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Öğe 1,10-Phenanthroline-5,6-dione and 9,10-phenanthrenequinone as redox mediators for amperometric glucose biosensors(Springer, 2014) Zor, Erhan; Oztekin, Yasemin; Mikoliunaite, Lina; Voronovic, Jaroslav; Ramanaviciene, Almira; Anusevicius, Zilvinas; Bingol, HalukIn this study, two ortho-quinoidal compounds, 1,10-phenanthroline-5,6-dione (PD) and 9,10-phenanthrenequinone (PQ), were examined as electron transfer mediators suitable for amperometric glucose biosensors. The dependences of the electrochemical responses of PD- and PQ-based amperometric glucose biosensors on varied concentrations of glucose were investigated under aerobic and anaerobic conditions. The PD-modified graphite rod (GR) electrode revealed a current response seven times higher than that of the PQ-modified GR electrode. The reactivity indices of ortho-quinoidals assessed by means of B3LYP functional method applying 6-311G(D) basis set showed that the electron-accepting potency for PD was markedly higher as compared with that of PQ. Compared to PQ, considerably higher reactivity of PD has been defined in the reactions with NADP(+)-ferredoxin reductase (FNR, EC 1.18.1.2) as a model single-electron transfer FAD-dependent enzyme, which provided an additional evidence for PD as a more efficient mediator compared to PQ. This study illustrates that PD can be applied as a redox mediator for glucose oxidase and it could be more suitable for a reagent-less biosensor design than PQ.Öğe Amperometric Glucose Biosensor Based on Glucose Oxidase, 1,10-Phenanthroline-5,6-dione and Carbon Nanotubes(Electrochemical Soc Inc, 2014) Zor, Erhan; Oztekin, Yasemin; Ramanaviciene, Almira; Anusevicius, Zilvinas; Bingol, Haluk; Barkauskas, Jurgis; Ersoz, MustafaA biosensor for glucose determination was fabricated by the immobilization of glucose oxidase (GOx) on carbon nanotubes (CNTs) and/or 1,10-phenanthroline-5,6-dione (PD) modified graphite rod electrodes (GOx/PD/CNTs/GR) and its amperometric response toward glucose was investigated under aerobic and anaerobic conditions. The sensitivity of the GOx/PD/CNTs/GR electrode was found to be higher compared to that of a PD-modified GR electrode without CNTs (GOx/PD/GR), implying that CNTs play an important role in the facilitation of electron transfer between the redox active site of GOx and the electrode surface. The GOx/PD/CNTs/GR biosensor exhibited a linear dependency on substrate concentration in a range from 0.0 until 50.0 mM of glucose with oxygen present and from 0.0 until 62.5 mM of glucose in the absence of oxygen. With oxygen present, the limit of detection (LOD) values were determined to be 5.4 and 8.0 mM, and the limit of quantitation values (LOQ) were calculated as 16.2 and 24 mM for GOx/PD/GR and GOx/PD/CNTs/GR, respectively. In the absence of oxygen, the LOD values were calculated as 4.2 and 10.7 mM, and the LOQ values were calculated as 12.6 and 32.1 mM for GOx/PD/GR and GOx/PD/CNTs/GR, respectively. When examining the interference effect of uric acid for GOx/PD/GR and GOx/PD/CNTs/GR electrodes, no significant changes in the amperometric response of the modified electrodes were observed up to 100.0 mM of uric acid. (C) 2014 The Electrochemical Society. All rights reserved.Öğe Carbon quantum dot modified electrodes developed for electrochemical monitoring of Daunorubicin-DNA interaction(Elsevier Science Sa, 2020) Eksin, Ece; Senturk, Huseyin; Zor, Erhan; Bingol, Haluk; Erdem, ArzumThe carbon quantum dot (cQD) modified disposable pencil graphite electrodes were developed for the first time in this study for electrochemical monitoring of drug-DNA interaction. The biomolecular interaction between calf thymus double stranded DNA (ctDNA) and an anthracycline antineoplastic drug, Daunorubicin (DNR) was investigated by differential pulse voltammetry (DPV) technique. For this purpose, experimental conditions, such as, the concentration of ctDNA, concentration of DNR and interaction time were optimized. Under optimum conditions, the detection limits of DNR and ctDNA were found to be 0.02 mu g/mL and 0.89 mu g/mL, respectively. The effect of interaction time between DNR and ctDNA was explored upon to the changes at both DNR and guanine oxidation signals. Drug-DNA interaction process was also examined by electrochemical impedance spectroscopy (EIS) technique.Öğe Carboxylated-Graphene Decorated Pencil Graphite Electrode as a Platform for Voltammetric Detection of DNA(Electrochemical Soc Inc, 2017) Zor, Erhan; Eksin, Ece; Findik, Mukerrem; Bingol, Haluk; Erdem, ArzumContinuous technology miniaturization using nanoscale materials allows the design of DNA sensing platforms with not only far larger surface areas but alsomore effective characteristics. We herein synthesized benzoic acid-functionalized graphene oxide (GOB), characterized by FT-IR, XPS, Raman Spectroscopy, TGA, SEM, TEM techniques and then it was utilized as a supporting material. Due to the benzoic acid groups available on the surface of GOB, fsDNA was directly immobilized onto the disposable pencil graphite electrode (PGE). The limit of detection (LOD) for fish sperm DNA (fsDNA) concentration was estimated to be 1.11 mu g/mL by using differential pulse voltammetry (DPV) technique. It can be assumed that this simple modification protocol offers an alternative for the quick and robust monitoring of sequence-specific nucleic acids avoiding the need of complex or expensive requirements, and it can pave the way for new opportunities to design more novel DNA sensing strategies and applications on disposable platforms. (c) 2017 The Electrochemical Society. All rights reserved.Öğe Catalytic degradation of organic dye using reduced graphene oxide-polyoxometalate nanocomposite(Elsevier Science Sa, 2017) Ucar, Asuman; Findik, Mukerrem; Gubbuk, I. Hilal; Kocak, Nuriye; Bingol, HalukSilicotungstic acid (SiW) decorated reduced graphene oxide (rGO) nanocomposite (rGO-SiW) has been prepared and evaluated as a heterogeneous nanocatalyst for the degradation reactions of methylene blue (MB) and rhodamine B (RhB). The structural and morphological properties of rGO-SiW nanocomposite were investigated by various techniques such as Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), Atomic force microscopy (AFM) and Scanning electron microscope (SEM), which revealed the homogeneous and noncovalent anchoring of SiW nanoparticles on rGO sheets. The catalytic activity of rGO-SiW nanocomposite on the degradations of MB and RhB has been monitored using UV-visible absorption spectrometry in the presence of NaBH4 as the reducing agent at room temperature in water. The reduction reactions followed pseudo-first order kinetics and degradation were achieved in 34 min for MB and 81 min for RhB using rGO-SiW as catalysts. (C) 2017 Elsevier B.V. All rights reserved.Öğe Chiral sensors(Elsevier Sci Ltd, 2019) Zor, Erhan; Bingol, Haluk; Ersoz, MustafaChirality has a crucial effect on clinical, chemical and biological research since most bioactive substances possess chirality in the natural world. Thus, new effective methods and/or (nano)materials are required to explain chiral recognition of chiral substances, which always become a hot topic in pharmaceutical and chemo/biological study. Recently, the researchers have developed new methods by using (nano) materials which can offer many advantages, and they have received considerable attention in chiral recognition. In this review, we report an overview of chiral sensors in a view of various transduction principles including electrochemical, QCM and optical measurements used for detection and discrimination of chiral molecules. We discuss the general aspects and the used materials for the construction of chiral sensors with selected studies between 2009 and 2019. Additionally, we explore the capabilities of how these materials can help to fabricate simple but efficient chiral sensors. Finally, we discuss the challenges and future outlooks. (c) 2019 Elsevier B.V. All rights reserved.Öğe Discriminative sensing of DOPA enantiomers by cyclodextrin anchored graphene nanohybrids(Elsevier Science Bv, 2017) Ates, Salih; Zor, Erhan; Akin, Ilker; Bingol, Haluk; Alpaydin, Sabri; Akgemci, Emine G.Discriminative sensing of chiral species with a convenient and robust system is a challenge in chemistry, pharmaceutics and particularly in biomedical science. Advanced nanohybrid materials for discrimination of these biologically active molecules can be developed by combination of individual obvious advantages of different molecular scaffolds. Herein, we report on the comparison of the performance of cyclodextrin functionalized graphene derivatives (x-CD/rGO, x: alpha-, beta-, gamma-) for discrimination of DOPA enantiomers. Within this respect, electrochemical measurements were conducted and the experimental results were compared to molecular docking method. Thanks to cavity size of g-CD and the unique properties of graphene, rGO/gamma-CD nanohybrid is capable of selective recognition of DOPA enantiomers. Limit of detection (LOD) value and sensitivity were determined as 15.9 mu M and 0.2525 mu A mu M-1 for D- DOPA, and 14.9 mu M and 0.6894 mu A mu M-1 for L-DOPA. (C) 2017 Elsevier B.V. All rights reserved.Öğe Efficient adsorption of lead (II) and copper (II) from aqueous phase using oxidized multiwalled carbon nanotubes/polypyrrole composite(Taylor & Francis Inc, 2018) Nyairo, Wilfrida Nyanduko; Eker, Yasin Ramazan; Kowenje, Chrispin; Akin, Ilker; Bingol, Haluk; Tor, Ali; Ongeri, David MokonoPolypyrrole coated oxidized multiwalled carbon nanotubes (oMWCNT/Ppy) were applied to determine the adsorption characteristics of Pb(II) and Cu(II) from their aqueous solutions. Structural and morphological characterization studies using scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared and Raman spectroscopy showed successful preparation of the oMWCNT/Ppy composite. The influence of pH, contact time, and initial metal ion concentration on the adsorption of Pb(II) and Cu(II) was studied. The adsorption processes fitted well with Langmuir isotherm and pseudo-second-order kinetic models. The maximum adsorption capacities for Pb(II) and Cu(II) were determined as 26.32 and 24.39mg/g, respectively. Desorption studies indicated that the oMWCNT/Ppy composite could be reused for five cycles with minimum loss of its initial adsorption capacity.Öğe Efficient Removal of Lead(II) Ions from Aqueous Solutions Using Methyl-?-Cyclodextrin Modified Graphene Oxide(Springer, 2017) Nyairo, Wilfrida Nyanduko; Eker, Yasin Ramazan; Kowenje, Chrispin; Zor, Erhan; Bingol, Haluk; Tor, Ali; Ongeri, David MokonoGraphene oxide (GO) and graphene oxide modified with methyl-beta-cyclodextrin denoted as GO-m beta CD were prepared and applied as adsorbents to determine the adsorption characteristics of Pb(II) from aqueous solutions. The characteristic results of Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM) showed that m beta CD was successfully physically attached to GO to form the GO-m beta CD nano-composite. The adsorption equilibrium and kinetics of the adsorbents were well described by Langmuir isotherm and pseudo-second-order models, respectively. The maximum Pb(II) adsorption capacity of GO-m beta CD (at pH = 6 and room temperature) was determined as 312.5 mg/g which was significantly higher than that of GO (217.39 mg/g). This indicates that the modification of GO with m beta CD enhances the adsorption capacity of GO. The desorption studies show that the adsorbent GO-m beta CD can be used for at least five cycles with non-significant loss of its initial adsorption capacity for Pb(II) ions.Öğe An electrochemical and computational study for discrimination of D- and L-cystine by reduced graphene oxide/?-cyclodextrin(Royal Soc Chemistry, 2015) Zor, Erhan; Bingol, Haluk; Ramanaviciene, Almira; Ramanavicius, Arunas; Ersoz, MustafaHere, we report a novel enantioselective electrochemical biosensor for the discrimination of cystine enantiomers (D- and L-cystine) using a chiral interface for the specific recognition of D- and L-cystine. The biosensor is based on reduced graphene oxide modified by beta-cyclodextrin (rGO/beta-CD) at the GCE surface. During the preparation of rGO/beta-CD/GCE, the modified electrode surfaces were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The electrochemical behaviours of the D- and L-cystine were investigated using the rGO/beta-CD/GCE by CV and compared to bare GCE. A clear separation between the oxidation peak potentials of D- and L-cystine was observed at 1.32 and 1.42 V, respectively. The electrochemical discrimination performance of the fabricated chiral sensor was also examined by differential pulse voltammetry (DPV) in a mixed solution of D- and L-cystine. In addition, the DPV technique was used for the determination of D- and L-cystine at low concentration values in the range of 1.0-10.0 mM. To investigate the amperometric response of rGO/beta-CD/GCE towards D- and L-cystine, the chronoamperometry technique was used in the concentration range of 10.0-100.0 mu M. The interactions of the enantiomers with rGO/beta-CD were modelled by molecular docking using AutoDock Vina, and the interaction energies were predicted to be -4.8 and -5.3 kcal mol(-1) for D- and L-cystine, respectively. The corresponding values of binding constants were calculated to be 3.32 x 10(3) and 7.71 x 10(3) M-1, respectively. The experimental and molecular docking results indicate that the rGO/beta-CD/GCE has a different affinity for each enantiomer.Öğe An electrochemical biosensor based on human serum albumin/graphene oxide/3-aminopropyltriethoxysilane modified ITO electrode for the enantioselective discrimination of D- and L-tryptophan(Elsevier Advanced Technology, 2013) Zor, Erhan; Patir, Imren Hatay; Bingol, Haluk; Ersoz, MustafaA new electrochemical biosensor based on the human serum albumin/graphene oxide/3-aminopropyl-triethoxysilane modified indium tin oxide electrode (ITO/APTES/GO/HSA) has been developed for the discrimination of tryptophan (Trp) enantiomers. The electrode has been characterized by scanning electron microscopy (SEM) and electrochemical techniques. The electrochemical behaviors of the enantiomeric pairs (D- and L-Trp) at the ITO/APTES/GO/HSA electrode have been investigated by cyclic voltammetry in the concentration range of 0.10-1.0 mM. A clear separation between the oxidation peak potentials of D- and L-Trp, at 0.86 and 1.26 V, respectively, has suggested that the ITO/APTES/GO/HSA electrode can be used as an electrochemical biosensor for the discrimination of Trp enantiomers. In order to find the percentage of an enantiomeric form of tryptophan in a mixture, the ITO/APTES/GO/HSA electrode is used for the simultaneous detection of D- and L-Trp which showed that the percentage of one enantiomeric form can be easily measured in the presence of the other. (c) 2012 Elsevier B.V. All rights reserved.Öğe An electrochemical chiral sensor based on electrochemically modified electrode for the enantioselective discrimination of D-/L-tryptophan(Springer, 2019) Erbilen, Nesibe; Zor, Erhan; Saf, Ahmet Ozgur; Akgemci, Emine Guler; Bingol, HalukChirality is a universal characteristic of natural systems and discrimination of enantiomers of a chiral molecule plays a major role particularly in chemical biology and in pharmacology. In this study, a novel electrochemical chiral sensor was developed for direct discrimination of D- and L-tryptophan (Trp) in an aqueous medium. The chiral sensor was produced by hierarchical modification of reduced graphene oxide, gold nanoparticles, poly-L-cysteine, and poly-L-phenylalanine methyl ester on the glassy carbon electrode. Each of the layers was produced by electrochemical techniques, such as electrochemical reduction and polymerization. After structural and morphological characterizations, the electrochemical behaviors of the enantiomeric pairs of Trp at the modified electrode were investigated by cyclic voltammetry and square wave voltammetry. A distinctive separation between the oxidation peak potentials of D- and L-Trp was observed at 0.73 and 0.83 V, respectively. In order to investigate the amperometric response towards D- and L-Trp, chronoamperometry technique was also used in the concentration range of 0.1-0.8 mM. Furthermore, the electrochemical performance of the modified electrodes was investigated in a mixed solution of D- and L-Trp. The results showed that the prepared electrode could be used as an electrochemical chiral sensor for Trp enantiomers.Öğe Electrochemical detection of interaction between daunorubicin and DNA by hybrid nanoflowers modified graphite electrodes(Elsevier Science Sa, 2021) Findik, Mukerrem; Bingol, Haluk; Erdem, ArzumIn this study, two types of hybrid nanoflowers (NFs) modified disposable electrodes were developed to investigate the electrochemical behavior of anticancer drug-DNA interaction. Biocompatible hybrid NFs were synthesized by amino acids (L-glutamic acid and L-cysteine) via a simple, rapid and cost-effective methods. Structural characterizations of the synthesized hybrid NFs were performed with Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS), while morphological characterizations were performed using scanning electron microscopy (SEM) and energy diffuser X-ray (EDX) spectroscopy techniques. As the sensing platform in electrochemical studies, pencil graphite electrode (PGE) has been used because of its advantages such as low cost, easy-to-handle, portable and disposable. After PGEs modified with NFs were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques, differential pulse voltammetry (DPV) technique was used in the determination of calf thymus double stranded DNA (ctdsDNA) and also daunorubicin (DNR) as well as DNA-DNR interaction. The detection limits as a result of ctdsDNA determination were found to be 0.93 mu g/mL by using Lcysteine NFs modified PGE (c-NFs-PGE) and 2.37 mu g/mL by using L-glutamic acid modified PGE (ga-NFs-PGE). The detection limits obtained for the determination of DNR were found as 2.93 mu M and 2.06 mu M with c-NFs-PGE and ga-NFs-PGE, respectively. The optimum interaction time between DNR and ctdsDNA was determined by cNFs-PGE, which showed higher sensitivity performance against oxidation of guanine signals.Öğe Electrochemical monitoring of biointeraction by graphene-based material modified pencil graphite electrode(Elsevier Advanced Technology, 2017) Eksin, Ece; Zor, Erhan; Erdem, Arzum; Bingol, HalukRecently, the low-cost effective biosensing systems based on advanced nanomaterials have received a key attention for development of novel assays for rapid and sequence-specific nucleic acid detection. The electrochemical biosensor based on reduced graphene oxide (rGO) modified disposable pencil graphite electrodes (PGEs) were developed herein for electrochemical monitoring of DNA, and also for monitoring of biointeraction occurred between anticancer drug, Daunorubicin (DNR), and DNA. First, rGO was synthesized chemically and characterized by using UV-Vis, TGA, FT-IR, Raman Spectroscopy and SEM techniques. Then, the quantity of rGO assembling onto the surface of PGE by passive adsorption was optimized. The electrochemical behavior of rGO PGEs was examined by cyclic voltammetry (CV). rGO-PGEs were then utilized for electrochemical monitoring of surface-confined interaction between DNR and DNA using differential pulse voltammetry (DPV) technique. Additionally, voltammetric results were complemented with electrochemical impedance spectroscopy (EIS) technique. Electrochemical monitoring of DNR and DNA was resulted with satisfying detection limits 0.55 mu M and 2.71 mu g/mL, respectively.Öğe Evaluation of 1,10-phenanthroline-5,6-dione as redox mediator for glucose oxidase(Maik Nauka/Interperiodica/Springer, 2016) Zor, Erhan; Oztekin, Yasemin; Ramanaviciene, Almira; Anusevicius, Zilvinas; Voronovic, Jaroslav; Bingol, Haluk; Barauskas-Memenas, DanaA low-cost and simply fabricated amperometric glucose biosensor based on glucose oxidase (GOx) and 1,10-phenanthroline-5,6-dione (PD) modified graphite rod electrode was developed. The electrode exhibited good electrocatalytic activity with a well-defined hyperbolic dependence of amperometric signal upon glucose concentration in the presence and in the absence of oxygen. The electrode showed a good reproducibility and repeatability with relative standard deviation of less than 3 and 5%, respectively. The interaction of GOx with PD mediator was confirmed by means of UV?Vis absorbance spectroscopy.Öğe Fluorogenic ferrocenyl Schiff base for Zn2+ and Cd2+ detection(Springer, 2017) Findik, Mukerrem; Ucar, Asuman; Bingol, Haluk; Guler, Ersin; Ozcan, EmineA novel sensor based on acetylferrocene-containing Schiff base (ASB) was synthesized by reaction of alpha-chloroacetylferrocene and N-(salicylidene)-l-valinmethylester. The structure of the compound was characterized by using elemental analysis and Fourier-transform infrared (FT-IR), H-1 nuclear magnetic resonance (NMR), and C-13 NMR spectroscopy. Its metal-cation-sensing properties were investigated spectrofluorometrically. ASB served as selective chemosensor for Zn2+ and Cd2+ towards alkali, alkaline-earth, and various heavy-metal ions. It showed significant fluorescence enhancement for Zn2+ and Cd2+ ions, stemming from C=N isomerization and chelation-enhanced fluorescence. The binding modes of the complexes were determined to have 1:1 complexation stoichiometry, and the binding constants were calculated as (6.93 +/- 0.25) x 10(6) M-1 for ASB center dot Zn (2+) and (7.49 +/- 0.18) x 10(5) M-1 for ASB center dot Cd (2+) using the nonlinear curve-fitting method.Öğe Graphene Quantum Dots-based Photoluminescent Sensor: A Multifunctional Composite for Pesticide Detection(Amer Chemical Soc, 2015) Zor, Erhan; Morales-Narvaez, Eden; Zamora-Galvez, Alejandro; Bingol, Haluk; Ersoz, Mustafa; Merkoci, ArbenDue to their size and difficulty to obtain, cost/effective biological or synthetic receptors (e.g., antibodies or aptamers, respectively), organic toxic compounds (e.g., less than 1 kDa) are generally challenging to detect using simple platforms such as biosensors. This study reports on the synthesis and characterization of a novel multifunctional composite material, magnetic silica beads/graphene quantum dots/molecularly imprinted polypyrrole (mSGP). mSGP is engineered to specifically and effectively capture and signal small molecules due to the synergy among chemical, magnetic, and optical properties combined with molecular imprinting of tributyltin (291 Da), a hazardous compound, selected as a model analyte. Magnetic and selective properties of the mSGP composite can be exploited to capture and preconcentrate the analyte onto its surface, and its photoluminescent graphene quantum dots, which are quenched upon analyte recognition, are used to interrogate the presence of the contaminant. This multifunctional material enables a rapid, simple and sensitive platform for small molecule detection, even in complex mediums such as seawater, without any sample treatment.Öğe Graphene-based hybrid for enantioselective sensing applications(Elsevier Advanced Technology, 2017) Zor, Erhan; Morales-Narvaez, Eden; Alpaydin, Sabri; Bingol, Haluk; Ersoz, Mustafa; Merkoci, ArbenChirality is a major field of research of chemical biology and is essential in pharmacology. Accordingly, approaches for distinguishing between different chiral forms of a compound are of great interest. We report on an efficient and generic enantioselective sensor that is achieved by coupling reduced graphene oxide with gamma-cyclodextrin (rGO/gamma-CD). The enantioselective sensing capability of the resulting structure was operated in both electrical and optical mode for of tryptophan enantiomers (D-/L-Trp). In this sense, voltammetric and photoluminescence measurements were conducted and the experimental results were compared to molecular docking method. We gain insight into the occurring recognition mechanism with selectivity toward D- and L-Trp as shown in voltammetric, photoluminescence and molecular docking responses. As an enantioselective solid phase on an electrochemical transducer, thanks to the different dimensional interaction of enantiomers with hybrid material, a discrepancy occurs in the Gibbs free energy leading to a difference in oxidation peak potential as observed in electrochemical measurements. The optical sensing principle is based on the energy transfer phenomenon that occurs between photo excited D-/L-Trp enantiomers and rGO/gamma-CD giving rise to an enantioselective photoluminescence quenching due to the tendency of chiral enantiomers to form complexes with gamma-CD in different molecular orientations as demonstrated by molecular docking studies. The approach, which is the first demonstration of applicability of molecular docking to show both enantioselective electrochemical and photoluminescence quenching capabilities of a graphene-related hybrid material, is truly new and may have broad interest in combination of experimental and computational methods for enantiosensing of chiral molecules. (C) 2016 Elsevier B.V. All rights reserved.Öğe Graphene-based recyclable and bifunctional heterogeneous chiral catalyst for direct asymmetric aldol reaction(Elsevier Science Sa, 2020) Azlouk, Manel; Durmaz, Mustafa; Zor, Erhan; Bingol, HalukApplication of metal-free heterogeneous asymmetric catalysis is of great interest in the field of asymmetric synthesis. Herein, two novel graphene-supported praline-based bifunctional carbocatalysts were prepared by post-grafting c-proline onto graphene oxide sheets via organoamine-functIonalized graphene oxide (GO-NH2) and reduced graphene oxide (GO-NH2). Different methods such as Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron spectroscopy (TEM) were employed to examine the surface functionalization of GO. The catalytic properties of these materials were investigated in the direct asymmetric aldol reaction. r-proline grafted heterogeneous catalyst, GO-Pro, was found to be an efficient and powerful organocatalyst for the enantioselective aldol reaction under mild conditions in hexane and afforded the corresponding aldol adducts with satisfactory isolated yields (up to 88%) and enantiomeric excesses (up to 85%). Furthermore, graphene-based carbocatalyst could be recovered and recycled easily by a simple washing procedure and re-used for several times without substantial reduction in its catalytic activity.Öğe Green preparation of a novel red mud@carbon composite and its application for adsorption of 2,4-dichlorophenoxyacetic acid from aqueous solution(Springer Heidelberg, 2017) Kazak, Omer; Eker, Yasin Ramazan; Akin, Ilker; Bingol, Haluk; Tor, AliThis study reports the eco-friendly preparation of a novel composite material consisting of red mud and carbon spheres, denoted as red mud@C composite, and its application for the removal of 2,4-dichlorophenoxyacetic acid herbicide (2,4-D) from aqueous solution. The preparation route has a green approach because it follows the low-energy consuming one-step hydrothermal process by using starch as a renewable carbon precursor and red mud as a waste from aluminum production industry. Characterization of the red mud@C composite was performed by FT-IR, TGA, SEM, TEM, BET, XRD, and Raman microscopy analyses. The batch adsorption studies revealed that the red mud@C composite has higher 2,4-D adsorption efficiency than those of the red mud and the naked carbon spheres. The maximum removal at initial pH of 3.0 is explained by considering the pKa of 2,4-D and pH of point of zero charge (pH(pzc)) of the composite material. The adsorption equilibrium time was 60 min, which followed the pseudo-second-order kinetic model together with intra-particle diffusion model. The isotherm analysis indicated that Freundlich isotherm model better represented the adsorption data, with isotherm parameters of k [15.849 (mg/g) (mg/L)(-1/n) ] and n (2.985). The prepared composite is reusable at least 5 cycles of adsorption-desorption with no significant decrease in the adsorption capacity.
