High Molecular Weight Products Research Articles

Solvent-free processes to polyurea elastomers from diamines and diphenyl carbonate

Two solvent-free processes without using volatile organic chemical (VOC) for making polyurea elastomers have been successfully developed from diamines and diphenyl carbonate (DPC) to meet stringent public demands for a high standard green alternative Anastas and Eghbali (Chem Soc Rev 39 (1):301–312, 2010). In this new non-isocyanate route (NIR) which is an improvement over our previous process to polyurea elastomers, molten DPC are utilized as the carbonylation agents, where DPC reacts sequentially with 1,6-hexanediamine (HDA), polyether diamines of 2000 molecular weight and short chain diamines such as isophorondiamine (IPDA) or 4,4′-diaminodicyclohexylmethane (H12MDA). No solvent was added in the synthesis of these new non-solvent polyurea. Alternatively, the above process was modified with an 3 % addition of a water dispersant such as 3-[(2-aminoethyl)amino]-1-propane sulfonic acid sodium salt (ESA) to make waterborne polyurea elastomers to facilitate the mixing in the preparation and in the film-making steps for the final products. In both solvent-free processes, the long-chained polyether diamine and the phenol generated from the displacement reaction of diphenyl carbonate were utilized as diluents to lower the viscosities of the reaction mixtures. Unexpectedly, ultra high molecular weight products were resulted particularly for the waterborne polyurea products measuring in excess of 1,000,000 g/mol in some cases. All samples were characterized by FT-IR, H-NMR, TGA, DSC, AFM and GPC. Since the polymers were prepared under mild conditions in absence of a VOC solvent, the new products were found to mostly exist in highly phase-segregated states, exhibiting high heat-resistant temperatures with Td(5%) of well over 300 °C with high elongation (>600 %) for the optimized products. Thus, this solvent-free syntheses and environment-friendly polyurea products should find usefulness in many practical applications.

Effect of Group I alkali metal promoters on Fe/CNT catalysts in Fischer–Tropsch synthesis

Carbon nanotubes (CNTs) were used as support to prepare iron-based Fischer–Tropsch synthesis (FTS) catalysts. Because the CNT surface is comparatively inert, this catalyst system was employed to investigate the effect of three alkali metal promoters (Li, Na and K) and promoter loading (for Na) on the properties and catalytic performances of Fe/CNT in FTS in the absence of strong metal support interactions found for metal oxide supports. It was found that the addition of alkali promoters led to an increase in crystallite size of the iron oxide and decreased surface areas, as compared to the unpromoted Fe/CNT catalyst. The presence of Na and K promoters slightly hindered catalyst reducibility by increasing the reduction temperature of the iron oxide; while the potassium promoted catalyst showed the most pronounced effect and no effect was observed for Li. Scanning transmission electron microscopy–energy dispersive spectroscopy (STEM–EDS) results indicated that the promoter Na is found in the same regions on the catalyst support as the iron oxide. The sodium and potassium promoted catalysts were found to decrease the methane selectivity, increase the olefin production and shift the product selectivity to higher molecular weight hydrocarbons during FTS. Furthermore, Na and Li greatly increased the CO conversion, while the addition of K suppressed the activity. The Fe/CNT catalyst promoted by Na resulted in the largest increase in FTS reactivity compared to Li and K when equimolar amounts of alkali metals were added to the Fe/CNT catalyst. An increase in Na loading (atomic ratio: Fe:Na<100:3) further increased the olefin/paraffin ratio and long-chain hydrocarbon selectivity of the Fe/CNT catalyst, while it only had a slight effect on the activity and water gas shift rate. Increasing the sodium loading in the catalyst by a factor of 4 or 8 was found to affect the product selectivity: the Fe–24Na/CNT was the most selective catalyst toward higher molecular weight products. This study revealed when using a Fe/alkali atomic ratio of 100:3 that Na is the most effective promoter of the Fe/CNT catalyst, followed by K and lastly Li. In terms of the product selectivity, the Fe/CNT catalysts promoted by alkali metals show similar effects to those seen for Fe supported on metal oxides.

Purification and identification of high molecular weight products formed during storage of neutral formulation of human insulin.

To identify High Molecular Weight Products (HMWP) formed in human insulin formulation during storage. Commercial formulation of human insulin was stored at 37°C for 1year and HMWP was isolated using preparative size exclusion chromatography (SEC) and reverse phase (RP) chromatography. The primary structure of the isolated species was analysed using liquid chromatography mass spectrometry (LC-MS) and tandem mass spectrometry (MS/MS). To test the hypothesis that amino groups of insulin are involved in HMWP formation, the HMWP content of various formulations spiked with amine compounds or formulations of insulin with modified amino groups was measured. More than 20 species of HMWP were observed and 16 species were identified using LC-MS. All identified species were covalent dimers of human insulin linked via A21Asn and B29Lys, formed via the formation of an anhydride intermediate at A21Asn. Two types of HMWP were identified, with the covalent link in the open or closed (succinimidyl) form. Some species also contained single deamidation at B3 or the desPhe(B1)-N-oxalyl-Val(B2) modification. Reduced rate of HMWP formation was observed after addition of L-lysine, L-arginine or piperazine or when insulin analogues with methylated N-terminals and side chain amines and A21Gly mutation were used. Formulations of human insulin without zinc and m-cresol were found to contain a different pool of HMWP. HMWP formed in formulation of human insulin at pH 7.4 with zinc and m-cresol consists primarily of covalent dimers linked via A21Asn and B29Lys. Insulin formulation properties determine the amount and identity of formed HMWP.

Aqueous Phase Oligomerization of Methyl Vinyl Ketone by Atmospheric Radical Reactions

Aqueous phase oxidation reactions in atmospheric particles can yield high molecular weight products and create secondary organic aerosol (SOA) upon droplet evaporation. Oxidation by hydroxyl radicals to create oligomers in solution that form SOA has been previously investigated; however, mixed organic solutions that can initiate radical chemistry have been largely overlooked. In aqueous solution, pyruvic acid (PA), an α-keto acid found in both the gas and aqueous phases in the atmosphere, photolyzes via a radical mechanism. Here, we use this photochemistry of pyruvic acid to trigger oligomerization of methyl vinyl ketone (MVK), an α,β-unsaturated compound generated by the atmospheric oxidation of isoprene. We closely compare the reaction products and mechanism to a recent work in which the radical oligomerization of MVK initiated by hydroxyl radical is studied in depth. Using mass spectrometry, it is shown that the two reactions create oligomers of similar molecular weights, up to m/z 1200 for initial MVK...

Unprecedented selectivities in aldol condensation over Mg–Al hydrotalcite in a fixed bed reactor setup

Aldol condensation of furfural with acetone (molar ratio 1:10) was carried out in a flow fixed bed setup at 50°C using calcined hydrotalcite with Mg/Al of 3 as a catalyst. Complete conversion of furfural and stable catalyst performance was obtained during the initial 50h on stream. This period was followed by a rapid catalyst deactivation. In contrast to previous reports, higher molecular weight products that were identified as products of successive aldol condensation of acetone with furfural were observed. Their concentration was time-dependent with a maximum formation after 10 to 30h on stream.

Arabinogalactan hydrolysis and hydrolytic hydrogenation using functionalized carbon materials

Hydrolysis of the hemicellulose arabinogalactan was studied in this work over several functionalized carbon materials, which were specifically treated to increase their acidities. Hydrolytic hydrogenation of arabinogalactan was investigated using the same materials in a mechanical mixture with ruthenium supported on active carbon.Application of these mixtures resulted in formation of polyols, suppressing simultaneously the generation of side products hydroxymethylfurfural (HMF) and furfural. Formation of high molecular weight compounds (aggregates of sugars and humins) was still quite substantial with a mechanical mixture of Ru/C and a carbon material prepared from sucrose by activation with zinc chloride to increase porosity. Post-treatment of this carbonaceous material with sulphuric acid significantly influenced kinetics of high molecular weight products formation resulting also in elevation of sugar alcohols yields.

A simple method to detect plant based inhibitors of glycation induced protein cross-linking

Background: Glycation induced cross-linking of proteins are associated with chronic diabetic complications. Inhibition of protein glycation is one of the therapeutic approaches to prevent the progression of diabetic complications. Objective: Objective of this study was to establish a simple method to identify medicinal plants which can inhibit glycation induced protein cross-linking. Methods: Lysozyme was incubated at 37°C up to 4 weeks with different concentrations of glucose, fructose and ribose in sodium phosphate buffer (pH 7.4). Appropriate controls and blanks were carried out. Aminoguanidine (AG) was used as the standard inhibitor. Water extracts of Bryophyllum pinnatum leaves, Coriandrum sativum seed and Murraya koenigi leaves were used as potential inhibitors. Aliquots were removed from the incubation mixtures at intervals and analyzed for the presence of AGE induced protein cross-links, using SDS-PAGE. Appearance and the intensity of high molecular weight products were compared. Results: Extent of cross-linking was dependent on the sugar concentration. Cross-linking was slowest in the presence of glucose and fastest in the presence of ribose. AG inhibited glycation induced protein cross-linking in the presence of all three sugars. B. pinnatum leaves, C. sativum seeds and M. koenigi leaves inhibited protein cross-linking in the presence of sugar. This inhibition was greater than that of AG. Conclusions: We have established a simple SDS-PAGE method to identify medicinal plants which inhibit glycation induced protein cross-linking. We also demonstrated the effectiveness of B. pinnatum leaves, C. sativum seed and M. koenigi leaves in inhibiting glycation induced protein cross-linking in vitro. DOI: http://dx.doi.org/10.3126/ajms.v6i1.10181 Asian Journal of Medical Sciences Vol.6(1) 2015 28-33

Tyrosinase-catalyzed site-specific immobilization of engineered C-phycocyanin to surface.

Enzymatic crosslinking of proteins is often limited by the steric availability of the target residues, as of tyrosyl side chains in the case of tyrosinase. Carrying an N-terminal peptide-tag containing two tyrosine residues, the fluorescent protein C-phycocyanin HisCPC from Synechocystis sp. PCC6803 was crosslinked to fluorescent high-molecular weight forms with tyrosinase. Crosslinking with tyrosinase in the presence of L-tyrosine produced non fluorescent high-molecular weight products. Incubated in the presence of tyrosinase, HisCPC could also be immobilized to amino-modified polystyrene beads thus conferring a blue fluorescence. Crosslinking and immobilization were site-specific as both processes required the presence of the N-terminal peptide in HisCPC.

Safety of total dose iron dextran infusion in geriatric patients with chronic kidney disease and iron deficiency anemia

There are limited data on total dose infusion (TDI) using iron dextran in geriatric chronic kidney disease (CKD) patients with iron-deficiency anemia (IDA). Our goal was to evaluate the safety of TDI in this setting. We conducted a retrospective chart review spanning a 5 year period (2002–2007), including all patients with CKD and IDA who were treated with iron dextran TDI. Patient demographics were noted, and laboratory values for creatinine, hemoglobin and iron stores were recorded pre- and post-dose. TDI diluted in normal saline was administered intravenously over 4-6 hours after an initial test dose. One hundred fifty-three patients received a total of 250 doses of TDI (mean ± SD = 971 ± 175 mg); age was 69 ± 12 years and creatinine 3.3 ± 1.9 mg/dL. All stages of CKD were represented (stage 4 commonest). Hemoglobin and iron stores improved post-TDI (P < 0.001). None of the patients experienced an anaphylactic reaction or death. Adverse events (AEs) were noted in 8 out of 250 administered doses (3.2%). The most common AEs were itching, chills and back pain. One hundred and ten doses of high molecular weight (HMW) iron dextran produced 6 AEs (5.45%), whereas 140 doses of low molecular weight (LMW) iron dextran produced 2 AEs (1.43%), a non-significant trend (P = 0.1433 by Fishers Exact Test). Iron dextran TDI is relatively safe and effective in correcting IDA in geriatric CKD patients. Fewer AEs were noted with the LMW compared to the HMW product. LMW iron dextran given as TDI can save both cost and time, helping to alleviate issues of non-compliance and patient scheduling.

Synthesis and Characterization of Acrylamide-Based Anionic Copolymer and Investigation of Solution Properties

The copolymer of acrylamide (AM) and 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) was synthesized through radical solution polymerization by potassium persulfate as initiator. By changing the AMPS feed ratio from 10 to 70%, and keeping other reaction conditions constant, different copolymers were synthesized. The techniques of Fourier transform infrared (FTIR) and nuclear magnetic resonance (1H-13C-NMR) spectroscopy were used for identification of functional groups and confirmation of copolymers’ structure. Intrinsic and apparent viscosity of samples were measured in aqueous sodium chloride solution under standard conditions. The anionic degree of copolymers was determined by back titration method and by13C-NMR spectroscopy. Molecular weight of copolymers was determined by the Mark-Houwink relationship. The measured molecular weight of samples showed that we have acquired a high molecular weight product. The effect of different range of shear rates on solution viscosity was evaluated. The copolymer solutions showed non-Newtonian shear thinning behavior. The performance of copolymers with respect to shear resistance and molecular weight was evaluated from industry application standpoint.

Nitroxide‐Mediated Controlled Radical Styrene Polymerization Via a Mass‐Suspension Process

Well controlled nitroxide‐mediated polymerizations of styrene using TEMPO as controller for the production of high molecular weight (MW) polystyrene have been run in a mass‐suspension process at the bench scale using molar ratios of nitroxide (N) to initiator (I) as low as N/I = 0.9. Previously, a kinetic study has been run in bulk polymerization in vials. The two processes show very similar results which demonstrates that the kinetic data collected in bulk can be used to scale‐up the mass‐suspension process. A mathematical model which can emulate the kinetic behavior of both processes has been built. Its kinetic parameters have been mostly taken from the literature and subjected to minimal data fitting using bulk reaction data. Some differences in the outputs of the two processes, especially at low conversions, are explained by the model and ascribed to temperature differences in the two processes.

Effects of inorganic seed aerosols on the growth and chemical composition of secondary organic aerosol formed from OH-initiated oxidation of toluene

(NH4)2SO4, CaCl2, Na2SiO3 and NaNO3 were selected as surrogates of inorganic seed aerosols of ambient atmosphere of Chinese urban areas, respectively, to study their effects on the formation of secondary organic aerosol (SOA) in the toluene/CH3ONO/NOx photooxidation system. The SMPS and aerosol laser time-of-flight mass spectrometer (ALTOFMS) was used to measure the aerodynamic size and chemical composition of individual SOA particles in real-time. Experimental results indicate that either the growth or products of SOA is affected by the presence of inorganic seed aerosol. Inorganic seed aerosols would promote growth rates of SOA formation at the start of the reaction and inhibits its formation rate with prolonging the reaction time. In the case of about 100 μg m−3 seed aerosol load, the addition of Na2SiO3 induced a same growth rate of SOA formation as NaNO3. The influence of four individual seed aerosols on the generation of SOA decreased in the order of CaCl2 > (NH4)2SO4 > NaNO3, Na2SiO3. The presence of Na2SiO3 or NaNO3 has no obvious effect on the growth rates of SOA formation, but it does increase the yield of organic acid and nitrogen-containing organic compounds, respectively. Besides the significantly effect on the growth rate of SOA formation, the presence of CaCl2 or (NH4)2SO4 can lead to the formation of high-molecular weight species which is found to be positively correlated with the hygroscopic behavior of seed aerosols. The CaCl2 shows the strongest hygroscopic behavior among the four individual seed aerosols, and the most significant promotion effect on the formation of the high-molecular weight species. It is proposed that the SOA generation enhancement and high-molecular weight products are achieved by particle-phase heterogeneous reactions induced and catalyzed by the acidity of CaCl2 and (NH4)2SO4 seed aerosols.

Comparative Theoretical Study of the Ring-Opening Polymerization of Caprolactam vs Caprolactone Using QM/MM Methods

Candida antarctica lipase B (CALB) efficiently catalyzes the ring-opening polymerization of lactones to high molecular weight products in good yield. In contrast, an efficient enzymatic synthesis of polyamides has so far not been described in the literature. This obvious difference in enzyme catalysis is the subject of our comparative study of the initial steps of a CALB catalyzed ring-opening polymerization of ε-caprolactone and ε-caprolactam. We have applied docking tools to generate the reactant state complex and performed quantum mechanical/molecular mechanical (QM/MM) calculations at the density functional theory (DFT) PBE0 level of theory to simulate the acylation of Ser105 by the lactone and the lactam, respectively, via the corresponding first tetrahedral intermediates. We could identify a decisive difference in the accessibility of the two substrates in the ring-opening to the respective acyl enzyme complex as the attack of ε-caprolactam is hindered because of an energetically disfavored proton transfer during this part of the catalytic reaction while ε-caprolactone is perfectly processed along the widely accepted pathway using the catalytic triade of Ser105, His224, and Asp187. Since the generation of an acylated Ser105 species is the crucial step of the polymerization procedure, our results give an explanation for the unsatisfactory enzymatic polyamide formation and opens up new possibilities for targeted rational catalyst redesign in hope of an experimentally useful CALB catalyzed polyamide synthesis

Effects of alkaline-earth metals on the structure, adsorption and catalytic behavior of iron-based Fischer–Tropsch synthesis catalysts

Effects of alkaline-earth metals (magnesium, calcium, strontium and barium) on the physico-chemical properties and Fischer–Tropsch synthesis (FTS) performances of precipitated Fe/SiO2 catalysts were investigated by N2 physisorption, laser Raman spectroscopy, FT-IR spectroscopy, in situ X-ray diffraction, Mössbauer effect spectroscopy, temperature programmed reduction or desorption and fixed-bed reactions. The characterization results indicated that alkaline-earth metals strengthened FeO bonds of Fe2O3 in as-prepared catalysts, which consequently inhibited the reduction of catalysts under H2 atmosphere. Mg and Ca suppress the carbonization of catalysts while Sr and Ba enhance the carbonization. The H2 adsorption was suppressed while the CO adsorption was enhanced by alkaline-earth metals. In the FTS reaction, alkaline-earth metals had no apparent influence on the CO conversion of catalysts, whereas they suppressed the formation of methane and enhanced the selectivities to olefin and higher molecular weight products. Among these alkaline-earth metals, Sr has the most pronounced influence on inhibiting the light hydrocarbon production. Furthermore, the increased Sr content can further restrain the formation of light hydrocarbons.

Biological Properties of Melanoidins: A Review

Melanoidins are brown, high molecular weight products of Maillard reaction, which takes place during thermal processing of food. They are formed in a multistage reaction between reducing sugars and compounds possessing free amino groups and found in roasted coffee, bakery products, cooked meat, beer, honey, sweet wine, processed tomatoes, and fiber. Nowadays, melanoidins have attracted a lot of attention, not only as a functional food ingredient, but also as a potential pro-healthy dietary supplement. In this field, their antioxidant, antimicrobial, anticancer, and detoxifying activity have been described. Based on recent research developments, an overview of the biological properties of melanoidins with implications for human health is presented.

The Chemo- and Electropolymerization of Thiophene Derivatives Containing at the Third Position of A Substituent with A Stereogenic Phosphorus Atom

Recently, differently functionalized polythiophenes (PTs) have found a broad application in material chemistry. Now, we are working in our laboratories on the synthesis of such derivatives functionalized at the third postion of a thiophene ring with a substituent containing a stereogenic heteroatom. In this paper, we would like to report our preliminary results devoted to the chemo- and electropolymerizations of monomeric thiophene derivatives. The classical three-electrode system used for electropolymerization carried out on platinum (Pt), glassy carbon (GC), and gold (Au) electrodes in acetonitrile with lithium perchlorate as the supporting electrolyte electrolyte will be presented. The chemical polymerization was based on the oxidative coupling using ferric chloride, leading to high molecular weight products.

Effect of copper loadings on product selectivities in microwave-enhanced degradation of phenol on alumina-supported copper oxides

Alumina-supported copper oxides catalysts were prepared using impregnation method and characterized using XRD, SEM and BET. Catalytic activities in phenol removal from its aqueous solution (200ppm) were studied using hydrogen peroxide as an oxidant under microwave irradiation. Effects of copper loadings, reaction temperatures (50 and 70°C) and pH (5 and 9) were studied. The high loading samples (9–14wt%) exhibited 97% phenol removal efficiency corresponding to 90% total organic carbon (TOC) value. Lower loading samples (1wt%) showed significantly lower phenol removals and inferior catalyst stability. At similar levels of phenol degradations, there was higher proportion of high molecular weight products or intermediates on 14 than on 1wt% copper/Al2O3.

Preparation of phosvitin–dextran conjugates under high temperature in a liquid system

The conjugation reaction between phosvitin (Pv) and dextran (Dex) in an aqueous solution at the initial stage of Maillard reaction was investigated in this study. The formation of Pv–Dex conjugates was indirectly traced by measuring the absorbance at 200nm in the UV-vis spectrophotometer. The content of free amino groups in the glycosylated Pv decreased to 77.4% after reaction for 6h. The new band near the loading end of SDS-PAGE gel also suggested the high molecular weight products developed after conjugation. The shift of the main peak of Pv in size exclusion-high performance liquid chromatography from 9.16min to 8.87min and the minor peak from 6.56min to 6.13min confirmed the formation of covalent conjugates. Circular dichroism (CD) spectra demonstrated that significant changes of the secondary structure occurred to the grafted Pv. The optimum conjugation condition chosen was per Pv (5mg/ml) glycosylated with 4-fold dextran (Mw, 40kDa) at 100°C for 6h.

On-line product analysis of pine wood pyrolysis using synchrotron vacuum ultraviolet photoionization mass spectrometry

The pyrolysis process of pine wood, a promising biofuel feedstock, has been studied with tunable synchrotron vacuum ultraviolet photoionization mass spectrometry. The mass spectra at different photon energies and temperatures as well as time-dependent profiles of several selected species during pine wood pyrolysis process were measured. Based on the relative contents of three lignin subunits, the data indicate that pine wood is typical of softwood. As pyrolysis temperature increased from 300 to 700 °C, some more details of pyrolysis chemistry were observed, including the decrease of oxygen content in high molecular weight species, the observation of high molecular weight products from cellulose chain and lignin polymer, and potential pyrolysis mechanisms for some key species. The formation of polycyclic aromatic hydrocarbons (PAHs) was also observed, as well as three series of pyrolysis products derived from PAHs with mass difference of 14 amu. The time-dependent profiles show that the earliest products are formed from lignin, followed by hemicellulose products, and then species from cellulose.

A new polysialic acid production process based on dual-stage pH control and fed-batch fermentation for higher yield and resulting high molecular weight product

To determine the factors influencing the resulting molecular weight of polysialic acid (PSA), batch fermentations by using Escherichia coli were conducted. It was found that temperature and pH were significant factors affecting the PSA production and its resulting molecular weight. When pH was set at 6.4, temperature of 37 °C was suitable for cell growth and PSA production while 33 °C facilitated production of higher molecular weight of PSA. pH 6.4 was favorable for PSA production while pH 7.4 was good for higher molecular weight of PSA at 37 °C. Intramolecular self-cleavage of PSA might lead to relatively low molecular weight under mild acidic condition. Our data suggest that the PSA molecular weight is significantly affected by the pH condition rather than the temperature. It is concluded that the resulting PSA molecular weight not only depends on fermentation conditions but also relates to cell growth rate and PSA production rate. Higher PSA molecular weight was made when its production rate was faster than degradation rate. A novel two-stage pH control fermentation process for production of high molecular weight PSA was developed. At the first stage, pH was set at 6.4 to encourage cell growth and PSA production, whereas pH was set at 7.4 at the second stage to promote the formation of higher molecular weight PSA. PSA yield up to 5.65 g/L and its resulting molecular weight of 260 kDa was attained, the highest level ever reported.