S. Ali Tuncel

Poly(vinyl pyridine-poly ethylene glycol methacrylate-ethylene glycol dimethacrylate) beads for heavy metal removal.

Poly(vinyl pyridine-poly ethylene glycol methacrylate-ethylene glycol dimethacrylate) [poly(VP-PEGMA-EGDMA)] beads with an average size of 30-100 microm were prepared by suspension polymerization. Poly(VP-PEGMA-EGDMA) beads were characterized by swelling studies, scanning electron microscopy (SEM), elemental analysis, Fourier Transform Infrared Spectroscopy (FTIR). The beads with a swelling ratio of 65% were used for the heavy metal removal studies. Chelation capacity of the beads for the selected metal ions, i.e., Pb(II), Cd(II), Cr(III) and Cu(II) were investigated in aqueous media containing different amounts of these ions (5-80 mg/l) and at different pH values (2.0-10.0). The maximum chelation capacities of the poly(VP-PEGMA-EGDMA) beads were 18.23 mg/g for Pb(II), 16.50 mg/g for Cd(II), 17.38 mg/g for Cr(III) and 18.25 mg/g for Cu(II). The affinity order on mass basis was observed as follows: Cu(II)>Pb(II)>Cr(III)>Cd(II). pH significantly affected the chelation capacity of VP incorporated beads. Heavy metal adsorption on the poly(PEGMA-EGDMA) control microspheres was negligible. Regeneration of the chelating beads was easily performed with 0.1 M HNO3. It was shown that these beads can be used effectively for heavy metal removal from aqueous solutions with repeatedly adsorption-desorption operations. These features show that poly(VP-PEGMA-EGDMA) beads are potential candidate sorbent for heavy metal removal.

Immobilization of catalase in poly(isopropylacrylamide-co-hydroxyethylmethacrylate) thermally reversible hydrogels

Catalase was entrapped in thermally reversible poly(isopropylacrylamide-co-hydroxyethylmethacrylate) (pNIPAM/HEMA) copolymer hydrogels. The thermoresponsive hydrogels, in cylindrical geometry, were prepared in an aqueous buffer by redox polymerization. It was observed that upon entrapment, the activity retention of catalase was decreased between 47 and 14%, and that increasing the catalase loading of hydrogel adversely affected the activity. The kinetic behaviour of the entrapped enzyme was investigated in a batch reactor. The apparent kinetic constant of the entrapped enzyme was determined by the application of Michaelis–Menten model and indicated that the overall reaction rate was controlled by the substrate diffusion rate through the hydrogel matrix. Due to the thermoresponsive character of the hydrogel matrix, the maximum activity was achieved at 25 °C with the immobilized enzyme. The Km value for immobilized catalase (28.6 mM) was higher than that of free enzyme (16.5 mM). Optimum pH was the same for both free and immobilized enzyme. Operational, thermal and storage stabilities of the enzyme were found to increase with immobilization. © 1999 Society of Chemical Industry

Preparation and characterization of polyethyleneglycolmethacrylate (PEGMA)-co-vinylimidazole (VI) microspheres to use in heavy metal removal.

Polyethyleneglycolmethacrylate (PEGMA) and vinylimidazole (VI) were used in order to obtain microspheres of PEGMA-VI copolymers that can be used in heavy metal removal applications. The obtained copolymers were characterized and their use as sorbents in heavy metal removal was investigated. In the first part of the study, PEGMA-VI microspheres were prepared by suspension polymerization method. The obtained swellable microspheres with 10-50 microm average diameter did not have permanent porosity according to the morphological and physicochemical determinations. The sizes of microspheres became smaller with increasing VI and cross-linker ethyleneglycoldimethacrylate (EGDMA) contents and increasing agitation rate. The VI content, EGDMA ratio, pH and ionic strength were determined as the effective parameters on the swelling behavior of PEGMA-VI microspheres. In the second part of the study, Cu(II) ions were used as a model species in order to investigate the usability of the obtained PEGMA-VI microspheres in heavy metal removal. Adsorption capacities under optimum conditions were determined. The Cu(II) ion adsorption capacity increased by increasing the initial Cu(II) ion concentration, and it reached the maximum value (i.e., 30 mg Cu(II)/g PEGMA-VI microspheres) at 400 mg Cu(II)/L initial Cu(II) ion concentration under the determined optimum conditions. Microspheres were found to be reusable after desorption for several times.

Stimuli-responsive properties of conjugates of N-isopropylacrylamide-co-acrylic acid oligomers with alanine, glycine and serine mono-, di- and tri-peptides.

A random oligomer of N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc) with a AAc content of 3.1+/-0.19 mmol carboxylic acid groups per gram of the oligomer and with a number average molecular weight of 1400 was synthesised by a free radical polymerisation using AIBN in DMF. Then, mono-, di-, and tri-peptide conjugates of this oligomer were prepared by using carboxyl-ends-protected (with methyl ester hydrochloride) forms of alanine, glycine and serine, with a water-soluble carbodiimide. 95, 93, and 31% of the carboxylic acids were conjugated (loaded) at the first step (mono-peptides) with glycine, alanine and serine, respectively. At the second step, percentage of the conjugation of carboxylic acid groups with glycine, alanine and serine were between 99 and 80, 68 and 100, and 21 and 58%, respectively, while the third amino acids were attached to only 21-64% of the carboxylic acids available on the conjugate chains. A decrease was observed in the lower critical solution temperatures (LCSTs) of the amino acid conjugates at pH 4.0 compared with the unconjugated oligomer, which has LCST at 37.7 degrees C at the same pH. LCSTs of di- and tri-peptide conjugates at pH 4.0 were in the range of 38.4-43.3 degrees C, and 42.6-50.8 degrees C, respectively. At pH 7.4, LCSTs of the mono- and di-peptide conjugates were observed in the range of 41.6-43.9 degrees C, and 46.2-60.2 degrees C, respectively, while the co-oligomer at pH 7.4 did not show a LCST up to 60 degrees C. Tri-peptide conjugates did not display LCST at pH 7.4, except the one with glycine-alanine-serine sequence.

Synthesis and characterization of 1,4,8,11-tetraazacyclotetradecane carrying poly(p-chloromethyl styrene-ethylene glycol dimethacrylate) microbeads and its metal ion-chelated forms

Poly(p-chloromethyl styrene-ethylene glycol dimethacrylate) polymeric microbeads, poly(p-CMS-EGDMA), with an average size of 186 μm were synthesized by the suspension polymerization of p-CMS conducted in an aqueous medium. To increase the rigidity of the polymeric microbeads, EGDMA monomer was added to polymerization medium in the 25% for the cross-linking. 1,4,8,11-Tetraazacyclotetradecane ligand was reacted with polymer active groups that was p-CMS under a nitrogen atmosphere for 18 h at 65 °C. The maximum cyclam attachment was found 2.24 mmol/g polymer using an elemental analyser. Fourier transform infrared (FT-IR) spectrophotometer, thermogravimetric analyser (TGA) and differential scanning calorimeter (DSC) were used to characterize the plain, ligand modified microbeads and metal ion-chelated microbeads. TGA and DSC characterization of modified microbeads showed that stability of cyclam was increased attaching onto the polymer and metal ion-chelated form of the cyclam-modified polymer were more stable at high temperature for different applications.

MICROFLUIDIC DEVICE FOR SYNTHESIS OF CHITOSAN NANOPARTICLES

ABSTRACT Chitosan nanoparticles have a biodegradable, biocompati-ble, non-toxic structure, and commonly used for drug deliverysystems. In this paper, simulation of a microfluidic device for thesynthesis of chitosan nanoparticle is presented. The flow filed to-gether with the concentration field within the microchannel net-work is simulated using COMSOL Multiphysics R simulation en-vironment. Different microchannel geometries are analyzed, andthe mixing performance of these configurations are compared.As a result, a 3D design for a microfluidics platform which in-cludes four channel each of which performs the synthesis in par-allel is proposed. Future research directions regarding the fabri-cation of the microfluidic device and experimentation phase areaddressed and discussed. NOMENCLATURE A o coefficient used in Eq. (3)A 1 coefficient used in Eq. (3)A 2 coefficient used in Eq. (3)A 3 coefficient used in Eq. (3) Address all correspondence to this author. B o coefficient used in Eq. (4)B 1 coefficient used in Eq. (4)B