A facile synthesis of hydrophilic glycopolymers with the ether linkages throughout the main chains

A series of well-defined block glycopolymer with the ether linkages throughout the main chains were synthesized by an easy and efficient way. First, the block copolymer intermediates poly(ethylene oxide)-b-poly(allyl glycidyl ether) (PEO-b-PAGE) with narrow molecular weight distribution were prepared by living anionic ring-opening polymerization. Then, 2,3,4,6-tetra-O-acetyl-β-thioglucopyranose (AcGSH) molecules were attached to the PAGE blocks by free-radical addition reaction of –SH groups of saccharide molecules with the double bonds. Finally, removal of the acetyl protective groups afforded the corresponding glycopolymers poly(ethylene oxide)-b-poly(allyl glycidyl ether-glucose) (PEO-b-P(AGE-glucose)). The composition and structure of the glycopolymers were characterized by ¹HNMR, ¹³CNMR and FT-IR.     

Modification of the water-insoluble hemicelluloses via free radical copolymerization in diluted alkali aqueous medium

The synthesis of hemicelluloses-g-polyacrylamide (PAM) was carried out in diluted alkaline aqueous solution via free radical copolymerization initiated by redox initiator composed of potassium persulfate (KPS)/sodium thiosulfate (Na₂S₂O₃). The less substituted hemicelluloses, l-arabino-4-O-methyl-d-glucurono-d-Xylan (wis-AGX), are the main components of the hemicelluloses isolated from corncobs by the ultrasound-assisted diluted alkali extraction method and exhibit poor water solubility, which largely limit their applications. The factors, such as the initiator dosage, the monomer concentration, and the reaction time, which influenced both the grafting percent and the grafting efficiency, were investigated. The chemical structure and thermal and macromolecular weight properties of the graft copolymers were characterized by Fourier transform infrared spectrometer (FT-IR), ¹H nuclear magnetic resonance spectroscopy (NMR), thermogravimetric analysis (TGA), and gel permeation chromatography (GPC). The results indicated that the PAM moieties were successfully introduced into the side chains of the hemicelluloses, and the graft copolymers showed good solubility in water. Such modification is suggested to find a possible new way for broadening applications of water-insoluble hemicelluloses, and the resultant graft copolymers might have potential applications, such as gels, films, adsorbents, coatings, or drug delivery systems.     

Review of recent literature on the light absorption properties of black carbon: Refractive index,mass absorption cross section,and absorption function

Abstract

Knowledge of the optical properties of soot black carbon (BC) is required for the prediction of the radiative effects of freshly-emitted and aged BC particles. Here we review BC mass absorption cross section (MAC) and absorption function E(m) measurements, focusing on freshly-emitted BC. First, we review recently reported MACs at 550?nm wavelength as obtained from direct measurements of particulate absorption and mass concentration; we find an average of 8.0?±?0.7?m²/g from ten measurements, not significantly higher (p?>?0.26) than the widely used MAC of 7.5?±?1.2?m²/g recommended by Bond and Bergstrom [Bond, T. C., and R. W. Bergstrom. 2006. Light absorption by carbonaceous particles: An investigative review. Aerosol Sci. Technol. 40(1):27–67]. Second, we review recently reported E(m), whose retrieval is more complex due to the need to combine measurements with numerical models to estimate the contribution of scattering to extinction. Third, we review recent numerical studies that have aimed to predict the BC MAC using various complex refractive indices (m?=?n?+?ik). Most of these studies have used m?=?1.95?+?0.79i recommended by Bond and Bergstrom (2006), yet failed to predict a MAC as high as 7.5 or 8.0?m²/g at 550?nm wavelength. Fourth, we summarize a selected range of alternative values of m that has been reported by recent studies and place them in the context of measurements using a contour plot of E(m) on the n–k plane. We show that the widely used m?=?1.95?+?0.79i corresponds to an E(m) that is too low to be consistent with the measured MAC values. We conclude that the E(m) of BC in the visible and near infrared should be greater than 0.32, and that the commonly used BC models or the refractive index, or both, are still in need of improvement.     

Synthesis and Characterization of Linear and Tri-Block PLLA–PEG–PLLA Blends

This study was conducted to synthesize poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) triblock copolymer (PEGLA) with different poly(L-lactide) block length, and explore its applicability in a blend with linear poly(L-lactide) (3051D NatureWorks) with the intention of improving heat seal and adhesion properties at extrusion coating on paperboard. Poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) was obtained by ring opening polymerization of L-lactide using poly(ethylene glycol) (molecular weight 6000 g mol^?1) as an initiator and stannous octoate as catalyst. The structures of the PEGLAs were characterized by proton nuclear magnetic resonance spectroscopy. The melt flow and thermal properties of all PEGLAs and their blends were evaluated using dynamic rheology and differential scanning calorimeter. All blends containing 10 wt% of PEGLAs displayed similar zero shear viscosities to neat poly(L-lactide), while blends containing 30 wt% of PEGLAs showed slightly higher zero shear viscosity. However, all blends displayed higher shear thinning and increased melt elasticity (based on tan δ). No major changes in thermal properties were distinguished from differential scanning calorimetric studies. High molecular weight PEGLAs could be used in extrusion coating with 3051D without problems.     

Synthesis of poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene triblock copolymers by two-step atom transfer radical polymerization

The synthesis of ABC triblock copolymer poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene (PEO-b-PMMA-b-PS) via atom transfer radical polymerization (ATRP) is reported. First, a PEO-Br macroinitiator was synthesized by esterification of PEO with 2-bromoisobutyryl bromide, which was subsequently used in the preparation of halo-terminated poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymers under ATRP conditions. Then PEO-b-PMMA-b-PS triblock copolymer was synthesized by ATRP of styrene using PEO-b-PMMA as a macroinitiator. The structures and molecular characteristics of the PEO-b-PMMA-b-PS triblock copolymers were studied by FT-IR, GPC and ¹H NMR.     

Toughening of epoxy thermosets with nano-sized or micron-sized domains of poly(ethylene oxide)-b-poly(butadiene-co-acrylonitrile)-b-poly(ethylene oxide) triblock copolymers synthesized using room temperature ester coupling reaction

Poly(ethylene oxide)-b-poly(butadiene-co-acrylonitrile)-b-poly(ethylene oxide) (PEO-b-PBN-b–PEO) triblock copolymers with three different compositions were synthesized from poly(ethylene glycol) methyl ethers and carboxylic acid-terminated poly(butadiene-co-acrylonitrile) (CTBN) by ester coupling reaction at room temperature. The PEO-b-PBN-b-PEO was incorporated into anhydride cured epoxy thermosets to improve the fracture toughness by the formation of either nano-sized spherical micelles or micron-sized vesicles. The polymer chemical structure was confirmed by Fourier transform infrared spectroscopy, nuclear magnetic resonance, and gel permeation chromatography. The morphology of PEO-b-PBN-b–PEO within the epoxy thermosets was investigated using a transmission electron microscope, an atomic force microscope, and a scanning electron microscope. Also, we conducted impact testing and plane-strain fracture toughness testing to evaluate the fracture toughness in terms of the impact strength and the critical stress intensity factors (K_IC) for the modified epoxy thermosets. The results revealed that all the PEO-b-PBN-b-PEO triblock copolymers are more effective in the toughening of epoxy thermoset compare to CTBN. We found that the 5 wt% PEO-b-PBN-b-PEO modified epoxy thermoset containing micron-sized vesicles exhibited the highest K_IC, which was 3.23 times as high as the K_IC of pristine epoxy thermoset. Besides, the glass transition temperature remained and the tensile modulus did not reduce remarkably when the amount of PEO-b-PBN-b-PEO added into epoxy was 5 wt%.     

Strategies for introducing sulfur atom in a sugar ring: synthesis of 5-thioaldopyranoses and their NMR data

Thiosugars containing a sulfur atom as heteroatom in the sugar ring are highly interesting. In particular, 5-thioaldopyranoses have attracted considerable attention because they exhibit biologically important properties as the substrates for glycosidases also can be developed as potential therapeutical agents, such as antineoplastic, anti-diabetic, antiviral, and antithrombotic agents. In this review, we describe and discuss the advances in synthetic strategies for the preparation of 5-thioaldopyranoses (5-thio-d-hexoses, 5-thio-l-hexoses, 5-thio-d-pentoses and 5-thio-l-pentoses), as well as their spectroscopic NMR data as known to date. The study aims to give readers an easy understanding of thiosugars chemistry and provide a useful guide for carbohydrate chemists.     

Optimization of Process Parameters for Controlled Ring-Opening Polymerization of Lactide to Produce Poly(L-Lactide) Diols as Precursor for Polyurethanes

Series of poly(L-Lactide) diols with molecular weights (M_n) in 2,069–4,811?g mol^?1 were synthesized from L-Lactide using stannous octoate catalyst and 1,4-butanediol chain extender. Operating conditions, i.e., temperature, catalyst concentration, chain extender concentration, and reaction time, were optimized. Maximum monomer conversion and M_n were observed at 0.5?mol% SnOct₂ and 1.0?mol% 1,4 butanediol (BDO) at 145°C. Poly(L-Lactide) diols were analyzed by Fourier transform infrared, proton nuclear magnetic resonance, end-group analysis, and X-ray diffraction techniques. Fourier transform infrared confirmed the formation of poly(L-Lactide) diols. Poly(L-Lactide) diols’ % degree of crystallinity was determined by X-ray diffraction. M_n was calculated by proton nuclear magnetic resonance and end-group analysis.     

Purification of L‐Phenylalanine from a Ternary Amino Acid Mixture Using a Two‐Zone SMB/Chromatography Hybrid System

Abstract

A two‐zone SMB/chromatography hybrid system was studied to separate L‐phenylalanine, which is the intermediate retained component, from a ternary amino acid mixture; glycine, L‐phenylalanine, and L‐tryptophane. PVP (poly‐4‐vinylpyridine) and deionized water were used as solid and liquid phases, respectively. Single component linear isotherms and mass transfer rates were obtained from multiple frontal tests. For the mass transfer rate, the Lapidus and Amundson linear dispersion model was used with an effective dispersion coefficient calculated from the mass transfer rate and the axial dispersion coefficient. This model was validated by comparing the frontal data with the simulation results from Aspen Chromatography 2004^®. A single objective genetic algorithm was employed to determine optimal operating condition. Experiments using the two‐zone SMB/chromatography system were conducted to purify L‐phenylalanine. The results show that the two‐zone system successfully removed 95.0% of glycine and 79.2% of L‐tryptophane from the ternary mixture producing a L‐phenylalanine product purity of 88.2%.     

Critical Surface Tension of Acrylamide-Grafted Polypropylene Copolymer by the Contact Angle Method

The contact angles θ of polar liquids on PP-g-AM copolymer (AM content 0.19, 0.26, and 0.37 wt%) were measured. The critical surface tension γ_C of PP-g-AM films were evaluated by the Zisman plot (cos θ versus-γl), the Young-Dupre-Good-Girifalco plot (1 + cos θ) versus 1/γ^0.5 l, and the log(1 + cos θ) versus log-γl plot. The-γl values estimated by the plot log(1 + cos θ) versus log-γl were smaller than those obtained by the other plots.     

Distribution Behavior of Amino Acid by Extraction with Di(2-ethylhexyl) Phosphoric Acid

Abstract

The distribution equilibrium of l-tryptophan (l-Trp) by extraction with di(2-ethylhexyl) phosphoric acid (D2EHPA) dissolved in n-hexane was studied. The effects of L-Trp and D2EHPA concentrations, pH, and ionic strength, particularly of L-Trp loading in the organic phase, on extraction equilibrium were examined in detail. When the amino acid loading ratio (the molar concentration ratio of the equilibrium amino acid in the organic phase to the initial dimeric D2EHPA) was less than 3 × 10^?3, one L-Trp molecule was extracted by forming a complex with four monomeric D2EHPA molecules, and the extraction equilibrium constant (K _e) was determined to be 0.045 dm³/mol. Above this loading ratio the equilibrium formula did not hold, and the apparent equilibrium constant (K _a) increased significantly with increasing loading ratio. The phenomenon was explained by taking into account two parallel reactions in which fewer D2EHPA molecules, two and one respectively, were needed to extract one l-Trp molecule.     

Reactivity of disulfide peptide l-cystine with iodido (diethylenetriamine)platinum(II) and synthesis of products in the presence of an iodide ion

Substitution reactions of complex [PtI(dien)]⁺ (where, dien=diethylenetriamine ) with sulfur-containing peptide l-cystine has been studied in 1.0×10^?1 M aqueous perchlorate or acetate medium between 298≤T (K)≤323 and 2.30≤pH≤4.45 using a UV–visible spectrophotometer. Products obtained have characterized from their physico-chemical and spectroscopic methods at various pH and temperatures. From this characterization, products have indicated that [PtI(dien)]⁺ has formed a complex with l-cystine and acts as a bidentate ligand, through Pt–S bond at 2.30≤pH≤3.30 and through Pt–N and Pt–S bond of cystine in 3.95≤pH≤4.45. At 2.30≤pH≤3.30, ring opening and closing of dien have occurred at 308 and 323 K, respectively, and the same has happened at pH≥3.95. All reactions have followed the rate law – d[mixture]/dt=(k ₁+k ₂ [cystine]) [Pt(II)], where k ₂ denotes the second-order rate constant. Activation parameters E _a , Δ H ^# and Δ S ^# have been determined. Product formation and reversible and forward reaction rate constants have also been evaluated.     

Preparation of the Sulfonamide Containing Block Copolymer as Polymeric Sorbent for Removal of Mercury from Aqueous Solutions

A new sulfonamide containing polymeric sorbent for the removal of mercury ions from waste waters was prepared starting from poly(glycidyl methacrylate)-b-poly(ethylene glycol)-b-poly(glycidyl methacrylate) (PGMA- b -PEG- b -PGMA) triblock copolymer prepared by using the ATRP method. Epoxy groups on the block copolymer were functionalized with amino groups. Ammonia-functionalized PGMA- b -PEG- b -PGMA was treated with excess of benzenesulfonyl chloride to obtain a sulfonamide-based polymeric sorbent. The sulfonamide containing the polymeric sorbent with a 3.5 mmol · g^?1 total nitrogen content is able to selectively sorb mercury from aqueous solutions. The mercury sorption capacity of the resin is around 3.12 mmol g^?1 under non-buffered conditions. Experiments performed in identical conditions with several metal ions revealed that Cd(II), Pb(II), Zn(II), Fe(III), and Fe(II) also were extractable in quantities (0–0.45 mmol/g). The sorbed mercury can be eluted by repeated treatment with 4 M HNO₃ without hydrolysis of the sulfonamide groups.     

Sugar-based bicyclic monomers for aliphatic polyesters: a comparative appraisal of acetalized alditols and isosorbide

Three series of polyalkanoates (adipates, suberates and sebacates) were synthesized using as monomers three sugar-based bicyclic diols derived from D-glucose (Glux-diol and isosorbide) and D-mannose (Manx-diol). Polycondensations were conducted in the melt applying similar reaction conditions for all cases. The aim was to compare the three bicyclic diols regarding their suitability to render aliphatic polyesters with enhanced thermal and mechanical properties. The ensuing polyesters had molecular weights (M_w) in the 25,000–50,000 g mol^?1 range with highest values being attained for Glux-diol. All the polyesters started to decompose above 300 °C and most of them did not display perceivable crystallinity. On the contrary, they had glass transition temperatures much higher than usually found in homologous polyesters made of alkanediols, and showed a stress–strain behavior consistent with their T_g values. Glux-diol was particularly effective in increasing the T_g and to render therefore polyesters with high elastic modulus and considerable mechanical strength.     

Magnetite/poly(D,L-lactide-co-glycolide) and hydroxyapatite/poly(D,L-lactide-co-glycolide) prepared by W/O/W emulsion technique for drug carrier: Evaluation of in vitro release of dexamethasone from composite nanoparticles

Biocompatible polymeric carriers containing inorganic materials for delivering therapeutic agents to a targeted site are promising candidate for drug delivery. Two nanocomposite nanoparticles, magnetite/poly(D,L-lactide-co-glycolide) and hydroxyapatite/poly(D,L-lactide-co-glycolide) (Fe₃O₄/PLGA and HAp/PLGA, respectively), with different weight ratios of inorganics to polymer and different polymer molecular weights were prepared by water-in-oil-in-water (W/O/W) emulsion technique to determine incorporation and in vitro release profile of the small molecule drugs water-insoluble dexamethasone acetate (DEX-Ac) and water-soluble dexamethasone phosphate (DEX-P). The in vitro release for DEX-Ac nanoparticles showed an initial burst release followed by a continuous slower release, whereas DEX-P nanoparticles showed only rapid initial release behavior.     

Assessment of Cytocompatibility of Bulk Modified Poly-L-lactic Acid Biomaterials

The cytocompatibility and hydrophilicity tests were performed by culturing mouse fibroblastic cells on films of poly-L-lactic acid (PLLA), poly(L-lactic-co-glycolide) (PLGA) and poly(L-lactide-co-glycolide)/ bioactive glass (PLGA/BG) or in the presence of extracts from these polymeric materials. The solvent casting method was used to prepare these films. PLLA films were most hydrophobic and PLGA/BG was least hydrophobic. Compared to the other films, PLLA showed the worst results in cytocompatibility. PLGA also showed favorable results for fibroblastic cells viability. PLGA/BG films also demonstrated improved cell compatibility due to the good biocompatibility of the bioactive glass particles. The results of this study indicate the promising biocompatibility of PLGA/BG as biomaterials in medical field.     

Preparation and characterization of carvedilol-loaded poly(d,l) lactide nanoparticles/microparticles as a sustained-release system

Carvedilol poly(d,l)-lactide nanoparticles/microparticles were prepared. The size and morphology of the developed particles were optimized to study the carvedilol release profile by studying the effect of organic solvents and polymer amount through atomic force microscopy analysis. Spherical particles were obtained with a minimum size of 125?nm in the case of acetone and a maximum size of 970?nm in the case of dichloromethane affording microparticles formation. The interaction was confirmed by differential scanning calorimeter and Fourier transform infrared. The in vitro release profile of the multicompartment system (pure carvedilol, loaded nanoparticles and microparticles) has shown a sustained release with Korsmeyer–Peppas with T lag model.     

Stereoselective Formation of 1,4‐Anhydro‐2‐C‐carboxytetritols in the Degradation of 1,5‐Anhydroribitol and 1,5‐Anhydroxylitol with Oxygen in Aqueous Alkali

Abstract

In addition to other acid products, degradation of 1,5‐anhydroribitol (5) and 1,5‐anhydroxylitol (6) with oxygen in 1.25 M NaOH produced diastereomeric 1,4‐anhydro‐2‐C‐carboxy‐D‐erythritol (7) and 1,4‐anhydro‐2‐C‐carboxy‐D‐threitol (8) and their enantiomers as major products. However, the ratio of the diastereomers differed for the two reactants. Thus, their formation could not proceed solely by benzilic acid‐type rearrangements through α‐dicarbonyl intermediates as typically proposed for formation of alkyl C‐carboxyfuranosides from alkyl glycopyranosides in similar reactions. The α‐dicarbonyl species that can form from 5 and 6 are identical. Potential mechanisms to account for stereoselective formation of 7 and 8 are presented.     

Kinetics of L-Ascorbic Acid Degradation in Pineapple Drying under Ethanolic Atmosphere

The kinetics of L-ascorbic acid degradation during drying of pineapple in normal and modified atmosphere was studied. Drying experiments were carried out in a tunnel dryer at two drying temperatures and air velocities. The drying atmosphere was modified by the addition of ethanol (0.5% v/v). The presence of ethanol in the drying atmosphere promoted a more intense water evaporation compared to the conventional process. Although the L-ascorbic acid degradation rate during the pineapple drying (final moisture content of 27% wet basis) under ethanolic atmosphere was higher, these samples retained higher amounts of L-ascorbic acid. Moreover, the Weibull model was applied to fit the kinetics data.     

Synthesis of pH-Responsive Multilayer Micelles for Sustained Release of Folic Acid

Two novel triblock copolymers poly(hydroxypropyl acrylate)-b-poly (methyl methacrylate)-b-poly(N,N-dimethylaminoethyl methacrylate) and poly(hydroxypropyl acrylate)-b-poly(methyl methacrylate)-b-poly(acrylic acid) were successfully synthesized. In acetone media, using the electrostatic interactions between N,N-dimethylaminoethyl methacrylate and acrylic acid units, they could form spherically shaped multilayer micelles with pH-responsive, and have a mean diameter around 110 nm. The critical micelle concentration of it was determined to be 2.42 mg/L. In vitro release experiments, the folic acid-loaded micelles exhibited sustained release behavior and the drug release rate was affected by the pH value of release media. These results indicate that the multilayer micelles may serve as a novel intelligent drug delivery system.