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  • Küçük Resim
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    Environmentally-friendly preparation of chitosan microspheres and encapsulation studies of cinnamaldehyde: ?owards convenient sustained release system for cinnamaldehyde
    (Macedonian Journal of Chemistry and Chemical Engineering, 2021) Yeldir, Elif Karacan; Oral, Ayhan
    Chitosan, a biodegradable and biocompatible polysaccharide, is a biopolymer with high potential for biomedical applications. In the scope of this study, chitosan microcapsules were prepared via a green method, without using any surfactants or crosslinkers. Cinnamaldehyde encapsulated microspheres were obtained by the same method and characterized by FTIR spectroscopy, XRD spectroscopy, and SEM. The release study of encapsulated cinnamaldehyde was carried out in a pH 7.4 phosphate buffered saline (PBS) at 37 °C. The amount of cinnamaldehyde released was analyzed using UV-Vis spectroscopy and GC/MS-MS. Accordingly, it was found that 350 mg of cinnamaldehyde was encapsulated per gram of chitosan, and the maximum amount of cinnamaldehyde released into the PBS medium was about 8 ppm. In addition, the release was seen to continue when the buffer was renewed. It is thought that the obtained cinnamaldehyde encapsulated chitosan microspheres could be used as a sustained release system.
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    Investigation of electrochemical, optical, and thermal properties via oligomerization of aminophenol monomer containing halogen and nitro groups using two distinct oxidants
    (Elsevier, 2023) Yeldir, Elif Karacan; Kolcu, Feyza; Kaya, İsmet
    In this study, two different oligomers of 2-amino-4-chloro-5-nitrophenol (ACNP) with incorporated halogen atom and nitro groups were synthesized by oxidative oligomerization method using two different oxidants, namely H2O2 and ammonium persulfate (APS). Structural characterizations of the obtained products were elucidated by 1H NMR, 13C NMR, FT-IR, UV-Vis spectroscopy methods. The molecular masses of the oligomers were deter-mined through the utilization of Gel Permeation Chromatography (GPC). The analysis revealed that the Mw values of the oligomers synthesized via the oxidative oligomerization method using H2O2 and APS, denoted as OACNP-1 and OACNP-2 were 4150 Da and 2800 Da, respectively. Using the UV-vis spectrophotometer, the optical band gaps were calculated as 2.64 eV, 1.95 eV and 2.14 eV for ACNP, OACNP-1 and OACNP-2, respectively. Thermal properties of the oligomers were investigated using Thermal Gravimetric Analysis-Differential Thermal Analysis (TGA-DTA) and Differential Scanning Calorimetry (DSC). The results demon-strated that OACNP-1 exhibited significantly higher thermal stability when compared to both the monomer and OACNP-2. In addition, Fluorescence Spectroscopic analysis of the oligomers revealed that OACNP-1 emitted blue light at 440 nm when excited with light of a wavelength of 370 nm, exhibiting fluorescent characteristics. Furthermore, the surface properties and morphologies of the oligomers were analyzed with the help of Scanning Electron Microscopy (SEM), revealing a flower-like structure for the oxidative oligomerization product, OACNP-1, in the presence of H2O2. In course of a change in the oxidant, the oligomer, OACNP-2, had rough and spongy surface morphology with some pores.
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    Polyurethanes derived from triazole-based monomers and their application as fluorescent probe for Zn2+
    (Pergamon-Elsevier Science Ltd, 2024) Kaya, İsmet; Yeldir, Elif Karacan; Kolcu, Feyza; Nigiz, Simge
    Polyurethanes are one of the most encountered polymer classes in both industry and scientific research, with their tremendous physical and chemical properties, as well as numerous advantages such as a wide range of raw materials, the ratio of groups to be used during polymerization and adjustable mechanical properties. In this study, four distinct polyurethanes were synthesized using toluene diisocyanate (TDI) and hexamethylenediisocyanate (HMDI) derived from Schiff bases formed by reacting 3,5-diamino-1,2,4-triazole (DAT) and 4 different aldehydes (2-hydroxybenzaldehyde, 4-hydroxybenzaldehyde, 2-hydroxy napthaldehyde, o-vanillin). The structural characterizations of the synthesized Schiff bases and polyurethanes were elucidated using H-1-C-13 NMR and FT-IR, thermal stability was assessed via TGA, molecular weights of the polymers were determined using GPC, electrochemical properties were evaluated by CV, and optical properties were examined using UV-Vis and fluorescence spectrophotometry. The molecular weights of polyurethanes ranged from 4500 to 10300 Da. TGA analysis of the synthesized polyurethanes demonstrated significant thermal stability, maintaining integrity up to 310 degrees C. The band gap energy (E'(g)) values of polyurethanes were found to range from 2.30 to 2.51 eV, which is lower than that of their corresponding monomers, exhibiting semiconductor properties. It was determined that DATSA-PU, one of the synthesized polyurethanes, exhibited potential as a turn-on fluorescent sensor for Zn2+ ion with a LOD value of 2.03 x 10(-7) M.
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    Synthesis and characterization of a pyrene-based Schiff base and its oligomer: Investigation of fluorescent Cr3+ probe
    (Elsevier, 2022) Yeldir, Elif Karacan; Erdener, Digdem; Kaya, İsmet
    In this study, a unique Schiff base (SP) was synthesized from 1-aminopyrine (1-AP) and salicylaldehyde (SA) compounds. The obtained oligomer of this Schiff base was carried out by the oxidative polymerization method. The structural characterizations of 2-((pyren-1-yl-imino)methyl)phenol (SP) and oligo-2-((pyren-1-yl-imino)methyl)phenol (OSP) by FT-IR, H-1 NMR and C-13 NMR measurements, electrochemical properties by cyclic voltammetry (CV); optical properties by UV/Vis studies and photoluminescence (PL) spectrophotometry; thermal stability were performed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The molecular weight of the obtained oligomer was determined using gel permeation chromatography (GPC). Accordingly, Mn and Mw values of OSP were found to be 2800 and 3150 Da, respectively. The imine bond provided the structures with high thermal stability, and the maximum mass loss temperatures (T-max) of SP and OSP were found to be 350(0) and 343 degrees C, respectively. PL study showed that SP could be used as a Cr3+ sensor among a series of metals. The results revealed that the limit of detection (LOD) value of SP was 1.03 x 10(-)(9) M and was not affected by other ions in the environment.
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    Synthesis of Poly(azomethine) Containing Sulfonic Acid Unit Oxygen and Sulphur Bridged: Investigation of Its Thermal, Optical and Electrochemical Properties
    (2022) Yeldir, Elif Karacan
    In this study, a poly(azomethine) compound (SBP) containing sulfur and oxygen bridge was obtained from 4,4'-[thiobis(4,1-phenyleneoxy)]dibenzaldehyde (DBA)and 4,4'diamino-2,2'-biphenyl sulfonic acid from condensation reaction. Structural, optical, electrochemical and morphological analyzes of the obtained polymeric material were performed. Structural characterizations were performed from 1H-NMR and FT-IR spectra. Optical properties were determined in the UV-Vis spectrum and the optical band gap was calculated as 3.63 eV. Electrochemical properties were investigated by cyclic voltammetry (CV) and HOMO-LUMO and electrochemical band gap values were calculated. In addition, with the help of Gel Permeation Chromatography (GPC), the number average molecular mass was found to be 5050 Da. By thermogravimetric analysis (TGA), it was found that the thermal decomposition of SBP occurred in four steps and the maximum mass loss was 391 °C. The surface analysis of the obtained polymeric material was investigated with scanning electron microscope (SEM) and it was determined that the surface was rough.
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    Synthesis, characterization and investigation of fluorescent Sn2+ probe potential of pyrene-derived monomer and its oligo(azomethine) compound
    (Pergamon-Elsevier Science Ltd, 2022) Yeldir, Elif Karacan; Kaya, İsmet
    A monomer (2-methoxy-6-((pyren-1-yl-imino)methyl)phenol, VP) was synthesized by the Schiff base reaction of o-vanillin (VA) and 1-aminopyrene (AP), and an oligomer (oligo-2-methoxy-6-((pyren-1-yl-imino)methyl) phenol, OVP) was synthesized from this monomer via oxidative polycondensation reaction. The structural characterization of the obtained monomer and oligomer by FT-IR, H-1 NMR and C-13 NMR; electrochemical properties with cyclic voltammetry (CV); optical properties with UV-Vis and photoluminescence (PL) spectroscopy; thermal stability with thermogravimetric analysis (TGA); and the molecular weight of the oligomer were determined by gel permeation chromatography (GPC). From the fluorescence titration, VP was found to be sensitive to Sn2+ out of a range of metal ions. When the VP solution, to which 1 equivalent amount of Sn2+ was added, was excited with 320 nm light, it was observed that it emits bright blue color at 445 nm. It was found that VP, whose limit of detection (LOD) was calculated as 4.24 nM for Sn2+, had a sensitive and selective fluorescence sensor potential. In addition, it was found that the obtained oligo[2-methoxy-6-((pyren-1-yl-imino)methyl) phenol] (OVP) had a molecular mass of 3450 Da and showed fluorescent properties. The maximum emission of the OVP excited with 380 nm light was observed at 443 nm, with green emission.
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    Synthesis, characterization, and investigation of some properties of the new symmetrical bisimine Ni(II), Zn(II), and Fe(III) complexes derived from the monoimine ligand
    (Wiley, 2021) Portakal, Eylem Dilmen; Kaya, Yeliz; Demirayak, Emire; Yeldir, Elif Karacan; Ercağ, Ayşe; Kaya, İsmet
    The new symmetrical bisimine (ONNO donor, salen type) Ni(II), Zn(II), andFe(III) complexes were synthesized in one step from metal ions and mon-oimine ligand (HL: 4-amino-3-{[(2-hydroxynaphthalen-1-yl)methylidene]amino}phenyl)(phenyl)methanone). The complexes were characterized by ana-lytical, spectral, conductance, magnetic, and thermal data. According to theseanalysis results, while the bisimine ligand, spontaneously forming during com-plexation, is attached to the metal by two nitrogen atoms and two phenolicoxygen atoms (N2O2) in all complexes, in the Fe(III) complex, the fifth coordi-nation is completed by the chlorine molecule. A square pyramidal geometryfor [FeLCl] and a square planar geometry for [NiL], [ZnL] were proposed. Thethree-dimensional structure of [FeLC1] was also evaluated by single-crystal X-ray diffraction, and the square pyramidal structure was clearly revealed. Themolar conductivity data of the complexes confirmed their nonelectrolyticnature. Poly(imine) (PL) was obtained by the oxidative polymerization reactionof HL, and some of its properties were investigated. The electrochemical prop-erties of the ligand and the complexes were studied by means of cyclicvoltammetry. Highest and lowest occupied molecular orbital (HOMO-LUMO)energy levels and electrochemical band gaps were calculated. The ther-mogravimetric analysis (TGA) and differential thermal analysis (DTA) of thesynthesized compounds were carried out. TGA results showed that the thermalstability of the complexes is high. The solid-state electrical conductivities of theiodine doped states of the synthesized compounds were measured by the four-point probe technique. PL has approximately 35 times higher electrical con-ductivity than the HL and complexes. Fluorescence-sensor properties of HLwere also investigated and predicted that HL could be a selective fluorescenceprobe for Pb2+