A novel amphoteric,pH‐sensitive,biodegradable poly[chitosan‐g‐(L‐lactic‐co‐citric) acid] hydrogel

The novel amphoteric, pH‐sensitive, biodegradable poly([chitosan‐g‐(L ‐lactic‐co‐citric) acid]) hydrogel (CLC) was synthesized through the reaction of chitosan (CS) with poly(L ‐lactic‐co‐citric acid) (PLCA). The structure of CLC was characterized by Fourier transform infrared spectroscopy, elemental analysis, and wide‐angle X‐ray diffraction measurement. The degree of substitution of CS amino groups was evaluated from salicylaldehyde analysis. The swelling behavior of CLC film in an aqueous solution with various pHs and the apparent swelling kinetics were studied. The swelling mechanisms of CLC film in acidic and alkaline mediums are discussed. The results showed that CLC hydrogel had a higher degree of swelling in the pH range of 4 > pH > 8 and that the swelling rate order in different buffers was neutral > acidic > basic mediums. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3850–3854, 2003     

13‐Hydroxy‐9Z,11E‐Octadecadienoic Acid Production by Recombinant Cells Expressing Burkholderia thailandensis 13‐Lipoxygenase

Linoleate 13‐lipoxygenase from Burkholderia thailandensis was expressed in Escherichia coli for the production of 13‐hydroxyoctadecadienoic acid (13‐HODE), an antiseptic emulsifier. Linoleate 13‐lipoxygenase in cells had higher thermal stability than the purified enzyme. To increase 13‐HODE production, recombinant cells were permeabilized by solvents, detergents, salts, and other chemicals. The enzymatic activity in cells was the highest for permeabilized cells treated with 0.5 M NaCl among the permeabilizers tested. The optimal reaction conditions for the production of 13‐HODE from linoleic acid by permeabilized cells treated with 0.5 M NaCl were at pH 7.5, 25 °C, 20 g/l linoleic acid, 15 g/l cells, 0.15 mM Cu²⁺, and 6 % (v/v) methanol in a 100‐ml baffled flask containing a 5‐ml working volume with agitation at 200 rpm. Under these conditions, permeabilized cells produced 15.8 g/l 13‐HODE after 30 min with a conversion yield of 79 % (w/w) and a productivity of 31.6 g/l/h. The conversion yield and productivity of permeabilized cells for 13‐HODE production were higher than those of purified and crude enzymes as well as nonpermeabilized cells. Therefore, permeabilized cells were efficient biocatalysts for 13‐HODE production. To the best of our knowledge, this is the first report of the production of 13‐HODE using cells.     

4,4‐Dimethyl‐ and Diastereomeric 4‐Hydroxy‐4‐methyl‐ (2S)‐Glutamate Analogues Display Distinct Pharmacological Profiles at Ionotropic Glutamate Receptors and Excitatory Amino Acid Transporters

Subtype‐selective ligands are of great interest to the scientific community, as they provide a tool for investigating the function of one receptor or transporter subtype when functioning in its native environment. Several 4‐substituted (S)‐glutamate (Glu) analogues were synthesized, and altogether this approach has provided important insight into the structure–activity relationships (SAR) for ionotropic and metabotropic glutamate receptors (iGluRs and mGluRs), as well as the excitatory amino acid transporters (EAATs). In this work, three 4,4‐disubstituted Glu analogues 1 – 3 , which are hybrid structures of important 4‐substituted Glu analogues 4 – 8 , were investigated at iGluRs and EAATs. Collectively, their pharmacological profiles add new and valuable information to the SAR for the iGluRs and EAAT1–3.     

Highly branched and tartaric acid‐based water‐borne resins

In this study, water‐borne polyurethane resins were produced using poly(propylene‐ethylene) copolymer triol, toluene diisocyanate, and hydrophilic monomers, dimethylol propionic acid and tartaric acid. The hydrophilic monomers were used separately. In either case, the ratio of isocyanate functional groups to the sum of hydroxyl groups of polyol and hydrophilic monomer was kept constant. The increase in the amount of hydrophilic monomer increased the hardness of resins when used as varnish. Tartaric acid resulted in higher hardness than dimethylol propionic acid. The dispersions made by using tartaric acid had much larger particle sizes than those of dimethylol propionic acid. In another set of experiments, the samples carrying the optimum properties from the two sets were mixed with methylol urea that served as crosslinker in the baking step. The physical and mechanical properties were determined by changing the weight percentages of the two types of samples in the mixture, and by changing the methylol urea percentage of the mixture which exhibited the maximum hardness. All samples showed superior impact resistance, adhesion, and flexibility. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 604–612, 2001     

13‐Phenyltridec‐9‐enoic and 15‐phenylpentadec‐9‐enoic acids in Arum maculatum seed oil

The seed oil of Arum maculatum has been found to contain 13‐phenyltridec‐9‐enoic (0.4%) and 15‐phenyl‐pentadec‐9‐enoic (1%) acids, detected by gas chromatographymass spectrometry of the picolinyl ester and related derivatives.     

Oxidation in EPA‐ and DHA‐rich oils: an overview

Oxidation of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) rich omega‐3 oils (hereafter referred to as either EPA and DHA or omega‐3) is a complicated topic, but an important one to understand. A significant number of consumers cite fishy burp and/or taste, thought to be the result of oxidation, as one of the main reasons they do not consume EPA and DHA rich oils. In addition, consumers note that some articles have raised concerns about the potential for adverse effects associated with consumption of oxidized oils. Measuring oxidation in omega‐3 oils is complicated due to the differences in chemical and physical characteristics of many commercially available products, which means not all methods to determine quality are appropriate for all types of oils. A number of consumer advocacy groups, product quality seal programs and academic groups have published data on levels of oxidation in omega‐3 oils. Overall, this data shows that commercially available omega‐3 supplements are low in oxidation. If consumers have a poor sensory experience with their omega‐3 product, they should try another product as an alternative.     

Electrochemical preparation of poly(N‐acetylaniline)/poly‐(4‐styrenesulfonic acid‐co‐maleic acid) composite film towards ascorbic acid sensing

Poly(N‐acetylaniline)/poly(4‐styrenesulfonic acid‐co‐maleic acid) (PNAANI/PSSMA) composite film was prepared by cyclic voltammetry (CV), and was characterized by FTIR and X‐ray photoelectron spectrum (XPS). The electroactivity of the composite film was high in neutral and basic solutions, and it had been used for amperometric determination of ascorbic acid (AA). Compared with pure PNAANI film, the catalytic activity of the composite film was much better. AA was detected amperometrically in sodium citrate buffer at a potential of 0.3 V (versus SCE). The response current was proportional to the concentration of ascorbic acid in the range of 4.7 × 10^?6 to 5.0 × 10^?5M and 5.0 × 10^?5 to 2.5 × 10^?3M, respectively, with the detection limit of 1.9 × 10^?6 mol L^?1 at a signal to noise ratio 3. In addition, the stability and reusability of the composite film were performed well, and it was satisfying to be used for determination of AA in real fruit juice samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Determination of swelling behavior and morphological properties of poly(acrylamide‐co‐itaconic acid) and poly(acrylic acid‐co‐itaconic acid) copolymeric hydrogels

Poly(acrylamide‐co‐itaconic acid) (PAAmIA) and poly(acrylic acid‐co‐itaconic acid) (PAAIA) copolymeric hydrogels were prepared with different compositions via free‐radical polymerization. Ethylene glycol dimethacrylate (EGDMA) was used as an original crosslinker for these monomers. Gelation percentages of the monomers were studied in detail and it was found that addition of IA into the monomer mixture decreased the gelation percentage. The variation in swelling values (%) with time, temperature, and pH was determined for all hydrogels. PAA, which is the most swollen hydrogel, has the swelling percentage value of 2000% at pH = 7.4, 37°C. Swelling behaviors were explained with detailed SEM micrographs, which show the morphologic differences between dry and swollen hydrogels. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5994–5999, 2006     

Solvent‐ and thermal‐induced crystallization of poly‐L‐lactic acid in supercritical CO2 medium

The effect of different annealing treatments with supercritical carbon dioxide (SCCO₂) on the structural and mechanical properties of semicrystalline poly‐L ‐lactic acid (L ‐PLA) was investigated. 2000, 27,000, 100,000, and 350,000 g mol^?1 molecular weight L ‐PLA polymers were used in the study. The solid‐state processing of L ‐PLA at temperatures lower than the effective melting point led to solvent‐ and thermal‐induced crystallization. Solvent‐induced and isothermal crystallization mechanisms could be considered similar regarding the increase of polymer chain mobility and mass‐transfer in the amorphous region; however, quite different microstructures were obtained. SCCO₂ solvent‐induced crystallization led to polymers with high crystallinity and melting point. On the contrary, SCCO₂ thermal‐induced crystallization led to polymers with high crystallinity and low melting point. For these polymers, the hardness increased and the elasticity decreased. Finally, the effect of dissolving SCCO₂ in the molten polymer (cooling from the melt) was analyzed. Cooling from the melt led to polymers with high crystallinity, low melting point, low hardness, and low elasticity. Distinctive crystal growth and nucleation episodes were identified. This work also addressed the interaction of SCCO₂‐drug (triflusal) solution with semicrystalline L ‐PLA. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Radiation synthesis and characterization of 2‐hydroxyethyl‐methacrylate‐based hydrogels containing di‐ and tri‐protic acid and its application on wastewater treatment

Radiation‐crosslinked 2‐hydroxyethylmethacrylate/citric acid (HEMA/CAc), 2‐hydroxyethylmethacrylate/tartaric acid (HEMA/TA), and 2‐hydroxyethylmethacrylate/succinic acid (HEMA/Sc) copolymers were prepared by using ⁶⁰Co γ‐rays. The gel fraction yield and the swelling behavior of the prepared hydrogels were studied. It was shown that increasing irradiation doses was accompanied by an increase in yield of gel fraction and a decrease in swelling degree. The parameters of equilibrium swelling, maximum swelling, initial swelling rate, swelling exponent, and diffusion coefficient of the hydrogels were determined by studying the swelling behavior of the hydrogels prepared. It was seen that the equilibrium swelling degree increases as the content of acid increases, as a result of introducing more hydrophilic groups. When the hydrophilic polymer (acids) varies in the content range of 40–80 mg, swelling exponents (n) decreases, thereby indicating a shift in the water‐transport mechanism from the anomalous (non‐Fickian)‐type to the Fickian‐type. Characterization and some selected properties of the prepared hydrogels were studied, and accordingly the possibility of its practical use in the treatment of industrial wastes such as dyes and heavy metals (Fe, Ni, Co, and Cu) were also studied. The effect of treatment time, pH of feed solution, initial feed concentration, and temperature on the dye and heavy metals uptake was determined. The uptake order for a given metal was HEMA/TA hydrogel > HEMA/CAc > HEMA/Sc hydrogel. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal decomposition kinetics of thermotropic copolyesters made from trans‐p‐hydroxycinnamic acid and p‐hydroxybenzoic acid

A series of thermotropic copolyesters were synthesized by direct thermal melt polycondensation of p‐acetoxybenzoic acid (PHB) with trans‐p‐acetoxycinnamic acid (PHC). The dynamic thermogravimetric kinetics of the copolyesters in nitrogen were analyzed by four single heating‐rate techniques and three multiple heating‐rate techniques. The effects of the heating rate, copolyester composition, degradation stage, and the calculating techniques on the thermostability and degradation kinetic parameters of the copolyesters are systematically discussed. The four single heating‐rate techniques used in this work include Friedman, Freeman–Carroll, Chang, and the second Kissinger techniques, whereas the three multiple heating‐rate techniques are the first Kissinger, Kim–Park, and Flynn–Wall techniques. The decomposition temperature of the copolyesters increases monotonically with increasing PHB content from 40 to 60 mol %, whereas their activation energy exhibits a maximal value at the PHB content of 50 mol %. The decomposition temperature, activation energy, the order, and the frequency factor of the degradation reaction for the thermotropic copolyester with PHB/PHC feed ratio of 50/50 mol % were determined to be 374°C, 408 kJ/mol, 7.2, and 1.25 × 10²⁹ min^?1, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 445–454, 2004     

Trifluoromethanesulfonic Acid‐Catalyzed Tandem Semi‐Pinacol Rearrangement/Alkyne‐Aldehyde Metathesis Reaction of Arylpropagylsulfonamide‐Tethered 2,3‐Epoxycyclohexan‐1‐ols to Spiropiperidines

A simple and efficient trifluoromethanesulfonic acid‐catalyzed cycloisomerization of arylpropagylsulfonamide‐tethered 2,3‐epoxycyclohexan‐1‐ols is described. The cyclization proceeds via tandem semi‐pinacol rearrangement/alkyne‐aldehyde metathesis to afford spiropiperidines under mild reaction conditions.     

6‐Amino‐6‐deoxy‐5,6‐di‐N‐(N′‐octyliminomethylidene)nojirimycin: Synthesis,Biological Evaluation,and Crystal Structure in Complex with Acid β‐Glucosidase

6‐Amino‐6‐deoxy‐5,6‐di‐ N ‐( N ′‐octyliminomethylidene)nojirimycin , a reducing analogue of N‐nonyl‐1‐deoxynojirimycin, proved to be a potent and very selective inhibitor of β‐glucosidases, including human acid β‐glucosidase. Structural studies of the enzyme–inhibitor complex showed a binding mode in which the anomeric hydroxy group is accommodated in the “wrong” α configuration.

     

Fibrous long‐chain organic acid cellulose esters and their characterization by diffuse reflectance FTIR spectroscopy,solid‐state CP/MAS 13C‐NMR,and X‐ray diffraction

Unsaturated and saturated organic acids with 11 and 18 carbon atoms, respectively, were used in a heterogeneous esterification reaction in the pyridine/toluene sulfonyl chloride system to prepare fibrous cellulose esters with different degrees of substitution. Highly bleached sulfite cellulose fibers were esterified during a 1‐ or 2‐h reaction time with the following organic acids: undecylenic acid, undecanoic acid, oleic acid, and stearic acid. In all cases, the heterogeneous esterification yielded partially substituted cellulose esters retaining their fibrous structure. The substitution reaction was confirmed by diffuse reflectance infrared spectroscopy and the chemical structures of cellulose esters were identified by solid‐state CP/MAS ¹³C‐NMR (75.3 MHz). X‐ray diffraction analyses showed broadening of the diffraction peaks with a higher degree of substitution of cellulose esters, which suggests structural changes within the cellulose fibers. Because the broadening peaks of X‐ray spectra or the unassigned C‐4 region of substituted cellulose chains in NMR spectra do not allow the calculation of dimensional changes of cellulose crystallites in cellulose esters, the lateral dimensions of crystallites in only cellulose fibers were calculated. The value derived from NMR (4.6 nm) differs by about 11% when compared with the value calculated from X‐ray diffraction data (4.1 nm). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1354–1365, 2000     

Development of an Efficient G‐Quadruplex‐Stabilised Thrombin‐Binding Aptamer Containing a Three‐Carbon Spacer Molecule

The thrombin‐binding aptamer (TBA), which shows anticoagulant properties, is one of the most studied G‐quadruplex‐forming aptamers. In this study, we investigated the impact of different chemical modifications such as a three‐carbon spacer (spacer‐C₃), unlocked nucleic acid (UNA) and 3′‐amino‐modified UNA (amino‐UNA) on the structural dynamics and stability of TBA. All three modifications were incorporated at three different loop positions (T3, T7, T12) of the TBA G‐quadruplex structure to result in a series of TBA variants and their stability was studied by thermal denaturation; folding was studied by circular dichroism spectroscopy and thrombin clotting time. The results showed that spacer‐C₃ introduction at the T7 loop position (TBA‐SP7) significantly improved stability and thrombin clotting time while maintaining a similar binding affinity as TBA to thrombin. Detailed molecular modelling experiments provided novel insights into the experimental observations, further supporting the efficacy of TBA‐SP7. The results of this study could provide valuable information for future designs of TBA analogues with superior thrombin inhibition properties.     

Synthesis of Chiral Amino Acid Anilides by Ligand‐Free Copper‐Catalyzed Selective N‐Arylation of Amino Acid Amides

An atom‐economic, practical and cost‐effective protocol for synthesis of chiral amino acid anilides via ligand‐free copper‐catalyzed selective C N cross coupling of chiral amino acid amides and aryl halides, hetereoaryl halides and a vinyl bromide has been developed. No racemization occurred during the C N coupling. A plausible mechanism is proposed.     

Adsorption of cationic dyes on poly(acrylic acid‐co‐sodium acrylate‐co‐acrylamide) superabsorbents

Inverse suspension polymerization was carried out to synthesize poly(acrylic acid‐co‐sodium acrylate‐co‐acrylamide) superabsorbent polymers (SAPs) crosslinked with ethylene glycol dimethacrylate (EGDMA). The equilibrium swelling capacities of the SAPs, determined by swelling them in DI water, were found to vary with the acrylamide (AM) content. The SAPs were used to adsorb four cationic dyes (Acriflavine, Auramine‐O, Azure‐I and Pyronin‐Y). The effect of AM content in the SAPs on the adsorption of the cationic dyes was investigated. Different initial concentrations of Azure‐I were used with the same amount of the SAP to explore the effect of initial dye concentration on the adsorption. The effect of the adsorbent amount was investigated by taking different amounts of SAP with a fixed initial concentration of Acriflavine. The kinetics of the dye adsorption was modeled by a first order model and the equilibrium amount of the dye adsorbed, adsorption rate coefficients, removal efficiency and partition coefficients were determined. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Factors influencing absorbent properties of saponified starch‐g‐(acrylic acid‐co‐acrylamide)

Mixtures of acrylamide (AM) and acrylic acid (AA) were grafted onto gelatinized maize starch by using ceric ammonium nitrate (CAN) as an initiator. These graft copolymers were hydrolyzed with alkali to yield hydrogels. The effects of different reaction variables, such as the concentration of the initiator and crosslinker, initial dilution of monomers, gelatinization conditions of starch, and the ratio of AM and AA in the monomer feed, on the water absorption capacities of these hydrogels have been examined. Absorption increases on gelatinizing starch at a higher temperature for a longer time as smaller granules gelatinize only under these conditions. The higher proportion of AA in the monomer feed enhances absorption due to formation of polyelectrolyte. The optimum conditions for obtaining maximum water absorbency established in the present study are granular maize starch = 2.0 g; gelatinization temperature = 95°C; gelatinization time = 60 min; AM = 1.0 g; AA = 4.0 g; CAN = 0.008 mol/L; N,N′‐methylene bisacrylamide = 1%. The product so formed was saponified with NaOH and then precipitated in excess of methanol. The dried and finely powdered product showed the maximum water absorbency of 510 g/g. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2480–2485, 2000