Chemical Engineering / Kimya Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/14
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Article Citation - WoS: 19Citation - Scopus: 23Inhibition of Catechol-O (comt) by Some Plant-Derived Alkaloids and Phenolics(Elsevier Ltd., 2010) Yalçın, Dilek; Bayraktar, OğuzIn this study, as an alternative to the medicines, natural compounds extracted from plant species (Peganum harmala, Cistus parviflorus and Vitex agnus-cactus) were investigated in order to inhibit the catechol-O-metyhltranferase (COMT) activity. In fluorometric enzyme assay, S-adenosylmethionine (SAM) and aesculetin (ES) were used as methyl donor and acceptor substrates, respectively. Their Km values were determined as 3.5 ± 0.3 μM and 6.4 ± 0.4 μM in absence of inhibitor. Inhibition performances of the plant-derived polyphenolics and alkaloids were determined. Inhibitory effect of alkaloids extracted from P. harmala seeds was found the highest among the plant extracts; however, it was lower than that of 3,5-DNC. In case of inhibition mechanism, mixed type inhibition was observed for alkaloid extract whereas uncompetitive inhibition was observed for 3,5-DNC. In case of polyphenolic extracts obtained from C. parviflorus and V. agnus-cactus leaves, mechanism were also explained as mixed type inhibition and their αKi values were calculated as 1.99 ± 0.35 μg/ml and 9.48 ± 0.58 μg/ml, respectively. © 2009 Elsevier B.V. All rights reserved.Article Citation - WoS: 42Citation - Scopus: 60Pistacia Terebinthus Extract: as a Potential Antioxidant, Antimicrobial and Possible Ss-Glucuronidase Inhibitor(Elsevier Ltd., 2010) Demirbüker Kavak, Dilek; Altıok, Evren; Bayraktar, Oğuz; Ülkü, SemraIn this study, inhibition of Escherichia coli glucuronidase (GUS) by a plant extract of Pistacia terebinthus was investigated. P. terebinthus (from Karaburun region in Turkey) leaf extract exhibits various bioactivities, such as antioxidant, antimicrobial and cytotoxic property because of its flavonoid, phenolic and alkaloid contents. HPLC analyses were performed to evaluate the composition of the extract and main flavonoid compounds such as luteolin, luteolin-7-glucoside and apigenin-7-glucoside were detected in extract. GUS activity and kinetic data of the GUS were obtained by measuring rate of production of resulting fluorescent 4-methylumbelliferone (4-MU) and phenolphthalein fluorometrically and spectrophotometrically, respectively. Plant leaves showed higher antioxidant capacity as 85 TEAC (trolox equivalent antioxidant capacity) value and higher antimicrobial activity towards Staphylococcus aureus. 92.4% GUS enzyme inhibition was achieved with 8.3 μg ml-1 crude extract concentration, where IC50 value was found as 2.1 (±0.2) μg ml-1. Kinetic studies by nonlinear regression revealed that inhibition type caused by plant extract was mixed type (noncompetitive and competitive together). Km and Vmax values were 96.94 ± 9.68 nM and 7.81 ± 0.16 nmol min-1 mg-1, respectively. Inhibition constant (αKi) was found as 7.00 ± 0.93 nM having α value 2.17 ± 0.93. Our results may provide useful information regarding the inhibition of microbial GUS activity, preventing deglucuronidation and reducing possible cancer risk by bioactive P. terebinthus crude extract. © 2010 Elsevier B.V. All rights reserved.Article Citation - WoS: 16Citation - Scopus: 21Ph- and Electro-Responsive Characteristics of Silk Fibroin-Hyaluronic Acid Polyelectrolyte Complex Membranes(Elsevier Ltd., 2009) Malay, Özge; Batıgün, Ayşegül; Bayraktar, OğuzpH-responsiveness of recently developed silk fibroin (SF) and hyaluronic acid (HA) polyelectrolyte complex (PEC) membranes and their potential use in electro-responsive drug release systems were investigated. PEC membranes were prepared within a narrow pH window (3.0-3.5) for a SF-HA weight ratio of 20 and they were characterized by Atomic Force Microscopy in addition to characterization studies previously reported by our group. Swelling kinetics of the membranes was studied for a pH window of 2.5-7.4 and cyclic swelling test was performed to determine the pH-responsiveness of the membranes. It was shown that membranes swelled more in alkaline conditions and responded to variations in pH of the medium. Electric-stimuli assisted drug permeation and release studies were performed with a custom-made diffusion cell under both passive condition and electric field applied in pulsatile fashion. The instantaneous flux raised as the current was applied and then declined when the current application was terminated, and this process was repeated on subsequent applications. SF-HA complex membranes were found promising for the electric-stimuli-sensitive release of a high molecular weight and charged model drug for a membrane-permeation controlled formulation.Article Citation - WoS: 10Citation - Scopus: 10Clinoptilolite-Rich Mineral as a Novel Carrier for the Active Constituents Present in Ginkgo Biloba Leaf Extract(Elsevier Ltd., 2008) Göktaş, Selda; Ülkü, Semra; Bayraktar, OğuzThe possible use of clinoptilolite-rich mineral as a novel carrier for the active constituents present in Ginkgo biloba leaf extract solutions was investigated. The flavonoid aglycone constituents were found to be selectively adsorbed on the clinoptilolite surface. The antioxidant activity determinations of the extract solutions were performed by the Trolox Equivalent Antioxidant Capacity (TEAC) assay. The antioxidant activity measurements performed for the Ginkgo leaf extract solutions showed decreasing antioxidant activities due to adsorption. The decrease in antioxidant activity was attributed to the adsorption of phenolic constituents on the clinoptilolite surface.Article Citation - WoS: 68Citation - Scopus: 70Complex Coacervation of Silk Fibroin and Hyaluronic Acid(Elsevier Ltd., 2007) Malay, Özge; Bayraktar, Oğuz; Batıgün, AyşegülThis study aimed to investigate the pH-induced complexation of silk fibroin (SF) and hyaluronic acid (HA). SF-HA complex coacervation was investigated by monitoring turbidity of the SF-HA system under slow acidification. Gravimetric analysis was performed to determine the yield of complex coacervation and viscosity of the system was measured to study the formation of the complexes at different pH values. The influences of total biopolymer concentration and biopolymer weight ratio on complex coacervation were examined during the analyses. Formation of the complexes was evidenced by the minimum viscosity and the maximum turbidity observed in the system. SF-HA complexes were formed within the pH-window of 2.5-3.5 regardless of the total biopolymer concentration or biopolymer ratio. Complex coacervation of SF-HA showed a reversible behavior and coacervation could be handled even in excess amounts of the biopolymers, which pointed out a non-stoichiometric complexation.Article Citation - WoS: 157Citation - Scopus: 177Isolation of Polyphenols From the Extracts of Olive Leaves (olea Europaea L.) by Adsorption on Silk Fibroin(Elsevier Ltd., 2008) Altıok, Emre; Bayçın, Deniz; Bayraktar, Oğuz; Ülkü, SemraGeneral objective of the present work was to assess the isolation of polyphenols from olive leaves. The effects of extraction conditions on the total phenol content and antioxidant activity of olive leaf extract (OLE) were investigated. An extract with good antioxidant activity (7.52 mmol of Trolox equivalent antioxidant capacity (TEAC)/g olive leaf extract), and a high content of oleuropein (13.4%) and rutin (0.18%) could be obtained using 70% ethanol as extraction solvent. There was a good correlation between the antioxidant activity and the total phenol content. Furthermore, silk fibroin was used as a novel adsorbent to recover the polyphenols from the olive leaf extracts. The adsorbed amounts of rutin and oleuropein were 15 mg rutin/g silk fibroin and 96 mg oleuropein/g silk fibroin. Fraction consisting of mainly oleuropein and fraction rich in rutin, luteolin-7-glucoside, verbascoside, apigenin-7-glucoside were obtained by using silk fibroin filled column. Silk fibroin was found to be a promising adsorbent for the purification of oleuropein and rutin from olive leaf extracts. © 2008 Elsevier B.V. All rights reservedArticle Citation - WoS: 106Citation - Scopus: 122Silk Fibroin as a Novel Coating Material for Controlled Release of Theophylline(Elsevier Ltd., 2005) Bayraktar, Oğuz; Malay, Özge; Özgarip, Yarkın; Batıgün, AyşegülThe aim of this study was to explore potential use of the silk fibroin (SF) as an aqueous coating material for theophylline tablets. We have examined the film forming and coating properties of heat-treated fibroin, SF solution having different amounts of polyethylene glycol (PEG) and 1-ethyl-3-(3-dimethyl aminopropyl)carbodiimide (EDC) cross-linked SF. Heat-treated SF material possessed a brittle structure, which resulted in poor film forming and coating properties. The optimum PEG amount in SF solution was determined as 17% (by weight) for an acceptable film forming and zero order release profile. EDC cross-linked SF has shown a very good film forming and coating property with a potential for sustaining the drug release from coated theophylline tablets. Dissolution data for coated theophylline tablets were analyzed using Ritger and Peppas equation to describe the mechanism of drug release. Drug release from the EDC coated tablets followed zero-order kinetics. Release rate constants were found to be 0.26, 0.19, 0.16% min-1 for single-coated, double coated, and triple coated tablets, respectively. These results clearly demonstrated that silk fibroin has high utility as a novel aqueous coating material for controlled release products.Article Citation - WoS: 11Citation - Scopus: 14Effect of Pretreatment on the Performance of Metal-Contaminated Fluid Catalytic Cracking (fcc) Catalysts(Elsevier Ltd., 2004) Bayraktar, Oğuz; Kugler, Edwin L.Effects of both hydrogen and methane pretreatment on the performance of metal-contaminated equilibrium fluid catalytic cracking (FCC) catalysts from a refinery were investigated. Both hydrogen and methane pretreatment at 700°C were proven to be advantageous since the yields of hydrogen and coke from sour imported gas oil (SIHGO) cracking decrease while light cycle oil (LCO) and gasoline yields increase. The catalysts pretreated with hydrogen have shown slightly better improvement than the catalysts pretreated with methane. The decrease in the yields of hydrogen and coke was attributed to decrease in the dehydrogenation activity of vanadium oxides, which are present at high concentrations on the equilibrium FCC catalysts. This decrease in dehydrogenation activity after the pretreatment was also confirmed by low hydrogen-to-methane ratio. It was found that reduced vanadium has lower dehydrogenation activity since it produces less coke and hydrogen compared to oxidized vanadium. Hydrogen transfer reactions were evaluated by measuring C4 paraffin-to-C4 olefin ratios. Hydrogen transfer reactions decreased with increasing metal concentration. Both hydrogen and methane pretreatment caused the hydrogen transfer reactions to increase. Improved hydrogen transfer reactions caused an increase in the gasoline range products.Article Citation - WoS: 24Citation - Scopus: 25Temperature-Programmed Reduction of Metal-Contaminated Fluid Catalytic Cracking (fcc) Catalysts(Elsevier Ltd., 2004) Bayraktar, Oğuz; Kugler, Edwin L.A temperature-programmed reduction study of equilibrium fluid catalytic cracking (FCC) catalysts has shown three hydrogen-consumption peaks associated with contaminanted metals. A low-temperature peak, located near 510°C, is produced by the reduction of several components in the catalyst. Highly-dispersed vanadium contributes to this peak. A high-temperature peak, located near 800°C, is produced by reduction of nickel aluminate or nickel silicate compounds. A linear relationship exists between the area of the high-temperature peak and nickel concentration on equilibrium catalysts. An intermediate-temperature peak, located near 690°C, appears to be related to some form of vanadium compound. The intermediate-temperature peak does not occur on low-vanadium-concentration equilibrium catalysts, but is observed at higher vanadium-contamination levels. The presence of the 690°C peak was found by deconvoluting hydrogen-consumption data. The existence of this intermediate-temperature peak was proven by external reduction of highly-contaminated equilibrium catalyst at 500 and 700°C. External reduction at 500°C removes the low-temperature peak from the temperature-programmed reduction (TPR) spectrum. External reduction at 700°C removes both the low-temperature and intermediate-temperature peaks from the TPR spectrum. The difference in spectrum between calcined and 700°C reduced samples shows a clear spectrum with only the low and intermediate-temperature peaks present.