Serpil Aksoy

Stability of α-amylase immobilized on poly(methyl methacrylate-acrylic acid) microspheres

Poly(methyl methacrylate-acrylic acid) microspheres were prepared and the acid groups were activated by using either carbodiimide (CDI) or thionyl chloride (SOCl2). alpha-Amylase was covalently bound on these activated microspheres. The properties of the immobilized enzyme were investigated and compared with those of the free enzyme. The relative activities were found to be 80.4 and 67.5% for carbodiimide and thionyl chloride bound enzymes, respectively. Maximum activities were obtained at lower pHs and higher temperatures upon immobilization compared to free enzyme. No change in Vmax and approximately 12-fold increase in K(m) were observed for immobilized enzymes. The enzyme activities, after storage for 1 month, were found to be 24.5 and 52.5% of the initial activity values for CDI and SOCl2 activated matrices, respectively. On the other hand the free enzyme lost its activity completely in 20 days. Immobilization, storage stability and repeated use capability experiments carried out in the presence of Ca2+ ions demonstrated higher stability, such as SOCl2 immobilized enzyme retained 83.7% and CDI immobilized enzyme retained 90.3% of the original activity of the enzyme. The immobilized enzymes that were used 20 times in 3 days in repeated batch experiments demonstrated that, in the absence of Ca2+ ions about 75% and in the presence of Ca2+ ions greater than 90% of the original enzyme activity was retained.

Covalent immobilization of α-amylase onto poly(2-hydroxyethyl methacrylate) and poly(styrene-2-hydroxyethyl methacrylate) microspheres and the effect of Ca2+ ions on the enzyme activity.

Abstract α-Amylase (1,4-α- d -glucan-glucanohydrolase; EC 3.2.1.1, Type VI-B from porcine pancreas, extra pure 29 units mg−1) was covalently immobilized on poly (2-hydroxyethyl methacrylate), p(HEMA), and poly (styrene- 2- hydroxyethyl methacrylate), p(St-HEMA) microspheres, which were activated by using epichlorohydrin (ECH). The properties of the immobilized enzyme were investigated and compared with those of the free enzyme. For the assays carried out at 25°C and pH 6.9, the relative activities were found to be 61.7 and 67.0% for ECH-activated P(HEMA) and P(St-HEMA) bound enzymes, respectively. The maximum activities were obtained at lower pH values and higher temperatures upon immobilization compared to free enzyme. Kinetic parameters were calculated as 2.51, 22.4 and 6.62 g dm−3 for Km and 1.67×10−3, 1.63×10−3 and 1.35×10−3 g dm−3 min−1 for Vmax in the case of free, P(HEMA) and P(St-HEMA) bound enzymes, respectively. Enzyme activity was found to be ca. 38.9% for ECH-activated P(HEMA) bound enzyme after storage for 1 month. On the other hand, free enzyme lost its activity completely in 20 days. Immobilization, storage stability and repeated use capability experiments that were carried out in the presence of Ca2+ ions demonstrated higher stability. The enzymes immobilized in the presence of Ca2+ ions retained 90.7 and 80.0% of their original activities even after 30 days for ECH-activated P(HEMA) and P(St-HEMA) systems, respectively. In repeated batch experiments, 20 uses in 3 days, in the absence of Ca2+ ions, retention of 79% of the original enzyme activities was observed for ECH-activated P(HEMA) immobilized enzymes. On addition of Ca2+ ions to the assay medium, 90.0 and 80.0% of retention was observed for ECH-activated P(HEMA) and P(St-HEMA) systems, respectively.

Synthesis and surface modification of polyurethanes with chitosan for antibacterial properties

Surface modification and providing antibacterial properties to the materials or devices are getting great attention especially in the last decades. In this study, polyurethane (PU) films were prepared by synthesizing them in medical purity from toluene diisocyanate and polypropylene ethylene glycol without using any other ingredients and then the film surfaces were modified by covalent immobilization of chitosan (CH) which has antibacterial activity. CH immobilized PU films (PU-CH) were found to be more hydrophilic than control PU films. Electron Spectroscopy for Chemical Analysis (ESCA) and Atomic Force Microscopy (AFM) analyses showed higher nitrogen contents and rougher surface topography for PU-CH compared to PU films. Modification with CH significantly increased antibacterial activity against Gram positive (Staphylococcus aureus) and Gram negative (Pseudomonas aeruginosa) bacteria. It was observed that the number of bacteria colonies were less about 10(2)-10(5) CFU/mL and number of attached viable bacteria decreased significantly after CH modification of PU films.

Immobilization of laccase in κ-carrageenan based semi-interpenetrating polymer networks

Laccase enzyme (L) was immobilized by entrapment into semi-interpenetrating polymer networks (semi-IPNs) prepared from kappa-carrageenan with either poly(acrylamide-acrylic acid) [P(AAm-AA)/kappa-car] or poly(acrylamide-itaconic acid) [P(AAm-IA)/kappa-car]. For both systems, immobilized enzymes achieved the same optimum values observed for free enzyme (pH=5.0 and T=40 degrees C), except for P(AAm-IA)/kappa-car system there was a shift to 5.5 in optimum pH value. At the end of 42 days of storage immobilized enzymes retained more than 80% of their original activities while the retained activities of both systems after 10 uses in batch type application were found to be higher than 50%. K(m) values were calculated as 2.52x10(-2) mM and 1.08x10(-2) mM and V(max) values were found as 6.8x10(-3) mM min(-1) and 4.4x10(-3) mM min(-1), for P(AAm-AA)/kappa-car-L and P(AAm-IA)/kappa-car-L, respectively. When methyl orange containing solutions (10 mg/L) were treated with the immobilized laccases (68.2U), enzymatic decolorization of methyl orange in 6 h was achieved to the level of 35% for both systems. Supplementing the reaction medium with ABTS as the redox mediator increased this value to about 70%. These initial results show that, laccase containing semi-IPNs can find some applications in decolorization of the industrial wastes.

Effects of thermal ageing on the properties and lifetime prediction of hydroxyl-terminated polybutadiene

Abstract Thermal ageing of hydroxyl-terminated polybutadiene propellant binders was carried out at various temperatures between 50 and 100°C. The changes caused by this treatment in properties such as melt viscosity, functional end-groups, molecular weight, tensile strength, elastic modulus and ultimate elongation were examined. The viscosity and average molecular weight increased with the ageing temperature and ageing period. A decrease in ultimate elongation and an increase in elastic modulus were observed. Tensile strength of the matrices prepared by curing hydroxyl-terminated polybutadiene with isophorone diisocyanate did not change. Lifetime for usability was predicted from the application of the Arrhenius equation to be 7 years.

Covalent Immobilization of a α‐Amylase onto Poly(methyl methacrylate‐2‐hydroxyethyl methacrylate) Microspheres and the Effect of Ca2+ Ions on the Enzyme Activity

α-Amylase was covalently immobilized onto poly(methyl methacrylate-2-hydroxyethyl methacrylate) microspheres, which were activated by using either epichlorohydrin (ECH) or cyanuric chloride (C3N3Cl3). The properties of the immobilized enzyme were investigated and compared with those of the free enzyme. For the assays carried out at 25 °C and pH 6.9, the relative activities were found to be 73.0% and 90.8% for epichlorohydrin and cyanuric chloride bound enzymes, respectively. Upon immobilization, the maximum activities were obtained at lower pH values and higher temperatures as compared with the free enzyme. Kinetic parameters were calculated as 2.51 g/L, 28.54 g/L and 15.50 g/L for Km and 1.67 × 10−3 gL−1 min−1 2.89 × 10−4 gL−1 min−1 and 1.89 × 10−3 gL−1 min−1 for Vmax for free, epichlorohydrin and cyanuric chloride bound enzymes, respectively. Enzyme activities were found to be ca. 32.7% for ECH and 41.1% for C3N3Cl3 activated matrices after storage for one month. On the other hand the free enzyme lost its activity completely within 20 days. Immobilization, storage stability and repeated use capability experiments carried out in the presence of Ca2+ ions demonstrated higher stability in the presence of these ions. The enzymes immobilized in the presence of Ca2+ ions retained 90.6% and 90.8% of the original activities even after 30 days in the case of ECH and C3N3Cl3 activations, respectively. In repeated batch experiments, i.e., 20 uses of the enzyme in 3 days; in the absence of Ca2+ ions retentions of 79.2% and 77.1% of the original enzyme activities were observed for ECH and C3N3Cl3 immobilized enzymes, respectively, whereas, in the case of addition of Ca2+ ions to the assay medium, these values were enhanced to 95.3% and 92.2%.

Monomer-bound ion pairs in the stereoregular polymerization of propylene oxide by the Pruitt-Baggett catalyst

Abstract The Pruitt-Baggett adduct (PBA) (MW = 438 g mol−1) that formed from the reaction of FeCl3 with propylene oxide (PO) was hydrolysed in diethyl ether (ether) solutions at different r = H 2 O Fe molar ratios. The hydrolysates ( PBH r ), which were insoluble in ether, could be converted into catalytically active form ( PBC r ) by a thermal treatment. PBC r (r was soluble in etheric solvents and in pyridine. These solutions, in contrast to PBA and PBH r , were electrical conductors. Profound differences in the electrical conductivity of PBC r was observed by varying the hydrolysis ratio r. The observed conductivity decayed and finally vanished with a kinetically second-order process. This is explained by the free ions, formed from PBC 0.67 (MW = 4400 g mol−1), being bound together with an ether (or PO) molecule to yield ether- (or PO-) bound ion pairs (PBCB). PBC 0.67 and the electrical conductivity of its freshly prepared solutions could be retrieved by ‘driving off’ (by drying under vacuum at 40°C) the ‘binding molecule’ (ether or PO) from PBCB. In contrast to this system, the electrical conductivity of solutions of PBC 0.20 (which shows inferior catalytic activity) did not change with ageing.

Immobilization of heparin on chitosan-grafted polyurethane films to enhance anti-adhesive and antibacterial properties

Infections caused by bacteria adhering to implant surfaces are one of the main reasons for the failure of the implants. In this study, polyurethane (PU), which is the most commonly used polymer in the production of medical devices, was synthesized and surfaces of polyurethane films were modified by chitosan (CH) grafting and heparin (Hep) immobilization in order to enhance anti-adhesiveness and antibacterial properties. Functional groups present on the surface, topographical shapes, and free energies of the polyurethane films were determined. Pristine polyurethane, chitosan-grafted polyurethane (PU–CH), and heparin immobilized polyurethane (PU–CH–Hep) films demonstrated high anti-adhesive efficacy against bacteria in the given order, where PU–CH–Hep was the most effective one. When PU–CH–Hep samples were incubated with different bacteria, complete death was observed for Pseudomonas aeruginosa (Gram negative), Staphylococcus aureus (Gram positive), and Staphylococcus epidermidis (Gram positive). Some living Escherichia coli (Gram negative) were observed after 24 h of incubation. Pristine and modified polyurethane samples demonstrated no adverse effect on proliferation of L929 fibroblast cells and were found to be biocompatible according to MTT cytotoxicity tests.

Estimation of monomer content in polymethyl methacrylate contact lens materials by Raman spectroscopy.

Polymethyl methacrylate is the most commonly used contact lens material due to its excellent optical properties. However the presence of residual monomer in the structure alters its transparency as well as its biocompatibility, thus, there is a need to detect any remaining methyl methacrylate. Raman spectroscopy is a rapid, sensitive, and non destructive method as compared to other spectroscopic, chromatographic or polarographic methods. In this study, the spectra of some lens materials (prepared from methyl methacrylate, 2-hydroxy ethyl methacrylate, hexamethyl disiloxane and polypropylene glycol with or without the addition of crosslinker ethylene glycol dimethylacrylate) were obtained by Raman spectroscopy. It was observed that an amount of crosslinker present in the structure proves effective for the unpolymerized monomer content. None of the samples, except those containing hexamethyl disiloxane, demonstrated any monomer residue.

Polymerization of propylene oxide and copolymerization of carbon disulphide and propylene oxide with xanthate salts

Abstract Anionic polymerization of propylene oxide (PO) using several xanthate salts was studied. Low molecular weight oily polymers with variable sulphur content were obtained by using either potassium ethyl xanthate or potassium benzyl xanthate. The highest attainable conversion of PO was limited to ca 10%. The polymerization was accompanied by formation and precipitation of a by-product salt. In the presence of CS 2 , an oily copolymer with about 40% sulphur was obtained from the above mixtures. In reaction systems with CS 2 /PO mole ratio larger than unity, all the PO in the feed could be copolymerized without precipitation of salt. Zinc isopropyl xanthate (ZnXt 2 ) polymerized PO into a partially stereoregular high polymer. Addition of CS 2 to PO and ZnXt 2 solution yielded high copolymers with monomeric unit ratios (CS 2 /PO) of 0.06–0.15.