Mustafa Yiğitoğlu

Studies on the activity and stability of immobilized horseradish peroxidase on poly(ethylene terephthalate) grafted acrylamide fiber

Having been activated with glutaraldehyde, modified poly(ethylene terephthalate) grafted acrylamide fiber was used for the immobilization of horseradish peroxidase (HRP). Both the free HRP and the immobilized HRP were characterized by determining the activity profile as a function of pH, temperature, thermal stability, effect of organic solvent and storage stability. The optimum pH values of the enzyme activity were found as 8 and 7 for the free HRP and the immobilized HRP respectively. The temperature profile of the free HRP and the immobilized HRP revealed a similar behaviour, although the immobilized HRP exhibited higher relative activity in the range from 50 to 60 °C. The immobilized HRP showed higher storage stability than the free HRP.

Selective removal of Cr(VI) ions from aqueous solutions including Cr(VI), Cu(II) and Cd(II) ions by 4-vinly pyridine/2-hydroxyethylmethacrylate monomer mixture grafted poly(ethylene terephthalate) fiber

In this study, a new reactively fibrous adsorbent was prepared by grafting 4-vinyl pyridine (4-VP) and 2-hydroxyethylmethacrylate (HEMA) monomer mixture onto poly(ethylene terephthalate) (PET) fibers for removal of Cr(VI), Cu(II) and Cd(II) metal ions from aqueous solution by using batch adsorption method. The influence of various parameters such as graft yield (GY), pH, adsorption time, initial ion concentration and adsorption temperature was investigated. The selectivity of the reactive fiber was also examined. The results show that the adsorbed amount of metal ions followed as given in the order Cr(VI)>Cd(II)>Cu(II). At pH 3, Cr(VI) was removed by 99% while the initial concentration of ions was at 5 mg L(-1) and by 94% at 400 mg L(-1). It was found that the grafted fiber is more selective for Cr(VI) ions in the mixed solution of Cr(VI)-Cu(II), Cr(VI)-Cd(II) and Cr(VI)-Cu(II)-Cd(II) at pH 3 and it was observed that the grafted fibers are stable and regenerable by acid and base without losing their activity.

Determination of zinc, cadmium, cobalt and nikel by flame atomic absorption spectrometry after preconcentration by poly(ethylene terephthalate) fibers grafted with methacrylic acid☆

Abstract A method for the determination of Zn, Cd, Co and Ni by flame atomic absorption spectrophotometry after preconcentrating on poly(ethylene terephthalate) fibers grafted with methacrylic acid has been developed. The batch adsorption method was used for the preconcentration studies. Effect of pH, amount of adsorbent, concentration and volume of elution solution, shaking time and interfering ions on the recovery of the analytes have been investigated. Recoveries of Zn, Cd, Co and Ni were 97.3±0.4%, 98.3±0.2%, 94.1±0.3% and 96.5±0.6% at 95% confidence level, respectively, at optimum conditions. Langmuir adsorption isotherm curves were also studied for the analytes. The adsorption capacity of the adsorbent was found as 298, 412, 325 and 456 mg/g for Zn, Cd, Co and Ni, respectively. Poly(ethylene terephthalate) fibers grafted with methacrylic acid are suitable for repeated use without loss of capacity for more than thirty cycles. The proposed method was applied to the determination of trace metals in river water and synthetic sea water. Trace metals have been determined with high precision.

Adsorption behavior of copper(II) ion from aqueous solution on methacrylic acid-grafted poly(ethylene terephthalate) fibers

The adsorption behavior of methacrylic acid-grafted poly(ethylene terephthalate) fibers was studied toward the copper(II) ion in aqueous solutions by a batch equilibriation technique. The influence of treatment time, temperature, pH of the solution, metal ion concentration, and graft yield were considered. One hour of adsorption time was found sufficient to reach adsorption equilibrium for the copper(II) ion. It was found that the adsorption isotherm of Cu(II) fits Langmuir-type isotherms. The adsorption process is not affected by the temperature when treated with low ion concentration, but is remarkably decreased at a high ion concentration. The heat of adsorption value was calculated as 0.71 kcal/mol. It was found that the reactive fibers are stable and regenerable by acid without losing their activity.

Microwave-assisted synthesis of alginate-g-polyvinylpyrrolidone copolymer and its application in controlled drug release

The aim of this study is to synthesize graft copolymer (NaAlg-g-PVP) in microwave oven and prepare pH-responsive beads with high entrapment efficiency. For this purpose, PVP was grafted onto sodium alginate using microwave radiation. The copolymer obtained was characterized using FTIR, 1H-NMR, elemental analysis and thermogravimetric analysis. A series of NaAlg-g-PVP beads were prepared as drug delivery matrices for ibuprofen (IB) by cross-linking into beads via glutaraldehyde. The chemical stability of IB after encapsulation into beads was confirmed by FTIR, DSC, and X-RD analysis. Synthesis conditions of beads were optimized by considering entrapment efficiency, particle size, swelling capacity and their release data. Effects of such variables as graft yield and drug/polymer ratio were investigated at 1.2 and 7.4 pH values. Increasing the drug/polymer ratio and extent of cross-linking caused decrease in the IB release. On the other hand, increase in the graft yield led to increase in the IB release as well. The results also showed that NaAlg-g-PVP beads were positive pH-responsive.

The study of kinetic models for ligand exchange of anions as ligands using ligand‐exchange resin

A comparative study of kinetic models for ligand exchange of I− Cl− and Br− Cl− as ligands as a function of pH and concentration using diaminoethyl-sporopollenin (DAE-sporopollenin) resin were investigated during the ligand-exchange reaction of the liquid phase. A batch technique was employed for the study of the kinetics of I and Br/Cl exchange as ligands. Five kinetic models were applied to the experimental data. The rate of ligand exchange was increased with decreasing of the hydrated ionic radius and pH. The curve fitting of the mathematical models and the behavior of the kinetic curves are discussed for direct ligand exchange under the conditions employed.

Graft copolymerization of n-vinyl-2-pyrrolidone on dimethyl sulfoxide pretreated poly(ethylene terephthalate) films using azobisisobutyronitrile initiator

Poly(ethylene terephthalate) (PET) films were grafted with n-vinyl-2-pyrrolidone (n-VP) using an azobisisobutyronitrile (AIBN) initiator. Films were pre-treated in dimethyl sulfoxide (DMSO) for 1 h at 140°C before the polymerization reaction was carried out. Variations of graft yield with time, temperature, initiator, and monomer concentrations were investigated. The optimum temperature and polymerization time was found to be 70°C and 4 h, respectively. Increasing monomer concentration from 0.28 to 1.22M and initiator concentration from 1.77 × 10−3 to 4.20 × 10−3M enhanced the percent grafting. The effects of monomer and initiator diffusion on PET films were also studied. The overall activation energy for grafting was calculated as 11.5 kcal/mol. Further changes in properties of PET films such as water-absorption capacity and intrinsic viscosity were determined. The grafted films were characterized with FTIR and scanning electron microscopy (SEM).

Controlled release of indomethacin from crosslinked alginate beads

Abstract Beads of the sodium alginate (NaAlg) were prepared by dropping aqueous sodium alginate (NaAlg) into glutaraldehyde (GA) as a crosslinker and HCl as a catalyst mixture solution. Beads prepared were used to deliver a model non-steroid, anti-inflammatory drug, indomethacin (IM). The beads were characterized with Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Chemical stability of the IM after encapsulation into beads was confirmed by FTIR. SEM photograph indicated that alginate bead has spherical shape and rough surface. Preparation conditions of the beads were optimized by considering the percentage of entrapment efficiency, swelling capacity of the beads, particle size and their release data. In vitro release studies were performed in simulated gastric fluid (pH 1.2) for the initial 2 h, followed by simulated intestinal fluid (pH 7.4) for 4 h. Effects of variables such as, GA concentration, exposure time to GA, drug/polymer (d/p) ratio and percentage of HCl on the release of the IM were investigated. It was observed that, IM release from the beads decreased with increasing GA concentration, exposure time to GA, d/p ratio and percentage of HCl. The highest cumulative IM release obtained at the end of 6 h was 68% for alginate beads which were prepared with 0.5% HCl. On the other hand the least cumulative IM release obtained was to be 20 % for alginate beads which were prepared with 30 min exposure time to GA. In order to understand the crosslinking of the polymeric matrix, the molar mass between crosslinks were calculated using the swelling parameters. It was also found from the swelling experiments that swelling degree of the beads increases with increase in the temperature. The release data have been fitted to an empirical equation to estimate the kinetic parameters. The diffusion coefficient was also calculated for the transport of the drug through the polymeric beads. Values of these parameters were found to be consistent with the release data.

Use of 4-vinylpyridine and 2-hydroxyethylmethacrylate monomer mixture grafted poly(ethylene terephthalate) fibers for removal of congo red from aqueous solution

Abstract In this study, a novel fibrous adsorbent made by grafting 4-vinyl pyridine (4-VP) and 2-hydroxyethylmethacrylate (HEMA) monomer mixture onto poly(ethylene terephthalate) (PET) fibers was used for removal of Congo red (CR) in aqueous solutions by a batch equilibration technique. The influence of treatment time, pH of solution, dyes concentration, and reaction temperature on adsorbed amount was investigated. Adsorption time of 60 min. was found sufficient to reach adsorption equilibrium for CR. It was found that the adsorption isotherm of CR fits to Langmuir type isotherms. The highest adsorption capacity was found to be 11.87 mg CR per gram adsorbent. The adsorption rate of CR is much higher on the comonomers grafted PET fibers than on the ungrafted PET fibers. CR was removed 97 % when the initial dye concentration was 5 mg L-1 and 38% at 150 mg L-1 by monomers mixture grafted PET fibers. The adsorption of the dye was endothermic in nature (ΔH°=45.3 KJmol-1). It was found that the reactive fibers are stable and regenerate by acid without losing its activity.

Use of chemically modified poly(ethylene terephthalate)-g- (acryl amide) fibers for α-amylase immobilization

Abstract Acryl amide grafted Poly(ethylene terephthalate) (AAm-g-PET) fiber was used for covalent coupling of α-amylase. The amide groups of Poly(acryl amide) were converted to the amine groups by Hofmann degradation reaction. The amine groups were activated by glutaraldehyde, before coupling of the enzyme. The free α-amylase and immobilized α-amylase were characterized by determining the activity profile as function of pH, temperature, thermal stability and storage stability. For the immobilized α-amylase, operational stability was also determined. The immobilization of α-amylase on support caused the optimal reaction pH to shift from 5 to 6. The maximum activity of the free and immobilized enzymes occurred at 50 0C. Km for the immobilized system was higher than that for the free enzyme. The activity of the free enzyme ended in 30 days, whereas the activity of the immobilized enzyme lasted for 60 days at storage conditions. α-Amylase immobilized on matrix maintained 40% of its original activity after 30 times of repeated use.