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A calix[4]arene derivative-doped perchlorate-selective membrane electrodes with/without multi-walled carbon nanotubes
(SPRINGER HEIDELBERG, 2017) Erturun, H. Elif Kormali; Ozel, Ayca Demirel; Ayanoglu, Melek Nur; Sahin, Ozlem; Yilmaz, Mustafa
In this study, poly (vinyl chloride)(PVC) membrane electrodes with/without multi-walled carbon nanotubes (MWCNTs) based on a calix[4]arene derivative for perchlorate ion were described. The influence of membrane composition, pH, conditioning solution on the potentiometric response of the electrodes was investigated. Perchlorate-selective PVC membrane electrode exhibited a slope of 47.8 +/- 0.6 mV/pClO(4) in the range of 1.0 x 10(-7)-1.0 x 10(-1) mol L-1 at pH 4.0 while the coated Pt electrodes with MWCNT-OH, MWCNT-COOH and MWCNT displayed slopes of 46.1 +/- 0.7 mV/pClO(4) (5.0 x 10(-6)-1.0 x 10(-1) mol L-1), 50.4 +/- 1.9 mV/pClO(4) (1.0 x 10(-6)-1.0 x 10(-1) mol L-1) and 44.4 +/- 0.3 mV/pClO(4) (1.0 x 10(-5)-1.0 x 10(-1) mol L-1), respectively. Other response characteristics of these electrodes such as response time, lifetime and detection limit were identified, and the selectivity coefficients towards various anions were calculated by separate solution method. Moreover, the perchlorate-selective electrodes described here were successfully used as an indicator electrode for the determination of perchlorate in real samples such as tap water, river water and human urine by direct calibration method.
Calixarene-proline functionalized iron oxide magnetite nanoparticles (Calix-Pro-MN): An efficient recyclable organocatalyst for asymmetric aldol reaction in water
(ELSEVIER SCIENCE BV, 2015) Akceylan, Ezgi; Uyanik, Arzu; Eymur, Serkan; Sahin, Ozlem; Yilmaz, Mustafa
Calix[4]arene-based chiral organocatalyst derived from L-proline supported onto well-defined (15 +/- 3 nm) magnetic Fe3O4 nanoparticles was used as a highly active, recoverable, and reusable catalyst for the asymmetric aldol reaction in water without need for organic solvents. The chiral organocatalyst showed high catalytic activity (up to 94%), enantioselectivity (up to 93%) and diastereoselectivity (up to 97:3) for the reaction between cyclohexanone and aromatic aldehydes. The catalyst could easily separated using an external magnetic field and reused for several times without any significant loss of activity. (C) 2015 Elsevier B.V. All rights reserved.
Chiral Calix[4]arenes-Bearing Prolinamide Functionality as Organocatalyst for Asymmetric Direct Aldol Reactions in Water
(TAYLOR & FRANCIS LTD, 2018) Sahin, Ozlem; Eymur, Serkan; Uyanik, Arzu; Akceylan, Ezgi; Yilmaz, Mustafa
The chiral calix[4]arene derivative (6) bearing an L-prolinamido group has been designed and proved to be a water compatible efficient organocatalysts for a direct enantioselective aldol reaction. Compound 6 catalyzes the aldol reaction of cyclohexanone and a variety of aromatic aldehydes yielding anti-aldol products in high yield with enantioselectivities of up to 93% and diastereoselectivity of up to 95:5.
A comparative study of electrochemical methods on Pt-Ru DMFC anode catalysts: The effect of Ru addition
(PERGAMON-ELSEVIER SCIENCE LTD, 2013) Sahin, Ozlem; Kivrak, Hilal
In the present study comparative electrochemical study of methanol electro-oxidation reaction, the effect of ruthenium addition and experimental parameters on methanol electro-oxidation reaction at high performance carbon supported Pt and Pt-Ru catalysts have been studied by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) in H2SO4 (0.05-2.00 M) + CH3OH (0.01-4.00 M) at 20-70 degrees C. Tafel plots for the methanol oxidation reaction on Pt and Pt-Ru catalysts show reasonably well-defined linear region with the slopes of 128-174 mV dec(-1)(alpha = 0.34-0.46). The activation energies from Arrhenius plots have been found as 39.06-50.65 kJ mol(-1). As a result, methanol oxidation is enhanced by the addition of ruthenium. Furthermore, Pt-Ru (25:1) catalyst shows best electro-catalytic activity, higher resistance to CO, and better long term stability compared to Pt-Ru (3:1), Pt-Ru (1:1), and Pt. Finally, the EIS measurements on Pt-Ru (25:1) catalyst reveals that methanol electro-oxidation reaction consists of two process: methanol dehydrogenation step at low potentials (<700 mV) and the oxidation removal of COads by OHads at higher potentials (>700 mV). Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
A complementary study on novel PdAuCo catalysts: Synthesis, characterization, direct formic acid fuel cell application, and exergy analysis
(PERGAMON-ELSEVIER SCIENCE LTD, 2018) Kivrak, Hilal; Atbas, Dilan; Alal, Orhan; Cogenli, M. Selim; Bayrakceken, Ayse; Mert, Suha Orcun; Sahin, Ozlem
At present, Pd containing (10-40 wt%) multiwall carbon nanotube (MWCNT) supported Pd monometallic, Pd:Au bimetallic, and PdAuCo trimetallic catalysts are prepared via NaBH4 reduction method to examine their formic acid electrooxidation activities and direct formic acid fuel cell performances (DFAFCs) when used as anode catalysts. These catalysts are characterized by advanced analytical techniques as N-2 adsorption and desorption, XRD, SAXS, SEM-EDX, and TEM. Electronic state of Pd changes by the addition of Au and Co. Moreover, formic acid electrooxidation activities of these catalysts measured by CV indicates that particle size changes in wide range play a major role in the formic acid electrochemical oxidation activity, ascribed the strong structure sensitivity of formic acid electrooxidation reaction. PdAuCo (80:10:10)/MWCNT catalyst displays the most significant current density increase. On the other hand, lower CO stripping peak potential obtained for PdAuCo (80:10:10)/MWCNT catalyst, attributed to the awakening of the Pd-adsorbate bond strength down to its optimum value, which favors higher electrochemical activity. DFAFCs performance tests and exergy analysis reveal that fuel cell performances increase with the addition of Au and Co which can be attributed to synergetic effect. Furthermore, temperature strongly influences the performance of formic acid fuel cell. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Direct enantioselective aldol reactions catalyzed by calix[4]arene-based L-proline derivatives in the water
(PERGAMON-ELSEVIER SCIENCE LTD, 2014) Eymur, Serkan; Akceylan, Ezgi; Sahin, Ozlem; Uyanik, Arzu; Yilmaz, Mustafa
Two novel p-tert-butylcalix[4]arene-based chiral organocatalysts derived from L-proline have been developed to catalyze direct aldol reactions between cyclohexanone and aromatic aldehydes in water. Under the optimal conditions, high yields (up to 95%), enantioselectivities (up to 90%), and moderate diastereoselectivities (up to 65:35) were obtained. Considering the catalytic inefficiency of sole proline for the aldol reaction in water, these results clearly display the enormous effect of the hydrophobic part of calix[4]arene of compound A. (C) 2014 Elsevier Ltd. All rights reserved.
Effect of the glutaraldehyde derivatives of Calix[n]arene as cross-linker reagents on lipase immobilization
(SPRINGER, 2009) Erdemir, Serkan; Sahin, Ozlem; Uyanik, Arzu; Yilmaz, Mustafa
Synthesis of the glutaraldehyde derivatives calix[n]arene (n = 4,6,8) (Calix[n]-GA) and using as cross-linkers for immobilization of Candida rugosa lipase (CRL) have been discussed in this paper. The amino functional calix[n]arene derivatives (Calix[n]-NH (2)) were synthesized via reduction of dinitrile, hexanitrile and octanitrile derivatives of calix[n]arenes. These amino functional calix[n]arene derivatives (Calix[n]-NH (2)) were converted to their aldehyde derivativatives with glutaraldehyde. The calix[n]arene derivatives were used in lipase immobilization in order to see the role of calix[n]arene binding site on the lipase activitiy and stability. The activity recovery of calix[n]arene-supported lipases (Calix[n]-CRL) based on the Calix[4]-CRL, Calix[6]-CRL and Calix[8]-CRL reaches to 53.5, 66.1 and 76.4%, respectively.
Enantioselective hydrolysis of (R/S)-Naproxen methyl ester with sol-gel encapculated lipase in presence of calix[n]arene derivatives
(ELSEVIER SCIENCE BV, 2009) Sahin, Ozlem; Erdemir, Serkan; Uyanik, Arzu; Yilmaz, Mustafa
Lipases are enzymes that catalyses a variety of reactions, such esterifications, interesterification and hydrolysis. Several methods have been reported for the immobilization of lipases, such as deposition onto solid supports, covalent binding and encapsulation within a polymer matrix or silica glasses obtained by sol-gel techniques. In this study, the Candido rugosa lipase was encapsulated within a chemically inert sol-gel support prepared by polycondensation by tetraetoxysilane (TEOS)and octyltrietoxysilane(OTES) in the presence and absence of calix[n]arene, calix[n]-NH2 and calix[n]-COOH (n = 4,6,8) compounds as additives. The catalytic activity of the encapsulated lipases was evaluated into model reactions, i.e. the hydrolysis of p-nitrophenylpalmitate (p-NPP), and the enantioselective hydrolysis of rasemic Naproxen methyl ester that was studied in aqueous buffer solution/isooctane reaction system. The results indicated that the particularly calix[4,6]-NH2 and calix[6]-COOH based encapsulated lipases had higher conversion and enantioselectivity compared to the sol-gel free lipase. (C) 2009 Elsevier B.V. All rights reserved.
An ethanol electrooxidation study on carbon-supported Pt-Ru nanoparticles for direct ethanol fuel cells
(TAYLOR & FRANCIS INC, 2016) Sahin, Ozlem; Duzenli, Derya; Kivrak, Hilal
Carbon supported Pt-Ru catalysts were prepared at varying Pt:Ru ratios by polyol method. The crystallite sizes of these catalysts were determined by X-ray diffraction technique. The specific surface areas of these catalysts were also defined by Brunauer-Emmett-Teller technique. Cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy measurements were conducted on these carbon supported Pt-Ru catalysts to investigate the effect of ruthenium on the ethanol electrooxidation kinetics. Results indicated that Pt-Ru (25:1) catalyst showed the best ethanol electrooxidation activity. In conclusion, ethanol electrooxidation mechanism was proposed.
Facile and Rapid Synthesis of Microwave Assisted Pd Nanoparticles as Non-Enzymatic Hydrogen Peroxide Sensor
(ESG, 2017) Sahin, Ozlem; Kivrak, Hilal; Kivrak, Arif; Kazici, Hilal Celik; Alal, Orhan; Atbas, Dilan
Carbon supported Pd catalyst was prepared with microwave-assisted polyol method (M-Pd@C) and investigated sensing activity for non-enzymatic hydrogen peroxide (H2O2). Moreover, M-Pd@C and Pd@C catalyst which synthesized via polyol method (P-Pd@C) were compared to each other in terms of electrocatalytic activity. X-ray diffraction (XRD), X-ray photo electron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate structural and morphological properties of these catalysts. Furthermore, electrochemical measurements were performed via cyclic voltammetry (CV), chronoamperometry (CA) techniques. CV results exhibited that M-Pd/C catalyst showed perfect electrocatalytic activity in terms of reduction of H2O2. M-Pd/C catalyst showed a fast response of less than 7 s with a linear range of 5.0x10(-3)-11.0 mM and a relatively low detection limit of 1.2 mu M amperometric response. M-Pd/C catalyst exhibited great selectivity for detecting H2O2 in the existence of several hindering species such as uric acid and ascorbic acid.
Facile and Rapid Synthesis of Microwave Assisted Pd Nanoparticles as Non-Enzymatic Hydrogen Peroxide Sensor (vol 12, pg 762, 2017)
(ESG, 2018) Sahin, Ozlem; Kivrak, Hilal; Kivrak, Arif; Kazici, Hilal Celik; Alal, Orhan; Atbas, Dilan
[Abstract not Available]
Improvement of catalytic activity of lipase in the presence of wide rim substituted calix[4]arene carboxylic acid-grafted magnetic nanoparticles
(SPRINGER, 2014) Akceylan, Ezgi; Sahin, Ozlem; Yilmaz, Mustafa
Candida rugosa lipase immobilized on calix[4] arene carboxylic acid-grafted magnetic nanoparticles using a sol-gel encapsulation technique was tested for activity, which was assessed both in the enantioselective hydrolysis of racemic Naproxen methyl ester and that of p-nitrophenylpalmitate. It has also been noticed that, compared to the free enzyme (E = 137) with an ee value of [98 %, S-Naproxen calix[4] arene carboxylic acid-grafted magnetic nanoparticles based on encapsulated lipase (Calix-1-MN and Calix-2-MN) offer excellent enantioselectivity (E = 373 and E = 381). Moreover, the results indicated that after the fifth reuse in the enantioselective reaction, the encapsulated lipase (Calix-2-MN) still retained about 43 % of its conversion power.
Methanol Electrooxidation Study on Mesoporous Silica Supported Pt-Co Direct Methanol Fuel Cell Anode
(WALTER DE GRUYTER GMBH, 2014) Kivrak, Hilal; Can, Mukaddes; Duru, Hatice; Sahin, Ozlem
At present, Pt was impregnated by incipient wetness impregnation method on Co-doped SBA-15 catalysts prepared by sol-gel method at different weight percentages of Co to investigate the effect of Pt: Co ratio on methanol electrooxidation reaction (MOR). Cyclic voltammetry (CV), chronoamperometry (CA), and linear sweep voltammetry (LSV) techniques were employed to examine the MOR activities, poisoning capacity, and stability of these Pt/SBA-15 and Pt-Co/SBA-15 catalysts. Co presence in the platinum structure enhances the electrocatalytic activity of MOR, due to oxidation of Co at relatively low positive potentials. CV and CA measurements indicated that the most active catalyst was Pt-Co (86:14)/SBA-15 catalyst for MOR. Stability and poisoning measurements revealed that Co presence in the catalyst increases CO poisoning resistance and its stability, in agreement with CV and CA measurements.
A new anthracene derivative of calix[4]arene as a fluorescent chemosensor
(SCIENTIFIC TECHNICAL RESEARCH COUNCIL TURKEY-TUBITAK, 2013) Sahin, Ozlem; Sahin, Mustafa; Kocak, Nuriye; Yilmaz, Mustafa
A new anthracene derivative of calix[4]arene was synthesized as a highly fluorescent compound. This compound was examined for its fluorescent properties towards different metal ions (Li+, Na+, Mg2+, Ca2+, Ba2+, Ni2+, Cu2+, Zn-2+, Pb2+) by UV and fluorescence spectroscopy. On complexation by alkaline earth metal cations and transition metal cations, the fluorescence spectrum was quenched. In particular, Ca2 + caused greater than 98% quenching of the anthracene derivative of calix[4] arene.
A phenanthrene-based calix[4]arene as a fluorescent sensor for Cu2+ and F-
(PERGAMON-ELSEVIER SCIENCE LTD, 2014) Sahin, Ozlem; Akceylan, Ezgi
A new phenanthrene-based fluorescent calix[4]arene (4) has been synthesized in cone conformation. This compound was examined for its fluorescent properties towards different metal ions (Na+, Li+, Mg2+, Ni2+, Ba2+, Ca2+, Cu2+, Pb2+) and anions (F-, Cl-, Br-, H2PO4-, NO3-, HSO4-, CH3COO-) by fluorescence spectroscopy. The properties of the compound were evaluated and show that it is a fluorescence sensor for Cu2+ and F-. With the addition of Cu2+ and F-, the fluorescence was severely quenched. (C) 2014 Elsevier Ltd. All rights reserved.
The role of fluorodeoxyglucose-positron emission tomography/computed tomography in differentiating between benign and malignant adrenal lesions
(LIPPINCOTT WILLIAMS & WILKINS, 2011) Kara, Pelin Ozcan; Kara, Taylan; Gedik, Gonca Kara; Kara, Fatih; Sahin, Ozlem; Gunay, Emel Ceylan; Sari, Oktay
Objectives This retrospective study was designed to investigate the clinical role of whole-body positron emission tomography/computed tomography (PET/CT) by using 2[(18)F]fluoro-2-deoxy-D-glucose (FDG), for the evaluation of adrenal lesions and to find the best index to distinguish benign from malignant lesions in various cancer patients. Materials and methods A total of 81 patients (55 male and 26 female, age range: 31-81 years, mean: 61.5) who had confirmed primary malignancies (lung cancer in 47 patients, gastrointestinal malignancies in 13 patients, malignant melanoma in one patient, renal cell cancer in three patients, mesothelioma in two patients, breast carcinoma in nine patients, cervical cancer in one patient, ovarian cancer in two patients, pheochromocytoma in one patient, unknown primary in two patients) underwent PET/CT examinations for cancer screening, staging, restaging, and detection of suspected recurrence. Of the 81 patients, 104 adrenal lesions (34 benign and 70 malignant adrenal lesions) were shown by CT. On visual analysis of PET/CT imaging, adrenal uptake was based on a three-scale grading system. For final assessment standards of references for adrenal malignant lesions was based on biopsy (n=2), interval growth, or reduction after chemotherapy. An adrenal lesion, which remained unchanged on clinical and imaging follow-up of at least 7 months (mean follow-up time 19.31 months +/- 6.46, range 7-30 months), was decided as a benign lesion. Results In adrenal malignant lesions maximum standardized uptake value (SUV(max)) (8.82 +/- 4.47) was higher than that of adrenal benign lesions (3.02 +/- 1.15, P<0.0001). In the differentiation of adrenal benign and malignant lesions, a CT threshold of 10 Hounsfield units corresponded to a sensitivity of 64.7%, specificity of 98.6%, and accuracy of 87.5%. An SUV(max) cut-off value of 2.5 corresponded to a sensitivity of 100%, specificity of 38.2%, and accuracy of 80%. An SUV(max) cut-off value of 4.2 corresponded to a sensitivity of 88.6%, specificity of 88.2%, and accuracy of 88.5%. The ratio of tumor SUV(max) to liver SUV(mean) was 3.61 +/- 1.77 for adrenal malignant lesions whereas it was 1.20 +/- 0.38 for adrenal benign lesions (P<0.0001). T/L SUV ratio cut-off value of 1.8 corresponded to a sensitivity of 87%, specificity of 91%, and accuracy of 88.5%. T/L SUV ratio cut-off value of 1.68 corresponded to a sensitivity of 90%, specificity of 91.1%, and accuracy of 90.4%. Conclusion 2-[(18)F]fluoro-2-deoxy-D-glucose-PET/CT improves the diagnostic accuracy in the differentiation of benign from malignant adrenal lesions in various cancer patients. Combined information obtained from PET/CT (SUV(max) T/L SUV ratio, visual analysis) and unenhanced CT (size, Hounsfield units measurement) is recommended for better differentiation. Nucl Med Commun 32:106-112 (C) 2011 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins. Nuclear Medicine Communications 2011, 32:106-112
Salicylate Ion-Selective Electrode Based on a Calix[4]arene as Ionophore
(WILEY-V C H VERLAG GMBH, 2015) Ayanoglu, Melek Nur; Erturun, H. Elif Kormali; Ozel, Ayca Demirel; Sahin, Ozlem; Yilmaz, Mustafa; Kilic, Esma
A salicylate-selective electrode based on calix[4]arene derivative was developed and its response characteristics were investigated. The optimum membrane composition was 1% ionophore, 30% PVC, 69% DOS. The electrode exhibited a Nernstian slope of 58.8 +/- 0.5mV/pSal in the range of 1.0x10(-5)-1.0x10(-1)M with a detection limit of 4.3x10(-6)M at pH4.0, 20 +/- 1 degrees C. The potentiometric response of the electrode in the presence of different anions was investigated by the separate solution method. The lifetime was found at least 4months, and its response time was 5-10s. It was successfully used for the potentiometric determination of salicylate in pharmaceutical preparations.
Synthesis and Dichromate Anion Extraction Ability of Calix[4]arene Schiff Base Derivatives
(TAYLOR & FRANCIS INC, 2014) Sahin, Ozlem; Sahin, Mustafa; Yilmaz, Mustafa
[Abstract not Available]
Synthesis and fluorescence sensing properties of a new naphthalimide derivative of calix[4]arene
(PERGAMON-ELSEVIER SCIENCE LTD, 2012) Sahin, Ozlem; Yilmaz, Mustafa
A new naphthalimide derivative of calix[4]arene was synthesized as a highly selective fluorescent compound for Cu2+ among the selected metal ions. This compound was examined for its fluorescent properties toward different metal ions (Na+, Li+, Mg2+, Ni2+, Ba2+, Ca2+, Cu2+, Pb2+, Zn2+) and anions (F-, Cl-, Br-, H2PO4-, NO3-, HSO4-, CH3COO-) by UV, NMR and fluorescence spectroscopy. (C) 2012 Elsevier Ltd. All rights reserved.
Synthesis and fluorescence sensing properties of novel pyrene-armed calix[4] arene derivatives
(PERGAMON-ELSEVIER SCIENCE LTD, 2011) Sahin, Ozlem; Yilmaz, Mustafa
Fluorogenic tert-butylcalix[4]arenes bearing two pyrene pendant groups at the lower rim were synthesized. Based on ratiometric changes of monomer and excimer emissions, the pyrene amine derivative of calix[4]arene has been found to act as a selective sensor for Pb2+ and Cu2+ ions, respectively, due to a conformational change upon chelation of these ions. (c) 2011 Elsevier Ltd. All rights reserved.

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