/Al). Before measurement, the film was designed to have uniform molecular weight, cross-linked carbazole for high electron mobility, high transmittance at the visible wavelength range and smoothness in morphology. Results showed that the film provided 70 times more of current value at open circuit voltage than without the film under light illumination, at optimized thickness from 15 to 25 cycles of deposition at 25 mV/s using cyclic voltammetry.

Effects of Caustic Extraction on Properties of Viscose Grade Dissolving Pulp

Viscose, a cellulose-based commodity fibre, is produced by pulping and bleaching of wood, yielding a high quality “dissolving pulp” which is then spun. During pulping and bleaching, effective hemicellulose extraction is required to allow fibre production. We present a design of experiments (DoE) approach to optimise caustic extraction in a total chlorine free (TCF) bleaching sequence (O-CE-Z-P) of beech wood sulphite pulp. Temperature and sodium hydroxide concentration were varied to identify highest xylan extraction yield, and a maximum xylan removal of 83% was achieved at 20 °C and 120 g/L NaOH. Additionally, caustic extraction conditions were derived from the DoE model that led to pulps with high yield, high alpha cellulose content or uniform cellulose molecular weight distribution. Pulps from verification experiments exhibited good reactivity in viscose application tests. Hence, the presented O-CE-Z-P bleaching sequence can be considered as suitable for integrated viscose fibre production. We assume that the presented caustic extraction model will be useful for pulp and biorefinery researchers who work on caustic biorefinery processes involving hardwood feedstocks.

A fast semi-continuous anionic process for fluorene-functionalized homo and block oligomers with uniform molecular weights

A semi-continuous strategy based on anionic reactions was developed for the step-by-step synthesis of oligomers with uniform molecular weights.

KINETIKA DEGRADASI SELULOSA ASETAT DARI SABUT PINANG

Cellulose Acetate is a material with wide range in applications. Cellulose acetate may obtain from natural resources, such as areca fiber. Polymers should have uniform molecular weight for the applications and could be modify by ultrasonic waves. Ultrasonic treatment on polymer entangled with polymer degradation. In this research, degradation kinetics of cellulose acetate in acetone had been studied. Analysis was performed by determination of intrinsic viscosity in polymer solution system. Intrinsic viscosity was successfully obtained by fitting data using Huggins equation, indicate molecular interaction in polymer solution should not be neglected. Increasing in sonication time reducing the intrinsic viscosities as well as molecular size in solutions. Degradation rate constant and reaction order were obtained 5,975x10-3(g.mL-1)0,1.min-1 and 1,0616, respectively. Kinetics model was successful to determine the degradation rates of cellulose acetate on acetone by correlation coefficient (R2) at 0,966.

Inactivation of an intracellular poly-3-hydroxybutyrate depolymerase of Azotobacter vinelandii allows to obtain a polymer of uniform high molecular mass

A novel poly-3-hydroxybutyrate depolymerase was identified in Azotobacter vinelandii. This enzyme, now designated PhbZ1, is associated to the poly-3-hydroxybutyrate (PHB) granules and when expressed in Escherichia coli, it showed in vitro PHB depolymerizing activity on native or artificial PHB granules, but not on crystalline PHB. Native PHB (nPHB) granules isolated from a PhbZ1 mutant had a diminished endogenous in vitro hydrolysis of the polyester, when compared to the granules of the wild-type strain. This in vitro degradation was also tested in the presence of free coenzyme A. Thiolytic degradation of the polymer was observed in the nPHB granules of the wild type, resulting in the formation of 3-hydroxybutyryl-CoA, but was absent in the granules of the mutant. It was previously reported that cultures of A. vinelandii OP grown in a bioreactor showed a decrease in the weight average molecular weight (Mw) of the PHB after 20h of culture, with an increase in the fraction of polymers of lower molecular weight. This decrease was correlated with an increase in the PHB depolymerase activity during the culture. Here, we show that in the phbZ1 mutant, neither the decrease in the Mw nor the appearance of a low molecular weight polymers occurred. In addition, a higher PHB accumulation was observed in the cultures of the phbZ1 mutant. These results suggest that PhbZ1 has a role in the degradation of PHB in cultures in bioreactors and its inactivation allows the production of a polymer of a uniform high molecular weight.

Silica nanoparticles coated by poly(acrylic acid) brushes via host-guest interactions for detecting DNA sequence of Hepatitis B virus

Poly(acrylic acid) (PAA) brushes coated onto silica nanoparticles have been widely utilized in bioassays due to their abilities of providing favorable microenvironments and ensuring good biological activities for biomolecules. However, traditional PAA brushes are synthesized by reversible addition–fragmentation chain transfer polymerization. Hence, it is generally difficult to control and characterize the molecular weight of the PAA brushes, which may depress the reproducibility and bring more uncertain results. Herein, atom transfer radical polymerization method is employed to synthesize β-cyclodextrin-cored PAA with uniform and controllable molecular weight. After loading on the surfaces of adamantane-functionalized silica nanoparticles via host-guest interactions, glucose oxidase and probe single strand DNA (ssDNA) are further immobilized on the as-prepared nanoparticles. Meanwhile, capture ssDNA is functionalized on amino modified magnetic beads. In the presence of ssDNA sequence of Hepatitis B Virus (HBV) containing completely matched sequence of both probe and capture ssDNA, a bioconjugate is formed and can be separated by an external magnet. The isolated glucose oxidase can further catalyze glucose into gluconic acid and H2O2, and then reduce HAuCl4 on Au seeds. By monitoring the absorption intensity change of the Au NPs at 530nm, the proposed biosensor with novel signal amplification probes can be used to detect DNA sequence of HBV with high sensitivity and selectivity in both buffer and serum samples. This developed strategy has presented a new way to construct silica nanoparticles coated by PAA brushes for the fields of clinical diagnosis and other life sciences.

Photoswitchable Heparinase III for Enzymatic Preparation of Low Molecular Weight Heparin.

A photocontrollable biocatalyst was rationally designed by site-specifically linking a photoswitchable azobenzene derivative to the only cysteine residue in heparinase III mutant (K130C). Upon photoswitch, the enzymatic degradation of heparin could be artificially controlled to produce low molecular weight heparin with more uniform molecular weight and an increase in anticoagulant activity.

Synthesis and Structural Analysis of (Imido)vanadium Dichloride Complexes Containing 2-(2'-Benz-imidazolyl)pyridine Ligands: Effect of Al Cocatalyst for Efficient Ethylene (Co)polymerization.

(Imido)vanadium(V) dichloride complexes containing 2-(2′-benzimidazolyl)-6-methylpyridine ligand (L) of type V(NR)Cl2(L) [R = 1-adamantyl (Ad, 1), C6H5 (2), and 2,6-Me2C6H3 (3)] have been prepared, and their structures were determined by X-ray crystallography as distorted trigonal bipyramidal structures around vanadium. Reactions with ethylene using 1–3 in the presence of methylaluminoxane (MAO) afforded a mixture of oligomer and polymers, and the compositions were affected by the imido ligand employed. By contrast, 1–3 exhibited remarkable catalytic activities for ethylene polymerization in the presence of Me2AlCl; the phenylimido complex (2) exhibited the highest activity [80 100 kg-PE/mol-V·h turn over frequency (TOF, 2 850 000 h–1, 792 s–1)]. The ethylene copolymerizations with norbornene afforded ultrahigh-molecular-weight copolymers with uniform molecular weight distributions and compositions [e.g., Mn = 1.71–2.66 × 106, Mw/Mn = 2.27–2.53]. On the basis of V nuclear magnetic resonance (51V NMR), electron spin resonance, and V K-edge X-ray absorption near-edge structure (XANES) spectra of the catalyst solution, the observed difference in the catalyst performance in the presence of (between) MAO and Me2AlCl cocatalyst should be due to the formation of different catalytically active species with different oxidation states. Apparent changes in the oxidation state were observed in the (especially in the NMR and XANES) spectra upon addition of Me2AlCl, whereas no significant changes in the spectra were observed in presence of MAO.

Effect of Al Cocatalyst in Ethylene and Ethylene/Norbornene (Co)polymerization by (Imido)vanadium Dichloride Complexes Containing Anionic <i>N</i>-Heterocyclic Carbenes Having Weakly Coordinating Borate Moiety

Effect of Al cocatalyst in ethylene polymerization using (imido)vanadium(V) complexes containing anionic N-heterocyclic carbenes with a weakly coordinating borate moiety in 4-position (WCA-NHC), [V(N-2,6-Me2C6H3)Cl2(WCA-NHC)] [1; NHC=1,3-bis(2,6-dimethylphenyl)-imidazolin-2-ylidene], have been explored. The activities by 1 upon presence of AliBu3 in ethylene polymerization and in the copolymerization with norbornene (NBE) were higher than those in the presence of MAO, and the resultant poly(ethylene-co-NBE)s prepared by 1-AliBu3 catalyst possessed uniform molecular weight distributions and compositions. Formation of vanadium(III) species could be assumed upon presence of AliBu3, especially on the basis of both NMR and ESR spectra (silent) and certain significant changes in the V K-edge XANES (pre-edge and edge region) spectrum, whereas no significant changes in the XANES spectrum were observed from the toluene solution containing 1 upon addition of MAO. It is thus suggested that a difference in the catalyst performances between in the presence of MAO and AliBu3 should be due to a formation of different catalytically active species with different oxidation states.

A Dendritic Supramolecular Complex as Uniform Hybrid Micelle with Dual Structure for Bimodal In Vivo Imaging

In this study, a uniform complex dual micelle bearing a gadolinium-substituted polyoxometalate core, a hydrophobic middle, and a biocompatible organic shell, which exhibits a uniform size and definite molecular weight and chemical composition, is constructed through a simple two-step process for use as a fluorescence and magnetic resonance imaging (MRI) contrast agent. A paramagnetic polyoxometalate cluster, K13 [Gd(β2 -SiW11 O39 )2 ], is first encapsulated with a cationic 3-generation dendron (D-3) bearing triethylene glycol monomethyl ether terminal groups through ionic substitution. The formed electrostatic complex, (D-3)13 [Gd(β2 -SiW11 O39 )2 ] (D-GdSiW), which displays an ambivalent micellar structure, is then demonstrated to act as a suitable carrier for the uptake of cationic fluorescent dyes, forming a loaded complex. The dye-loaded complex D-GdSiW-D is thus proven to display high relaxivity as a contrast agent, maintaining its structural stability under physiological conditions with low cell cytotoxicity. Confocal laser scanning microscopic observation also demonstrates the fluorescence imaging property of the prepared complex upon consumption by MCF-7 cells. Both in vivo fluorescence imaging and MRI further confirm that the complex micelle with dual micellar structure may be a suitable liver-specific contrast agent for clinical diagnosis.

Synthesis of (Imido)niobium(V)–Alkylidene Complexes That Exhibit High Catalytic Activities for Metathesis Polymerization of Cyclic Olefins and Internal Alkynes

The (imido)niobium(V)–alkylidene complexes Nb(CHSiMe3)(NR)[OC(CF3)3](PMe3)2 (R = 2,6-Me2C6H3, 2,6-iPr2C6H3, 1-adamantyl), which could be isolated from the dialkyl analogues by α-hydrogen elimination in the presence of PMe3, exhibited remarkable catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene, and the polymerizations proceeded in a living manner. Metathesis polymerizations of (unstrained) disubstituted acetylenes also took place, affording polymers with uniform (narrow) molecular weight distributions.