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Öğe CHIRAL STATIONARY PHASES USED FOR ENANTIOMERIC RESOLUTION(Bilal GÜMÜŞ, 2015) Erdoğan, Ömer; Topal, GirayEnantiomer separation has attracted increasing attentions in pharmaceutical industry, due to great differences in pharmacological, toxicological and/or metabolic activities of enantiomeric drugs in living system. Several methods have been succesfully used to achieve chiral separation. To date the chromatographic method is one of the most effective. Numerous kinds of CSPs have been developed for chiral separation these include cyclo-dextrins, polysaccharides, macrocyclic antibiotics, ligand-exchange, Pirkle, crown ethers and protein derivatives. İn this rewiev we will inform ligands and macromolecules used as CSP.Öğe Complexation studies of some newly synthesized precursors for substituted dibenzo and dibenzodiaza crown ethers(John Wiley & Sons Inc, 2004) Çakır, Ümit; Uğraş, Halil İbrahim; Temel, Hamdi; Topal, Giray; 0000-0002-7056-3912; 0000-0001-9225-7425; 0000-0002-9430-4069This study represents the synthesis of dibenzo and dibenzodiaza crown ether precursors with various functional groups in good yield by employing four different methods using polar protic and aprotic solvents with high boiling points. Also the complexation abilities of all synthesized ligands with Cu2+, Zn2+, and Ag+ were studied by conductometry; thus the conductometric behavior of Cu(NO3)(2), ZnCI2, and AgNO3 in 80% dioxane-water mixture was investigated in the presence of these ligands. The order of formation constant for complexes of the ligands with Cu2+, Zn2+, and Ag+ ions was found to be: Cu2+ > Zn2+ > Ag+ for the ligands of VI, VIL XI, and XII; Cu2+ > Ag+ > Zn2+ for the ligands of III and VIII; and Zn2+ > Cu2+ > Ag+ for the ligands of I, II, IV, V, IX, and X. (C) 2003 Wiley Periodicals, Inc.Öğe Comprehensive study of all Gundelia L. taxa exists in the globe: An insight on LC-MS/MS based phytochemical investigation and bioactivity potential of 22 species(Elsevier Ltd, 2023) Tarhan, Abbas; Fırat, Mehmet; Topal, GiraySpecies from the Gundelia genus are among the important main therapeutic herbs widely used in Middle Eastern nations' traditional medicine. The emphasis of the current investigation was on the bioactive phytochemicals and biopharmaceutical efficacy of all 22 species of Gundelia taxa worldwide. Herewith, ethanolic extracts of root, stem-leaf and flower parts of twenty two Gundelia species were prepared and their bioactive phytochemicals were quantified by a comprehensive and validated LC-MS/MS (liquid chromatography tandem mass spectrometry) method. The results of the LC-MS/MS study revealed that, chlorogenic acid (0.042–93.52 mg/g extract), quinic acid (3.860–63.761 mg/g extract), kaempferol-3-O-glucoside (0.019–42.737 mg/g extract), luteolin-7-O-glucoside (cymaroside) (0.013–34.017 mg/g extract), quercetin-3-O-glucoside (0.021–24.241 mg/g extract), apigenin-7-O-glucoside (0.006–15.859 mg/g extract), 1,5-dicaffeoylquinic acid (0.014–4.827 mg/g extract) and caffeic acid (0.020–4.082 mg/g extract) amounts were remarkable in the overall assessment of the quantification results. Furthermore, bioactivities of the studied extracts were determined by evaluating total phenolic-flavonoid contents and ABTS (cation radical scavenging activity), DPPH (free radical scavenging activity) and CUPRAC (cupric reducing antioxidant capacity) antioxidant test assays. With a few exceptions, all antioxidant test assays showed that the root ethanol extracts of the examined Gundelia species had stronger antioxidant activity than their flower and stem-leaf extract counterparts. Based on the results of the ABTS assay, it was discovered that the antioxidant capacities of root-ethanol extracts of G. purpurascens, G. dersim, G. armeniaca, G. armata, G. aragatsi, G. microcephala, G. tournefortii and G. tehranica (IC50 < 10 μg/mL) were at least as high as those of BHT (Butylated hydroxytoluene) (IC50: 11.35 ± 0.22 μg/mL) and α-tocopherol (IC50: 9.23 ± 0.12 μg/mL), which were used as the reference compounds. To conclude, this is the first study in which the phytochemical contents and antioxidant activities of different parts of all Gundelia taxa in the world were determined together. Moreover, in this study, the phytochemical quantitation and bioactivity of G. microcephala, G. cappadocica, G. tehranica, G. aragatsi, and G. tenuisecta species were evaluated for the first time.Öğe Covalent Immobilization of Candida rugosa Lipase on Epichlorohydrin-Coated Magnetite Nanoparticles: Enantioselective Hydrolysis Studies of Some Racemic Esters and HPLC Analysis(Springer, 2020) Cakmak, Resit; Topal, Giray; Cinar, ErcanIn this study, a new biocatalyst was prepared by immobilizing Candida rugosa lipase epichlorohydrin-functionalized onto the surface of the nanoparticles. Magnetite nanoparticles were obtained by chemical co-precipitation method of Fe2+ and Fe3+, and then the prepared uncoated and coated nanoparticles were characterized by XRD, FT-IR and TGA. Lipase was covalently attached to activated nanoparticles. The catalytic properties of free and immobilized lipases were determined. It was found that the optimum temperature for free and immobilized lipases was 30 degrees C and 35 degrees C, respectively. The optimum pH values were found to be 7.0 and 8 for free and immobilized lipases, respectively. Immobilized lipase was found to retain significant activity even after the seventh use. In the final section of the study, optically pure compounds were obtained by carrying out the enantioselective hydrolysis studies of racemic esters by using immobilized lipase. Enantiomeric excesses of the products in the enantioselective hydrolysis of racemic ibuprofen and naproxen methyl ester and racemic butyl mandelate were determined to be 94.93, 77.30 and 68.15, respectively.Öğe Design, preparation and application of a Pirkle-type chiral stationary phase for enantioseparation of some racemic organic acids and molecular dynamics studies(Acg Publications, 2017) Cakmak, Resit; Ercan, Selami; Sunkur, Murat; Yilmaz, Hayrullah; Topal, GirayThis study consists of two parts. In the first part of the study; a Pirkle-type chiral stationary phase was prepared by synthesizing an aromatic amine derivative of (R)-2-amino-1-butanol as a chiral selector and binding to L-tyrosine-modified cyanogen bromide (CNBr)-activated Sepharose 4B and then, packed into the separation column. The chromatographic performance of the separation column was evaluated with racemic mandelic acid and 2-phenylpropionic acid by using phosphate buffers at three different pHs as mobile phase. In the resolution processes, the prepared solutions were loaded onto the separation column at two different concentrations and at three different pHs for each racemic organic acid, separately. Enantiomeric excess (ee%) of the eluates was determined on CHIRALPAK AD-H chiral analytical column by HPLC. The maximum ee% for mandelic acid and 2-phenylpropionic acid was determined to be 60.84 and 27.4, respectively. Separation factors (k(1)', k(2)', alpha, and Rs) were calculated for each acid. The structures of the obtained compounds were characterized using the spectroscopic methods (NMR, and elemental analysis). In the second part of the study; enantioselective interactions between the prepared CSP and the analytes have been widely studied by docking, molecular dynamics simulation and quantum mechanical computation methods. The reason of column eluation of rac-2-phenylpropionic acid with lower enantiomeric yield was explained by these techniques.Öğe Design, synthesis and biological evaluation of novel nitroaromatic compounds as potent glutathione reductase inhibitors(Pergamon-Elsevier Science Ltd, 2011) Cakmak, Resit; Durdagi, Serdar; Ekinci, Deniz; Senturk, Murat; Topal, GirayDiscovery of GR inhibitors has become very popular recently due to antimalarial and anticancer activities. In this study, the synthesis and GR inhibitory capacities of novel nitroaromatic compounds (NCs) (1-3) were reported. Some commercially available molecules were also tested for comparison reasons. The novel NCs were obtained in high yields using simple chemical procedures and exhibited much potent inhibitory activities against GR at low micromolar concentrations with K-i values ranging from 0.211 to 4.57 mu M as compared with well-known agents. Inhibition mechanism was assessed as being due to occlusion of the active site entrance by means of the NCs. Molecular docking results have shown that docking poses of ligands are able to construct binding interactions with the essential amino acids. (C) 2011 Elsevier Ltd. All rights reserved.Öğe Determination of kinetic and equilibrium parameters of the batch adsorption of Mn(II), Co(II), Ni(II) and Cu(II) from aqueous solution by black carrot (Daucus carota L.) residues(Elsevier, 2008) Guzel, Fuat; Yakut, Hakan; Topal, GirayIn this study, the effect of temperature on the adsorption of Mn(II), Ni(II), Co(II) and Cu(II) from aqueous solution by modified carrot residues (MCR) was investigated. The equilibrium contact times of adsorption process for each heavy metals-MCR systems were determined. Kinetic data obtained for each heavy metal by MCR at different temperatures were applied to the Lagergren equation, and adsorption rate constants (k(ads)) at these temperatures were determined. These rate constants related to the adsorption of heavy metal by MCR were applied to the Arrhenius equation, and activation energies (E-a) were determined. In addition, the isotherms for adsorption of each heavy metal by MCR at different temperatures were also determined. These isothermal data were applied to linear forms of isotherm equations that they fit the Langmuir adsorption isotherm, and the Langmuir constants (q(m) and b) were calculated. b constants determined at different temperatures were applied to thermodynamic equations, and thermodynamic parameters such as enthalpy (Delta H), free energy (Delta G), and entropy (Delta S) were calculated and these values show that adsorption of heavy metal on MCR was an endothermic process and process of adsorption was favoured at high temperatures. (C) 2007 Elsevier B.V. All rights reserved.Öğe Diester Molecules for Organic-Based Electrical and Photoelectrical Devices(Springer, 2017) Topal, Giray; Tombak, Ahmet; Yigitalp, Esref; Batibay, Derya; Kilicoglu, Tahsin; Ocak, Yusuf SelimDiester derivatives of terephthalic acid molecules were synthesized according to the literature. Au/Diester derivatives/n-Si organic-inorganic (OI) heterojunction-type devices were fabricated, and the current-voltage (I-V) characteristics of the devices have been investigated at room temperature. I-V characteristics demonstrated that all diodes had excellent rectification properties. Primary diode parameters such as series resistance and barrier height were extracted by using semi-log I-V plots and Norde methods, and were compared. It was seen that there was a substantial agreement between results obtained from two methods. Calculated barrier height values were about the same with 0.02-eV differences that were attributed to the series resistance. Ideality factors, which show how the diode closes to ideal diodes, were also extracted from semi-log I-V plots. Thus, the modification of the Au/n-Si diode potential barrier was accomplished using diester derivatives as an interlayer. The I-V measurements were repeated to characterize the devices at 100 mW/cm(2) illumination intensity with the help of a solar simulator with an AM1.5G filter.Öğe Enantioseparation of mandelic acid enantiomers with magnetic nano-sorbent modified by a chiral selector(Wiley, 2015) Tarhan, Tuba; Tural, Bilsen; Tural, Servet; Topal, Giray; 0000-0001-7555-2481; 0000-0003-2479-9438; 0000-0002-7056-3912; 0000-0003-2656-4464In this study, R(+)--methylbenzylamine-modified magnetic chiral sorbent was synthesized and assessed as a new enantioselective solid phase sorbent for separation of mandelic acid enantiomers from aqueous solutions. The chemical structures and magnetic properties of the new sorbent were characterized by vibrating sample magnetometry, transmission electron microscopy, Fourier transform infrared spectroscopy, and dynamic light scattering. The effects of different variables such as the initial concentration of racemic mandelic acid, dosage of sorbent, and contact time upon sorption characteristics of mandelic acid enantiomers on magnetic chiral sorbent were investigated. The sorption of mandelic acid enantiomers followed a pseudo-second-order reaction and equilibrium experiments were well fitted to a Langmuir isotherm model. The maximum adsorption capacity of racemic mandelic acid on to the magnetic chiral sorbent was found to be 405 mg g(-1). The magnetic chiral sorbent has a greater affinity for (S)-(+)-mandelic acid compared to (R)-(-)-mandelic acid. The optimum resolution was achieved with 10 mL 30 mM of racemic mandelic acid and 110 mg of magnetic chiral sorbent. The best percent enantiomeric excess values (up to 64%) were obtained by use of a chiralpak AD-H column. Chirality 27:835-842, 2015. (c) 2015 Wiley Periodicals, Inc.Öğe Evaluation of synthesized new chitin derivatives in Schottky diode constructions(Taylor & Francis Inc, 2020) Uzun, Ilhan; Aksoy, Onder; Topal, Giray; Celik, Omer; Ocak, Yusuf SelimChitin was reacted with coumarin-3-carboxylic acid (C3CA) and benzophenone-3,3MODIFIER LETTER PRIME,4,4MODIFIER LETTER PRIME-tetracarboxylic dianhydride (B33MODIFIER LETTER PRIME44MODIFIER LETTER PRIMETD), and the synthesized chitin derivatives (CC3CA and CB33MODIFIER LETTER PRIME44MODIFIER LETTER PRIMETD) were characterized by spectroscopic methods and other techniques (FTIR, C-13 CP/MAS solid-state NMR, XRPD, SEM, and TGA). Also, the charge carrier density, hole mobility, and electrical conductivity of CB33MODIFIER LETTER PRIME44MODIFIER LETTER PRIMETD were determined. Lastly, Schottky diodes were constructed using these derivatives, and some electrical properties (barrier height, ideality factor, and series resistance) and photoelectrical properties (light sensitivity, short circuit current, and open circuit voltage) of the diodes were determined. It was seen that the diodes have very good ideality factor and light sensitivity.Öğe Facile synthesis of mono and dibenzo N, N-disubstituted diaza 18-crown-6 derivatives(Hetero Corporation, 2001) Topal, Giray; Demirel, Nadir; Toğrul, Mahmut; Turgut, Yılmaz; Hoşgören, Halil; 0000-0002-7056-3912; 0000-0002-8571-5552; 0009-0000-3823-0467This study represents a facile synthesis of building blocks (1-3) of crown ethers and amine precoursers (4a-d). The study also involves synthesis of mono and dibenzo N,N'-disubstituted diaza 18-crown-6 derivatives with high yield without chromatographic purification and high vacuum distillation. The complex ability of host the ethers was evaluated in terms of structural modification.Öğe Kiral monoza ve diaza taç eter sentezi ve enantiyoselektif Michael katılmasında katalizör olarak kullanılması(2001) Turgut, Yılmaz; Demirel, Nadir; Topal, Giray; Toğrul, Mahmut; Özbey, Süheyla; Hoşgören, Halil[Abstract Not Available]Öğe New chitin derivatives and their Schottky diodes: Synthesis and characterization(Sage Publications Ltd, 2019) Aksoy, Onder; Uzun, Ilhan; Topal, Giray; Celik, Omer; Ocak, Yusuf Selim; Batibay, DeryaFirst, chitin was reacted with 4,5-dichlorophthalic acid and diphenic acid, and thus two new chitin derivatives (C45DA and CDA) were synthesized. Then, C45DA and CDA were characterized by various spectroscopies and techniques (FTIR, C-13 CP-MAS solid-state NMR, XRPD, SEM, and TGA/DTA). Besides, some electrical properties of C45DA were measured. After the characterization process, the Schottky diodes of C45DA and CDA were made. It was determined that these diodes showed photodiode characteristics at the same time. Later on, both electrical properties (phi(b), n, and R-s) and photoelectrical properties (I-illumination/I-Dark, I-SC and V-OC) of these diodes were determined.Öğe Öğretmen adaylarının su hakkındaki bilgi düzeyleri ve kavram yanılgıları(International Balkan University, 2018) Çakmak, Mürşet; Çakmak, Reşit; Topal, GirayÖz:Bu çalışma, öğretmen adaylarının cinsiyete, okudukları bölüme,öğrenim gördükleri sınıfa göre ve su hakkındaki bilgi düzeyleri ilekavram yanılgılarını incelemek amacı ile yapılmıştır. Çalışma, 2018yılında Dicle Üniversitesi Ziya Gökalp Eğitim Fakültesi’nde okuyan fenbilgisi ve kimya öğretmen adayları (N=87) ile yapılmıştır. Bu çalışmadatarama modeli kullanılmıştır. Çalışmada veri toplama aracı olarak SuBilgisi Testi (SBT) kullanılmıştır. Araştırmacılar tarafından hazırlananbu test, suyun fiziksel, kimyasal ve biyolojik özellikleri ile ilgili toplam57 madde olarak yazılmış ve geliştirilmiştir. Geliştirilen testin geçerlikve güvenirlik analizleri yapılmıştır. Testin madde güçlük ve ayırt edicilikindisleri hesaplanmıştır Yapılan analiz sonucunsa madde ayırt edicilikve güçlük indisleri 0,20’den düşük olan 26 madde testten elenmiştir.Geriye kalan diğer 31 madde ise SBT’de kullanılmıştır. Testin KR-20güvenirliği 0,79’dur. Verilerin değerlendirilmesi için yüzde ve frekansdeğerleri çıkartılmıştır. Elde edilen testin bulgularına göre öğretmenadaylarının su hakkındaki bilgi seviyelerinin yüzde 50’ye yakın olduğuve su hakkında kavram yanılgı oranlarının çok olduğu görülmüştür.Ayrıca cinsiyete, okudukları bölüm ve bulundukları sınıfa göre yapılanincelemeye göre de benzer sonuçların olduğu söylenebilir. Öğretmenadaylarının en çok “Suyun sıcaklığı artıkça içinde çözünen gazlarınmiktarı artar”, “Su ile tuz (NaCI) karıştırıldığında aralarında kimyasalbir reaksiyon gerçekleşir ve tuz parçalanır”, “Kar ve yağmur suları doğada bulunan en saf sulardır”, “Su tüm sıvı haldeki maddelerlekarışır”, “Su net bir dipol momente sahiptir”, “Bir insanın biyolojikihtiyaçlarını karşılaması ve yaşamını sürdürebilmesi için, günde en az 1litre su tüketmesi gerektiği kabul edilir” gibi maddelerde kavramyanılgıları taşıdıkları görülmüştür. Bu bulgulardan hareketlearaştırmacı ve uygulayıcılar için bazı öneriler verilmiştir.Öğe Preparation of a novel ionic hybrid stationary phase by non-covalent functionalization of single-walled carbon nanotubes with amino-derivatized silica gel for fast HPLC separation of aromatic compounds(Elsevier Science Bv, 2016) Aral, Hayriye; Celik, K. Serdar; Aral, Tarik; Topal, GiraySingle-walled carbon nanotubes (SWCNTs) were immobilized on spherical silica gel with a 4-mu m average particle size and a 60-angstrom average pore size. The amino-derivatized silica gel was non-covalently coated with carboxylated SWCNTs to preserve the structure of the nanotubes and their physico-chemical properties. The novel ionic hybrid stationary phase was characterized by scanning electron microscopy (SEM), infra-red (IR) spectroscopy and elemental analysis, and then, it was used to fill an empty 150 x 4.6 mm(2) high-performance liquid chromatography (HPLC) column. Chromatographic parameters, such as the theoretical plate number, retention factor and peak asymmetry factor, and analytical parameters, such as the limit of detection (LOD), limit of quantification (LOQ), linear range, calibration equation, and R-2 value, and quantitative analysis parameters were calculated for all of the analytes. Using different mobile phases, five different classes of aromatic hydrocarbons were separated in a very short analysis time of 4-8 min. Furthermore, a high theoretical plate number (up to 25000) and an excellent peak asymmetry factor (1.0) were obtained. The results showed that the surface of the SWNTs had very strong interactions with aromatic groups, therefore providing high selectivity for the separation of different classes of aromatic compounds. This study indicates that SWCNTs enable the extension of the application range of the newly prepared stationary phases for the fast separation of aromatic compounds by HPLC. (C) 2015 Elsevier B.V. All rights reserved.Öğe Preparation of some N-alkyl nitro anthranilic acid derivatives and use in solvent extraction(1995) Topal, Giray; Hoşgören, Halil[Abstract Not Available]Öğe Resolution of (±)-?-Methylphenylethylamine by a Novel Chiral Stationary Phase for Pirkle-Type Column Chromatography(Wiley, 2010) Yılmaz, Hayrullah; Topal, Giray; Çakmak, Reşit; Hoşgören, Halil; 0000-0002-5275-6606; 0000-0003-0401-7419; 0000-0002-7056-3912In this study, a new Pirkle-type chiral column stationary phase for resolution of beta-methylphenylethyl amine was described by using activated Sepharose 4B as a matrix, L-tyrosine as a spacer arm, and an aromatic amine derivative of L-glutamic acid as a ligand. The binding capacities of the stationary phase were determined at different pH values (pH = 6, 7, and 8) using buffer solutions as mobile phase, and enantiomeric excess (ee) was determined by HPLC equipped with chiral column. The ee was found to be 47%. Chirality 22:252-257, 2010. (C) 2009 Wiley-Liss, Inc.Öğe Schottky Diodes Based on the New Chitin Derivatives(Maik Nauka/Interperiodica/Springer, 2019) Aksoy, Onder; Uzun, Ilhan; Topal, Giray; Ocak, Yusuf Selim; Celik, Omer; Batibay, DeryaNew chitin derivatives were synthesized by the reactions of chitin with o-acetylsalicyloyl chloride and phthaloyl chloride and their structure was characterized by FTIR and C-13 CP-MAS solid-state NMR spectroscopy and X-ray powder diffraction technique. Also, the thermal and surface properties of the chitin derivatives were investigated by thermogravimetric analysis and a scanning electron microscope. In addition, some electrical properties of the polymers were determined using Hall effect technique. Then, the Schottky diodes were fabricated by the formation of interlayers of chitin derivatives between Au metal and n-Si semiconductor, and the electrical and photoelectrical properties of the diodes were determined.Öğe SOME NOVEL SCHIFF BASE DERIVATIVES AS PROMISING CHOLINESTERASE INHIBITORS WITH ANTIOXIDANT ACTIVITY AGAINST ALZHEIMER’S DISEASE: SYNTHESIS, CHARACTERIZATION AND BIOLOGICAL EVALUATION(2022) Boğa, Mehmet; Çınar, Ercan; Topal, Giray; Çakmak, ReşitIn this study, five novel Schiff base derivatives (6-10) except for 9 were synthesized for the first time, characterized, and tested for their inhibition activities against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Also, the Antioxidant activities of these molecules were examined by DPPH and ABTS assays. Their molecular structures were characterized by three spectroscopic techniques. In AChE assay, compound 6 (95.87±1.59 % inhibition) inhibited this enzyme better than galanthamine (76.98±0.42 % inhibition). In BChE assay, compound 10 with an 87.92±1.08% inhibition value in the series indicated the highest activity compared to galanthamine (76.30±0.28 % inhibition). In ABTS radical scavenging assay, compounds 7, 8, and 9 except for 6 and 10 indicated higher antioxidant activities compared to butylated hydroxytoluene (BHT). It is believed that these results may contribute to the design and synthesis of novel antioxidant agents, AChE, and BChE inhibitors.Öğe A study of complexation-ability of neutral Schiff bases to some metal cations(Mdpi, 2007) Topal, Giray; Tuemerdem, Recep; Basaran, Ismet; Guemues, Arzu; Cakir, UmitThe constants of the extraction equilibrium and the distribution for dichloromethane as an organic solvent having low dielectric constant of metal cations with chiral Schiff bases, benzaldehydene-(S)- 2- amino- 3- phenylpropanol (I), o-hydroxybenzaldehydene(S)- 2- amino- 3- phenyl- propanol (II), benzaldehydene-(S)- 2amino- 3- methylbutanol (III) with anionic dyes [4-(2- pyridylazo)- resorcinol mono sodium monohydrate (NaPar), sodium picrat (NaPic) and potassium picrat (KPic)] and some heavy metal chlorides were determined at 25 degrees C. All the ligands have given strongest complexation for NaPar. In contrast, similar behaviour for both alkali metal picrates is not apparent in the complexation of corresponding ligands.
