This issue has been dedicated to Prof. Dr. Olgun Güven

Dear readers of the Hacettepe Journal of Biology and Chemistry, In honour of Prof.Dr. Olgun Güven

This volume of Hacettepe Journal of Biology and Chemistry is dedicated to Prof.Dr. Olgun Güven on the occasion of his retirement.

Cellulose is the most abundant organic material on the earth: it is the main constituent of plants, also pres- ent in bacteria, fungi, algae and even in animals. Despite all its advantageous properties like high strength, durability, thermal stability, biocompatibility, biodegradability, relatively low cost and low density, cellulose lacks some of the versatile properties of synthetic polymers. Therefore, chemical modification of the cellulose structure is necessary in most cases to overcome the existing drawbacks. The synthesis of cellulosic graft copolymers through the introduction of branches (grafts) of synthetic polymers that impart specific proper- ties onto the cellulose substrate is one of the key ways of modifying the physical and chemical properties of cellulose. The recent advances in the field of controlled radical polymerization (CRP) methods provide unique opportunities to tailor the surface properties of graft copolymers by controlling the graft length, the architec- ture and the composition. This study reviews our previous works investigating the modification of cellulose via graft copolymerization mediated by Reversible Addition Fragmentation chain Transfer (RAFT) polymerization, one of the most powerful CRP methods. 

Especially, in last decade considerable attention has recently been directed to the modification and prepa- ration of low-molecular weight-fractions or oligosaccharides of kappa carrageenan, sodium alginate [1-4] and Chitosan [5-10] by radiation induced degradation in dry, and various concentrations in aqueous solutions in order to use mainly in the plant growth promoter, plant protectors and tissue engineering applications.

Neither in these radiation induced degradation studies of NaAlg, nor in other studies on the preparation of oligosaccharides of sodium alginate, Chitosan, galactomannans as the plant growth promoter and plant pro- tectors [10-12] the effect of structural parameters of polysaccharide type natural polymers was considered by the authors. By the recent studies Şen et al., [13-15], this deficiency in the literature was filled and the effects of the structural parameters of some polysaccharide on the radiation-induced degradation are explained in details. All these recent studies are summarized in this review. 

Application of radiation technology to the rubber and tire industries is in progress and is being developed. In this review, recent studies on radiation processing in rubber and tire industries are reviewed. Both academic investigations and industrial applications in non-tire rubber goods, tire production and tire reinforcing materials are mentioned. Current trends, new challenges and opportunities of technologies and the tire reinforcing materials are also given. 

N-isopropylacrylamide/itaconic acid copolymeric hydrogels (NIPAAm/IA) containing different quantities of itaconic acid have been irradiated with g radiation. The hydrogels were used in an experiment concerning the uptake and release behavior of Vitamin B₁₂. In the experiment of the adsorption of Vitamin B₁₂, type S ad- sorption isotherm was found. The effect of comonomer concentration and irradiation dose on the uptake and release behavior of the hydrogels was studied. 

Nylon3 was prepared through base-catalayzed hydrogen transfer polymerization of acrylamide. The polymer was fully characterized by FTIR, FT-Raman, ¹H-NMR, ¹³C-NMR, DSC, TGA, XRD, MALDI-MS, and end-group analyses. Glass transition temperature, thermal degradation temperature, d-space values, crystallinity, average molecular weights and polydispersity of nylon3 obtained were determined. Initiation, propagation and termination mechanisms of base-catalyzed hydrogen transfer polymerization of acrylamide were proposed using the structural analyses of nylon3 obtained. 

Gamma radiation-induced radicals in poly(β-alanine), poly(α-methyl-β-alanine) and poly(β-methyl-β-alanine) have been investigated by Electron Spin Resonance Spectrometry technique. ESR spectra of polymers irradiated in nitrogen and air have been simulated by curve fitting software (Winsim2002). The type of radicals generated, their relative abundances, conversion into other radicalic species and their room temperature stability were evaluated. At least two types of radicals have been detected for each polymer. Most stable radicals have been obtained in the case of poly(α-methyl-β-alanine). 

Collagen is very important part of the fibrous proteins in the living organism. Animal tissues, especially tendons main structure contain collagen. In this investigation, natural collagen (coll) modified with differ- ent synthetic monomers such as 2-hydroxy ethylmethacrylate (HEMA) and acrylamide (AAm) was prepared as p(Coll-co-HEMA) and p(Coll-co-AAm) composites to enhance collagen natural characteristics. Biocompatibility of the prepared interpenetrating polymeric network (IPN) was tested with MTT Assay and found biocompat- ible. Model drugs, such as Trimetoprim (TMP) and Naproxene (NP) were used as antibacterial active agents for release studies from the synthesized composite hydrogel-collagen IPN matrices. The drug-loaded IPN films release studies were carried out in bio-mimetic media. It was found that collagen-synthetic polymer matrices can be readily prepared and used for drug delivery system in the release of active agents, providing great po- tential in wound dressing applications. 

In this study, sorption behaviors of water absorbing materials on the basis of acrylamide copolymers as semi- IPNs and composite systems have been investigated. Highly swollen hydrogels made by the polymerization of acrylamide with some hydrophilic co-monomers, some linear polymer and some clays were investigated as a function of composition to find materials with swelling and sorption properties of some metal ions, some pollutant-organics and some dyes. The hydrogels, the semi-IPNs and the composites were prepared by γ-irradiation or free radical solution polymerization in aqueous solutions of monomers and some multifunctional crosslinkers. Swelling experiments were performed in water or other swelling media at 25°C, gravimetrically. For sorption of some metal ions and some dyes into the hydrogels was studied by batch sorption technique at 25°C. This review introduces water sorption studies and adsorptive features of acrylamide based hydrogels as semi-IPNs and composites, synthetic methods, the hydrogel characteristics and their applications. 

Porous and non-porous Poly(isobutyl methacrylate) (PiBMA) microspheres were synthesized by suspension polymerization technique in aqueous medium to remove light petroleum derivatives from sea water. Influ- ence of the crosslinking agent, porogen and reaction parameters on the solvent uptake, porosity and networks structure of the PiBMA spheres were investigated. Gasoline and small aliphatic hydrocarbons (pentane, he- xane and heptane) were used as model solvents. Swelling behavior and network properties were found to be dependent on the crosslinking density of the sphere, crosslinking agent, porosity and solvent. Highest solvent uptake for both porous and non-porous PiBMA spheres was observed in gasoline. PiBMA microsphere shown to be good candidates for the removal of light petroleum derivatives and they preserved their uptake capacity and shape over several usages. 

The synthesis of poly(acrylonitrile-co-acrylamide) (p(AN-co-AAm)) hydrogels with different amounts of acrylonitrile (AN) and acrylamide (AAm) monomers were carried out by concurrent use of redox and microemulsion polymerization techniques. The prepared hydrogels were amidoximated for sorption of uranyl ion from aqueous medium. Batch type UO₂ ²⁺ ion sorption by p(AN-co-AAm) (0.25:1 mole ratio) was carried out and an sorption capacity of 220 mg UO₂ ²⁺ mg/g dried hydrogel was found. The highest amount of UO₂²⁺ ion sorption, 277 mg/g dry gel was accomplished at pH 4. 

Tunable properties fascinate scientists because of the opportunity to develop functional materials for stimuli- responsive, sensing and biomimetic applications. Over half a century ago, advances allowed the realisation of molecularly imprinted polymers.They enable to specifically target sugars, pesticides, herbicides, viruses, drugs and amino acid together with their derivatives.In fact, due to their simplicity, ability of building robust polymer networks, reusability and low costs, molecularly imprinted polymers (MIPs) still are of great interest both in academia and industry.They enable the use of lot of techniques for their implementation although our attention will be addressed to the ones realised via gamma-irradiation. 

This paper reviews the synthesis and characterization of allyl alcohol based copolymers and their applicati- on into woods and the improvement of dimensional, mechanical and biological stability of woods by using gamma-radiation. Selection of monomer and/or monomer pairs, copolymerization, impregnation, gamma-irradiation, artifical ageing, dimensional and mechanical stability, biodegradation of treated woods are menti- oned. Novel treatments and technologies are also presented. 

Various organic compounds including textile dyes, pesticides and pharmaceutical compounds were detected in aquatic environment. A large number of studies were examined to remove these types of compounds from water. This paper includes the applications of radiation technology to decompose such organic compounds with various combinations such as ozone and H₂O₂. Changes in amounts of organic pollutants, their intermediates, toxicity, decoloration and Chemical Oxygen Demand (COD)-Biological Oxygen demand (BOD) with irradiation dose were followed. The results showed that gamma irradiation based water treatment technologies are effective for the water treatment even in drinking water. 

Acrylamide hydrogel was prepared by γ-irradiating ofthe aqueous solution of acrylamide monomer with 4.65 kGy γ-rays. Spectroscopic, thermal and mechanical properties, swelling properties, diffusional behavior of water, diffusion coefficients and network properties of AAm hydrogel are examined.

In vitro swelling and in vivo biocompatibility of acrylamide hydrogel were investigated. The swellings of AAm hydrogelare investigated in distilled water, human serum and some simulated physiological fluids such as phosphate buffer at pH 7.4, glycine-HCl buffer at pH 1.1 physiological saline solution. For the analysis of human sera biocompatibility, acrylamide hydrogel was incubated in 10 different human sera for 24 hours and its biocompatibility with some biochemical parameters have been investigated. No significant difference in values before and after the test procedures has been found. AAm hydrogel was subcutaneously implanted in rats for up to 10 weeks and the tissue response to these implants was studied. Histological analysis indicated that tissue reaction at the implant site progressed from an initial acute inflammatory response characterized. No necrosis, tumorigenesis or infection was observed at the implant site up to 10 weeks. In vivo studies indicated that the radiation induced acrylamide hydrogel was found to be well-tolerated, non-toxic and highly biocompatible. 

Polymers and their blends undergo various thermal or radiation effects in areas of usage. Therefore, in the academic investigations and industrial applications, radiolysis and thermal degradation of polymers, polymer blends and mixed polymers is very important. In this study, recent studies on ther- mal degradation of heated and irradiated polymers and their blends being done by the second branch in left side of our polymer tree (Fig.1) are reviewed. The studies have been classified as preparation and investigation of graft copolymer structures with γ-rays, determination of gelation dose for γ-irradiated polymers, thermal degradation of γ-irradiated polymers, determination of thermal gelation points of polymers, comparison of various isothermal thermogravimetric methods and new compact method, and preparation and thermal degradation of maleic anhydride copolymers and terpolymers. 

In order to prepare fibrous polymeric ligand exchanger (PLE) adsorbent for the removal of As(V), 4-vinyl pyridine (VP) monomer was first grafted onto polyethylene/polypropylene nonwoven fabrics (NWF) made of polypropylene coated by polyethylene (PE/PP) in emulsion medium by using radiation induced graft polymerization (RIGP). 4-Vinyl pyridine grafting conditions were optimized and about 150% VP grafted samples were used for further experiments. For the preparation of the suitable polymer ligand exchanger (PLE) for the removal of As(V), VP grafted NWF were loaded with Cu(II) ions. Copper loading capacity of PLE was determined to be 0.5 mmol Cu(II)/g polymer. As(V) adsorption experiments were performed in batch mode at different contact time, pH (3-9) and initial As(V) concentrations. The As(V) adsorption rate onto PLE adsorbent was rapid and adsorption equilibrium was established within 4 hours. It was found that As(V) adsorption by Cu(II) loaded VP grafted NWF did not change significantly over a wide pH range. The effect of initial concentration of As(V) on the adsorption behaviour of PLE was determined for different As(V) concentrations (0.1-500 ppm) at pH 7. The new PLE showed high affinity for As(V), the maximum adsorption capacity was found to be 51 mg As(V)/g PLE from Langmuir isotherm. It was found that the theoretical capacity found from Langmuir isotherm is very good accordance with experimental capacity 47 mg As(V)/g PLE.