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Öğe A COMPARATIVE STUDY ON THE ANTIBACTERIAL ACTIVITIES OF THE AMINOPHENOLS: SOME NOVEL ASPECTS OF THE ANTIBACTERIAL ACTION OF p-AMINOPHENOL(Parlar Scientific Publications (P S P), 2011) Akgul, Cahit; Pinar, GuldenPhenol and phenolics are widely used industrial chemicals and they are hazardous environmental pollutants when they are released from wide range of industrial processes. This study was carried out to investigate the antibacterial potentials of three structural isomers of the aminophenol. Antibacterial activities of o-aminophenol, m-aminophenol and p-aminophenol were initially determined using the standard disc diffusion method. The results obtained from these studies demonstrated that p-aminophenol could inhibit the bacterial growth much better than the other two structural isomers when they were used in the same concentrations. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of p-aminophenol were then determined against gram (+) and gram (-) reference strains using the broth macrodilution method. MIC and MBC values were found between 31,25 and 500 mu g/mL. pH of the growth medium had a slight effect on the MIC values and the MIC value was higher in the growth medium with a lower pH. Time-kill analyses of p-aminophenol were performed against Staphylococcus aureus and concentration dependent killing curves were obtained. Postantibiotic effect of p-aminophenol was also investigated against Staphylococcus aureus which was the most susceptible strain and found to be approximately 15 min for the MIC concentration. From our experimental results, we conclude that p-aminophenol, but not the other two structural isomers, displays a potent antibacterial activity against standard reference strains. We here also present some novel data on the antibacterial activity of p-aminophenol.Öğe A comparative study on the antibacterial activities of the aminophenols: Some novel aspects of the antibacterial action of p-aminophenol(2011) Akgul, Cahit; Pinar, GuldenPhenol and phenolics are widely used industrial chemicals and they are hazardous environmental pollutants when they are released from wide range of industrial processes. This study was carried out to investigate the antibacterial potentials of three structural isomers of the aminophenol. Antibacterial activities of o-aminophenol, m-aminophenol and p-aminophenol were initially determined using the standard disc diffusion method. The results obtained from these studies demonstrated that p-aminophenol could inhibit the bacterial growth much better than the other two structural isomers when they were used in the same concentrations. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of p-aminophenol were then determined against gram (+) and gram (-) reference strains using the broth macrodilution method. MIC and MBC values were found between 31, 25 and 500 ?g/mL. pH of the growth medium had a slight effect on the MIC values and the MIC value was higher in the growth medium with a lower pH. Time-kill analyses of p-aminophenol were performed against Staphylococcus aureus and concentration dependent killing curves were obtained. Postantibiotic effect of p-aminophenol was also investigated against Staphylococcus aureus which was the most susceptible strain and found to be approximately 15 min for the MIC concentration. From our experimental results, we conclude that p-aminophenol, but not the other two structural isomers, displays a potent antibacterial activity against standard reference strains. We here also present some novel data on the antibacterial activity of paminophenol. © by PSP.Öğe A Self-Powered Enzymatic Glucose Sensor Utilizing Bimetallic Nanoparticle Composites Modified Pencil Graphite Electrodes as Cathode(Springer, 2024) Emir, Gamze; Dilgin, Yusuf; Sahin, Samet; Akgul, CahitEnzymatic biofuel cells (EBFC) are promising sources of green energy owing to the benefits of using renewable biofuels, eco-friendly biocatalysts, and moderate operating conditions. In this study, a simple and effective EBFC was presented using an enzymatic composite material-based anode and a nonenzymatic bimetallic nanoparticle-based cathode respectively. The anode was constructed from a glassy carbon electrode (GCE) modified with a multi-walled carbon nanotube (MWCNT) and ferrocene (Fc) as a conductive layer coupled with the enzyme glucose oxidase (GOx) as a sensitive detection layer for glucose. A chitosan layer was also applied to the electrode as a protective layer to complete the composite anode. Chronoamperometry (CA) results show that the MWCNT-Fc-GOx/GCE electrode has a linear relationship between current and glucose concentration, which varied from 1 to 10 mM. The LOD and LOQ were calculated for anode as 0.26 mM and 0.87 mM glucose, respectively. Also the sensitivity of the proposed sensor was calculated as 25.71 mu\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mu$$\end{document}A/mM. Moreover, the studies of some potential interferants show that there is no significant interference for anode in the determination of glucose except ascorbic acid (AA), uric acid (UA), and dopamine (DA). On the other hand, the cathode consisted of a disposable pencil graphite electrode (PGE) modified with platinum-palladium bimetallic nanoparticles (Nps) which exhibit excellent conductivity and electron transfer rate for the oxygen reduction reaction (ORR). The constructed EBFC was optimized and characterized using various electroanalytical techniques. The EBFC consisting of MWCNT-Fc-GOx/GCE anode and Pt-PdNps/PGE cathode exhibits an open circuit potential of 285.0 mV and a maximum power density of 32.25 mu W cm-2 under optimized conditions. The results show that the proposed EBFC consisting of an enzymatic composite-based anode and bimetallic nanozyme-based cathode is a unique design and a promising candidate for detecting glucose while harvesting power from glucose-containing natural or artificial fluids.Öğe Concomitant polymorphism of a pyridine-2,6-dicarboxamide derivative in a single space group: Experimental and molecular modeling study(Pergamon-Elsevier Science Ltd, 2012) Ozdemir, Namik; Dayan, Osman; Cetinkaya, Bekir; Akgul, CahitThe title compound, N-2,N-6-bis{2-[(Z)-2-hydroxybenzylideneamino]phenyl}pyridine-2,6-dicarboxamide (3), has been synthesized by the reaction of 2-{(2-aminophenylimino)methyl}phenol (1) with pyridine2,6-dicarbonyl dichloride (2), and characterized by elemental analysis. FT-IR and NMR spectroscopies and thermal analysis. Compounds 1 and 3 were evaluated for their antibacterial activities against Grampositive and Gram-negative bacteria. The catalytic activity of 3 was also studied, and as a result, the in situ prepared three component system Ru(II)/3/KOH is shown to be an efficient catalyst for the transfer hydrogenation reaction of various ketones under mild conditions. Compound 3 has been crystallized in two polymorphic forms under the same conditions, and their crystal structures have been determined using single crystal X-ray diffraction technique. The molecular geometry, vibrational frequencies and gauge-independent atomic orbital (CIAO) H-1 and C-13 NMR chemical shift values of 3 in the ground state have been calculated using the density functional theory (DFT/B3LYP) method with the 6-31G(d) basis set, and compared with the experimental data. The results are in good agreement with experimental data. The effect of different solvents on the geometry, vibrational frequencies, total energies and dipole moments was also studied using the same method by applying the Onsager Model. There are subtle differences in the conformations and packing of the two polymorphs as a consequence of intermolecular hydrogen bonding interactions. Therefore, DFT calculations for the hydrogen bond interactions in the polymorphs were carried out using same basis set. The changes of thermodynamic properties from the monomers to 3 with the temperature ranging from 200 K to 400 K have been obtained using the statistical thermodynamic method. (C) 2011 Elsevier B.V. All rights reserved.Öğe Fine-tuned preparation of cross-linked laccase nanoaggregates(Taylor & Francis Ltd, 2019) Sahutoglu, Arif Sercan; Akgul, CahitThis study focuses on well-known but commonly overlooked or unreported factors in the preparation of cross-linked enzyme nano-aggregates (nano-CLEAs). The parameters including the ionic strength of the protein solution, protein, precipitant and cross-linker concentrations, pH and addition order of the reagents were fine-tuned for nanoaggregate preparation without the need of non-protein support material, special equipment or sophisticated procedures. For this purpose, precipitation as nano-aggregates and then cross-linking while maintaining submicron size distribution were studied independently. Moreover, nano-aggregate formation from reverse micellar solutions was also investigated to improve the scope of the method to membrane-bound enzymes. Five different precipitation agents together with three different cross-linkers were investigated for immobilization of the Trametes versicolor laccase as cross-linked nano-aggregates. Although complete activity recovery was possible for micro-aggregates, the best activity results for nano-aggregates were 40.5%+/- 5.0. The K-m values of the immobilized enzymes were slightly lower than the K-m values of the free counterparts which indicate little or no mass transfer limitation due to the nano-immobilization process. However, V-max values were also lower. The activity loss and V-max reduction upon immobilization were found to mainly result from the modification of the amine groups instead of excess crosslinking. The thermal stabilities of the crosslinked laccase nano-aggregates were significantly higher (similar to 10-30 fold at 60 degrees C) compared to free laccase and the nano-CLEAs retained up to 30% of their initial activities upon 7 consequent usages. The sizes of the obtained immobilized enzyme products were found to be greatly variable depending on the cross-linker type. The smaller particles (similar to 200 nm radius) were obtained when EDAC was used as the cross-linker. The larger products (similar to 600 nm radius) were prepared when the cross-linker was dextran poly-aldehyde. The addition order of the reagents was found to be effective on particle size and thermal stability values.Öğe Immobilisation of Aspergillus oryzae ?-amylase and Aspergillus niger glucoamylase enzymes as cross-linked enzyme aggregates(De Gruyter Open Ltd, 2015) Sahutoglu, A. Sercan; Akgul, CahitCross-linked enzyme aggregates (CLEA) of Aspergillus oryzea a-amylase (AoAA) and Aspergillus niger glucoamylase (AnGA) were prepared using glutaraldehyde and dextran polyaldehyde as crosslinkers. The maximum activity recoveries for glutaraldehyde cross-linking were 21.8 % and 41.2 %, respectively. The addition of a proteic feeder (bovine serum albumin) exhibited a negative effect on the activity recoveries for both enzymes. Dextran polyaldehyde was used as a cross-linking agent instead of glutaraldehyde to reduce the activity losses. As a result, an activity recovery of 60.0 % was obtained for Aspergillus oryzea a-amylase. On the other hand, no activity recovery was observed for Aspergillus niger glucoamylase due to the latter enzymes affinity for dextran.(C) 2014 Institute of Chemistry, Slovak Academy of SciencesÖğe Molecular weight dependent antistaphylococcal activities of oligomers/polymers synthesized from 3-aminopyridine(Serbian Chemical Soc, 2010) Akgul, Cahit; Yildirim, MehmetThe main aim of this study was to investigate the relationship between molecular weight and the antistaphylococcal activity of oligomers/polymers synthesized from 3-aminopyridine. Different oligomers/polymers were synthesized from 3-aminopyridine by changing the oxidative polycondensation reaction conditions. They were characterized by size exclusion chromatography and their antibacterial activities were compared by employing standardized susceptibility assays. The obtained experimental results demonstrated that 3-aminopyridine had no antistaphylococcal activity. However, as a result of polymerization, strong antistaphylococcal activity was obtained. Oligomers/polymers synthesized from 3-aminopyridine had varying degrees of antistaphylococcal activity and the maximum activity was obtained from relatively very short oligomers. It was therefore concluded that polymerization of 3-aminopyridine is required for antistaphylococcal activity and strength of this activity depends on the molecular weights of the synthesized molecules.Öğe One-phase synthesis of single enzyme nanoparticles (SENs) of Trametes versicolor laccase by in situ acrylamide polymerisation(Taylor & Francis Ltd, 2020) Sahutoglu, Arif Sercan; Akgul, CahitSingle enzyme nanoparticles (SENs) are a state of art technology that allows immobilisation of individual enzyme molecules in a nanometre scale cross-linked polymer matrix that is covalently bonded to the enzyme. Although the method has great potential in the enzyme immobilisation, it has attracted relatively low attention from researchers over the last decade. Therefore, it can be very fruitful to apply this method to several enzymes in order to increase the understanding about the mechanisms and parameters important for the technique. In this study, Trametes versicolor laccase enzyme (TvL) was immobilised as SENs without phase transfer. The enzyme was immobilised via acryloyl chloride modification that is followed by an in situ polyacrylamide polymerisation in the water phase. The resulting single TvL nanoparticles were found to be less than 50 nm in diameter and round in shape with an activity recovery of 66.33 +/- 2.57%. Both V-max and K-m values of the TvL SENs were lower than the free counterpart. However, approximately the same K-cat/K-m values suggested similar catalytic efficiencies for the free and the immobilised enzymes. The significantly lower (similar to 2 fold) K-m value of the immobilised enzyme suggested an affinity increase towards 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) upon immobilisation. Whilst the immobilised and the free enzymes showed similar thermal stabilities at 60 degrees C for 240 min, the immobilised form showed higher stability in solution at ambient temperature after 15 days which may suggest an increase in microbial stability.Öğe Photoelectrochemical glucose biosensor based on a dehydrogenase enzyme and NAD+/NADH redox couple using a quantum dot modified pencil graphite electrode(Royal Soc Chemistry, 2016) Ertek, Bensu; Akgul, Cahit; Dilgin, YusufA simple, disposable and economical modified electrode was prepared by electrodeposition of hybrid quantum dots (ZnS-CdS) onto a pencil graphite electrode (PGE) surface and subsequent immobilization of glucose dehydrogenase (GDH) onto the quantum dot modified electrode (GDH/ZnS-CdS/PGE). The prepared electrode was effectively used for the photoelectrochemical determination of glucose in a flow injection analysis (FIA) system using a new home-made flow cell which was designed for PGEs for the first time. Results from the cyclic voltammetric and FI amperometric measurements revealed that the GDH/ZnS-CdS/PGE is capable of signaling photoelectrocatalytic activity involving NADH when the surface of the GDH/ZnSr-CdS/PGE is irradiated with a light source with a fiber optic cable (250 W halogen lamp). The currents of NADH produced by the enzymatic reaction in the photoamperometric FIA system under optimized conditions (carrier stream: 0.1 M phosphate buffer solution (pH 7.0) containing 1.0 M KCl and 10.0 mM NAD(+), applied potential: +0.8 V vs. Ag/AgCl/KCl(sat.); flow rate: 0.6 mL min(-1), sample loop: 100 mu L; transmission tubing length: 10 cm) were linearly correlated with the glucose concentration. Calibration curves were obtained for glucose concentrations within a range from 0.2 to 8.0 mM. The detection limits were found to be 0.09 and 0.05 mM for the amperometric and photoamperometric methods, respectively. The relative standard deviations (n = 7) for 0.5 mM glucose were 4.5% and 3.5% from the photoamperometric and amperometric results respectively. The photoelectrochemical biosensor was applied to real samples successfully. The results with this biosensor showed good selectivity, repeatability and sensitivity for monitoring glucose in amperometric and photoamperometric FIA studies.Öğe Sodium salicylate promotes neutrophil apoptosis by stimulating caspase-dependent turnover of Mcl-1(American Association of Immunologists, 2006) Derouet, Mathieu; Thomas, Luke; Moulding, Dale A.; Akgul, Cahit; Cross, Andrew; Moots, Robert J.; Edwards, Steven W.Mcl-1 is an antiapoptotic member of the Bcl-2 family of proteins that plays a central role in cell survival of neutrophils and other cells. The protein is unusual among family members in that it has a very short half-life of 2-3 h. In this report, we show that sodium salicylate (at 10 mM) greatly enhances the rate at which neutrophils undergo apoptosis and, in parallel, greatly accelerates the turnover rate of Mcl-1, decreasing its half-life to only 90 min. Whereas constitutive and GM-CSF-modified Mcl-1 turnover is regulated by the proteasome, the accelerated sodium salicylate-induced Mcl-1 turnover is mediated largely via caspases. Sodium salicylate resulted in rapid activation of caspase-3, -8, -9, and -10, and salicylate-accelerated Mcl-1 turnover was partly blocked by caspase inhibitors. Sodium salicylate also induced dramatic changes in the activities of members of the MAPIC family implicated in Mcl-1 turnover and apoptosis. For example, sodium salicylate blocked GM-CSF-stimulated Erk and Akt activation, but resulted in rapid and sustained activation of p38-MAPK, an event mimicked by okadaic acid that also accelerates Mcl-1 turnover and neutrophil apoptosis. These data thus shed important new insights into the dynamic and highly regulated control of neutrophil apoptosis that is effected by modification in the rate of Mcl-1 turnover. Copyright © 2006 by The American Association of Immunologists, Inc.
