Papers by Prof.Dr. Yuksel Guvenilir
The First International Conference on “Green” Polymer Materials 2020, 2020
Polymers are extensively used as advanced materials. The most commonly used polymers in industry ... more Polymers are extensively used as advanced materials. The most commonly used polymers in industry are non-biodegradable and petroleum derived. The increasing demand for these types of polymers results in a problem of accumulation of plastic waste in the environment and depletion of fossil resources. Because of this point, the biodegradability of polymers gains great importance as well as for the bio-based polymers produced from renewable resources. In this study, bio-based polyamide 5.6 polymer (PA56) was incorporated with olive stone powder (OSP) in order to manufacture a biodegradable polyamide compound, and its degradability was investigated. The olive stone powder was incorporated into polyamide 5.6 at 10% (w/w) with a twin-screw extruder to manufacture the compound, PA56/OSP10. The characterization of the PA56/OSP10 compound was conducted using Fourier transform infrared (FTIR) spectroscopy. The biodegradability of the PA56/OSP10 compound was examined by a natural soil burial test of six months duration. The signs of degradation were assessed by both weight loss measurements and visual observations. At the end of six months, 5.24% weight loss and surface deformation were determined for the PA56/OSP10 compound. These results suggest that olive stone powder can be considered as a green alternative to conventional biodegradation additives for polymer compounding.
European Journal of Pharmaceutics and Biopharmaceutics, 2021
Development of drug delivery systems is an extensively researched area in biomedical field. In re... more Development of drug delivery systems is an extensively researched area in biomedical field. In recent years, there is an increasing interest on fabrication of biocompatible nanofibrous drug delivery systems. In the present study, poly(ω-pentadecalactone-co-ε-caprolactone)/gelatin nanofibrous membranes were fabricated for the controlled delivery and release of tetracycline hydrochloride (TCH) antibiotic. Poly(ω-pentadecalactone-co-ε-caprolactone) content provides an originality to the membrane, since it has been synthesized enzymatically previously. Varied amounts of tetracycline hydrochloride including poly(ω-pentadecalactone-co-ε-caprolactone)/gelatin (1:1, v:v) binary polymer blend was electrospun and characterizations (morphological and molecular structure, wettability characteristics, and thermal behavior) were applied to investigate the incorporation of drug molecule. Afterwards, in vitro drug release studies were carried out and mathematical modelling was applied to drug release data in order to clarify the transport mechanism of drug. TCH release profile comprised of an initial burst release in first hour and followed by a sustained release through 14 days which allowed sufficient antibacterial activity against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus and Bacillus subtilis) bacteria. The presented drug delivery system may be applied as an antibacterial wound dressing device for skin infections.
New Biotechnology, 2018
Osteoarthritis (OA), the most common human arthritis, is considered as polygenic disease causing ... more Osteoarthritis (OA), the most common human arthritis, is considered as polygenic disease causing pain and disability in affected individuals, with very high incidence and prevalence across the globe. Several risk factors have been involved in OA development including age, gender, obesity, injury, family history and genetic variations. More than 80% of the adults with OA have knee OA (KOA) in which body weight plays a very crucial role. Moreover, genetic studies revealed that OA has a substantial hereditary
Advanced Materials Letters, 2016
New Biotechnology, 2016
Formaldehyde is the simplest aldehyde and a toxic compound because of ability to react with prote... more Formaldehyde is the simplest aldehyde and a toxic compound because of ability to react with protein, nucleic acids and lipids. This is the cause of nasopharyngeal cancer and sick building syndrome. With respect to removal of aldehyde, aldehyde dehydrogenase catalyzes the pyridine nucleotide-dependent oxidation of a variety of aldehyde substrates to their corresponding carboxylic acids. In this study, we have designed the method using aldehyde dehydrogenase from recombinant Saccharomyces cerevisiae to treat formaldehyde. ALD6 gene was cloned under the GAL1 promoter in the pYES2 and attached to GFP. To reduce the enzyme activity, dominant mutant was constructed which was deleted catalytic residues. These strains were successfully transformed in Saccharomyces cerevisiae and confirmed green signal by fluorescence microscope. When the strains were exposed formaldehyde-stress, it was shown that NADH levels increase in overexpressed ALD6. On the other hand, there was decrease of NADH in dominant negative strain. Also, it was treated to formaldehyde that the enzymes isolated from each strain. Confirmation of formaldehyde was measured luminescence of Vibrio fischeri. Formaldehyde was the most decreased in enzyme from the overexpressed ALD6. In these results, we expect that ALD6 would be applied to field of hazardous substances removal related to aldehyde.
Itudergisi D, Oct 28, 2011
Bu çalışmada, enzimatik halka açılımı polimerizasyon yöntemi kullanılarak polilaktik asit sentezi... more Bu çalışmada, enzimatik halka açılımı polimerizasyon yöntemi kullanılarak polilaktik asit sentezi gerçekleştirilmiş ve elde edilen polimerin proteaz enzimi ile biyobozundurulması incelenmiştir. Candida cylindracea lipaz katalizörlüğünde laktitten halka açılımı reaksiyonunun optimize edilmesi amacıyla, reaksiyon şartları değiştirilerek farklı sıcaklıklarda gerçekleştirilen polimerizasyon işlemlerinde, reaksiyona giren Candida cylindracea lipaz konsantrasyonuna bağlı olarak oluşan polilaktik asitin molekül ağırlığı, polidispersitesi ve dönüşüm verimi değerleri tespit edilmiştir. Elde edilen polilaktik asit, proteaz DSM enzimi ile biyobozundurma işlemine tabii tutulmuş ve polimerin yapısındaki ester grupları ile biyobozundurma mekanizması takip edilmiştir. Biyobozunma süresince molekül ağırlığı kaybı izlenmiş ve orjinal polimerin morfolojik ve termal geçiş özelliklerinin değişimi incelenmiştir. Candida cylindracea lipaz kullanılarak laktitin halka açılımı polimerizasyonunda, yüksek molekül ağırlıklı polimer sentezinde, en uygun reaksiyon şartı, sıcaklığın 80ºC ve lipaz konsantrasyonunun ağırlıkça %4 olduğu durum olarak belirlenmiştir. Bu sıcaklık değerinde, sabit enzim konsantrasyonunda, sürenin artmasıyla birlikte molekül ağırlığı ve monomer dönüşümü belirgin bir şekilde artış göstermiş, polidispersite değerleri yaklaşık 1.5 civarında olan polimerler sentezlenmiştir. Proteaz DSM ile yapılan biyobozundurma işlemi sonucunda ise, ilk 15 günlük süre içersinde, polimerin bozunmasına ilişkin molekül ağırlığı kaybı son derece düşük seviyede olduğu, bu süreden sonra molekül ağırlığı kaybında belirgin bir artış gözlenerek 90 günlük süre sonunda %23'lük bir kayıp meydana geldiği saptanmıştır. Biyobozundurma işlemine tabii tutulan polimerin çeşitli özellikleri incelenerek orijinal polimer ile arasındaki farklar tespit edilmiştir.
Applied Biochemistry and Biotechnology, Feb 1, 2005
Export Date: 3 April 2014, Source: Scopus, References: Schmid, R., Verger, R., (1998) Angewandte ... more Export Date: 3 April 2014, Source: Scopus, References: Schmid, R., Verger, R., (1998) Angewandte Chemie International Edition, 37, pp. 1608-1633;
Energy, 2013
Polymeric hydrogels derived from SPM (3-sulfopropyl methacrylate) of micrometer size were used in... more Polymeric hydrogels derived from SPM (3-sulfopropyl methacrylate) of micrometer size were used in the preparation of a composite-catalyst system for hydrogen generation from hydrolysis of NaBH 4. In situ Co and Ni nanoparticles were prepared by chemical reduction of absorbed Co (II) and Ni (II) ions inside the hydrogel networks, and the whole composite was used as a catalyst system. The catalytic activity of the metal nanoparticles within the p(SPM) hydrogel matrix was better and faster using Co than with Ni. Additionally, other parameters that affect the hydrogen generation rate, such as temperature, metal reloading, the catalyst amounts as well as reusability, were also investigated. It was found that p(SPM)eCo micro hydrogels were even effective for hydrogen generation at 0 C with a hydrogen generation rate of 966 (mL H 2) (min) À1 (g of Co) À1. The activation energy, activation enthalpy, and activation entropy for the hydrolysis reaction of NaBH 4 with micro p(SPM)eCo catalyst system were calculated as 44.3 kJ/mol, 43.26 kJ/mol K, and À150.93 J/mol K, respectively.
Applied Biochemistry and Biotechnology, 1996
Enzymes have been extensively used in many industries for the last 20 years. They are becoming mo... more Enzymes have been extensively used in many industries for the last 20 years. They are becoming more common because of new areas of application. The limitations of applications of enzymes are activity, specificity, stability, and price. Higher enzyme activities and less susceptibility of process conditions are desirable. Therefore, in some cases, purified enzyme extracts are needed. The purpose of this study is the isolation and purification of diamine oxidase (DAO) of pea seedlings and pig liver. The relationship between pea seedlings growth rate and enzyme activity is established. DAO of pea seedlings and pig liver is prepared by way of tissue disruption with homogenization, centrifugation, fractionation with ammonium sulfate, precipitation of inert components, column electrophoresis, and DEAE-cellulose column chromatography. The specific activity of disrupted pea seedlings cells was measured as 0.017 (U/mg protein), and the pig liver DAO activity was measured as 0.00037 (U/mg protein). The specific enzyme activity from pea seedlings was increased to 6.750 (U/mg protein). On the other hand, the specific enzyme activity from pig liver was increased to 0.30 (U/mg protein). The final enzyme extract from pea is 400-fold purer than raw material, and the final enzyme extract from pig liver is 820-fold purer than raw material.
Applied Biochemistry and Biotechnology, 2005
The aim of this experimental study was to isolate and partially purify protease enzyme from Bacil... more The aim of this experimental study was to isolate and partially purify protease enzyme from Bacillus cereus and Bacillus subtilis. Protease enzyme is obtained by inducing spore genesis of bacteria from Bacillus species in suitable nutrient plates. The partial purification was realized by applying, respectively, ammonium sulfate precipitation, dialysis, and DEAE-cellulose ion-exchange chromatography to the supernatant that was produced later. Optimum pH, optimum temperature, pH stability, and temperature stability were determined, as well as the effects of pH, temperature, substrate concentration, reaction time, and inhibitors and activators on enzyme activity. In addition, the molecular mass of the obtained enzyme was investigated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The specific activity of partially purified enzyme from B. subtilis was determined to be 84 U/mg. The final enzyme preparation was eight-fold more pure than the crude homogenate. The molecular mass of the partially purified enzyme was found to be 45 kDa by using SDS-PAGE. The protease enzyme that was partially purified from B. cereus was purified 1.2-fold after ammonium sulfate precipitation. The molecular mass of the partially purified enzyme was determined to be 37 kDa by using SDS-PAGE.
Polymers, 2016
The immobilization of Candida antarctica lipase B (CALB) was performed by physical adsorption on ... more The immobilization of Candida antarctica lipase B (CALB) was performed by physical adsorption on both neat and organo-modified forms of sepiolite and montmorillonite. The influence of different parameters, e.g., solvent, enzyme loading, cross-linking, and type of clay support, on immobilization efficiency and catalyst hydrolytic activity has been investigated. The highest hydrolytic activities were obtained for CALB immobilized on organo-modified clay minerals, highlighting the beneficial effect of organo-modification. The esterification activity of these CALB/organoclay catalysts was also tested in the ring-opening polymerization of ε-caprolactone. The polymerization kinetics observed for clay-immobilized catalysts confirmed that CALB adsorbed on organo-modified montmorillonite (CALB/MMTMOD) was the highest-performing catalytic system.
In the present study, the recovery of activity of <i>Candida antarctica</i> lipase B ... more In the present study, the recovery of activity of <i>Candida antarctica</i> lipase B (CALB) immobilized onto surface-modified rice husk ash (RHA) was 90% for both cross-linking and adsorption methods. Both cross-linked and adsorbed immobilized preparations were very stable, retaining more than 48% of their activity over the range of temperatures studied. The optimum temperature and optimum pH values were 37 °C and 7.0, respectively for both immobilized preparations, while the relative activities after storage at 4.0 °C for 60 days were 55% and 65% using cross-linking and adsorption methods, respectively. Also, the activity of the immobilized lipase began to decrease after 10 cycles, more than 58% of the initial activities were still retained after 10 cycles for both immobilization methods. These results indicated that lipase immobilized by cross-linking and adsorption not only effected activity recovery, but also remarkably effected stability, reusability and application...
European Journal of Pharmaceutical Sciences, 2022
In recent years, there is an increasing attention on biocompatible electrospun nanofibers for dru... more In recent years, there is an increasing attention on biocompatible electrospun nanofibers for drug delivery applications since they provide high surface area, controlled and sustained drug release, and they mimic the extracellular matrix. In the present study, tetracycline hydrochloride (TCH) antibiotic loaded poly(ω-pentadecalactone-co-ε-caprolactone)/gelatin/chitosan nanofibrous membranes were fabricated as a controlled drug delivery system. Poly(ω-pentadecalactone-co-ε-caprolactone) copolymer has been enzymatically synthesized in previous studies, thus it provides an originality to the membrane. Combination of a synthetic polymer, a protein, and a polysaccharide in order to obtain a synergetic effect is another novelty of this work and there exists limited examples for such electrospun membrane. Varied amounts of TCH was electrospun together with poly(ω-pentadecalactone-co-ε-caprolactone)/gelatin/chitosan (50/40/10 volume ratio) polymer blend (fiber diameters ranged between 85.7-225.2 nm) and several characterizations (morphological and molecular structure, wettability characteristics, and thermal behavior) were applied to examine the drug incorporation. Subsequently, in vitro drug release studies were conducted and mathematical modelling was applied for the detection of transport mechanism of drug. TCH release proceeded 14 days through an initial burst release in first hour and followed by a sustained release. 1% TCH-loaded sample was shown as optimal preparation with 96.5% total drug release and 11.8% initial burst release. TCH-loaded preparations demonstrated a good antibacterial activity against Gram-positive (Staphylococcus aureus and Bacillus subtilis) bacteria and a limited effect (no inhibition zone observed below 3% TCH concentration) against Gram-negative (Escherichia coli) bacterium. Thus, TCH concentrations of ≥ 3% could be preferred to obtain a wide-spectrum effectiveness. The presented drug delivery system is suggested to be applied for treatment of skin infections as a wound dressing device.
In parallel with the development of biotechnology, the production o f organic and biochemical sub... more In parallel with the development of biotechnology, the production o f organic and biochemical substances by fermentation process is one of the most current issue of our age's technology. Many chemical substances widely used in various industrial fields, such as organic solvents, antibiotics and enzymes that are produced by microorganisms in fermentation processes. Many common organic acids such as citric acid, lactic acid, fumaric acid, malic acid and salicylic acid used in food, pharmaceutical, chemical, textile, plastics, cosmetics and paper industries can be produced by fermentation. In the present study, L (+ ) lactic acid was produced from refectory wastes through fermentation process and fermentation process was optimized for the maximum lactic acid yield. Process variables for batch system were optimized for the production o f lactic acid from pretreated macaroni-milk and rice-green pea-salad broths by L. casei culture. For the fermentation of the macaroni-milk and rice-g...
Journal of Biomedical Materials Research Part B: Applied Biomaterials, 2021
The spin ability of flaxseed mucilage (FM) as a new source was evaluated through electrospinning.... more The spin ability of flaxseed mucilage (FM) as a new source was evaluated through electrospinning. At various experimental conditions and different solution properties, it was impossible to fabricate FM nanofiber. Thus, polyvinyl alcohol (PVA) was applied as co-polymer to facilitate nanofiber formation. In terms of morphology, FM:polyvinyl alcohol (PVA) nanofiber using a mixture of 3% FM solution and 12% (PVA) solution at ratio of 60:40 was selected as the best sample. The physicochemical properties of the nanofiber was evaluated by scanning electron microscopy (SEM), fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA) and X-ray diffraction (XRD). SEM images showed beadless, uniform and smooth nanofibers with an average diameter of 230 nm. Based on DSC and TGA results, the thermal stability of the nanofiber was improved by adding PVA. FTIR data revealed that there was no chemical interaction between functional groups of FM and PVA in the nanofiber.
Journal of Macromolecular Science, Part A, 2019
Polycaprolactone (PCL) based a,x-methacrylated macromonomer (DMPCL) was synthesized via enzymatic... more Polycaprolactone (PCL) based a,x-methacrylated macromonomer (DMPCL) was synthesized via enzymatic ring-opening polymerization (eROP) by using Novozyme 435 as the enzyme immobilized catalyst. DMPCL was further photopolymerized with monofunctional poly(ethylene glycol) methyl ether methacrylate (PEGMA-950) macromonomer and trimethylolpropane triacrylate (TMPTA) as tri-functionalized crosslinking agent in glass vials when CHCl 3 was the solvent and Irgacure 819 was the photoinitiator. Ultraviolet (UV) Light Emitting Diode (LED) bulbs enabled photoinduced reactions at room temperature with low heat generation and high reaction efficiency. The obtained gels were characterized with Fourier Transform Infrared Spectroscopy (FT-IR) and Differential Scanning Calorimetry (DSC). DMPCL participated as an effective crosslinking agent in the photopolymerization of PEGMA-950. Combined usage of DMPCL and PEGMA-950 resulted in significantly more effective polymerization than the separate photopolymerizations of these macromonomers.
Journal of Renewable Materials, 2019
Novozyme 435, which is the commercially available immobilized form of Candida antarctica lipase B... more Novozyme 435, which is the commercially available immobilized form of Candida antarctica lipase B, has been successfully conducted ring opening polymerization of lactones in organic solvents. In this paper, it was aimed to introduce an alternative biocatalyst for Novozyme 435. Candida antarctica lipase B immobilized onto rice husk ashes via physical adsorption (with a specific activity of 4.4 U/mg) was prepared in previous studies and used as a biocatalyst for poly(δ-valerolactone) synthesis in the present work. Polymerization reactions were proceeded at various reaction temperatures and periods via both two immobilized enzyme preparations. The resulting products were characterized spectroscopically and thermally. The highest molecular weight (Mn = 9010 g/mol) was obtained via Novozyme 435 catalysis at 40℃ and 24 hours. The performance of home-made lipase, which resulted in a molecular weight of 8040 g/mol, was close to commercial one.
Pure and Applied Chemistry, 2019
In this study, rice husk ash (RHA) silanized with 3-glycidyloxypropyl trimethoxysilane was used a... more In this study, rice husk ash (RHA) silanized with 3-glycidyloxypropyl trimethoxysilane was used as support material to immobilize Candida antarctica lipase B. The developed biocatalyst was then utilized in the ring opening polymerization (ROP) of ε-caprolactone and in situ development of PCL/Silica nanohybrid. The silanization degree of RHA was determined as 4 % (w) by thermal gravimetric analysis (TGA). Structural investigations and calculation of molecular weights of nanohybrids were realized by proton nuclear magnetic resonance (1H NMR). Crystallinity was determined by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Scanning Electron Microscopy (SEM) was used for morphological observations. Accordingly, the PCL composition in the nanohybrid was determined as 4 %, approximately. Short chained amorphous PCL was synthesized with a number average molecular weight of 4400 g/mol and crystallinity degree of 23 %. In regards to these properties, synthesized PCL/RHA c...
Advanced Materials Letters, 2016
In the present study, ring opening polymerization of e -caprolactone was performed by a novel enz... more In the present study, ring opening polymerization of e -caprolactone was performed by a novel enzymatic catalyst, Candida antarctica lipase B (CALB) immobilized on a modified silica-based material by physical adsorption. Molecular weight distributions and chain structures were compared by using gel permeation chromatography (GPC) and hydrogen nuclear magnetic resonance ( 1 H NMR) analysis, respectively. In addition, for the determination of thermal properties, thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) were performed. Scanning electron microscopy (SEM) was applied to observe the surface structure of the polymer. Effects of temperature, reaction time, and enzyme concentration on molecular weight of poly (e
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Papers by Prof.Dr. Yuksel Guvenilir