H. Nursevin Öztop

Immobilization of catalase on chitosan film

Catalase was immobilized on the chitosan film that is a natural polymer. Studies were done on free catalase and immobilized catalase on chitosan film concerning the determination of optimum temperature, optimum pH, thermal stability, storage stability, operational stability, and kinetic parameters. It was determined that optimum temperature for free catalase and immobilized catalase on chitosan film is 25 degrees C, and optimum pH is 7.0. It was found as K(m) = 25.16 mM, V(max) = 24042 µmole/min mg protein for free catalase, K(m) = 27.67 mM, V(max) = 1022 µmole/min mg protein for immobilized catalase on chitosan. It was observed that there was a big difference between V(max) value of the free catalase and V(max) value of immobilized catalase on chitosan film whereas there were minor changes in the value of K(m) for free catalase and immobilized catalase. It was found that storage stability at 5 degrees C for immobilized catalase stored wet is greater than free catalase and immobilized catalase stored dry, and immobilized catalase showed a operational stability.

Adsorption of bovine serum albumin onto acrylamid—maleic acid hydrogels

In this study, acrylamide-maleic acid hydrogels containing different amounts of maleic acid have been prepared by irradiating with gamma radiation. They have been used in experiments on bovine serum albumin (BSA) adsorption. Acrylamide-maleic acid hydrogel containing 60 mg of maleic acid and irradiated at 5.20 kGy has been used for swelling and diffusion studies in water, solutions of NaCl and BSA. For this hydrogel, maximum and minimum swellings have been observed with water (1680%) and the solution of BSA (1085%), respectively. Diffusions of water, NaCl and BSA within hydrogels have been found as non-Fickian types of diffusion. In the experiments of BSA adsorption, Langmuir type adsorption has been found. The hydrogel prepared with 60 mg maleic acid and having been irradiated at 2.00 kGy has been found to be the best adsorption system for BSA. The adsorption capacity of acrylamide hydrogel has been increased by the addition of maleic acid almost 1.5-3-fold.

Immobilization of Saccharomyces cerevisiae on to acrylamide–sodium acrylate hydrogels for production of ethyl alcohol

Abstract Acrylamide/sodium acrylate (AAm/SA) copolymers, prepared by using various crosslinkers, were used in experiments on swelling, diffusion, immobilization of yeast cells (Saccharomyces cerevisiae) and production of ethyl alcohol. AAm/SA hydrogels were used for swelling and diffusion studies in the nutrient medium of the cells. The parameters of equilibrium swelling, maximum swelling, initial swelling rate, diffusional exponent, network constant and diffusion coefficient of the hydrogel/penetrant systems were calculated and evaluated. Yeast cells were immobilized onto the hydrogels by adsorption method during multiplication and ethyl alcohol production of the hydrogels was investigated. Swelling of AAm increased with the addition of SA and ethyl alcohol production increased with increasing SA in the hydrogels. The best system for immobilization is found to be AAm/SA hydrogels containing N,N′-methylenebisacrylamide as crosslinker.

Influence of some amino acids on the dynamic swelling behavior of radiation-induced acrylamide hydrogel

The influence of some amino acids—alanine, glycine, valine, glutamine, histidine, phenylalanine, and tryptophan—on the swelling behavior of acrylamide (AAm) hydrogel prepared by γ-radiation was investigated. Swelling experiments of AAm hydrogel were made in the universal buffer solutions and the amino acid solutions at certain pHs at 37°C. These selected pH values were pK1, pK2 and isoelectric point (pI) values such as ionization of α-carboxyl groups, ionization of α-amino groups, and the pIs of the amino acids, respectively. The swelling of AAm hydrogel increased when pH values of solutions were increased. The value of equilibrium swelling of AAm hydrogel in the solution of universal buffer was 880% at pH 10.0, whereas it was 670% at pH 2.0. The values of equilibrium swelling of AAm hydrogel in amino acid solutions were between 830 and 965% at pH 10.0, whereas they were between 635 and 775% at pH 2.0. The rate constant of swelling, initial swelling rate, theoretical maximum swelling, diffusional exponent, network parameter, and diffusion coefficient were calculated by swelling kinetics. Diffusions of the amino acid solutions into the hydrogel were generally found as non-Fickian in character. The diffusion coefficients of the hydrogel were between 0.91 × 10−6 and 2.41 × 10−6 cm2/s.

The use of immobilized Saccharomyces cerevisiae on radiation crosslinked acrylamide–maleic acid hydrogel carriers for production of ethyl alcohol

Abstract Radiation crosslinked acrylamide/maleic acid (AAm/MA) copolymers were prepared by γ-irradiation. They were used in experiments on swelling, diffusion, and immobilization of yeast cells ( Saccharomyces cerevisiae ) for the production of ethyl alcohol. AAm/MA hydrogels containing different amount of MA, irradiated at different doses, were used for swelling and diffusion studies. The parameters of swelling, diffusional exponents, network constants, diffusion coefficients and percent porosity of the hydrogel/penetrant systems were calculated and evaluated. Yeast cells were immobilized on to the hydrogels by adsorption during multiplication, and ethyl alcohol production by the hydrogels was investigated. Swelling of AAm/MA increased with increase in MA content. Ethyl alcohol production also increased with increasing MA in the hydrogels but decreased with an increase of irradiation dose.

Immobilization of Saccharomyces cerevisiae on to radiation crosslinked HEMA/AAm hydrogels for production of ethyl alcohol

Radiation crosslinked 2-hydroxyethyl methacrylate/acrylamide (HEMA/AAm) copolymers prepared by γ-irradiation were used in experiments on swelling, diffusion, immobilization of yeast cells (Saccharomyces cerevisiae) and production of ethyl alcohol. HEMA/AAm hydrogels irradiated at 3 kGy were used for swelling and diffusion studies in water and the nutrient medium of the cells. The parameters of equilibrium swelling, maximum swelling, initial swelling rate, diffusional exponent, network constant and diffusion coefficient of the hydrogel/penetrant systems were calculated and evaluated. All parameters for the hydrogel/water system were higher than that of the hydrogel/nutrient medium systems. Yeast cells (Saccharomyces cerevisiae) were immobilized on to the hydrogels by adsorption during multiplication and ethyl alcohol production of the hydrogels was investigated. Swelling of HEMA increased with the addition of AAm and ethyl alcohol production increased with increasing AAm in the hydrogels.

pH-sensitive chitosan films for baker’s yeast immobilization

Dried baker’s yeast cells were immobilized on a chitosan film, which is a natural polymer. Prepared chitosan films were treated with glutaraldehyde to facilitate the immobilization of the cells. The effects of the amount of glutaraldehyde, incubation time, pH, and temperature on immobilization were investigated. The amount of glutaraldehyde was chosen to be 0.01% (weight). The highest amount of yeast immobilization was obtained with 5 h incubation. It was determined that optimum temperature for immobilization is 25°C, and the optimum pH for immobilization is 6. Immobilized cells were allowed to stand for 3 d in distilled water and buffer solution (pH 6) to investigate the desorption, but no desorption was found. The maximum immobilization capacities were found to be 90 µg protein cm−2 film in optimum conditions.

Acrylamide–Sepiolite Based Composite Hydrogels for Immobilization of Invertase

Novel composite hydrogels, poly(acrylamide)-sepiolite (PAS), poly(acrylamide/acrylic acid)-sepiolite (PAAS), and poly(acrylamide/itaconic acid)-sepiolite (PAIS) were prepared and used for the immobilization of invertase. The parameters of equilibrium swelling, diffusional exponent, and diffusion coefficient of these hydrogels were calculated from swelling experiments. Invertase was immobilized onto PAS, PAAS, and PAIS and immobilized invertases (PASI, PAASI, and PAISI) were prepared. Optimum pH values for free invertase, PASI, PAASI, and PAISI are found to be 5, 5.5, 4.5, and 6, respectively, and the optimum temperatures were 30, 50, 50, and 35 degrees C for free invertase PASI, PAASI, and PAISI. It was found that K(m) values of free invertase, PASI, PAASI, and PAISI were 11.3, 41.0, 94.5, and 56.0 mM, respectively. V(max) values were 2 mumol/min for free invertase, 8.10 mumol/min for PASI, 1.30 mumol/min for PAASI, and 0.42 mumol/min for PAISI, respectively. The invertase immobilized hydrogels showed excellent, temperature, storage, and operational stability.

Adsorption of Bovine Serum Albumin onto Radiation-crosslinked Poly(acrylamide/acrylic acid)

Poly(acrylamide/acrylic acid) (AAm/AAc) hydrogels were prepared at initial acrylic acid compositions of 70, 80 and 85 mol%, respectively. Mixtures of AAm and AAc monomers were irradiated in a 60Co γ-ray source at a dosage of 8 kGy. These hydrogels were used in experiments associated with the swelling, diffusion and adsorption of bovine serum albumin (BSA) from aqueous solution. The data obtained allowed the swelling and diffusion parameters for the hydrogels to be calculated. In the BSA adsorption experiments, the adsorption kinetics together with the influence of the pH of the medium, the initial BSA concentration and the composition of the hydrogels on the adsorption efficiency of the AAm/AAc hydrogels were all studied. The rates of BSA adsorption were found to conform to pseudo-first-order kinetics and a kinetic model was used to calculate the corresponding rate constant for the adsorption processes. The adsorption of BSA onto AAm/AAc hydrogels decreased with increasing pH, with the maximum adsorption being observed at a pH value of 3.7. In terms of the Giles classification, the adsorption was of type C. BSA adsorption increased as the AAc content of the hydrogels increased. Significant amounts of adsorbed BSA (up to 95%) were eluted when an elution medium containing 1.0 M NaSCN was employed at a pH value of 8.0.